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.

Dynamical structure factor in disordered systems

Abstract: We study the spectral width as a function of the external momentum for the dynamical structure factor of a disordered harmonic solid, considered as a toy model for supercooled liquids and glasses. In the contexts of both the single-link coherent potential approximation and a single-defect approximation, two different regimes are clearly identified: if the density of states at zero energy is zero, the usual p^(4) law is recovered for small momentum. On the contrary, if the disorder induces a nonvanishing density of states at zero energy, a linear behavior is obtained. The dynamical structure factor is numerically calculated in lattices as large as 96^(3) and satisfactorily agrees with the analytical computations.

Vector vibrations and the Ioffe-Regel crossover in disordered lattices

Abstract: The spectral density for vector vibrations in the face-centred cubic lattice with force-constant disorder is analysed within the coherent potential approximation. The phase diagram showing the weak- and strong-scattering regimes is presented and compared with that for electrons. The weak-scattering regime for external long-wavelength vibrational plane waves is shown to be due to sum-rule correlations in the dynamical matrix. A secondary peak below the Brillouin peak for sufficiently large wavevectors is found for the lattice models. The results obtained are supported by precise numerical solutions.

A theoretical study of the hyperfine fields in BCC FexCr1-x and FexCo1-x alloys

Abstract: The hyperfine fields in the substitutionally disordered BCC alloy systems FexCr1-x and FexCo1-x have been studied by means of charge self-consistent Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA) electronic structure calculations. For the various components, the contribution to the Fermi contact hyperfine field due to core polarisation was found to be proportional to the corresponding local spin moment. The contributions of the conduction band, however, did not show such a simple behaviour and turned out to be dominated by the occupation of the s bands for spin up and down. To study the influence of relativistic effects on the hyperfine fields the corresponding matrix elements for the Fermi contact interaction have been calculated nonrelativistically as well as fully relativistically. The importance of contributions to the hyperfine fields coming from non-s electrons have been investigated by performing spin-polarised relativistic linear muffin tin orbital method (SPRLMTO) band structure calculations for hypothetically ordered alloys.

Fermi sea term in the relativistic linear muffin-tin-orbital transport theory for random alloys

Abstract: We present a formulation of the so-called Fermi sea contribution to the conductivity tensor of spin-polarized random alloys within the fully relativistic tight-binding linear muffin-tin-orbital (TB-LMTO) method and the coherent potential approximation (CPA). We show that the configuration averaging of this contribution leads to the CPA-vertex corrections that are solely due to the energy dependence of the average single-particle propagators. Moreover, we prove that this contribution is indispensable for the invariance of the anomalous Hall conductivities with respect to the particular LMTO representation used in numerical implementation. Ab initio calculations for cubic ferromagnetic $3d$ transition metals (Fe, Co, Ni) and their random binary alloys (Ni-Fe, Fe-Si) indicate that the Fermi sea term is small against the dominating Fermi surface term. However, for more complicated structures and systems, such as hexagonal cobalt and selected ordered and disordered Co-based Heusler alloys, the Fermi sea term plays a significant role in the quantitative theory of the anomalous Hall effect.

Resistivity and thermopower calculations in half-Heusler Ti1-xScxNiSn alloys from the KKR-CPA method

Abstract: The Korringa–Kohn–Rostoker method with the coherent potential approximation (KKR-CPA) was applied to calculate electronic structure and transport coefficients in disordered Ti1−xScxNiSn, where semiconductor-to-metal crossovers have recently been observed in resistivity and thermopower experiments (Horyn et al 2004 J. Alloys Compounds 363 10; Romaka et al 2005 J. Alloys Compounds 396 64). We have investigated the effect of chemical disorder on Fermi surface features (i.e. group velocities and life-times related to real and imaginary parts of complex dispersion curves, respectively). This analysis allowed us to shed light on the principal mechanism responsible for the variation of thermoelectric properties. Using the well-known formulae and performing integration over the complex Fermi surface, the residual conductivity and the thermopower slope S/T were estimated. Satisfying agreement between theoretical results and experimental data (measured at 90 and 300 K) has been found. This may indicate that modifications of electronic structure near EF are predominantly responsible for the strong decrease of thermopower in Ti1−xScxNiSn.