DEVELOPMENT OF NONADDITIVE INTERMOLECULAR POTENTIALS USING MOLECULAR-DYNAMICS - SOLVATION OF LI+ AND F- IONS IN POLARIZABLE WATER

Nonadditive intermolecular potentials for ion-H2O and ion-(H2O)2 complexes (ion = Li+ and F-) were derived using molecular-dynamics methods. The successive H2O binding energies and structural properties of Li+ (H2O)n and F-(H2O)n (n = 3-6) clusters, including simulations of aqueous ionic solutions, were examined using these potential parameters. The results reproduce well-observed solvation enthalpies as well as structural properties for these ions. For n < 5, water molecules distributed almost symmetrically around the Li+ ion, while water molecules preferred to cluster on the same side of the F- ion. These features are in agreement with earlier Monte Carlo, molecular dynamics, and molecular mechanics studies on similar systems. We studied the relationships between ionic clusters and bulk simulations by comparing structural properties for these simulations. In many cases, we found these properties were quite similar. These results provide valuable information in understanding the relationships between ionic clusters and solution chemistry.