Oxygen 1sx-ray absorption of tetravalent titanium oxides: A comparison with single-particle calculations

The oxygen 1s x-ray-absorption spectra of ${\mathrm{SrTiO}}_{3}$ and ${\mathrm{TiO}}_{2}$, in both the rutile and anatase crystal structure, are analyzed using the oxygen p-projected density of states of ground-state band-structure calculations. Good agreement is found and it is concluded that multielectron effects, transition matrix elements, and the core-hole potential present only small, largely undetectable, influences on the spectral shape. From the site- and symmetry-projected density of states the rutile peaks could be assigned to the 3d band (4--8 eV), antibonding oxygen 2p states (10--18 eV), and the titanium 4sp band (20--25 eV). For anatase the titanium 4sp band is shifted to lower energy by about 5 eV, which can be related to the lower density of anatase. From differences in the crystal structure it is argued that the core-hole potential is considerably more effective in perovskite ${\mathrm{SrTiO}}_{3}$ than in both ${\mathrm{TiO}}_{2}$ crystal structures. This is in accordance with the experimental findings.