Free energy of solvation for the reference interaction site model: Critical comparison of expressions

We investigate expressions of excess chemical potential in the reference interaction site model (RISM) integral equation theory. In addition to the previous expressions from the Gaussian density fluctuation theory and from the extended RISM (XRISM) theory, we examine a new free energy functional from the distributed partial wave expansion of molecular correlation functions, using the embedded site model and alcohols with different parameter sets. The results clearly show that the free energy of solvation in the XRISM theory includes a serious error, which is related to the number of interaction sites and the geometry of a solute molecule. (C) 2001 American Institute of Physics.