Calculation of the eels spectra of the Ni(001) surface with p(2×2) and c(2×2) overlayers of oxygen

We present a force constant slab calculation of the nickel (001) surface phonons with p(2×2) and c(2×2) oxygen overlayers. According to very recent experimental results we assume in both configurations an equal distance of 0.9 Å between the oxygen overlayer and the nickel surface. With two adjustable parameters (the ONi force constants) we are able to reproduce with good accuracy the position and the lineshape of the four peaks present in the experimental EELS spectra. The nature of these peaks is investigated in detail and the noticeable difference between the spectra of the two overlayers is explained.