For Co/Mg 9 O 9 , the EOM-EE-CCSD-in-DFT susceptibility curve obtained using the C2 partitioning scheme shows better agreement with the all-atom EOM-EE-CCSD susceptibilities than the curve computed with the C1 partitioning scheme. For the C2 model, increasing the cluster size to Co/Mg 25 O 25 has a negligible effect. For Co adatoms on MgO(001), experimental susceptibility plots are not available. However, at 300 K, the calculated χT product for Co/Mg 9 O 9 (C2, embedded EOM-EE-CCSD) is 4.51 cm 3 • K/mol, closely matching both the theoretical 41 (4.89 cm 3 • K/mol) and the experimental 66 (4.80 cm 3 • K/mol) value reported for the Co(II)-SMM. These values significantly exceed the spin-only prediction of 1.876 cm 3 • K/mol for an isotropic spin-3/2 ion that follows the Curie law, consistent with the magnetic behavior of a system with a substantial orbital angular momentum contribution (L = 3).