Excluded volume anisotropy and two-cavity distribution functions in hard sphere fluids

A new model for the distribution of spherical cavity pairs in a hard sphere fluid is derived by extending exact low density results to include the effects of cavity pair anisotropy at finite solvent density. In particular, the unitless excluded surface-area-to-volume ratio is used to quantitate the anisotropy dependence of the excess chemical potential of a solute cavity pair. The Carnahan-Starling contact radial distribution function of a single component hard sphere fluid is used to fix this anisotropy dependence. Predictions of the resulting excluded volume anisotropy (EVA) model for the two-cavity distribution function are found to compare favorably with previous simulation and analytical results. Generalization of the EVA model to predict solvation thermodynamics of arbitrary shaped solutes in molecular liquids, as well as multi-cavity distribution functions in hard sphere fluids are suggested. (C) 1997 American Institute of Physics.