The BS-DFT approach to calculating magnetic exchange coupling is extremely popular owing to its computational simplicity and efficiency. However, it is plagued by various errors that reduce the accuracy of the magnitude of magnetic exchange. One such drawback is the self-interaction error which leads to spurious delocalization of spin densities and overestimation of 2J values. This issue can be rectified by using the spin-constrained BS-DFT (CBS-DFT) approach where the spin densities on a particular atom or group of atoms can be constrained to a given value. The spin density constraint is applied on both the BS as well as the triplet determinants of the diradical and the resulting 2J is calculated by using eq. 2. Another drawback of the BS-DFT method is its reliance on a single determinant. It represents the low-spin state as the single determinant broken-symmetry (BS) state, disregarding other potential configurations. To adequately describe the singlet state, a multistate approach that incorporates at least two Slater determinants is necessary. The collinear SF-TDDFT method is one such approach, where excited states are generated from a high-spin (HS) reference by performing spin-flip excitations. These excitations can involve both single and double excitations, capturing all possible singlet states. Thus the better description of the singlet state leads to a more precise calculation of 2J.