Relativistic configuration-interaction calculations ofn=2 triplet states of heliumlike ions

Eigenfunctions and eigenvalues of the relativistic no-pair Hamiltonian are determined for n=2 triplet states of heliumlike ions with charges in the range Z=5–100. The eigenfunctions are expanded in a basis of two-electron wave functions constructed from Dirac-Coulomb orbitals restricted to a finite cavity. The Hamiltonian matrix is evaluated and Davidson’s method is then used to determine the lowest few eigenfunctions and eigenvalues. These calculations, which include the Coulomb interaction and the retarded Breit interaction, are corrected for QED and mass-polarization effects using values from Drake’s unified method and are compared with other calculations and with experiment. For low-Z ions, the present calculations agree well with many-body perturbation theory and with the unified method, but disagree substantially with multiconfiguration Dirac-Fock (MCDF) calculations corrected for correlations. At Z=36, our term energies are lower than the unified method by λ${\mathrm{\alpha }}^4$ ${\mathit{Z}}^4$ a.u., where λ=0.033, 0.51, 0.16, and 0.003 for the 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$, 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$, 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_1$, and 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_2$ states, respectively. For Z=47 and 64, the present values of the 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_{0–}$2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_1$ fine structure agree better with MCDF predictions than with the unified method. The energy intervals 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$-2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$, 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_1$-2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$, 2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_2$-2