Optical response and band structure of LiCoO2 including electron-hole interaction effects

Abstract

The optical response functions and band structures of ${\mathrm{LiCoO}}_{2}$ are studied at different levels of approximation, from density functional theory (DFT) in the generalized gradient approximation (GGA) to quasiparticle self-consistent $\mathrm{QS}GW$ (with $G$ for Green's function and $W$ for screened Coulomb interaction) without and with ladder diagrams $(\mathrm{QS}G\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{W})$ and the Bethe Salpeter Equation (BSE) approach. The $\mathrm{QS}GW$ method is found to strongly overestimate the band gap and electron-hole or excitonic effects are found to be important. They lower the quasiparticle gap by only about 11% but the lowest energy peaks in absorption are found to be excitonic in nature. The contributions from different band to band transitions and the relation of excitons to band-to-band transitions are analyzed. The excitons are found to be strongly localized. A comparison to experimental data is presented.