CASSCF calculations with follow-up NEVPT2 corrections were performed using the def2-TZVP basis set and def2/J auxiliary basis set, consistent with the BS-DFT geometry optimizations. The resolution of identity approximation was applied to accelerate the computation of Coulomb and exchange integrals (RIJK). Initially, minimal active spaces were utilized: (2,2) for the copper dimer, (4,4) for the nickel dimer, and (8,8) for the iron dimer.