The tuning most commonly follows the ∆SCF method. Here, the energetic positions of HOMO and LUMO of a given system are tuned to the IP and EA according to Koopmans' theorem. The LUMO can thereby be substituted with the HOMO of N + 1-electron system. The IP and EA are computed as the differences between ground state (gs) energies of a given multiplicity with N and N ± 1 electrons, i.e.,