D. Density Analysis. We employed Hirshfeld charges 42 to obtain a systematic estimate of the charge based on the real-space total density, simplifying the comparison of partial charges across distinct basis sets and electronic structure methods or software. To compare the electron density calculated with CPCM DFT at different dielectric constants relative to the gas-phase reference electron density calculated by orb-opt CCSD(T), we performed Hirshfeld population analysis 42 on all small zwitterions using Multiwfn, which read molecular orbital information from molden files generated by TeraChem or converted from ORCA gbw files. Additional comparisons were done with other charge methods, including atomic dipole moment corrected Hirshfeld (ADCH), Bader, 45 charge model 5 (CM5), and Merz-Singh-Kollman (MK). The Gaussian cube file's grid spacing was set to 0.04 Bohr to ensure convergence (Supplementary Material Table ).