ture Methods (a) Various approximations to the QED-TD-DFT method (Eq. 142), generating the usual (but generalized to many states) QED models such as Jaynes-Cummings (JC), Rabi, and the rotating wave approximation (RWA), as well as an approximation to the electronic subsystem within the Tamm-Dancoff approximation (TDA). (b) The coupled cluster (CC) method can be understood via linear combinations of the excitation operators generated by the exponential of the total cluster operator (Eq. 129).