Looking back at the difference operator expression in Eq. 10, it relies on the onsite electron density, weighted by the repulsion between two electrons on the same atom (U µ ), plus twice the on-site energy (ε µ ). This calculation is then summed over the entire molecule. Therefore, we can consider whether |⟨ D⟩| can be determined using the total molecular energies obtained from quantum chemistry methods. Indeed, an effective molecular electron-electron repulsion energy U ef f can be estimated as the difference between the ionization potential and the electron affinity of the PLY radical, 127,128 U ef f = E(P LY -) + E(P LY + ) -2E(P LY ), where E is the DFT ground state radical total energy in the different oxidation states. Similarly, the effective on-site energy ε ef f can be obtained from the radical ionization potential as ε ef f = E(P LY ) -E(P LY + ), thus leading to the effective |D| ef f = U ef f + 2ε ef f . Of course, similar reasoning applies to other radicals as well.