DENSITY-FUNCTIONAL STUDY OF SHORT-RANGE INTERACTION FORCES BETWEEN IONS AND WATER-MOLECULES

Short-range interaction forces between ions (Li+, Na+, F-, and Cl-) and polar solvents (H2O) were studied by using density functional methods. These short-range interaction forces, e.g., ion-water and hydrogen bonding between the solvent molecules, determine the properties of small clusters. Our study indicates that the interaction between an ion and a water molecule is usually underestimated by ab initio Hartree-Fock methods and only when electron correlation is included can structurally reliable results be obtained. The proper representation of the ion-water interactions also affects the strength of the hydrogen bonding between the solvent molecules and, therefore, plays a major role in determining the structure of these small clusters, i.e., differentiating between surface or interior states. Density functional theory does an excellent job at accomplishing these demands with greatly reduced CPU times.