QUANTUM MONTE-CARLO VIBRATIONAL DYNAMICS IN A PROPERTY-BASED INTERACTION POTENTIAL SCHEME FOR WEAKLY-BOUND CLUSTERS

The typical shallowness of the potential surfaces of weakly bound clus ters implies sizable ground-state vibrational excursions in the weak m odes, a feature often complicated by considerable anharmonicity. The d ifficulties of vibrational analysis are exacerbated as the number of w eak modes increases with the number of molecules in a cluster. Quantum Monte Carlo (QMC) approaches offer a general suitability to the probl em of vibrational dynamics of weakly bound clusters in that they can f ully account for anharmonicity and large amplitude motions. We report on the effectiveness and convergence behavior of diffusion quantum Mon te Carlo for both energies and the key spectroscopic values of vibrati onally averaged rotational constants. QMC involves recurring evaluatio ns of the interaction potential, and we show how property-based, two- and three-body potentials (e.g.,those involving intrinsic molecular te nsor properties) may be carefully Linked to the QMC propagation steps. (C) 1997 by John Wiley & Sons, Inc.