Atomic and electronic structure of the corundum (α-alumina) (0001) surface

Using a tight-binding, total-energy model, we predict the atomic and electronic structure of the relaxed (1×{}1) corundum (0001) surface. The surface shows a large, bond-length-conserving relaxation, which is allowed by the topology of the surface. The relaxation is driven by a rehybridization of the surface Al atoms to sp², and an accompanying drop in the energy of occupied surface states, during the relaxation. Displacements of surface atoms from bulk positions are as large as 0.7 {}, and should be observable using a low-energy electron diffraction intensity analysis. Full relaxed atomic positions are reported, as well as a wavelength-resolved surface band structure, including orbital characters of surface states.