The remaining classes of range-separated hybrids and double hybrids are in principle the highest rungs considered on "Jacob's ladder" in this work. Despite their promise for functional tuning to recover exact conditions, examination of range-separated hybrids reveals that both LRC-wPBEh 173 and wB97X 174 favor HS states and predict only a few systems (≤ 2) to be SCO complexes (Supporting Information Figure and Table ). All double-hybrids strongly favor HS states (average DGH-L between -39.6 to -59.8 kcal/mol) and thus, never predict any systems to be SCO compounds, in contrast to prior work 175 which showed double-hybrids to predict electronic spin splitting energies accurately (Supporting Information Figure and Table ). In particular, PBE0-DH 176 was shown 175 to predict accurate DEH-L for 16 small homoleptic transition metal complexes (TMCs) that do not show SCO behavior and consist of Fe(II/III) and Co(II/III) metals with ligands of varying strengths: CO, NCH, NH3, and H2O. The accuracy of these gasphase PBE0-DH/def2-TZVPP 177 calculations in this study 175 was determined through comparison with diffusion Monte Carlo studies as opposed to experimental data. However, in our work with 95 Fe(II) SCO complexes, PBE0-DH strongly favors HS states and fails to predict SCO behavior as shown by both DEH-L and DGH-L (Supporting Information Figure and Table ). The double-hybrids studied here , like most double-hybrids, have very high aHF values (between 0.50 and 0.71 across DFAs), which could explain the strong preference towards HS states (Supporting Information Figure and Table ). This highlights the limitations of higher-rung DFAs in predicting SCO behavior and shows that caution must be exercised in determining the appropriate DFAs for SCO predictions. Now, we focus on the consistency of the predictions among the three best-performing functionals. Comparison of DGH-L predicted by modB3LYP (aHF = 0.10), TPSSh, and M06-L functionals reveals a stronger correlation between DGH-L predicted by modB3LYP (aHF = 0.10) and TPSSh than between modB3LYP (aHF = 0.10) and M06-L (Pearson's r of 0.92 vs 0.76; Figure ). For most complexes where SCO behavior is predicted by modB3LYP (aHF = 0.10) but not by TPSSh or M06-L, the DGH-L predicted by these functionals differ by ca. 3 kcal/mol or less, with TPSSh stabilizing LS states and M06-L HS states slightly more relative to modB3LYP (Supporting Information Table ). Closer examination reveals that for one complex with a hexadentate nitrogen-coordinating ligand (refcode: OSABOB 179 ), TPSSh strongly favors an LS ground state compared to modB3LYP (aHF = 0.10), i.e., DGH-L of 11.9 kcal/mol vs 2.1 kcal/mol (Supporting Information Table and). This complex has been experimentally 179 determined to exhibit SCO behavior with the aid of variable-temperature NMR spectroscopy, UV/Vis spectroscopy, magnetic susceptibility measurements and differential scanning calorimetry, suggesting this is an example of a limitation of TPSSh or the modelling approach. We also observe that all complexes where DGH-L predicted by M06-L and modB3LYP (aHF = 0.10) differ by a larger amount (refcodes: JAFBUO 180 , JIQDET 181 , QACKAJ 149 , SESNEM 49 , TEPVIW 182 , and WIHQIQ 156 ) have ligands that are rigid with higher denticities (half contain tridentates, Supporting Information Table and Figure ). In these cases, M06-L strongly stabilizes the HS states relative to modB3LYP and fails to predict SCO behavior. All of these complexes are experimentally shown to exhibit SCO behavior through analysis of X-ray crystal structures and/or magnetic susceptibility measurements. Thus, these molecules represent challenging test cases for further DFA tuning and development.