Valence correlation energies from pseudopotential calculations

Total valence correlation energies of first-row atoms, their anions and cations as well as their homonuclear dimers have been determined in all-electron and [He]-core pseudopotential calculations using the coupled-cluster method and large uncontracted basis sets containing up to g-type functions. The inaccuracies mainly caused by the pseudo-orbital transformation of the 2s valence orbitals are discussed. The relative errors in total valence correlation energies are found to be 6% at most. Correlation contributions to excitation energies, ionization potentials, electron affinities or binding energies are accurate with absolute errors of 0.1 eV or less.