Systematic first-principles calculations were made of vacancy formation energies for most metallic elements with face-centered cubic or body-centered cubic structures, as well as of bulk properties such as lattice parameters and moduli. The calculations were based upon the generalized-gradient approximation of the density-functional formalism. The full-potential Korringa-Kohn-Rostoker Green’s function method for perfect crystals and point-defect systems was applied. It was shown that the calculated bulk properties were in excellent agreement with experimental results. The generalized-gradient approximation corrected the deficiencies (under-estimation of lattice parameters, over-estimation of bulk moduli) of the local spin density approximation for metals, and the theoretical errors lattice parameters and moduli were reduced to within 1 and 10% of experimental results, respectively. It was shown that the vacancy formation energy for most face-centered cubic metals was reproduced to within experimental errors, while that for most body-centered cubic metals was over-estimated by 10 to 20%. It was noted that a comparison with experimental results required the inclusion of a thermal lattice expansion effect in the first-principles calculations because most of the experimental results were derived from positron annihilation measurements at high temperatures.

Full-Potential KKR Calculations for Point Defect Energies in Metals, Based on the Generalized-Gradient Approximation - I. Vacancy Formation Energies in FCC and BCC Metals. T.Hoshino, T.Mizuno, M.Asato, H.Fukushima: Materials Transactions, 2001, 42[11], 2206-15

Systematic first-principles calculations were made of impurity-impurity interaction energies of 4d elements in body-centered cubic Nb and Mo, and face-centered cubic Pd and Ag. The calculations were based upon the generalized-gradient approximation of density-functional formalism, and applied the full-potential Korringa-Kohn-Rostoker Green’s function method for point defects. The distance dependence, from 1st to 8th-nearest neighbors, of the interaction energy was examined and it was shown that, for most cases, the first-nearest neighbor impurity-impurity interaction energies predominated. It was also shown that most of types of phase diagram could be discriminated on the basis of the sign and magnitude of the first-nearest neighbor interaction energy. The temperature dependence of the solid solubility limit of Rh in Pd, which was segregated at low temperatures and became disordered at high temperatures, was reproduced fairly well by free-energy calculations which were based upon the cluster variation method; plus the present results for interaction energies up to the 8th-nearest neighbor. It was shown that the inclusion of impurity-cluster interaction energies up to the 4-body (a tetrahedron of 1st-nearest neighbors) led to a complete agreement with experimental result.

Full-Potential KKR Calculations for Point Defect Energies in Metals, Based on the Generalized-Gradient Approximation - II. Impurity-Impurity Interaction Energies and Phase Diagrams. M.Asato, T.Mizuno, T.Hoshino, H.Sawada: Materials Transactions, 2001, 42[11], 2216-24