Square well model

Square well model:

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

where V(r) is the potential energy of interaction between pairs of particles, r is the distance, σ is the hard diameter and λ > 1.