ACCURATE VACUUM-POLARIZATION CALCULATIONS

A numerical scheme for evaluating the part of the one-photon vacuum-po larization effect not accounted for by the Uehling potential (the Wich mann-Kroll effect) is presented. The method can be used with an arbitr ary atomic model potential describing the bound electrons. Benchmark r esults for this effect are presented for hydrogenlike levels using a u niform nuclear-charge distribution. The effect of direct and exchange electron screening on the vacuum polarization are discussed in connect ion with the accurately measured 2p1/2-2s1/2 transition in lithiumlike uranium.