Ab initio study of Cr interactions with point defects in bcc Fe

The properties of Cr in alpha Fe have been investigated by ab initio calculations based on density functional theory. The intrinsic point defect formation energies were found to be larger in model bcc Cr as compared to those in ferromagnetic bcc Fe. The interactions of Cr with point defects (vacancy and self-interstitials) have been characterized. Single Cr atoms interact weakly with vacancies but significantly with self-interstitial atoms (SIA). Mixed interstitials of any interstitial symmetry are bound. Configurations where two Cr atoms are in nearest-neighbor position are generally unfavorable in bcc Fe except when they are a part of a < 111 > interstitial complex. Mixed < 110 > interstitials do not have as strong directional stability as pure Fe interstitials have. The effects on the results using the atom description scheme of either the ultrasoft pseudopotential (USPP) or the projector augmented wave (PAW) formalisms are connected to the differences in local magnetic moments that the two methods predict. As expected for the Fe-Cr system, the results obtained using the PAW method are more reliable than the ones obtained with USPP.