Nonadiabatic ImF instanton rate theory

TL;DR

This paper develops a new nonadiabatic instanton rate theory based on the ImF premise, addressing previous limitations and successfully capturing quantum effects like tunnelling across different regimes.

Contribution

It introduces a rigorous nonadiabatic ImF rate theory that overcomes the shortcomings of earlier approaches and bridges the gap between tunnelling and high-temperature regimes.

Findings

Reliable results for deep tunnelling regimes.

Limitations observed in high-temperature rate predictions.

Effective in asymmetric and multidimensional systems.

Abstract

Semiclassical instanton theory captures nuclear quantum effects such as tunnelling in chemical reactions. It was originally derived from two different starting points, the flux correlation function and the ImF premise. In pursuit of a nonadiabatic rate theory, a number of methods have been proposed; almost all based on the less rigorous ImF premise. Only recently, we introduced a rigorous nonadiabatic ring-polymer instanton rate theory in the flux-correlation function framework which successfully bridges from the Born-Oppenheimer to the golden-rule limit. Here, we examine the previous ImF-based attempts and conclude that they do not capture the two limits correctly. In particular, we will highlight how the last in a series of developments, called mean-field ring-polymer instanton theory, breaks down in the golden-rule limit. We develop a new nonadiabatic ImF rate theory to remedy the failings of previous attempts while taking inspiration from them. We also consider the crossover from deep tunnelling to a high-temperature rate theory. We test our new nonadiabatic ImF theory on a range of models including asymmetric and multidimensional systems and we show reliable results for the deep-tunnelling regime but limitations for the related high-temperature rate theory.