On the accuracy of valence correlation energies in pseudopotential calculations

Total valence correlation energies of X(5+), X(+), X, X(-), and X(2) (X=F,Cl,Br,I) have been calculated with the coupled-cluster method for the all-electron and the pseudopotential case using large uncontracted basis sets containing up to g-type functions. The overestimation of valence correlation energies due to the modified nodal structure of the pseudo-orbitals is discussed. The errors are found to be less than 10% in all cases of chemical interest and reduce to 2 mH or less in correlation contributions to ionization potentials, electron affinities or binding energies. (C) 1996 American Institute of Physics.