QED calculation of the ground-state energy of berylliumlike ions

Ab initio QED calculations of the ground-state binding energies of berylliumlike ions are performed for the wide range of the nuclear charge number: $Z=18–96$. The calculations are carried out in the framework of the extended Furry picture starting with three different types of the screening potential. The rigorous QED calculations up to the second order of the perturbation theory are combined with the third- and higher-order electron-correlation contributions obtained within the Breit approximation by the use of the large-scale configuration-interaction Dirac-Fock-Sturm method. The effects of nuclear recoil and nuclear polarization are taken into account. The ionization potentials are obtained by subtracting the binding energies of the corresponding lithiumlike ions. In comparison with the previous calculations the accuracy of the binding energies and the ionization potentials is significantly improved.

Figure 1

The interelectronic-interaction diagrams. The double line denotes the electron moving in the effective potential (2). The symbol $\otimes$ represents the local screening potential counterterm.

Figure 2

First- and second-order QED diagrams (excluding the one-electron two-loop diagrams). The notations are the same as in Fig. 1.