Semiquantal molecular dynamics simulations of hydrogen-bond dynamics in liquid water using multi-dimensional Gaussian wave packets

Junichi Ono, Koji Ando

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

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 Hamiltons 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.

Original languageEnglish
Article number174503
JournalJournal of Chemical Physics
Volume137
Issue number17
DOIs
Publication statusPublished - 2012 Nov 7
Externally publishedYes

Fingerprint

Wave packets
Molecular Dynamics Simulation
wave packets
Molecular dynamics
Hydrogen
Hydrogen bonds
hydrogen bonds
molecular dynamics
Water
Computer simulation
Liquids
liquids
water
simulation
Covariance matrix
Space Simulation
Bond number
Anisotropy
Hamiltonians
variational principles

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry
  • Medicine(all)

Cite this

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abstract = "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 Hamiltons 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.",
author = "Junichi Ono and Koji Ando",
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AU - Ando, Koji

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