SEMICLASSICAL APPROXIMATIONS FOR THE CALCULATION OF THERMAL RATE CONSTANTS FOR CHEMICAL-REACTIONS IN COMPLEX MOLECULAR-SYSTEMS

Two different semiclassical approaches are presented for extending flu x correlation function methodology for computing thermal reaction rate constants, which has been extremely successful for the ''direct'' cal culation of rate constants in small molecule (similar to 3-4 atoms) re actions, to complex molecular systems, i.e., those with many degrees o f freedom. First is the popular mixed quantum-classical approach that has been widely used by many persons, and second is an approximate ver sion of the semiclassical initial value representation that has recent ly undergone a rebirth of interest as a way for including quantum effe cts in molecular dynamics simulations. Both of these are applied to th e widely studied system-bath model, a one-dimensional double well pote ntial linearly coupled to an infinite bath of harmonic oscillators. Th e former approximation is found to be rather poor while the latter is quite good. (C) 1998 American Institute of Physics.