Optical absorption of rutile SnO2 and TiO2

The electronic band-edge structure and optical response of rutile SnO2 and TiO2 are studied, employing a fully relativistic projected augmented wave method within the local density approximation (LDA). A quasi-particle model corrects the LDA band-gap energies, which is used to fit the on-site self-interaction correction (SIC) potential LDA+U-SIC. We show that inclusion of this k-dependent SIC-like potential correction, as well as inclusion of polaronic screening are of outermost importance for accurately determining the electronic structure and optical properties. For both SnO2 and TiO2, the calculated absorption coefficient alpha(omega) reveals a very small optical band-edge absorption in the photon energy region E-g <= h omega <= similar to E-g+Delta (Delta = 0.8 eV and 0.5 eV for SnO2 and TiO2, respectively). The main difference between SnO2 and TiO2 is the presence of the unoccupied low-energy 3d conduction-band states in TiO2 which yield flat conduction bands and a very strong optical absorption for h omega > E-g+Delta. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim