Method Of Band Structure Calculation Research Articles

Screened full-potential KKR calculations for transition metals, based on the generalized-gradient approximation

The screened full-potential Korringa–Kohn–Rostoker (SFPKKR) band-structure calculation method, developed by the Jülich group, may be one of the most efficient methods for the study of structural, electronic, and magnetic properties of large systems. We show the accuracy of the SFPKKR method combined with the generalized-gradient approximation of density-functional theory. The present calculations reproduce the ground-state structure of Fe as well as the sequence of crystal structures through the 4d transition metal series (HCP–BCC–HCP–FCC).

Gain and threshold-current calculation of V-groove quantum-wire InGaAs-InP laser

This paper presents material-gain and threshold-current calculation of a InGaAs-InP quantum-wire laser in the framework of the k/sub /spl middot//p method, with included conduction-band nonparabolicity for the first time. The method for band-structure calculation is based on conformal mapping and Fourier expansion. The calculation shows that high material gain (7000 cm/sup -1/) can be achieved at room temperature for polarization along the free axis of the quantum wire. We propose an optimized laser structure, based on a stack of quantum wires.

Symmetry properties of the scattering path operator for arbitrary translationally invariant systems

In order to optimize the efficiency of relativistic band-structure calculations for complex systems, one should take full advantage of the magnetic space-group symmetry. Most important for the description of systems with reduced symmetry using the Korringa-Kohn-Rostoker method of band-structure calculation, a general derivation of magnetic symmetry properties of the scattering path operator both in real and reciprocal space is presented. In a straightforward way, this approach can be used to minimize the section of $\stackrel{\ensuremath{\rightarrow}}{k}$ space to be sampled for two- and three-dimensional numerical Brillouin-zone integration. Practical aspects of an implementation of the very general scheme presented are discussed in detail.

Solution of periodic Poisson's equation and the Hartree–Fock approach for solids with extended electron states: Application to linear augmented plane wave method

AbstractWe formulate a Hartree–Fock‐LAPW method for electronic band structure calculations. The method is based on the Hartree–Fock–Roothaan approach for solids with extended electron states and closed core shells where the basis functions of itinerant electrons are linear augmented plane waves. All interactions within the restricted Hartree–Fock approach are analyzed and in principle can be taken into account. In particular, we obtained the matrix elements for the exchange interactions of extended states and the crystal electric field effects. To calculate the matrix elements of exchange for extended states, we first introduce an auxiliary potential and then integrate it with an effective charge density corresponding to the electron exchange transition under consideration. The problem of finding the auxiliary potential is solved by using the strategy of the full potential LAPW approach, which is based on the general solution of periodic Poisson's equation. Here, we use an original technique for the general solution of periodic Poisson's equation and multipole expansions of electron densities. We apply the technique to obtain periodic potentials of the face‐centered cubic lattice and discuss its accuracy and convergence in comparison with other methods. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Decomposition of the relativistic hyperfine interaction operator: Application to the ferromagnetic alloy systems fccFexNi1−x,fccFexPd1−x,and fccCoxPt1−x

A scheme developed by Pyper to decompose within relativistic Hartree-Fock theory the hyperfine interaction operator into the conventional Fermi contact, spin dipolar and orbital contributions is modified to split the hyperfine field of magnetic solids calculated in a fully relativistic way on the basis of spin-density-functional theory in an analogous way. The resulting expressions are used to examine the hyperfine fields for the disordered alloy systems fcc ${\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x},$ fcc ${\mathrm{Fe}}_{x}{\mathrm{Pd}}_{1\ensuremath{-}x},$ and fcc ${\mathrm{Co}}_{x}{\mathrm{Pt}}_{1\ensuremath{-}x}$ making use of the spin-polarized relativistic Korringa-Kohn-Rostoker coherent-potential approximation method of band-structure calculation. In particular the contribution of non-$s$ electrons to the hyperfine fields are discussed in detail. Special emphasize is laid on their relationship to the corresponding contributions to the spin and spin-orbit-induced orbital magnetic moments.

Magnetic circular x-ray dichroism of the 4d elements indisordered CoxRh1-x and FexPd1-x alloys

The magnetic properties of the disordered alloy systemsface-centred-cubic (fcc) CoxRh1-x and fcc FexPd1-xhave been investigated by means of the spin-polarized relativisticversion of the Korringa-Kohn-Rostoker method of band-structurecalculation on the basis of the coherent potential approximationalloy theory. In particular, the spin and spin-orbit-inducedorbital magnetic moments have been calculated. In addition, themagnetic circular x-ray dichroism (MCXD) for the x-ray absorptioncoefficient has been determined. The relationship of thecorresponding MCXD spectra and the magnetic moments of the absorberatom is discussed, with most emphasis put on the 4d element, whosemagnetism is induced by the alloy partner.

