DFT study of the Au(3 2 1) surface reconstruction by consecutive deposition of oxygen atoms

The consecutive deposition of oxygen atoms on the Au(3 2 1) surface was studied carrying out calculations based in the spin polarized density functional theory within the GGA/PW91 exchange-correlation functional. The clean and oxygen covered Au(3 2 1) surfaces were modeled by a periodic supercell approach; the unit cell has 15 gold atoms, the outermost five define the (1 1 1) terrace and the step. The adsorption of a single oxygen atom is more favorable if it occurs at a fcc hollow site on the (1 1 1) terrace adjacent to the step while for the co-adsorption of two oxygen atoms on the Au(3 2 1) surface, hollow sites nearby the step are preferred. The introduction of an additional oxygen atom on the already optimized slabs containing two oxygen atoms yield, in some cases, structures with a single oxygen atom attached to the surface and an oxygen molecule far from the slab. In the other cases, several initial geometries converged to the same final structure and, in general, the adsorption of three oxygen atoms per unit cell was found to be thermodynamically unfavorable. The exception was a planar structure formed after reconstruction of the surface. The simultaneous adsorption of four oxygen atoms per unit cell is characterized by relatively high adsorption energies of −0.53 and −0.56 eV, corresponding to a porous structure containing sub-surface oxygen atoms forming a gold oxide layer and to a well ordered folded structure. The addition of a fifth oxygen atom to the structures already containing four oxygen atoms on the surface resulted in an endothermic processes suggesting that they will be hard to found even after exposure to high pressures of oxygen.