Applying CPCM to DFT leads to better agreement between the HOMO-LUMO gap and IP CCSD(T) -EA CCSD(T) . To check the multireference characters of these zwitterions, we performed CAS (12,12) calculations with OpenMolcas 22.06 and found the leading determinant to be the ground state determinant with the weight 𝐶 - 7 > 0.91 (Supplementary Material Table and). Based on the 𝐶 - 7 thresholds defined in previous literature, these zwitterions do not have significant multireference character. In summary, the four tested zwitterions are not intrinsically gapless and do not have significant multireference character, so applying CPCM to these molecules to improve SCF convergence is physically meaningful. However, whether the CPCM-induced increase of the HOMO-LUMO gap is reasonable for a general molecule is beyond the scope of this work and needs investigation on a case-by-case basis.