``Hard-Core'' Model of Liquids

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Abstract
Variants of the ``hard‐core'' model for liquids were studied. In the hard‐core model the interaction between molecules consists of a perfectly rigid repulsive core and finite, negative outer potential. Of primary concern were values of the potential energy per molecule, call it u, for the various model systems. The model systems studied were the lattice gas, hard‐core models with long‐range outer potentials, and hard‐core models at high temperatures. For the cases studied it was found that at high density u is dominated by a term which is a function only of the density n. Furthermore, in several cases this function of density is given either approximately or exactly by —an, where a is a constant. It was noted that certain thermodynamic properties of liquids at high density and low pressure are consistent with a potential energy with a dominant term of the form —an.