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Sample records for hueckel band calculations

  1. Extended-Hueckel-theory calculation of hyperfine interactions of the positive divacancy in silicon

    International Nuclear Information System (INIS)

    Using extended Huckel theory, an LCAO-MO wavefunction was calculated for the unpaired electron of the positive divacancy in silicon. Calculations were carried out in the molecular unit cell approach for the GAMMA point. The unit cell of the periodic array was a 62 atom cluster, that is, a 64 atom perfect cell with two atoms removed to form the divacancy. The unpaired divacancy electron occupies a level of symmetry type Bsub(u), which is located in the valence band near the band edge. From the wavefunction, expressed in Slater-type 3s and 3p atomic orbitals, the hyperfine interactions of the defect electron with 29Si nuclei surrounding the divacancy were obtained. A systematic study was made of the effects of Jahn-Teller deformations of the six nearest-neighbour atoms of the divacancy, for the two distortion modes which reduce the trigonal symmetry of the defect to monoclinic. Also, the effects of symmetric relaxation of the nearest neighbours, and of relaxation of the next-nearest-neighbour atoms were considered. Results for the tensors calculated were compared with the tensors determined experimentally by electron-nuclear double resonance. (author)

  2. Relativistic extended Hueckel (REX) interpretation of 237 Np nuclear quadrupole coupling and isomer shifts in neptunyl compounds

    International Nuclear Information System (INIS)

    The 237 Np nuclear quadrupole coupling constants and isomer shifts in neptunyl systems are discussed using relativistic extended Hueckel calculations. Other actinide compounds with multiple bonds are briefly reviewed. 36 refs

  3. Calculations of laser dye absorption band shape

    International Nuclear Information System (INIS)

    Brilliant green molecule vibrational frequencies were determined by calculation its Hessian matrix. Calculated absorption band of the molecule was compared with spectral ellipsometry experimental data. The band shape was treated in frames of ? conjugated chain model. Numerical simulation with complete active space approach confirmed the presence of the chain in the molecule.

  4. Debye-Hueckel-Bjerrum theory for charged colloids

    OpenAIRE

    Tamashiro, M. N.; Levin, Yan; Barbosa, Marcia C.

    1998-01-01

    We formulate an extension of the Debye-Hueckel-Bjerrum theory [M. E. Fisher and Y. Levin, Phys. Rev. Lett. 71, 3826 (1993)] to the fluid state of a highly asymmetric charged colloid. Allowing for the formation of clusters consisting of one polyion and n condensed counterions, the total Helmholtz free energy of the colloidal suspension is constructed. The thermodynamic properties, such as the cluster-density distribution and the pressure, are obtained by the minimization of t...

  5. Band structure calculations using the transcorrelated method

    Science.gov (United States)

    Sakuma, Rei; Sodeyama, Keitaro; Tsuneyuki, Shinji

    2007-03-01

    We have been developing a new wave-function-based method for calculating the electronic properties of solids. The main feature of this method, called the transcorrelated (TC) method, is a similarity transformation of the Hamiltonian using the Jastrow-Slater trial wave function, which leads to an effective non-hermitian Hamiltonian with three-body interactions. Correlation effects are incorporated in the effective Hamiltonian via the similarity transformation. The wave function is optimized by solving a set of Hartree-Fock-like single particle equations derived by minimizing the variance of the effective Hamiltonian. In this work, the TC method is applied to the band structure calculations of sp semiconductors. In the TC method, Koopmans' theorem holds, in which the eigenenergies of the single particle orbitals are interpreted as the ionization energies and electron affinities. By applying the Jastrow function derived from the random phase approximation (RPA), the screening effect is incorporated in the effective Hamiltonian, which significantly reduces the value of band gaps of semiconductors from their Hartree-Fock values.

  6. Comparison of EH with SW-Xsub(alpha) calculations

    International Nuclear Information System (INIS)

    The electronic structure of octahedral metal atom clusters Me6 of 3d, 4d, and 5d transition metal atoms (V, Cr; Nb, Mo; Ta, W) has been calculated applying two different quantum-chemical approximation methods (Extended Hueckel (EH) method; SW-Xsub(alpha) method). Equilibrium structures, energy level schemes, Fermi energies and band widths as well as densities of states of clusters are discussed in detail

  7. Energy Band Calculations for Maximally Even Superlattices

    Science.gov (United States)

    Krantz, Richard; Byrd, Jason

    2007-03-01

    Superlattices are multiple-well, semiconductor heterostructures that can be described by one-dimensional potential wells separated by potential barriers. We refer to a distribution of wells and barriers based on the theory of maximally even sets as a maximally even superlattice. The prototypical example of a maximally even set is the distribution of white and black keys on a piano keyboard. Black keys may represent wells and the white keys represent barriers. As the number of wells and barriers increase, efficient and stable methods of calculation are necessary to study these structures. We have implemented a finite-element method using the discrete variable representation (FE-DVR) to calculate E versus k for these superlattices. Use of the FE-DVR method greatly reduces the amount of calculation necessary for the eigenvalue problem.

  8. Band structure calculations of high pressure phases of selenium

    International Nuclear Information System (INIS)

    We report a detailed theoretical calculation of the electronic band structure of Se in hexagonal and monoclinic phases under pressure. The first principle tight-binding linear Muffin-Tin orbital method (TBLMTO) within local density approximation (LDA) has been used. The total energy calculations have been carried out within the atomic-sphere approximation (ASA) for both phases in order to study the phase stability. Apart from the electronic band structure and structural stability calculations, the density of states (DOS) and Fermi energies at various pressures are calculated. The calculated lattice parameters, transition pressure, bulk modulus and the pressure-volume relation were found to be in good agreement with recent experimental results. Our calculations show that the ambient pressure hexagonal phase has a band gap of 1.49 eV whereas the high pressure monoclinic phase is found to be metallic. (author)

  9. Linear scaling calculation of band edge states and doped semiconductors

    CERN Document Server

    Xiang, H J; Hou, J G; Zhu, Q; Yang, Jinlong; Zhu, Qingshi

    2006-01-01

    Linear scaling methods provide total energy, but no energy levels and canonical wavefuctions. From the density matrix computed through the density matrix purification methods, we propose an order-N (O(N)) method for calculating both the energies and wavefuctions of band edge states, which are important for optical properties and chemical reactions. In addition, we also develop an O(N) algorithm to deal with doped semiconductors based on the O(N) method for band edge states calculation. We illustrate the O(N) behavior of the new method by applying it to boron nitride (BN) nanotubes and BN nanotubes with an adsorbed hydrogen atom. The band gap of various BN nanotubes are investigated systematicly and the acceptor levels of BN nanotubes with an isolated adsorbed H atom are computed. Our methods are simple, robust, and especially suited for the application in self-consistent field electronic structure theory.

  10. First-principles electronic-band calculations on organic conductors

    OpenAIRE

    Shoji Ishibashi

    2009-01-01

    Predicting electronic-band structures is a key issue in understanding the properties of materials or in materials design. In this review article, application examples of first-principles calculations, which are not based on adjustable empirical parameters, to study electronic structures of organic conductors are described.

  11. Reduced Bloch mode expansion for periodic media band structure calculations

    CERN Document Server

    Hussein, Mahmoud I

    2008-01-01

    Reduced Bloch mode expansion is presented for fast periodic media band structure calculations. The expansion employs a natural basis composed of a selected reduced set of Bloch eigenfunctions. The reduced basis is selected within the irreducible Brillouin zone at high symmetry points determined by the medium's crystal structure and group theory (and possibly at additional related points). At each of the reciprocal lattice selection points, a number of Bloch eigenfunctions are selected up to the frequency range of interest for the band structure calculations. Since it is common to initially discretize the periodic unit cell and solution field using some choice of basis, reduced Bloch mode expansion is practically a secondary expansion that uses a selected set of Bloch eigenvectors. Such expansion therefore keeps, and builds on, any favorable attributes a primary expansion approach might exhibit. Being in line with the well known concept of modal analysis, the proposed approach maintains accuracy while reducing...

