Inclusion of all the roots in the state-averaging scheme results in quite large values of ∆E DQ of 317.3 and 2907.5 cm -1 at SA-CASSCF level (Table ) and corresponding NEVPT2 predicts incorrect ground-spin state. This result highlights the importance of selection of only low-lying roots. For a triradical system with three unpaired electrons localized in different regions, the most important orbital configuration is [111] where each electron occupies orbitals localized around those regions. This configuration gives rise to 1 quartet and two doublet states which contribute to the low-energy spectrum. Therefore, it is necessary to include these states in state-averaging to obtain active orbitals which can describe these three states properly. With this state-averaging scheme, we have carried out SA-CASSCF calculation with CAS(3,3) active space followed by enlargement of active space to CAS (5,5), CAS (7,7) and CAS (9,9). To check the low-energy spectrum, we have computed the CAS-CI energies (without further optimizing orbitals) of two quartets and three doublets for each of these active spaces. The results shown in Figure and Table demonstrate that the second quartet and the third doublet are much higher in energy. Therefore, it can be concluded that the low-energy spectrum contains only 1 quartet and 2 doublet states, as expected for a triradical with localized electrons. After confirming this, NEVPT2 computations have been carried out on each state. Both SA-CASSCF and NEVPT2 results are shown in Table .