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Full-Text Articles in Physics
Coherent-Potential And Average T-Matrix Approximations For Disordered Muffin-Tin Alloys: 1. Formalism, A. Bansil
Arun Bansil
The average density of states 〈ρ(E)〉 and the component charge density associated with an A(B) atom in the alloy, 〈ρA(B)(E)〉, are discussed for the disordered alloy AₓB₁₋ₓ within the framework of the muffintin Hamiltonian. A new version of the average t-matrix (ATA) is developed. The structure in the spectral density function, 〈ρ(k,E)〉, in the coherent-potential approximation (or the new ATA) is seen to result from not only the Bloch-type states in the medium of coherent-potential effective atoms tCP (or the average t-atoms 〈t〉) but also from non-Bloch-type impurity levels arising when a single A or B atom …
Multiple-Scattering Theory Of Itinerant Electron Magnetism In Random Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Multiple-Scattering Theory Of Itinerant Electron Magnetism In Random Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Arun Bansil
We discuss the equilibrium electronic structure of a random binary alloy within the framework of a spin-dependent muffin-tin Hamiltonian. The disorder is treated on the basis of the single-site approximations (SSA), especially the average t-matrix and the coherent potential approximations. The local-spin-density (LSD) functional approach is employed to relate the electron and the spin densities with the atomic potentials, thus providing a fully self-consistent description of the ground-state properties of the random alloy. By using the atomic magnetic moments as expansion parameters, a Stoner-type linearized form of the full SSA-LSD formalism is developed. This analysis yields insights into the nature …
Coherent-Potential And Average T-Matrix Approximations For Disordered Muffin-Tin Alloys: 2. Application To Realistic Systems, A. Bansil
Arun Bansil
In an earlier article, the electronic spectrum of the disordered alloy AₓB₁₋ₓ, using the coherent-potential (CPA) and the average t-matrix (ATA) approximations, was discussed within the framework of the muffintin Hamiltonian. Using the illustrative examples of CuₓNi₁₋ₓ and CuₓZn₁₋ₓ, the present paper exposes the physically relevant aspects of the electronic spectra of disordered transition and noble-metal alloys. Bloch spectral densities, complex energy bands, impurity levels, and average total and component densities of states are considered. We also discuss how the effects of transfer of charge between the constituents on their atomic potentials can be included in a semiempirical manner in …
Application Of Coherent-Potential Approximation To Disordered Muffin-Tin Alloys, A. Bansil
Application Of Coherent-Potential Approximation To Disordered Muffin-Tin Alloys, A. Bansil
Arun Bansil
I report implementation of the coherent-potential approximation for obtaining the electronic density of states and component charge densities in disordered muffin-tin alloys. Illustrative results for CuₓNi₁₋ₓ are presented. The extent to which the self-consistency in treating disorder influences the electronic spectrum is considered.
Effects Of The Positron Spatial-Distribution On Momentum Densities In Random Muffin-Tin Alloys, A. Bansil, P. E. Mijnarends
Effects Of The Positron Spatial-Distribution On Momentum Densities In Random Muffin-Tin Alloys, A. Bansil, P. E. Mijnarends
Arun Bansil
We consider the problem of incorporating positron spatial distribution effects on the two-photon momentum density 〈ρ2γ(p)〉 in a disordered alloy. 〈ρ2γ(p)〉 formally involves the average 〈GG₊〉 of the product of electron and positron Green's functions. Our approach utilizes the framework of the average-t-matrix and coherent-potential approximations to treat disorder in the alloy and neglects the vertex corrections which arise in evaluating 〈GG₊〉. The influence of disorder on the positron state is delineated in terms of the properties of 〈G₊〉. Illustrative results for Cu, Cu₇₅Ni₂₅, Cu₅₀Ni₅₀, and Ni are presented and discussed.
Electron Momentum Densities In Disordered Muffin-Tin Alloys, A. Bansil, R. S. Rao, P. E. Mijnarends, L. Schwartz
Electron Momentum Densities In Disordered Muffin-Tin Alloys, A. Bansil, R. S. Rao, P. E. Mijnarends, L. Schwartz
Arun Bansil
The application of average t-matrix (ATA) and coherent potential (CPA) approximations to the calculation of average electron momentum density ρ(p) in random muffin-tin alloys AₓB₁₋ₓ is considered. The necessary equations for the general matrix elements of the operators describing scattering by the CPA atom and also by an A or B atom embedded in the effective medium are derived. Various versions of the ATA for ρ(p) are discussed. Several ρ(p) curves calculated on the basis of the CPA and ATA in CuₓNi₁₋ₓ are presented. These results are used to delineate the effects on ρ(p) of self-consistency in the treatment of …
Green’S Function And A Generalized Lloyd Formula For The Density Of States In Disordered Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Green’S Function And A Generalized Lloyd Formula For The Density Of States In Disordered Muffin-Tin Alloys, S. Kaprzyk, A. Bansil
Arun Bansil
We consider the Korringa-Kohn-Rostoker coherent-potential-approximation Green’s function for a disordered system of muffin-tin potentials and evaluate its integral over the Wigner-Seitz cell rigorously throughout the complex energy plane. The resulting expression is shown to possess a perfect derivative form, provided the angular-momentum summations are extended to infinity; for a finite angular-momentum cutoff this result is valid to a good approximation. For real energies our expression constitutes a generalization of the Lloyd formula for the density of states. The conventional Lloyd formula contains unphysical singularities that are not only unsatisfactory from a formal viewpoint, but also make its use increasingly cumbersome …