Square well model page on SklogWiki - a wiki for statistical mechanics and thermodynamics

The square well model is given by ^[1]

\Phi _{12}\left(r\right)=\left\{{\begin{array}{ccc}\infty &;&r<\sigma \\-\epsilon &;&\sigma \leq r<\lambda \sigma \\0&;&r\geq \lambda \sigma \end{array}}\right.

where $\Phi _{12}(r)$ is the intermolecular pair potential, $\epsilon$ is the well depth, $r$ is the distance between site 1 and site 2 $r:=|\mathbf {r} _{1}-\mathbf {r} _{2}|$ , σ is the hard diameter and λ > 1. For an infinitesimally narrow well one has the sticky hard sphere model proposed by Baxter.