Hyperfine fields and electronic structure of hydrogen impurities in transition metals

Abstract

The hyperfine fields and charge and spin densities around hydrogen impurity sites in iron, cobalt, and nickel are calculated using the local-density formalism in an embedded cluster model. The sensitivity of the self-consistent spin density to embedding constraints and the cluster boundary conditions is explored. A continuum-state boundary condition is developed which serves to broaden the discrete cluster levels in a physically satisfactory manner. The hyperfine field is seen to result from a delicate balance between negatively exchange-polarized "bound-paired" states and positive "unpaired-band" contributions. The theory shows a reduction in moment for atoms around the impurity site as observed; the calculated moments and fields are in fairly good agreement with experiment, using up to 38 atom clusters. The pressure dependence of the muon hyperfine field is presented.