X-ray absorption and resonant x-ray emission at the carbon edge of Li2CO3

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 bandgaps and bandwidths 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 shortcomings. Although 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 Li2CO3. 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.