A density-functional theory for the submonolayer adsorbed film is developed. The adsorbate interactions are restricted to hard repulsions and described with a nonlocal density functional for the free energy, which allows for the presence of intrinsic crystalline order. The competition with the substrate ordering is studied as a function of the temperature and the coverage for different values of the substrate lattice parameter. The phase diagrams obtained include fluid, commensurate, and incommensurate phases.

• Received 9 June 1986

DOI:https://doi.org/10.1103/PhysRevB.35.3376