First-principles study of oxygen adsorption on Fe(1 1 0) surface

We investigate three superstructures c(2 × 2), c(3 × 1) and c(1 × 1) of oxygen atom adsorption on Fe(1 1 0) surface by using first-principles density functional theory. The former two superstructures have been found by experiments at low oxygen exposures. The oxygen adsorption results in some electron transfer from surface Fe atom to O atom due to the strong electronegativity of oxygen atom, which also causes a positive work function change. For all three superstructures, the calculated surface spin density at Fermi level is positive, unlike that on a clean Fe(1 1 0) surface. The adsorbate–substrate hybridization is mainly from the interaction between O 2p and Fe 3d orbitals, and O 2p state exhibits obvious exchange spin–split induced by the Fe–O magnetic interaction. The adsorbate O 2p bands of c(2 × 2) and c(3 × 1) superstructures exhibit a weaker dispersion, whereas those bands of c(1 × 1) structure show larger dispersion due to the O–O interaction. Through the band structure calculation, we also calculate the exchange splitting energy of O 2px orbital for c(3 × 1) structure in k space and compare them with experimental results.