Effect of lattice relaxations on the hyperfine fields of heavy impurities in Fe

We present first-principles calculations of hyperfine fields of heavy impur ities in bcc Fe. In particular, the effect of lattice relaxations on the ca lculated hyperfine fields are studied. The calculations are based on a full -potential Korringa-Kohn-Rostoker Green's-function method for defects and e mploy the local spin-density approximation for the exchange and correlation effects. The calculated lattice relaxations around the 5sp and 6sp impurit ies in Fe are found to be relatively small, for the first and second neares t neighbor shells less than 6% of the nearest neighbor distance. Also the e stimated relative volume changes induced by the sp impurities are found to be around 60-95% of the elementary volume of Fe, surprisingly small in view of the large atomic volumes of the impurities. The calculated hyperfine fi elds of 5sp and 6sp elements are compared with available experimental data and it is shown that the inclusion of lattice relaxations in the calculatio n improves the agreement with experiments.