Showing papers on "Coherent potential approximation published in 2011"
TL;DR: Its implementation on the basis of the fully relativistic Korringa-Kohn-Rostoker band structure method together with the Coherent Potential Approximation (CPA) alloy theory allows application to a wide range of situations.
Abstract: A Kubo-Greenwood-like equation for the Gilbert damping parameter α is presented that is based on the linear response formalism. Its implementation using the fully relativistic Korringa-Kohn-Rostoker band structure method in combination with coherent potential approximation alloy theory allows it to be applied to a wide range of situations. This is demonstrated with results obtained for the bcc alloy system Fe1−xCox as well as for a series of alloys of Permalloy with 5d transition metals. To account for the thermal displacements of atoms as a scattering mechanism, an alloy-analogy model is introduced. The corresponding calculations for Ni correctly describe the rapid change of α when small amounts of substitutional Cu are introduced.
126 citations
TL;DR: In this article, the effect of Ga doping on thermoelectric properties has also been investigated by measurements of thermopower, electrical resistivity, Hall coefficient and thermal conductivity in temperature range from 300 to 850 K.
86 citations
TL;DR: A fully relativistic description of the spin-orbit induced spin Hall effect is presented that is based on Kubo's linear response formalism and a decomposition of the SHC into intrinsic and extrinsic contributions is suggested.
Abstract: A fully relativistic description of the spin-orbit induced spin Hall effect is presented that is based on Kubo’s linear response formalism. Using an appropriate operator for the spin-current density a KuboStryeda-like equation for the spin Hall conductivity (SHC) is obtained. An implementation using the Korringa-Kohn-Rostoker band structure method in combination with the coherent potential approximation allow detailed investigations on various alloy systems. A decomposition of the SHC into intrinsic and extrinsic contributions is suggested. Accompanying calculations for the skew-scattering contribution of the SHC using the Boltzmann equation demonstrate the equivalence to the Kubo formalism in the dilute alloy regime and support the suggested decomposition scheme.
73 citations
TL;DR: In this paper, the elastic properties of substitutionally disordered Cr- and Fe-rich Fe-Cr alloys are derived from first-principles calculations using the exact muffin-tin orbitals method and the coherent potential approximation.
Abstract: Elastic properties of substitutionally disordered Cr- and Fe-rich Fe-Cr alloys are derived from first-principles calculations using the exact muffin-tin orbitals method and the coherent potential approximation A peculiarity in the concentration dependence of elastic constants in Fe-rich alloys is demonstrated and related to a change in the Fermi surface topology Our calculations predict high values for the elastic constants of Cr-rich Fe-Cr alloys, but at the same time show that these alloys could be rather brittle according to the Pugh criterion (the ratio between shear and bulk moduli is calculated to be greater than 05)
50 citations
TL;DR: In this article, the band gap of ternary group-III nitride InxGa1−xN in both the wurtzite and zincblende form, within the linear muffin-tin orbital (LMTO) density functional theory method was investigated.
Abstract: We report first principles analysis of the band gap Eg of ternary group-III nitride InxGa1−xN in both the wurtzite and zincblende form, within the linear muffin-tin orbital (LMTO) density functional theory method We have implemented the semilocal modified Becke–Johnson (MBJ) exchange potential to accurately determine the band gap The doping of In atoms into the GaN crystal is handled by the InxGa1−xN alloy model within the coherent potential approximation (CPA) The LMTO-CPA-MBJ approach allows us to predict Eg as a function of arbitrary In concentration x Quantitative comparison to the experimental data is made
48 citations
TL;DR: In this article, the porosity and the pore interfacial area concentration were used to predict the thermal conductivity of crystalline nanoporous silicon, and a physics-based model was developed by combining kinetic theory and the coherent potential approximation.
Abstract: This study establishes that the effective thermal conductivity keff of crystalline nanoporous silicon is strongly affected not only by the porosity f ν and the system’s length Lz but also by the pore interfacial area concentration Ai. The thermal conductivity of crystalline nanoporous silicon was predicted using non-equilibrium molecular dynamics simulations. The Stillinger-Weber potential for silicon was used to simulate the interatomic interactions. Spherical pores organized in a simple cubic lattice were introduced in a crystalline silicon matrix by removing atoms within selected regions of the simulation cell. Effects of the (i) system length ranging from 13 to 130 nm, (ii) pore diameter varying between 1.74 and 5.86 nm, and (iii) porosity ranging from 8% to 38%, on thermal conductivity were investigated. A physics-based model was also developed by combining kinetic theory and the coherent potential approximation. The effective thermal conductivity was proportional to (1 − 1.5f ν) and inversely propor...
