CRITICAL-STUDY OF FLUORIDE WATER INTERACTIONS

A new parametrization of the fluoride-water interaction within a polar izable water model is presented. Because of the absence of accurate ex perimental data for the enthalpy of formation of the F-(H2O) cluster, the results of ab-initio calculations were used to parametrize the ion -water interaction. The ab-initio results suggest that this interactio n is 10% stronger than what was previously thought. The accuracy of th e present parametrization was evaluated by comparing the model potenti al with the ab-initio results along the minimum energy profile for the fluoride-water interaction for various F-O separations. The energetic and structural properties of the clusters F-(H2O)(n), n = 1-10, as we ll as of aqueous fluoride solution are studied using molecular dynamic s simulation techniques. The stronger ion-water interaction results in the appearance of interior states (configurations in which the ion is ''solvated'' by water molecules) for finite clusters with six or more water molecules. The results of the aqueous ionic solution simulation s provide a reasonable description of many structural and thermodynami c properties of the solvated ion such as the solvation enthalpy, the r adial distribution function, and the hydration number.