The variational quantum eigensolver (VQE) with shallow or constant-depth quantum circuits is one of the most pursued approaches in the noisy intermediate-scale quantum (NISQ) devices with incoherent errors. In this study, the divide-and-conquer (DC) linear scaling technique, which divides the entire system into several fragments, is applied to the VQE algorithm based on the unitary coupled cluster (UCC) method, denoted as DC-qUCC/VQE, to reduce the number of required qubits. The unitarity of the UCC ansatz that enables the evaluation of the total energy as well as various molecular properties as expectation values can be easily implemented on quantum devices because the quantum gates are unitary operators themselves. Based on this feature, the present DC-qUCC/VQE algorithm is designed to conserve the total number of electrons in the entire system using the density matrix evaluated on a quantum computer. Numerical assessments clarified that the energy errors of the DC-qUCC/VQE calculations decrease by using the constraint of the total number of electrons. Furthermore, the DC-qUCC/VQE algorithm could reduce the number of quantum gates and shows the possibility of decreasing incoherent errors.

We report the successful synthesis of tetramesityldiborane(4) (Mes4B2) through the reductive coupling of a dimesitylborinium ion. Owing to the steric protection conferred by the mesityl groups, Mes4B2 shows exceptional chemical stability and remains intact in water. Single-crystal X-ray analysis revealed that Mes4B2 has an orthogonal geometry, where the B–B center is completely hidden by the mesityl groups. Remarkably, Mes4B2 emits dual fluorescence at 460 and 620 nm, both in solution and in the solid state. Theoretical calculations showed that Mes4B2 in the excited S1 state adopts a twisted or planar geometry, which is responsible for the shorter- or longer-wavelength fluorescence, respectively. The intensity ratio of the dual fluorescence is sensitive to the viscosity of the medium, which suggests that Mes4B2 has potential as a ratiometric viscosity sensor.

This letter presents an efficient algorithm for local unitary transformation based on the spin-free infinite-order two-component relativistic method for the two-electron interaction, which is assisted by one-center relativistic two-electron integral (TEI) database. The database stores a set of TEIs, one for each element-basis set combination. The algorithm is numerically assessed for hydrogen halide chains, (HX)n (X = Cl and At), Aun, Ir(ppy)3, Pt3(C7H7)2(HCN)3, and PtCl2(NH3)2. The computational cost (time and memory size) at the Hartree-Fock level is lower than that of the conventional method, especially for small and medium-sized molecules.

Hydrogen (H) atom adsorption and migration over the CeO2-based materials surface are of great importance because of its wide applications to catalytic reactions and electrochemical devices. Therefore, comprehensive knowledge for controlling the H atom adsorption and migration over CeO2-based materials is crucially important. For controlling H atom adsorption and migration, we investigated irreducible divalent, trivalent, and quadrivalent heterocation-doping effects on H atom adsorption and migration over the CeO2(111) surface using density functional theory (DFT) calculations. Results revealed that the electron-deficient lattice oxygen (Olat) and the flexible CeO2matrix played key roles in strong adsorption of H atoms. Heterocations with smaller valence and smaller ionic radius induced the electron-deficient Olat. In addition, smaller cation doping enhanced the CeO2matrix flexibility. Moreover, we confirmed the influence of H atom adsorption controlled by doping on surface proton migration (i.e.surface protonics) and catalytic reaction involving surface protonics (NH3synthesis in an electric field). Results confirmed clear correlation between H atom adsorption energy and surface protonics.

Hydrogen (H) atomic migration over a metal oxide is an important surface process in various catalytic reactions. Control of the interaction between H atoms and the oxide surfaces is therefore important for better catalytic performance. For this investigation, we evaluated the adsorption energies of the H atoms over perovskite-type oxides (Sr1−xBaxZrO3; 0.00 ≤x≤ 0.50) using DFT (Density Functional Theory) calculations, then clarified the effects of cation-substitution in the A-site of perovskite oxides on H atom adsorption, migration, and reaction. Results indicated local distortion at the oxide surface as a key factor governing H atom adsorption. Subtle Ba2+substitution for Sr2+sites provoked local distortion at the Sr1−xBaxZrO3oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr2+/Ba2+ratio on the H atoms' reactivities was examined experimentally using a catalytic reaction, which was promoted by activated surface H atoms. Results show that the surface H atoms activated by the substitution of Sr2+sites with a small amount of Ba2+(x= 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations.

We implemented the picture change correction method for two-electron Coulomb interaction and density opeiator, which was based on the infinite-order two-component method with the local unitary transformation, to the GAMESS program. Numerical assessments for molecules containing heavy element confirmed the accuracies and efficiencies of the implementation. Furthermore, the comparison with several types of treatments indicated that whole picture change corrections of one- and two-electron operators and the density operator are necessary for accurate two-component density functional theory calculations.

<p>Relativistic quantum chemical calculations are performed based on one of two physical pictures, namely the Dirac picture and the Schrödinger picture. With regard to the latter, the so-called picture-change effect...</p>

The machine-learned electron correlation (ML-EC) model is a regression model in the form of a density functional that reproduces the correlation energy density based on wavefunction theory. In a previous study [T. Nudejima et al., J. Chem. Phys. 151, 024104 (2019)], the ML-EC model was constructed using the correlation energy density from all-electron calculations with basis sets including core polarization functions. In this study, we applied the frozen core approximation (FCA) to the correlation energy density to reduce the computational cost of the response variable used in machine learning. The coupled cluster singles, doubles, and perturbative triples [CCSD(T)] correlation energy density obtained from a grid-based energy density analysis was analyzed within FCA and correlation-consistent basis sets without core polarization functions. The complete basis set (CBS) limit of the correlation energy density was obtained using the extrapolation and composite schemes. The CCSD(T)/CBS correlation energy densities based on these schemes showed reasonable behavior, indicating its appropriateness as a response variable. As expected, the computational time was significantly reduced, especially for systems containing elements with a large number of inner-shell electrons. Based on the density-to-density relationship, a large number of data (5 662 500 points), which were accumulated from 30 molecules, were sufficient to construct the ML-EC model. The valence-electron correlation energies and reaction energies calculated using the constructed model were in good agreement with the reference values, the latter of which were superior in accuracy to density functional calculations using 71 exchange-correlation functionals. The numerical results indicate that the FCA is useful for constructing a versatile model.

Bacteriorhodopsin (BR) is a model protein for light-driven proton pumps, where the vectorial active proton transport results in light-energy conversion. To clarify the microscopic mechanism of primary proton transfer from retinal Schiff base (SB) to Asp85 in BR, herein, we performed quantum-mechanical metadynamics simulations with the isolated BR model (similar to 3750 atoms). The simulations showed a novel proton transfer mechanism, viz. the hydroxide ion mechanism, in which the deprotonation of specific internal water (Wat452) yields the protonation of Asp85 via Thr89, after which the resulting hydroxide ion accepts the remaining proton from retinal SB. Systematic investigations adopting four sequential snapshots obtained by the time-resolved serial femtosecond crystallography revealed that proton transfer took 2-5.25 mu s on the photocycle. The presence of Wat401, which is the main difference between snapshots at 2 and 5.25 mu s, is found to be essential in assisting the primary proton transfer. Furthermore, the hydroxide ion mechanism was confirmed by the minimum energy path for the primary proton transfer in BR obtained by the nudged elastic band calculations with the embedded BR model (10,119 atoms), in which BR was embedded within lipid membranes in between water solvents.

A solvent selection scheme for optimization of reactions is proposed using machine learning, based on the numerical descriptions of solvent molecules. Twenty-eight key solvents were represented using 17 physicochemical descriptors. Clustering analysis results implied that the descriptor represents the chemical characteristics of the solvent molecules. During the assessment of an organometallic reaction system, the regression analysis indicated that learning even a small number of experimental results can be useful for identifying solvents that will produce high experimental yields. Observation of the regression coefficients, and both clustering and regression analysis, can be effective when selecting a solvent to be used for an experiment.

An efficient calculation scheme for obtaining free energy surfaces (FESs) in chemical or biological systems from multiple metadynamics (metaD) simulations was developed. In this study, the biased probability distributions of the collective variables and other degrees of freedom were separately calculated in multiple short-time metaD simulations using the reweighting method. The corresponding equilibrium probability distribution was finally constructed using the weighted histogram analysis method (WHAM). This method was applied for the conformational transitions of alanine dipeptide in the gas phase as an illustrative application. The results confirmed that this method was feasible for efficiently generating the converged FES.

© 2018 Elsevier B.V. Development of a highly efficient ammonia synthesis process is desirable for achieving a sustainable society. Regarding conventional heterogeneous catalysts, Ru-supported catalyst exhibits higher turn-over frequency (TOF) than Fe-supported or Ni-supported catalysts. However, we found that Fe-supported and Ni-supported catalysts show higher TOF than Ru-supported catalyst in an electric field at the low temperature of 373 K. Density functional theory (DFT) calculations revealed that N2 dissociation through the “associative mechanism” plays a key role in the electric field. The ammonia synthesis activity in the electric field is determined by the N2H formation energy at the metal-support interface.

Copyright © 2020 American Chemical Society. For effective utilization of ethane in natural gas, catalytic dehydrogenation of ethane is a promising option that offers better efficiency than ethane cracking to produce ethylene, the most important fundamental chemical. Recently, it was reported that catalytic dehydrogenation of ethane proceeds effectively on doped perovskite oxide via the Mars-van Krevelen (MvK) mechanism. For this work, the reaction mechanism was investigated using density functional theory calculations. Results demonstrated that ethane activation over perovskite (La1-xBaxMnO3-δ) proceeds at the surface lattice oxygen coordinated with Ba, resulting in a low energy barrier of the C-H bond activation. Based on Bader charge analysis, the electron-deficient surface lattice oxygen, which is favorable for hydrogen abstraction from light alkanes, forms around Ba. In addition, the electronic charges of the surface lattice oxygen are important for H2 desorption. The electronic charge depends on hydrogen coverage: electron-rich surface lattice oxygen, which is favorable for H2 desorption, forms at high hydrogen coverage. Therefore, a part of the surface lattice oxygens of perovskite would be covered with hydrogen atoms under the reaction atmosphere, leading to effective H2 desorption and the proceeding catalytic cycle via the MvK mechanism.

The "Relativistic And Quantum Electronic Theory (RAQET)" program was released for academic use. One-component (spin-free) and two-component (spin-dependent) relativistic calculations are possible based on the infinite-order Douglas−Kroll−Hess transformation and local unitary transformation. This review describes available features, registration/installation, and input/output of the RAQET program.

A cationic Ir complex was reported to show specific catalytic activity in C-H bond activation reaction of benzanilides. The present study examined reaction energy profiles of the C-H bond activation with Ir and Rh catalysts based on non-relativistic and relativistic quantum chemical calculations. We found that the relativistic effect is essential to demonstrate the difference in the catalytic activity. In particular, the activation of the d orbital of Ir, which is caused by the s- and p- orbital contraction followed by the self-consistent d-orbital expansion, leads to stabilization of the transition state and product of the C-H bond activation.

© 2019 Author(s). Efficient ammonia synthesis at low temperatures is anticipated for establishing a hydrogen carrier system. We reported earlier that application of an electric field on the Cs/Ru/SrZrO3 catalyst enhanced catalytic ammonia synthesis activity. It is now clear that N2 dissociation is activated by hopping protons in the electric field. Efficient ammonia synthesis proceeds by an "associative mechanism" in which N2 dissociates via an N2H intermediate, even at low temperatures. The governing factor of ammonia synthesis activity in an electric field for active metals differed from that in the conventional mechanism. Also, N2H formation energy played an important role. The effects of dopants (Al, Y, Ba, and Ca) on this mechanism were investigated using activity tests and density functional theory calculations to gain insights into the support role in the electric field. Ba and Ca addition showed positive effects on N2H formation energy, leading to high ammonia synthesis activity. The coexistence of proton-donating and electron-donating abilities is necessary for efficient N2H formation at the Ru-support interface.

© 2019 The Chemical Society of Japan. We examined a virtual simulation scheme for reaction condition optimization using machine learning for a small number of experiments with nine reaction conditions, consisting of five continuous and four discrete variables. Simulations were performed for predicting product yields in a synthetic reaction of tetrasilabicyclo[1.1.0]but-1(3)-ene (SiBBE). The performances in terms of accuracy and efficiency in the simulations and the chemical implications of the results were discussed.

The crossing of potential energy surfaces plays an important role in photo-decay processes and photochemical reactions. The energies and geometries of the crossing points have been reported for various molecules using quantum chemical calculations. In this research, excitation energy components of uracil are investigated to understand the characteristics of the crossing points. We revealed that the HOMO−LUMO exchange integral becomes approximately zero at the minimum energy conical intersection between S0 and S1 states. Furthermore, it was found that the HOMO−LUMO gap is close to the HOMO−LUMO Coulomb integral at the crossing structures.

The Relativistic And Quantum Electronic Theory (RAQET) program is a new software package, which is designed for large-scale two-component relativistic quantum chemical (QC) calculations. The package includes several efficient schemes and algorithms for calculations involving large molecules which contain heavy elements in accurate relativistic formalisms. These calculations can be carried out in terms of the two-component relativistic Hamiltonian, wavefunction theory, density functional theory, core potential scheme, and evaluation of electron repulsion integrals. Furthermore, several techniques, which have frequently been used in non-relativistic QC calculations, have been customized for relativistic calculations. This article introduces the brief theories and capabilities of RAQET with several calculation examples.

