New Stable and Fast Ring-Polymer Molecular Dynamics for Calculating Bimolecular Rate Coefficients with Example of OH + CH_4

TL;DR

This paper introduces a new stable and fast ring-polymer molecular dynamics method using the Cayley propagator to accurately compute bimolecular reaction rate coefficients, demonstrated on the OH + CH4 reaction.

Contribution

The study develops a dimension-free Cayley propagator to enhance the efficiency and stability of RPMD for calculating reaction rates on high-dimensional potential energy surfaces.

Findings

Excellent agreement with experimental data across temperature range

High computational efficiency with minimal accuracy loss

Confirmed RPMD's applicability for bimolecular rate calculations

Abstract

The accurate and efficient calculation of the rate coefficients of chemical reactions is a key issue in the research of chemical dynamics. In this work, by applying the dimension-free ultra-stable Cayley propagator, the thermal rate coefficients of a prototypic high dimensional chemical reaction OH + CH4 -> H2O + CH3 in the temperature range of 200 K to 1500 K are investigated with ring polymer molecular dynamics (RPMD), on a highly accurate full-dimensional potential energy surface. Kinetic isotope effects (KIEs) for three isotopologues of the title reaction are also studied. The results demonstrate excellent agreement with experimental data, even in the deep tunneling region. Especially, the Cayley propagator shows high calculation efficiency with little loss of accuracy. The present results confirmed the applicability of the RPMD method, particularly the speed-up by Cayley propagator, in theoretical calculations of bimolecular reaction rates.