On the use of QM/MM Surface Hopping simulations to understand thermally-activated rare event nonadiabatic transitions in the condensed phase

TL;DR

This paper introduces a QM/MM surface hopping simulation approach to study thermally-activated nonadiabatic transitions in condensed phases, providing insights into electron transfer mechanisms in solution.

Contribution

The authors develop a rare-event sampling scheme using the INAQS package interfaced with GROMACS, enabling detailed simulation of nonadiabatic electron transfer in condensed phase systems.

Findings

Solvent participation ratio affects electron transfer rates.

Refinements are needed for frustrated hops in condensed phase simulations.

The methodology is adaptable to various condensed phase nonadiabatic phenomena.

Abstract

We implement a rare-event sampling scheme for quantifying the rate of thermally-activated nonadiabatic transitions in the condensed phase. Our QM/MM methodology uses the recently developed INAQS package to interface between an elementary electronic structure package and a popular open-source molecular dynamics software (GROMACS) to simulate an electron transfer event between two stationary ions in a solution of acetonitrile solvent molecules. Nonadiabatic effects are implemented through a surface hopping scheme and our simulations allow further quantitative insight into the participation ratio of solvent and the effect of ion separation distance as far as facilitating electron transfer. We also demonstrate that the standard gas-phase approaches for treating frustrated hops and velocity reversal must be refined when working in the condensed phase with many degrees of freedom. The code and methodology developed here can be easily expanded upon and modified to incorporate other systems, and should provide a great deal of new insight into a wide variety of condensed phase nonadiabatic phenomena.