A semi-local kinetic energy density functional (KEDF) was constructed based on machine learning (ML). The present scheme adopts electron densities and their gradients up to third-order as the explanatory variables for ML and the Kohn-Sham (KS) kinetic energy density as the response variable in atoms and molecules. Numerical assessments of the present scheme were performed in atomic and molecular systems, including first- and second-period elements. The results of 37 conventional KEDFs with explicit formulae were also compared with those of the ML KEDF with an implicit formula. The inclusion of the higher order gradients reduces the deviation of the total kinetic energies from the KS calculations in a stepwise manner. Furthermore, our scheme with the third-order gradient resulted in the closest kinetic energies to the KS calculations out of the presented functionals.

A semi-local kinetic energy density functional (KEDF) was constructed based on machine learning (ML). The present scheme adopts electron densities and their gradients up to third-order as the explanatory variables for ML and the Kohn-Sham (KS) kinetic energy density as the response variable in atoms and molecules. Numerical assessments of the present scheme were performed in atomic and molecular systems, including first- and second-period elements. The results of 37 conventional KEDFs with explicit formulae were also compared with those of the ML KEDF with an implicit formula. The inclusion of the higher order gradients reduces the deviation of the total kinetic energies from the KS calculations in a stepwise manner. Furthermore, our scheme with the third-order gradient resulted in the closest kinetic energies to the KS calculations out of the presented functionals.

This letter proposes an approximate treatment of the harmonic solvation model (HSM) assuming the solute to be a rigid body (RB-HSM). The HSM method can appropriately estimate the Gibbs free energy for condensed phases even where an ideal gas model used by standard quantum chemical programs fails. The RB-HSM method eliminates calculations for intra-molecular vibrations in order to reduce the computational costs. Numerical assessments indicated that the RB-HSM method can evaluate entropies and internal energies with the same accuracy as the HSM method but with lower calculation costs.

We report theoretical calculations of positron-electron annihilation spectra of noble gas atoms and small molecules using the nuclear orbital plus molecular orbital method. Instead of a nuclear wavefunction, the positronic wavefunction is obtained as the solution of the coupled Hartree-Fock or Kohn-Sham equation for a positron and the electrons. The molecular field is included in the positronic Fock operator, which allows an appropriate treatment of the positron-molecule repulsion. The present treatment succeeds in reproducing the Doppler shift, i.e., full width at half maximum (FWHM) of experimentally measured annihilation (γ-ray) spectra for molecules with a mean absolute error less than 10%. The numerical results indicate that the interpretation of the FWHM in terms of a specific molecular orbital is not appropriate.

We report theoretical calculations of positron-electron annihilation spectra of noble gas atoms and small molecules using the nuclear orbital plus molecular orbital method. Instead of a nuclear wavefunction, the positronic wavefunction is obtained as the solution of the coupled Hartree-Fock or Kohn-Sham equation for a positron and the electrons. The molecular field is included in the positronic Fock operator, which allows an appropriate treatment of the positron-molecule repulsion. The present treatment succeeds in reproducing the Doppler shift, i.e., full width at half maximum (FWHM) of experimentally measured annihilation (γ-ray) spectra for molecules with a mean absolute error less than 10%. The numerical results indicate that the interpretation of the FWHM in terms of a specific molecular orbital is not appropriate.

This article proposes a gauge-origin independent formalism of the nuclear magnetic shielding constant in the two-component relativistic framework based on the unitary transformation. The proposed scheme introduces the gauge factor and the unitary transformation into the atomic orbitals. The two-component relativistic equation is formulated by block-diagonalizing the Dirac Hamiltonian together with gauge factors. This formulation is available for arbitrary relativistic unitary transformations. Then, the infinite-order Douglas-Kroll-Hess (IODKH) transformation is applied to the present formulation. Next, the analytical derivatives of the IODKH Hamiltonian for the evaluation of the nuclear magnetic shielding constant are derived. Results obtained from the numerical assessments demonstrate that the present formulation removes the gauge-origin dependence completely. Furthermore, the formulation with the IODKH transformation gives results that are close to those in four-component and other two-component relativistic schemes.

The divide-and-conquer (DC) method was extended to time-dependent density functional tight-binding (TDDFTB) theory to enable excited-state calculations of large systems, as denoted by DC-TDDFTB. In this article, the implementation of TDDFTB and DC-TDDFTB methods into our in-house program, DC-DFTB-K, is explained. Dependence of CPU time on system-size for the DC-TDDFTB calculations indicates significant reduction of computational cost by adopting the DC method. Owing to the feature, excited-state calculations for whole photoactive yellow protein (PYP) surrounded by 4684 water molecules could be carried out in order to examine the hydrogen bond between p-coumaric acid and Glu46 in PYP.

NH3 synthesis on Ru, Os, and Rh nanoparticle catalysts was investigated using density functional theory calculations. The Ru and Os nanoparticles exhibited similar shapes, while that of Rh differed significantly. For all metal species, step sites appeared at nanoparticle diameters (d) &gt
2–4 nm. The calculated activation barriers (Ea) were small at step sites, and Ru and Os step sites exhibited similar Ea values despite the former having a higher turnover frequency. This is likely due to the surface coverage of vacant sites being higher on Ru. Although the increase in NH3 synthesis rate at d = 2–4 nm was common to Ru, Os, and Rh, the reaction rates decreased in the order: Ru &gt
Os &gt
Rh. Our results show that Ea values, surface vacant sites, and the number of step sites are important factors for NH3 synthesis. The Ru nanoparticles exhibited high activity due to satisfying all three factors.

© 2018 American Chemical Society. Detailed reaction mechanisms for the oxidative coupling of methane (OCM) over Ce 2 (WO 4 ) 3 catalysts at low temperatures in an electric field were investigated. The influence of Ce cations in the Ce 2 (WO 4 ) 3 catalyst was evaluated by comparing the OCM activity over various Ln 2 (WO 4 ) 3 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) catalysts in an electric field. The electronic states of Ln and W cations and the relationship between the distorted Ce 2 (WO 4 ) 3 structure and methane activation were examined using X-ray absorption fine structure (XAFS) measurements and first-principles calculations. The results reveal that the Ln 2 (WO 4 ) 3 catalysts with redox-active Ln cations (Ce, Pr, Sm, Eu, and Tb) show OCM activity. First-principles calculations indicate that Ce 3+ species in the Ce 2 (WO 4 ) 3 structure are oxidized to Ce 4+ species in an electric field by extracting electrons from the Ce 4f orbitals near the Fermi level; as a result, its structure is distorted. The results indicate that the redox reaction of Ln cations in Ln 2 (WO 4 ) 3 induced by an electric field brings lattice strain and a high OCM activity in an electric field.

Divide-and-conquer-type density-functional tight-binding molecular dynamics simulations of the CO2 absorption process in monoethanolamine (MEA) solution have been performed for systems containing thousands of atoms. The formation of carbamate anions has been widely investigated for neutral systems via ab initio molecular dynamics simulations, yet the present study is aimed at identifying the role of hydroxide ions in acid-base equilibrium. The structural and electronic analyses reveal that the hydroxide ion approaches, via Grotthuss-type shuttling, the zwitterionic intermediates and abstracts a proton from the nitrogen atom of MEA. We also estimated the fraction of reacted CO2 and carbamate formed at different initial CO2 concentrations that confirm a high absorbed CO2 concentration decreases the fraction of MEA(C) formed due to the abundance of MEA(Z) in the solution.

© 2017 The Royal Society of Chemistry. Highly efficient ammonia synthesis at a low temperature is desirable for future energy and material sources. We accomplished efficient electrocatalytic low-temperature ammonia synthesis with the highest yield ever reported. The maximum ammonia synthesis rate was 30099 μmol gcat-1 h-1 over a 9.9 wt% Cs/5.0 wt% Ru/SrZrO3 catalyst, which is a very high rate. Proton hopping on the surface of the heterogeneous catalyst played an important role in the reaction, revealed by in situ IR measurements. Hopping protons activate N2 even at low temperatures, and they moderate the harsh reaction condition requirements. Application of an electric field to the catalyst resulted in a drastic decrease in the apparent activation energy from 121 kJ mol-1 to 37 kJ mol-1. N2 dissociative adsorption is markedly promoted by the application of the electric field, as evidenced by DFT calculations. The process described herein opens the door for small-scale, on-demand ammonia synthesis.

<p>We have proposed a novel quantum chemical model to evaluate condensed-phase thermodynamic properties, that is, the harmonic solvation model (HSM). This paper explains the theoretical background of HSM and the practical procedure to use for the HSM with some sample inputs. Illustrative applications demonstrate the usefulness and accuracy of HSM.</p>

&lt;p&gt;In this letter, effective exchange integrals of radical dimers obtained by density functional calculations are decomposed into atomic-pair components. The bond energy density analysis, which was originally proposed to evaluate the energy of a chemical bond, was found to be a useful tool to analyze the magnetic interaction of radical dimers.&lt;/p&gt;

© 2017 American Chemical Society. The diffusion of the hydroxide ion in bulk water was examined by linear-scaling divide-and-conquer density-functional tight-binding molecular dynamics (DC-DFTB-MD) simulations using three different-sized unit cells that contained 522, 1050, and 4999 water molecules as well as one hydroxide ion. The repulsive potential for the oxygen-oxygen pair was improved by iterative Boltzmann inversion, which adjusted the radial distribution function of DFTB-MD simulations to that of the reference density functional theory-MD one. The calculated diffusion coefficients and the Arrhenius diffusion barrier were in good agreement with experimental results. The results of the hydroxide ion coordination number distribution and potential of mean force analyses supported a dynamical hypercoordination diffusion mechanism. (Graph Presented).

© 2017 Elsevier B.V. This Letter proposes a density functional treatment based on the two-component relativistic scheme at the infinite-order Douglas-Kroll-Hess (IODKH) level. The exchange-correlation energy and potential are calculated using the electron density based on the picture-change corrected density operator transformed by the IODKH method. Numerical assessments indicated that the picture-change uncorrected density functional terms generate significant errors, on the order of hartree for heavy atoms. The present scheme was found to reproduce the energetics in the four-component treatment with high accuracy.

© 2017 Elsevier B.V.We have derived and implemented a universal formulation of the second-order generalized Møller–Plesset perturbation theory (GMP2) for spin-dependent (SD) two-component relativistic many-electron Hamiltonians, such as the infinite-order Douglas–Kroll–Hess Hamiltonian for many-electron systems, which is denoted as IODKH/IODKH. Numerical assessments for He- and Ne-like atoms and 16 diatomic molecules show that the MP2 correlation energies with IODKH/IODKH agree well with those calculated with the four-component Dirac–Coulomb (DC) Hamiltonian, indicating a systematic improvement on the inclusion of relativistic two-electron terms. The present MP2 scheme for IODKH/IODKH is demonstrated to be computationally more efficient than that for DC.

© 2016 Wiley Periodicals, Inc.This study presents an efficient algorithm to search for the poles of dynamic polarizability to obtain excited states of large systems with nonlocal excitation nature. The present algorithm adopts a homogeneous search with a constant frequency interval and a bisection search to achieve high accuracy. Furthermore, the subtraction process of the information about the detected poles from the total dynamic polarizability is used to extract the undetected pole contributions. Numerical assessments confirmed the accuracy and efficiency of the present algorithm in obtaining the excitation energies and oscillator strengths of all dipole-allowed excited states. A combination of the present pole-search algorithm and divide-and-conquer-based dynamic polarizability calculations was found to be promising to treat nonlocal excitations of large systems. © 2016 Wiley Periodicals, Inc.

© 2017 American Chemical Society. Arylboronic esters can be used as versatile reagents in organic synthesis, as represented by Suzuki-Miyaura cross-coupling. Here we report a serendipitous finding that simple arylboronic esters are phosphorescent in the solid state at room temperature with a lifetime on the order of several seconds. The phosphorescence properties of arylboronic esters are remarkable in light of the general notion that phosphorescent organic molecules require heavy atoms and/or carbonyl groups for the efficient generation of a triplet excited state. Theoretical calculations on phenylboronic acid pinacol ester indicated that this molecule undergoes an out-of-plane distortion at the (pinacol)B-Cipsomoiety in the T1excited state, which is responsible for its phosphorescence. A compound survey with 19 arylboron compounds suggested that the phosphorescence properties might be determined by solid-state molecular packing rather than by the patterns and numbers of boron substituents on the aryl units. The present finding may update the general notion of phosphorescent organic molecules.

© 2017 Author(s). In this study, we developed an excited-state calculation method for large systems using dynamical polarizabilities at the time-dependent density functional theory level. Three equivalent theories, namely, coupled-perturbed self-consistent field (CPSCF), random phase approximation (RPA), and Green function (GF), were extended to linear-scaling methods using the divide-and-conquer (DC) technique. The implementations of the standard and DC-based CPSCF, RPA, and GF methods are described. Numerical applications of these methods to polyene chains, single-wall carbon nanotubes, and water clusters confirmed the accuracy and efficiency of the DC-based methods, especially DC-GF.

