as, E S -E T = 2J, where E S and E T are the energies of singlet and triplet spin states. In a triradical, there are three S = 1/2 magnetic centers well localized and coupled to two doublet (D 1 and D 2 ) and one quartet (Q) states, giving rise to two different quartet-doublet energy gaps (∆E DQ ). While, the Hamiltonian involves three magnetic coupling constants (J 12 , J 23 , J 13 , where 1, 2 and 3 correspond to each magnetic center). Thus, from the low-lying energy spectrum with two doublet-quartet energy gaps, it is not possible to determine three magnetic coupling constants. To avoid this problem, it is customary to either neglect one of the coupling constant (such as coupling between terminal spin centers for linear systems) or to rely on symmetry. For the case of symmetric coupling, with J 12 = J 23 = J 13 = J, the two doublets will be degenerate and ∆E DQ can then be written as, E D -E Q = 3/2J, where E D and E Q are the energies of doublet and quartet states. Although the energy of HS state can be determined accurately using conventional single-reference (UDFT/UHF) methods, the multi-determinantal nature of low spin state enforces the use of broken symmetry (BS) solutions. For a diradical, ∆E ST , viz, 2J values was then extracted using a generalized formula proposed by Yamaguchi et al. in which the energy difference is corrected for the effect of spin contamination by scaling with the calculated < S 2 > values as: