Strong excitonic effects in CuAlO2 delafossite transparent conductive oxides

The imaginary part of the dielectric function of CuAlO2 has been calculated including the electron-hole correlation effects within Bethe-Salpeter formalism (BSE). In the initial step of the BSE solver the band structure was calculated within density-functional theory plus an orbital field (LDA/GGA+U) acting on Cu atoms. We discuss the influence of the strength of the additional orbital field on the band structure, electric field gradients, and the dielectric function. The calculated dielectric function shows very strong electron-hole correlation effects manifested with large binding energies of the lowest excitons. The electron-hole pair for the lowest excitations are very strongly localized at a single Cu plane and confined within only a few neighboring shells.