State‐selective cross sections from ring polymer molecular dynamics

Adrien Marjollet,Ralph Welsch

doi:10.1002/qua.26447

Abstract

AbstractUnderstanding the influence of different forms of energy (eg, translational, vibrational, rotational) on chemical reactions is a key goal and great challenge in physical chemistry. Very recently, we proposed a new approach to obtain state‐selective cross sections that approximately include quantum effects such as zero‐point energy and tunneling. The method is a combination of the widely used quasiclassical trajectory approach (QCT) and the ring polymer molecular dynamics method and thus is numerically very efficient and easily employed. Here, we present a detailed description of the method and exhaustive tests of its accuracy and applicability. The robustness of the approach is tested, as well as the convergence with the number of beads. The approach is then applied to several prototypical X + H2(ν = 0, 1), X = Mu, H, D, F, Cl reactions over a wide range of collision energies. Good agreement with rigorous quantum dynamics simulations is found for most cases. Encouraging improvement over QCT results is found for particular cases, while only a small increase in numerical cost is required.

Highlights

The detailed study and understanding of reaction processes is a central challenge of chemical physics and theoretical chemistry
Before we go into the details of the specific reactions, we will investigate the robustness of our vibrational excitation scheme, the choice of β, and the convergence with the number of beads
We employ the Mu + H2(ν = 0, 1) reaction as a test case as this reaction shows the biggest difference between exact quantum dynamics and quasiclassical trajectory approach (QCT)

Summary

Introduction

The detailed study and understanding of reaction processes is a central challenge of chemical physics and theoretical chemistry. Chemisorption of a molecule onto a surface and bimolecular reactions in the gas phase are two important classes of reactions studied Their detailed understanding is of relevance in many areas, for example, atmospheric and interstellar chemistry, combustion, and catalysis.[1,2,3,4,5,6,7,8,9,10] The most detailed results, initial state-selected and fully quantum state-resolved reaction probabilities and cross sections, can be computed from full-dimensional quantum dynamics simulations for reactions involving only few atoms. They require fitted or interpolated potential energy surfaces (PESs) that can be evaluated efficiently and dedicated curvilinear coordinate systems with complicated kinetic energy operators.[31,32,33]

Results

Discussion

Conclusion