First-principles study of surface and subsurface O structures at Al(111) -art. no. 085405

The structural and electronic properties of oxygen atoms adsorbed in on-sur face and subsurface sites at the Al(111) surface are investigated from firs t principles using the density functional theory within the generalized gra dient approximation and a supercell approach for a range of oxygen coverage s 0 less than or equal to Theta less than or equal to1, in some cases in tw o layers. For on-surface adsorption the binding energy increases with Theta , predicting formation of islands in agreement with earlier calculations an d experiments. The most stable subsurface adsorption site is found for the (1 x 1) structure, i.e., Theta = 1, in tetrahedral sites 1.92 Angstrom belo w the topmost, 25% relaxed, Al atomic plane and 0.4 eV/atom higher in energ y than the most preferred energy state in the on-surface fee hollow site. T he adsorption of O has a significant effect on surface buckling relaxation. Oxygen atoms adsorbed in subsurface octahedral sites induce very large (60 %) outward relaxation of the topmost layer spacing, which points to the wea kening of metal-metal bonds between the two outer Al layers. For the simult aneous subsurface and on-surface adsorption at Theta = 1. the binding energ y in the subsurface site is 0.2 eV/atom lower than the binding energy in ov er-surface fee hollow sites. The sizable work-function changes for differen t structures are presented and discussed.