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.

Deviation from Matthiessen rule in magnetic disordered alloys-theoretical investigation

Abstract: The model of the magnetic disordered alloys, including the itinerant electrons, localized spins and phonons, was elaborated in details in the paramagnetic region with the use of the Coherent Potential Approximation (CPA) approach. The expression for the DC electrical conductivity was taken from the Kubo-Greenwood formula for an alloys. The separate (residual, phonon and magnetic) contributions to the resistivity for the temperatures above Curie transition temperature, different sets of the model parameters were calculated. The linear temperature dependence of the phonon contribution to the resistivity was reproduced except from the anomalous behavior observed for the parameters sets for which the Fermi level locates near the band's edges. For the same parameters sets our calculations showed the largest percentage deviations from the Matthiessen's rule. Our model calculations confirmed the Matthiessen's rule generalized to the case of the three, residual, phonon and magnetic contributions to the resistivity of the magnetic disordered alloys with the partially filled band when the Fermi level locates far from the bands edges. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Impurity modes in Frenkel exciton systems with dipolar interactions and cubic symmetry

Abstract: We introduce a continuum model for impurity modes of Frenkel excitons in fully occupied face-centered and body-centered cubic lattices with dipole-dipole interactions and parallel moments. In the absence of impurities, the model reproduces the small-k behavior found in numerical calculations of dipolar lattice sums. The exciton densities of states near the upper and lower band edges are calculated and compared with the corresponding results for a random array of dipoles. The Green function obtained with the continuum model, together with a spherical approximation to the Brillouin zone, is used to determine the conditions for the formation of a localized exciton mode associated with a shift in the transition energy of a single chromophore. The dependence of the local mode energy on the magnitude of the shift is ascertained. The formation of impurity bands at high concentrations of perturbed sites is investigated using the coherent potential approximation. The contribution of the impurity bands to the optical absorption is calculated in the coherent potential approximation. The locations of the optical absorption peaks of the dipolar system are shown to depend on the direction of propagation of the light relative to the dipolar axis, a property that is maintained in the presence of short-range interactions.

Configurational Energies in Terms of Effective Cluster Interactions in Binary Substitutional Alloys: Connection between the Embedded Cluster Method and the Generalized Perturbation Method

Abstract: Starting from the formal expansion of the configurational energy in terms of fully renormalized effective cluster interactions, it is shown that the Embedded Cluster Method (ECM) and the Generalized Perturbation Method (GPM) lead to identical expressions for the energy of a given alloy configuration within the Coherent Potential Approximation (CPA). Correction terms associated with fluctuations in the reference medium can be calculated in both methods. Numerical results are presented for a model tight binding Hamiltonian which clearly indicate the significance of multisite cluster interactions in the determination of the tendencies toward ordering or phase separation and phase stability in alloys.

On the Interplay of Disorder and Correlations

Abstract: I address here the question of the mutual interplay of strong correlations and disorder in the system. I consider random version of the Hubbard model. Diagonal randomness is introduced via random on-site energies and treated by the coherent potential approximation. Strong, short ranged, electron - electron interactions are described by the slave boson technique and found to induce additional disorder in the system. As an example I calculate the density of states of the random interacting binary alloy and compare it with that for non-interacting system.

Static transport properties of random alloys: vertex corrections in conserving approximations

Abstract: The theoretical formulation and numerical evaluation of the vertex corrections in multiorbital techniques of theories of electronic properties of random alloys are analyzed. It is shown that current approaches to static transport properties within the so-called conserving approximations lead to the inversion of a singular matrix as a direct consequence of the Ward identity relating the vertex corrections to one-particle self-energies. We propose a simple removal of the singularity for quantities (operators) with vanishing average values for electron states at the Fermi energy, such as the velocity or the spin torque; the proposed scheme is worked out in details in the self-consistent Born approximation and the coherent potential approximation. Applications involve calculations of the residual resistivity for various random alloys, including spin-polarized and relativistic systems, treated on an ab initio level, with particular attention paid to the role of different symmetries (inversion of space and time).