RELATIVISTIC ALL-ORDER MANY-BODY CALCULATIONS OF THE N = 1 AND N = 2 STATES OF HELIUM-LIKE IONS

An all-order procedure is used to determine the energies of the n = 1 and n = 2 states of heliumlike ions with nuclear charges in the range Z = 3-100. The Coulomb energies and wave functions are obtained from a no-pair Hamiltonian by an iterative scheme that sums all orders of ma ny-body perturbation theory. The Breit energy is determined by taking the expectation value of the instantaneous Breit Hamiltonian between t he Coulomb wave functions. Corrections for the frequency dependence of the Breit interaction and for two Breit interactions are included. Qu antum-electrodynamic and mass-polarization corrections are taken from Drake's unified method [Can. J. Phys. 66, 586 (1988)]. The resulting e nergies are complete through order (Zalpha)3 a.u. and include new term s of order (Zalpha)4 a.u. Comparisons are made with experiment and wit h recent configuration-interaction calculations.