J-independent relativistic contributions to thes-dinterconfiguration energies of the iron series: Some consequences for density-functional theory

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Abstract
It has been found that, when the occupancy of the 3d orbital changes in the iron series (such as in s-d transfer and electron removal), the J-independent relativistic energy contributions (mass-velocity, one- and two-body Darwin, and electron-spin contact terms) to the corresponding energy differences are non-negligible. Thus they should be taken into account when a comparison of the calculated quantities with the experimental values is made for the purpose of testing the accuracy of a given theoretical approximation. In particular, the s-d interconfiguration energies and the removal energies are often used to test various approximations for exchange-correlation and correlation-energy functionals in density-functional theory. One of the conclusions of this study is that density-functional theory with its various approximations for the correlation-energy functional does not reproduce adequately the correlation-energy contributions to these energy differences for the iron-series elements.