SOLVATION FREE-ENERGY CALCULATIONS USING A CONTINUUM DIELECTRIC MODELFOR THE SOLVENT AND GRADIENT-CORRECTED DENSITY-FUNCTIONAL THEORY FOR THE SOLUTE

Electrostatic solvation free energies are calculated using a self cons istent-reaction field(SCRF) procedure that combines a continuum dielec tric model of the solvent with both Hartree-Fock (HF) and density func tional theory (DFT) for the solute. Several molecules are studied in a queous solution. They comprise three groups: nonpolar neutral, polar n eutral, and ionic. The calculated values of Delta G(el) are sensitive to the atomic radii used to define the solute molecular surface, parti cularly to the value of the hydrogen radius. However, the values of De lta G(el) exhibit reasonable correlation with experiment when a previo usly determined, physically motivated set of atomic radii were used to define the van der Waals surface of the solute. The standard deviatio n between theory and experiment is 2.51 kcal/mol. for HF and 2.21 kcal /mol for DFT for the 14 molecules examined. The errors with HF or DFT are similar. The relative difference between the calculated values.of Delta G(el) and experiment is largest for nonpolar neutral molecules, intermediate for polar neutral molecules, and smallest for ions. This is consistent with the expected relative importance of nonelectrostati c contributions to the free energy that are omitted in the model.