Widom-Rowlinson model

The Widom-Rowlinson model (Ref. 1) for mixtures takes the form:

$\mathrm{\Phi }(r_{ij})=0$; if $i$ and $j$ are particles of the same species

$\mathrm{\Phi }(r_{ij})={\mathrm{\Phi }}_{HS}(r_{ij});$ if $i$ and $j$ belong to different species,

where ${\mathrm{\Phi }}_{HS}(r)$ is the hard sphere pair potential

References

1. B. Widom and J. S. Rowlinson, "New Model for the Study of Liquid–Vapor Phase Transitions", J. Chem. Phys. 52, pp. 1670-1684 (1970)