Theory and simulation of the loss of coherence in thermal and nonequilibrium environments

In this paper, we describe recent work on modelling the loss of quantum coherence in condensed phase systems. We review numerical methodology based on a semiclassical limit of the quantum Liouville equation for simulating quantum coherent processes using classical-like molecular dynamics simulation and ensemble averaging, and apply the approach to simulating vibrational dephasing of I₂ in cryogenic rare gas matrices and the quantum vibrations of OH stretches of HOD in D₂O. We then describe a simple analytic and numerical model that highlights novel behaviour that can be exhibited by quantum coherent processes in the presence of a nonequilibrium environment.