IMPROVED DOUBLE-ZETA DESCRIPTION FOR THE ATOMS LI THROUGH XE

The conventional double-zeta (DZ) approximation uses two Slater-type functions (chinlm)'s with different exponents for the description of each occupied atomic orbital phi(nlm), where the two principal quantum numbers n's are assumed to be the same. We show that the removal of this implicit restriction improves the DZ functions nontrivially for the ground-state atoms Li through Xe. The largest improvement 0.0267 a.u. in the atomic energy is found for Pd. The valence orbital energies are generally improved, particularly for the 4d-orbital of the fourth-row atoms. It is also found that the conventional DZ functions given in the literature can be further improved by reoptimization of the exponents.