In the present work, the nature and magnitude of the ferromagnetic exchange in tb 2 SH 2+•• were studied using the broken-symmetry (BS) DFT method. With the experimental value as a reference, several popular density functionals were benchmarked to determine the consistency and accuracy of the BS-DFT approach. Apart from this, spin-constrained BS-DFT (CBS-DFT) and spin-flip time-dependent DFT (SF-TDDFT) were also performed to obtain a more accurate estimate of magnetic exchange coupling. Since DFT methods cannot account for the inherent multireference nature of the system, the complete active space self consistent field (CASSCF) method with N-electron valence perturbation theory (NEVPT2) correction was used for a precise quantitative description of magnetic exchange coupling. For the newly designed diradical dications, the magnetic exchange coupling constant was calculated using BS-DFT and CASSCF+NEVPT2 methods where the appropriate functional and size of the active space were taken from the benchmarking study on the synthesized molecule.