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

TL;DR

This study investigates the optical properties and electronic band structure of LiCoO2 using advanced theoretical methods, highlighting the importance of electron-hole interactions and excitonic effects in accurately describing its optical response.

Contribution

The paper applies multiple levels of approximation, including QS$GW$ and BSE, to analyze excitonic effects in LiCoO2, providing detailed insights into its optical response and band structure.

Findings

Excitonic effects significantly influence the optical absorption peaks.

Electron-hole interactions lower the quasiparticle gap by about 11%.

Excitons in LiCoO2 are strongly localized.

Abstract

The optical response functions and band structures of LiCoO$_2$ are studied at different levels of approximation, from density functional theory (DFT) in the generalized gradient approximation (GGA) to quasiparticle self-consistent QS$GW$ (with $G$ for Green's function and $W$ for screened Coulomb interaction) without and with ladder diagrams (QS$G\hat W$) and the Bethe Salpeter Equation (BSE) approach. The 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.