Bonding and magnetism of chemisorbed oxygen on Fe(001)

Abstract

The electronic structure and magnetism of 1×1 O/Fe(001) was studied by the self-consistent localized-orbital (SCLO) method. A five-layer Fe(001) substrate was adopted in which the first interplanar spacing was 7.5% expanded compared with the bulk spacing. Oxygen atoms filled the fourfold hollow sites on both sides of the slab, with an Fe-O interplanar spacing of 0.48 Å. This interface geometry was determined in a previous low-energy-electron-diffraction (LEED) analysis. We find that the oxygen atoms have significant bonding to both the surface and subsurface Fe layers. ‘‘Horizontal’’ bonding (within the surface plane) is primarily due to the & on Fe atoms, and 2$p_x$ and 2$p_y$ orbitals on oxygen. ‘‘Vertical’’ bonding of oxygen to subsurface iron is accomplished through Fe & and O 2$p_z$ orbitals. Oxygenlike energy bands were obtained 4 to 8 eV below the Fermi energy $E_F$, with exchange splittings of 0.5 to 1.0 eV. The oxygen adlayer has a magnetic moment of 0.24${\mu }_B$ per atom, while surface Fe atoms have a moment of 2.93${\mu }_B$, essentially unchanged from the clean-surface value 2.89${\mu }_B$. Oxygen atoms have a net charge of 0.6 electron drawn from the surface and subsurface iron planes; as a result the work function increases 1.4 eV compared with the clean substrate, in disagreement with measurements on O/Fe(001), which obtain much smaller shifts. The discrepancy may be due to absorption of oxygen into the metal.