We also evaluated the DFT errors associated with the ΔET-Q and IEs of HfCO (Figures and and ESI Tables and). Among all the functionals considered, for these quantities, the double hybrids (DHs), with the exception of PBE0-DH, yield the closest results to CCSD(T). This result differs from the De analysis where DHs performed poorly. Specifically, the DHs display values within 0-3 kcal/mol of the CCSD(T) reference for ΔET-Q and 0-0.11 eV for IE.