Surface lattice dynamics of clean and covered nickel

The phonon spectrum of the (111) and (001) clean surfaces ofnickel has been evaluated by using the slab method In order todescribe the bulk fcc nickel we have introduced bond stretchingand angle bending force constants up to second nelghbours Thenumerical values of the force constants have been determined by aleast-square fit of the experimental bulk phonons The calculationshave been carried out with a 31 layer slabThe available EELS experiments on these surfaces wereperformed with covered surfaces, where some interacuon occursbetween the over-layer and the substrate In order to make acomparison between theory and experiments we have thereforeevaluated the phonon spectrum of N1 (111) covered with halfmonolayer of oxygen with the p(2 x 2) and (3 x 3)R30 ° orderedstructures The comparison between the loss spectra and oursurface local densities of phonon states turns out to be very good.