A self-consistent-phonon approximation was used to calculate the ground-state properties and phonon density of states for the square-root 3 x square-root 3 R 30-degrees commensurate phase of monolayer H-2, HD, and D2 adsorbed on graphite. The adsorbed molecules were assumed to be in a pure J=0 rotational state, and the wave function for the solid included coordinates both parallel and perpendicular to the surface. The proper inclusion of the surface-normal terms in the wave function was found to have a significant effect on both the phonon spectrum and the ground-state properties. The calculations for the ground-state energy and the phonon spectrum of these solids were done both with and without the inclusion of short-range correlations, these short-range correlations being treated within a version of the T-matrix approximation. The possible effects of various substrate-mediated interactions, anisotropic admolecule-carbon interactions, and finite temperatures were also investigated. The current theoretical results are compared to those of recent inelastic-neutron-scattering experiments and to previous theoretical results for these systems.
Title
Phonon spectrum and density of states for commensurate monolayer phases of H2, HD, and D2 on graphite
Novaco, A. D. (1992). "Phonon spectrum and density of states for commensurate monolayer phases of H2, HD, and D2 on graphite." Physical Review B 46 (13): 8178-8194.