GWquasiparticle calculations in atoms

We present quasiparticle calculations done in atoms using various versions of Hedin's GW approximation. The performance of GW in major-group elements is illustrated by calculations of first and second ionization energies from the same initial configuration, along with various promotion energies. The results significantly improve Hartree-Fock eigenvalues and are comparable, in accuracy, to Hartree-Fock, total-energy differences. In the 3d (iron-series) transition metals, there are also significant improvements in the 4s- and 3d-state electron addition energies in the first half of the series. In the second half of the series, we find that strong correlations among 3d electrons of opposite spin are not accounted for by GW. We also study the screening effects by cores on valence-electron addition and removal energies. In particular, we examine the ``alkalilike'' problem of one valence electron bound to a closed-shell core. Extensive tests show that here the generalized GW approximation describes quantitatively important effects of core-relexation and core-valence correlation on the valence electrons. In the following paper it is shown that these core-relaxation and core-valence correlation effects can be incorporated into an effective potential suitable for use in calculations of valence properties of atoms, molecules, and solids.