© 2017 Elsevier B.V.This Letter examines the enthalpy of formation for 12 transition metal diatomic molecules and 23 transition metal complexes from the viewpoint of effect of the relativistic effect by using the infinite-order Douglas–Kroll–Hess method with the local unitary transformation and three types of pseudopotentials for several levels of theory. The spin-orbit effect contribution to the enthalpy of formation is more than 10 kcal/mol for third transition metal complexes. Frozen orbital approximation at the outermost orbitals in pseudopotential methods shows a contribution to the enthalpy of formation that is more than two times larger than those of inner core orbitals.

© 2017 Wiley Periodicals, Inc. An open-shell Hartree–Fock (HF) theory for spin-dependent two-component relativistic calculations, termed the Kramers-restricted open-shell HF (KROHF) method, is developed. The present KROHF method is defined as a relativistic analogue of ROHF using time-reversal symmetry and quaternion algebra, based on the Kramers-unrestricted HF (KUHF) theory reported in our previous study (Int. J. Quantum Chem., doi:10.1002/qua.25356). As seen in the nonrelativistic ROHF theory, the ambiguity of the KROHF Fock operator gives physically meaningless spinor energies. To avoid this problem, the canonical parametrization of KROHF to satisfy Koopmans&#039; theorem is also discussed based on the procedure proposed by Plakhutin et al. (J. Chem. Phys. 2006, 125, 204110). Numerical assessments confirmed that KROHF using Plakhutin&#039;s canonicalization procedure correctly gives physical spinor energies within the frozen-orbital approximation under spin–orbit interactions.

© 2017 Wiley Periodicals, Inc. An open-shell Hartree–Fock (HF) theory for spin-dependent, two-component relativistic calculations, termed the Kramers-unrestricted HF (KUHF) method, is developed. The present KUHF method, which is formulated as a relativistic counterpart of nonrelativistic UHF, is based on quaternion algebra and partly uses time-reversal symmetry. The fundamental characteristics of KUHF are discussed in this study. From numerical assessments, it was revealed that KUHF gives a corresponding solution to nonrelativistic UHF; furthermore, KUHF properly describes spin-orbit interactions. In addition, KUHF can improve the self-consistent field convergence behavior in spin-dependent calculations, for example, for f-block elements.

© 2017 American Chemical Society. The reduction of NO x is crucial for reducing air pollution from vehicle exhaust. In the presence of Rh-based catalysts, the dissociation of NO and the formation of N 2 O and N 2 constitute the important elementary steps of NO x reduction. The present study used density functional theory (DFT) to investigate the catalytic performances of the Rh(111) surface and Rh 55 and Rh 147 clusters toward these elementary reactions. The NO dissociation reaction was found to have minimum activation barriers (E a ) of 0.63, 0.68, and 1.25 eV on Rh 55 , Rh 147 , and Rh(111), respectively. Therefore, it is the fastest on small Rh clusters. In contrast, the N 2 formation reaction is relatively inefficient on small clusters, with corresponding E a values of 2.14, 1.79, and 1.71 eV. Because of the stronger binding of N atoms to the Rh clusters than to the Rh surface, N 2 formation through the recombination of N atoms has a higher E a value on Rh clusters. The calculated reaction rate constants confirmed that small Rh clusters are less reactive for N 2 formation than Rh(111), especially at low temperatures. Our results also suggest that N 2 O formation is largely end

© 2017 Wiley Periodicals, Inc. We have implemented a linear-scaling divide-and-conquer (DC)-based higher-order coupled-cluster (CC) and Møller–Plesset perturbation theories (MPPT) as well as their combinations automatically by means of the tensor contraction engine, which is a computerized symbolic algebra system. The DC-based energy expressions of the standard CC and MPPT methods and the CC methods augmented with a perturbation correction were proposed for up to high excitation orders [e.g., CCSDTQ, MP4, and CCSD(2) TQ ]. The numerical assessment for hydrogen halide chains, polyene chains, and first coordination sphere (C1) model of photoactive yellow protein has revealed that the DC-based correlation methods provide reliable correlation energies with significantly less computational cost than that of the conventional implementations. © 2017 Wiley Periodicals, Inc.

© 2017 American Chemical Society. Predicting pK a values for different types of amine species with high accuracy and efficiency is of critical importance for the design of high performance and economical solvents in carbon capture and storage with aqueous amine solutions. In this study, we demonstrate that density-functional tight-binding-based metadynamics simulations are a promising approach to calculate the free energy difference between the protonated and neutral states of amines in aqueous solution with inexpensive computational cost. The calculated pK a values were in satisfactory agreement with the experimental values, the mean absolute deviation being only 0.09 pK a units for 34 amines commonly used in CO 2 scrubbing. Such superior reproducibility and correlation compared to estimations by static quantum mechanical calculations highlight the significant effect of dynamical proton transfer processes in explicit solvent molecules for the improvement of the estimation accuracy.

© 2017 American Chemical Society. The structural, dynamical, and energetic properties of the excess proton in ice were studied using density-functional tight-binding molecular dynamics simulations. The ice systems investigated herein consisted of low-density hexagonal and cubic crystalline variants (ice I h and I c ) and high-density structures (ice III and melted ice VI). Analysis of the temperature dependence of radial distribution function and bond order parameters served to characterize the distribution and configuration of hundreds of water molecules in a unit cell. We confirmed that ice I h and I c possess higher hexagonal symmetries than ice III and melted ice VI. The estimated Grotthuss shuttling diffusion coefficients in ice were larger than that of liquid water, indicating a slower proton diffusion process in high-density structures than in low-density systems. The energy barriers calculated on the basis of the Arrhenius plot of diffusion coefficients were in reasonable agreement with experimental measurement for ice I h . Furthermore, the energy barriers for high-density structures were several times larger than those of low-density systems. The simulation results were

© 2017 Wiley Periodicals, Inc. A low-computational-cost algorithm and its parallel implementation for periodic divide-and-conquer density-functional tight-binding (DC-DFTB) calculations are presented. The developed algorithm enables rapid computation of the interaction between atomic partial charges, which is the bottleneck for applications to large systems, by means of multipole- and interpolation-based approaches for long- and short-range contributions. The numerical errors of energy and forces with respect to the conventional Ewald-based technique can be under the control of the multipole expansion order, level of unit cell replication, and interpolation grid size. The parallel performance of four different evaluation schemes combining previous approaches and the proposed one are assessed using test calculations of a cubic water box on the K computer. The largest benchmark system consisted of 3,295,500 atoms. DC-DFTB energy and forces for this system were obtained in only a few minutes when the proposed algorithm was activated and parallelized over 16,000 nodes in the K computer. The high performance using a single node workstation was also confirmed. In addition to liquid wate

The nuclear orbital plus molecular orbital (NOMO) method is a quantum chemical theory introducing the concept of orbital into nuclei. The nuclear orbital energy, obtained as a solution of the Hartree-Fock equation for the NOMO method, has not been noticed in comparison with total energy and nuclear orbital itself. In this paper, physical meaning and application of nuclear orbital energy for the NOMO method are discussed. In particular, proton binding energy calculations, based on the recently developed proton propagator method, are mentioned, including examples of calculations.

An efficient computational method to evaluate the binding energies of many protons in large systems was developed. Proton binding energy is calculated as a corrected nuclear orbital energy using the second-order proton propagator method, which is based on nuclear orbital plus molecular orbital theory. In the present scheme, the divide-and-conquer technique was applied to utilize local molecular orbitals. This use relies on the locality of electronic relaxation after deprotonation and the electron-nucleus correlation. Numerical assessment showed reduction in computational cost without the loss of accuracy. An initial application to model a protein resulted in reasonable binding energies that were in accordance with the electrostatic environment and solvent effects.

This letter proposes a relaxation scheme for core electrons based on the frozen core potential method at the infinite-order Douglas-Kroll-Hess level, called FCP-CR. The core electrons are self-consistently relaxed using frozen molecular valence potentials after the valence SCF calculation is performed. The efficiency of FCP-CR is confirmed by calculations of gold clusters. Furthermore, FCP-CR reproduces the results of the all-electron method for the energies of coinage metal dimers and the core ionization energies and core level shifts of vinyl acetate and three tungsten complexes at the Hartree Fock and/or symmetry-adapted cluster configuration interaction levels. (C) 2016 Elsevier B.V. All rights reserved.

An efficient computational method to evaluate the binding energies of many protons in large systems was developed. Proton binding energy is calculated as a corrected nuclear orbital energy using the second-order proton propagator method, which is based on nuclear orbital plus molecular orbital theory. In the present scheme, the divide-and-conquer technique was applied to utilize local molecular orbitals. This use relies on the locality of electronic relaxation after deprotonation and the electron-nucleus correlation. Numerical assessment showed reduction in computational cost without the loss of accuracy. An initial application to model a protein resulted in reasonable binding energies that were in accordance with the electrostatic environment and solvent effects.

Energy fitting schemes based on informatics techniques using hierarchical basis sets with small cardinal numbers were numerically investigated to estimate correlation energies at the complete basis set limits. Numerical validations confirmed that the conventional two-point extrapolation models can be unified into a simple formula with optimal parameters obtained by the same test sets. The extrapolation model was extended to two-point fitting models by a relaxation of the relationship between the extrapolation coefficients or a change of the fitting formula. Furthermore, n-scheme fitting models were developed by the combinations of results calculated at several theory levels and basis sets to compensate for the deficiencies in the fitting model at one level of theory. Systematic assessments on the Gaussian-3X and Gaussian-2 sets revealed that the fitting models drastically reduced errors with equal or smaller computational effort. © 2016 Wiley Periodicals, Inc.

We present an efficient quantum algorithm for beyond-Born-Oppenheimer molecular energy computations. Our approach combines the quantum full configuration interaction method with the nuclear orbital plus molecular orbital method. We give the details of the algorithm and demonstrate its performance by classical simulations. Two isotopomers of the hydrogen molecule (H-2, HT) were chosen as representative examples and calculations of the lowest rotationless vibrational transition energies were simulated. (C) 2016 Wiley Periodicals, Inc.

© 2016 Elsevier B.V. All rights reserved.CO2 chemical absorption and regeneration processes in aqueous amine solutions were investigated using density-functional tight-binding molecular dynamics simulations. Extensive analyses of the structural, electronic, and dynamical properties of 100 independent trajectories supported the contrasting mechanisms in the absorption and regeneration processes. In the CO2 absorption process, bicarbonate formed where the hydroxyl anion migrated through the hydrogen-bond network of water molecules, namely, by a Grotthuss-type mechanism. On the other hand, direct proton transfer from the protonated amine to the hydroxyl group of bicarbonate, which is called the ion-pair mechanism, was the key step to the release of CO2.

<p>This Letter provides an implementation of an efficient and accurate relativistic method based on the infinite-order two-component scheme with the local unitary transformation (LUT-IOTC) to the GAMESS program. The sample input and major capabilities in GAMESS are shown as well as the accuracies and efficiencies in energy and analytical energy gradient calculations. The scheme realizes calculations of molecules containing heavy elements with four-component relativistic accuracy and the non-relativistic computational cost.</p>

The carbon dioxide capture and storage (CCS), which is a technique to reduce an amount of emission of CO₂, has many attentions. The chemical absorption method, which is one scheme of the CCS technique, consists of two processes: a separation process for absorbing CO₂ in a basic absorbent and a collection process for emitting high concentrate CO₂ by high temperature. Many amines have been studied and developed to reduce the energy in the CO₂ absorption. To explore an amine with a high efficiency in the CO₂ absorption, the time courses in concentrations of chemical species for each amine give important information. In this study, we develop a reaction predictor to reproduce the experimental data, which uses elementary processes in a CO₂<br>-amine reaction and the swarm intelligence. Furthermore, equilibrium constants for elementary processes are estimated from reaction Gibbs energies obtained by quantum chemical calculations in order to predict loading dependencies of chemical species in any amines.

In the field of chemoinformatics, computer-aided reaction prediction systems have been developed. However, the systems have not been widely used by experimental chemists because of its low accuracy for predicting chemical reactions. Recently, a reaction prediction scheme, which is based on the machine learning method and utilizes topological information of molecules as descriptors, has shown high effectiveness for organic reactions. Nevertheless, the application has been limited due to lack of steric and electronic information of molecules. The present study has developed a novel scheme, which uses the machine learning with descriptors obtained from quantum chemical calculation, in order to realize an accurate prediction for reactions including arbitrary chemical species such as organometallic and ionic reactions. The accuracy of present system has been clarified to be close to that of the previous system for basic polar and radical organic chemical reactions. In this presentation, we will show the details of the system and the dependencies on conditions of quantum chemical calculations.

<p>Chemical absorption of CO₂ employing alkanolamines is currently considered to be the most promising approach for CO₂ emission reduction from power plants. Extensive efforts have been devoted by experimental and theoretical researchers in the development of amine solutions, with the main purpose of reducing the energy cost of solvent regeneration. In the present Commentary, we show how theoretical calculations have been utilized in the analysis of the amine-CO₂ reaction mechanism. Theoretical studies with quantum chemistry calculations and ab initio molecular dynamics are mainly focused on.</p>

<p>We have developed a novel reaction prediction system, which uses machine learning with quantum chemical descriptors. Numerical assessments of the system were performed on basic polar and radical organic chemical reactions. The accuracy of the present system was close to that of a previous system having machine learning with topological information, which is termed ReactionPredictor.</p>

Low density polyethylene (LDPE) and polypropylene (PP) exhibit a photoluminescence (PL) band, which emits photons with an energy of around 4.3 eV when excited by photons with energies around 6.4 eV. The origin of this PL band has been assigned to α, β -unsaturated carbonyl. In this paper, the appearance of PL was examined for four kinds of polyolefin and four kinds of biodegradable polymers. As a result, it has become clear that all the polymers show a PL band with a PL excitation spectrum and a PL spectrum similar to those of the above-mentioned PL band in LDPE and PP. The decay profiles observed for these PL bands indicate that they are fluorescence. Furthermore, the intensity of the PL becomes weak for all the four polyolefin samples and the polylatic acid sample if ultraviolet photons were irradiated to the sample. Quantum chemical calculations carried out by assuming a model of α, β -unsaturated carbonyl have revealed that the PL originates in the π∗to π transition of electrons in the carbon-carbon double bond.

