PNNL

Abstract

A new method is presented for the calculation of quantum mechanical rate constants for activated processes. This method is a hybrid approach involving Feynman path integrals and classical dynamics that is an extension of previous work of Messina, Schenter, and Garrett [J. Chem. Phys. 98, 8525 (1993)]. We make an ansatz for the quantum mechanical analog to the classical flux correlation function expression for the rate constant. This expression involves an imaginary-time, phase-space Feynman path integral, with the dividing surface and characteristic function expressed as a function of the phase-space centroid variables. The reactive flux correlation function is obtained from a classical-like expression in which the characteristic function is evaluated by evolving the phase-space centroid variables as if they were classical dynamical variables. We show that the theory gives exact analytic results in the high temperature and harmonic limits. The theory is further tested on a model anharmonic two-dimensional system of an Eckart barrier coupled to a harmonic oscillator. The results of the theory compare favorably to accurate numerical calculations.