Here, E 0 is a charge-independent reference energy, which we set to zero throughout. The second term (labeled 'Site-Energy') is the well-known second-order Taylor expansion of the atomic energy with respect to the charge, with the atomic electronegativity χ A and the hardness η A . It provides the energetic contribution incurred by adding or removing electron density from a given atom. The third term (labeled 'Coulomb-Integral') is the classical Coulomb potential of the fluctuation density δρ. This integral can be computed analytically, using the definition of δρ (see Eq. 2):