CENTROID-DENSITY QUANTUM RATE THEORY - DYNAMICAL TREATMENT OF CLASSICAL RECROSSING

A new method is presented for the calculation of quantum mechanical ra te constants for activated processes. This method is a hybrid approach involving Feynman path integrals and classical dynamics that is an ex tension of previous work of Messina, Schenter, and Garrett [J. Chem. P hys. 98, 8525 (1993)]. We make an ansatz for the quantum mechanical an alog to the classical flux correlation function expression for the rat e constant. This expression involves an imaginary-time, phase-space Fe ynman path integral, with the dividing surface and characteristic func tion expressed as a function of the phase-space centroid variables. Th e reactive flux correlation function is obtained from a classical-like expression in which the characteristic function is evaluated by evolv ing the phase-space centroid variables as if they were classical dynam ical variables, We show that the theory gives exact analytic results i n the high temperature and harmonic limits. The theory is further test ed on a model anharmonic two-dimensional system of an Eckart barrier c oupled to a harmonic oscillator. The results of the theory compare fav orably to accurate numerical calculations.