© 2016 the Owner Societies. An efficient computational method to evaluate the binding energies of many protons in large systems was developed. Proton binding energy is calculated as a corrected nuclear orbital energy using the second-order proton propagator method, which is based on nuclear orbital plus molecular orbital theory. In the present scheme, the divide-and-conquer technique was applied to utilize local molecular orbitals. This use relies on the locality of electronic relaxation after deprotonation and the electron-nucleus correlation. Numerical assessment showed reduction in computational cost without the loss of accuracy. An initial application to model a protein resulted in reasonable binding energies that were in accordance with the electrostatic environment and solvent effects.

Low density polyethylene (LDPE) and polypropylene (PP) exhibit a photoluminescence (PL) band, which emits photons with an energy of around 4.3 eV when excited by photons with energies around 6.4 eV. The origin of this PL band has been assigned to α, β -unsaturated carbonyl. In this paper, the appearance of PL was examined for four kinds of polyolefin and four kinds of biodegradable polymers. As a result, it has become clear that all the polymers show a PL band with a PL excitation spectrum and a PL spectrum similar to those of the above-mentioned PL band in LDPE and PP. The decay profiles observed for these PL bands indicate that they are fluorescence. Furthermore, the intensity of the PL becomes weak for all the four polyolefin samples and the polylatic acid sample if ultraviolet photons were irradiated to the sample. Quantum chemical calculations carried out by assuming a model of α, β -unsaturated carbonyl have revealed that the PL originates in the π∗to π transition of electrons in the carbon-carbon double bond.

© 2015 American Chemical Society.The process of proton diffusion in liquid water was investigated using molecular dynamics (MD) simulations, and the total energy and atomic forces were evaluated by the divide-and-conquer-type density-functional tight-binding (DC-DFTB) method. The effectiveness of this approach was confirmed by comparing the computational time of water clusters with conventional treatments. The unit cell employed herein, which contained 523 water molecules and 1 excess proton, was moderately large in comparison with those used in previous studies. The reasonable accuracy obtained by using this unit cell was confirmed by examining the temperature fluctuation. The diffusion coefficients for the vehicular and Grotthuss processes were accurately reproduced by the DC-DFTB-MD simulations with the unit cell containing 523 water molecules. Furthermore, the energy barriers were evaluated from the temperature dependence of the diffusion coefficient for each process. The calculated barrier for Grotthuss diffusion was in good agreement with the experimental value.

© 2016 Elsevier B.V. All rights reserved. Gibbs free energy of hydration of a proton and standard hydrogen electrode potential were evaluated using high-level quantum chemical calculations. The solvent effect was included using the cluster-continuum model, which treated short-range effects by quantum chemical calculations of proton-water complexes, and the long-range effects by a conductor-like polarizable continuum model. The harmonic solvation model (HSM) was employed to estimate enthalpy and entropy contributions due to nuclear motions of the clusters by including the cavity-cluster interactions. Compared to the commonly used ideal gas model, HSM treatment significantly improved the contribution of entropy, showing a systematic convergence toward the experimental data.

© 2016 American Chemical Society.An analytical energy gradient for the spin-dependent general Hartree-Fock method based on the infinite-order Douglas-Kroll-Hess (IODKH) method was developed. To treat realistic systems, the local unitary transformation (LUT) scheme was employed both in energy and energy gradient calculations. The present energy gradient method was numerically assessed to investigate the accuracy in several diatomic molecules containing fifth- and sixth-period elements and to examine the efficiency in one-, two-, and three-dimensional silver clusters. To arrive at a practical calculation, we also determined the geometrical parameters of fac-tris(2-phenylpyridine)iridium and investigated the efficiency. The numerical results confirmed that the present method describes a highly accurate relativistic effect with high efficiency. The present method can be a powerful scheme for determining geometries of large molecules, including heavy-element atoms.

© 2016 Elsevier B.V. All rights reserved.This Letter assesses the self-consistent field (SCF) convergence behavior in the generalized Hartree-Fock (GHF) method. Four acceleration algorithms were implemented for efficient SCF convergence in the GHF method: the damping algorithm, the conventional direct inversion in the iterative subspace (DIIS), the energy-DIIS (EDIIS), and a combination of DIIS and EDIIS. Four different systems with varying complexity were used to investigate the SCF convergence using these algorithms, ranging from atomic systems to metal complexes. The numerical assessments demonstrated the effectiveness of a combination of DIIS and EDIIS for GHF calculations in comparison with the other discussed algorithms.

© 2016 Elsevier B.V. All rights reserved.The harmonic solvation model (HSM) was applied to the solvation of gaseous molecules and compared to a procedure based on the ideal gas model (IGM). Examination of 25 molecules showed that (i) the accuracy of ΔGsolv was similar for both methods, but the HSM shows advantages for calculating ΔHsolv and TΔSsolv; (ii) TΔSsolv contributes more than ΔHsolv to ΔGsolv in the HSM, i.e. the solvation of gaseous molecules is entropy-driven, which agrees well with experimental understanding (the IGM does not show this); (iii) the temperature dependence of Henry&#039;s law coefficient was correctly reproduced with the HSM.

© 2016 Wiley Periodicals, Inc.The linear-scaling divide-and-conquer (DC) quantum chemical methodology is applied to the density-functional tight-binding (DFTB) theory to develop a massively parallel program that achieves on-the-fly molecular reaction dynamics simulations of huge systems from scratch. The functions to perform large scale geometry optimization and molecular dynamics with DC-DFTB potential energy surface are implemented to the program called DC-DFTB-K. A novel interpolation-based algorithm is developed for parallelizing the determination of the Fermi level in the DC method. The performance of the DC-DFTB-K program is assessed using a laboratory computer and the K computer. Numerical tests show the high efficiency of the DC-DFTB-K program, a single-point energy gradient calculation of a one-million-atom system is completed within 60 s using 7290 nodes of the K computer. © 2016 Wiley Periodicals, Inc.

© 2016 Elsevier B.V.This letter proposes a relaxation scheme for core electrons based on the frozen core potential method at the infinite-order Douglas–Kroll–Hess level, called FCP-CR. The core electrons are self-consistently relaxed using frozen molecular valence potentials after the valence SCF calculation is performed. The efficiency of FCP-CR is confirmed by calculations of gold clusters. Furthermore, FCP-CR reproduces the results of the all-electron method for the energies of coinage metal dimers and the core ionization energies and core level shifts of vinyl acetate and three tungsten complexes at the Hartree–Fock and/or symmetry-adapted cluster configuration interaction levels.

© 2016 Elsevier B.V.Gibbs free energy of hydration of a proton and standard hydrogen electrode potential were evaluated using high-level quantum chemical calculations. The solvent effect was included using the cluster-continuum model, which treated short-range effects by quantum chemical calculations of proton-water complexes, and the long-range effects by a conductor-like polarizable continuum model. The harmonic solvation model (HSM) was employed to estimate enthalpy and entropy contributions due to nuclear motions of the clusters by including the cavity-cluster interactions. Compared to the commonly used ideal gas model, HSM treatment significantly improved the contribution of entropy, showing a systematic convergence toward the experimental data.

An efficient algorithm for the rapid evaluation of electron repulsion integrals is proposed. The present method, denoted by accompanying coordinate expansion and transferred recurrence relation (ACE-TRR), is constructed using a transfer relation scheme based on the accompanying coordinate expansion and recurrence relation method. Furthermore, the ACE-TRR algorithm is extended for the general-contraction basis sets. Numerical assessments clarify the efficiency of the ACE-TRR method for the systems including heavy elements, whose orbitals have long contractions and high angular momenta, such as f- and g-orbitals.

The extrapolation scheme of correlation energy is revisited to evaluate the complete basis set limit from double-zeta (DZ) and triple-zeta levels of calculations. The DZ level results are adjusted to the standard asymptotic behavior with respect to the cardinal number, observed at the higher levels of basis sets. Two types of adjusting schemes with effective scaling factors, which recover errors in extrapolations with the DZ level basis set, are examined. The first scheme scales the cardinal number for the DZ level energy, while the second scheme scales the prefactor of the extrapolation function. Systematic assessments on the Gaussian-3X and Gaussian-2 test sets reveal that these calibration schemes successfully and drastically reduce errors without additional computational efforts. (c) 2015 Wiley Periodicals, Inc.

The extrapolation scheme of correlation energy is revisited to evaluate the complete basis set limit from double-zeta (DZ) and triple-zeta levels of calculations. The DZ level results are adjusted to the standard asymptotic behavior with respect to the cardinal number, observed at the higher levels of basis sets. Two types of adjusting schemes with effective scaling factors, which recover errors in extrapolations with the DZ level basis set, are examined. The first scheme scales the cardinal number for the DZ level energy, while the second scheme scales the prefactor of the extrapolation function. Systematic assessments on the Gaussian-3X and Gaussian-2 test sets reveal that these calibration schemes successfully and drastically reduce errors without additional computational efforts. (c) 2015 Wiley Periodicals, Inc.

We report the implementation of the local response dispersion (LRD) method in an electronic structure program package aimed at periodic systems and an assessment combined with the Perdew-Burke-Ernzerhof (PBE) functional and its revised version (revPBE). The real-space numerical integration was implemented and performed exploiting the electron distribution given by the plane-wave basis set. The dispersioncorrected density functionals revPBE1LRD was found to be suitable for reproducing energetics, structures, and electron distributions in simple substances, molecular crystals, and physical adsorptions.

Using energy density analysis, total energy is partitioned into the atomic energy densities of constituent elements. The atomization energy of each element is then evaluated by subtracting the atomic energy density from the energy of the isolated neutral atom. This recent approach to the energy expression is reviewed of the chemical bond between atoms in hydrides and oxides. For various hydrides, the atomization energies, ΔE H for H atom and ΔE M for metal atom, are evaluated and the ΔE H vs. ΔE M diagram called atomization energy diagram is made. All the hydrides including complex hydrides and metal hydrides can be located on this diagram, although there are significant differences in the nature of the chemical bond among them. Also, for hydrocarbons, CmH, the atomization energy for carbon, ΔE C, increases linearly with the ratio of carbon number to hydrogen number, m/n, while keeping ΔE H constant. It is no longer needed for us to give expression for the C-C bond to be either single, or double or triple bond in CmHn. For metal oxides, the atomization energies, ΔE M for metal atom and ΔE O for O atom, reflect the average structure as well as the local structure. As a result, their values change with the overall density of binary metal oxides. For perovskite-type oxides, the ΔE O value increases by the phase transition from cubic to tetragonal phase, regardless of the tilting-type or the &lt
100&gt
displacement-type transition. One of the applications of this approach is the quantitative evaluation for the catalytic activities of metal oxides (e.g., Nb2O5) on the dehydrogenation reaction of magnesium hydride (MgH2), MgH2 → Mg + H2. The atomization energy concept will provide us a new clue to materials design, for example, catalysts design.

To elucidate the catalytic reaction mechanism of BH₄^－ (a reducing agent) on metal surfaces during electroless deposition, its oxidation reaction was investigated theoretically using density functional theory (DFT) calculation. Particularly in this study, dehydrogenation reaction of BH₄^－ was modeled and analyzed because it is the most important elementary step of overall oxidation for the catalytic behavior of metal surfaces. To ascertain the tendencies of catalytic activity of metal surfaces, the reaction on Cu(111) and that on Pd(111) were compared. Actually, Cu shows little catalytic activity toward BH₄^－ oxidation, whereas Pd shows strong catalytic activity. Results of reaction energy calculations show that the BH₄^－ dehydrogenation occurs with difficulty on Cu(111), but it occurs easily on Pd(111), which corresponds to experimental results. Detailed analyses of reaction system electronic structures show that the d-band states of each surface are important to assess the background of the difference. Because the Pd surface has a high-energy d-band, it can interact with high-energy unoccupied orbitals of BH₄^－, leading to electron donation from the surface toward BH₄^－. This electron donation effect from Pd provides dissociation activity of the B-H bond, which promotes dehydrogenation of BH₄^－.

:An efficient algorithm for the rapid evaluation of electron repulsion integrals is proposed. The present method, denoted by accompanying coordinate expansion and transferred recurrence relation (ACE-TRR), is constructed using a transfer relation scheme based on the accompanying coordinate expansion and recurrence relation method. Furthermore, the ACE-TRR algorithm is extended for the general-contraction basis sets. Numerical assessments clarify the efficiency of the ACE-TRR method for the systems including heavy elements, whose orbitals have long contractions and high angular momenta, such as f- and g-orbitals.

