Spin-orbit operators Dirac-Fock equations

We introduce the change of the metric characteristic of DPT, and expand in powers of c. To 0(c ) we get the non-relativistic Hartree-Fock equations in Levy-Leblond form. The leading relativistic correction to the energy is then expressible in terms of nonrelativistic HF spin orbitals or rather the corresponding lower components xf - For the Dirac-Coulomb operator we get after some rearrangement [17, 18] ... 

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