PNNL

Abstract

A new parametrization of the fluoride-water interaction within a polarizable water model is presented. Because of the absence of accurate experimental 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 interaction is 10% stronger than what was previously thought. The accuracy of the present parametrization was evaluated by comparing the model potential 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 well as of aqueous fluoride solution are studied using molecular dynamics 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 simulations provide a reasonable description of many structural and thermodynamic properties of the solvated ion such as the solvation enthalpy, the radial distribution function, and the hydration number.