First-principles modeling of excited states at finite temperatures: phonon-induced localization, dissociation and screening

The excited state properties of semiconductors and insulators are critical to optoelectronic devices such as photovoltaics. These devices typically operate at room temperature, however, most first-principles excited state calculations ignore finite temperature effects, due to the challenges that their inclusion into current theoretical methods poses, leading to a disconnect between theory and practical applications.

In this talk I will present extensions of the ab initio GW-Bethe Salpeter Equation (BSE) approach within many-body perturbation theory to account for finite temperature effects on excited states. In the first part of the talk I will demonstrate how finite displacement methods can be used alongside GW-BSE, to understand the temperature-dependent exciton bandwidth of molecular crystals due to phonon-induced exciton localization [1], including the important role of anharmonic phonons [2]. High-frequency phonons are found to couple weakly to delocalized excitations [3], allowing us to demonstrate design rules for minimizing non-radiative recombination losses in organic systems [4]. In the second part of the talk, building on a framework introduced in prior work [5], I will present a first-principles extension of GW-BSE to include phonon screening of excited states at finite temperatures. Using an efficient computational implementation of this scheme [6], we demonstrate strong temperature dependence of exciton binding energies in several systems, as well as accurate predictions of exciton dissociation rates [7].

[1] Alvertis, Haber, Engel, Sharifzadeh, Neaton, Phys. Rev. Lett. 130, 086401, (2023)

[2] Alvertis, Engel, Phys. Rev. B 105, L180301, (2022)

[3] Alvertis et al. Phys. Rev. B 102, 081122(R), (2020)

[4] Ghosh, Alvertis et al. submitted (2023)

[5] Filip, Haber, Neaton, Phys. Rev. Lett. 127, 067401 (2021)

[6] Li, Alvertis, Gant, Neaton, Louie, in preparation

[7] Alvertis, Haber, Li, Coveney, Louie, Filip, Neaton, submitted (2023)