The state-averaged (SA) CASSCF has also been carried out with ORCA 5.0 program to calculate the magnetic coupling. SA CASSCF is more convenient and computationally efficient to conduct a constrained minimization of a weighted sum of energies pertaining multiple electronic states, whereas the state-specific (SS) CASSCF approach often encounters convergence issues due to root flipping. Thus, SA CASSCF provides a more balanced treatment of multiple states and is better suited for studying magnetic interactions. RIJK approximation has been used to speed up the SCF calculations. The exchange fitting basis, def2/JK, has been used. The singlet and quintet states have been considered for TRI dimer, TRI-CC, TRI-CCCC, and TRI-Ph, while the singlet and triplet states have been calculated for the other molecules in the dataset because the TRI-series dimers possess 4 unpaired electrons, while the other diradicals only have 2 spins. Considering the degeneracy of the orbitals, CAS (12, 12) has been used for TRI monomer, TRI dimer, TRI-CC, TRI-CCCC, TRI-Ph, while CAS(10, 10) has been used for the other diradicals. This means, for all the molecules in the dataset, we have applied a consistent active space, includes 4 occupied orbitals, 4 virtual orbitals, and all the SOMOs. While it would be ideal to include all the πelectrons in the active space, the resources required for this scale exponentially and make CAS (14,14) calculations impractical. In addition, adding nearly fully occupied or virtual orbitals to the active space may lead to convergence problems. On top of the CASSCF-optimized wave function, the RI-NEVPT2 method has been employed to include the dynamic correlation. We have noticed major progress in the development of density matrix renormalization group (DMRG) technique recently, allowing for the inclusion of more orbitals and electrons in the active space. This improvement leads to enhanced accuracy that aligns with experimental data, particularly for systems containing numerous SOMOs and necessitating large active spaces, such as the chromium dimer, where notable discrepancies between experimental and computational data have been reported. In this study, we stick to the more traditional ab initio methods as they are sufficient for the small number of SOMOs and show excellent agreement to experiment if available.