Spline implementation of generalized gradient approximations to the exchange-correlation functional and study of the sensitivity of density functional accuracy to localized domains of the reduced density gradient

We present a natural cubic spline implementation of the exchange enhancement factor as a function of the reduced density gradient, and we demonstrate its performance by replicating the results of common GGA functionals. We also investigate the effect on the accuracy of various calculated properties of changing the shape of the exchange enhancement factor and an analogous factor for correlation. The properties considered are main group atomization energies, ionization potentials, electron affinities, proton affinities, alkyl bond dissociation energies, difficult hydrocarbon cases, barrier heights for chemical reactions, noncovalent interactions, atomic energies, metal bond energies, and main group bond lengths.