COMPUTER-SIMULATIONS OF NACL ASSOCIATION IN POLARIZABLE WATER

Classical molecular dynamics computer simulations have been used to in vestigate the thermodynamics and kinetics of sodium chloride associati on in polarizable water. The simulations make use of the three-site po larizable water model of Dang [J. Chem. Phys. 97, 2659 (1992)], which accurately reproduces many bulk water properties. The model's static d ielectric constant and relaxation behavior have been calculated and fo und to be in reasonable agreement with experimental results. The ion-w ater interaction potentials have been constructed through fitting to b oth experimental gas-phase binding enthalpies for small ion-water clus ters and to the measured structures and solvation enthalpies of ionic solutions. Structural properties and the potential of mean force for s odium chloride in water have been calculated. In addition, Grote- Hyne s theory has been used to predict dynamical features of contact ion-pa ir dissociation. All of the calculated ionic solution properties have been compared with results from simulations using the extended simple point charge (SPC/E), nonpolarizable water model [J. Phys. Chem. 91, 6 296 (1987)]. The dependence on polarizability is found to be small, ye t measurable, with the largest effects seen in the solvation structure around the highly polarizable chlorine anion. This work validates the use of some nonpolarizable water models in simulations of many conden sed-phase systems of chemical and biochemical interest.