  12. The calculation of band gap energy in zinc oxide films

    Science.gov (United States)

    Arif, Ali; Belahssen, Okba; Gareh, Salim; Benramache, Said

    2015-01-01

    We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor; the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 200 and 500 °C. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation (2), so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.

  13. Diffraction Calculations and Measurements in Millimeter Frequency Band

    Directory of Open Access Journals (Sweden)

    P. Pechac

    2004-09-01

    Full Text Available The paper deals with a study of diffraction on dielectric wedge(building corner in millimeter frequency band, both theoretically andexperimentally, to provide knowledge support for ray tracing/launchingcalculations of MWS interference issues in urban areas. The mainmotivation was to find balance between reasonably reliable results andnecessary demands on calculation complexity and input data accuracy.Verification of Uniform Theory of Diffraction (UTD was made both forperfectly conducting and dielectric wedge-shaped obstacle. Comparisonsof theoretical results and experimental measurement at millimeter wavesin anechoic chamber are presented.

  14. Band structure calculations of Mo2BC under pressure

    Science.gov (United States)

    Falconi, R.; Alvarez, F.; Escamilla, R.; Escudero, R.

    2010-03-01

    Mo2B is a superconductor with a Tc of about 5.8 K and a body centered tetragonal cristalline structure. When carbon is added to the structure it is formed the intermetallic Mo2BC compound, which is a superconductor with a Tc of about 7 K and has a crystalline face centered orthorhombic structure. In this work we make ab initio calculations of the electronics bands for Mo2BC at several pressures up to 5 GPa in order to explain why chemical pressure, generated by decreasing the carbon concentration, decreases TC in a non linear rate. The density of state at the Fermi level is reduced in a non monotonic way suggesting some correlation. We complement the study with high pressure electrical resistivity measurements up to 4.8 GPa which reveal a decreasing of Tc at the rate dTC/dP = - 0.03 K/GPa.

  15. Comparison of EH with SW-X/sub alpha/ calculations

    International Nuclear Information System (INIS)

    The electronic structure of small niobium clusters Nb/sub n/ (n = 2, 4, 6, 9) has been calculated applying two different quantum-chemical approximation methods (Extended Hueckel (EH) method; SW-X/sub alpha/ method). It was found that both the methods led to the same results concerning equilibrium structures, energy level schemes, Fermi energies and band widths as well as the densities of states of the clusters. In solving solid state problems of transition metals with the aid of the cluster model a better adaptation of the EH method should be expected by adjusting the EH parameters to the SW-X/sub alpha/ results. (author)

  16. Self-consistent Hartree energy band calculation for manganese oxide (MnO)

    International Nuclear Information System (INIS)

    A self-consistent Hartree energy band calculation was done for the MnO crystal using the linear combination of atomic orbitals (LCAO) method. Gaussian type atomic orbitals were used in the LCAO method. This calculation was done for paramagnetic MnO with the NaCl lattice structure. The results show that the energy bands around the Fermi level of MnO are unusually flat, meaning that the electrons in this region are strongly localized. Therefore short range correlation was added to the results of this band calculation. The short range correlation effects were added by calculating atomic type corrections to the original band structure. The results of this correlation calculation show that a large amount of energy is required to excite an electron from the Mn 3d band. Therefore the lowest excitation (the one that requires the least energy) is an excitation from the top of the O 2p band to the Fermi level. This yields a fundamental band gap of 4.8 eV which is in good agreement with optical absorption experiments. This fundamental band gap of 4.8 eV implies that MnO is an insulator, in agreement with conductivity experiments. The Hartree results for the valence bands of MnO agree very well with the results of photoemission experiments. In comparison to the photoemission data, the results of the self-consistent Hartree calculation are an order of magnitude better than the results of the only other band calculation for MnO. Comparison with band calculations for other transitiowith band calculations for other transition metal oxides (other than MnO) imply that with a good self-consistent Hartree energy band calculation for MnO can be superior

  17. Calculations of the intensities of ir bands and Raman lines in torsional spectra of dioxybenzene

    International Nuclear Information System (INIS)

    We present the calculated intensities of IR bands and Raman lines in torsion spectra of dioxy benzenes. The intensities have been determined calculating, the matrix elements of the components of the dipole momentum and polarizability tensor. (authors)

  18. Energy bands in graphene: Comparison between the tight-binding model and ab initio calculations

    Science.gov (United States)

    Kogan, E.; Nazarov, V. U.; Silkin, V. M.; Kaveh, M.

    2014-04-01

    We compare the classification of the electron bands in graphene, obtained by group theory algebra in the framework of a tight-binding model (TBM), with that calculated in a density-functional-theory (DFT) framework. Identification in the DFT band structure of all eight energy bands (four valence and four conduction bands) corresponding to the TBM-derived energy bands is performed and the corresponding analysis is presented. The four occupied (three ?-like and one ?-like) and three unoccupied (two ?-like and one ?-like) bands given by the DFT closely correspond to those predicted by the TBM, both by their symmetry and their dispersion law. However, the two lowest lying at the ?-point unoccupied bands (one of them of a ?-like type and the other of a ?-like one), are not of the TBM type. According to both their symmetry and the electron density these bands are plane waves orthogonal to the TBM valence bands; dispersion of these states can be determined unambiguously up to the Brillouin zone borders. On the other hand, the fourth unoccupied band given by the TBM can be identified among those given by the DFT band calculations; it is situated rather high with respect to energy. The interaction of this band with the free-electron states is so strong that it exists only in part of the k space.

  19. Band-structure calculation of MBe13 (M = La, Ce, Th and U)

    International Nuclear Information System (INIS)

    The one-electron energy band structures for LaBe13, CeBe13, ThBe13 and UBe13 were calculated by the self-consistent APW method with the local density approximation. It was found that the Be s(p) bands form wide valence bands below a pseudogap at 0.8 eV below the Fermi energy Esub(F) in UBe13; and the Be p bands extend mostly above a pseudogap at 1.9 eV above Esub(F) in UBe13. Between these bands, there are M d-Be p mixed bands. In CeBe13 and UBe13, the f bands are inserted among the d-p mixed bands. Due to the squeezing effect of the p-f mixings from both above and below the f bands, the f band widths in CeBe13 and UBe13 are very small, only 1 eV in UBe13, much narrower than the experimentally observed PES-BIS peak, indicating the importance of the many-body effect. In LaBe13 and ThBe13, the f band widths are much larger, more than twice that in UBe13, due to the reversed p-f mixing effect. The p-f mixing parameters for these materials were also evaluated from the present band calculation. (author)

  20. CCMR: Steps Toward Direct Comparison of Band Structure Calculations and Photoemission Spectra in 3D Materials

    Science.gov (United States)

    Hristov, Alexander

    2009-08-15

    Steps are taken to unite theoretical predictions of electronic band structure with direct measurements from high-resolution angle-resolved photoemission spectroscopy (ARPES). A new process of accessing data from self-consistent eld calculations allows for calculations of band structure along any path in momentum space. Using the inner potential model, a primitive model is developed for direct comparison of photoemission measurements and augmented plane-wave + local orbitals (APW+lo) band structure calculations close to the Fermi energy, Ef. This model is then applied to ARPES measurements for URu2Si2.

  1. BoltzTraP. A code for calculating band-structure dependent quantities

    OpenAIRE

    Madsen, Georg K. H.; Singh, David J.

    2006-01-01

    A program for calculating the semi-classic transport coefficients is described. It is based on a smoothed Fourier interpolation of the bands. From this analytical representation we calculate the derivatives necessary for the transport distributions. The method is compared to earlier calculations, which in principle should be exact within Boltzmann theory, and a very convincing agreement is found.

  2. BoltzTraP. A Code for Calculating Band-structure Dependent Quantities

    Energy Technology Data Exchange (ETDEWEB)

    Madsen, Georg K [University of Aarhus, Denmark; Singh, David J [ORNL

    2006-01-01

    A program for calculating the semi-classic transport coefficients is described. It is based on a smoothed Fourier interpolation of the bands. From this analytical representation we calculate the derivatives necessary for the transport distributions. The method is compared to earlier calculations, which in principle should be exact within Boltzmann theory, and a very convincing agreement is found.

  3. First-principle band calculation of ruthenium for various phases

    CERN Document Server

    Watanabe, S; Kai, T; Shiiki, K

    2000-01-01

    The total energies and the magnetic moments of Ru for HCP, BCC, FCC, BCT structures were calculated by using a first-principle full-potential linearized augmented plane-wave (FLAPW) method based on the generalized gradient approximation (GGA). HCP has the lowest energy among the structures calculated, which agrees with the experimental result that HCP is the equilibrium phase of Ru. The total energy of BCT Ru has the local minimum at c/a=sq root 2 (FCC) with a=5.13 au, c=7.25 au and c/a=0.83 with a=6.15 au, c=5.11 au. It is pointed out that these phases are possibly metastable. The BCC structure, which corresponds to BCT with a=c=5.78 au, is unstable because it is at a saddle point of the total energy. BCT Ru of c/a<1 has a magnetic moment at the stable volume.

  4. Emergence of rotational bands in ab initio no-core configuration interaction calculations of light nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Caprio, M.A. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556-5670 (United States); Maris, P.; Vary, J.P. [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011-3160 (United States)

    2013-02-12

    The emergence of rotational bands is observed in no-core configuration interaction (NCCI) calculations for the odd-mass Be isotopes (7?A?13) with the JISP16 nucleon–nucleon interaction, as evidenced by rotational patterns for excitation energies, quadrupole moments, and E2 transitions. Yrast and low-lying excited bands are found. The results demonstrate the possibility of well-developed rotational structure in NCCI calculations using a realistic nucleon–nucleon interaction.

  5. Calculation of the frequency band of a Bragg waveguide

    International Nuclear Information System (INIS)

    Transmission regions of the silica-core Bragg optical waveguides are analysed. It is shown that a relatively small decrease in the refractive index of the core allows one to narrow down the waveguide transmission region so that to suppress in the spectrum the undesirable emission line propagating in the waveguide, thus ensuring a minimal loss of the fundamental mode at the working wavelength. The example of calculations of a frequency filter based on a Bragg optical fibre is considered, in which the fundamental mode has minimal losses at 0.925 ?m but completely suppressed at 1.06 ?m. The loss spectrum of a Bragg waveguide and the field distribution of the fundamental mode are presented. (optical waveguides and fibres)

  6. Self-consistent field variational cellular method as applied to the band structure calculation of sodium

    International Nuclear Information System (INIS)

    The band structure of metallic sodium is calculated, using for the first time the self-consistent field variational cellular method. In order to implement the self-consistency in the variational cellular theory, the crystal electronic charge density was calculated within the muffin-tin approximation. The comparison between our results and those derived from other calculations leads to the conclusion that the proposed self-consistent version of the variational cellular method is fast and accurate. (author)

  7. Definition of two band parameters for use in photon transport calculations

    Energy Technology Data Exchange (ETDEWEB)

    Cullen, D.E.

    1978-04-01

    The multigroup photon diffusion equations are derived from the Boltzmann equation. Limitations and assumptions imposed by the diffusion equation are thus apparent. In addition, this approach serves to define all of the required diffusion parameters in terms of cross sections; the relationship to the multi-band parameters used in neutron transport calculations can thus be clearly established. All required two-band parameters are defined in terms of Planckian and Rosseland mean values. (RWR)

  8. Definition of two band parameters for use in photon transport calculations

    International Nuclear Information System (INIS)

    The multigroup photon diffusion equations are derived from the Boltzmann equation. Limitations and assumptions imposed by the diffusion equation are thus apparent. In addition, this approach serves to define all of the required diffusion parameters in terms of cross sections; the relationship to the multi-band parameters used in neutron transport calculations can thus be clearly established. All required two-band parameters are defined in terms of Planckian and Rosseland mean values

  9. Band structure calculations of Cu(In1-xGax)Se2

    International Nuclear Information System (INIS)

    First principles density calculations of the band structure, and density of states of the Cu(In1-xGax)Se2 in the chalcopyrite type structure have been carried out using the density functional theory. The relationship between the band gap and chemical composition in the structure is discussed. The effective masses of the electrons and holes in the different composition crystals are reported.

  10. Calculation of Energy Band Diagram of a Photoelectrochemical Water Splitting Cell

    CERN Document Server

    Cendula, P; Gimenez, S; Schmid, M; Bisquert, J; Graetzel, M; Schumacher, J O

    2014-01-01

    A physical model is presented for a semiconductor electrode of a photoelectrochemical (PEC) cell, accounting for the potential drop in the Helmholtz layer. Hence both band edge pinning and unpinning are naturally included in our description. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials is presented. Calculated current-voltage curves are compared with established analytical models and measurement. Our model calculations are suitable to enhance understanding and improve properties of semiconductors for photoelectrochemical water splitting.

  11. Dielectric band structure of crystals: General properties, and calculations for silicon

    International Nuclear Information System (INIS)

    We shift the dielectric band structure method, orginially proposed by Baldereschi and Tosatti for the description of microscopic electronic screening in crystals. Some general properties are examined first, including the requirements of causality and stability. The specific test case of silicon is then considered. Dielectric bands are calculated, according to several different prescriptions for the construction of the dielectric matrix. It is shown that the results allow a very direct appraisal of the screening properties of the system, as well as of the quality of the dielectric model adopted. The electronic charge displacement induced by ?sub(25') and X3 phonon-like displacements of the atoms is also calculated and compared with the results of existent full self-consistent calculations. Conclusions are drawn on the relative accuracies of the dielectric band structures. (author)

  12. Electron momentum distribution in vanadium: Compton scattering measurements and band-structure calculation

    International Nuclear Information System (INIS)

    The [100], [110], and [111] Compton profiles and reciprocal form factors have been derived from Compton scattering measurements made with 60-keV 241Am ? rays on single-crystal samples of vanadium. The same quantities have also been obtained theoretically on the basis of a self-consistent linear-muffin-tin-orbital band-structure calculation, using the local-density approximation for the exchange-correlation potential. An r-space procedure was adopted to calculate the reciprocal form factor B(r) directly from the wave functions. The experimental and theoretical results are compared with previous 412-keV Compton scattering measurements and other band-structure calculations. All calculations overestimate the Compton profile anisotropies at low momenta

  13. Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra

    DEFF Research Database (Denmark)

    Christensen, N. Egede; Feuerbacher, B.

    1974-01-01

    The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi-surface experiments and to optical-reflectance measurements up to 5-eV photon energy. The temperature and strain responses in the band structure are estimated from band calculations with four different lattice constants. The band structure was determined in the entire Brillouin zone and is applied to a calculation of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.

  14. Electronegativity calculation of bulk modulus and band gap of ternary ZnO-based alloys

    International Nuclear Information System (INIS)

    In this work, the bulk moduli and band gaps of MxZn1?xO (M = Be, Mg, Ca, Cd) alloys in the whole composition range were quantitatively calculated by using the electronegativity-related models for bulk modulus and band gap, respectively. We found that the change trends of bulk modulus and band gap with an increase of M concentration x are same for BexZn1?xO and CdxZn1?xO, while the change trends are reverse for MgxZn1?xO and CaxZn1?xO. It was revealed that the bulk modulus is related to the valence electron density of atoms whereas the band gap is strongly influenced by the detailed chemical bonding behaviors of constituent atoms. The current work provides us a useful guide to compositionally design advanced alloy materials with both good mechanical and optoelectronic properties.

