ALL-ORDER RELATIVISTIC MANY-BODY CALCULATIONS FOR THE ELECTRON-AFFINITIES OF CA-, SR-, BA-, AND YB- NEGATIVE-IONS

Electron affinities are evaluated for negative ions formed by the atta chment of one electron to atoms with closed subshells, using relativis tic many-body perturbation theory. In particular, we investigate the C a-, Sr-, Ba-, and Yb- ions. Starting from a model space that consists of nondegenerate valence Dirac-Hartree-Fock orbitals, we first approxi mate the energy of the attached electron as the lowest eigenvalue of a second-order effective Hamiltonian. Higher-order correlation correcti ons are calculated in the linear cluster approximation. The Breit inte raction is also included in the first order. Our results are in good a greement with recent experiments and show a clear improvement over the second-order Dyson equation. Comparisons with other many-body calcula tions are also presented.