A MULTI-CONFIGURATIONAL TIME-DEPENDENT HARTREE APPROACH TO THE DIRECTCALCULATION OF THERMAL RATE CONSTANTS

A method employing the multi-configurational time-dependent (MCTDH) ap proach for the direct calculation of the thermal rate constant is pres ented. It is based on the flux-position correlation function of Miller et al. [J. Chem. Phys. 79, 4889 (1983)]. Eigenvalues of the thermal f lux operator (F) over cap(T) = e(-<(H)over cap /2kT>) (F) over cap e(- <(H)over cap /2kT>) are calculated employing an iterative diagonalizat ion scheme suitable for the MCTDH approach. (F) over cap(T), has only a few significant eigenvalues, which can be interpreted as contributio ns of the ground and excited vibrational states of the activated compl ex. The rate constant is calculated by propagating the eigenfunctions of (F) over cap(T) in time. As an example, the H+H-2 reaction is studi ed. Exact results for vanishing total angular momentum (J=0) are given . The total thermal rate constant is calculated by a J shifting scheme which takes the linear geometry of the transition state into account. (C) 1997 American Institute of Physics.