A program of theoretical research on the structures and thermodynamics of thin physically adsorbed layers is described. The main goal is to achieve a quantitative understanding of a few adsorbate/substrate combinations in which recent experimental data show effects of the competing spatial periodicity of an adlayer lattice and the substrate lattice. Several topics are described which could lead to improved specification of the energy barriers to lateral motion of adsorbed atoms on the substrate surface. The substrates considered are the (111) face of platinum, the basal plane surface of graphite and the (001) face of magnesium oxide. The adsorbates include xenon, krypton and molecular hydrogen and nitrogen. The calculations include variational quantum mechanics for the ground state of hydrogen and deuterium and lattice dynamics and cell model approximations for the near classical adsorbates. The proposed work relies heavily on experimental data obtained from refinements of low energy electron diffraction, x-ray diffraction, thermal neutron scattering, and thermal helium atom scattering.
