Hard core Yukawa potential

Hard core attractive Yukawa potential:

$V(r)=\{\begin{array}{ccc}\mathrm{\infty }& ;& r<\sigma \\ -(\frac{ϵ\sigma }{r})\exp [-\kappa (\frac{r}{\sigma }-1)]& ;& r\ge \sigma \end{array}$

where $V(r)$ is the potential energy of interaction between pairs of particles, $r$ is the distance, $\sigma$ is the hard diameter, $ϵ$ is the energy well depth ($ϵ>0$), and $\kappa$ is a parameter that controls the interaction range ($\kappa >0$).