M. Asato

First-principles calculations for vacancy formation energies in Cu and Al; non-local effect beyond the LSDA and lattice distortion

Abstract We show ab initio calculations for vacancy formation energies in Cu and Al. The calculations are based on density-functional theory and the full-potential Korringa–Kohn–Rostoker Greens function method for impurities. The non-local effect beyond the local-spin-density approximation (LSDA) for density-functional theory is taken into account within the generalized-gradient approximation (GGA) of Perdew and Wang. The lattice relaxation around a vacancy is also investigated using calculated Hellmann–Feynman forces exerted on atoms in the vicinity of a vacancy. We show that the GGA calculations reproduce very well the experimental values of vacancy formation energies and bulk properties of Cu and Al, as they correct the deficiency of LSDA results (underestimation of equilibrium lattice parameters, overestimation of bulk moduli, and vacancy formation energies). It is also shown that the GGA calculations reduce the LSDA results for the lattice relaxation energy for a vacancy in Cu.

Vacancy formation energies in FCC metals : non-local effect beyond the LSDA

The non-local effect (NLE) beyond the local-spin-density approximation (LSDA) for vacancy formation energies in Al, Cu, and Ni is examined using the generalized-gradient approximation of Perdew and Wang. The calculations are based on the full-potential Korringa—Kohn—Rostoker Greens-function method. The NLE reduces the vacancy formation energies obtained by the LSDA and leads to nice agreement with the experimental values. The lattice parameter dependence for vacancy formation energies is discussed.

First-principles calculations for point-defect energies in metals and phase diagrams of binary alloys

Abstract We discuss the present status of the first-principles electronic-structure calculations for defect energies in metals. The calculations apply density functional theory in the generalized-gradient approximation of Perdew and Wang, together with a full-potential version of Korringa–Kohn–Rostoker Greens function method, developed by the Julich group. It is shown that: (1) the present calculations reproduce very well the experimental results for vacancy formation energies in metals, as well as the bulk properties such as equilibrium lattice parameters and bulk moduli of metals; and (2) the type of the phase diagram of a binary A–B alloy can be characterized by the interaction energies between a pair of impurity B (A) atoms in the host metal A (B). The observed temperature dependence of the solid solubility limit of Rh in Pd is also reproduced very well by the free-energy calculations based on the cluster variation method with the pair- (up to the eighth neighbor) and many-body (up to a tetrahedron of first-nearest neighbors) interaction energies, all of which are determined by the present first-principles calculations.

First-principles calculations for solid solubility limit of impurities in metals:: many-body interaction effect

Abstract We present the first-principles calculations for the temperature dependence of the solid solubility limit of Rh impurities in Pd, which is segregated at low temperatures and becomes disordered at high temperatures. The impurity pair and cluster interaction energies, which are needed to obtain the internal energy of the free energy, are calculated by use of the KKR–Green’s function method for impurities combined with density functional theory in the generalized gradient approximation of Perdew and Wang, while the configurational entropy is treated by the cluster variation method in the tetrahedron approximation. It is shown that the observed temperature dependence of the solid solubility limit of Rh in Pd can be reproduced almost completely by the present first-principles calculations including the impurity cluster interaction energies up to the tetrahedron.

Accuracy of atomic-sphere approximation in electronic-structure calculations for transition-metal systems

The simple atomic-sphere approximation (ASA) is used very often for the first-principles calculations based on density-functional theory, in order to study the electronic structure of complex transition-metal systems. We clarify the accuracy of ASA, comparing with the full-potential (FP) calculation results. We show that the ASA calculations reproduce very well the bulk properties, obatined by the FP calculations, while its accuracy decreases significantly for the non-periodic transition-metal system properties, such as vacancy formation energies and solution energies of 3d impurities. It is discussed that the ASA error worsens together with the anisotropic part of FP and the charge transfer between defect and host atoms. It is also discussed that the ASA error may become larger with the generalized-gradient approximation than with the local-spin-density approximation.

Non-self-consistent first-principles calculations for total-energy differences

Abstract We assess the accuracy of two non-self-consistent first-principles calculations. The first one is the accuracy of frozen-potential approximation which may be useful for the study of phase diagrams of alloys. Secondly, we show that the structural properties obtained by the self-consistent calculations based on the generalized-gradient approximation (GGA) are accurately reproduced by the non-self-consistent calculations with the GGA functional, using the electron density obtained by the local-spin-density approximation.