First-principles calculation of defect free energies: General aspects illustrated in the case of bcc Fe

• DOI: 10.1103/physrevb.92.064103
• Publication Date: 2015-08-07T10:13:58Z
• Authors: D. Murali; M. Posselt; M. Schiwarth
• Keywords: Supercell

Modeling of nanostructure evolution in solids requires comprehensive data on the properties defects such as vacancy and foreign atoms. Since most processes occur at elevated temperatures, not only energetics ground state, but also their temperature-dependent free energies must be known. The first-principles calculation contributions phonon electron excitations to formation, binding, migration is illustrated case bcc Fe. First all, ground-state vacancy, atoms Cu, Y, Ti, Cr, Mn, Ni, V, Mo, Si, Al, Co, O, O-vacancy pair are determined under constant volume (CV) well zero-pressure (ZP) conditions, relations between results both kinds calculations discussed. Second, contribution defect calculated within harmonic approximation using equilibrium atomic positions state CV ZP conditions. In cases, ZP-based formation energy decreases monotonously with temperature, whereas for CV-based an increase a decrease were found. application quasiharmonic correction does modify this picture significantly. However, corrected valid conditions higher temperatures than framework purely approach. difference CV- mainly due change supercell since relative arrangement environment nearly identical two cases. A simple transformation similar approach found frequencies. Therefore, it necessary calculate these quantities corresponding separately. contrast energetics, do become equal increasing size. Third, was that can lead additional deviation total from value or compensate caused by contribution. Finally, self-diffusion via mechanism investigated. ratio respective diffusivity reciprocal concentration. This behavior leads almost values coefficient. Obviously, agreement accidental. consideration temperature dependence magnetization yields very good experiments.