Comparison of full multiple spawning, trajectory surface hopping, and converged quantum mechanics for electronically nonadiabatic dynamics

We present calculations employing the simplest version of the full multiple spawning method, FMS-M or minimal FMS, for electronically nonadiabatic qua ntum dynamics using three model potential energy matrices with different st rengths and ranges for the diabatic coupling. We first demonstrate stabilit y of the branching probabilities and final energy distributions with respec t to the parameters in the FMS-M method. We then compare the method to a va riety of other semiclassical methods, as well as to accurate quantum mechan ical results for three-dimensional atom-diatom reactions and quenching proc esses; the deviations of the semiclassical results from the accurate quantu m mechanical ones are averaged over nine cases. In the adiabatic electronic representation, the FMS-M method provides some improvement over Tully's fe west switches trajectory surface hopping method. However, both methods, irr espective of electronic representation, systematically overpredict the exte nt of reaction in comparison to the exact quantum mechanical results. The p resent work provides a baseline for understanding the simplest member of th e hierarchy of FMS methods and its relationship to established surface hopp ing methods. (C) 2001 American Institute of Physics.