From molecules to solids with the DMol3 approach

Recent extensions of the DMol3 local orbital density functional method for band structure calculations of insulating and metallic solids are described. Furthermore the method for calculating semilocal pseudopotential matrix elements and basis functions are detailed together with other unpublished parts of the methodology pertaining to gradient functionals and local orbital basis sets. The method is applied to calculations of the enthalpy of formation of a set of molecules and solids. We find that the present numerical localized basis sets yield improved results as compared to previous results for the same functionals. Enthalpies for the formation of H, N, O, F, Cl, and C, Si, S atoms from the thermodynamic reference states are calculated at the same level of theory. It is found that the performance in predicting molecular enthalpies of formation is markedly improved for the Perdew–Burke–Ernzerhof [Phys. Rev. Lett. 77, 3865 (1996)] functional.

Fully relativistic description of the magneto-optical properties of arbitrary layered systems

A fully relativistic formalism is presented that allows us to define the frequency-dependent optical conductivity tensor for arbitrary layered systems in a layer-resolved way. This opens in particular the way to deal with the magneto-optical properties of magnetic surface layer systems and to calculate the corresponding magneto-optical Kerr spectra. The formalism, based on a fully relativistic description of response theory in arbitrary order, is described in some detail. For an implementation the very flexible spin polarized relativistic Korringa-Kohn-Rostoker method of band structure calculation has been used. Results of corresponding applications to the elemental ferromagnets bcc-Fe and fcc-Co treated as homogeneous layer systems are presented.

An Efficient Method for Band Structure Calculations in 2D Photonic Crystals

An efficient method for band structure calculations in dielectric photonic crystals is presented. The method uses a finite element discretization coupled with a preconditioned subspace iteration algorithm. Numerical examples are presented which illustrate the behavior of the method.

Magnetic dichroism in valence-band photoemission spectroscopy of disordered bccFexCo1−xalloys

A fully relativistic calculation of spin-resolved valence-band photoemission spectra for bcc ${\mathrm{Fe}}_{x}{\mathrm{Co}}_{1\ensuremath{-}x}$ alloys is presented that is based on the Korringa-Kohn-Rostoker coherent-potential approximation method of band-structure calculation. The result for the spin-integrated spectra for unpolarized radiation was found to be in very satisfying agreement with corresponding experimental data. For the spin-resolved spectra a pronounced magnetic circular dichroism is predicted that should be observable in a corresponding experiment.

Electronic and magnetic properties of

The electronic properties of monoclinic in its paramagnetic, ferromagnetic and antiferromagnetic states have been studied by means of the linear muffin-tin orbital method of band-structure calculation. On the basis of the corresponding results, the magnetic properties of are discussed in comparison with experimental data stemming from neutron scattering and nuclear magnetic resonance.

Full-potential spin-polarized relativistic Korringa-Kohn-Rostoker method implemented and applied to bcc Fe, fcc Co, and fcc Ni

The full-potential spin-polarized relativistic Korringa-Kohn-Rostoker (FP-SPR-KKR) method of band-structure calculation has been implemented in a self-consistent way. This scheme deals with the nonspherical potential as well as spin polarization and all relativistic effects on the same level. Technical details of this approach as well as its formal extension to account for the so-called orbital polarization (OP) mechanism are described in some detail. Results of corresponding applications to the elemental ferromagnets bcc-Fe, fcc-Co, and fcc-Ni are presented with an emphasis on the consequences of nonspherical and OP-potential terms.

Extension of the Fenske-Hall Molecular Orbital Approach to Tight-Binding Band Structure Calculations: Bulk and Surface Electronic Structure of MoS(2).

A new tight-binding band structure calculation method is described. This method, which is based on the Fenske-Hall molecular orbital technique, should be extremely useful in the study of the bulk and surface electronic structure of inorganic materials. The approximations used in the Fenske-Hall method are reviewed, and the extension of this approach to periodic band structure calculations is outlined. Results of calculations for bulk MoS(2) are in good agreement with previous experimental and theoretical results. Results of calculations for two-dimensional MoS(2) slabs exposing (100) edge planes provide a description of coordinatively unsaturated Mo and S atoms on these edges. Coordinative unsaturation at the Mo atoms introduces new surface states near the Fermi level. Coordinative unsaturation at the S atoms leads to high-energy occupied bands that can be attributed to S lone pair electrons. Surface bonds between Mo atoms and terminal S atoms are stronger than bulk Mo-S bonds, suggesting that terminal S atoms may be more difficult to remove from the edges of MoS(2) than bridging S atoms. Bonding in a single two-dimensional layer of MoS(2) is found to be more ionic than the bonding in the full three-dimensional structure. This effect is also observed in one-dimensional MoS(2) ribbons that expose (100) edge planes. The simplified one-dimensional ribbons will be used for further studies of the electronic structure of the edge planes of MoS(2).

Crystallographic and magnetic properties of fe 2p

Summary The crystallographic and magnetic properties of Fe 2 P have been studied by neutron diffraction experiments, magnetization measurements and KKR method for band structure calculations. The measured atomic magnetic moments of tetrahedral Fe(3f) and pyramidal Fe(3g) sites are respectively (0.59±0.02)μ B and (2.22±0.01)μ B , resulting in a net moment of (2.82±0.03)μ B . This value is very close to that obtained from saturation magnetization measurements (H=150kOe, T=4K) which yield 2.87μ B per formula unit. The results obtained from the KKR method are 0.80, 2.33, −0.03(1), −0.02(8)μ B for Fe and P sites respectively. The values are comparable with the measured atomic magnetic moments. Thermal evolution of magnetic moments, magnetization at saturation and cell parameters presents a sharp drop at the Curie temperature (217±2)K indicating a first order ferro - paramagnetic transition.

