SrTiO₃(001)(2×1) reconstructions: First-principles calculations of surface energy and atomic structure compared with scanning tunneling microscopy images

(1×1) and (2×1) reconstructions of the (001) SrTiO₃ surface were studied using the first-principles full-potential linear muffin-tin orbital method. Surface energies were calculated as a function of TiO₂ chemical potential, oxygen partial pressure p_O2and temperature. The (1×1) unreconstructed surfaces were found to be energetically stable for many of the conditions considered. Under conditions of very low oxygen partial pressure the (2×1) Ti₂O₃ reconstruction [ Martin R. Castell Surf. Sci. 505 1 (2002)] is stable. The question as to why STM images of the (1×1) surfaces have not been obtained was addressed by calculating charge densities for each surface. These suggest that the (2×1) reconstructions would be easier to image than the (1×1) surfaces. The possibility that the presence of oxygen vacancies would destabilise the (1×1) surfaces was also investigated. If the (1×1) surfaces are unstable then there exists the further possibility that the (2×1) DL-TiO₂ reconstruction [ Natasha Erdman et al. Nature (London) 419 55 (2002)] is stable in a TiO₂-rich environment and for p_O2>10⁻¹⁸ atm.