Quantum Dynamics With Classical and Quantum Trajectories

Abstract

The forward-backward semiclassical dynamics (FBSD) approximation provides a rigorous and practically useful methodology for simulating the dynamics of condensed phase systems that exhibit quantum mechanical effects. It is shown that FBSD autocorrelation functions of momentum and position-dependent operators satisfy rigorously the time symmetry relation of the quantum mechanical expression. The detailed balance condition follows from this symmetry in the special case where the density is given by the Boltzmann operator. The characteristics of phase space distributions in FBSD calculations are investigated. By virtue of Liouville's theorem and energy conservation, the volume of the negative regions is rigorously conserved and the energy distribution is invariant during time evolution. Thus, while the phase space density is not invariant under FBSD, exhibiting a weak time dependence mostly in its wings, it retains its quantum mechanical characteristics and does not revert to a classical Boltzmann distribution at long times. Illustrative applications on liquid neon are presented.