Accelerating the convergence of path integral dynamics with a generalized Langevin equation

TL;DR

This paper introduces a PI-GLE method that accelerates convergence of path integral molecular dynamics, effectively capturing quantum effects like zero-point energy and tunnelling in anharmonic systems such as liquid water.

Contribution

It extends the generalized Langevin equation approach to improve the efficiency of path integral simulations for strongly anharmonic quantum systems.

Findings

PI-GLE accelerates convergence in quantum simulations.

Effective in modeling tunnelling and zero-point energy.

Applied successfully to liquid water and double-well systems.

Abstract

The quantum nature of nuclei plays an important role in the accurate modelling of light atoms such as hydrogen, but it is often neglected in simulations due to the high computational overhead involved. It has recently been shown that zero-point energy effects can be included comparatively cheaply in simulations of harmonic and quasi-harmonic systems by augmenting classical molecular dynamics with a generalized Langevin equation (GLE). Here we describe how a similar approach can be used to accelerate the convergence of path integral (PI) molecular dynamics to the exact quantum mechanical result in more strongly anharmonic systems exhibiting both zero point energy and tunnelling effects. The resulting PI-GLE method is illustrated with applications to a double-well tunnelling problem and to liquid water.