Conical intersections: Relaxation, dephasing, and dynamics in a simple model

Conical intersections occur on potential energy surfaces of many medium-sized and larger molecules. Their investigation, which has been ongoing for more than six decades, shows that vibronic coupling and relaxation behaviors at conical intersections can become quite complex and show large quantum effects. We present calculations of dynamical behavior in very simple (two-dimensional, degenerate, non-displaced) conical intersection models. The focus is placed on the effects of bath interactions on conical behavior - that is, the extent to which electronic dephasing, nuclear relaxation, and electronic relaxation affect the initially excited wave packet evolving on conical intersection surface. The calculations are carried through using a density matrix picture, with a Lindblad semi-group formalism to characterize relaxation. We observe large quantum effects that act particularly on true conical structures (anti-symmetric with respect to the mixing coordinate), as opposed to comparable-strength interactions without this symmetry. Significant changes in excited-state population decay, and even larger and more striking changes in the (observable) bleach recovery signal, are found.