Coherent potential approximation

About: Coherent potential approximation is a research topic. Over the lifetime, 1930 publications have been published within this topic receiving 36805 citations.

Magnetism and structural ordering on a bcc lattice for highly magnetostrictive Fe-Ga alloys: A coherent potential approximation study

Abstract: We calculate the electronic structure, magnetic moments, and ordering energies of highly magnetostrictive Fe1−xGax alloys from first-principles in the composition range up to x=0.25. The coherent potential approximation was used to treat effects of chemical disorder. Given an underlying bcc lattice in whole range compositions investigated, the DO3 type of ordering is found to have a lower energy than A2- and B2-type structures. We find that ordering energies strongly depend on the state of magnetic order such that thermal magnetic disorder strongly favors chemical ordering (DO3 and B2). The values of the magnetic moments of Fe on different sublattices of ordered structures are found to have a distinctive dependency on the Ga concentration. By taking into account the results of earlier fully relativistic and full potential calculations of magnetostriction for ordered stoichiometric Fe3Ga compounds and available experimental phenomenology, our results for disordered alloys suggest an eventually more complex...

The CPA and Anderson's model of cellular disorder

Abstract: We examine calculations of the ensemble-averaged Green function for Anderson's disordered Hamiltonian within the coherent potential approximation and show how the result of this procedure becomes exact if a Lorentzian distribution of site-energy is used. The application of these results to calculations of energy band properties is discussed and an exact analytical expression for the band-width is derived in the case of a rectangular distribution. Finally, we investigate the implications of a localization criterion proposed by Economou and Cohen (1970, 1972) [EC] in this context for various distributions of site-energy and demonstrate the possibility of a mobility edge moving outwards from the unperturbed band edge as randomness increases. The results for square-root and rectangular distributions are shown to be qualitatively similar, resolving a puzzling dissimilarity suggested by Brouers (1971) and Schonhammer (1971).

Comparative study of the electronic structure of ordered, partially ordered, and disordered phases of the Cu3Au alloy.

Abstract: We present a theoretical study of the electronic structure of ordered, partially ordered, and disordered phases of the ${\mathrm{Cu}}_{3}$Au alloy using the scalar-relativistic linear muffin-tin orbitals (LMTO) method in conjunction with the coherent-potential approximation. We study the change in the electronic structure caused by the gradual increase of disorder in the alloy by varying the long-range-order parameter S continuously from its maximum (S=1) to the minimum (S=0) possible value. Calculations for the disordered phase (S=0) are performed with and without relaxation of the lattice. The relaxed-lattice calculation takes into account, in an approximate way, the possible deviations from the ideal lattice structure due to the difference in the sizes of the constituent atoms. As a side issue, we address the problem of transferability of the LMTO parameters of the individual alloy components in the pure crystalline phase to the alloy calculation.

Theory of the spin wave stiffness constant in ferromagnetic transition metal alloys

Abstract: Previous numerical calculations for a model of nickel alloys, employing the coherent potential approximation (CPA) and the random phase approximation (RPA), are extended to iron alloys. It is shown that often the effective scattering potentials are sufficiently weak for a rigid band calculation of the spin wave stiffness constant D to be a good guide to the more elaborate CPA calculations. The case of NiFe alloys is re-examined in the light of a recent calculation by Riedinger and Nauciel-Bloch (ibid., vol.5, p.732 (1975)). It is shown that D is very sensitive to the assumed exchange splitting in pure nickel and that within the RPA reasonable agreement with experiment is obtained only by assuming an unusually large value for this parameter.

Self-consistent alloy treatment of the periodic anderson model: Susceptibility and specific heat of intermediate valence compounds

Abstract: To describe the electronic properties of mixed valence compounds we study the periodic Anderson model within the frame of the alloy analog approximation. In this approach the model Hamiltonian is replaced by the sum of two single-particle alloy Hamiltonians the parameters of which have to be determined self-consistently. The alloy problem is solved within the coherent potential approximation. In contrast to other treatments of the periodic Anderson model this approximation scheme is exact in both trivially solvable limits of vanishing hybridization and Coulomb repulsion, respectively. For model parameters corresponding to a mixed valence situation only nonmagnetic solutions of the self-consistency equations exist. After discussing the limit of small hybridization analytically we numerically calculate the magnetic susceptibility and the electronic specific heat as a function of temperature for realistic values of the hybridization and Coulomb repulsion. The results are in very good qualitative agreement with experimental data.