Molecular realism in default models for information theories of hydrophobic effects

This tercer considers several physical arguments about contributions to hyd rophobic hydration of inert gases, constructs default models to test them w ithin information theories, and gives information theory predictions using those default models with moment information drawn from simulation of liqui d water. Tested physical features include packing or steric effects, the ro le of attractive forces that lower the solvent pressure, and the roughly te trahedral coordination of water molecules in liquid water. Packing effects (hard-sphere default model) and packing effects plus attractive forces (Len nard-Jones default model) are ineffective in improving the prediction of hy drophobic hydration free energies of inert gases over the previously used f iat default model. However, a conceptually simple cluster Poisson model tha t incorporates tetrahedral coordination structure in the default model is e ffective for these predictions. These results provide a partial rationaliza tion of the remarkable performance of the flat default model with two momen ts in previous applications. The cluster Poisson default model thus will be the subject of further refinement.