Investigation of the relativistic equivalent Hamiltonian in the LS coupling scheme

Armstrong's method of relativistic description of atoms in LS coupling usin g the equivalent operator is developed. Its form in terms of standard unit operators acting within a space of one shell is obtained. The interpretatio n of separate terms of equivalent Breit operator is investigated in a gener al case of nonequivalent electrons. The relativistic Dirac-Fock equations f or the level and term in LS coupling are derived. The equivalent operator i s applied to obtain the averages of relativistic operators too. (C) 2001 Am erican Institute of Physics.