Image potential states and electronic structure of Na/Cu(111)

We report a density functional theory investigation of the electronic structure of a monolayer of Na adsorbed on a Cu(111) 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 Cu(111) 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.