De, IE, and the ΔET-Q (X 3 Σ -and b 5 Δ) values to evaluate DFT functional errors. Specifically, we assessed 23 functionals that span multiple rungs (GGAs, meta-GGAs, global GGA hybrids, meta-GGA hybrids, range-separated hybrids, and double hybrids) of "Jacob's ladder" (see Computational Details). We generally expect higher accuracy from the functionals that are in higher rungs of the ladder that comes with higher computational cost. However, our most expensive double hybrids have large De errors compared to less expensive functionals (Figure ). We next extended our comparison to the evaluation of errors in HfCS and HfCSe (ESI Figures and). The DFA errors are 7-24% higher for HfCO compared to the errors of HfCS and HfCSe for all functionals except for the B3LYP, SCAN0, and ωB97X functionals that have < ~7% errors (ESI Tables ). On the whole, the dissociation of all three systems is predicted