  We recently showed that the DFT+U approach with a linear-response U yields
adiabatic energy differences biased towards high spin [Mariano et al. J. Chem.
Theory Comput. 2020, 16, 6755-6762]. Such bias is removed here by employing a
density-corrected DFT approach where the PBE functional is evaluated on the
Hubbard U -corrected density. The adiabatic energy differences of six Fe(II)
molecular complexes computed using this approach, named here PBE[U], are in
excellent agreement with coupled luster-corrected CASPT2 values for both weak-
and strong-field ligands resulting in a mean absolute error (MAE) of 0.44 eV,
smaller than the recently proposed Hartree-Fock density-corrected DFT (1.22 eV)
and any other tested functional, including the best performer TPSSh (0.49 eV).
We take advantage of the computational efficiency of this approach and compute
the adiabatic energy differences of five molecular crystals using PBE[U] with
periodic boundary conditions. The results show, again, an excellent agreement
(MAE=0.07 eV) with experimentally-extracted values and a superior performance
compared with the best performers TPSSh (MAE=0.08 eV) and M06-L (MAE=0.31 eV)
computed on molecular fragments.
