We will first discuss the results in the CMO representation. Depending on basis set, the dipeptide in question has at most two (very slightly) bound virtual orbitals, with orbital energies ε LUMO = -0.15 eV and ε LUMO+1 = -4.4 × 10 -5 eV at the CAM-B3LYP/ 6-31(9+,9+)G* level, whereas the 6-31G* and 6-31++G* basis sets do not afford any bound virtual orbitals at all. Even the Rydberg state S 3 (Fig. ) is relatively compact as compared to these unbound CMOs, which requires significantly configuration mixing amongst spatially diffuse basis functions in order to generate the target state. The result is large values of σ ia when ε a > 0, with mixing In the Boys-localized representation, these metrics behave somewhat similarly for S 0 → S 1 although their numerical values are certainly different. For S 0 → S 3 , however, Γ Boys increases dramatically as the basis set becomes more diffuse, reaching Γ Boys = 516 Å for n = 9! As compared to Γ CMO , consistently larger values of Γ Boys are driven by the fact that (∆r) Boys also becomes very large, e.g., (∆r) Boys = 228 Å for n = 9 as compared to (∆r) CMO = 5 Å. These outrageously large values in the Boys-localized representation prompt us to remind the reader that this is the same S 0 → S 3 state that is visualized in Fig. for n = 1, and (with little difference) in Fig. for n = 9. Similar artifacts are observed in the 6-31G(n+)G* basis set, e.g., Γ Boys = 413 Å for n = 9 (Table ).