Coordination number for the Li+–F− ion pair in water

Abstract

A cluster of 200 molecules of water containing the Li⁺−F⁻ ion pair has been studied using Monte Carlo techniques. Two temperatures (T = 298 and 500°K) and three different distances for the Li⁺−F⁻ separation [R (Li−F) = 2.0, 6.0, and 10.0 Å] have been considered. The water−water potential is obtained from quantum−mechanical Hartree−Fock−type computations corrected by inclusion of dispersion forces; the ion−water potential has been obtained from Hartree−Fock computations for the Li⁺−F⁻−H₂O complex. The Monte Carlo simulation provides reproducible information on the cluster shape, on the cluster structure, and on the coordination numbers for the Li⁺ cation and the F⁻ anion, when in presence of one another.