Here, E BS and E HS represent the energy of the broken symmetry approximation to low-spin singlet state and the high-spin triplet state, respectively, and < S 2 > HS and < S 2 > BS stand for the < S 2 > values of the respective two states. A similar BS approach was used for computing ∆E DQ for triradicals as well. However, the open shell doublet states calculated using BS formalism, had significant spin contamination. The < S 2 > values indicates < S 2 > BS ∼ 1.80 vs. the expected value of S(S + 1) = 0.75 for a doublet, while for quartet states < S 2 > HS ∼ 3.80 is close to the expected value of S(S + 1) = 3.75. The value of ∆E DQ was then obtained by correcting the energy gap for spin contamination using approximate spin-projection (AP) method 48 as: