Stochastic classical trajectory approach to relaxation phenomena. II. Vibrational relaxation of impurity molecules in Debye solids

The stochastic classical trajectory approach is extended through introduction of a systematic class of phonon mode densities. Convenient algorithms are presented for generating the required random forces and damping integrals corresponding to mode spectra which approach, as closely as desired, the Debye spectrum. Extension to realistic mode densities involving irregular and discontinuous features is discussed. Application to vibrational relaxation of impurities in solids demonstrates that rates can depend sensitively on the structure of the phonon density of states, particularly at low temperatures.