Alkaline metals are an ideal negative electrode for rechargeable batteries. Forming a fluorine-rich interphase by a fluorinated electrolyte is recognized as key to utilizing lithium metal electrodes, and the same strategy is being applied to sodium metal electrodes. However, their reversible plating/stripping reactions have yet to be achieved. Herein, we report a contrary concept of fluorine-free electrolytes for sodium metal batteries. A sodium tetraphenylborate/monoglyme electrolyte enables reversible sodium plating/stripping at an average Coulombic efficiency of 99.85 % over 300 cycles. Importantly, the interphase is composed mainly of carbon, oxygen, and sodium elements with a negligible presence of fluorine, but it has both high stability and extremely low resistance. This work suggests a new direction for stabilizing sodium metal electrodes via fluorine-free interphases.

In this study, 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 and is denoted by DC-TDDFTB. The efficient diagonalization algorithms of TDDFTB and DC-TDDFTB methods were implemented into our in-house program. Test calculations of polyethylene aldehyde and p-coumaric acid, a pigment in photoactive yellow protein, in water demonstrate the high accuracy and efficiency of the developed DC-TDDFTB method. Furthermore, the (TD)-DFTB metadynamics simulations of acridinium in the ground and excited states give reasonable pK(a) values compared with the corresponding experimental values.

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.

An analytical method based on a three-time correlation function and the corresponding two-dimensional (2D) lifetime spectrum is developed to elucidate the time-dependent couplings between the multi-timescale (i.e., hierarchical) conformational dynamics in heterogeneous systems such as proteins. In analogy with 2D NMR, IR, electronic, and fluorescence spectroscopies, the waiting-time dependence of the off-diagonal peaks in the 2D lifetime spectra can provide a quantitative description of the dynamical correlations between the conformational motions with different lifetimes. The present method is applied to intrinsic conformational changes of substrate-free adenylate kinase (AKE) using long-time coarse-grained molecular dynamics simulations. It is found that the hierarchical conformational dynamics arise from the intra-domain structural transitions among conformational substates of AKE by analyzing the one-time correlation functions and one-dimensional lifetime spectra for the donor-acceptor distances corresponding to single-molecule Forster resonance energy transfer experiments with the use of the principal component analysis. In addition, the complicated waiting-time dependence of the off-diagonal peaks in the 2D lifetime spectra for the donor-acceptor distances is attributed to the fact that the time evolution of the couplings between the conformational dynamics depends upon both the spatial and temporal characters of the system. The present method is expected to shed light on the biological relationship among the structure, dynamics, and function. (C) 2015 AIP Publishing LLC.

A semiquantal (SQ) molecular dynamics (MD) simulation method using spherical Gaussian wave packets (WPs) is applied to a microscopic analysis of hydrogen-bond (H-bond) exchange dynamics in liquid water. We focus on the molecular jump mechanism of H-bond reorientation dynamics proposed from a classical MD simulation by Laage and Hynes (Science 2006, 311, 832). As a notable quantum effect, broadenings of both the oxygen and hydrogen WPs of jumping water are observed associated with the H-bond switching events. Nonetheless, quantum effects on averaged trajectories of structural parameters measured with respect to the WP centers are rather minor. A 1/f fluctuation of local H-bond number is observed in both SQ and classical simulations. This is obtained straightforwardly from the real-time trajectories, in contrast with the originally found 1/f fluctuation (Sasai et al., J. Chem. Phys. 1992, 96, 3045) of the total potential energies collected at quenched inherent structures. The quantum effects are found to accelerate the relaxation of H-bond number fluctuation, which is reflected in the region near the lower bound of the 1/f behavior in the power spectra. New developments in the implementation of SQMD simulations including all atoms are also described. (c) 2012 Wiley Periodicals, Inc.

A semiquantal (SQ) molecular dynamics (MD) simulation method based on an extended Hamiltonian formulation has been developed using multi-dimensional thawed Gaussian wave packets (WPs), and applied to an analysis of hydrogen-bond (H-bond) dynamics in liquid water. A set of Hamilton's equations of motion in an extended phase space, which includes variance-covariance matrix elements as auxiliary coordinates representing anisotropic delocalization of the WPs, is derived from the time-dependent variational principle. The present theory allows us to perform real-time and real-space SQMD simulations and analyze nuclear quantum effects on dynamics in large molecular systems in terms of anisotropic fluctuations of the WPs. Introducing the Liouville operator formalism in the extended phase space, we have also developed an explicit symplectic algorithm for the numerical integration, which can provide greater stability in the long-time SQMD simulations. The application of the present theory to H-bond dynamics in liquid water is carried out under a single-particle approximation in which the variance-covariance matrix and the corresponding canonically conjugate matrix are reduced to block-diagonal structures by neglecting the interparticle correlations. As a result, it is found that the anisotropy of the WPs is indispensable for reproducing the disordered H-bond network compared to the classical counterpart with the use of the potential model providing competing quantum effects between intra- and intermolecular zero-point fluctuations. In addition, the significant WP delocalization along the out-of-plane direction of the jumping hydrogen atom associated with the concerted breaking and forming of H-bonds has been detected in the H-bond exchange mechanism. The relevance of the dynamical WP broadening to the relaxation of H-bond number fluctuations has also been discussed. The present SQ method provides the novel framework for investigating nuclear quantum dynamics in the many-body molecular systems in which the local anisotropic fluctuations of nuclear WPs play an essential role. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4762840]

We theoretically investigate intermolecular motions in liquid water in terms of third-order infrared (IR) spectroscopy. We calculate two-dimensional (2D) IR spectra, pump-probe signals, and three-pulse stimulated photon echo signals from the combination of equilibrium and nonequilibrium molecular dynamics simulations. The 2D IR spectra and the three-pulse photon echo peak shift exhibit that the frequency correlation of the librational motion decays with a time scale of 100 fs. The two-color 2D IR spectra and the pump-probe signals reveal that the energy transfer from the librational motion at 700 cm(-1) to the low frequency motion below 300 cm(-1) occurs with a time scale of 60 fs and the subsequent relaxation to the hot ground state takes place on a 500 fs time scale. The time scale of the anisotropy decay of the librational motion is found to be similar to 115 fs. The energy dissipation processes are investigated in detail by using the nonequilibrium molecular dynamics simulation, in which an electric field pulse is applied. We show that the fast energy transfer from the librational motion to the low frequency motion is mainly due to the librational-librational energy transfer. We also show that the fast anisotropy decay mainly arises from the rapid intermolecular energy transfer. (C) 2009 American Institute of Physics. [doi:10.1063/1.3254518]