Assessing Parameters for Ring Polymer Molecular Dynamics Simulations at Low Temperatures: DH+H Chemical Reaction

TL;DR

This paper evaluates how to optimize parameters in ring polymer molecular dynamics simulations for low-temperature chemical reactions, specifically for the DH + H system, to improve accuracy in rate calculations.

Contribution

It identifies specific parameter adjustments needed for accurate RPMD rate calculations at low temperatures, extending the method's applicability.

Findings

Standard parameters work well at T >= 100 K.

At 50 K, increasing asymptotic distance and force constant improves accuracy.

Decreasing the umbrella integration step enhances low-temperature results.

Abstract

Ring polymer molecular dynamics (RPMD) is an accurate method for calculating thermal chemical reaction rates. It has recently been discovered that low-temperature calculations are strongly affected by the simulation parameters. Here, for the thermally activated reaction DH + H -> D + H2, we calculate the RPMD rate constants at T = 50, 100, and 300 K and demonstrate that for T >= 100 K the standard input parameters yield accurate results, but at low temperatures (e.g., 50 K) one must increase the asymptotic distance and force constant, and decrease the umbrella integration step.