Higher-order QED corrections for multi-charged ions

The higher-order QED corrections for one- and two-electron heavy ions are analysed. The different methods of renormalization are discussed: the traditional potential-expansion method and the new one, based on the direct numerical subtraction of divergencies. The extraction of the reference state from the sums over the intermediate states in higher-order corrections is considered. It is shown, that this extraction leads to some special corrections to the energy. The Low theory of the line profile is used for the calculation of the higher-order QED corrections and the nonresonant corrections distorting the Lorentz line profile are also discussed. (orig.)