Relativistic configuration-interaction calculation of $K\alpha$   transition energies in beryllium-like argon
  Relativistic configuration-interaction calculations have been performed for the energy levels of the low-lying and core-excited states of beryllium-like argon, Ar$^{14+}$. These calculations include the one-loop QED effects as obtained by two different methods, the screening-potential approach as well as the model QED operator approach. The calculations are supplemented by a systematic estimation of uncertainties of theoretical predictions. 
V. A. Yerokhin, A. Surzhykov, S. Fritzsche
physics.atom-ph