Ab-initio Optimized Effective Potentials for Real Molecules in Optical Cavities: Photon Contributions to the Molecular Ground state

TL;DR

This paper presents an efficient ab-initio method within quantum-electrodynamical density functional theory to compute photon contributions to molecular ground states, enabling detailed study of electron-photon interactions in optical cavities.

Contribution

It introduces a novel optimized-effective potential scheme using the Sternheimer equation for QEDFT, allowing for the first 3D ab-initio calculations of electron-photon systems in cavities.

Findings

Photon exchange-correlation significantly alters molecular ground states.

The scheme accurately computes electronic and photon observables.

Electron-photon interactions distort electronic structures in molecules.

Abstract

We introduce a simple scheme to efficiently compute photon exchange-correlation contributions due to the coupling to transversal photons as formulated in the newly developed quantum-electrodynamical density functional theory (QEDFT). Our construction employs the optimized-effective potential (OEP) approach by means of the Sternheimer equation to avoid the explicit calculation of unoccupied states. We demonstrate the efficiency of the scheme by applying it to an exactly solvable GaAs quantum ring model system, a single azulene molecule, and chains of sodium dimers, all located in optical cavities and described in full real space. While the first example is a two-dimensional system and allows to benchmark the employed approximations, the latter two examples demonstrate that the correlated electron-photon interaction appreciably distorts the ground-state electronic structure of a real molecule. By using this scheme, we not only construct typical electronic observables, such as the electronic ground-state density, but also illustrate how photon observables, such as the photon number, and mixed electron-photon observables, e.g. electron-photon correlation functions, become accessible in a DFT framework. This work constitutes the first three-dimensional ab-initio calculation within the new QEDFT formalism and thus opens up a new computational route for the ab-initio study of correlated electron-photon systems in quantum cavities.