HF DIMER - EMPIRICALLY REFINED ANALYTICAL POTENTIAL-ENERGY AND DIPOLEHYPERSURFACES FROM AB-INITIO CALCULATIONS

The interaction between two HF molecules as a function of all six inte rnal coordinates is reported as calculated for 3284 selected points in configuration space at counterpoise-corrected explicitly correlated l evels and fitted to an analytical expression, which is described in de tail. The unweighted rms deviation for all 3284 points is 21 cm(-1). E mpirical refinements are applied through mixing and scaling of the ab initio data, guided by the comparison of multidimensional nuclear quan tum energy levels with experimental data. The resulting semiempirical pair potentials (labeled SC-2.9 and SO-3) contain 67 and 61 freely adj usted parameters and are combined with a four parameter monomer potent ial of generalized Poschl-Teller type. Various minimum energy paths an d cuts are investigated. Major improvements over earlier HF dimer pote ntials are demonstrated via multidimensional solutions of the nuclear Schrodinger equation. Comparison with other high level ab initio calcu lations and with various experimental data reveals very good overall c onsistency. The new potential suggests strong Coriolis coupling in the librational degrees of freedom. Best estimates of stationary points, of the dimer dissociation energy (D-e=19.1+/-0.2 kJ/mol), of the elect ronic barrier to hydrogen bond exchange (4.2+/-0.2 kJ/mol), of the ele ctronic barrier to linearity (3.9+/-0.2 kJ/mol), and of the electronic barrier to hydrogen exchange (175+/-10 kJ/mol) are inferred. Based on accurate electric dipole functions for the monomer and distortion con tributions calculated with a large basis at SCF level, a simple analyt ical six-dimensional electric dipole hypersurface is presented. (C) 19 98 American Institute of Physics.