Nonadiabatic Car-Parrinello Molecular Dynamics

An extension of Car-Parrinello (CP) molecular dynamics for efficient treatment of electronically nonadiabatic processes is presented. The current approach couples the $S_1$ restricted open-shell Kohn-Sham excited state to the $S_0$ ground state using a surface hopping scheme. Efficient evaluation of the nonadiabatic couplings is achieved by exploiting the available wave function time derivatives. Since the computational cost scales linearly with the number of excited states, the technique makes possible nonadiabatic ab initio simulations of systems of similar complexity to those typically studied by standard CP methods. It is thus ideally suited to study the photochemistry of large molecules, particularly in condensed phases.