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.

Auxiliary coherent medium theory for lattice vibrations in random binary alloys with mass and force-constant disorders

Abstract: The inevitable and random impurities or defects can significantly influence the lattice-vibrational properties of materials and devices. Thus, the capability of effectively treating disorder effects is indispensable for theoretical simulations. In this paper, we report an auxiliary coherent medium theory, in the framework of multiple scattering theory, to simulate disordered vibrational systems containing both mass and force-constant disorders. In this method, the physical Green's function is related to an auxiliary Green's function by introducing a separable force-constant model to describe disordered systems. As an important result, the force-constant disorder can be transformed to a diagonal-like disorder in the auxiliary Hamiltonian while maintaining the important force-constant sum rule. In combination with the single-site and cluster coherent potential approximation, the configurational average over the auxiliary Green's function can be performed to obtain the configuration-averaged physical properties. To demonstrate the effectiveness of this method, we apply it to a one-dimensional harmonic chain with atomic disorders and find our calculations agree very well with the exact results for a wide range of mass and force constants. Moreover, we show that the phonon transport property of disordered devices can be derived based on the auxiliary Green's function formalism in combination with vertex corrections. The auxiliary coherent medium theory features easy implementation and feasible incorporation with diagrammatic technique in many-body perturbation and various cluster approximations, providing an important approach to analyze disorder effects on the vibrational properties. Moreover, it is also straightforward to apply the present formalism to treat the general atomic disorder in electronic systems.

Strong interplay between electron-phonon interaction and disorder in low-doped systems

Abstract: The effects of doping on the spectral properties of low-doped systems are investigated by means of the coherent potential approximation to describe the distributed disorder induced by the impurities and the phonon-phonon noncrossing approximation to characterize a wide class of electron-phonon interactions that dominate the low-energy spectral features. When disorder and electron-phonon interaction work on comparable energy scales, a strong interplay between them arises, the effect of disorder can no longer be described as a mere broadening of the spectral features, and the phonon signatures are still visible despite the presence of strong disorder. As a consequence, the disorder-induced metal-insulator transition is strongly affected by a weak or moderate electron-phonon coupling, which is found to stabilize the insulating phase.

Pressure effect on magnetic moments in ordered Ni3Mn and disordered Ni100−x Mn x alloys: ab initio calculation and experiment

Abstract: We have revealed a substantial difference in the pressure behavior of magnetization of the ordered Ni3Mn and the disordered Ni75Mn25 and Ni80Mn20 alloys in the pressure range up to 1.2 GPa. To explain in detail the peculiarities of magnetic properties of the Ni-rich NiMn alloys, the reference electronic structure of the alloys was calculated using the tight-binding linear muffin-tin orbital approach. The effect of disorder was described by the coherent potential approximation. The theoretical ab initio calculations (with changes of the lattice parameters up to 1%) elucidated the pressure stability of the magnetic Mn moments and revealed that the very pronounced decrease in the magnetization of the disordered alloys under pressure is caused by the relatively small change in portion of the Mn moments with parallel and anti-parallel orientation with respect to the total moment. The quantitative agreement with experiment has been reached for the pressure parameters dln M/dP.

Temperature-dependent magnetic properties of ultrathin Fe films: Interplay between local environment and itinerant ferromagnetism

Abstract: The magnetic properties of ultrathin Fe films are determined as a function of temperature in the framework of a functional-integral itinerant-electron theory. The environment-dependent electronic structure is derived from a realistic $d$-band model and a real-space recursive expansion of the local Green's functions. The statistical average of spin fluctuations is performed within the static approximation and a layer-resolved alloy analogy by treating disorder in the virtual crystal approximation and in the coherent potential approximation. Results are given for the temperature dependence of the local moments, layer magnetizations ${M}_{l}(T)$, and spin fluctuation energies of ultrathin bcc (001) films. These are compared with the corresponding bulk results in order to quantify the role of dimensionality. Strain and local environment effects are quantified by varying the interatomic bond length $d$. A strong nonmonotonous dependence of ${M}_{l}(T)$ as a function of $d$ is revealed, which can be correlated with the environment dependence of the electronic structure and with the resulting changes in the ground-state magnetic moments and spin fluctuation energies. Finally, goals, limitations, and possible extensions are briefly discussed.

Electronic origin of the step-like character of the discharge curve for NaxCoO2-y cathode

Abstract: This paper shows electronic approach to an explanation of the step-like character of the discharge/charge curve of Na/Na+/NaxCoO2-y battery. On a basis of comprehensive experimental studies of physicochemical properties of NaxCoO2-y cathode material (XRD, electrical conductivity, thermoelectric power, electronic specific heat) supported by calculations performed using the Korringa–Kohn–Rostoker method with the coherent potential approximation to account for chemical disorder, it has been shown that the observed step-like character of the discharge curve reflects the variation of the chemical potential of electrons (Fermi level) in the density of states of NaxCoO2-y, which is anomalously perturbed by a presence of the oxygen vacancy defects and sodium ordering.