A comparison of Green's function and slab methods of calculating surface vibration spectral densities: p(2 × 2)O on Ni(100) as an example

Abstract

A comparison of a Green's function calculation and a slab calculation of perpendicular vibrational spectral density of the oxygen adatoms is made using the p(2 × 2)O on Ni(100) system. It is shown that with proper broadening functions, results of Green's function and slab calculations are identical. The physical origin of the two electron energy loss peaks in the Ni bulk phonon band is determined. The higher frequency peak is due to a surface mode resonance while the lower peak is due to a high-density of bulk modes with perpendicular vibration in the adatom layer. A rough guide, here termed the “slab resolution”, is proposed to set an upper limit on the resolution of a slab calculation for interpreting data of bulk mode peaks.