Fluids of pseudo-hard bodies

A new kind of particle (body), which may form a reference fluid in the thermodynamic perturbation theory of associating fluids, is introduced. The bodies are made up of real hard body cores with additional embedded interaction sites which only under certain circumstances interact as hard spheres but are 'transparent' otherwise. The properties of the fluid of such bodies are exemplified by presenting the results for the structural and thermodynamic properties of the model of pseudo-hard penta-atomics, i.e. hard spheres with four additional tetrahedrally arranged interaction sites.