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| Book/Report | FZJ-2018-03235 |
; ; ;
1990
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18726
Report No.: Juel-2356
Abstract: We investigated the interaction energies of solute-vacancy and solute-solute complexes in copper and nickel for 3d- and 4sp- impurities from Sc to Br. Within the framework of local density functional theory and the KKR Green's function method, selfconsistent ab-initio-calculations have been performed for a cluster of 20 perturbed potentials embedded correctly in the ideal host crystal. The cluster consists of two defects on nearest neighbor sites in an fcc lattice and of all host atoms which are nearest neighbors to at least one of the defects. Interaction energies were determined independently by total energy calculations and the Hellmann-Feynman theorem. We used an accurate total energy formalism -taking advantage of extremal properties - to calculate the interaction energy of a defect complex as total energy differences between the pair complex and its single defects. Lloyd's formula was employed for the single particle energies, thus including contributions over all space and for all angular momenta. We evaluated the double counting contributions for both the Coulomb and the exchange energies with the full anisotropic charge density in each cell. Integrals over Wigner-Seitz cells were approximated by integrals over atomic spheres. More refined calculations with integrations over the exactly faceted cell proved the accuracy of this approximation. We derived a new expression for interaction energies based on the Hellmann-Feynman theorem. It allows a direct electrostatic interpretation of interaction energies in terms of charge densities screening the impurities. This formula was used to estimate the shell dependence of the vacancy-solute interaction for spatoms and the agglomeration of another sp-atom to a vacancy-solute complex in Cu. Results from total energy calculations and the Hellmann-Feynman theorem agree well and confirm experimental data. They show that 3d-atoms dissolved in Cu or Ni are repelled from a vacancy whereas 4sp-atoms are strongly attracted with a binding energy proportional to the valence difference $\Delta$Z. Defect complexes of two identical 4sp-atoms tend to dissociate in both host crystals. Analogous pairs of 3d-atoms show attraction in Cu but a weak repulsion in Ni.
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