Electronic and geometrical structure of rutile surfaces

The periodic Hartree-Fock approach is used in all-electron calculations on bulk rutile (TiO₂) and various slabs modeling the (001), (100), and (110) surface to study possible geometric and electronic surface relaxations, convergence of properties with slab thickness, and the relative stability of the different surfaces. Results are discussed by means of a Mulliken population analysis, band structures, and the density of states. We find displacements of surface atoms ranging from 5 to nearly 40 pm; the (001) surface appears to be significantly unstable with respect to the other two [(100) and (110)], in accord with experimental findings. Specific features of the density of states projected onto different Ti sites and the relative stability of the different surfaces agree with a possible dissociation behavior of the rutile structure into TiO₂ chains, which are calculated to be stable.