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 excha nge in a fully self-consistent density functional approach with gradie nt corrections leads to atomization energies close to experimental acc uracy. Validation of Politzer's energy formula, E(molecule) = Sigma(k) V(k)(mol)/gamma(k)(mol), where V-k(mol) is the potential energy involv ing the nucleus of atom k in the molecule and gamma(k)(mol) is a param eter (similar to 7/3 for atoms other than H), with better than Hartree -Fock wave functions provides a useful link with classical chemical co ncepts, namely bond energies.