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Wave Method (wave + method)
Selected AbstractsFrequency/time-domain modelling of 3D waveguide structures by a BI-RME approachINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2002P. Arcioni This paper presents a full wave method for the determination of the mathematical model of a 3D waveguide structure in the form of the pole expansion in the s -plane of its generalized admittance matrix. The method is based on a boundary integral-resonant mode expansion approach. By the introduction of appropriate state-variables, the method leads to the pole expansion by solving a linear generalized eigenvalue problem, like in the well-known techniques used up to now in frequency/time domain modelling based on finite difference or finite element methods. With respect to these methods we have the advantage of a significant reduction in both memory allocation and computing time. Two examples show the accuracy of the results and the efficiency of the method. Copyright © 2002 John Wiley & Sons, Ltd. [source] Ab-initio simulations of materials using VASP: Density-functional theory and beyondJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Jürgen Hafner Abstract During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science,promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, chemical reactions, and catalysis) are reviewed. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Half-metallicity and magnetism at Heusler alloy surfaces: Co2MSi(001) (M = Ti, Cr)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008Ying Jiu Jin Abstract We investigated the electronic structures, magnetism, and half-metallicity at the (001) surfaces of full-Heusler alloys, Co2MSi (M = Ti, Cr), by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. Both the Co-terminated (Co-term) and the MSi-terminated (MSi-term) surfaces were considered. From the calculated atom-resolved density of states, we found that the half-metallicity was destroyed at the Co-term surfaces for both alloys. The electronic structures at the MSi-term surfaces of the two alloys showed much different behavior. The half-metallicity was retained at the TiSi-term for Co2TiSi(001) but the minority spin gap was much reduced due to surface states located just below the Fermi level. On the other hand the half-metallicity was destroyed at the CrSi-term of Co2CrSi(001) due to the surface states located at the Fermi level. The calculated magnetic moment of the surface Co atom of the Co-term for Co2CrSi(001) was increased slightly to 1.05,B with respect to that of the deep inner layers (,1.00,B), while that for Co2TiSi(001) was decreased to 0.88,B. Large enhancement of the magnetic moment was found for the surface Ti atoms at TiSi-term of Co2TiSi(001) and Cr atoms at CrSi-term of Co2CrSi(001) with values of 0.07,B and 2.91(B, respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Description of band structures of armchair nanotubes using the symmetry-adapted linear augmented cylindrical wave methodPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009P. N. D'yachkov Abstract Using a symmetry-adapted linear augmented cylindrical wave method, the total band structures and the densities of states of the armchair single-walled carbon nanotubes (SWNTs) (n,n) with 4 , n , 20, n = 30, 40, 60 and 100 are calculated. The approximations are made in the sense of muffin-tin potentials and density functional theory only. The electronic states are presented as the functions of the two quantum numbers, namely, the continuous wave vector k corresponding to the screw symmetry operations and an integer rotational quantum number L between 0 and n , 1. An account of rotational and helical symmetry properties of the armchair SWNTs and particularly an introduction of the quantum number L permit to elaborate a more detailed classification of the armchair SWNTs electronic states. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The electronic structure and magnetism of a rocksalt FeN(001) surface: A density functional studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007J. I. Lee Abstract We investigated the electronic structure and magnetism of the rocksalt FeN(001) surface. We considered both the ferromagnetic and antiferromagnetic configurations. We calculated the electronic structure using the full-potential linearized augmented plane wave method within generalized gradient approximation. We found that the antiferromagnetic phase is more stable than the ferromagnetic one, as in bulk, with an energy difference of 0.14 eV per the considered slab. The magnetic moments of the Fe atoms in the antiferromagnetic phase slab are 2.90 ,B, ,2.26 ,B and 2.37 ,B for the surface, subsurface, and center layers, respectively, while the values for the ferromagnetic one are 2.85 ,B, 1.81 ,B, and 2.37 ,B, respectively. The detailed electronic structures for ferromagnetic and antiferromagnetic phases are compared and discussed with the calculated spin-densities and density of states. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Lattice dynamics of CuAlO2 under high pressure from ab initio calculationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007P. Rodríguez-Hernández Abstract The density functional perturbation theory is employed to study the vibrational properties of CuAlO2 under pressure. The calculations are preformed using the pseudopotential wave method and the local density approximation for the exchange-correlation (XC) potential. The d electrons of Cu are treated as valence states. We present the phonon dispersion curves. Our results are in good agreement with the available experimental Raman scattering experiments. Ab initio calculations show the presence of a dynamical instability, possibly related with the experimentally observed phase transition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] How do electronic properties of conventional III,V semiconductors hold for the III,V boron bismuth BBi compound?PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2005D. Madouri Abstract We have performed ab-initio self-consistent calculations using the full potential linear augmented plane wave method to investigate the structural and the electronic properties of the boron bismuth III,V compound BBi. Our calculations provide the first available information about the structural and electronic ground-state properties of BBi. Total energy calculations of the cubic zinc-blende, wurtzite, rock-salt, cesium chloride and orthorhombic Cmcm phases are made. The zinc-blende structure is found to be the ground-state phase of BBi; within the generalized gradient approximation (local density approximation), we found a lattice constant of 5.529 Å (5.416 Å) and a bulk modulus of 72.20 GPa (86.27 GPa). We found that, contrary to other boron compounds, the band gap of BBi is direct at the , point. The relativistic contraction of the 6s orbital of Bi has a strong influence on the bands and bonds of BBi. Consequently, the electronic properties of BBi are shown to differ considerably from those of common group III,V semiconductors (e.g. GaAs); in particular, we found an unusually strong p,p mixing of the valence-band maximum relative to most of the other III,V compounds. Furthermore, the calculated valence charge density shows an anomalous behavior, characterized by a charge transfer towards the ,cation' B atom, further illustrating the rich behavior of boron bismuth compounds. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculationsANNALEN DER PHYSIK, Issue 8 2010U. Schwingenschlögl We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As2, for the tetragonal I4/mmm as well as the orthorhombic Fmmm structure. In comparison to full potential linear augmented plane wave calculations, we obtain significantly smaller magnetic energies. This finding is remarkable, since the augmented spherical wave method, in general, is known for a most reliable description of magnetism. [source] Addressing non-uniqueness in linearized multichannel surface wave inversionGEOPHYSICAL PROSPECTING, Issue 1 2009Michele Cercato ABSTRACT The multichannel analysis of the surface waves method is based on the inversion of observed Rayleigh-wave phase-velocity dispersion curves to estimate the shear-wave velocity profile of the site under investigation. This inverse problem is nonlinear and it is often solved using ,local' or linearized inversion strategies. Among linearized inversion algorithms, least-squares methods are widely used in research and prevailing in commercial software; the main drawback of this class of methods is their limited capability to explore the model parameter space. The possibility for the estimated solution to be trapped in local minima of the objective function strongly depends on the degree of nonuniqueness of the problem, which can be reduced by an adequate model parameterization and/or imposing constraints on the solution. In this article, a linearized algorithm based on inequality constraints is introduced for the inversion of observed dispersion curves; this provides a flexible way to insert a priori information as well as physical constraints into the inversion process. As linearized inversion methods are strongly dependent on the choice of the initial model and on the accuracy of partial derivative calculations, these factors are carefully reviewed. Attention is also focused on the appraisal of the inverted solution, using resolution analysis and uncertainty estimation together with a posteriori effective-velocity modelling. Efficiency and stability of the proposed approach are demonstrated using both synthetic and real data; in the latter case, cross-hole S-wave velocity measurements are blind-compared with the results of the inversion process. [source] | ||||||||||