Hard sphere model

The hard sphere (HS) interaction potential is given by

$V(r)=\{\begin{array}{ccc}\mathrm{\infty }& ;& r<\sigma \\ 0& ;& r\ge \sigma \end{array}$

where $V(r)$ is the potential energy between two spheres at a distance $r$, and $\sigma$ is the sphere diameter.

HS Fluid: Equation of State (EoS); See Carnahan-Starling