Nonadiabatic Excited-State Molecular Dynamics (NA-ESMD): Numerical tests of convergence and parameters

Nonadiabatic molecular dynamics simulations, involving multiple coupled potential energy surfaces, often requires a large number of independent trajectories in order to achieve the desired convergence of the results, and simulation relies on different parameters that should be tested and compared. In addition to influencing the speed of the simulation, the chosen parameters combined with frequently implemented approximations can lead to unanticipated changes in the accuracy of the simulated dynamics. We have previously developed a nonadiabatic excited state molecular dynamics (NA-ESMD) methodology employing Tully's fewest switches surface hopping (FSSH) algorithm. In this study, we seek to investigate the impact of the number of trajectories and the various parameters on the simulation of the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene) within our developed framework. Various user-defined parameters are analyzed: classical and quantum integration time steps, and the number of trajectories used for statistical averaging. Common approximations such as reduced number of nonadiabatic coupling terms and the classical path approximation (CPA) are also investigated.