Quantum-classical description of environmental effects on electronic dynamics at conical intersections.

Quantum-classical Liouville theory is used to simulate the dynamics of systems containing conical intersections. In particular quantum dynamical effects on the electronic population transfer and coherence in a quantum subsystem that arise from the presence of an environment are studied. The environment, in turn, is partitioned into an immediate environment representing, say, local molecular vibrations, and a bath representing other degrees of freedom. Population transfer may be enhanced or suppressed, depending on the relative values of the characteristic frequencies of the immediate environment and bath. Electronic decoherence and the destruction of geometric phase effects were observed for bath frequencies that are large relative to the molecular vibrations. The dynamics at higher dimensional conical intersections was found to be very sensitive to the environmental coupling. When a single collective solvent coordinate couples directly to the electronic subsystem, the characteristic frequency of the new coordinate, relative to that of the nuclear vibrational modes, has a strong effect on the population dynamics. The results also serve as a test of the QCL dynamical scheme for future applications to more detailed molecular descriptions of condensed phase environments for conical intersection dynamics.