  We propose a scheme of decomposition of the total relativistic energy in
solids to intra- and interatomic contributions. The method is based on a
variation of the speed of light from its value in relativistic theory to
infinity (a non-relativistic limit). As an illustration of the method, we
tested such decomposition in the case of a spin-orbit interaction variation for
decomposition of the magnetic anisotropy energy (MAE) in CoPt. We further
studied the {\alpha}''-Fe16N2 magnet doped by Bi, Sb, Co and Pt atoms. It has
been found that the addition of Pt atoms can enhance the MAE by as large as
five times while Bi and Sb substitutions double the total MAE. Using the
proposed technique we demonstrate the spatial distribution of these
enhancements. Our studies also suggest that Sb, Pt and Co substitutions could
be synthesized by experiments.
