QED calculation of the n=1 and n=2 energy levels in He-like ions

Abstract

We perform ab initio QED calculations of energy levels for the $n=1$ and $n=2$ states of He-like ions with the nuclear charge in the range $Z = 12$-100. The complete set of two-electron QED corrections is evaluated to all orders in the parameter $\aZ$. Uncalculated contributions to energy levels come through orders $\alpha^3 (\aZ)^2$, $\alpha^2 (\aZ)^7$, and higher. The calculation presented is the first treatment for excited states of He-like ions complete through order $\alpha^2 (\aZ)^4$. A significant improvement in accuracy of theoretical predictions is achieved, especially in the high-$Z$ region.