To determine the dependence on geometry optimization in spin crossover calculations, spin crossover energies were calculated for each compound in the test set using the same three types of geometries as in the exchange coupling calculations described above: (1) crystal structures; (2) optimized UDFT geometries; and (3) AP optimized geometries where the HS geometry is used when the ground state is HS. The complete collection of these results is given in Tables and, including spin crossover gaps calculated on different geometries and by different projection methods, with and without inclusion of (implicit) solvent effects. These combinations of geometry and projection method (and their notations) include crystal structure without projection methods (Crystal), UDFT geometry without projection (UDFT) and with AP (UDFT//AP), and AP geometry with AP (AP//AP). This can be understood by considering the AP α parameter defined by Eq. ( ), which represents the degree of contamination in a broken symmetry determinant. The closer α is to 1.0, the less contaminated a solution. Therefore, AP will have little (or no) effect on spin crossover gaps when α is close to 1.0. Calculations without solvent effect were also performed and yielded very similar results.