On-the-fly, electric-field-driven, coupled electron-nuclear dynamics.

An on-the-fly, electric field driven, coupled electron-nuclear dynamics approach is developed and applied to model the photodissociation of water in the A((1)B1) excited state. In this method, a quantum propagator evolves the photon-induced electronic dynamics in the ultrafast time scale, and a quasi-classical surface hopping approach describes the nuclear dynamics in the slower time scale. In addition, strong system-field interactions are explicitly included in the electronic propagator. This theoretical development enables us to study rapid photon-induced bond dissociation dynamics and demonstrates the partial breakdown of electronic coherence as well as electronic population trapping in the excited state when the molecular vibrations detune the system with respect to the applied field. The method offers a practical way to use on-the-fly dynamics for modeling light-molecule interactions that lead to interesting photochemical events.