In general, the size of the QED-CASCI wavefunction grows as (N p + 1)N det where N p denotes the maximum photon occupation state. We will use the nomenclature PN-QED-CASCI(N el , N orb )-N p / CS-QED-CASCI(N el , N orb )-N p to denote the electronic active space and photonic space truncation in the photon number and coherent state formulations of QED-CASCI, respectively.