Tin dioxide from first principles: Quasiparticle electronic states and optical properties

The structural, electronic, and optical properties of the semiconducting oxide SnO₂ are investigated using first-principles calculations. We employ the G₀W₀ formalism based on hybrid-functional calculations to compute the quasiparticle band structure and density of states for which we find good agreement with results from photoemission and two-photon absorption experiments. We also address open questions regarding the band ordering and band symmetries. In a second step we use our electronic structure as a starting point to calculate optical spectra by solving the Bethe-Salpeter equation including the electron-hole interaction. The dielectric tensor is predicted for a wide range of photon energies. Our results resolve the long-standing discrepancy between theory and experiment on the highly anisotropic onsets of absorption. The anisotropy can be explained in terms of dipole-allowed direct transitions in the vicinity of the valence-band maximum without having to invoke lower-lying valence bands.