Theory of the exciton-phonon coupling*

The influence of electron-phonon interactions on optical absorption spectra requires a special treatment in materials with strong electron-hole interactions. We conceptualize these effects as exciton-phonon coupling [1]. Through phonon absorption and emission processes, the optically accessible excitons are scattered into other dark, finite-momentum exciton states. The exciton-phonon self energy therefore contributes to the temperature dependence of the optical transitions and their broadening. Two-bands model [2] shows how the full exciton-phonon self energy differs both qualitatively and quantitatively from commonly used approximations. We present the implementation of a first-principles calculation scheme, making use of density functional theory (DFT), density function perturbation theory (DFPT), and the Bethe-Salpeter equation (GW-BSE) formalism.
[1] Gabriel Antonius and Steven G. Louie. arXiv:1705.04245 [cond-mat], May 2017.
[2] Daniel Gunlycke and Frank Tseng. PCCP, 18(12):8579–8586, March 2016.