:The extrapolation scheme of correlation energy is revisited to evaluate the complete basis set limit from double-zeta (DZ) and triple-zeta levels of calculations. The DZ level results are adjusted to the standard asymptotic behavior with respect to the cardinal number, observed at the higher levels of basis sets. Two types of adjusting schemes with effective scaling factors, which recover errors in extrapolations with the DZ level basis set, are examined. The first scheme scales the cardinal number for the DZ level energy, while the second scheme scales the prefactor of the extrapolation function. Systematic assessments on the Gaussian-3X and Gaussian-2 test sets reveal that these calibration schemes successfully and drastically reduce errors without additional computational efforts.

:The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH&HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

:Graphical processing units (GPUs) are emerging in computational chemistry to include Hartree-Fock (HF) methods and electron-correlation theories. However, ab initio calculations of large molecules face technical difficulties such as slow memory access between central processing unit and GPU and other shortfalls of GPU memory. The divide-and-conquer (DC) method, which is a linear-scaling scheme that divides a total system into several fragments, could avoid these bottlenecks by separately solving local equations in individual fragments. In addition, the resolution-of-the-identity (RI) approximation enables an effective reduction in computational cost with respect to the GPU memory. The present study implemented the DC-RI-HF code on GPUs using math libraries, which guarantee compatibility with future development of the GPU architecture. Numerical applications confirmed that the present code using GPUs significantly accelerated the HF calculations while maintaining accuracy.

To realize quantum-chemical calculations with chemical accuracy (> 1 kcal/mol), efficient estimations of accurate electron correlation energies in a complete basis set (CBS) limit are important. Several extrapolation schemes to CBS limit, and composite schemes in combination with energies calculated with some levels of theories and basis sets have been proposed. This study proposes efficient estimation schemes of electron correlation energies in a CBS limit at the CCSD(T) level utilizing informatics technique.

The origin of the stability of diamondoid dimers containing very long carbon–carbon bonds was examined using density functional theory (DFT) calculations with local response dispersion correction. It has been suggested that noncovalent CH···HC contacts are the probable source of their extraordinary stability as evidenced by dispersion-corrected DFT calculations. In this work, we numerically proved that the small radical stabilization energy, which was achieved through the geometric relaxation of cleaved radicals, led to the high stability of diamondoid dimers compared to other hydrocarbons. The bond energy density analysis showed that the CH···HC contacts are repulsive though the dispersion force somewhat stabilizes the dimer. We further decomposed CH···HC interaction energies to discover strong attractive interaction between C&lt;sup&gt;δ−&lt;/sup&gt;···H&lt;sup&gt;δ+&lt;/sup&gt; intermonomer contacts.

The authors group has developed the program named DC-DFTB-K for the on-the-fly quantum mechanical molecular dynamics (MD) simulation of huge systems using the density-functional tight binding (DFTB) method. The combination with the divide-and-conquer (DC) method enables linear-scaling calculation of DFTB energy and its derivatives. Due to the massively parallel implementation, the program can treat systems containing one million atoms on the K computer. In this paper, the recent extension of DC-DFTB-MD technique is outlined together with the illustrative application to chemical reaction dynamics in lithium-ion device.

© 2015 AIP Publishing LLC. An efficient algorithm for the rapid evaluation of electron repulsion integrals is proposed. The present method, denoted by accompanying coordinate expansion and transferred recurrence relation (ACE-TRR), is constructed using a transfer relation scheme based on the accompanying coordinate expansion and recurrence relation method. Furthermore, the ACE-TRR algorithm is extended for the general-contraction basis sets. Numerical assessments clarify the efficiency of the ACE-TRR method for the systems including heavy elements, whose orbitals have long contractions and high angular momenta, such as f- and g-orbitals.

© 2015, Springer-Verlag Berlin Heidelberg. This study proposes two efficient algorithms of the linear-scaling divide-and-conquer self-consistent field (DC-SCF) method for parallel computations. These algorithms minimize the amount of network communication required for determining the common Fermi level by adopting an approximate Fermi level. One algorithm adopts the quasi-converged Fermi level during DC-SCF iterations, while the other uses the quasi-converged electron numbers of individual subsystems. A numerical assessment demonstrates the high parallel efficiency for both methods without loss in accuracy.

© 2015 AIP Publishing LLC.This paper reviews a series of theoretical studies to develop efficient two-component (2c) relativistic method for large systems by the author&#039;s group. The basic theory is the infinite-order Douglas-Kroll-Hess (IODKH) method for many-electron Dirac-Coulomb Hamiltonian. The local unitary transformation (LUT) scheme can effectively produce the 2c relativistic Hamiltonian, and the divide-and-conquer (DC) method can achieve linear-scaling of Hartree-Fock and electron correlation methods. The frozen core potential (FCP) theoretically connects model potential calculations with the all-electron ones. The accompanying coordinate expansion with a transfer recurrence relation (ACE-TRR) scheme accelerates the computations of electron repulsion integrals with high angular momenta and long contractions.

DNAs, which have charge transport abilities, are expected to apply to advanced materials in nanotechnology as conducting nano-wires. While the hole-transfer in DNA has been extensively investigated in many experimental and theoretical studies, the knowledge on the transfer of a negative charge, i.e., the excess-electron transfer (EET), is limited so far. In the present study, we evaluated the rate constants of EET in DNA, using the Marcus theory with density functional theory (DFT) calculations. The computed rate constant of EET between thymine bases, 2.31 − 3.49 × 10&lt;sup&gt;10&lt;/sup&gt; s&lt;sup&gt;−1&lt;/sup&gt;, showed good agreement with the experimental value, 4.4 ± 0.3 × 10&lt;sup&gt;10&lt;/sup&gt; s&lt;sup&gt;−1&lt;/sup&gt;. Furthermore, the mechanism of the decrease of EET rates due to miss-match base pairs was elucidated.

PicoGreen (PG) is used as a probe to selectively quantitate double-stranded (ds-) DNA because it shows unique fluorescence enhancement when complexed with DNA. By binding to ds- and single-stranded (ss-) DNA, the quantum yields of PG-DNA complexes become remarkably larger than that of a free molecule. In the present theoretical study, the fluorescence enhancement mechanism of PG-DNA complexes was investigated using molecular docking simulations and ab initio quantum chemical methods. The binding energies between PG and ds-DNA were calculated to be larger than those in the case of PG and ss-DNA owing to the existence of an extra pi-pi stacking interaction. Nonradiative deactivation paths through conical intersections between the ground and the first excited states were obtained for a free PG molecule, while steric repulsions between PG and DNA hindered such deactivation processes in the case of PG-DNA complexes.

Thermodynamics in the condensed phase is a challenging target of the present quantum chemistry. Because the widely-spread quantum chemical programs such as Gaussian and GAMESS adopt the ideal gas model (IGM) even for the liquid systems. We have recently proposed a novel approach, named harmonic salvation model (HSM), to properly treat the condensed phase. In the presentation, I will explain the theoretical aspects and introduce several applications of HSM.

DNAs, which have charge transport abilities, are expected to apply to advanced materials in nanotechnology as conducting nano-wires. While the hole-transfer in DNA has been extensively investigated in many experimental and theoretical studies, the knowledge on the transfer of a negative charge, i.e., the excess-electron transfer (EET), is limited so far. In the present study, we evaluated the rate constants of EET in DNA, using the Marcus theory with density functional theory (DFT) calculations. The computed rate constant of EET between thymine bases, 2.31 − 3.49 × 1010 s−1, showed good agreement with the experimental value, 4.4 ± 0.3 × 1010 s−1. Furthermore, the mechanism of the decrease of EET rates due to miss-match base pairs was elucidated.

The article discusses a highly efficient and accurate theory for electronic-state calculations of large-scale heavy-element compounds. After overviewing the current relativistic quantum-chemical theories, the authors describe what points should be considered and improved in order to attain the objective. In addition, they have developed an efficient and accurate two-component relativistic scheme, termed local unitary transformation (LUT) scheme based on infinite-order Douglas-Kroll-Hess method. Numerical applications show the effectiveness of the scheme. Furthermore, the extension of the LUT scheme to the divide-and-conquer (DC) method achieves overall linear-scaling computational cost. In particular, the present scheme would realize a paradigm shift from a non-relativistic (NR) framework to a relativistic one in the quantum chemistry field because the scheme gives close results to four-component relativistic ones with NR computational costs.

:We propose a novel quantum chemical method, called the harmonic solvation model (HSM), for calculating thermochemical parameters in the condensed phase, particularly in the liquid phase. The HSM represents translational and rotational motions of a solute as vibrations interacting with a cavity wall of solvent molecules. As examples, the HSM and the ideal-gas model (IGM) were used for the standard formation reaction of liquid water, combustion reactions of liquid formic acid, methanol, and ethanol, vapor-liquid equilibration of water and ethanol, and dissolution of gaseous CO2 in water. The numerical results confirmed the reliability and applicability of the HSM. In particular, the temperature dependence of the Gibbs energy of liquid molecules was accurately reproduced by the HSM; for example, the boiling point of water was reasonably determined using the HSM, whereas the conventional IGM treatment failed to obtain a crossing of the two Gibbs energy curves for gaseous and liquid water.

:An algorithm of the accompanying coordinate expansion and recurrence relation (ACE-RR), which is used for the rapid evaluation of the electron repulsion integral (ERI), has been extended to the general-contraction (GC) scheme. The present algorithm, denoted by GC-ACE-RR, is designed for molecular calculations including heavy elements, whose orbitals consist of many primitive functions with and without higher angular momentum such as d- and f-orbitals. The performance of GC-ACE-RR was assessed for (ss|ss)-, (pp|pp)-, (dd|dd)-, and (ff|ff)-type ERIs in terms of contraction length and the number of GC orbitals. The present algorithm was found to reduce the central processing unit time compared with the ACE-RR algorithm, especially for higher angular momentum and highly contracted orbitals. Compared with HONDOPLUS and GAMESS program packages, GC-ACE-RR computations for ERIs of three-dimensional gold clusters Aun (n = 1, 2, …, 10, 15, 20, and 25) are more than 10 times faster.

:The Lagrange interpolation of molecular orbital (LIMO) method, which reduces the number of self-consistent field iterations in ab initio molecular dynamics simulations with the Hartree-Fock method and the Kohn-Sham density functional theories, is extended to the theory of multiconfigurational wave functions. We examine two types of treatments for the active orbitals that are partially occupied. The first treatment, as denoted by LIMO(C), is a simple application of the conventional LIMO method to the union of the inactive core and the active orbitals. The second, as denoted by LIMO(S), separately treats the inactive core and the active orbitals. Numerical tests to compare the two treatments clarify that LIMO(S) is superior to LIMO(C). Further applications of LIMO(S) to various systems demonstrate its effectiveness and robustness.

MK-4965, 3-{5-[(6-Amino-1H-pyrazolo[3,4-b]pyridine-3-yl)methoxy]-2- chlorophenoxy}-5-chloro-benzonitrile, is a novel non-nucleoside reverse transcriptase inhibitor (NNRTI) revealing high levels of potency against wild-type (WT) the human immunodeficiency virus type-1 (HIV-1) and some important mutants. The divide-and-conquer (DC) based Hartree-Fock (HF) and second-order Møller-Plesset perturbation theory (MP2) calculations were performed for the binding modes of MK-4965 in the reverse transcriptase (RT) of the WT HIV-1 and a mutant Y181C, 181 tyrosine mutated by cysteine. The binding pockets of MK-4965 consisting of 19 residues are selected for the study. Numerical assessments confirmed the efficiency and accuracy of the DC-MP2 method in comparison with the conventional MP2 one. Subsystem interaction energies obtained by the DC-MP2 calculations clarified the key parts of the binding between MK-4965 and HIV-1: hydrogen bonding with 102 lysine, which is apart from mutated 181 residue. The present information can give a helpful guide for the future inhibitor design. © 2012 Wiley Periodicals, Inc.

This study presents the self-consistent field (SCF) treatment of the local response dispersion (LRD) method. The implementation of SCF involves the modification of the KohnSham Fock matrix by adding the dispersion potential. The derivatives of atomic pseudo-polarizabilities with respect to the density variables, which are required for evaluating the dispersion potential, are efficiently updated in the SCF procedure. Analytical energy gradient of the LRD method is also developed based on the SCF treatment. Numerical assessments of the present treatment clarified that the SCF effect brings about minor changes in both energy and electronic structure. The computational time, and number of SCF iterations, are essentially unaffected by moving from a non-self-consistent implementation to a self-consistent one. For the geometry optimizations for weakly interacting systems, the inclusion of the LRD energy gradients is shown to be essential for accurately demonstrating the intermolecular geometric parameters. (c) 2012 Wiley Periodicals, Inc.

:In this study, the analytical energy gradient for the spin-free infinite-order Douglas-Kroll-Hess (IODKH) method at the levels of the Hartree-Fock (HF), density functional theory (DFT), and second-order Møller-Plesset perturbation theory (MP2) is developed. Furthermore, adopting the local unitary transformation (LUT) scheme for the IODKH method improves the efficiency in computation of the analytical energy gradient. Numerical assessments of the present gradient method are performed at the HF, DFT, and MP2 levels for the IODKH with and without the LUT scheme. The accuracies are examined for diatomic molecules such as hydrogen halides, halogen dimers, coinage metal (Cu, Ag, and Au) halides, and coinage metal dimers, and 20 metal complexes, including the fourth-sixth row transition metals. In addition, the efficiencies are investigated for one-, two-, and three-dimensional silver clusters. The numerical results confirm the accuracy and efficiency of the present method.