44 citations
TL;DR: In this article, total and partial densities of constituent atoms of two tetragonal phases of Tl 3 PbCl 5 have been calculated using the full potential linearized augmented plane wave (FP-LAPW) method and Korringa-Kohn-Rostoker method within coherent potential approximation (KKR-CPA).
42 citations
TL;DR: In this article, the LSDA + DMFT (local spin density approximation plus dynamical mean field theory) approach is used to study magnetic and spectroscopic properties of transition metals, alloys and their surfaces.
Abstract: Recent results on magnetic and spectroscopic properties of transition metals, alloys and their surfaces which were obtained by using the LSDA + DMFT (local spin density approximation plus dynamical mean field theory) approach are reviewed. Corresponding calculations exploit the various advantageous features offered by an LSDA + DMFT implementation on the basis of the KKR (Korringa–Kohn–Rostoker) band structure method. This fully self-consistent, with respect to charge and self-energy, approach allows one to investigate the impact of correlation effects in ordered as well as disordered systems. For the latter case the coherent potential approximation is used. The fully relativistic formulation implemented for space filling potentials gives us the opportunity to study various ground state properties, for example, orbital magnetic moments and total energies. Here, in addition, it is demonstrated that the combination of the one-step model of valence band photoemission with the LSDA + DMFT approach gives detailed insight, in particular for the angle-resolved mode of this spectroscopy.
39 citations
TL;DR: In this paper, the first-principles dynamical coherent potential approximation (CPA) combined with the local density approximation (LDA) + U Hamiltonian in the tight-binding linear muffintin orbital (TB-LMTO) representation has been investigated.
Abstract: Magnetic properties of Fe, Co, and Ni at finite temperatures have been investigated on the basis of the first-principles dynamical coherent potential approximation (CPA) combined with the local density approximation (LDA) + U Hamiltonian in the tight-binding linear muffintin orbital (TB-LMTO) representation. The Hamiltonian includes the transverse spin fluctuation terms. Numerical calculations have been performed within the harmonic approximation with 4th-order dynamical corrections. Calculated single-particle densities of states in the ferromagnetic state indicate that the dynamical effects reduce the exchange splitting, suppress the band width of the quasi-particle state, and causes incoherent excitations corresponding the 6 eV satellites. Results of the magnetization vs temperature curves, paramagnetic spin susceptibilities, and the amplitudes of local moments are presented. Calculated Curie temperatures ( T C ) are reported to be 1930 K for Fe, 2550 K for Co, and 620 K for Ni; T C for Fe and Co are ov...
36 citations
TL;DR: In this article, the spin-orbit induced Rashba splitting of Shockley-type surface states is discussed using a fully relativistic description, and the impact of chemical disorder within surface layers can be handled by the coherent potential approximation (CPA) alloy theory.
34 citations
TL;DR: In this paper, the authors studied the structure of the Sn1−xGex random alloys using density functional theory and the coherent potential approximation, and found that the deviation from Vegard's law is quantitatively and qualitatively different between the Sn 1−x-Gex and Si 1 −x Gex alloys.
Abstract: The structure of the Sn1−xGex random alloys is studied using density functional theory and the coherent potential approximation. We report on the deviation of the Sn1−xGex alloys from Vegard’s law, addressing their full compositional range. The findings are compared to the related Si1−xGex alloys and to experimental results. Interestingly, the deviation from Vegard’s law is quantitatively and qualitatively different between the Sn1−xGex and Si1−xGex alloys. An almost linear dependence of the bulk modulus as a function of composition is found for Si1−xGex, whereas for Sn1−xGex the dependence is strongly nonlinear.
TL;DR: In this paper, a coherent potential approximation method of treating quantum thermal transport properties of nanoscale systems with mass disorder was proposed, based on the phonon version of nonequilibrium vertex correction theory.
Abstract: We report the coherent potential approximation method of treating quantum thermal transport properties of nanoscale systems with mass disorder. Instead of massive efforts required in brute-force calculations, configuration averaging of disordered systems can be efficiently handled in a self-consistent manner by setting up the phonon version of nonequilibrium vertex correction theory. The accuracy of the method is verified by comparing with the exact results and Monte Carlo experiments in one-dimensional atomic chains. Results obtained for disordered harmonic chains and carbon nanotubes provide evidence of anomalous thermal transport in such systems. We also observe crossover in the transport where phonon scattering by disorder becomes important. Our results show that disorder plays a role in thermal conductance reduction.
