A first principles survey of stoichiometric (1×2) reconstructions on the rutile surface

First principles slab calculations on the reconstructed stoichiometric (1 1 0) surface of rutile TiO2 are reported. Motivated by experimental observations, this systematic density functional survey has yielded 36 low energy (1×2) reconstructions (ΔESurf<1.0 J m−2). Some isomers show only slight differences in energy, so that careful estimation of the surface energy is necessary: by computing both singly and doubly reconstructed slabs we are confident in comparing surface energies to within ±0.04 J m−2. The bulk-terminated unreconstructed surface is confirmed to be the most stable for the stoichiometric oxide. However, reconstructions featuring tetrahedrally-coordinated Ti cations at the vertically-oriented interstitial sites are computed to occur on top of any bulk-terminated surface section and destabilise the surface by just 0.04 J m−2. Destabilisation is calculated to be greater for the rich variety of other possible reconstructions, such as incomplete bulk-terminated sections, or reconstructed Ti at the other interstitial site. Oxide anions generally occupy positions of the bulk sub-lattice.