  X-ray absorption spectra calculated within an effective one-electron approach
have to be broadened to account for the finite lifetime of the core hole. For
Green's function based methods this can be achieved either by adding a small
imaginary part to the energy or by convoluting the spectra on the real axis
with a Lorentzian. We demonstrate on the case of Fe K and L2,3 spectra that
these procedures lead to identical results only for energies higher than few
core level widths above the absorption edge. For energies close to the edge,
spurious spectral features may appear if too much weight is put on broadening
via the imaginary energy component. Special care should be taken for dichroic
spectra at edges which comprise several exchange-split core levels, such as the
L3 edge of 3d transition metals.
