X-ray Absorption and Resonant X-ray Emission at the Carbon Edge of Li$_2$CO$_3$

TL;DR

This study combines experimental X-ray absorption and emission measurements with advanced first-principles calculations, including GW and Bethe-Salpeter methods, to analyze the electronic structure of Li₂CO₃.

Contribution

It demonstrates the application of GW and Bethe-Salpeter calculations to interpret X-ray spectra of Li₂CO₃, highlighting many-body effects.

Findings

Experimental spectra show broadening consistent with quasiparticle lifetimes.

GW corrections improve the agreement between theory and experiment.

Excitonic effects are significant in the spectral features.

Abstract

While highly successful, density functional theory is known to have limitations owing to its neglect of many-body electron-electron interactions. This neglect leads to errors in the single-particle energies, leading to underestimated band gaps and band widths as well as errors in band alignment at interfaces. Many-body perturbation theory, in the form of the $GW$ self-energy correction, has been widely used to improve upon these short-comings. Though less well studied, the same $GW$ method is also able to predict the finite quasiparticle lifetime that is seen to cause anomalous broadening in the lowest-lying lines of valence emission spectra. Using near-edge x-ray absorption and emission, we probe the electronic structure of Li$_2$CO$_3$. Our measurements are compared to first-principles calculations, including $GW$ self-energy corrections to the single-particle energies and excitonic effects from the Bethe-Salpeter equation.