Many-Body Polarization, a Cause of Asymmetric Solvation of Ions and Quadrupoles

Three models are used to study the effect of many-body polarization in the solvation of non-dipolar molecules and ions in water. Two of the models are very simplified and are used to show a number of basic principles of correlation of solvent degrees of freedom and asymmetric solvent structures. These principles are used to interpret results from the third model: an accurate simulation of para-benzoquinone (PBQ) in aqueous solution with a combined quantum chemical statistical mechanical solvent model with an explicit solvent. It is found that nonzero polarizability of PBQ introduces correlation in the solvent degrees of freedom through the many-body nature of the polarization. The fluctuating electric field from the solvent on the solute increases in magnitude with the correlation. Solvent effects are hence modified. This correlation is not described within the mean-field approximation. In practice, the correlation will show up as an increased probability for asymmetric solvation of the molecule.