Many-body effects in molecular dynamics simulations of Na+(H2O)<i>n</i> and Cl−(H2O)<i>n</i> clusters

Many-body effects were examined in a series of molecular dynamics computer simulations on the ionic aqueous clusters Na+(H2O)n (n=4,5,6,14) and Cl−(H2O)n (n=4,5,6,7,8,14). Two potential models were used in the simulations. In one model (TIP4P) the potential was pairwise additive, while in the second model (SPCE/POL) the many body effects were explicitly included through a self-consistent polarization routine. The two models produce equilibrium structures which are significantly different in energy and geometry. The SPCE/POL model consistently predicts energetically more stable products. In addition, for the anion cluster systems the SPCE/POL model places the Cl− on the surface of the water cluster.