In addition to the exact HF exchange, double hybrid functionals include a second order perturbation theory correction term (MP2) for the correlation part of the functional. This improves mainly the consideration of dispersion forces. However, the computational time is comparable to MP2. Therefore, we have also included some traditional post-HF approaches with comparable computational cost, CIS and CIS(D), in our study. As can be seen in Table as well as in Figure , double hybrid functionals produce large errors comparable to CIS. Including perturbative double corrections results in even larger errors of the CI approach. However, we would like to highlight that the employed basis set is only of double-ζ quality due to the system size. The strong systematic overestimation of absorption energies for the double hybrid functionals and post HF methods suggests a scaling of the obtained absorption energies. Indeed, the results are significantly improved and an accuracy comparable to CAM-B3LYP can be reached (see Figure and Table ). Thus, CIS(D) with and Table ). The worse performance cannot explained by the ϵ (HOMO) criterion (see SI, Table ). Also scaling of energy does not improve results since including diffuse basis sets increases the scattering of the calculated absorption energies in most cases (see SI, Figure ). Thus, unintuitively, the smallest basis set provides the most accurate results.