Mixed quantum-classical dynamics response function approach to spectroscopy

An attempt was made to calculate the optical linear response function, which is normally expressed in terms of the two-point dipole moment correlation functions, in mixed quantum-classical systems. It was calculated by two different approaches: (a) linear response function approach of Nielsen et al. and (b) the alternative way developed previously. The end results of both approaches were identical. An important assumption used in deriving the linear dipole moment correlation function was the Condon approximation.