Testing electron-photon exchange-correlation functional performance for many-electron systems under weak and strong light-matter coupling

TL;DR

This paper introduces a new local density approximation exchange-correlation functional for QEDFT that accurately describes many-electron systems under various light-matter coupling strengths, improving computational efficiency and applicability.

Contribution

The paper develops a photon-free pxcLDA functional for QEDFT that effectively captures electron-photon correlations across different coupling regimes, extending previous one-electron work to larger systems.

Findings

pxcLDA reproduces cavity-modified densities accurately

Renormalization factor approaches unity with system size

Method offers practical application for realistic electron systems

Abstract

We present results of a photon-free exchange-correlation functional within the local density approximation (pxcLDA) for quantum electrodynamics density functional theory (QEDFT) that efficiently describes the electron density of many-electron systems across weak to strong light-matter coupling. Building on previous work [I-Te. Lu et al., Phys. Rev. A 109, 052823 (2024)] that captured electron-photon correlations via an exchange-correlation functional derived from the nonrelativistic Pauli-Fierz Hamiltonian and tested on one-electron systems, we use a simple procedure to compute a renormalization factor describing electron-photon correlations and inhomogeneity in the weak-coupling regime by comparing it with quantum electrodynamics coupled-cluster, and previous QEDFT optimized effective potential methods. Across various atoms and molecules, pxcLDA reproduces cavity-modified densities in close agreement with these references. The renormalization factor approaches unity as the system size or collective coupling increases, reflecting an electron-photon exchange-dominated behavior and improved accuracy for larger systems. This approach now offers a practical route to applying QEDFT functionals based on electron density to realistic electron systems.