Sampling the isothermal-isobaric ensemble by Langevin dynamics

TL;DR

This paper introduces a novel Langevin dynamics-based method for molecular simulations in the isothermal-isobaric ensemble, ensuring correct statistical sampling and providing practical implementation guidance.

Contribution

It presents a new Langevin dynamics approach with a validated numerical scheme for accurate isothermal-isobaric ensemble sampling in molecular dynamics.

Findings

Stationary distribution matches the isothermal-isobaric ensemble

Numerical scheme is second order and symmetric

Method is validated with numerical examples

Abstract

We present a new method of conducting molecular dynamics simulation in isothermal-isobaric ensemble based on Langevin equations of motion. The stochastic coupling to all particle and cell degrees of freedoms is introduced in a correct way, in the sense that the stationary configurational distribution is proved to be in consistent with that of the isothermal-isobaric ensemble. In order to apply the proposed method in computer simulations, a second order symmetric numerical integration scheme is developed by Trotter's splitting of the single-step propagator. Moreover, a practical guide of choosing working parameters is suggested for user specified thermo- and baro-coupling time-scales. The method and software implementation are carefully validated by a numerical example.