Chemical Reaction Rate Coefficients from Ring Polymer Molecular Dynamics: Theory and Practical Applications

Abstract

This Feature Article presents an overview of the current status of ring polymer molecular dynamics (RPMD) rate theory. We first analyze the RPMD approach and its connection to quantum transition-state theory. We then focus on its practical applications to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rate coefficients in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a well-established and validated alternative to conventional techniques for calculating thermal chemical rate coefficients. We also hope it will motivate further applications of RPMD to various chemical reactions.

Low temperature rates for key steps of interstellar gas-phase water formation

“…The QCT calculations presented in ( 21 ) are distinctly lower at both low and room temperatures. QCT’s reliability is sometimes uncertain ( 35 , 37 ), particularly at low energies and temperatures, as this approximation completely ignores important quantum effects such as tunneling, resonances, and—presumably more importantly for the present essentially barrierless reactions (1) and (2)—ZPE conservation along the reaction path (see the energy diagrams in the Supplementary Materials). For instance, for another complex-formation astrochemical reaction in the H 5 + system, it was recently shown that the ZPE leakage in QCT simulations can lead to strong deviations from experimental data at low temperatures ( 37 ).…”

Kinetics of low-temperature transitions and a reaction rate theory from non-equilibrium distributions

“…A number of investigations have provided examples of several chemical reactions within this regime. A series of experimental kinetic data and of benchmark quantum mechanical calculations [87][88][89][90][91][92][93][94] has established that, for example, the reaction of a fluorine atom with molecular hydrogen represents a prototypical case of sub-Arrhenius behaviour [95,96] has been experimentally confirmed [97].…”

Rigorous close-coupling quantum dynamics calculation of thermal rate constants for the water formation reaction of H2 + OH on a high-level PES

“…33,[48][49][50][51][52] Besides the exact calculation of thermal rate constants employing the quantum transition state concept, various approximate methods have been employed to calculate thermal rate constants on modern PES. Successful approximate approaches include instanton calculations, 53 the ring-polymer molecular dynamics (RPMD) approach, 54,55 and various semi-empirical tunneling corrections to transition state theory (TST). 56 All these approaches have been employed to study the title reaction.…”