Structures, energetics, and spectra of fluoride-water clusters F-(H2O)(n),n = 1-6: Ab initio study

F-(H2O)(n) (n=1-6) clusters have been studied using ab initio calculations. This is an extensive work to search for various low-lying energy conformer s, for example, including 13 conformers for n=6. Our predicted enthalpies a nd free energies are in good agreement with experimental values. For n=4 an d 6, both internal and surface structures are almost isoenergetic at 0 K, w hile internal structures are favored with increasing temperature due to the entropic effect. For n=5, the internal structure is favored at both 0 and 298 K under 1 atm. These are contrasted to the favored surface structures i n other small aqua-halide complexes. The ionization potential, charge-trans fer-to-solvent (CTTS) energy, and O-H stretching vibrational spectra are re ported to facilitate future experimental work. Many-body interaction potent ial analyses are presented to help improve the potential functions used in molecular simulations. The higher order many-body interaction energies are found to be important to compare the energetics of the various conformers a nd compare the stability of the internal over the surface state. (C) 1999 A merican Institute of Physics. [S0021-9606(99)30318-4].