Abstract
It has long been known that the Dirac‐Coulomb Hamiltonian HDC, often used in the past as the basis for relativistic calculations of the spectra of heavy atoms, has no bound states. A review is given of a QED‐based approach to this problem. It yields a configuration‐space Hamiltonian H+, which is protected from the troubles of HDC by the appearance of positive‐energy projection operators surrounding the electron‐electron interaction. Several choices for H+ are considered and compared. The relation between the Dirac‐Hartree‐Fock type equations obtained from HDC and H+ is discussed. Applications to concrete physical problems which have been made with H+‐type hamiltonians are described.