:We proposed a novel kinetic energy decomposition analysis based on information theory. Since the Hirshfeld partitioning for electron densities can be formulated in terms of Kullback-Leibler information deficiency in information theory, a similar partitioning for kinetic energy densities was newly proposed. The numerical assessments confirm that the current kinetic energy decomposition scheme provides reasonable chemical pictures for ionic and covalent molecules, and can also estimate atomic energies using a correction with viral ratios.

:In order to perform practical electron correlation calculations, the local unitary transformation (LUT) scheme at the spin-free infinite-order Douglas-Kroll-Hess (IODKH) level [J. Seino and H. Nakai, J. Chem. Phys. 136, 244102 (2012); and ibid. 137, 144101 (2012)], which is based on the locality of relativistic effects, has been combined with the linear-scaling divide-and-conquer (DC)-based Hartree-Fock (HF) and electron correlation methods, such as the second-order Mo̸ller-Plesset (MP2) and the coupled cluster theories with single and double excitations (CCSD). Numerical applications in hydrogen halide molecules, (HX)n (X = F, Cl, Br, and I), coinage metal chain systems, Mn (M = Cu and Ag), and platinum-terminated polyynediyl chain, trans,trans-{(p-CH3C6H4)3P}2(C6H5)Pt(C≡C)4Pt(C6H5){(p-CH3C6H4)3P}2, clarified that the present methods, namely DC-HF, MP2, and CCSD with the LUT-IODKH Hamiltonian, reproduce the results obtained using conventional methods with small computational costs. The combination of both LUT and DC techniques could be the first approach that achieves overall quasi-linear-scaling with a small prefactor for relativistic electron correlation calculations.

:In this study, the divide-and-conquer (DC) method is extended to configuration-interaction singles, time-dependent density functional, and symmetry-adapted cluster configuration interaction (SACCI) theories for enabling excited-state calculations of large systems. In DC-based excited-state theories, one subsystem is selected as the excitation subsystem and analyzed via excited-state calculations. Test calculations for formaldehyde in water and a conjugated aldehyde demonstrate the high accuracy and effectiveness of these methods. To demonstrate the efficiency of the method, we calculated the π-π* excited state of photoactive yellow protein (PYP). The numerical applications to PYP confirm that the DC-SACCI method significantly accelerates the excited-state calculations while maintaining high accuracy.

:This study presents a numerical assessment of total energy related physical quantities estimated using the orbital-specific (OS) global and range-separated hybrid functionals, designed to satisfy the linearity condition for orbital energies (LCOE). The numerical assessment demonstrates that accurate evaluation of the reaction energies, reaction barrier, and dissociation curve can be achieved via the OS hybrid functional, for systems in which self-interaction is expected to be dominant. Therefore, the LCOE offers an accurate description of orbital energies as well as total energies for self-interaction dominant systems.

:We recently proposed a linear-scaling evaluation scheme for the second-order Mo̸ller-Plesset perturbation (MP2) energy based on the divide-and-conquer (DC) method [M. Kobayashi, Y. Imamura, and H. Nakai, J. Chem. Phys. 127, 074103 (2007)]. In this paper, we propose an approximate but effective expression for the first derivative of the DC-MP2 energy. The present scheme evaluates the one- and two-body density matrices, which appear in the MP2 gradient formula, in the DC manner; that is, the entire matrix is obtained as the sum of subsystem matrices masked by the partition matrix. Therefore, the method requires solving only the local Z-vector equations. Illustrative applications to three types of systems, peptides, Si surface model, and delocalized polyenes, reveal the effectiveness of the present method.

A new xenicane diterpenoid, cristaxenicin A (1), has been isolated from the deep sea gorgonian Acanthoprimnoa cristata. The structure of 1 was elucidated on the basis of spectral analysis including NMR and MS. The absolute configuration of 1 was determined on the basis of quantum chemical calculation of CD spectra. Cristaxenicin A (1) showed antiprotozoal activities against Leishmania amazonensis and Trypanosoma congolense with IC50 values of 0.088 and 0.25 μM, respectively. © 2012 American Chemical Society.

Direct alkoxysilylation, which is a powerful tool to provide explicit alkoxysiloxanes, is developed and its versatility is investigated. Siloxane pentamers Si[OSiR1(OMe)(2)](4) having various functional groups (R-1 = methyl, vinyl, phenyl, chloropropyl and n-butyl groups) were successfully obtained by direct alkoxysilylation of Si(OR)(4) (R= t-Bu, CHPh2). Thus, the versatility of the reaction is confirmed on organic functional groups R-1. Functional group tolerance of the reaction is discussed on the basis of electro-negativity of the R-1 groups. Alkoxysilylation of Si(Ot-Bu)(2)(OMe)(2) and Si(Ot-Bu)(OMe)(3) selectively gives trimer (MeO)(2)Si[OSiMe(OMe)(2)](2) and dimer (MeO)(3)SiOSiMe(OMe)(2), respectively. Thus, the feasibility on siloxane structure is also confirmed. Various siloxane compounds are synthesized by this newly developed reaction for the first time. (C) 2012 Published by Elsevier B.V.

We report the extension of the local response dispersion (LRD) method to the excited-state calculation based on time-dependent density functional theory. The difference density matrix, which is usually used for excited-state response properties, enables a state-specific dispersion correction. The numerical assessment proves that interaction energies of exciton-localized molecular complexes and their shifts from the ground state are accurately reproduced by the LRD method. Furthermore, we find that the dispersion correction is important in reproducing binding energies of aromatic excimers, despite the existence of other attractive forces such as exciton delocalization and charge-transfer interaction. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754508]

An accurate and efficient scheme for two-component relativistic calculations at the spin-free infinite-order Douglas-Kroll-Hess (IODKH) level is presented. The present scheme, termed local unitary transformation (LUT), is based on the locality of the relativistic effect. Numerical assessments of the LUT scheme were performed in diatomic molecules such as HX and X 2 (X = F, Cl, Br, I, and At) and hydrogen halide clusters, (HX) n (X = F, Cl, Br, and I). Total energies obtained by the LUT method agree well with conventional IODKH results. The computational costs of the LUT method are drastically lower than those of conventional methods since in the former there is linear-scaling with respect to the system size and a small prefactor. © 2012 American Institute of Physics.

The influence of water molecules on the reaction behavior of hypophosphite ion, which acts as a reducing agent for electroless deposition, on metal surfaces was elucidated by calculating the adsorption structure of hydrated hypophosphite ion on a Pd surface using Monte-Carlo simulation and density functional theory calculations. Through geometrical optimization, the most favorable structure of the hydrated hypophosphite ion was obtained, in which six water molecules interact with the oxygen of hypophosphite ion and no water interacts with the hydrogen of hypophosphite ion. Further calculations indicated that the hydrated hypophosphite ion adsorbed on the Pd surface via hydrogen. (C) The Electrochemical Society of Japan, All rights reserved.

This Letter proposes a scheme to incorporate electron-electron (e-e) correlation for the explicitly correlated Gaussian-nuclear orbital plus molecular orbital (ECG-NOMO) theory, which offers accurate descriptions for electronic and nuclear states. The second order Moller-Plesset perturbation theory and coupled-cluster theory with singles and doubles in the ECG-NOMO framework are adopted for evaluating the e-e correlation. Illustrative applications for dihydrogen, trihydrogen cation molecules, and their isotopomers confirm significant improvement for the total energies and zero-point energies. (C) 2012 Elsevier B. V. All rights reserved.

This Letter explores the potential utility of the constrained self-consistent field (CSCF) method as an efficient methodology for estimating the external fields that reproduce desired physical quantities. Using the fact that a Lagrange multiplier introduced in CSCF corresponds to an external field (perturbation), numerical assessments of CSCF were carried out on the benzene molecule. The activation energies and critical electric fields that reverse the polarizations of the ferroelectric material tetrathiafulvalene-p-chloranil (TTF-CA) were efficiently estimated. The numerical assessments demonstrate the potential applicability of CSCF for the practical designs of materials possessing certain desired physical quantities induced by external fields. (C) 2012 Elsevier B. V. All rights reserved.

We report a linear-scaling computation method for evaluating the dynamic first hyperpolarizability beta based on the divide-and-conquer (DC) method. In the present scheme, we utilized the quasi-density-matrix expression derived from Wigner's (2n + 1) rule for beta, where the quasi-density matrices are constructed from the solution obtained via the DC time-dependent self-consistent field (TD-SCF) method [T. Touma, M. Kobayashi, and H. Nakai, Chem. Phys. Lett. 485, 247 (2010)]. Numerical evaluation of pi-conjugated and saturated organic chain systems verified that the present scheme considerably reduces the computational time for the beta evaluation with a slight loss of accuracy, even around the singular frequency appearing at the electronic excitation energy. This evaluation indicates that the present linear-scaling TD-SCF scheme can also be used to estimate the molecular excitation energy. Furthermore, we succeeded in accurately evaluating the macroscopic second-harmonic generation coefficient of the polyvinylidene fluoride from the molecular (hyper)polarizabilities. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3687341]

The article discusses chemical principles such as concept, theorem, rule, and hypothesis, which fulfil the role of so-called milestone in the chemical researches. After overviewing the history of quantum chemistry, the author would like to raise the issue how modern-day theoretical chemists should confront the chemical principles. Next, the symmetry rules for degenerate excitations, which are the chemical principles discovered by the authors group, are described. In particular, this article explains the background of the discovery, the verification by the numerical assessments, and the theoretical interpretation.

:The local unitary transformation (LUT) scheme at the spin-free infinite-order Douglas-Kroll-Hess (IODKH) level [J. Seino and H. Nakai, J. Chem. Phys. 136, 244102 (2012)], which is based on the locality of relativistic effects, has been extended to a four-component Dirac-Coulomb Hamiltonian. In the previous study, the LUT scheme was applied only to a one-particle IODKH Hamiltonian with non-relativistic two-electron Coulomb interaction, termed IODKH/C. The current study extends the LUT scheme to a two-particle IODKH Hamiltonian as well as one-particle one, termed IODKH/IODKH, which has been a real bottleneck in numerical calculation. The LUT scheme with the IODKH/IODKH Hamiltonian was numerically assessed in the diatomic molecules HX and X(2) and hydrogen halide molecules, (HX)(n) (X = F, Cl, Br, and I). The total Hartree-Fock energies calculated by the LUT method agree well with conventional IODKH/IODKH results. The computational cost of the LUT method is reduced drastically compared with that of the conventional method. In addition, the LUT method achieves linear-scaling with respect to the system size and a small prefactor.

:We report the extension of the local response dispersion (LRD) method to the excited-state calculation based on time-dependent density functional theory. The difference density matrix, which is usually used for excited-state response properties, enables a state-specific dispersion correction. The numerical assessment proves that interaction energies of exciton-localized molecular complexes and their shifts from the ground state are accurately reproduced by the LRD method. Furthermore, we find that the dispersion correction is important in reproducing binding energies of aromatic excimers, despite the existence of other attractive forces such as exciton delocalization and charge-transfer interaction.

:An accurate and efficient scheme for two-component relativistic calculations at the spin-free infinite-order Douglas-Kroll-Hess (IODKH) level is presented. The present scheme, termed local unitary transformation (LUT), is based on the locality of the relativistic effect. Numerical assessments of the LUT scheme were performed in diatomic molecules such as HX and X(2) (X = F, Cl, Br, I, and At) and hydrogen halide clusters, (HX)(n) (X = F, Cl, Br, and I). Total energies obtained by the LUT method agree well with conventional IODKH results. The computational costs of the LUT method are drastically lower than those of conventional methods since in the former there is linear-scaling with respect to the system size and a small prefactor.

:The authors have developed a fragmentation-based linear-scaling electronic structure calculation strategy named the divide-and-conquer (DC) method, which has been implemented into the Gamess program package. Although there are many sorts of fragmentation-based linear-scaling schemes, most of them require the charge and spin multiplicity of each fragment a priori. Therefore, their applications to delocalized and/or open-shell systems have been limited. However, the DC method is a notable exception because the distribution of electrons in the entire system is automatically determined by the universal Fermi level. In this perspective, the authors have summarized the performance of the linear-scaling self-consistent field (SCF) and post-SCF calculations of delocalized and/or open-shell systems based on the DC method. Furthermore, some future prospects of the method have been discussed.

:We report a linear-scaling computation method for evaluating the dynamic first hyperpolarizability β based on the divide-and-conquer (DC) method. In the present scheme, we utilized the quasi-density-matrix expression derived from Wigner's (2n + 1) rule for β, where the quasi-density matrices are constructed from the solution obtained via the DC time-dependent self-consistent field (TD-SCF) method [T. Touma, M. Kobayashi, and H. Nakai, Chem. Phys. Lett. 485, 247 (2010)]. Numerical evaluation of π-conjugated and saturated organic chain systems verified that the present scheme considerably reduces the computational time for the β evaluation with a slight loss of accuracy, even around the singular frequency appearing at the electronic excitation energy. This evaluation indicates that the present linear-scaling TD-SCF scheme can also be used to estimate the molecular excitation energy. Furthermore, we succeeded in accurately evaluating the macroscopic second-harmonic generation coefficient of the polyvinylidene fluoride from the molecular (hyper)polarizabilities.

