Simulating dynamics after an excitation such as induced by an x-ray pulse involves electronic and nuclear motions that are highly correlated with each other, where going beyond the Born-Oppenheimer approximation is essential. Trajectory-based surface hopping dynamics has proven to be a powerful tool to study such coupled nuclear-electronic dynamics, but several ad hoc features such as momentum-rescaling and decoherence corrections can muddy its predictivity. Recently, a modified surface-hopping algorithm that includes a decoherence term derived from the exact factorization approach, SHXF, was proposed. We present a detailed study of this approach for four small molecules for which non-adiabatic dynamics follows a photo-excitation: ethylene, methaniminium cation, fulvene, and the uracil cation (within a vibronic coupling model), for which either highly accurate ab initio multiple spawning or multi-configuration time-dependent Hartree methods are available as reference. We find that the exact-factorization-based decoherence term acts on trajectories in a very different way than the more ad hoc Granucci-Persico energy-based decoherence correction, and augmented fewest-switches surface-hopping schemes. Once averaged over all trajectories, the results from the different methods are similar in some cases, but not always. In particular striking differences appear in the exact-factorization-derived approach compared to the others when more than one non-adiabatic coupling regions are encountered.

Exact -factorization based surface-hopping for ultrafast non-adiabatic dynamics

ACS Spring 2022

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