The statistical analysis performed on the resulting 48 cases is presented in Table , using the aug-cc-pVTZ values as reference. According to the reported statistical indicators, the For states with 6 non-hydrogens atoms, Q-CC3/aug-cc-pVTZ becomes too computational demanding. Encouraged by the performances of aug-cc-pVDZ for smaller compounds we took aug-cc-pVDZ data as references to evaluate the performances of 6-31+G(d) when larger compunds are considered as well. The 𝛿 TPA values as well as energies for 34 excited states showing a 𝛿 TPA > 3 a.u. with aug-cc-pVDZ are reported in Table , while states with smaller response values are reported in Tables and in the SI. This set encompasses 13 valence states (7 𝜋 → 𝜋 * and 6 𝑛 → 𝜋 * ) transitions. The 1𝐴 𝑔 state of hexatriene and the 1𝐸 2𝑔 state of benzene exhibit a substantial double character with %T 1 of 66.5% and 67.8%, respectively. Within this set there are also 20 Rydberg states, and one mixed state, the 3𝐴 1 state of pyridazine. We evaluated the performance of 6-31+G(d) with respect to aug-cc-pVDZ on 82 states: 48 states collected in Table and 34 states on Table . The results are provided in Table . For the full set we found that 𝛿 TPA with the 6-31+G(d) basis significantly differ from the aug-cc-pVDZ values with a MAPE of 24.7%, and a MAE of 15.1 a.u. These values are essentially unchanged with respect to the ones of Table , indicating that basis set differences are not strongly dependent on the considered molecules. The large MAX + in Table comes from the 1𝐴 𝑔 state of hexatriene, with an overestimation that might be ascribed to the worse description of double excitations with the compact basis. By excluding the 6 states where double excitations are not negligible (i.e., %T 1 < 80 %), we observe a slight increase of the MAPE but a large improvement of the others indicators. Table also indicates a generally better performance of 6-31+G(d) for the valence states, although the indicators stay in the same range for Rydberg transitions. Further comment should be made on the size of 𝛿 TPA and its implications for practical applications. The studied molecules exhibit rather small values of 𝛿 TPA and corresponding 𝜎 TPA . For instance, one of the largest 𝛿 TPA values was found for the 1𝐴 𝑔 transition in hexatriene (1358.3 a.u.), which translates to a 𝜎 TPA value of 17 GM (assuming Lorentzian broadening of 0.2 eV). This value is an order of magnitude smaller than the values reported for push-pull systems such as 4-dimethylamino-4'-nitrostilbene. Despite the small values, studying such small responses is crucial for evaluating the performance of QM methods and understanding their predictive power and limitations.