The special features of using the configuration interaction (CI) method in the case of the quasirelativistic radial orbitals (ROs) are described. The integrals composing the matrix elements of the one-electron part of the Breit–Pauli energy operator are rewritten in non-traditional forms. The correlation effects are taken into account within the CI approach on the basis of the transformed ROs (TROs) describing the virtual excitations of the electrons. The TROs with variable parameters are obtained from the RO of the investigated configuration by using the exponential transforming function. Calculations of the spectral characteristics of three ions (Ne V, Fe XXI and Xe XLIII) have been performed to demonstrate the potentiality of the new approach. The energy spectra of all three ions are presented. The lifetimes of the levels of Ne V and the transition probabilities of Fe XXI ion are also shown. All the results are compared with the experimental data and with the calculations of other authors.
Absorption-line spectroscopy is a powerful tool used to estimate element abundances in the nearby as well as distant universe. The accuracy of the abundances thus derived is, naturally, limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform the new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state-of-the-art quantal calculations. Here we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts (GRBs). We report new extensive calculations of a large number of energy levels of S II, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree-Fock framework, and utilize both non-ralativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes (≈ 0.04 dex) to the metallicities estimated from S II in past studies. These results will be readily applicable to other studies of S II in the Milky Way and other galaxies.
The properties of the quasirelativistic Hartree-Fock equations are investigated. Different ways of forming the equations are discussed. The relativistic corrections employed in the traditional quasirelativistic Hartree-Fock equations are compared with the ones used within the Breit-Pauli approach. The two-electron contact interactions are revised and the new versions of the quasirelativistic Hartree-Fock equations are considered. The solutions of these equations are compared among themselves and also with those obtained within the Dirac-Fock and nonrelativistic Hartree-Fock approaches. Solution data are provided for some heliumlike, neonlike, and mercurylike ions.
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