Full-Potential KKR Calculations for Point Defect Energies in Fe-Based Dilute Alloys, Based on the Generalized-Gradient Approximation

We present systematically ab-initio calculations for defect energies of 3d and 4sp impurities (Sc-Ge) in Fe. The calculations are based on the Generalized-Gradient-Approximation in the density-functional formalism and the full-potential Korringa-Kohn-Rostoker (FPKKR) Green's function method. First we examine the distance dependence, from the 1st- to the 10th-neighbors, of the impurity-impurity (I-I; I = Sc-Ge) interaction energies (E-int) and show that for most cases, the 1st-neighboring I-I interaction energies (E-int(1)) are dominant. We found that fundamental features of phase diagrams of Fe-based binary alloys, such as segregation, solid solution and order, known experimentally, may be classified by use of the sign and magnitude of E-int(1). Second we discuss the calculated results for the 1st- and 2nd-neighboring interaction energies of 3d and 4sp impurities with perturbed-angular-correlation (PAC)-probe Sn in Fe. The comparison of the calculated results with available experimental results shows that the observed attraction for Sn-Co, Sn-Ni and Sn-Cu may be understood by the 1st-neighboring interaction energies of these impurity pairs, while the obsreved repulsion for Sn-Ga, and Sn-Ge by the 2nd-neighboring interaction energies of these impurity pairs. We also discuss the magnetism of single impurities X (= Sc-Cu) in Fe. The anti-parallel coupling to the bulk magnetization of the neighboring Fe atoms is stable for Sc-Mn, while the parallel coupling for Fe-Cu.