Coupling a polarizable water model to the hydrated ion-water interaction potential:: A test on the Cr3+ hydration

A strategy to build interaction potentials for describing ionic hydration of highly charged monoatomic cations by computer simulations, including the polarizable character of the solvent, is proposed. The method is based on the hydrated ion concept that has been previously tested for the case of Cr3+ aqueous solutions [J. Phys. Chem. 100, 11748 (1996)]. In the present work, the interaction potential of [Cr(H2O6)](3+) with water has been adapted to a water model that accounts for the polarizable character of the solvent by means of a mobile charge harmonic oscillator representation (MCHO model) [J. Chem. Phys. 93, 6448 (1990)]. Monte Carlo simulations of the Cr3+ hexahydrate plus 512 water molecules have been performed to study the energetics and structure of the ionic solution. The results show a significant improvement in the estimate of the hydration enthalpy [Delta H-hydr(Cr3+)=-1109.6 +/- 70 kcal/mol] that now matches the experimental value within the uncertainty of this magnitude. The use of the polarizable water model lowers by similar to 140 kcal/mol the statistical estimation of the [Cr(H2O6)](3+) hydration enthalpy compared to the nonpolarizable model. (-573 kcal/mol for the polarizable model vs -714 kcal/mol for the nonpolarizable one.) This improvement reflects a more accurate treatment of the many-body nonadditive effects. (C) 2000 American Institute of Physics. [S0021-9606(00)50804-6].