On the local and nonlocal components of solvation thermodynamics and their relation to solvation shell models

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Abstract
A procedure for identifying the local and nonlocal components of excess partial molar quantities is presented. This procedure is based on an analysis of the excess thermodynamic quantities expressed as integrals of local estimators over the system volume. The local components can be described in terms of the solvation shell model and are independent of the condition of solute insertion. The nonlocal components are related to the asymptotic behavior of distribution functions at large distances from the solute and they give rise to the ensemble dependence of the thermodynamic quantities of solvation. It is shown that in the constant pressure process, by using natural choices for the local estimators, the nonlocal components of the excess partial molar energy, enthalpy, entropy, and volume are absent. The relationship between our analysis and a phenomenological model which expresses excess thermodynamic quantities in terms of the solute volume, surface area, and diameter is also considered and the validity of the local interpretation is discussed.