In conclusion of this section, examining the response of the ground and excited electronic structure to the presence of molecule-cavity coupling is of extreme importance for all theoretical applications. The significant changes to the properties can elucidate a new and powerful method for manipulating chemical reactions in the ground state and tuning the local excitonic character of excited states to use in photo-chemistry and optoelectronic property modification. Further, the use of either pQED and scQED schemes will give the same result in the infinite basis limit; however, each have strength and limitations that need to be considered when applying to a specific calculation. For all of the current theoretical work, it seems that only Ĥpl in Eq. 106 is used, which is limited to the single cavity mode situation. Connecting with the majority of the experiments conducted with many molecules coupled to many cavity modes inside a Fabry-Pérot cavity, one needs to consider the Hamiltonian Ĥ[N] PF in Eq. 101. Developing ab initio polaritonic methods for such a Hamiltonian could be a very attractive direction for the electronic structure community in future.