The researchers further established a link based on conceptual density functional theory. They proposed that, as a first approximation, the pKa value of a compound is directly proportional to the MESP centered on the dissociating proton's nucleus. . Moreover, they confirmed the equivalence between the nuclear electrostatic potential and the energy of valence NAO energy as descriptors of molecular acidity for both the acidic atom (oxygen in this case) and the departing proton.