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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.


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TL;DR: In this article, the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co2[Cr1−xMnx][Al1−ySiy] employing three different approaches: (i) the coherent potential approximation; (ii) the virtual crystal approximation; and (iii) supercell calculations.
Abstract: We study the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co2[Cr1−xMnx][Al1−ySiy] employing three different approaches: (i) the coherent potential approximation; (ii) the virtual crystal approximation; and (iii) supercell calculations. All three methods give similar results, and the local environment manifests itself only for small details of the density of states. All alloys under study are shown to be half-metals, and their total spin moments follow the so-called Slater–Pauling behavior of the ideal half-metallic systems. We especially concentrate on the properties related to the minority-spin band gap. We present the possibility to engineer the properties of these alloys by changing the relative concentrations of the low-valent transition metal and sp atoms in a continuous way. Our results show that for realistic applications, compounds rich in Si and Cr are ideal since they combine large energy gaps (around 0.6 eV), robust half-metallicity with respect to defec...

27 citations

Journal ArticleDOI
TL;DR: In this paper, a theoretical approach based on a tight-binding model is developed for studying the effects of finite concentration gas adsorption (for what are known as diatomic, triatomic and quadratomic gas molecules in the general forms denoted by XY, XY2 and XY3, respectively) on electronic properties of armchair graphene nanoribbons.
Abstract: A theoretical approach based on a tight-binding model is developed for studying the effects of finite concentration gas adsorption (for what are known as diatomic, triatomic and quadratomic gas molecules in the general forms denoted by XY, XY2 and XY3, respectively) on electronic properties of armchair graphene nanoribbons (AGNRs). To consider the edge effects on electronic properties of pure AGNRs for the first time, two hopping parameters, for hydrogen–carbon and carbon–carbon nearest neighbor hopping, are considered. We found, for some specified values of hopping integrals and random on-site energies, that adsorbed molecule AGNRs act as donors or acceptors, which is consistent with reported experimental results for CO, NO2, O2, N2, CO2 and NH3 adsorption on graphene. Then by using these parameters and the coherent potential approximation, we investigated the effect of finite concentration gas molecule adsorption on the average density of states. Our results could be used to make p-type or n-type semiconductors by means of finite concentration adsorption of gas molecules or a gas sensor.

27 citations

Posted Content
TL;DR: In this article, the spin-orbit induced Rashba-splitting of Shockley-type surface states is discussed using a fully relativistic description and the impact of chemical disorder within surface layers can be handled by means of the Coherent Potential Approximation (CPA) alloy theory.
Abstract: Various technical developments enlarged the potential of angle-resolved photo emission (ARPES) tremendously during the last one or two decades. In particular improved momentum and energy resolution as well as the use of photon energies from few eV up to several keV makes ARPES a rather unique tool to investigate the electronic properties of solids and surfaces. Obviously, this rises the need for a corresponding theoretical formalism that allows to accompany experimental ARPES studies in an adequate way. As will be demonstrated by several examples this goal could be achieved by various recent developments on the basis of the one-step model of photo emission: The spin-orbit induced Rashba-splitting of Shockley-type surface states is discussed using a fully relativistic description. The impact of chemical disorder within surface layers can be handled by means of the Coherent Potential Approximation (CPA) alloy theory. Calculating phonon properties together with the corresponding electron-phonon self-energy allows a direct comparison with features in the ARPES spectra caused by electron-phonon interaction. The same holds for the influence of electronic correlation effects. These are accounted for by means of the dynamical mean field theory (DMFT) that removes the most serious short comings of standard calculations based on the standard LDA. The combination of this approach with the CPA allows the investigation of correlated transition metal alloys. Finally, accounting for the photon momentum and going beyond the single scatter approximation for the final state allows to deal quantitatively with ARPES in the HAXPES regime that reduces the influence of the surface on the spectra and probing primarily the bulk electronic structure this way. Corresponding calculations of ARPES spectra, however, have to deal with thermal vibrations in an adequate way.

27 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed the theory of nonequilibrium coherent potential approximation (NECPA) for analysis of disorder effects in none-ilibrium quantum transport of nanoelectronic devices.
Abstract: Since any realistic electronic device has some degree of disorder, predicting disorder effects in quantum transport is a critical problem. Here we report the theory of nonequilibrium coherent potential approximation (NECPA) for analyzing disorder effects in nonequilibrium quantum transport of nanoelectronic devices. The NECPA is formulated by contour ordered nonequilibrium Green's function (NEGF) where the disorder average is carried out within the coherent potential approximation on the complex-time contour. We have derived a set of new rules that supplement the celebrated Langreth theorem and, as a whole, the generalized Langreth rules allow us to derive NECPA equations for real time Green's functions. The solution of NECPA equations provide the disorder averaged nonequilibrium density matrix as well as other relevant quantities for quantum transport calculations. We establish the excellent accuracy of NECPA by comparing its results to brute force numerical calculations of disordered tight-binding models. Moreover, the connection of NECPA equations which are derived on the complex-time contour, to the nonequilibrium vertex correction theory which is derived on the real-time axis, is made. As an application, we demonstrate that NECPA can be combined with density functional theory to enable analysis of nanoelectronic device physics from atomistic first principles.

26 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20234
202222
202127
202030
201930
201840