Unified ab initio quantum-electrodynamical density-functional theory for cavity-modified electron-phonon-photon coupling in solids

TL;DR

This paper introduces a comprehensive first-principles QEDFT framework for accurately modeling how optical cavities modify electronic, phononic, and optical properties of solids, enabling predictions of experimental signatures.

Contribution

It develops a unified, self-consistent QEDFT approach combining electronic, phononic, and optical excitations for solids in optical cavities, which was previously lacking.

Findings

Cavity vacuum fields alter electronic, phononic, and polarization properties in GaN.

The framework predicts cavity-induced modifications in dispersions and optical spectra.

Results show experimentally observable signatures in transmission and absorption spectra.

Abstract

Quantum-electrodynamical density-functional theory (QEDFT) provides a first-principles framework for describing materials coupled to quantized electromagnetic fields. While QEDFT has successfully captured cavity-induced modifications of electronic structures in atoms and molecules, a fully self-consistent and accurate framework to simulate and predict the structural, phonon-related, polarization and optical response of periodic solids in optical cavities has remained elusive. Here, we introduce a unified QEDFT approach that incorporates collective light-matter coupling in the electronic ground state, density functional perturbation theory for phonons, and real-time time-dependent QEDFT for optical excitations. This framework enables \textit{ab initio} calculations of cavity-modified electronic and phononic dispersions, Born effective charges, dielectric tensors, and both resonant and non-resonant optical absorption spectra. Using wurtzite \ac{GaN} in an optical cavity as a case study, we demonstrate that the quantized vacuum field reshapes electronic, phononic and polarization properties, producing experimentally accessible signatures in the transmission and absorption spectra. These results establish QEDFT as a general first-principles platform for predicting and exploring cavity-modified quantum materials.