Describing the photo-isomerization of a retinal chromophore model with coupled and quantum trajectories.

The exact factorization of the electron-nuclear wavefunction is applied to the study of photo-isomerization of a retinal chromophore model. We describe such an ultrafast nonadiabatic process by analyzing the time-dependent potentials of the theory and by mimicking nuclear dynamics with quantum and coupled trajectories. The time-dependent vector and scalar potentials are the signature of the exact factorization, as they guide nuclear dynamics by encoding the complete electronic dynamics and including excited-state effects. Analysis of the potentials is, thus, essential-when possible-to predict the time-dependent behavior of the system of interest. In this work, we employ the exact time-dependent potentials, available for the numerically exactly solvable model used here, to propagate quantum nuclear trajectories representing the isomerization reaction of the retinal chromophore. The quantum trajectories are the best possible trajectory-based description of the reaction when using the exact-factorization formalism and, thus, allow us to assess the performance of the coupled-trajectory, fully approximate schemes derived from the exact-factorization equations.