Figure 1
Left: Schematic illustration of the numbering of the Fe atoms in the two topmost atomic layers. The surface-layer atoms are numbered from 1 to 6 and the subsurface-layer atoms from 7 to 10. The three oxygen adsorption sites considered are the on-top site (‘ot’) over atom 1, the hollow site (‘ho’) over atom 7 and the bridge site (‘br’) between atoms 1 and 4. Middle: Atomic positions within the unit cell of the dilute Fe–Cr alloy with two Cr atoms (blue–grey) at sites 1 and 7. The positions of the adsorbed oxygen atom at the on-top, hollow and bridge adsorption sites are illustrated by the smaller dark blue, red and light blue spheres, respectively. Right: Same as Middle but with the viewpoint shifted so that the vertical positions of the oxygen atoms can be perceived.
