DFT 167 is formally exact, up to the choice of the exchange correlation functional, which is currently not known. To make it practical for realistic systems, multitudes of approximate density functionals have been developed with varying complexity that involves different orders of derivatives on the electronic density in order to capture long-range correlation. For the electronphoton hybridized system, one must extend this ideology to include correlations between the electronic and photonic subsystems, which has only recently been studied. We will only give a general outline of this