Semiquantal molecular dynamics simulations of hydrogen‐bond dynamics in liquid water using spherical gaussian wave packets

Abstract

AbstractA 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. © 2012 Wiley Periodicals, Inc.