Single adatom adsorption on metal surfaces by first principles: effects of symmetry gap and surface states on the adatom electronic properties

The adsorption of a single atom on an extended substrate is a fundamental step in processes occurring at surfaces. But its theoretical description is still extremely difficult. After the ``adatom on jellium'' approach by Lang and Williams, only very few methods have been developed in order to treat a single adatom on a more realistic substrate than jellium. In this paper we present a new theoretical approach, within the density functional theory framework, which is able to take into account i) the semi-infinite nature of the substrate, ii) the presence of gap in the surface projected bulk bands, and iii) the existence of surface states. These ingredients are basic for a suitably realistic description of adsorption. We will show the effects of the symmetry gap on the line width of the adsorbate resonances for alkali (Li-Cs), Ba, and magnetic 3$d$ adatoms (Ti-Co) on noble metals.