Hyperfine fields and electronic structure of hydrogen impurities in transition metals

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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.