Square well model

Square well model:

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

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.