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 quantum dynamics using three model potential energy matrices with different strengths and ranges for the diabatic coupling. We first demonstrate stability of the branching probabilities and final energy distributions with respect to the parameters in the FMS-M method. We then compare the method to a variety of other semiclassical methods, as well as to accurate quantum mechanical results for three-dimensional atom-diatom reactions and quenching processes; the deviations of the semiclassical results from the accurate quantum mechanical ones are averaged over nine cases. In the adiabatic electronic representation, the FMS-M method provides some improvement over Tully's fewest switches trajectory surface hopping method. However, both methods, irrespective of electronic representation, systematically overpredict the extent of reaction in comparison to the exact quantum mechanical results. The present work provides a baseline for understanding the simplest member of the hierarchy of FMS methods and its relationship to established surface hopping methods. (C) 2001 American Institute of Physics.