Accurate valence band maximum determination for SrTiO3(0 0 1)

We reexamine a well-established method for determining valence band maxima (VBM) in semiconductors based on fitting photoemission valence band spectra to theoretical densities of states. In contrast to the situation for covalent semiconductors, application of this technique to SrTiO3 produces poor fits when the density of states is computed within the local density or generalized gradient approximation. The resulting VBM is too high by several tenths of an eV. However, an excellent fit, and a more physically reasonable VBM, is obtained when the density of states is computed within a recently-developed self-consistent GW approximation. Extrapolating the X-ray excited leading edge to the energy axis, and finding the energy at which the UV-excited leading edge intensity goes to zero, also yield physically reasonable VBM values that are in good mutual agreement, and in good agreement with the VBM obtained by fitting to GW theory. These numbers are useful for accurate band offset determination.