Incorporating Berry Force Effects into The Fewest Switches Surface Hopping Algorithm: Intersystem Crossing and The Case of Electronic Degeneracy

TL;DR

This paper introduces a surface-hopping algorithm that incorporates Berry force effects to model intersystem crossing dynamics between singlet and triplet states, capturing new physics in degenerate electronic systems.

Contribution

The paper presents a novel surface-hopping method that accounts for Berry force effects in intersystem crossing involving degenerate triplet states.

Findings

Captures new physics in model problems

Tracks quasi-diabatic indices for triplet states

Sets groundwork for realistic simulations

Abstract

We present a preliminary surface-hopping approach for modeling intersystem crossing (ISC) dynamics between four electronic states: one singlet and one (triply degenerate) triplet. In order to incorporate all Berry force effects, the algorithm requires that, when moving along an adiabatic surface associated with the triplet manifold, \mycomment{one must also keep track of a quasi-diabatic index (akin to a "$m_s$" quantum number) for each trajectory. For a simple model problem, we find that a great deal of new physics can be captured by our algorithm, setting the stage for larger, more realistic (or perhaps even {\em ab initio}) simulations in the future.