  15. Calculation of photonic energy bands of TiO2 hollow spherical arrays.

    Science.gov (United States)

    Buffaz, Amandine; Oikawa, Eri; Hashimoto, Takuya; Matsushita, Sachiko

    2009-01-01

    The photonic energy bands of titanium dioxide (TiO2) hollow spherical arrays, which are self-assembled photonic crystals, were investigated. The finite-difference time domain (FDTD) method was applied to both the face-centred-cubic (fcc) and body-centred-cubic (bcc) packing structures of TiO2 hollow spherical arrays to determine the energy bands from the perspective of photoelectrode applications. Calculations were carried out on the basis of the TiO2 shell wall thickness. The spectral behaviour of light in the hollow spherical arrays was also studied, with particular interest devoted to the pseudogap found in one of the structures. A three-dimensional (3D) TiO2 hollow spherical array was then experimentally synthesized in three steps: the preparation of synthetic opal templates, replication by spin coating, and sintering. The diffuse scattering spectrum of the obtained array was finally measured and compared with the calculated photonic band structure. PMID:19441294

  16. Calculation of isotopic profile during band displacement on ion exchange resins

    International Nuclear Information System (INIS)

    A method has been developed to calculate the isotopic profile during band displacement on ion exchange resins using computer simulation. Persoz had utilized this technique earlier for calculating the isotopic profile during band displacement as well as frontal analysis. The present report deals with a simplification of the method used by Persoz by reducing the number of variables and making certain approximations where the separation factor is not far from unity. Calculations were made for the typical case of boron isotope separation. The results obtained by the modified method were found to be in very good agreement with those obtained by using an exact equation, at the same time requiring conside--rably less computer time. (author)

  17. Correlation of CO2 solubility in N-methyldiethanolamine + piperazine aqueous solutions using extended Debye-Hueckel model

    International Nuclear Information System (INIS)

    Solubility data of CO2 in aqueous N-methyldiethanolamine (MDEA) solutions of concentration (2.52, 3.36, and 4.28) kmol/m3 were obtained at temperatures (313, 323, and 343) K and partial pressures ranging from about (30 to 5000) kPa. A thermodynamic model based on extended Debye-Hueckel theory was applied to predict and correlate of CO2 solubility in various aqueous amine solutions. The effect of piperazine (PZ) concentration on CO2 loading in MDEA solutions was determined at PZ concentration (0.36, 0.86, and 1.36) kmol/m3. Using experimental data in various temperatures the interaction parameters of activity coefficient model for these systems were determined. The results show the model consistency with experimental and literature data and PZ is beneficial to the CO2 loading. The comparison of results of this study with previous data work shows the wide range of CO2 loading considered in this work and the better agreement of model with experimental data. The average absolute relative deviation percent (?AAD) for all data points were 8.11%.

  18. Correlation of CO{sub 2} solubility in N-methyldiethanolamine + piperazine aqueous solutions using extended Debye-Hueckel model

    Energy Technology Data Exchange (ETDEWEB)

    Vahidi, Mehdi [Research Institute of Petroleum Industry (R.I.P.I.), National Iranian Oil Company (N.I.O.C.), P.O. Box 14665-1998, Tehran (Iran, Islamic Republic of)], E-mail: vahidim@ripi.ir; Matin, Naser Seyed [Research Institute of Petroleum Industry (R.I.P.I.), National Iranian Oil Company (N.I.O.C.), P.O. Box 14665-1998, Tehran (Iran, Islamic Republic of); Goharrokhi, Mahdi [Department of Chemical Engineering, Tehran South Campus, Islamic Azad University, Tehran (Iran, Islamic Republic of); Jenab, Masih Hosseini; Abdi, Majid Abedinzadegan [Research Institute of Petroleum Industry (R.I.P.I.), National Iranian Oil Company (N.I.O.C.), P.O. Box 14665-1998, Tehran (Iran, Islamic Republic of); Najibi, Seyed Hesam [Department of Petroleum Engineering, Petroleum University of Technology, Ahwaz (Iran, Islamic Republic of); R and D Department, National Iranian Gas Co. (N.I.G.C.), Tehran (Iran, Islamic Republic of)

    2009-11-15

    Solubility data of CO{sub 2} in aqueous N-methyldiethanolamine (MDEA) solutions of concentration (2.52, 3.36, and 4.28) kmol/m{sup 3} were obtained at temperatures (313, 323, and 343) K and partial pressures ranging from about (30 to 5000) kPa. A thermodynamic model based on extended Debye-Hueckel theory was applied to predict and correlate of CO{sub 2} solubility in various aqueous amine solutions. The effect of piperazine (PZ) concentration on CO{sub 2} loading in MDEA solutions was determined at PZ concentration (0.36, 0.86, and 1.36) kmol/m{sup 3}. Using experimental data in various temperatures the interaction parameters of activity coefficient model for these systems were determined. The results show the model consistency with experimental and literature data and PZ is beneficial to the CO{sub 2} loading. The comparison of results of this study with previous data work shows the wide range of CO{sub 2} loading considered in this work and the better agreement of model with experimental data. The average absolute relative deviation percent ({delta}{sub AAD}) for all data points were 8.11%.

  19. Band gap engineering of early transition-metal-doped anatase TiO?: first principles calculations.

    Science.gov (United States)

    Li, C; Zhao, Y F; Gong, Y Y; Wang, T; Sun, C Q

    2014-10-21

    The thermal stability and electronic structures of anatase TiO2 doped with early transition metals (TM) (group III-B = Sc, Y and La; group IV-B = Zr and Hf; group V-B = V, Nb and Ta) have been studied using first principles calculations. It was found that all doped systems are thermodynamically stable, and their band gaps were reduced by 1-1.3 eV compared to pure TiO2. Doping with transition metals affects the strength of the hybrid orbital of TM-O bonding, and the band gap increases approximately linearly with the MP value of TM-O bonding. PMID:25183457

  20. BoltzTraP. A code for calculating band-structure dependent quantities

    Science.gov (United States)

    Madsen, Georg K. H.; Singh, David J.

    2006-07-01

    A program for calculating the semi-classic transport coefficients is described. It is based on a smoothed Fourier interpolation of the bands. From this analytical representation we calculate the derivatives necessary for the transport distributions. The method is compared to earlier calculations, which in principle should be exact within Boltzmann theory, and a very convincing agreement is found. Program summaryTitle of program:BoltzTraP Catalogue identifier:ADXU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADXU_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions:none Programming language used:Fortran 90 Computer:The program should work on any system with a F90 compiler. The code has been tested with the Intel Fortran compiler Operating system:Unix/Linux RAM:bytes up to 2 GB for low symmetry, small unit cell structures No. of lines in distributed program, including test data, etc.:1 534 213 No. of bytes in distributed program, including test data, etc.:27 473 227 Distribution format:tar.gz External routines:The LaPack and Blas libraries are needed Nature of problem:Analytic expansion of energy-bands. Calculation of semi-classic integrals. Solution method:Smoothed Fourier expansion of bands. Running time:Up to 3 hours for low symmetry, small unit cell structures.

  1. CdSe/CdTe interface band gaps and band offsets calculated using spin-orbit and self-energy corrections

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, M. [Centro de Pesquisas Avancadas Wernher von Braun, Av. Alice de Castro P.N. Mattosinho 301, CEP 13098-392 Campinas, SP (Brazil); Ferreira, L.G. [Departamento de Fisica dos Materiais e Mecanica, Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Fonseca, L.R.C. [Center for Semiconductor Components, State University of Campinas, R. Pandia Calogeras 90, 13083-870 Campinas, SP (Brazil); Ramprasad, R. [Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269 (United States)

    2012-09-20

    We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme to obtain corrected band gaps and band offsets. Our calculations include the spin-orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8-1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.

  2. Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors

    CERN Document Server

    Kokabi, Alireza; Khorasani, Sina; Fardmanesh, Mehdi

    2011-01-01

    We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results.

