<i>Ab initio</i>reflectance difference spectra of the bare and adsorbate covered Cu(110) surfaces

The reflectance difference spectra of the bare Cu(110) surface, of the oxygen induced $(2\ifmmode\times\else\texttimes\fi{}1)\mathrm{O}$ reconstruction, and of the carbon monoxide covered Cu(110) surface are calculated using density functional theory and the independent particle approximation. Generally, good agreement with experiment is found at energies below $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, where a resonance between two surface states dominates the spectrum for the bare surface. The resonance is progressively quenched from the bare surface, over the oxygen covered surface, to the CO covered surface. At higher energies, a rather deep minimum in the reflectance difference spectrum is calculated for all three surfaces, which agrees qualitatively with experiment, but details such as the shape and depth of the minimum are not in good agreement with experiment. We argue that a treatment beyond standard density functional theory is required at higher energies, in particular, for adsorbate covered surfaces. The calculated spectra and the surface band structures are carefully analyzed with respect to transitions between specific electronic states, confirming previous experimental and theoretical assignments. An essential result of the study is that the anisotropy of the intraband plasma frequency tensor (Drude-like term) is important and must be calculated on the same level of theory as the interband contributions to the dielectric function. Only then the results converge with increasing layer numbers.