THEORY OF ELECTRONIC-STRUCTURE AND OVERLAYER STRUCTURES OF OXYGEN ON THE NICKEL (001) SURFACE

A new physical model for the O on Ni(001) system which can explain the observed series of overlayer structures is discussed. The picture is of a local orbital for the O atom which is very spread out parallel to the surface and contains a full shell of six electrons. It therefore repels other O atoms at short distances due to closed shell repulsion, whereas at long distances the large orbitals will attract due to enhanced Van der Waals interaction, thus preventing the formation of a p(1 × 1) structure and stabilising the p(2 × 2) structure in preference to c(2 × 2). The O orbital includes bonding overlap with the neighbouring Ni 4s4p states and is therefore consistent with the small net change in workfunction. In this paper the physical picture is discussed in some detail and calculations of the O orbital and its properties are presented. Further implications of the picture, for example for chemical reactivity and NiO formation, are also considered. Although developed in detail for O on Ni(001) the model should also be applicable to other rather open adsorbate overlayer structures on transition metals. © 1979.