  3. Two-band calculations on the upper critical field of superconductor NbSe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Chen Lei; Zuo Jing; Lu Yanyan [Department of Mathematics and Physics, North China Electric Power University, Beijing 102206 (China); Huang Hai, E-mail: huanghai@pku.edu.cn [Department of Mathematics and Physics, North China Electric Power University, Beijing 102206 (China); State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871 (China)

    2011-12-15

    We study the temperature dependence of upper critical field for NbSe{sub 2}. Temperature dependence of the anisotropy parameter is also determined. The band with the smaller gap is most probably located on the bonding Nb Fermi sheet. Based on two-band Ginzburg-Landau theory, we study the temperature dependence of upper critical field for superconducting crystal NbSe{sub 2}. The results reproduce the experimental data in a broad temperature range, especially the upward curvature near the transition temperature. Our calculations also indicate that in NbSe{sub 2} the band with the smaller gap is almost isotropic, and most probably located on the bonding Nb Fermi sheets.

  4. Analysis of form factors observed with polarized neutrons; comparison with band structure calculations

    International Nuclear Information System (INIS)

    For the analysis of observed magnetic neutron factors of transition metals and alloys deffdifferent methods are being used. These methods are i) fitting of theoretical free-ion form factors to the experimental data, ii) Fourier analysis, as introduced by Moon, which does not require any a knowledge of the form factor but, instead, extracts its spin and orbital parts from the data, and iii) a modified version of ii) that properly takes into account the full symmetry of the crystal lattice. Spherical spin form factors appearing in i), ii) and iii) are compared with those based upon band structure calculations for Fe and Ni. It is found that only the results of iii) are in agreement with band theory. Since neither band theory nor method iii) leads to the existence of a uniform negative spin density this concept should be abandoned. (orig.)

  5. Tight binding electronic band structure calculation of achiral boron nitride single wall nanotubes

    International Nuclear Information System (INIS)

    In this paper we report the Tight-Binding method, for the electronic structure calculations of achiral single wall Boron Nitride nanotubes. We have used the contribution of ? electron only to define the electronic band structure for the solid. The Zone-folding method is used for the Brillouin Zone definition. Calculation of tight binding model parameters is done by fitting them to available experimental results of two-dimensional hexagonal monolayers of Boron Nitride. It has been found that all the boron nitride nanotubes (both zigzag and armchair) are constant gap semiconductors with a band gap of 5.27eV. All zigzag BNNTs are found to be direct gap semiconductors while all armchair nanotubes are indirect gap semiconductors. (author)

  6. Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow

    Science.gov (United States)

    Jain, Sonal Kumar; Bhardwaj, Anil

    2011-07-01

    A model for N2 Vegard-Kaplan (VK) band (A3?u+ - X1?g+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet states of N2, the population of any given level of N2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, first positive (B3?g - A3?u+), second positive (C3?u - B3?g), and Wu-Benesch (W3?u - B3?g) bands of N2. A reduction in the N2 density by a factor of 3 in the Mars thermospheric general circulation model is required to obtain agreement between calculated limb profiles of VK (0-6) and SPICAM observation. Calculations are carried out to asses the impact of model parameters, namely, electron impact cross sections, solar EUV flux, and model atmosphere, on the emission intensities. Constraining the N2/CO2 ratio by SPICAM observations, we suggest the N2/CO2 ratios to be in the range 1.1-1.4% at 120 km, 1.8-3.2% at 140 km, and 4-7% at 170 km. During high solar activity the overhead intensity of N2 VK band emissions would be ˜2.5 times higher than that during low solar activity.

  7. Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow

    OpenAIRE

    Jain, Sonal Kumar; Bhardwaj, Anil

    2011-01-01

    A model for N2 Vegard-Kaplan (VK) band (A^3Sigma_u^+ - X^1Sigma_g^+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet sta...

  8. Efficient calculation of inelastic vibration signals in electron transport: Beyond the wide-band approximation

    DEFF Research Database (Denmark)

    Lu, Jing Tao; Christensen, Rasmus Bjerregaard

    2014-01-01

    We extend the simple and efficient lowest order expansion (LOE) for inelastic electron tunneling spectroscopy (IETS) to include variations in the electronic structure on the scale of the vibration energies. This enables first-principles calculations of IETS line shapes for molecular junctions close to resonances and band edges. We demonstrate how this is relevant for the interpretation of experimental IETS using both a simple model and first-principles simulations.

  9. Complete active space self-consistent field calculations of the vibrational band strengths for C3

    International Nuclear Information System (INIS)

    Complete active space self-consistent calculations of the energy and dipole moment functions were carried out for C3 in its electronic ground state. The absorption coefficient between 0.7 and 75 microns is calculated on the basis of the vibrational band strength of transitions between the 800 lowest states with v less than or equal to (4, 39, 3). In cool carbon stars with a high C/O ratio, C3 is found to be the most prevalent of the known opacity sources. 49 refs

  10. Calculation of the band structure of 2d conducting polymers using the network model

    International Nuclear Information System (INIS)

    the network model has been used to calculate the band structure the gap energy and Fermi level of conducting polymers in two dimensions. For this purpose, a geometrical classification of possible polymer chains configurations in two dimensions has been introduced leading to a classification of the unit cells based on the number of bonds in them. The model has been applied to graphite in 2D, represented by a three bonds unit cell, and, as a new case, the anti-parallel Polyacetylene chains (PA) in two dimensions, represented by a unit cell with four bons. The results are in good agreement with the first principles calculations. (author)

  11. First-principles calculation of the three-dimensional band structure of poly(phenylene vinylene)

    Science.gov (United States)

    Gomes da Costa, P.; Dandrea, R. G.; Conwell, E. M.

    1993-01-01

    We have carried out a local-density-functional calculation of the three-dimensional (3D) band structure of the conducting polymer poly(phenylene vinylene) (PPV). The motivation was to investigate the effects of interchain coupling. The major effects are due to coupling of carbons in the rings to their closest neighbors, hydrogens on rings in adjacent chains. Among the effects of this coupling are splitting by up to 0.4 eV at various points of the Brillouin zone of the double degeneracy that would exist if the two chains in the unit cell were uncoupled; loss of electron-hole symmetry; the band edge at a point in the Brillouin zone off the chain direction; and a band gap smaller by 0.2 eV than that obtained from 1D calculations. The calculation results in a ratio of the transfer integral t? perpendicular to the chains to t?, parallel to the chains, ~=0.03. This value is too large to permit the existence of polarons in a perfect PPV crystal. Nevertheless, there is evidence for the existence of polarons in PPV crystals currently available. The large value of t?/t? means that polaron existence must be due to defects, such as inclusions of precursor polymer. This would result in the polarons having a wide range of properties, i.e., extent on the chain and energy levels.

  12. Band-gap shrinkage calculations and analytic model for strained bulk InGaAsP

    Science.gov (United States)

    Connelly, Michael J.

    2015-02-01

    Band-gap shrinkage is an important effect in semiconductor lasers and optical amplifiers. In the former it leads to an increase in the lasing wavelength and in the latter an increase in the gain peak wavelength as the bias current is increased. The most common model used for carrier-density dependent band-gap shrinkage is a cube root dependency on carrier density, which is strictly only true for high carrier densities and low temperatures. This simple model, involves a material constant which is treated as a fitting parameter. Strained InGaAsP material is commonly used to fabricate polarization insensitive semiconductor optical amplifiers (SOAs). Most mathematical models for SOAs use the cube root bandgap shrinkage model. However, because SOAs are often operated over a wide range of drive currents and input optical powers leading to large variations in carrier density along the amplifier length, for improved model accuracy it is preferable to use band-gap shrinkage calculated from knowledge of the material bandstructure. In this letter the carrier density dependent band-gap shrinkage for strained InGaAsP is calculated by using detailed non-parabolic conduction and valence band models. The shrinkage dependency on temperature and both tensile and compressive strain is investigated and compared to the cube root model, for which it shows significant deviation. A simple power model, showing an almost square-root dependency, is derived for carrier densities in the range usually encountered in InGaAsP laser diodes and SOAs.

