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.

Nonequilibrium dual-fermion approach to electronic transport in disordered nanostructures

Abstract: First-principles transport modeling of disordered nanostructures commonly resorts to certain effective medium theory constructed with single-site methods. These methods are essentially approximations that account for the diffusive aspect of the problem, but missing the interference-induced long-range effects such as localization, which also plays an important role in the mesoscopic regime. In this work, we report a real-space implementation of the dual-fermion method in the nonequilibrium Keldysh formalism for correcting the transport coefficients given by single-site methods. A mapping between the Keldysh Green's function and its dual counterpart is established, and a diagrammatic perturbation technique is used in the dual space, whereby the long-range Cooperon is taken into account. When treated at the zeroth order, this theory reproduces the nonequilibrium coherent potential approximation. We require self-consistency on two aspects: the dual Green's function is solved consistently with its self-energy, and the medium Green's function must have its real-space diagonal equal to that of the local impurity. The method is applied to a quasi-one-dimensional hopping lattice which mimics a disordered transport structure. The numerically computed transmission coefficient shows quantitative agreement with the exact solution in the weak-localization regime, significantly correcting the single-site results. In addition, we find that the dual-fermion method leads to a power-law dependency of resistance on the channel length, instead of the classical Ohm's law, and the exponent is insensitive to disorder strengths. We also show that the negative magnetoresistance effect, a phenomenon associated with weak localization, is obtained by our numerical model when a perpendicular magnetic field is introduced. The method presented here paves the way for an ab initio atomistic implementation to simulate disordered quantum transport in real nanostructures.

Theory of electrical conductivity in disordered binary alloys; discussion of the validity of CPA

Abstract: Using the functional derivative techniques, the coherent potential approximation (CPA) is analysed for a two s-d band model relevant to the investigation of some concentration dependent properties of noble and transition metal based disordered alloys. The discussion reveals that when delta , the difference between site potentials may not be regarded as a small parameter, the natural small parameter of the theory is ( gamma 2/ delta wsZ) where gamma is the hybridization constant, ws the band width and Z the number of nearest neighbours. This quantity is the product of the one band small parameter (1/Z) and the small parameter relevant to discuss the two band model split band limit.

Vibrations of a Chain with Glass-Like Disorder

Abstract: The frequency spectrum of a monatomic chain with a nearest neighbour force constant which has a Gaussian and a rectangular distribution is studied by means of the Green's function method. It is shown that the frequency spectra calculated by coherent potential approximation agree pretty well with the results of computer experiments for the corresponding models.

Coexistence of Itinerant Electrons and Self-Trapped Electrons

Abstract: The ground-state properties of the low-density electron system with the short-range electron-phonon interaction is investigated theoretically in connection with the self-trapping of an electron. The energy change of the system due to lattice distortions is calculated with the use of Fumi's theorem and the coherent potential approximation. It is shown that the itinerant electrons and the self-trapped electrons coexist in a certain range of the parameters.