A chemical and theoretical way to look at bonding on surfaces

Abstract

An account is given of a theoretical approach to surface structure and reactivity that is within the framework of solid-state theory, yet strives for chemical ways of interpretation. One begins from highly delocalized band structures, but introduces interpretational tools (density-of-states decompositions, crystal orbital overlap populations) that allow a tracing of local, chemical acts. It is quite feasible to construct interaction diagrams for surfaces, and to make frontier orbital arguments, just as for molecules. There are some interesting ways in which the surface-adsorbate interaction differs from simple molecular binding—in particular, in the way that two-orbital four-electron and zero-electron interactions can turn into bonding. The surface and bulk acting as a reservoir of electrons or holes at the Fermi level are important in this context. Chemisorption emerges as a compromise in a continuum of bonding whose extremes are dissociative adsorption and surface reconstruction.