  13. Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow

    CERN Document Server

    Jain, Sonal Kumar

    2011-01-01

    A model for N2 Vegard-Kaplan (VK) band (A^3Sigma_u^+ - X^1Sigma_g^+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet states of N2, the population of any given level of N2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, first positive (B^3Pi_g - A^3Sigma_u^+), second positive (C^3Pi_u - B^3Pi_g), and Wu-Benesch (W^3Delta_u - B^3Pi_g) bands of N2. A reduction in the N2 density by a factor of 3 ...

  14. Extracting E Versus K Effective Band Structure from Supercell Calculations on Alloys and Impurities

    Energy Technology Data Exchange (ETDEWEB)

    Popescu, V.; Zunger, A.

    2012-02-15

    The supercell approach to defects and alloys has circumvented the limitations of those methods that insist on using artificially high symmetry, yet this step usually comes at the cost of abandoning the language of E versus k band dispersion. Here we describe a computational method that maps the energy eigenvalues obtained from large supercell calculations into an effective band structure (EBS) and recovers an approximate E(k) for alloys. Making use of supercells allows one to model a random alloy A{sub 1-x}B{sub x}C by occupying the sites A and B via a coin-toss procedure, affording many different local environments (polymorphic description) to occur. We present the formalism and implementation details of the method and apply it to study the evolution of the impurity band appearing in the dilute GaN:P alloy. We go beyond the perfectly random case, realizing that many alloys may have nonrandom microstructures, and investigate how their formation is reflected in the EBS. It turns out that the EBS is extremely sensitive in determining the critical disorder level for which delocalized states start to appear in the intermediate band. In addition, the EBS allows us to identify the role played by atomic relaxation in the positioning of the impurity levels.

  15. Ab initio calculations of band structure and thermophysical properties for SnS2 and SnSe2

    International Nuclear Information System (INIS)

    The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.

  16. Calculated energy levels and intensities for the nu1 and 2nu2 bands of HDO

    International Nuclear Information System (INIS)

    A Hamiltonian taking explicitly into account both Fermi and Coriolis interactions has been set up for triatomic molecules of symmetry C/sub s/ and used to reproduce very satisfactorily the available rotational energy levels of the [(100), (020)] interacting states of HDO, providing realistic wavefunctions as well as precise rotational constants and vibrational energies. To calculate line intensities, these wavefunctions were used together with suitably chosen transition moment operators expanded up to degree 2 in Jvector and having the correct symmetry in the C/sub s/ group, leading to hybrid bands of both A- and B- type. Using this formalism, it has been possible to determine, from the fit of the existing experimental intensities, the coefficients appearing in the expansions of the transition moments operators of the 2nu2 and nu1 bands of HDO. 2 references

  17. Bloch mode synthesis: Ultrafast methodology for elastic band-structure calculations

    Science.gov (United States)

    Krattiger, Dimitri; Hussein, Mahmoud I.

    2014-12-01

    We present a methodology for fast band-structure calculations that is generally applicable to problems of elastic wave propagation in periodic media. The methodology, called Bloch mode synthesis, represents an extension of component mode synthesis, a set of substructuring techniques originally developed for structural dynamics analysis. In Bloch mode synthesis, the unit cell is divided into interior and boundary degrees-of-freedom, which are described, respectively, by a set of normal modes and a set of constraint modes. A combination of these mode sets then forms a reduced basis for the band structure eigenvalue problem. The reduction is demonstrated on a phononic-crystal model and a locally resonant elastic-metamaterial model and is shown to accurately predict the frequencies and Bloch mode shapes with a dramatic decrease in computation time in excess of two orders of magnitude.

  18. Self-consistent band calculations for an Anderson Hamiltonian treatment of anisotropic f-electron systems

    Science.gov (United States)

    Wills, J. M.; Cooper, B. R.; Thayamballi, P.

    1985-04-01

    The unusual magnetic ordering, magnetic excitation behavior, and anomalous crystal-field splitting in CeBi and CeSb can be explained using a model Hamiltonian obtained by applying the Schrieffer-Wolff transformation to the Anderson Hamiltonian. It is highly desirable to obtain a first principles prediction of the parameters of the theory in order to extend this understanding quantitatively to other cerium and light actinide materials. To this end, we have calculated the electronic structure of CeBi and CeSb with the linear muffin-tin orbital (LMTO) method, using a self-consistent fully warped potential, and have obtained the coupling between non-f band states and f states localized in the sense of the Anderson Hamiltonian. This is applied to a calculation of the anomalous crystal-field splitting in CeBi and CeSb, and application to calculating the anisotropic two-ion interaction is discussed. We find that the dominant contribution to the anomalous crystal-field effect (about two thirds) comes from hybridization with d bands.

  19. Accounting for many-body correlation effects in the calculation of the valence band photoelectron emission spectra of ferromagnets

    International Nuclear Information System (INIS)

    The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa-Kohn-Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented

  20. Electronic band structure calculations for biaxially strained Si, Ge, and III-V semiconductors

    Science.gov (United States)

    Kim, Jiseok; Fischetti, Massimo V.

    2010-07-01

    Electronic band structure and effective masses for relaxed and biaxially strained Si, Ge, III-V compound semiconductors (GaAs, GaSb, InAs, InSb, InP) and their alloys (InxGa1-xAs, InxGa1-xSb) on different interface orientations, (001), (110), and (111), are calculated using nonlocal empirical pseudopotential with spin-orbit interaction. Local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and to obtain correct workfunctions. The nonlocal and spin-orbit terms are linearly interpolated between anions and cations for III-V semiconductors. The virtual crystal approximation is employed for the InxGa1-xAs and InxGa1-xSb alloys and deformation potentials are determined using linear deformation-potential theory. Band gap bowing parameters are extracted using least-square fitting for relaxed alloys and for strained InxGa1-xAs on (001), (110), and (111) InP. The dependence on biaxial strain of the electron and hole effective masses at the symmetry points ?, X, and L exhibits a continuous variation at ? and L but sudden changes appear at ? minima caused by the flatness of the dispersion along the ? line near the minimum.

  1. Analysis of plasmonic properties of heavily doped semiconductors using full band structure calculations

    Science.gov (United States)

    Jung, Jesper; Pedersen, Thomas G.

    2013-03-01

    Surface plasmon polaritons (SPPs) and localized surface plasmon (LSP) resonances are not limited to noble metals. Any material with a substantial amount of free carriers will support surface plasma oscillations which, when coupled to an electromagnetic field, will result in surface plasmon polaritons and localized surface plasmon resonances in confined systems. Utilizing a full band structure approach, we analyze the plasmonic properties of several heavily doped semiconductors. We present rigorous quantum mechanical calculations of the plasma frequency, and study in detail its dependence on impurity doping concentration. Results are presented for silicon, germanium, gallium arsenide, zinc oxide, and gallium nitride. For silicon and zinc oxide, the surface plasmon resonance frequency is calculated for a large range of doping concentrations and we study the dispersion of surface plasmon polaritons on thin films. The investigated properties of heavily doped semiconductors hold promises for several interesting applications within plasmonics.

