# Square well model

The square well model is given by [1]

$\Phi_{12}\left( r \right) = \left\{ \begin{array}{ccc} \infty & ; & r < \sigma \\ - \epsilon & ; &\sigma \le r < \lambda \sigma \\ 0 & ; & r \ge \lambda \sigma \end{array} \right.$

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.

## Equation of state

Main article: Equations of state for the square well model

## Virial coefficients

Main article: Square well potential: virial coefficients