Unified first-principles theory of exciton polarons across coupling regimes

Develop a unified ab initio framework for exciton polarons that seamlessly bridges weak- and strong-coupling regimes by formulating and solving self-consistent exciton–phonon many-body equations (for example, a generalization of the Hedin–Baym equations to the two-particle electron–hole Green’s function) that yield exciton-polaron energies, wavefunctions, and dynamics in real materials.

Background

The review surveys recent progress on exciton polarons and self-trapped excitons, noting that current methods treat weak and strong coupling separately. While exciton-polaron equations and supercell approaches exist, they do not yet constitute a single all-coupling, self-consistent theory comparable to charged-polaron frameworks.

A unified theory would clarify how exciton–phonon interactions produce localization and spectral features across materials, and would connect exciton-polaron equations to Fock-space exciton–phonon Hamiltonians or generalized Green’s-function approaches.

References

Here, we limit ourselves to drawing the reader's attention to six open questions that in our view are the most urgent. First, the first-principles theory of exciton polarons is still in its infancy. Recent developments in ab initio methods have succeeded in addressing the weak- and strong-coupling limits of this problem, yet a unifying conceptual framework that seamlessly bridges these regimes is still lacking.

— Polarons from first principles (2512.06176 - Dai et al., 5 Dec 2025) in Section 7: Conclusions and Outlook