Breit interaction in heavy atoms

In this letter we discuss how to include Breit interaction in calculations of low-energy properties of heavy atoms in accurate and effective way. In order to illustrate our approach we give some results for Cs and Tl. Introduction. It is well known that in high accuracy atomic calculations one may need to go beyond the Coulomb approximation for the two-electron interaction. The usual next step is to include the Breit interaction. A number of commonly used atomic packages, such as GRASP package [1], allows to do this routinely. However, in many precision calculations one needs to account for different corrections, which are not included in standard packages. Thus, it may be important to analyze the role of the Breit interaction on different stages of atomic calculations. Below we present several simple observations which may help to include Breit interaction in atomic calculations in an optimal way. Breit interaction between electrons 1 and 2 has the form