Dissipative mixed quantum-classical simulation of the aqueous solvated electron system

Abstract

A direct integration of quantum decoherence into the mixed quantum-classical (MQC) molecular dynamics (MD) method mean field with surface hopping (MF/SH) is explored from the context of the aqueous solvated electron system. Within this framework, the time evolution of the reduced density matrix via the MQC Liouville–von Neumann equation includes dissipation of the off-diagonal elements according to some prescribed decoherence time scale. This fixed parameter corresponds, for example, to the characteristic thermal average decay time of nuclear overlaps of the bath. The MF/SH implementation includes decoherence only within the evolution of the primary subsystem that is responsible for transition probabilities but not within the auxiliary equations governing environmental molecular dynamics. Within this implementation, adiabatic MQC propagation is independent of decoherence rate, and only transition times are affected. Simulations with an average decoherence parameter of 6 fs extend the excited-state lifetime of the solvated electron by three and a half times compared to coherent evolution. Since condensed phase environments typically destroy the electronic coherence on such femtosecond time scales, standard MQC methods based on coherent propagation will, in general, overestimate the true transition rate.