We report a density functional theory investigation of the electronic structure of a monolayer of Na adsorbed on a Cu͑111͒ substrate. We approach this problem by taking into account a truly semi-infinite substrate within the embedding Green function method, which allows one to clearly distinguish surface states from bulk projected ones and to describe them with high accuracy. The quantum-well state induced by Na adsorption is discussed and compared with the surface state of the clean Cu͑111͒ surface. By suitably modifying the method, we are able to study image potential induced states which are normally not available in standard density functional theory calculations. In our approach these states are fully accounted for by introducing the image tail in the effective potential. The theoretical results are compared with experiments when available, for both the clean metal surface and the adsorbate system.

We report a theoretical investigation of the electronic structure of ultrathin MgO films on Ag͑001͒. Such a study has been motivated by recent experiments in which a peculiar behavior was observed when the film thickness is less than a few layers, suggesting that the interface properties may play a crucial role. We tried to verify such a statement by a comparative analysis between the clean surfaces of Ag and MgO, and the 1-, 2-, and 3-monolayer (ML) adsorbed systems. To perform these calculations we applied the embedding method {proposed by Inglesfield [J. E. Inglesfield, J. Phys. C 14, 3795 (1981)]} which allows us to consider a semi-infinite substrate and is therefore one of the state-of-the-art methods for the theoretical treatment of surfaces. We find evidences of a weak interaction between the silver substrate and the MgO overlayers and we show how, as the film thickness exceeds the 2 ML width, the electronic properties converge on those of a clean MgO surface. In the last part of the work we also suggest a possible interpretation of the ultraviolet photoelectron spectroscopy data obtained on these systems.

Abstract.We discuss how different properties at surfaces could ask for different theoretical treatments within the first principle density functional theory. Energies and structures are accurately determined by adopting the supercell geometry. Surface states are more conveniently described by the Green function embedding approach, which is able to take into account a truly semi-infinite solid and hence real continuous spectra. In this way a detailed analysis of discrete and resonant states is provided. We mainly describe the embedding method and provide examples to compare the two approaches. We focus next on the structural and electronic properties of alkali adatoms. The adsorption structure of Na/Cu(001) at low coverages is calculated within the supercell geometry motivated by the results of the Cambridge group on surface diffusion by 3 He spin echo scattering. The dispersion, energy, effective mass, and width of surface (quantum well and image) states of alkali atoms on Cu(111) are worked out by the embedding approach and compared with experiments.