On the contribution of the diamagnetic coupling term to the two-body retarded dispersion interaction

The contribution of the leading diamagnetic coupling term to the retarded dispersion interaction between a pair of neutral atoms or randomly oriented molecules in the ground electronic state, is investigated using the multipolar formalism of non-relativistic quantum electrodynamics. Within this framework the interaction energy is viewed as arising from the exchange of two virtual photons and is calculated using conventional time-dependent perturbation theory. Explicit expressions are presented for energy shifts involving the interaction of a diamagnetic species with (a) an electric-dipole polarizable body, (b) a magnetic-dipole susceptible body, (c) an electric-quadrupole polarizable body and (d) another diamagnetic species. The resulting potentials obtained are applicable for all separation distances beyond the electron overlap region. Also given are the limiting forms of the energy shift at large and small inter-atomic/molecular separations.