Indium-oxide polymorphs from first principles: Quasiparticle electronic states

The electronic structure of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ polymorphs is calculated from first principles using density functional theory (DFT) and many-body perturbation theory (MBPT). DFT calculations with a local exchange-correlation (XC) functional give the relaxed atomic coordinates of the two stable polymorphs. Their electronic structure, i.e., the band structure and density of states, is studied within MBPT. The quasiparticle equation is solved in two steps. As the zeroth approximation for the XC self-energy the nonlocal potential resulting from a HSE03 hybrid functional is used. In the sense of a self-consistent procedure ${G}_{0}{W}_{0}$ quasiparticle corrections are computed on top. The calculated direct quasiparticle gaps at $\ensuremath{\Gamma}$ amount to $3.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (rhombohedral) and $3.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (cubic). The rhombohedral polymorph is found to exhibit a near degeneracy of the valence-band maxima at the $\ensuremath{\Gamma}$ point and on the $\ensuremath{\Gamma}\text{\ensuremath{-}}L$ line, while the valence-band maximum of the cubic polymorph occurs near $\ensuremath{\Gamma}$. Interconduction band transitions are identified as possible origin of conflicting experimental reports, claiming a much larger difference between the direct and indirect gap. The results for gaps, $d$-band positions, and density of states are compared with available experimental data.