The adiabatic molecule-metal surface interaction: Theoretical approaches

Ab initio methods for calculating the adiabatic electronic properties of a single isolated molecule interacting with a metal surface are reviewed. First the fundamental approaches of Anderson, Grimley, and Newns for chemisorption, as well as of Zaremba and Kohn, for physisorption, are outlined. Then the density-functional theory and its approximations are considered. The different models for the adsorbate system are described. They comprise those in which the system has a finite volume-i.e., the cluster, the slab, and the supercell models-and those which take into account the semi-infinite nature of the substrate-i.e., the embedding approach based either on the Dyson equation or on Green's-function matching. Those definitions are also introduced that we deem important for the understanding of the physical properties of systems to be presented in this article. The lack of full screening in a localized region around the adsorbate, and hence the existence of long-range Friedel's oscillations induced by the adsorbate in the metal, are discussed. The way in which the lack of full screening influences the calculated adsorption energies is estimated by the grand-canonical functional. Recent ab initio results on physisorption of a noble-gas atom on metals deal mainly with the limits of validity of the simpler effective-medium theory and with the anticorrugating effect of He. Atomic chemisorption is considered in order to deal with the concept of bonding at a metal. Dissociative chemisorption calculations mainly treat the H-2 metal system. Here both the adiabatic electronic properties and the sticking probabilities recently obtained using the ab initio potential-energy surfaces are analyzed. Carbon monoxide chemisorption, lateral interactions between adsorbates, adatom diffusion, and chemisorption on stepped surfaces are presented as prototypes of the large Variety of ab initio results currently available. Finally, the conclusions are devoted to the respective merits of the different theoretical approaches and to some future directions.