| Abstract
| - The recently proposed Hartree−Fock−Heitler−London, HF−HL, method (Corongiu, G. J. Phys. Chem. A2006, 110, 11584) previously tested for single bond molecules is validated by potential energy computationsfor open and closed shells, single and multiple bonds, in ground and excited states of homopolar diatomicmolecules of the first and second period. The simple HF−HL function, including the configurations for 2s/2pnear degeneracy and avoiding state crossing, yields correct dissociation products, qualitatively correct binding,and accounts for non-dynamical correlation. Addition of ionic structures improves the ab initio HF−HL functionand yields about 95% of the experimental binding energies on average. Computed excitation energies arealso in agreement with laboratory values as verified for the 3Πu and 3excited states of the C2 molecule.Computation of the remaining dynamical correlation using a semiempirical functional yields binding energieswith an average deviation of 1.5 kcal/mol from laboratory values, and total energies with an average deviationof 0.7 kcal/mol from exact nonrelativistic dissociation energies.
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