Conceptual Density Functional Theory
Conceptual density functional theory connects derivatives of the energy with respect to electron number and external potential to chemical reactivity concepts: the chemical potential (negative electronegativity), the hardness and its inverse the softness, and the Fukui function, which localizes reactivity to particular atoms. These quantities underpin principles such as electronegativity equalization and hard and soft acids and bases, and are often evaluated by finite differences of N-1, N and N+1 electron calculations.
Electronegativity and local softness as descriptors of amine-CO2 reactivity (2012)
Lee and Kitchin computed finite-difference electronegativities and nitrogen local softness (global softness times a Bader-condensed Fukui function) for a series of functionalized amines and tested them against DFT reaction energies with CO2 (Lee 2012). Following electronegativity equalization, the electronegativity difference between amine and carbonic acid correlated with the amine-bicarbonate complex energy, robustly across low energy conformers. The local hard and soft acids and bases principle explained the carbamic acid energy only partially: trifluoroalkylamines and the alkyl and alkanolamines fell on two distinct trends, consistent with the caveat that local softness comparisons hold only for chemically similar reactants. Summary: lee2012.