Germanium K edge in GeO2 polymorphs. Correlation between local coordination and electronic structure of germanium

The electronic properties of two room temperature persistent phases of germanium dioxide have been studied by means of experimental and theoretical techniques. We collected the Ge-k edge XANES spectra of these materials at the GILDA beamline of ESRF. The density of states of the two crystal phases, obtained from fully periodic Hartree-Fock and density functional calculations, is taken as the reference term to rationalise and assign the manifolds of the XANES spectra. Although this scheme requires a number of severe approximations, we obtained a good overall agreement between experiment and theory. The topological analysis of the theoretical electron density distribution in the crystals gave further information regarding the electronic properties of germanium dioxide.