When one of the coupling is assumed to be negligible due to larger distance between spincenters, the two quartet-doublet energy gaps can be used to extract two coupling constants unambiguously. For the case for three spin-half centers, as discussed by Reta et al., it is not possible to extract three different coupling constants from two quartet-doublet energy gaps. Although the energy of high-spin (E Q ) state can be determined accurately from computations, the determination of energies of low-spin (E D ) state is a challenging problem within the single-reference methods (UHF or UKS), due to their multideterminantal nature. An alternative approach to calculating the exchange coupling constant within DFT is proposed by Yamaguchi et al. as