  We study the phase behavior and the interfacial tension of the screened
Coulomb (Yukawa) restricted primitive model (YRPM) of oppositely charged hard
spheres with diameter s using Monte Carlo simulations. We determine the
gas-liquid and gas-solid phase transition using free energy calculations and
grand-canonical Monte Carlo simulations for varying inverse Debye screening
length k. We find that the gas-liquid phase separation is stable for k s <= 4,
and that the critical temperature decreases upon increasing the screening of
the interaction (decreasing the range of the interaction). In addition, we
determine the gas-liquid interfacial tension using grand-canonical Monte Carlo
simulations. The interfacial tension decreases upon increasing the range of the
interaction. In particular, we find that simple scaling can be used to relate
the interfacial tension of the YRPM to that of the restricted primitive model,
where particles interact with bare Coulomb interactions.
