| In recent years, with the rapid development of the heterogeneous catalysts, surface adsorption which plays a key role in the heterogeneous catalysis shows its great foreground. Transition metals, such as Nickel and Iron, which have special d electronic structure, have good activity, stability and selectivity, so most metal catalysts are Ni, Pd, Fe, Pt and other transition metals. Moreover, oxygen adsorption on the surfaces of transition metals is a more important step of catalytic reactions, so it is necessary to do theoretical research of oxygen adsorption on the surfaces of transition metals. Detailed knowledge of the adsorption of oxygen on the metallic surfaces would be very useful to gain some insight into the nature of the interaction between adsorbates and substrates and to understand the corresponding catalytic processes. It can verify experimental results and explain experimental phenomena. It can also provide some important information that could not be obtained through experimental observation.Within decade years ascribed to the increasing of computation level and calculation method, the density functional theory has gone through a rapid development, and has been widely used in investigating the transition metal systems. In this paper, a systematic investigation of the geometric structure and the electronic structure of O adsorption on Ni(110) and Ni(111) surface with different coverage has been carried out by the CASTEP package, which is based on the density functional theory, the generalized gradient approximation, plane-wave pseudopotential and super-cell approach.Research indicates that the favorite adsorption site of Ni(110)-O system is impacted by coverage.O adsorbs on the short bridge site at low coverage, while O adsorbs on the long bridge site at high coverage. The favorite adsorption site of Ni(111)-O system is apparently independent of coverage. Oxygen atoms adsorb on the fcc site at all coverage. The study also finds that there is little difference of the adsorption energy of O adsorption on the fcc, hcp and bridge site of the Ni(111) surface, so the adsorption on these sites may exist at the same time. The study also finds that the surface relaxation effects of the clean Ni(110) and Ni(111) surface is the same with the relaxation of transition-metal sufaces, the outermost atomic layer shows an inward relaxation; Bur he outermost atomic layer of Ni(110)-O and Ni(111)-O system is drawn out. In addition we find that the chemical properties of the clean Ni (110) and Ni (111) surface are relatively active. It is easy for the surface to adsorb oxygen atoms and to be quickly filled up by oxygen atoms, and then to form a structure whose the coverage is 1 ML.Through investigating the charge density difference, population and the density of states, we find the electrons are transferred to oxygen atoms from the surface atoms in Ni(110)-O and Ni(111)-O system. In addition, we find a surface local state which is formed by the interactions between O2p and Ni3d orbits in the vicinity of -5eV. The main contribution of bonding between oxygen atoms and nickel atoms is from O2p and Ni3d orbits. |
