Relativity: Gaunt vs. Breit in molecules

 Hello everyone,
 The leading term in relativistic electron-electron interaction is described
 by the Breit Hamiltonian.  It is often stated in the literature that the
 Gaunt (magnetic) part of this interaction is more important than the rest
 (the effect of retardation).  Is anyone aware of the calculation on
 molecular (as opposed to atomic) system that compares these two effects?
 	Vitaly Rassolov
 	Department of Chemistry		tel. (847) 491-3423
 	Northwestern University
 	2145 Sheridan Rd.		rassolov -8 at 8-
 	Evanston, IL 60208-3113