Collective coordinates for semiclassical femtosecond dissipative dynamics in Liouville space

A semiclassical path-integral algorithm for propagating the reduced density matrix of a quantum-particle coupled to a harmonic bath with an arbitrary temperature and distribution of timescales is developed. Using a canonical transformation of the action in Liouville space, a unique prescription is provided for constructing collective bath coordinates for a given nuclear spectral density. The number of relevant collective coordinates depends on the structure of the spectral density and increases at lower temperatures. (C) 1998 Elsevier Science B.V. All rights reserved.