Hybridization between Cu-O chain and Cu(110) surface states in the O(2×1)/Cu(110) surface from first principles

The O(2×1)/Cu(110) surface reconstruction of the Cu(110) surface is induced by 0.5 ML of oxygen adsorption and is formed by Cu-O chains running along the [001] direction. Here, we show that hybridization between surface states of the Cu(110) substrate and one-dimensional states of the Cu-O chains is crucial in understanding the electronic structure of this surface. Specifically, the interaction between one occupied antibonding band of the Cu-O chain with O(p(y)) character (y-axis taken along the Cu-O chain direction) and the partially occupied surface state at the Y point of the clean Cu(110) surface with Cu(p(y)) character causes major changes in the electronic structure close to the Fermi energy (E(F)). This surface state decays very slowly into the bulk and a thick slab is needed to properly describe it, which might explain why the importance of this hybridization has not been recognized so far. In our calculations we obtain two hybrid bands: (i) a fully occupied band that strongly hybridizes with the bulk Cu sp states nearby E(F), becoming a very broad resonance, thus explaining why it is not observed in photoemission experiments; (ii) an empty band that acquires surface state character, including its dispersion close to the zone boundary at the Y point. This splitting induces a partial population of the p(y) antibonding band that is necessary to reconcile the calculated charge transfer from the Cu(110) substrate to the Cu-O chain (~0.5 electrons/f.u.) with the apparently fully occupied band structure of the adsorbed Cu-O chain (consistent with 1 electron transferred per formula unit).