Lattice relaxations and hyperfine fields of heavy impurities in Fe

We present first-principles calculations of the lattice relaxations and hyp erfine fields of heavy impurities in bcc Fe. We consider impurities of the 5sp and 6sp series, containing the largest atoms in the periodic table. As an application we calculate the hyperfine fields of these impurities and in particular the effects of lattice relaxations on these fields. The calcula tions are based on a full-potential Korringa-Kohn-Rostoker Green's-function method for defects and employ the local spin-density approximation for the exchange and correlation effects. The nonspherical parts of the potential and the charge density are included in the calculations and the forces are calculated by an ionic version of the Hellmann-Feynman theorem. The resulti ng lattice relaxations are relatively small, even for the largest impuritie s considered. The comparison of the calculated hyperfine fields with the ex perimental data shows that the inclusion of lattice relaxations improves th e overall agreement with experiment.