  Density functional theory was applied to study influence of the isolated
impurity located on the regular site of the alpha-Fe crystal on the charge and
spin density (hyperfine interactions) on the iron nucleus. Calculations were
performed by using both pseudopotential and the full potential methods. The
scalar relativistic approximation was applied. Perturbations of the charge and
spin density on iron were calculated for all d impurities soluble in iron and
additionally for Ga impurity. It was found that impurities have measurable
effect on the iron charge and spin density up to the second or third
coordination shell depending on the impurity. Hyperfine parameters of iron
adjacent to the impurity are affected by two intermixed physical mechanisms,
i.e., the volume mismatch due to the impurity and electron band mixing caused
by the electronic configuration of the impurity outer shells. Some correlations
between ab initio calculations and Moessbauer experimental results are
discussed. A table is provided with the parameters allowing calculate
Moessbauer spectrum of the binary iron alloy with d impurity or Ga. On the
other hand, provided parameters allow extraction from the Moessbauer data
information about impurity concentration and eventual order.
