where the coefficients c a α,n (R) = ⟨ϕ α (R), n|Ψ a (R)⟩ can be used to compute any observables of the resulting polaritonic system (which will be revisited later). Note that the expansion coefficients also explicitly depend on the nuclear configuration, due to the R-dependent adiabatic states |ϕ α (R)⟩. This is also the common procedure in quantum optics to solve polariton eigenstates of model systems couple to cavity, for example, the results presented in Fig. .