Nonadiabatic forward flux sampling for excited-state rare events

TL;DR

This paper introduces NAFFS, a nonadiabatic forward flux sampling method that efficiently simulates rare excited-state events in molecular systems, extending the capabilities of traditional trajectory surface hopping techniques.

Contribution

The authors develop NAFFS, a novel rare event sampling scheme combining forward flux sampling with nonadiabatic dynamics, enabling efficient simulation of rare excited-state transitions.

Findings

NAFFS can be several orders of magnitude more efficient than brute-force TSH.

NAFFS accurately captures transition rates in regimes inaccessible to traditional methods.

The method is applicable to models with avoided crossings and conical intersections.

Abstract

We present a rare event sampling scheme applicable to coupled electronic excited states. In particular, we extend the forward flux sampling (FFS) method for rare event sampling to a nonadiabatic version (NAFFS) that uses the trajectory surface hopping (TSH) method for nonadiabatic dynamics. NAFFS is applied to two dynamically relevant excited-state models that feature an avoided crossing and a conical intersection with tunable parameters. We investigate how nonadiabatic couplings, temperature, and reaction barriers aspect transition rate constants in regimes that cannot be otherwise obtained with plain, traditional TSH. The comparison with reference brute-force TSH simulations for limiting cases of rareness shows that NAFFS can be several orders of magnitude cheaper than conventional TSH, and thus represents a conceptually novel tool to extend excited-state dynamics to time scales that are able to capture rare nonadiabatic events.