ACCURATE QUANTUM-MECHANICAL CALCULATION OF THERMALLY AVERAGED REACTION-RATE CONSTANTS FOR POLYATOMIC SYSTEMS

A new approach to the calculation of quantum mechanical Boltzmann averaged reaction rate constants for polyatomic systems is described. The rate constant is obtained by integrating a set of coupled first order temperature-dependent differential equations, the number of which grows linearly with the size of the system. This is accomplished by (i) representing the complex time evolution operator in mixed position and operator form and (ii) introducing two-body correlations in the conventional time-dependent self-consistent field approximation, as suggested recently [Chem. Phys. Lett. 169, 541 (1990)]. The method is accurate and numerically stable; it is therefore expected to find considerable utility in the study of gas phase bimolecular reactions with the reaction path Hamiltonian formalism, as well as in the calculation of rate constants for reactive processes in condensed media.