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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 influence of a random field induced by impurities, boundary irregularities etc. on the superfluidity of a quasi-two-dimensional (2D) system of spatially indirect excitons in coupled quantum wells is studied.
Abstract: The influence of a random field induced by impurities, boundary irregularities etc. on the superfluidity of a quasi-two-dimensional (2D) system of spatially indirect excitons in coupled quantum wells is studied. The interaction between excitons is taken into account in the ladder approximation. The random field is allowed to be large compared to the dipole-dipole repulsion between excitons. The coherent potential approximation (CPA) allows us to derive the exciton Green’s function for a wide range of the random field, and the CPA results are used in the weak-scattering limit, which results in the second-order Born approximation. The Green’s function of the collective excitations for the cases of (1) equal electron and hole masses and (2) the “heavy hole” limit are derived analytically. For quasi-two-dimensional excitonic systems, the density of the superfluid component and the Kosterlitz-Thouless temperature of the superfluid phase transition are obtained, and are found to decrease as the random field increases. This puts constraints on the experimental efforts to observe excitonic superfluidity.

53 citations

Journal ArticleDOI
TL;DR: In this article, the Korringa-Kohn-Rostoker-coherent potential approximation (KKR-CPA) method for treating electronic states in random alloys has been made charge self-consistent.
Abstract: The Korringa-Kohn-Rostoker-coherent-potential-approximation (KKR-CPA) method for treating electronic states in random alloys has been made charge self-consistent. Results are presented for a Ag0.2Pd0.8 alloy that were obtained using the Hedin-Lundqvist local density exchange-correlation potential.

53 citations

Journal ArticleDOI
TL;DR: The inclusion of disorder results in a better agreement between calculated and measured spectra for the chlorosomes of green bacteria as compared to the previous report, and it is shown that the circular dichroism spectrum may still show a strong dependence on the cylinder length, even when the exciton wave function is localized in a region smallCompared to the cylinder's size.
Abstract: We study the linear optical properties of helical cylindrical molecular aggregates accounting for the effects of static diagonal disorder. Absorption, linear dichroism, and circular dichroism spectra are presented, calculated using brute force numerical simulations and a modified version of the coherent potential approximation that accounts for finite size effects by using the appropriate open boundary conditions. Excellent agreement between both approaches is found. It is also shown that the inclusion of disorder results in a better agreement between calculated and measured spectra for the chlorosomes of green bacteria as compared to our previous report, where we restricted ourselves to homogeneous cylinders [Didraga, Klugkist, and Knoester, J. Phys. Chem. B 106, 11474 (2002)]. For the excitons that govern the optical response, we also investigate the disorder-induced localization properties. By analyzing an autocorrelation function of the exciton wave function, we find a strongly anisotropic localization behavior, closely following the properties of chiral wave functions which previously have been found for homogenoeus helical cylinders [Didraga and Knoester, J. Chem. Phys. 121, 946 (2004)]. It is shown that the circular dichroism spectrum may still show a strong dependence on the cylinder length, even when the exciton wave function is localized in a region small compared to the cylinder’s size.

53 citations

Journal ArticleDOI
TL;DR: In this paper, the thermodynamic properties of alloys can be described from the knowledge of the underlying lattice and the atomic numbers of the alloy species by using a first-principles electronic structure approach based on the tight-binding linear muffin-tin orbital method within the coherent potential approximation and the local density approximation of density functional theory.
Abstract: The thermodynamic properties of alloys can be described from the knowledge of the underlying lattice and the atomic numbers of the alloy species by using a first-principles electronic structure approach based on the tight-binding linear muffin-tin orbital method within the coherent potential approximation (TB-LMTO-CPA) and the local density approximation of density functional theory. The generalized perturbation method (GPM) permits direct mapping of the configurational part of the effective one-electron Hamiltonian onto an Ising-like model thus insuring the necessary link between quantum mechanics and statistical thermodynamics. To test the practical application of this approach to multi-component alloys, data assessment has been successfully performed for the Cr-Ta-W alloy system by using the thermodynamic results derived from the TB-LMTO-CPA-GPM and the cluster variation method (CVM) in the tetrahedron approximation for Ta-W alloys as functions of temperature and concentration. These later results predict B2 ordering for the bcc-based Ta-W system with a maximum ordering temperature near 1000 K at 43 at.% Ta. The output thermodynamics were converted to a Redlich-Kister/Bragg-Williams format with an acceptable level of accuracy. The results were then combined with those of the CALPHAD description of the Cr-W and Cr-Ta systems to calculate isothermal sections of the ternary phase diagram of the Cr-Ta-W system.

53 citations

Journal ArticleDOI
TL;DR: In this paper, the coherent potential approximation (CPA) has been generalized to describe spin waves in a dilute Heisenberg ferromagnet at T = 0 and the full T matrix of an isolated vacancy in an effective medium is evaluated.
Abstract: The coherent potential approximation (CPA) has been generalized to describe spin waves in a dilute Heisenberg ferromagnet at T=0. The full T matrix of an isolated vacancy in an effective medium is evaluated and the self-energy is obtained selfconsistently. In order to project out the spurious degrees of freedom associated with the fictitious spins on the vacancy sites, a class of pseudopotentials are constructed. The response functions G(k, omega ) and density of states rho ( omega ) for two such pseudopotentials are evaluated in detail. The had core pseudopotential is found to yield the best CPA approximation although it fails near the critical percolation concentration of magnetic sites, as do all the effective medium theories in the face of large fluctuations. The spin-wave stiffness D is calculated and the magnetization and specific heat near T=0. The random phase approximation is used to find Tc, the transition temperature.

53 citations


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