On decoherence in surface hopping: the nonadiabaticity threshold

This work presents a strategy to efficiently and safely account for decoherence in the fewest switches surface hopping method. Standard decoherence corrections often lead to too strong coherence suppression. A simple and general solution to this problem is to restrict decoherence to regions of low nonadiabaticity measured by the dimensionless Massey parameter. The same threshold values are suitable for a variety of systems, regardless of their size and absolute energy scale. When restricted to uncoupled regions, a Gaussian overlap decoherence correction consistently leads to more accurate populations than using no correction. The article also examines under what circumstances it is appropriate to decohere instantaneously.