However, the Cu-N bond distances remain effectively unchanged. Likewise, the optimized geometry for the T 0 state is planar and has quite similar Cu-N bond distances with an elongation of only +0.010 Å with respect to the S 0 structure. In the XMS-CASPT2 S 1 and T 0 structures for the unfunctionalized corrole, the Cu-N distances are shorter on average than those in the planar structures obtained with DFT. Specifically, the PBE0-D3 functional has an average Cu-N distance that is +0.042 Å longer in the T 0 state, perhaps due the open-shell character in the XMS-CASPT2 singlet states leading to fewer differences in metal to ligand charge transfer compared to DFT. Likewise, the XMS-CASPT2 T 0 geometry for the unfunctionalized corrole has an average Cu-N distance of 1.908 Å, while the DFT geometries have slightly longer distances ranging from 1.910-1.933 Å (Table ). The BLYP-D3 geometry has the largest difference of +0.025 Å with respect to XMS-CASPT2.