Widom-Rowlinson model

The Widom-Rowlinson model for mixtures takes the form:

$V\left(r_{ij}\right)=0$ if $i$ and $j$ are particles of the same species

$V\left(r_{ij}\right)=V_{HS}(r_{ij})$ if $i$ and $j$ belong to different species,

with $V_{HS}(R)$ is the hard sphere pair potential

References

B. Widom and J. S. Rowlinson, New Model for the Study of Liquid–Vapor Phase Transitions J. Chem. Phys. 52, 1670 (1970)