Interconfigurational energies and ionization potentials: Test of a correlation energy functional

A recently proposed correlation energy functional [S. Ragot, P. Cortona, J. Chem. Phys. 121 (2004) 7671] has been tested by calculating the interconfigurational energies and the ionization potentials of the third row transition metal atoms and the ionization potentials of a selected set of molecules. A great and almost systematic improvement, with respect to the results of standard local-density calculations, has been found for the ionization potentials: the accuracy of the new approximation is similar to that of the B3LYP hybrid functional. The interconfigurational energies are also improved, but the improvement is smaller than in the case of the ionization potentials. This is due to the fact that the local-density results largely benefit from the compensation of the errors. Calculations performed correcting the exchange-correlation functional for the self-interaction effects (by the D-SIC method) have also been done for the transition metal atoms: a further general improvement of the results is found.