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 conformers, for example, including 13 conformers for n=6. Our predicted enthalpies and free energies are in good agreement with experimental values. For n=4 and 6, both internal and surface structures are almost isoenergetic at 0 K, while 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 in other small aqua-halide complexes. The ionization potential, charge-transfer-to-solvent (CTTS) energy, and O-H stretching vibrational spectra are reported to facilitate future experimental work. Many-body interaction potential 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 and compare the stability of the internal over the surface state. (C) 1999 American Institute of Physics. [S0021-9606(99)30318-4].