SPIN-DEPENDENT UNITARY-GROUP APPROACH TO THE PAULI-BREIT HAMILTONIAN .2. 1ST-ORDER ENERGY-LEVEL SHIFTS DUE TO SPIN-SPIN INTERACTION

This paper is a continuation of a previous investigation of the Pauli- Breit Hamiltonian in the framework of the graphical spin-dependent uni tary group approach to many electron systems. The SU(2) tensor form fo r the spin-spin interaction and its corresponding zero spin-shift comp onent are determined explicitly and applied to investigate the first o rder energy level splitting due to the spin-spin interaction, entirely within the context of the unitary group approach. Our results are als o discussed in terms of the unitary group density matrix formalism.