Medium-Dependent Intermolecular Potential for Liquids and Its Use in Obtaining Free Energy and Entropy

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Abstract
It has been found that even in nonpolar liquids an intermolecular pair potential derived from gas properties may be affected by as much as 10%–40% due to the medium effect of the liquid, and many-atom forces. An effective intermolecular pair potential for liquids was recently derived. It takes into account the local solvation structure around the two molecules in an analytical form with an explicit dependence on the relative sizes of the solute and solvent molecules. Its parameters are specified mainly in terms of some macroscopic properties. The potential is defined so as to reproduce the total thermodynamic energy of the system correctly. In the present paper, based on a statistical-mechanical perturbation theory, it is shown that the effective pair potential may be used as though it were an ordinary two-body potential, not only in the total energy, but also in quantities like free energy and entropy.
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