Phonon Spectrum and Density of States for the 3×3R30° Phase of D2 and H2 on Graphite

Abstract

A self-consistent phonon calculation was used to calculate the phonon spectrum and density of states of ${\mathrm{D}}_2$ and ${\mathrm{H}}_2$ adsorbed on graphite. The adsorbed molecules are assumed to be in a free-rotor state and the molecular solid is taken to be the $\sqrt{3}\times \sqrt{3}R30\mathrm{}°$ commensurate phase. The theoretical results are compared to recent neutron-scattering results for the phonon modes of ${\mathrm{D}}_2$ and with older data for ${\mathrm{H}}_2$. The effect of the use of coordinates both parallel to and perpendicular to the surface in the functional form for the wave function was found to be significant. Thus these are not purely two-dimensional systems.