  2. SGFM applied to the calculation of surface band structure of V

    International Nuclear Information System (INIS)

    The surface Green function matching (SGFM) method has been developed recently to deal with a great variety of problems in a unified way. The method was first developed for continuum systems. The recent advances for discrete structures can deal with surfaces, interfaces, quantum wells, superlattices, intercalated layered compounds, and other systems. Several applications of this formalism are being carried out. In the present note we will describe how the formalism applies to the calculation of the electronic surface band structure of vanadium which is a quite interesting transition metal with very active magnetic properties at the surface, in particular at the (100) surface. It is straightforward, on the basis of the calculation presented here, to obtain the magnetic moment on the surface, for example, through the method followed by G. Allan or the surface paramagnon density which should be particularly enhanced at this surface as compared to the bulk

  3. The photodissociation of NO2 in the second absorption band: Ab initio and quantum dynamics calculations

    International Nuclear Information System (INIS)

    The photodissociation of NO2 in the second absorption band (217 nm) is investigated by electronic structure as well as quantum mechanical and classical dynamics calculations. Potential energies are calculated for the five lowest 2A' states using the internally contracted multi-reference configuration interaction method and the standard correlation consistent polarized quadruple zeta basis set. The two N-O bond lengths and the O-N-O bond angle are varied over wide ranges. Our calculations unambiguously verify that the second absorption band is due to excitation of state 32A' (22B2 in C2v), which is the only state with non-vanishing transition dipole moment in this energy range. State 32A' correlates diabatically with O(1D) + NO(2?), but it connects adiabatically with the ground-state product channel O(3P) + NO(2?). In the present study, we construct a three-dimensional potential energy surface (PES) for only one adiabatic state, 32A', and primarily focus on the absorption cross-section due to excitation of this state. The general form of the absorption spectrum and the progression of diffuse vibrational structures are well reproduced by the quantum mechanical calculations. The vibrational and rotational state distributions of NO in the O(3P) + NO(2?) channel are also determined. The predicted internal energy distrid. The predicted internal energy distributions are relatively narrow over the entire range of the absorption spectrum - in quantitative agreement with the experimental result for dissociation at 226 nm, but in severe qualitative disagreement with measurements near 202 nm

  4. Emergence of rotational bands in ab initio no-core configuration interaction calculations of the Be isotopes

    CERN Document Server

    Maris, P; Vary, J P

    2014-01-01

    The emergence of rotational bands is observed in no-core configuration interaction (NCCI) calculations for the Be isotopes (7<=A<=12), as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. Yrast and low-lying excited bands are found. The results indicate well-developed rotational structure in NCCI calculations, using the JISP16 realistic nucleon-nucleon interaction within finite, computationally-accessible configuration spaces.

  5. Camel-back band-induced power factor enhancement of thermoelectric lead-tellurium from Boltzmann transport calculations

    International Nuclear Information System (INIS)

    Band structures of PbTe can be abnormally bended via dual-doping on both the cationic and anionic sites to form camel-back multivalley energy band structures near the band edge. As a result, additional carrier pockets and strong intervalley scattering of carriers are introduced. Boltzmann transport calculations indicate that their contradictory effects yield remarkably enhanced power factor due to the improved thermopower and almost unchanged electrical conductivity in low temperature and high carrier concentration ranges. These findings prove dual-doping-induced band bending as an effective approach to improve the thermoelectric properties of PbTe and other similar materials

  6. Camel-back band-induced power factor enhancement of thermoelectric lead-tellurium from Boltzmann transport calculations

    Energy Technology Data Exchange (ETDEWEB)

    Wang, X. G., E-mail: wang2006@mail.ustc.edu.cn; Wang, L., E-mail: sqtb@mail.ustc.edu.cn; Liu, J., E-mail: jingliu@mail.ustc.edu.cn; Peng, L. M., E-mail: penglm@ustc.edu.cn [CAS Key Laboratory for Mechanical Behavior and Design of Materials, Department of Modern Mechanics, School of Engineering Science, University of Science and Technology of China, Hefei 230026 (China)

    2014-03-31

    Band structures of PbTe can be abnormally bended via dual-doping on both the cationic and anionic sites to form camel-back multivalley energy band structures near the band edge. As a result, additional carrier pockets and strong intervalley scattering of carriers are introduced. Boltzmann transport calculations indicate that their contradictory effects yield remarkably enhanced power factor due to the improved thermopower and almost unchanged electrical conductivity in low temperature and high carrier concentration ranges. These findings prove dual-doping-induced band bending as an effective approach to improve the thermoelectric properties of PbTe and other similar materials.

  7. The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot

    International Nuclear Information System (INIS)

    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations

  8. Laboratory measurements and theoretical calculations of O2 A band electric quadrupole transitions

    International Nuclear Information System (INIS)

    Frequency-stabilized cavity ring-down spectroscopy was utilized to measure electric quadrupole transitions within the 16O2 A band, b 1?g+(leftarrow)X 3?g-(0,0). We report quantitative measurements (relative uncertainties in intensity measurements from 4.4% to 11%) of nine ultraweak transitions in the NO, PO, RS, and TS branches with line intensities ranging from 3x10-30 to 2x10-29 cm molec.-1. A thorough discussion of relevant noise sources and uncertainties in this experiment and other cw-cavity ring-down spectrometers is given. For short-term averaging (t-10 cm-1 Hz-1/2. The detection limit was reduced further by co-adding up to 100 spectra to yield a minimum detectable absorption coefficient equal to 1.8x10-11 cm-1, corresponding to a line intensity of ?2.5x10-31 cm molec.-1. We discuss calculations of electric quadrupole line positions based on a simultaneous fit of the ground and upper electronic state energies which have uncertainties -27 cm molec.-1 which is equal to only ?8x10-6 of the magnetic dipole band intensity.

  9. A combined representation method for use in band structure calculations. 1: Method

    Science.gov (United States)

    Friedli, C.; Ashcroft, N. W.

    1975-01-01

    A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.

  10. Nitrogen defects in wide band gap oxides: defect equilibria and electronic structure from first principles calculations.

    Science.gov (United States)

    Polfus, Jonathan M; Bjørheim, Tor S; Norby, Truls; Haugsrud, Reidar

    2012-09-01

    The nitrogen related defect chemistry and electronic structure of wide band gap oxides are investigated by density functional theory defect calculations of N(O)(q), NH(O)(×), and (NH2)(O)(·) as well as V(O)(··) and OH(O)(·) in MgO, CaO, SrO, Al(2)O(3), In(2)O(3), Sc(2)O(3), Y(2)O(3), La(2)O(3), TiO(2), SnO(2), ZrO(2), BaZrO(3), and SrZrO(3). The N(O)(q) acceptor level is found to be deep and the binding energy of NH(O)(×) with respect to N(O)' and (OH(O)(·) is found to be significantly negative, i.e. binding, in all of the investigated oxides. The defect structure of the oxides was found to be remarkably similar under reducing and nitriding conditions (1 bar N(2), 1 bar H(2) and 1 × 10(-7) bar H(2)O): NH(O)(×) predominates at low temperatures and [N(O)'] = 2[V(O)(··) predominates at higher temperatures (>900 K for most of the oxides). Furthermore, we evaluate how the defect structure is affected by non-equilibrium conditions such as doping and quenching. In terms of electronic structure, N(O)' is found to introduce isolated N-2p states within the band gap, while the N-2p states of NH(O)(×) are shifted towards, or overlap with the VBM. Finally, we assess the effect of nitrogen incorporation on the proton conducting properties of oxides and comment on their corrosion resistance in nitriding atmospheres in light of the calculated defect structures. PMID:22828729

  11. Band-theoretic calculations of the optical-activity tensor of ?-quartz and trigonal Se

    Science.gov (United States)

    Zhong, Hua; Levine, Zachary H.; Allan, Douglas C.; Wilkins, John W.