TL;DR: In this paper, the triatomic and tetratomic gas molecule adsorption effects on the electrical conductivity of graphene were investigated by the tight-binding model, Green's function method, and coherent potential approximation.
Abstract: The triatomic and tetratomic gas molecule adsorption effects on the electrical conductivity of graphene are investigated by the tight-binding model, Green's function method, and coherent potential approximation. We find that the electrical conductivity of graphene sheet is sensitive to the adsorption of these gases.
TL;DR: G G\'orski and Mizia as discussed by the authors analyzed the full Hubbard model with added hopping interaction within the full- Hubbard III approximation in the Green's-function decoupling process, including intersite kinetic correlation functions.
Abstract: We analyze the Hubbard model with added hopping interaction within the full Hubbard III approximation In the Green's-function decoupling process, the intersite kinetic correlation functions are included This is an extension of our previous paper [G G\'orski and J Mizia, Phys Rev B 79, 064414 (2009)] in which the basic Hubbard model with the intersite kinetic correlations was analyzed in the framework of the coherent potential approximation (CPA) In the CPA method, the up-spin electrons propagated in the lattice of frozen down-spin electrons The full Hubbard III solution used now takes into account the itinerancy of down-spin electrons The combined effect of the hopping interaction and intersite kinetic correlation leaves the position of spin bands unaffected, but it deforms the density of states (DOS) of electrons, changing in this way the average electron energy It is the main driving force behind the ferromagnetism as opposed to the rigid shift of the entire band, which takes place in the conventional Stoner magnetism In the numerical calculations, we have used the bands with symmetrical DOS (semielliptic or bcc-like DOS) and also with asymmetrical DOS resembling the fcc DOS The spontaneous ferromagnetic transition was obtained under the combined action of the hopping interaction and the intersite correlation in the systems that contain even a moderately strong peak in the DOS, such as the bcc- and fcc-like DOS
TL;DR: In this article, the spectral, optical, and transport properties of an anisotropic three-dimensional Holstein model are studied within the adiabatic approximation for organic semiconductors used in single-crystal-based field effect transistors.
Abstract: Spectral, optical, and transport properties of an anisotropic three-dimensional Holstein model are studied within the adiabatic approximation. The parameter regime is appropriate for organic semiconductors used in single-crystal-based field-effect transistors. Different approaches have been used to solve the model: the self-consistent Born approximation valid for weak electron-phonon coupling, the coherent potential approximation exact for infinite dimensions, and numerical diagonalization for finite lattices. With increasing temperature, the width of the spectral functions gets larger and larger, making the approximation of a quasiparticle less accurate. On the contrary, their peak positions are never strongly renormalized in comparison with the bare ones. As expected, the density of states is characterized by an exponential tail corresponding to localized states at low temperature. For weak electron-lattice coupling, the optical conductivity follows a Drude behavior, while for intermediate electron-lattice coupling, a temperature-dependent peak is present at low frequency. For high temperatures and low particle densities, the mobility always exhibits a power-law behavior as a function of temperature. With decreasing particle density, at low temperature, the mobility shows a transition from metallic to insulating behavior. Results are discussed in connection with available experimental data.
TL;DR: In this paper, the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation was employed to calculate the total energy and local magnetic moments of paramagnetic Fe.
Abstract: Employing the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic Fe ...
TL;DR: In this article, the relativistic multiple scattering KKR-Green function is used to describe electronic transport of disordered alloys in a material specific way, with the possibility to combine it with a linear response Kubo framework, allowing for a detailed investigation of many transport phenomena which are of immediate relevance for applications in which electrons and their spin are manipulated.
Abstract: We present a first-principles approach to describe electronic transport of disordered alloys in a material specific way. The electronic structure is represented in terms of the relativistic multiple scattering KKR-Green function. Disorder with possible inclusion of short-ranged order effects is taken into account by the coherent-potential approximation or its non-local formulation. A salient feature of the presented method is the possibility to combine it with a linear response Kubo framework, allowing for a detailed investigation of many transport phenomena which are of immediate relevance for applications in which electrons and/or their spin are manipulated. This is illustrated by several examples and developments, among them the description of the residual resistivity of K-state- and ferromagnetic alloys. Inclusion of relativistic effects by using the Dirac-formalism represents the basis to deal with the anomalous Hall effect and to derive a relativistic spin-projection scheme for currents.
TL;DR: In this paper, the authors have revealed a substantial difference in the pressure behavior of magnetization of the ordered Ni3Mn and the disordered Ni75Mn25 and Ni80Mn20 alloys in a pressure range up to 1.2 GPa.
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.
