High precision calculations and QED effects for two- and three-electron atoms

Abstract

Essentially exact results can now be obtained for the nonrelativistic energy and lowest-order relativistic corrections of helium. A combination of variational calculations and asymptotic expansion methods covers the entire singly-excited spectrum. Comparisons with recent high precision experiments allow the Lamb shift for the 1s2s1S state to be extracted with an accuracy approaching that in one-electron He+(2s). Techniques for calculating the two-electron Lamb shift are discussed, including recent asymptotic expansion methods for the Bethe logarithm. Extensions to lithium and other three-electron ions up to U89+ are briefly mentioned.