Relativistic configuration-interaction calculations for the ground state and<i>n</i>=2 singlet states of heliumlike ions

Abstract

Term energies are determined for the ground state and n=2 singlet states of heliumlike ions with nuclear charges in the range 4\ensuremath{\le}Z\ensuremath{\le}92. These calculations are based on the relativistic no-pair Hamiltonian which includes both the Coulomb interaction and the retarded Breit interaction. Single-particle wave functions are expanded in a B-spline basis constructed from Dirac-Coulomb orbitals restricted to a finite cavity. The Hamiltonian matrix is evaluated and Davidson's method is used to determine the lowest few eigenenergies and eigenfunctions for each angular symmetry. Quantum electrodynamic corrections are also calculated. We find good, but not precise, agreement between theory and experiment for the K\ensuremath{\alpha} x-ray energies. It is argued that high-precision x-ray measurements for highly charged ions are needed to further test the theory.