Dynamics of a frustrated rare-gas monolayer adsorbed on a MgO(100) substrate

The dynamics of a frustrated rare-gas monolayer adsorbed on a square-symmetry MgO(100) surface is investigated. It is shown that the four nonequivalent rare-gas atoms contained in the Brillouin zone of the (3×{}2) monolayer structure are responsible for the occurrence of four different and slightly dispersed modes perpendicular to the surface and of strongly dispersed optical modes in the directions parallel to the surface of the substrate. The coupled dynamics of the monolayer with a simplified quasicontinuum substrate is also investigated, in order to determine the influence of the hybridization on the dispersion of the frequencies of the monolayer, in the long-wavelength limit. For the resonance frequencies considered here, the hybridization remains weak. Problems connected to the ability, for the harmonic treatment, to give accurate dispersion relations in the short-wavelength region are also discussed.