We now discuss a simple approach to solve the QED problem where one treats the electronic and photonic basis states as frozen (i.e., not self-consistently updated). This is often referred to as the "adiabatic", frozen basis, or parameterized QED approach, and is commonly used in the atomic cavity QED problems. We will exclusively refer to this procedure as the parameterized QED (pQED) approach in this review. In this approach, one first solves Eq. 21 using any electronic structure method of choice, obtaining the adiabatic electronic states, |ψ α (R)⟩. One can then construct the tensor product of adiabatic electronic states, |ψ α (R)⟩, and Fock states, |n⟩, as the basis, |ψ α (R), n⟩ ≡ |ψ α (R)⟩ ⊗ |n⟩, where the character of this basis explicitly depends on the nuclear position, R. This basis is commonly referred to as the adiabatic-Fock basis.