TL;DR: In this paper, the formation of a self-organized quasi-one-dimensional nano-structure (Konbu-phase) under a layer-by-layer crystal growth condition of Cu-Ni alloy was simulated.
Abstract: Based upon ab initio electronic structure calculations by the Korringa–Kohn–Rostoker coherent potential approximation and Monte Carlo simulation of the two-dimensional spinodal nano-decomposition, we simulate the formation of a self-organized quasi-one-dimensional nano-structure (Konbu-Phase) under a layer-by-layer crystal growth condition of Cu–Ni alloy. We propose a new mechanism of the giant Peltier coefficient dramatically enhanced by the one-dimensional singular density of states in the Konbu-Phase in addition to the conventional Peltier cooling and the spin-entropy expansion cooling.
TL;DR: In this paper, it was shown that the dynamical coherent potential approximation (CPA) theory combined with the harmonic approximation (HA) is applicable to the quantitative description of magnetic properties in high dimensional systems, but one needs to take into account higher-order dynamical corrections in orde...
Abstract: Magnetic and electronic properties of the Hubbard model on the Bethe and fcc lattices in infinite dimensions have been investigated numerically on the basis of the dynamical coherent potential approximation (CPA) theory combined with the harmonic approximation (HA) in order to clarify the quantitative aspects of the theory. It is shown that the dynamical CPA+HA reproduces well the sublattice magnetizations, the magnetizations, susceptibilities, and the Neel temperatures ( T N ) as well as the Curie temperatures calculated by the Quantum Monte-Carlo (QMC) method. The critical Coulomb interactions ( U c ) for the metal–insulator (MI) transition are also shown to agree with the QMC results above T N . Below T N , U c deviate from the QMC values by about 30% at low temperature regime. These results indicate that the dynamical CPA+HA is applicable to the quantitative description of the magnetic properties in high dimensional systems, but one needs to take into account higher-order dynamical corrections in orde...
TL;DR: In this article, the magnetic properties of Fe, Co, and Ni at finite temperatures have been investigated on the basis of the first-principles dynamical CPA combined with the LDA (Local Density Approximation) + $U$ Hamiltonian in the Tight-Binding Linear Muffintin Orbital (TB-LMTO) representation.
Abstract: Magnetic properties of Fe, Co, and Ni at finite temperatures have been investigated on the basis of the first-principles dynamical CPA (Coherent Potential Approximation) combined with the LDA (Local Density Approximation) + $U$ Hamiltonian in the Tight-Binding Linear Muffintin Orbital (TB-LMTO) representation The Hamiltonian includes the transverse spin fluctuation terms Numerical calculations have been performed within the harmonic approximation with 4th-order dynamical corrections Calculated single-particle densities of states in the ferromagnetic state indicate that the dynamical effects reduce the exchange splitting, suppress the band width of the quasi-particle state, and causes incoherent excitations corresponding the 6 eV satellites Results of the magnetization vs temperature curves, paramagnetic spin susceptibilities, and the amplitudes of local moments are presented Calculated Curie temperatures ($T_{\rm C}$) are reported to be 1930K for Fe, 2550K for Co, and 620K for Ni; $T_{\rm C}$ for Fe and Co are overestimated by a factor of 18, while $T_{\rm C}$ in Ni agrees with the experimental result Effective Bohr magneton numbers calculated from the inverse susceptibilities are 30 $\mu_{\rm B}$ (Fe), 30 $\mu_{\rm B}$ (Co), and 16 $\mu_{\rm B}$ (Ni), being in agreement with the experimental ones Overestimate of $T_{\rm C}$ in Fe and Co is attributed to the neglects of the higher-order dynamical effects as well as the magnetic short range order
01 Jan 2011
TL;DR: In this article, the physical properties of Co-based Heusler alloys with the atomic composition or configuration dependence are carried out in first-principles approach, in particular, the electronic structure, magnetic moment and electrical resistivity due to disorder alloy effects.
Abstract: The statistical investigation of the physical property of Co-based Heusler alloys with the atomic composition or configuration dependence are carried out in first-principles approach. In particular, the electronic structure, magnetic moment and electrical resistivity due to disorder alloy effects of Co2MnAl1−zSiz (0.0 < z < 1.0) and Co2Mn1−yFeySi (0.0 < y < 1.0) with the L21, B2 and A2 structure are calculated by using the tight-binding linear muffin-tin orbital method combined with the coherent potential approximation based on the local spin-density functional approximation and by using the Kubo-Greenwood formula, respectively. The obtained results indicate that these properties of the Co-based Heusler alloys significantly depend on the atomic configuration and composition, especially, they are sensitive to the existence of the half-metallic property.
