Fine structure in light atoms is well described by the single-manifold extended average level (EAL) variant of relativistic multi-configuration Dirac-Fock (MCD) theory if the contribution from the Breit interaction is studied. The fine structure predicted by the optimal level (OL) variant is unreliable unless the corresponding result obtained by performing the OL calculation with an artificially large value of the velocity of light is subtracted. Since, after this subtraction, the results differ little from the EAL predictions, it is concluded that it is not worthwhile to perform the series of calculations needed to predict reliable fine structure in the OL method.
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N.C. Pyper (1983) studied this question.
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