Probing photodissociation dynamics using ring polymer molecular dynamics

The performance of the ring polymer molecular dynamics (RPMD) approach to simulate typical photodissociation processes is assessed. The correct description of photodissociation requires the calculation of correlation functions or expectation values associated with non-equilibrium initial conditions, which was shown to be possible with RPMD very recently [J. Chem. Phys. 145, 204118 (2016)]. This approach is combined with treatment of the nonadiabatic dynamics employing the ring polymer surface hopping approach (RPSH), which is based on Tully's fewest switches surface hopping (FSSH) approach. The performance is tested using one-dimensional photodissociation models. It is found that RPSH with non-equilibrium initial conditions can well reproduce the time-dependent dissociation probability, and adiabatic and diabatic populations for cases where the crossing point is below and above the Franck-Condon point, respectively, while standard FSSH fails to reproduce the exact quantum dynamics in the latter case. Thus, it is shown that RPSH is an efficient and accurate alternative to standard FSSH, which is one of the most widely employed approaches to study photochemistry.