Accurate vacuum-polarization calculations

A numerical scheme for evaluating the part of the one-photon vacuum-polarization effect not accounted for by the Uehling potential (the Wichmann-Kroll effect) is presented. The method can be used with an arbitary atomic model potential describing the bound electrons. Benchmark results for this effect are presented for hydrogenlike levels using a uniform nuclear-charge distribution. The effect of direct and exchange electron screening on the vacuum polarization are discussed in connection with the accurately measured 2${\mathit{p}}_{1/2\mathrm{-}}$2${\mathit{s}}_{1/2}$ transition in lithiumlike uranium.