Some limitations on the applicability of ε HOMO and ε LUMO as adsorption descriptors may arise in case of voluminous organic ions whose interaction with the electrode is poorly described by the MO energy level due to steric perturbations. Another limiting factor may be strong chemisorption involving the formation of a chemical bond with the surface, comparable in energy to the interatomic bond in a solid. In general, the descriptors provided in the manuscript are best suited for characterizing semiconductors and dielectrics.