Solvation of Sodium Chloride: An Effective Fragment Study of NaCl(H2O)n

Calculations on NaCl microsolvated with up to 10 water molecules were performed by treating the NaCl with restricted Hartree−Fock (RHF) 6-31G(d) ab initio wave functions and the waters with the effective fragment potential (EFP) model. Increasing numbers of local minima are found with the addition of successive water molecules. As the number of waters is increased, the Boltzmann-averaged NaCl bond distance lengthens from 2.397 to 3.167 A, the Mulliken charges increase to ±0.98, and the Boltzmann-averaged NaCl stretching frequency decreases from 359 to 94 cm-1. The incremental binding energies (in kcal/mol) as a function of n are 15.4 (n = 1), 15.1 (n = 2), 14.0 (n = 3), 13.9 (n = 4), 12.3 (n = 6), 12.8 (n = 8), 9.1 (n = 10).