where i and j represent different electronic coordinates; hence we see that the dipole self energy operator contains both a one-electron contribution and a two-electron contribution. The one-electron contribution can be recognized as the negative of the quadrupole operator multiplied by coupling vector components. A practical sc-QED approach will depend on introducing an orbital basis (e.g. an orthonormal spin orbital basis). In this case, we can write the the right-hand side of Eq. 25 in secondquantized notation as