Showing papers on "Coherent potential approximation published in 1986"
TL;DR: A density-functional--based theory is developed for calculation of the total energy and pressure of random substitutional alloys within the Korringa-Kohn-Rostoker coherent-potential approximation and it is found that the variation is almost linear and that it deviates from Vegard's rule.
Abstract: A density-functional--based theory is developed for calculation of the total energy and pressure of random substitutional alloys within the Korringa-Kohn-Rostoker coherent-potential approximation The theory is used to calculate the concentration variation of the equilibrium lattice spacing of cap alpha-phase Cu/sub c/Zn/sub 1-c/ alloys We find, in agreement with experiment, that the variation is almost linear and that it deviates from Vegard's rule
192 citations
TL;DR: In this paper, a model tight-binding Hamiltonian including off-diagonal disorder and Hartree-Fock electronic self-consistency was used to calculate the enthalpies of formation of the Mo-Cr, Mo-Nb, and Mo-Ta alloys.
Abstract: A model tight-binding Hamiltonian including off-diagonal disorder and Hartree-Fock electronic self-consistency is used to calculate the enthalpies of formation of the Mo-Cr, Mo-Nb, and Mo-Ta alloys. The approach combines the coherent-potential approximation, the generalized perturbation method, and the cluster-variation method. The model is also used to calculate the phase diagram and the equilibrium activities for the Mo-Cr system.
43 citations
TL;DR: In this article, the alloy effects to heavy electrons, particularly in the resistivity, are discussed in the symmetric Anderson lattice model consisting of magnetic and nonmagnetic atoms.
39 citations
TL;DR: In this paper, the pseudobinary alloy system Ti(FexCo1-x), including the pure binary phases, was analyzed and it was shown that the magnetic behavior of the pseudo-bipartite system is entirely governed by antistructure atoms.
Abstract: KKR GF and KKR CPA calculations are performed for the pseudobinary alloy system Ti(FexCo1-x), including the pure binary phases. The results indicate that, in accordance with experimental findings, the magnetic behaviour of the pseudobinary system is entirely governed by antistructure atoms.
14 citations
TL;DR: In this article, the effects of spin fluctuations on the first ten layers of the semi-infinite FCC lattice, described by the realistic canonical d-band model, are included by means of the functionalintegral method within the static and single-site coherent potential approximations.
Abstract: Magnetic and one-electron properties of Ni(100) at finite temperatures are studied by the author's recently developed calculation method in which effects of spin fluctuations on the first ten layers of the semi-infinite FCC lattice, described by the realistic canonical d-band model, are included by means of the functional-integral method within the static and single-site coherent potential approximations. It is shown that the surface moment, whose ground-state value is slightly enhanced compared with the bulk one, decreases more rapidly than the bulk upon heating. The calculation of spectral densities indicates that their exchange-split peaks at all the investigated wave-vectors in the surface Brillouin zone approach each other with broadened linewidth when the temperature is raised. The recent ARPE experiments probing the bulk band structure are discussed on the basis of the calculated surface and bulk spectral densities.
13 citations
TL;DR: In this article, the electronic and optical properties of superlattices made of semiconductor alloys were investigated. But the results were compared with those obtained within the virtual crystal approximation (VCA) which does not include disorder scattering.
Abstract: We report theoretical calculations of the electronic and optical properties of strained‐layer superlattices (SLS) made up of semiconductor alloys. The SLS conduction band states are obtained by using a two‐band model capable of correctly describing the band structure over the entire Brillouin zone. This allows us to study intervalley scattering among the various conduction band valleys (Γ, L, X, etc.). Our model also allows us to easily incorporate the effects of strain on the band structure. Using this model we have studied materials such as Si/GeSi SLS, and the effects of zone folding and strain on the band structure and photoabsorption are reported. We have also studied the effect of disorder scattering in SLS made of alloy semiconductors by generalizing the coherent potential approximation (CPA) to the treatment of superlattices. The results are compared with those obtained within the virtual crystal approximation (VCA) which does not include disorder scattering.
6 citations
TL;DR: In this article, a generalised coherent potential approximation is used to describe a chemically disordered material and the method gives not only the density of states for such a system but also reliable values of the total energy.