Control of valence states by a codoping method in CuInS 2

We deviate the valence and conduction band energies of stoichiometric CuInS 2 crystals based on ab initio electronic band structure calculations using the augmented spherical wave (ASW) method and discuss that at low doping levels, the Madelung energy is a good intrinsic parameter for stabilization of p- or n-type doped CuInS 2 crystals. We find that P and Sb atoms are eminently suitable dopants substituted for S atoms for p-type doped CuInS 2 crystals with lower resistivity from both the character of electronic states around E F and the Madelung energy. A closer study of the nature of chemical bonds of CuInS 2 crystals using first-principles band structure calculation method reveals that In with polyvalence codoping for p-type CuInS 2 doped with P results in a decrease of the Madelung energy compared with CuInS 2: P, to be an effective method for stabilizing of its ionic charge distributions.

Applicability of the two-current model for systems with strongly spin-dependent disorder

The resistivities of the ferromagnetic alloy systems Fe-Ni and Co-Ni were studied in detail by application of first-principles techniques. For that purpose the Kubo-Greenwood formalism was applied on the basis of electronic structure data obtained using the spin-polarized Korringa-Kohn-Rostoker coherent potential approximation method of band-structure calculation for randomly disordered ferromagnetic alloys. One set of calculations was carried out fully relativistically, while for a second one the well-known and often applied two-current model was used. We compare the results of the two approaches as well as the difference between the calculated two-current resistivities and the resistivities obtained experimentally by the usual decomposition based on the two-current model. We discuss the validity of the two-current model for the systems investigated and the reason for the apparent success of this model.

Optimized effective potential method for exact exchange energy applied to solids

A new method of the self-consistent electronic band-structure calculation, which uses the exact Kohn-Sham density-functional exchange instead of the LDA exchange, is presented. The results obtained for various systems including those for antiferromagnetic MnO and ferromagnetic iron have revealed that the method is feasible for a rather wide range of materials.

Nonlocal pseudopotentials in complex band-structure and photoemission calculations

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients ${\mathrm{V}}_{\mathrm{G}\ensuremath{-}\ensuremath{\rightarrow}\mathrm{G}\ensuremath{-}{\ensuremath{\rightarrow}}^{|\mathrm{I}\mathrm{H}}}$(k-\ensuremath{\rightarrow}) which can be decomposed into terms, each being quadratic in k-\ensuremath{\rightarrow} and multiplied by a function of (G-\ensuremath{\rightarrow}-G-${\ensuremath{\rightarrow}}^{|\mathrm{I}\mathrm{H}}$), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal ${\mathrm{TiSe}}_{2}$, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry's method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies.

KKR-ASA method in exact exchange-potential band-structure calculations.

We present a method of electronic band-structure calculation which incorporates the exact Kohn-Sham density-functional exchange (EXX) potential approach with the Korringa-Kohn-Rostoker (KKR) method in the atomic-sphere approximation (ASA). It takes full account of the energy dependence of the radial functions, and hence, provides more accurate treatment in principle than our previous one based on the linearized muffin-tin orbital method [Phys. Rev. Lett. 74, 2989 (1995)]. In this method, we treat C, Si, Ge, MgO, CaO, and MnO (Antiferro-II), which were previously studied in the framework of the linear-muffin-tin orbital method with EXX. The results are basically in agreement with the old ones, though small differences produce non-negligible effects on the results. Some numerical points as well as the strict formulation of KKR in the ASA are discussed. \textcopyright{} 1996 The American Physical Society.

First-principles studies of the magnetic hyperfine field in Fe multilayers

A detailed theoretical study of the magnetic moments and magnetic hyperfine fields in several Fe multilayers (Fe fcc(001)/5X fcc(001), X=Cu and Ag, and Fe bcc(001)/5X fcc(001), X=Ag and Au) as well as in bulk Fe is presented. The calculations have been performed using the spin-polarized, relativistic linear muffin-tin orbital (SPR-LMTO) method of band structure calculation. Therefore, not only the contribution to the hyperfine fields due to the conventional Fermi contact interaction but also due to the spin dipolar and orbital contributions induced by the crystal field and by spin-orbit coupling are accounted for. To decompose the hyperfine field of non-s-electrons into these contributions it has been assumed that they are proportional to the corresponding so-called magnetic dipole moment and the orbital magnetic moment, respectively. In contrast to previous results for pure metals and alloys not only the orbital but also the spin dipolar hyperfine field was found to be non-negligible. The anisotropy of the hyperfine field determined by calculations for in-plane and perpendicular orientation of the magnetisation was found to be very pronounced and closely connected with the corresponding anisotropy of the magnetic dipole moment and the orbital moment.