ARNHF (N=1-4) VAN-DER-WAALS CLUSTERS - A QUANTUM MONTE-CARLO STUDY OFGROUND-STATE ENERGIES, STRUCTURES AND HF VIBRATIONAL FREQUENCY-SHIFTS

Rigid-body diffusion quantum Monte Carlo (DQMC) calculations of the in termolecular vibrational ground states of ArnHF clusters with n = 1-4, for HF v = 0 and v = 1, are reported. The intermolecular degrees of f reedom of the clusters are treated in full dimensionality, and the bes t available pairwise additive potential surfaces are used. The calcula tions yield intermolecular ground state energies, probability distribu tions of intermolecular coordinates and HF vibrational red-shifts. The vibrationally averaged cluster structures are consistent with experim ental geometries. Small but systematic differences between the painwis e additive DQMC red-shifts and experimental values for the n = 2-4 clu sters are indicative of the need for the inclusion of nonadditive inte ractions.