Abstract: A generalised coherent potential approximation is used to describe a chemically disordered material. It is shown that the method gives not only the density of states for such a system but also reliable values of the total electronic energy. The model is applied to a binary metal alloy where it is seen that a pseudo gap develops prior to the development of an ordered phase and in both cases the conductivity is anticipated to be lowered.
6 citations
TL;DR: In this paper, the density of states on a randomly dilute Cayley tree (bonds are present with probability p) has been obtained both numerically and analytically.
Abstract: The density of states on a randomly dilute Cayley tree (bonds are present with probability p) has been obtained both numerically and analytically. The numerical procedure involves an average over randomly generated clusters of the dilute Cayley tree, whereas the analytical procedures define an effective medium through a self-consistency equation. One of them extends the coherent potential approximation to include the effect of nondiagonal disorder in disconnected lattices. This approximation reproduce very well the authors' simulation results in the whole range of dilution (0
5 citations
CNET1
TL;DR: In this paper, the average electronic propagator was calculated using a two-dimensional muffin-tin version of the coherent potential approximation for a quantum well whose thickness takes the random values of n−1, n or n+1 monolayers.
5 citations
TL;DR: In this paper, the coherent potential approximation (CPA) is incorporated into the self-consistent theory of Anderson localization in the form developed by Vollhardt and Wolfle.
Abstract: To describe electron localization in substitutionally random alloysAcB1−c the coherent potential approximation (CPA) is incorporated into the self-consistent theory of Anderson localization in the form developed by Vollhardt and Wolfle. Modifications of the localization theory arise from the tight-binding model with bimodal diagonal disorder of arbitrary strength. The mean-free path, correlation and localization lengths, and the zero-temperature conductivity are calculated at dimensionalityd=3. The metal-insulator transition is studied numerically for a CPA-induced band structure under semielliptical model assumptions.
5 citations
TL;DR: The theory of the conductivity for strongly disordered systems is applied to the Anderson model in this article, and it is shown that the metal-insulator transition occurs at the reasonable value of the strength of disorder.
Abstract: The theory of the conductivity for strongly disordered systems [J. Phys. Soc. Jpn. 54 (1985) 736] is applied to the Anderson model. It is shown that the metal-insulator transition occurs at the reasonable value of the strength of disorder.
TL;DR: In this paper, an expansion for generating functionals (partition sums) of models expressed as lattice functional integrals with local (on-site) interactions is presented, which renormalizes the standard perturbative expansion in such a way that certain its terms are summed up non-perturbatively.
Abstract: An expansion for generating functionals (partition sums) of models expressed as lattice functional integrals with local (on-site) interactions is presented. This expansion renormalizes the standard perturbative expansion in such a way that certain its terms are summed up non-perturbatively. A non-self-consistent and a self-consistent versions of the expansion are formulated and criteria for an estimation of validity of approximations resulting from the both expansions are given. The simplest approximation being the first term of this expansion is applied to two lattice models: classicalN-component spin model and the model of non-interacting electrons in a disordered crystal. In the former model the critical temperature is calculated within 10% accuracy and in the latter, the coherent potential approximation is obtained.
TL;DR: In this paper, the electronic structure and magnetic interactions in Mn-alloyed II-VI diluted magnetic semiconductors (DMS) are summarized using an empirical tight-binding, coherent potential approximation approach with input from experiment and local spin density band calculations.
Abstract: Recent calculations of the electronic structure and magnetic interactions in Mn - alloyed II-VI diluted magnetic semiconductors (DMS) are summarized. Detailed band structure results are obtained using an empirical tight-binding, coherent potential approximation approach with input from experiment and local spin density band calculations. The dominant magnetic interactions in these systems result from hybridization between spin-split Mn d states and sp valence bands. Superexchange between Mn moments is well described by a simple three-level model which yields accurate Mn - Mn exchange constants for a variety of II-VI DMS as well as the rocksalt insulators MnO and α-MnS.
TL;DR: In this article, a quantized Hamiltonian for optical phonons in disordered materials is presented, including both the short and long-range forces, including the competitive effects of the long range correlation and the local structural fluctuation on the optical phonon.
TL;DR: In this paper, the concentration dependence of the off-diagonal component of the electroconductivity tensor and the average magnetic moment were calculated for PdFe, PdCo, and PdNi alloys in the coherent potential approximation (CPA).
