Optimized Constant Pressure Stochastic Dynamics

TL;DR

This paper re-derives a Langevin-based method for NPT ensemble simulations using Kramers-Moyal formalism, introduces a stable integrator with large time steps, and discusses parameter optimization with numerical tests.

Contribution

It provides a new derivation and a symplectic integrator for constant pressure stochastic dynamics in NPT simulations.

Findings

The integrator is time-reversible and stable at small friction.

Large time steps are feasible without loss of stability.

Numerical tests demonstrate the method's effectiveness.

Abstract

A recently proposed method for computer simulations in the isothermal-isobaric (NPT) ensemble, based on Langevin-type equations of motion for the particle coordinates and the ``piston'' degree of freedom, is re-derived by straightforward application of the standard Kramers-Moyal formalism. An integration scheme is developed which reduces to a time-reversible symplectic integrator in the limit of vanishing friction. This algorithm is hence expected to be quite stable for small friction, allowing for a large time step. We discuss the optimal choice of parameters, and present some numerical test results.