Phonon screening of electron-hole interactions in lead-halide perovskite semiconductors and beyond*

Electronic and optical excitations are strongly influenced by the dielectric of properties
semiconductors and insulators. In general, photoexcited bound electron-hole pairs (excitons),
experience dielectric screening which originates both from electrons and ionic vibrations. While
the standard computational framework for the study of electronic and optical excitations based
on the GW method and the Bethe-Salpeter equation (GW+BSE) accurately and reliably
accounts for electronic screening effects [1], it neglects the contribution of ionic vibrations to the
electron-hole interaction.
In this talk, I will present our recent ab initio generalization of the BSE to include the contribution
of phonon screening effects to the electron-hole interaction [2]. I will introduce the formalism,
and implementation of this general approach, and demonstrate its applicability to the CsPbX3 (X
= Cl, Br, I) lead-halide perovskite series, as well as to other standard III-V and II-VI
semiconductors. I will show that phonon screening effects on the exciton binding energy can be
significant for materials with a large static dielectric constant, and LO phonon frequency
comparable with the exciton binding energy. Finally, I will discuss the importance of polaronic
effects for calculating exciton binding energies.
[1] Rohlfing & Louie, Phys. Rev. Lett. 81, 2312 (1998).
[2] Filip, Haber & Neaton, In Review (2020).