The article discusses chemical principles such as concept, theorem, rule, and hypothesis, which fulfil the role of so-called milestone in the chemical researches. After overviewing the history of quantum chemistry, the author would like to raise the issue how modern-day theoretical chemists should confront the chemical principles. Next, the symmetry rules for degenerate excitations, which are the chemical principles discovered by the authors group, are described. In particular, this article explains the background of the discovery, the verification by the numerical assessments, and the theoretical interpretation.

The authors have developed a fragmentation-based linear-scaling electronic structure calculation strategy named the divide-and-conquer (DC) method, which has been implemented into the GAMESS program package. Although there are many sorts of fragmentation-based linear-scaling schemes, most of them require the charge and spin multiplicity of each fragment a priori. Therefore, their applications to delocalized and/or open-shell systems have been limited. However, the DC method is a notable exception because the distribution of electrons in the entire system is automatically determined by the universal Fermi level. In this perspective, the authors have summarized the performance of the linear-scaling self-consistent field (SCF) and post-SCF calculations of delocalized and/or open-shell systems based on the DC method. Furthermore, some future prospects of the method have been discussed.

This Letter proposes two schemes for the efficient evaluation of electron repulsion integrals required for the explicitly correlated Gaussian-nuclear orbital plus molecular orbital (ECG-NOMO) theory, which offers accurate descriptions for electrons and nuclei. Two schemes, i.e., fully analytical and hybrid schemes for analytical and numerical integrations, for the ECG-NOMO/Hartree-Fock theory are assessed. Illustrative applications of these schemes to two-electron diatomic molecules demonstrate that the ECG-NOMO/HF theory provides significantly accurate zero-point energies within 123.5 cm(-1) deviation when compared with the experimental data. (C) 2011 Elsevier B.V. All rights reserved.

This article describes the finite-field (FF) approach for calculating static (hyper)polarizabilities based on the divide-and-conquer (DC) method. The method is assessed by the Hartree-Fock (HF) and post-HF calculations of pi-conjugated model systems: a terminal donor or acceptor substituent on polyene chains. The DC-FF approach enables the evaluation of molecular polarizabilities with highly accurate coupled-cluster theory. Numerical assessments demonstrate that the (hyper)polarizabilities calculated by the present DC-FF method agree with the conventional FF results to within a few percent by employing an appropriate buffer size.

A two-level hierarchical parallelization scheme including the second-order Moller-Plesset perturbation (MP2) theory in the divide-and-conquer method is presented. The scheme is a combination of coarse-grain parallelization assigning each subsystem to a group of processors, with fine-grain parallelization, where the computational tasks for evaluating MP2 correlation energy of the assigned subsystem are distributed among processors in the group. Test calculations demonstrate that the present scheme shows high parallel efficiency and makes MP2 calculations practical for very large molecules. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 2756-2764, 2011

We have developed the spin-unrestricted divide-and-conquer (DC)-based linear-scaling self-consistent field method for treating open-shell systems (Kobayashi et al. in Chem Phys Lett 500:172, 2010). Because the method does not require the position of excess spins or charges, it made the treatment of large spin-delocalized systems tractable. The present study extends the DC-based unrestricted open-shell scheme to the correlated second-order Moller-Plesset perturbation (MP2) theory. Numerical applications to polyene cations demonstrate that the present method gives highly accurate results with less computational costs even for spin-delocalized systems.

We have previously proposed the linearity condition for orbital energies (LCOE) in density functional theory for constructing orbital-specific exchange-correlation (XC) functionals and reported promising results in the case of range-separated functionals [24]. This Letter applies the LCOE to global hybrid functionals of which the OS Hartree-Fock exchange portions are determined by the LCOE. The numerical assessment demonstrates accurate descriptions of core and valence orbital energies for all global hybrid functionals. Thus, the LCOE is generally an effective and essential condition for constructing XC functionals. (C) 2011 Elsevier B. V. All rights reserved.

The present study theoretically revisits and numerically assesses two-body energy decomposition schemes including a newly proposed one. The new decomposition scheme is designed to make the equilibrium bond distance equivalent with the minimum point of bond energies. Although the other decomposition schemes generally predict the wrong order of the C-C bond strengths of C(2)H(2), C(2)H(4), and C(2)H(6), the new decomposition scheme is capable of reproducing the C-C bond strengths. Numerical assessment on a training set of molecules demonstrates that the present scheme exhibits a stronger correlation with bond dissociation energies than the other decomposition schemes do, which suggests that the new decomposition scheme is a reliable and powerful analysis methodology. (C) 2011 American Institute of Physics. [doi:10.1063/1.3636387]

The present study proposes a rigorous non-Born-Oppenheimer theory combining between the explicitly correlated Gaussian (ECG) method and the nuclear orbital plus molecular orbital (NOMO) method. The new method, called ECG-NOMO, adopts the ECG functions between the electronic and nuclear coordinates and, therefore, is capable of describing the nucleus-electron correlation effect accurately. The basic formalism of the ECG-NOMO method is close to the NOMO method, which starts with the Hartree-Fock type equations for NOs and MOs. The present method requires more computational cost than the original NOMO method. However, its cost is significantly smaller than that of the ECG method. The numerical tests was performed for hydrogen-like atoms (H-Ne9+) and dihydrogen cations (H2+, D2+ and T2+), and clarified that the ECG-NOMO method shows the sufficient accuracy. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3609806]

The chemical bond between atoms in metal oxides is expressed in an energy scale. Total energy is partitioned into the atomic energy densities of constituent elements in the metal oxide, using energy density analysis. The atomization energies, Delta E-M for metal atom and Delta E-O for O atom, are then evaluated by subtracting the atomic energy densities from the energy of the isolated neutral atom, M and O, respectively. In this study, a Delta E-O vs. Delta E-M diagram called atomization energy diagram is first proposed and used for the understanding of the nature of chemical bond in various metal oxides. Both Delta E-M and Delta E-O values reflect the average structure as well as the local structure. For example their values vary depending on the vertex, edge or face sharing of MO6 octahedron, and also change with the overall density of binary metal oxides. For perovskite-type oxides it is shown that the Delta E-O value tends to increase by the phase transition from cubic to tetragonal phase, regardless of the tilting-type or the &lt; 100 &gt; displacement-type transition. The bond formation in spinel-type oxides is also understood with the aid of the atomization energies. The present approach based on the atomization energy concept will provide us a new clue to the design of metal oxides. (C) 2011 Elsevier Ltd. All rights reserved.

A hexacoordinate hypervalent carbon compound with an ideal octahedral structure was proposed theoretically in a previous study (Chem. Phys. Lett. 2008, 460, 37). However, there is no report telling of success in synthesizing the compound and/or its derivatives. In order to perform a theoretical design for stronger hypervalent bonds, the present study systematically investigated the substituent effects at the para position of phenyl groups of axial C-C and equatorial C-O bonds by adopting 14 functional groups involving both electron-donating and -withdrawing groups. The results showed that the substituent effect at the former position is more influential than that at the latter. In the former case, a good correlation between the C-C and C-O distances is found and the hypervalent C-O bonds are strengthened as the substituent becomes more electron-withdrawing. In the latter case, both electron-donating and -withdrawing groups slightly weaken the hypervalent C-O bonds.

The intermolecular geometric isotope effect (GIE) in hydrogen bond A-X⋯B (X = H and D) is investigated theoretically using the nuclear orbital plus molecular orbital (NOMO) theory. To interpret the GIE in terms of physically meaningful energy components such as electrostatic and exchange-repulsion interactions, the reduced variational space self-consistent-field method is extended to the NOMO scheme. The intermolecular GIE is analyzed as a two-stage process: the intramolecular bond shrinkage and the intermolecular bond elongation. According to the isotopic shifts of energy components described by the NOMO/MP2 method, the intermolecular GIE is approximately interpreted as a process reducing the exchange-repulsion interaction after the decrease of electrostatic interaction. © 2011 American Chemical Society.

This study proposes a novel approach to construct the orbital-specific (OS) hybrid exchange-correlation functional by imposing the linearity condition: theta E-2/theta f(i)(2)vertical bar(0 &lt;= fi &lt;= 1) = theta epsilon i/theta fi vertical bar(0 &lt;= fi &lt;= 1) = 0, where E, epsilon(i), and f(i) represent the total energy, orbital energy, and occupation number of the ith orbital. The OS hybrid exchange-correlation functional, of which the OS Hartree-Fock exchange (HFx) portion is determined by the linearity condition, reasonably reproduces the ionization potentials not only from valence orbitals but also from core ones in a sense of Koopmans' theorem. The obtained short-range HFx portions are consistent with the parameters empirically determined in core-valence-Rydberg-Becke-3-parameter-Lee-Yang-Parr hybrid functional [Nakata et al., J. Chem. Phys., 124, 094105 (2006); ibid, 125, 064109 (2006)]. (C) 2011 American Institute of Physics. [doi:10.1063/1.3569030]

:The present study theoretically revisits and numerically assesses two-body energy decomposition schemes including a newly proposed one. The new decomposition scheme is designed to make the equilibrium bond distance equivalent with the minimum point of bond energies. Although the other decomposition schemes generally predict the wrong order of the C-C bond strengths of C(2)H(2), C(2)H(4), and C(2)H(6), the new decomposition scheme is capable of reproducing the C-C bond strengths. Numerical assessment on a training set of molecules demonstrates that the present scheme exhibits a stronger correlation with bond dissociation energies than the other decomposition schemes do, which suggests that the new decomposition scheme is a reliable and powerful analysis methodology.

:This study proposes a novel approach to construct the orbital-specific (OS) hybrid exchange-correlation functional by imposing the linearity condition: ∂(2)E/∂f(i)(2)|(0≤f(i)≤1) = ∂ɛ(i)/∂f(i)|(0≤f(i)≤1) = 0, where E, ε(i), and f(i) represent the total energy, orbital energy, and occupation number of the ith orbital. The OS hybrid exchange-correlation functional, of which the OS Hartree-Fock exchange (HFx) portion is determined by the linearity condition, reasonably reproduces the ionization potentials not only from valence orbitals but also from core ones in a sense of Koopmans' theorem. The obtained short-range HFx portions are consistent with the parameters empirically determined in core-valence-Rydberg-Becke-3-parameter-Lee-Yang-Parr hybrid functional [Nakata et al., J. Chem. Phys., 124, 094105 (2006); ibid, 125, 064109 (2006)].

:An analytical energy gradient formula for the density-matrix-based linear-scaling divide-and-conquer (DC) self-consistent field (SCF) method was proposed in a previous paper by Yang and Lee (YL) [J. Chem. Phys. 103, 5674 (1995)]. Since the formula by YL does not correspond to the exact gradient of the DC-SCF energy, we derive the exact formula by direct differentiation, which requires solving the coupled-perturbed equations while including the inter-subsystem coupling terms. Next, we present an alternative formula for approximately evaluating the DC-SCF energy gradient, assuming the variational condition for the subsystem density matrices. Numerical assessments confirmed that the DC-SCF energy gradient values obtained by the present formula are in reasonable agreement with the conventional SCF values when adopting a reliable buffer region. Furthermore, the performance of the present method was found to be better than that of the YL method.

To elucidate the mechanism of catalytic activity of metal surfaces on the reaction of hypophosphite ions, which act as a reducing agent for electroless deposition, molecular orbital interactions between hypophosphite ions and metal surfaces were analyzed using density functional theory. Pd (111) and Cu (111) were chosen as the surfaces with high and low catalytic activity, respectively. The electronic states of adsorption systems were analyzed using the Mülliken population analysis. The position of the d-band plays a key role in determining the catalytic activity on P-H bond cleavage of hypophosphite. The Pd surface has a d-band near the Fermi level and contains a vacancy; this enables the donation and back-donation effect to occur on the adsorbed hypophosphite and promotes P-H bond cleavage. On the other hand, the Cu surface has a d-band in the deep energy area and contains no vacancy; the donation and back-donation effect is not induced and P-H bond cleavage is not promoted. This difference in the degree of promotion of P-H cleavage is responsible for the difference in the catalytic activity on P-H cleavage and dehydrogenation of hypophosphite ions, which in turn explains the difference in the catalytic activity during the entire hypophosphite oxidation process.

An analytical energy gradient formula for the density-matrix-based linear-scaling divide-and-conquer (DC) self-consistent field (SCF) method was proposed in a previous paper by Yang and Lee (YL) [J. Chem. Phys. 103, 5674 (1995)]. Since the formula by YL does not correspond to the exact gradient of the DC-SCF energy, we derive the exact formula by direct differentiation, which requires solving the coupled-perturbed equations while including the inter-subsystem coupling terms. Next, we present an alternative formula for approximately evaluating the DC-SCF energy gradient, assuming the variational condition for the subsystem density matrices. Numerical assessments confirmed that the DC-SCF energy gradient values obtained by the present formula are in reasonable agreement with the conventional SCF values when adopting a reliable buffer region. Furthermore, the performance of the present method was found to be better than that of the YL method. (C) 2011 American Institute of Physics. [doi:10.1063/1.3524337]

:The intermolecular geometric isotope effect (GIE) in hydrogen bond A-X···B (X = H and D) is investigated theoretically using the nuclear orbital plus molecular orbital (NOMO) theory. To interpret the GIE in terms of physically meaningful energy components such as electrostatic and exchange-repulsion interactions, the reduced variational space self-consistent-field method is extended to the NOMO scheme. The intermolecular GIE is analyzed as a two-stage process: the intramolecular bond shrinkage and the intermolecular bond elongation. According to the isotopic shifts of energy components described by the NOMO/MP2 method, the intermolecular GIE is approximately interpreted as a process reducing the exchange-repulsion interaction after the decrease of electrostatic interaction.

