SrTiO3 (001) (2x1) reconstructions : first-principles calculations of surface energy and atomic structure compared with scanning tunnelling microscopy images

s131d and s231d reconstructions of the (001) SrTiO3 surface were studied using the first-principles fullpotential linear muffin-tin orbital method. Surface energies were calculated as a function of TiO2 chemical potential, oxygen partial pressure and temperature. The s131d unreconstructed surfaces were found to be energetically stable for many of the conditions considered. Under conditions of very low oxygen partial pressure the s231d Ti2O3 reconstruction [Martin R. Castell, Surf. Sci. 505, 1 (2002)] is stable. The question as to why STM images of the s131d surfaces have not been obtained was addressed by calculating charge densities for each surface. These suggest that the s231d reconstructions would be easier to image than the s131d surfaces. The possibility that the presence of oxygen vacancies would destabilise the s131d surfaces was also investigated. If the s131d surfaces are unstable then there exists the further possibility that the s2 31d DL-TiO2 reconstruction [Natasha Erdman et al. Nature (London) 419, 55 (2002)] is stable in a TiO2-rich environment and for pO2 .10−18 atm