Contribution of the screened self-energy to the Lamb shift of   quasidegenerate states
  Expressions for the effective Quantum Electrodynamics (QED) Hamiltonian due to self-energy screening (self-energy correction to the electron-electron interaction) are presented. We use the method of the two-time Green's function, which handles quasidegenerate atomic states. From these expression one can evaluate energy corrections to, e.g., 1s2p 3P1 and 1s2p 1P1 levels in helium and two-electron ions, to all orders in Z\alpha 
Eric-Olivier Le Bigot, Paul Indelicato, Vladimir M. Shabaev