The elementary steps of the reactions of hypophosphite ions with Cu, Ni, and Pd were calculated theoretically using Density Functional Theory (DFT) to demonstrate the reaction mechanism and gain insight at the molecular level. The elementary steps of these reactions are adsorption, dehydrogenation, and oxidation (hydroxyl base attack). In the adsorption step, hypophosphite ions adsorb onto each surface spontaneously with stabilities in the order of Ni (111) &gt; Pd (111) &gt; Cu (111). In the dehydrogenation step, hypophosphite ions dehydrogenate on Ni (111) and Pd (111) with small reaction barriers, whereas they react on Cu (111) with a large reaction barrier. The large reaction barrier on Cu (111) is not compensated for by the adsorption energy on the surface. In the oxidation step, dehydrogenated anions on each metal surface react spontaneously with the hydroxyl base. The reaction barriers on each metal surface in this step are not so significant compared to the adsorption energies on each surface, suggesting that a reaction barrier of hypophosphite ion oxidation should exist in the dehydrogenation step and only be observed for Cu (111). This proposition elucidates the experimental catalytic behaviors of metal surfaces in the electroless deposition process using hypophosphite ions. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3609000] All rights reserved.

Recently introduced local response dispersion method [T. Sato and H. Nakai, J. Chem. Phys. 131, 224104 (2009)], which is a first-principles alternative to empirical dispersion corrections in density functional theory, is implemented with generalized multicenter interactions involving both atomic and atomic pair polarizabilities. The generalization improves the asymptote of intermolecular interactions, reducing the mean absolute percentage error from about 30% to 6% in the molecular C-6 coefficients of more than 1000 dimers, compared to experimental values. The method is also applied to calculations of potential energy curves of molecules in the S22 database [P. Jurecka et al., Phys. Chem. Chem. Phys. 8, 1985 (2006)]. The calculated potential energy curves are in a good agreement with reliable benchmarks recently published by Molnar et al. [J. Chem. Phys. 131, 065102 (2009)]. These improvements are achieved at the price of increasing complexity in the implementation, but without losing the computational efficiency of the previous two-center (atom-atom) formulation. A set of different truncations of two-center and three-or four-center interactions is shown to be optimal in the cost-performance balance. (C) 2010 American Institute of Physics. [doi:10.1063/1.3503040]

In this Letter, the divide-and-conquer (DC) linear-scaling self-consistent field method is extended to the spin-unrestricted Hartree-Fock (UHF) method or Kohn-Sham density functional theory (UDFT) for treating large open-shell systems. Although the DC method is one of the fragmentation-based linear-scaling schemes, the present DC-UHF/UDFT framework can avoid specifying the number of up-and down-spin electrons in each fragment by introducing up-and down-spin Fermi levels. Test calculations for oligoth-iophenes demonstrate the high efficiency and accuracy of the DC-UHF/UDFT method even for spin-delocalized systems. (C) 2010 Elsevier B.V. All rights reserved.

To understand the phase transition from perovskite to postperovskite MgSiO3, total energy is partitioned into atomic energy densities of constituent elements in the oxide, using the energy density analysis. The atomization energies, delta E-Mg for Mg atom, delta E-Si for Si atom, and delta E-O for O atom, are then evaluated by subtracting the atomic energy density from the energy of the isolated neutral atom, Mg, Si, and O, respectively. It is found that delta E-Si and delta E-Mg are much larger than delta E-O in the perovskite phase, but delta E-O is much larger than delta E-Si and delta E-Mg in the postperovskite phase. This means that most of the energies partitioned into Mg and Si atoms in the perovskite phase transfer to the O atoms in the postperovskite phase during the transition. Such an extremely stable O-atom state is formed by the introduction of edge-shared SiO6 octahedra into the postperovskite structure. This is because the edge-sharing makes the Si-O interatomic distances longer even in very high pressure conditions. The unusual energy balance between atoms is also seen in the other postperovskite, MgGeO3 and NaMgF3.

The present study theoretically investigated hypervalent bonding systems with the skeleton of pentalene. Geometries and energetics were examined by density functional theory calculations with triple-zeta class basis sets. The bond energies of the O-X and N-X hypervalent three-center four-electron bonds were estimated. Furthermore, the relationships between the bond-switching equilibration reactions and the stabilities of the hypervalent bonding intermediates were examined.

Two perturbation (PT) theories are developed starting from a multiconfiguration (MC) zero-order function. To span the configuration space, the theories employ biorthogonal vector sets introduced in the MCPT framework. At odds with previous formulations, the present construction operates with the full Fockian corresponding to a principal determinant, giving rise to a nondiagonal matrix of the zero-order resolvent. The theories provide a simple, generalized Moller-Plesset (MP) second-order correction to improve any reference function, corresponding either to a complete or incomplete model space. Computational demand of the procedure is determined by the iterative inversion of the Fockian, similarly to the single reference MP theory calculated in a localized basis. Relation of the theory to existing multireference (MR) PT formalisms is discussed. The performance of the present theories is assessed by adopting the antisymmetric product of strongly orthogonal geminal (APSG) wave functions as the reference function.

Theoretical study of the mechanism of bond-switching of 5-(1-aminoethylimino)-3-methyl-1,2,4-thiadiazole and 5-(2-aminovinyl)isothiazole was carried out by using simplified models of 1,6-dihydro-6a-thia-1,6-diazapentalene (10-S-3) systems and corresponding oxygen analogs. Geometries and energetics were examined along unimolecular and bimolecular reaction paths by hybrid density functional theory (DFT) calculations with triple-zeta class basis sets by taking into account solvent effects which is estimated by the polarizable continuum model. It was clarified that the unimolecular reactions cannot proceed due to the high energy barriers around 70 kcal mol(-1). On the other hand, the bimolecular processes in neutral and acidic conditions can be accomplished for the sulfur compounds, not for the oxygen ones. The differences of the reactivities between the sulfur and oxygen compounds were found to be due to the difference of the stability of the symmetric intermediates with the hypervalent three-center four-electron bonds.

The CVB3LYP functional, which has been developed for evaluating both core and valence excitation energies with high accuracy, is applied to real-time time-dependent density functional theory (RT-TDDFT) calculations. The core excitation energies from the Is orbitals of several second-row atoms obtained by RT-TDDFT with the CVB3LYP functional were demonstrated and compared with those of the frequency-domain TDDFT.

We propose a novel acceleration method for self-consistent-field calculations in direct ab initio molecular dynamics/Monte Carlo (AIMD/AIMC) simulations and geometry optimization. This acceleration method, so-called LSMO, predicts an initial guess of molecular orbitals (MOs) for the next simulation step by using the geometric information with the least-squares technique. Numerical tests confirm that the LSMO method is both effective and feasible in the AIMD/AIMC simulations and geometry optimization. (C) 2010 Elsevier B.V. All rights reserved.

Energy density analysis (EDA), which partitions the total energy of a molecular system into atomic contributions, has been extended to periodic-boundary-condition calculations carried out by density-functional theory using plane-wave (PW) basis functions and pseudopotentials. The present analysis method, called PW-EDA, allows us to extract local-energy information by estimating atomic energy contributions. Numerical applications to an isolated molecule H2O and the adsorption of C2H2 on the Si(001)-(2x1) surface confirm the reliability and usefulness of PW-EDA.

We propose a novel analysis of real-time (RT) time-dependent Hartree-Fock and time-dependent density functional theory (TDHF/TDDFT) calculations using a short-time Fourier transform (STFT) technique. RT-TDHF/TDDFT calculations of model dimers were carried out and analyzed using the STFT technique, in addition to the usual Fourier transform (FT). STFT analysis revealed that the induced polarization propagated between the molecules through the intermolecular interaction; that is, it directly showed the electron dynamics of the excited system. The dependence of the propagation period on the intermolecular distance of the dimer was investigated. We also proved the possibility of describing, not just the valence, but also the core excitations by FT analysis of the RT-TDHF/TDDFT calculations of a formaldehyde monomer with Gaussian basis functions compared with conventional TDHF/TDDFT results. (c) 2010 American Institute of Physics. [doi:10.1063/1.3300127]

:Recently introduced local response dispersion method [T. Sato and H. Nakai, J. Chem. Phys. 131, 224104 (2009)], which is a first-principles alternative to empirical dispersion corrections in density functional theory, is implemented with generalized multicenter interactions involving both atomic and atomic pair polarizabilities. The generalization improves the asymptote of intermolecular interactions, reducing the mean absolute percentage error from about 30% to 6% in the molecular C(6) coefficients of more than 1000 dimers, compared to experimental values. The method is also applied to calculations of potential energy curves of molecules in the S22 database [P. Jurečka et al., Phys. Chem. Chem. Phys. 8, 1985 (2006)]. The calculated potential energy curves are in a good agreement with reliable benchmarks recently published by Molnar et al. [J. Chem. Phys. 131, 065102 (2009)]. These improvements are achieved at the price of increasing complexity in the implementation, but without losing the computational efficiency of the previous two-center (atom-atom) formulation. A set of different truncations of two-center and three- or four-center interactions is shown to be optimal in the cost-performance balance.

:We propose a novel analysis of real-time (RT) time-dependent Hartree-Fock and time-dependent density functional theory (TDHF/TDDFT) calculations using a short-time Fourier transform (STFT) technique. RT-TDHF/TDDFT calculations of model dimers were carried out and analyzed using the STFT technique, in addition to the usual Fourier transform (FT). STFT analysis revealed that the induced polarization propagated between the molecules through the intermolecular interaction; that is, it directly showed the electron dynamics of the excited system. The dependence of the propagation period on the intermolecular distance of the dimer was investigated. We also proved the possibility of describing, not just the valence, but also the core excitations by FT analysis of the RT-TDHF/TDDFT calculations of a formaldehyde monomer with Gaussian basis functions compared with conventional TDHF/TDDFT results.

The divide-and-conquer (DC) linear-scaling electronic structure method has been applied mainly to pure density functional theory (DFT) or semi-empirical molecular orbital (MO) calculations. The authors have applied the DC method to the Hartree-Fock (HF) and hybrid DFT calculations and confirmed its reliability and efficiency. In addition, they have developed a linear-scaling post-HF algorithm using subsystem orbitals obtained from DC-HF calculation by virtue of the idea of energy density analysis (EDA) and have shown its efficiency by applying it to second-order perturbation (MP2) and coupled-cluster (CCSD) calculations. In our group, these methods are implemented in the GAMESS quantum chemistry program and can easily be executed by slightly modifying the standard input file. In this paper, we describe the implementation and capabilities of our DC program on GAMESS and report the method to execute and the results of the calculations.

2H- and 13C-labelling studies on skeletal reorganization of 1,6-enynes having a terminal alkyne moiety have been performed with various catalysts. The products are 1-vinylcyclopentenes, but two possible isomers, type I and II products, can be formed. The formation of type I involves the cleavage of the original C-C double bonds and migration of the terminal alkene carbon atom to the terminus of the alkyne. On the other hand, the formation of type II involves a double cleavage of the C-C double bond and the C-C triple bond, which is an anomalous bond connection. The product ratio is affected by the nature of the catalyst used. Type II is obtained as a major isomer in the case of late transition metal halides. On the other hand, the type I product forms exclusively in the presence of a typical element halide, such as InCl3. Copyright © 2007 The Chemical Society of Japan.

We review a recent development in a rigorous non-Born-Oppenheimer method, i.e., nuclear orbital plus molecular orbital (NOMO) method, which determines the nuclear and electronic wave functions simultaneously. The NOMO theory is an exact theory for the non-BO problem in principle; for example, full-configuration interaction formulation for a complete configuration space. Hartree-Fock equations for nuclear orbitals and molecular orbitals are derived for practical calculations. The usage of Gaussian basis functions for nuclear orbitals is discussed. We formulate the elimination of translational and rotational contaminations in the NOMO method. Furthermore, many-body effects such as nucleus-nucleus, nucleus-electron, and electron-electron correlations are investigated by applying the second-order M&oslash;ller-Plesset perturbation theory to the NOMO method. The excited-state theories such as configuration interaction and generator coordinate method are examined to describe not only electronic but also vibrational excited states.

We investigated isotope effects in the reactions of protonated water dimer ions H⁺(H₂O)₂/D⁺(D₂O)₂ with acetone and dimethylsulfoxide (DMSO) using a guided ion beam apparatus. The reaction cross section, σ_r, of H⁺(H₂O)₂ with acetone was found to be slightly larger than that of D⁺(D₂O)₂ at low collision energies, <0.5 eV, where the ratio of the σ_r, was less than 1.5. The σ_r of H⁺(H₂O)₂ with DMSO was approximately twice as large as that of D⁺(D₂O)₂ with DMSO. Major reaction products were Y⁺X, where Y=H, D and X=acetone, DMSO. We examine two possible reaction processes, the proton transfer reaction via intermediate compounds and direct proton transfer.