Canonical transformations and radiative effects in electron-electron interactions

Canonical transformation techniques are used together with variational and perturbative methods to describe the effects of the coupling between electrons and the radiation field in the Coulomb gauge. A simple transformation, equivalent to the use of Glauber's coherent states (1963) is treated exactly, and the 'direct' part of the currently used Breit correction (1932) to the electron-electron interaction in relativistic Hartree-Fock theory is derived variationally. More general transformations leading to electron self-energy terms as well as electron-electron interaction corrections are discussed and compared to the procedure used by Mittleman (1972). The case where the unperturbed Hamiltonian is of Hartree-Fock type gives the generalized Breit interaction.