Chemisorption by simple oxide surfaces -: Ag on the MgO (100) surface

Metal oxide systems exhibit a wide degree of significant behaviors from a technological viewpoint that are associated with their chemisorption properties. Many serve as catalysts or as substrates on which catalysts are supported. Of such systems among the scientifically more interesting are the simple face centered cubic structures. These have properties in the main that places them in the category of ionic compounds. This is true based both on common chemical notions and on such measured scales as the Phillips Ionicity Scale. Formally then most such structures may be regarded as O- and a M++, where M is a metal. O-- is in a chemically satisfied state and is not expected to form covalent bonds. Depending on type, the metal is also chemically satisfied. This is true for such cases as Mg due to orbital occupancy, and has been found also true for Ni due to its ionic size. Thus in simple notions, one does not expect the formation of covalent chemical bonds to such surfaces. Never the less, such surfaces form covalent bonds. Experimental evidence indicates such behavior is associated with defects or impurities included at the oxide surface. In this article, we review some earlier results for these simple oxide surfaces, and then extend these ideas to consider the specific system of Ag on the MgO surface. This study uses an embedded cluster methodology at both the Hartree-Fock level and with direct correlation inclusions. Surface relaxation effects are included here. This study is intended to further identify the role played by correlation and relaxation effects, as well as to identify the primary features in the adsorption of Ag on MgO.