While bond distances and angles focus on specific differences in geometry, the overall difference between the calculated and experimental structures can be quantified in the root mean square deviation (RMSD) of the optimized geometries (Table ). Note that the phenyl rings were not included in the RMSD calculations since their positions are most sensitive to crystal packing. To the extent that a solid-state structure can act as a reference, the RMSD values support the conclusion that the XMS-CASPT2 and DFT functionals result in optimized geometries of similar quality. This also supports that XMS-CASPT2 optimizations can be performed with the minimal (4e,5o) active space.