SYMMETRY-ADAPTED PERTURBATION-THEORY OF NONADDITIVE 3-BODY INTERACTIONS IN VAN-DER-WAALS MOLECULES - II - APPLICATION TO THE AR-2-HF INTERACTION

Symmetry-adapted perturbation theory (SAPT) of three-body forces is ap plied to characterize the nonadditive interactions in the Ar-2-HF trim er. The origins of the anisotropy of the nonadditive Ar-2-HF potential are discussed, and the results are compared with the existing ab init io data. The multipole-expanded expressions for the induction, inducti on-dispersion, and dispersion nonadditivities in terms of the multipol e moments and (hyper)polarizabilities are derived for the special case of atom-atom-diatom complexes, and the validity of the multipole appr oximation is investigated by comparison of the expanded and nonexpande d energies computed at the same level of the theory and in the same ba sis sets. Finally, recent (semi)empirical models of nonadditive intera ctions in Ar-2-HF based on the exchange quadrupole electrostatic inter action are analyzed in terms of contributions as defined by SAPT. It i s shown that the present level of the SAPT theory correctly accounts f or the terms included in the exchange quadrupole electrostatic model. (C) 1998 American Institute of Physics.