R. Hackl et H. Pilkuhn, TRANSFORMATION OF BREIT OPERATORS INTO HYPERFINE-LIKE OPERATORS, Journal of physics. B, Atomic molecular and optical physics, 29(20), 1996, pp. 725-727
The relativistic Breit Hamiltonian between electrons is transformed in
to an effective vector potential A(i) for the ith electron. A(i) havin
g the structure of a recoil-corrected hyperfine operator. Apart from a
small three-body operator, the Dirac-Breit equation is now easier to
apply to relativistic magnetic properties of complex systems.