Momentum space approach to the relativistic atomic structure calculations

A simple and straightforward derivation of the relativistic no-pair equation in momentum space is given for hydrogenic species. This is achieved by starting with a QED Hamiltonian in momentum representation and making a rigorous reduction into a system that contains a single electron but no positrons. The integral equation was solved for a series of hydrogenic systems using the Kwon-Tabakin-Lande technique. Numerical results were compared with those recently obtained by Hess, who employed the basis set expansion technique to solve the no-pair equation in configuration space