Force correlations in molecular and stochastic dynamics

TL;DR

This study compares force correlations in molecular dynamics with stochastic models, revealing differences at short times but convergence at longer times, impacting how molecular systems are modeled and understood.

Contribution

The paper demonstrates the time-dependent behavior of force correlations in molecular dynamics and their relation to stochastic models, highlighting the conditions for ensemble equivalence.

Findings

Force correlation in MD differs from delta-function in SD at short times

Ensemble equivalence between MD and SD is restored at longer measurement times

Practical implications for modeling molecular systems are discussed

Abstract

A molecular gas system in three dimensions is numerically studied by the energy conserving molecular dynamics (MD). The autocorrelation functions for the velocity and the force are computed and the friction coefficient is estimated. From the comparison with the stochastic dynamics (SD) of a Brownian particle, it is shown that the force correlation function in MD is different from the delta-function force correlation in SD in short time scale. However, as the measurement time scale is increased further, the ensemble equivalence between the microcanonical MD and the canonical SD is restored. We also discuss the practical implication of the result.