Symmetry breaking of relativistic multiconfiguration methods in the nonrelativistic limit

The multiconfiguration Dirac-Fock method allows one to calculate the state of relativistic electrons in atoms or molecules. This method has been known for a long time to provide certain wrong predictions in the nonrelativistic limit. We study in full mathematical detail the nonlinear model obtained in the nonrelativistic limit for Be-like atoms. We show that the method with sp + pd configurations in the J = 1 sector leads to a symmetry breaking phenomenon in the sense that the ground state is never an eigenvector of L² or S². We thereby complement and clarify some previous studies.