To model the singlet-triplet gaps, we compute the vertical excitation energies at the equations of motion coupled cluster with singles and doubles (EOM-CCSD) level with the cc-pVDZ basis Energies are computed at the EOM-CCSD/cc-pVDZ level and are provided in meV. i S 1 has the same electronic configuration as T 2 , but is also lower in energy than T 1 . ii S 1 has the same electronic configuration as T 2 with the gap being E(S 1 -T 2 )= -99 meV. iii S 1 has the same electronic configuration as T 2 with the gap being E(S 1 -T 2 )= -184 meV.