Ring polymer molecular dynamics in gas-surface reactions: tests on initial sampling and potential energy landscape

Abstract

Given the exponential scaling of the standard quantum wavepacket method, accurate quantum dynamics calculations for gas-surface scattering remain a daunting challenge. Recent development of the ring polymer molecular dynamics (RPMD) approach has shed some light on calculating microcanonical dynamical quantities in non-thermal conditions, although most studied systems feature a notable barrier. Here we investigate the performance of RPMD reaction probability calculations in two gas-surface systems, one is an example for weakly-activated reactions (H₂+Co(0001)) and the other is a prototypical non-activated reaction (H₂+Pd(111)). Initial conditions of the molecule have been obtained with the Boltzmann sampling on the realistic potential energy surface or the approximate harmonic potential. The two sampling schemes lead to little difference in the weakly-activated H₂+Co(0001) system, both giving results in good agreement with the quantum ones. However, they yield distinguishable dynamics in the non-activated system, where harmonic Boltzmann sampling-based RPMD behaves similarly as the quasi-classical trajectory method and underestimates the reactivity at low energies. In comparison, the realistic Boltzmann sampling-based RPMD overestimates the reactivity but reasonably captures the trapping-mediated reaction mechanism. Possible reasons of this deficiency have been discussed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Ring polymer molecular dynamics
• dissociative adsorption
• zero point energy
• harmonic approximation
• gas-surface reaction

Acknowledgements

We thank Adrien Marjolle and Ralph Welsch very much for clarifying the detailed implementation of their initial sampling procedure. We would also like to thank Xuecheng Tao and Thomas F. Miller III for their help on using the Cayley propagator, and thank H. Fabio Busnengo for providing us the H₂+Pd(111) PES.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Natural Science Foundation of China [grant numbers 22073089, 22033007, 21503130, 11674212], Anhui Initiative in Quantum Information Technologies [grant number AHY090200], and The Fundamental Research Funds for the Central Universities [grant number WK2060000017].