Accurate adapted Gaussian basis sets for helium- and beryllium-like atomicspecies to be used in Dirac-Fock calculations

The closed-shell Generator Coordinate Dirac-Fock method is applied to perfo rm Dirac-Fock-Coulomb and Dirac-Fock-Breit calculations for He- and Be-like atomic species. With the Generator Coordinate Dirac-Fock method, the integ ral Dirac-Fock equations are integrated numerically in order to generate ac curate adapted Gaussian basis sets for the atomic species under study. The Dirac-Fock-Coulomb and Dirac-Fock-Breit energies obtained here for He- and Be-like atomic species with the Generator Coordinate Dirac-Fock formalism a re in general better than the corresponding energies obtained with previous Gaussian-type functions. The Dirac-Fock-Coulomb energies obtained for the atomic species hen studied are in excellent agreement with numerical-finite -difference calculations, and for several atomic species the Dirac-Fock-Cou lomb energy results obtained with our adapted Gaussian basis sets are lower than the corresponding energies obtained from numerical-finite-difference calculations. (C) 1999 Elsevier Science B.V. All rights reserved.