MIXED-ORDER SEMICLASSICAL DYNAMICS IN COHERENT-STATE REPRESENTATION -THE CONNECTION BETWEEN PHONON SIDE-BAND AND GUEST-HOST DYNAMICS

The formalism of mixed-order semiclassical molecular dynamics in coher ent state representation is developed and applied to calculations of q uantum time correlation functions in extended systems. The method allo ws the consistent treatment of a selected number of degrees of freedom to second order in the stationary phase approximation, through the He rman and Kluk propagator, while the rest of the system is treated to z eroth order, using frozen Gaussians. The formulation is applied to cal culate the absorption spectrum, of the B<--X transition of Cl-2 isolat ed in solid Ar a spectrum that shows zero-phonon lines and phonon side bands with relative intensities that depend on the excited state vibra tional level. The explicit simulation of quantum time correlation func tions of the system consisting of 321 degrees of freedom, reproduces t he spectrum and allows its interpretation in terms of the underlying m olecular motions. Details of the dynamics of a chromophore coupled to lattice phonons are discussed. (C) 1998 American Institute of Physics.