Exploring novel observables in strong light-matter coupling by using QEDFT

Recent advances in polaritonic chemistry unveiled the possibility of controlling molecular properties by strongly coupling light and matter in optical cavities. Novel computational tools are necessary to describe these systems from first principles and help interpret experiments. Quantum electrodynamical density functional theory (QEDFT), an extension of density functional theory (DFT) to light-matter systems, has been developed to effectively study complex systems involving strong light-matter interactions. This powerful method combines high computational efficiency with accurate modeling capabilities, making it a promising approach in the field. Recently, we introduced a new electron-photon (e-ph) exchange-correlation (XC) functional for QEDFT, called photon many-body dispersion (pMBD) [1]. Unlike previous e-ph XC approximations, pMBD includes anisotropic effects and higher-order photon processes for strong light-matter interactions. This new functional enables the study of multi-photon processes in optical cavities, such as cavity modulated van der Waals interactions. Utilizing pMBD, we explore new observables within the QEDFT framework, such as photon number and higher-order correlation functions.