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[en] The exact muffin-tin orbitals (EMTO) technique in conjunction with the coherent-potential approximation (CPA) as well as the projector-augmented-wave (PAW) method have been used to calculate the surface segregation energy of Cr at the (100) surface of Fe-rich bcc Fe-Cr alloys. We find that PAW results strongly depend on the supercell size used in the calculations. In particular, for large supercells, the surface segregation energy of Cr is positive, which means that Cr should not segregate toward the surface of diluted alloys. This is in agreement with our EMTO-CPA results as well as previous surface Green's-function calculations. However, the surface segregation energy of Cr is negative if small unit cells are used for simulations. This is in agreement with previous full-potential supercell calculations. We explain such a size dependence by a peculiar concentration dependence of interatomic interactions in ferromagnetic Fe-Cr alloys
[en] The energies of interaction between carbon impurity atoms in paramagnetic fcc iron (austenite) are calculated using electron density functional theory. Point defects in the paramagnetic matrix are described using a statistical approach that takes into account local magnetic fluctuations and atomic relaxation in the environment of impurity atoms. It is shown that, in addition to local deformations, magnetism significantly contributes to the energies of dissolution and interaction of carbon atoms. The values of the carbon-carbon interaction energy are indicative of a significant repulsion between these atoms in the first and second coordination spheres. The results of calculations are consistent with estimates obtained from experimental data on the activity of carbon impurity atoms in iron
[en] We show that effective chemical interactions in an alloy can be tuned by its global magnetic state, which opens exciting possibilities for materials synthesis. Using first-principles theory we demonstrate that at pressure of 20 GPa and at high temperatures, the effective chemical interactions in paramagnetic Fe-Si system are strongly influenced by the magnetic disorder favoring a formation of cubic Fe2Si phase with B2 structure, which is not present in the alloy phase diagram. Our experiments confirm theoretical predictions, and the B2 Fe2Si alloy is synthesized from Fe-Si mixture using multianvil press.