Abstract: The concentration dependence of the off-diagonal component of the electroconductivity tensor and that of the average magnetic moment are calculated for PdFe, PdCo, and PdNi alloys in the coherent potential approximation (CPA). These calculations are based on realistic models of the component densities of states (DOS's). Experimental and theoretical results are compared.
[Russian Text Ignored].
TL;DR: In this paper, the space extension of a single magnetization fluctuation in the disordered paramagnetic medium defined within the coherent potential approximation is discussed, and the thermodynamic potential functional for the subspace of nearly completely disordered configurations is derived.
Abstract: The space extension of a single magnetization fluctuation in the disordered paramagnetic medium defined within the coherent potential approximation is discussed. The thermodynamical potential functional for the subspace of nearly completely disordered configurations is derived.
TL;DR: In this article, the properties of polaritons in a disordered material were studied under the Coherent Potential Approximation (CPA) under the concept of effective wave vector.
Abstract: The properties of polaritons in a disordered material are studied under the Coherent Potential Approximation. The main results are as follows: (i) The concept of effective wave vector can be used to describe the polariton in a disordered material. (ii) The polariton dispersion in a disordered material is similar to that in a crystalline material. (iii) The polariton lifetime due to the disorder increases as its energy departs from the resonant region.
TL;DR: The coherent potential approximation (CPA) for ternary alloys proposed by Scarfone (1973) is used to analyse the experimental data, assuming a single Einstein oscillator model for the host crystal.
Abstract: Recently measurements on the infrared and Raman scattering spectra of several quaternary alloy systems such as Ga 1 _ xAI xAs 1 _ yP y have been reported. Depending on the concentration, this system can be thought of as either a GaAs-rich quaternary, where GaAs is the host containing the two kinds of impurity Al and P, or as a GaP-rich quaternary, where GaP is the host and Al and As are two impurities. Thus, the properties of such systems can be simulated by a ternary alloy. The coherent potential approximation (CPA) for ternary alloys proposed by Scarfone (1973) is used to analyse the experimental data, assuming a single Einstein oscillator model for the host crystal. The theory, consisting of both diagonal and off-diagonal randomness, agrees well with the observed values, but fails to predict the observed pair modes.
01 Jan 1986
TL;DR: In this article, the coherent potential approximation (CPA) within the tight binding Slater-Koster scheme is reviewed as a theoretical tool for the study of the electronic properties of amorphous semiconductor hydrides.
Abstract: The coherent potential approximation (CPA) within the tight binding Slater-Koster scheme is briefly reviewed as a theoretical tool for the study of the electronic properties of amorphous semiconductor hydrides.
TL;DR: In this article, a 1D binary random alloy model with interactions decaying as 1 r 2, for which the coherent potential approximation (CPA) equations can be obtained in closed form.
TL;DR: In this paper, the magnitudes of electron interactions in silver-rich Ag-Pd alloys were estimated from the experimental NMR data for 109 Ag, and Stoner's enhancement factor in the s-band spin susceptibility was found to be about 2.
TL;DR: In this article, the pseudopotential method in the coherent potential approximation was used to calculate the energy structure of the solid solutions Al1−xGaxAs and Al 1−xgaxSb and analyzed the effect of chemical disorder on the interband transitions and the electron mobility.
Abstract: Using the pseudopotential method in the coherent potential approximation we calculate the energy structure of the solid solutions Al1−xGaxAs and Al1−xGaxSb. We analyze the effect of chemical disorder on the interband transitions and the electron mobility. We show that it is important to take into account the effects of nondiagonal disorder.
01 Jan 1986
TL;DR: In this article, it was shown that, in spite of the great complexity of the potential felt by an electron moving in an amorphous semiconductor, the electronic structure of the latter possesses a certain universality.
Abstract: Recent advances based on the coherent potential approximation and the potential well analogy suggest that, in spite of the great complexity of the potential felt by an electron moving in an amorphous semiconductor, the electronic structure of the latter possesses a certain universality. As a result (and to a first approximation) only a few parameters matter. The situation is analoguous to that of a crystalline semiconductor, where a single quantity — the effective mass — allows one to bypass the complexity of the crystalline potential.