Multipole expansion of the retarded interatomic potential energy. VI. Dispersion and induction energy for relativistic hydrogen atoms

The inductive and dispersive retarded interaction energies of two ground-state hydrogen atoms described by Dirac theory are derived up to all multipole orders. The results are obtained by evaluation of Feynman diagrams and with the help of dispersion-relation methods. The non-relativistic and semi-relativistic approximations of the interaction energy are given in a form that shows explicitly the contributions of electron spin