Relativistic Interaction Energies between Atoms in Degenerate States

Abstract

The interaction of two like atoms in degenerate quantum states of the same energy and the interaction of two unlike atoms in arbitrary states is considered in the Breit—Pauli approximation. For these interactions the calculation of the relativistic long-range interaction energy, through O(α2), is discussed with specific allowance for degeneracy in the interacting atoms. Possible interactions where relativistic effects may be important are discussed. As a specific example the interaction of two spin-degenerate atoms (L=0, S≠0) is calculated through O(α2/R6) (where R is the interatomic separation). The nonrelativistic energy is given by the usual London dispersion energy which varies as 1/R6 while relativistic effects introduce an interaction energy which varies as α2/R3.