Internal Trajectories and Observation Effects in Langevin Splitting Schemes

TL;DR

This paper analyzes Langevin splitting schemes in molecular dynamics, focusing on internal trajectories and observation effects, revealing subtle biases at high friction and large time steps, and providing a framework for understanding their accuracy.

Contribution

It offers a new perspective on Langevin splitting schemes by examining internal trajectories and observation points, complementing existing generator-based analyses.

Findings

Schemes can be grouped by trajectory similarity through merging and permutation.

Biases emerge at high friction coefficients and large time steps.

Provides an intuitive understanding of observation effects in Langevin integrators.

Abstract

Langevin integrators based on operator splitting are widely used in molecular dynamics. This work examines Langevin splitting schemes from the perspective of their internal trajectories and observation points, complementing existing generator-based analyses. By exploiting merging, splitting, and cyclic permutation of elementary update operators, formally distinct schemes can be grouped according to identical or closely related trajectories. Accuracy differences arising from momentum updates and observation points are quantified for configurational sampling, free-energy estimates, and transition rates. While modern Langevin integrators are remarkably stable under standard simulation conditions, subtle but systematic biases emerge at large friction coefficients and time steps. These results clarify when accuracy differences between splitting schemes matter in practice and provide an intuitive framework for understanding observation effects.