Applications of density functional theory approaching chemical accuracy to the study of typical carbon-carbon and carbon-hydrogen bonds

This article examines the merits of cost-efficient density functional variants in the computation of prototype hydrocarbons: CH4, C2H6, C2H4, C2H2, benzene and cyclopropane. Inclusion of some Hartree-Fock exchange in a fully self-consistent density functional approach with gradient corrections leads to atomization energies close to experimental accuracy. Validation of Politzer's energy formula, E(molecule) = Sigma(k)V(k)(mol)/gamma(k)(mol), where V-k(mol) is the potential energy involving the nucleus of atom k in the molecule and gamma(k)(mol) is a parameter (similar to 7/3 for atoms other than H), with better than Hartree-Fock wave functions provides a useful link with classical chemical concepts, namely bond energies.