The phase diagram of a lattice gas confined between two parallel adsorbing walls is investigated via Monte Carlo simulation. For large wall separations, we find a line of first-order capillary-condensation transitions at chemical potentials shifted to smaller values, μ(T), than the bulk value ${\mu }_{\mathrm{sat}(\mathrm{T}}$). We also find a line of first-order prewetting transitions, terminating in a prewetting critical point and intersecting the line of capillary-condensation transitions in a triple point where thin-film, thick-film, and ‘‘liquid’’ phases all coexist. Although such a rich phase diagram had been conjectured earlier on the basis of mean-field calculations and thermodynamic arguments, we believe this is the first confirmation by simulation.

• Received 4 August 1988

DOI:https://doi.org/10.1103/PhysRevB.39.9336