Exciton dispersion from first principles

We present a scheme to calculate exciton dispersions in real materials that is based on the first-principles many-body Bethe-Salpeter equation. We assess its high level of accuracy by comparing our results for LiF with recent inelastic x-ray scattering experimental data on a wide range of energy and momentum transfer. We show its great analysis power by investigating the role of the different electron-hole interactions that determine the exciton band structure and the peculiar “exciton revival” at large momentum transfer. Our calculations for solid argon are a prediction and a suggestion for future experiments. These results demonstrate that the first-principles Bethe-Salpeter equation is able to describe the dispersion of localized and delocalized excitons on equal footing and represent a key step for the ab initio study of the exciton mobility.
We acknowledge financial support from Triangle de la Physique 2013-0013T IXST, the ERC Advanced Grant DYNamo (No. ERC-2010-AdG-267374), Spanish Grants (No. 2010-21282-C02-01 and No. PIB2010US-00652),Grupos Consolidados UPV/EHU del GobiernoVasco (Grant No. IT578-13) and European Commission projects CRONOS (Grant No. 280879-2 CRONOS CP-FP7). Computational time was granted by GENCI (Project No. 544) and by the CNANO-SIMULEE-2009 project.