Approximate switching algorithms for trajectory surface hopping

Three approximate switching algorithms for trajectory surface hopping calculations are presented using simple models to describe the dependence of the hopping probability on the nonadiabatic coupling strength. The switching algorithms are applied to the calculation of the electronic deexcitation in ethylene, methaniminium ion and trans-azobenzene. Compared with the results from the standard fewest switching algorithm (FSA), the simplest approximation based on a local diabatic representation shows some qualitative failures and overestimates the decay times severely. The other two approximate switching algorithms incorporate stochastic features and reproduce the FSA results well, with a deviation of typically 20-30% in the computed decay times. They offer a simple and efficient description of the nonadiabatic dynamics of the investigated systems. (c) 2008 Elsevier B.V. All rights reserved.