First-principles studies of oxygen chemisorption on Co(0001)

We perform density-functional theory calculations to study the adsorption of oxygen on Co(0001) for a wide coverage range from 0.11 to 2.0 monolayers (ML), including on-surface and subsurface adsorption. Present results demonstrate that atomic oxygen prefers on-surface hollow sites and a local p(2 × 2)-O overlayer is formed at 0.25 ML, in agreement with experimental observation. Upon one full monolayer oxygen on Co(0001), the incorporation of oxygen under the first Co layer is found to be exothermic and the adsorption energy changes very small with the increase of subsurface oxygen, implying an attractive interaction between adatoms O. Other coverage-dependent properties especially the d-band electronic structure modifications and the two-dimensional phase diagram are discussed in comparison with similar systems. Present results indicate that with the completion of the full monolayer oxygen on Co(0001), subsequent O atoms incorporate into the subsurface with an easy site-switch and finally it preferentially leads to an O-Co-O trilayer on top of the Co(0001) surface.