01 Mar 2011
TL;DR: In this paper, the non-local coherent potential approximation (NL-CPA) was extended to materials with multi-atom per unit cell lattices. And the method is described using a Green function formalism and illustrated by an implementation for a simplified one-dimensional tight binding model with substitutional disorder.
Abstract: Over the last few years the Non-Local Coherent Potential Approximation (NL-CPA) has been shown to provide an effective way to describe the electronic structure and related properties of disordered systems, where short-range order (SRO) and other local environment effects are important. Here we present its generalization to materials with multi-atom per unit cell lattices. The method is described using a Green function formalism and illustrated by an implementation for a simplified one-dimensional tight-binding model with substitutional disorder. This development paves the way for a natural reimplementation of the Korringa-Kohn-Rostoker (KKR) multiple scattering solution of Kohn-Sham equations for ab-initio calculations of real materials.
TL;DR: In this article, first-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA) were performed for the substitution of O by N or P.
Abstract: Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa—Kohn—Rostoker (KKR) method combined with the coherent potential approximation (CPA). Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content. Furthermore, the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands. The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.
TL;DR: This work studies the effective index of random media composed of two-layered spheres by using the energy-density coherent potential approximation method and finds that in the long-wavelength limit, the optical properties are identical to those of a random medium composed of the corresponding pure spheres.
Abstract: We study the effective index of random media composed of two-layered spheres by using the energy-density coherent potential approximation method. As expected from the Ewald-Oseen extinction theorem, in the long-wavelength limit, the optical properties of a random medium composed of two-layered spheres are identical to those of a random medium composed of the corresponding pure spheres, while in the Mie-scattering region, the single-scattering resonances lead to an overall shift of the effective refractive index with the modified volume fraction.
TL;DR: It is found that the dispersive inclusion of the two-layered spheres influences the transport velocities greatly and a resonant scattering taking place in a dilute disordered medium is smeared out in the corresponding densely disorderedmedium where the correlation effects of multiple scattering are taken into account.
Abstract: In this paper, we perform a coated coherent potential approximation method to investigate the transport properties of disordered media consisting of two-layered dielectric spheres whose constituent layer is dispersive. The admixture of quantum dots to polymers to a certain concentration is used as dispersive medium. We find that the dispersive inclusion of the two-layered spheres influences the transport velocities greatly and a resonant scattering taking place in a dilute disordered medium is smeared out in the corresponding densely disordered medium where the correlation effects of multiple scattering are taken into account.
TL;DR: In this paper, the influence of electronic structure evolution upon pressure on the temperature dependence of the electrical resistivity of pure Np, Pu, Am, and Cm metals has been investigated within the coherent potential approximation (CPA) for the many-bands conductivity model.
TL;DR: In this article, a cluster generalization of the coherent potential approximation in the tight-binding linear muffin-tin orbital method was proposed to account for the effect of the local environment on electronic and magnetic properties of substitutional random alloys.
Abstract: We use cluster generalization of the coherent potential approximation in the tight-binding linear muffin-tin orbital method to account for the effect of the local environment on electronic and magnetic properties of substitutional random alloys. This theory combines the augmented space formalism and conventional tight-binding linear muffin-tin orbital methods. In particular, we shall apply the technique to the bcc-based NiAl and fcc-based CuAu alloys and also compare with other approaches.
TL;DR: In this paper, the effects of doped boron concentration on the density of states and the temperature dependence of orbital magnetic susceptibility of graphene are studied within the tight-binding Hamiltonian model and coherent potential approximation.
Abstract: Within the tight-binding Hamiltonian model and coherent potential approximation, the effects of doped boron concentration on the density of states and the temperature dependence of orbital magnetic susceptibility of graphene are studied. An expression of susceptibility based on the linear response theory and Green's function technique is used. It is found that when dopants are introduced, van-Hove singularities in the density of states are broadened. It is also shown that the susceptibility crossover of the doped system is appeared in the lower value of temperature in comparison with pure graphene.
TL;DR: In this paper, the static spin susceptibility and spectral function of the system corresponding to the magnetic-ion-diluted Kondo insulator are calculated using the framework of dynamical mean-field theory with a coherent potential approximation.
Abstract: The static spin susceptibility and spectral function of the system corresponding to the magnetic-ion-diluted Kondo insulator is calculated using the framework of dynamical mean-field theory with a coherent potential approximation. The system is described by a periodic Anderson model with randomly distributed impurity sites which have no f electron. The impurity concentration dependence of the static spin susceptibility in the present result is in qualitative agreement with the experimental magnetic susceptibility measurements of (Yb,Lu)B 12 .