    1993-07-01

    We present a formalism to compute the optical-activity tensor in the long-wavelength limit neglecting local-field corrections with a nearly first-principles approach. The calculation of optical activity requires perturbation theory in the vector potential in order to describe the rotation of the plane of polarization perpendicular to the direction of propagation. We contrast this approach with perturbation theory in the scalar potential which can be used for the other optical response properties we compute. Band structures are obtained within the Kohn-Sham local-density approximation using standard plane-wave and separable norm-conserving pseudopotential techniques. Self-energy effects necessary to obtain the correct band gap are included by the use of a ``scissors operator.'' In the long-wavelength limit, two components of the optical-activity tensor are computed for both selenium and ?-quartz. For selenium in the low-frequency range, the optical rotatory power along the optic axis is about a factor of 2 too small compared with some of the experimental data. For ?-quartz, the ratio g11/g33 and the frequency dependence of both components obey the phenomenological coupled-oscillator model and are in agreement with experiment. Yet both g11 and g33 (or the optical rotatory power) are about a factor of 5 too small compared with the available experimental data. In addition, the dielectric constants and second-harmonic-generation susceptibilities including local-field corrections are calculated for selenium and ?-quartz in terms of scalar-potential theory. Excellent agreement (discrepancies of a few percent) is obtained with the experiments for these properties.

  12. Ab-initio calculations of the Optical band-gap of TiO2 thin films

    CERN Document Server

    Wunderlich, W; Tanemura, M; Tanemura, S; Jin, P; Kaneko, K; Terai, A; Nabatova-Gabin, N; Belkada, R; Wunderlich, Wilfried; Miao, Lei; Tanemura, Masaki; Tanemura, Sakae; Jin, Ping; Kaneko, Kenji; Terai, Asuka; Nabatova-Gabin, Nataliya; Belkada, Rachid

    2004-01-01

    Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band-gap of TiO2 plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO3 substrates was correlated to the lattice constants estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO3. In order to interpret the optical band gap expansion for both phases, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. T...

  13. Calculation of band gap in long alkyl-substituted heterocyclic-thiophene-conjugated polymers with electron donor-acceptor fragment

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Li; Zhang, Qiuyu; Ren, Hua; Yan, Hongling; Zhang, Junping; Zhang, Hepeng; Gu, Junwei [Key Laboratory of Applied Physics and Chemistry in Space, Ministry of Education, School of Science, Northwestern Polytechnical University, 127 Youyi Xilu, Shaanxi Xian 710072 (China)

    2008-05-15

    Since the interaction between alternating donors and acceptors results in a diminished band gap, a low band gap (<1.8 ev) will be expected in polymers containing donor-acceptor (D-A) repeating units. In order to predict the band gaps for guiding the synthesis of novel materials with low band gaps, we apply quantum-chemical techniques to calculate the band gaps in several polythiophene (PT) copolymers with D-A repeating units: poly{l_brace}5,7-bis(3-octyl thiophen-2-yl)thieno-[3,4-b]pyrazine{r_brace}(OTP), poly{l_brace}5,7-di(thiophen-2-yl)thieno[3,4-b]-pyrazine{r_brace}(TP), poly{l_brace}4-(4-hexyl-5-(3-hexylthiophen-2-yl)thiophen-2-yl)benzo-[c][1, 2, 5]thiadiazole(HH-OTB), and poly{l_brace}4-(5-(thiophen-2-yl)thiophen-2-yl) benzo[c]-[1,2,5]thiadiazole(TB). The geometries of the oligomers were optimized using semi-empirical AM1. The band gap calculations on these oligomers were performed by density functional theory (DFT) (B3LYP/3-21G*) and DFT (B3LYP/6-31G*). Band gaps of the corresponding polymers were obtained by extrapolating oligomers gaps to infinite chain lengths. The results indicate that calculated band gaps are in good agreement with the experimental values, in particular for long alkyl-substituted copolymer (HH-OTB/OTP). In addition, long alkyl side chain can induce steric hindrance, which leads to destroyed chain coplanar and increased band gap (>1.8 ev) in thiophene copolymers with alternate D-A units. (author)

  14. Bulk ionization potentials and band alignments from three-dimensional periodic calculations as demonstrated on rocksalt oxides

    Science.gov (United States)

    Logsdail, Andrew J.; Scanlon, David O.; Catlow, C. Richard A.; Sokol, Alexey A.

    2014-10-01

    The position of the band edges of a material plays a key role in determining the properties for a range of applications, but fundamental band bending is an interface-dependent property that cannot be quantified without knowledge of bulk electron energy levels. We present a method for calculating the bulk position of the valence band maximum, and therefore the bulk ionization potential, from periodic plane wave calculations as shown for a range of rocksalt ionic oxides. We demonstrate that, for the popular "slab alignment" technique, explicit consideration of any surface induced electronic polarization is necessary to calculate accurate bulk ionization potentials. Our proposed method to quantify these surface effects, using polarizable-shell based interatomic potentials, is very computationally affordable, and our updated slab alignment method yields much improved agreement with the available experimental data.

  15. Photon path length distributions for cloudy skies – oxygen A-Band measurements and model calculations

    Directory of Open Access Journals (Sweden)

    O. Funk

    Full Text Available This paper addresses the statistics underlying cloudy sky radiative transfer (RT by inspection of the distribution of the path lengths of solar photons. Recent studies indicate that this approach is promising, since it might reveal characteristics about the diffusion process underlying atmospheric radiative transfer (Pfeilsticker, 1999. Moreover, it uses an observable that is directly related to the atmospheric absorption and, therefore, of climatic relevance. However, these studies are based largely on the accuracy of the measurement of the photon path length distribution (PPD. This paper presents a refined analysis method based on high resolution spectroscopy of the oxygen A-band. The method is validated by Monte Carlo simulation atmospheric spectra. Additionally, a new method to measure the effective optical thickness of cloud layers, based on fitting the measured differential transmissions with a 1-dimensional (discrete ordinate RT model, is presented. These methods are applied to measurements conducted during the cloud radar inter-comparison campaign CLARE’98, which supplied detailed cloud structure information, required for the further analysis. For some exemplary cases, measured path length distributions and optical thicknesses are presented and backed by detailed RT model calculations. For all cases, reasonable PPDs can be retrieved and the effects of the vertical cloud structure are found. The inferred cloud optical thicknesses are in agreement with liquid water path measurements.

    Key words. Meteorology and atmospheric dynamics (radiative processes; instruments and techniques

  16. Band structure calculation of GeSn and SiSn

    Science.gov (United States)

    Amrane, Na.; Ait Abderrahmane, S.; Aourag, H.

    1995-08-01

    The band structure of GeSn and SiSn in zinc-blende structures is predicted using the empirical pseudopotential. Special emphasis is placed on the effects of inversions asymmetry such as ionicity. We found that GeSn exhibits a direct band gap whereas SiSn still remains indirect gap material.

  17. Scaling laws of band gaps of phosphorene nanoribbons: A tight-binding calculation

    Science.gov (United States)

    Taghizadeh Sisakht, Esmaeil; Zare, Mohammad H.; Fazileh, Farhad

    2015-02-01

    In this study, we analyze the band structure, the state characterization, and electronic transport of monolayer black phosphorus (phosphorene) zigzag nanoribbons (zPNRs) and armchair nanoribbons (aPNRs), using five-parameter tight-binding (TB) approximation. In zPNRs, the ratio of the two dominant hopping parameters indicates the possibility of a relativistic dispersion relation and the existence of a pair of separate quasiflat bands at the Fermi level. Moreover, the corresponding states are edge localized if their bands are well separated from the valence and conduction bands. We also investigated the scaling laws of the band gaps versus ribbon widths for the armchair and zigzag phosphorene nanoribbons. In aPNRs, the transverse electric field along the ribbon width enhances the band gap closure by shifting the energy of the valence and conduction band edge states. For zPNRs, a gap occurs at the middle of the relatively degenerate quasiflat bands; thus, these ribbons are a promising candidate for future field-effect transistors.

  18. First-principles calculation of the electronic band of ZnO doped with C

    International Nuclear Information System (INIS)

    Using the first-principles approach based upon the density functional theory (DFT), we have studied the electronic structure of wurtzite ZnO systems doped with C at different sites. When Zn is substituted by C, the system turns from a direct band gap semiconductor into an indirect band gap semiconductor, and donor levels are formed. When O is substituted by C, acceptor levels are formed near the top of the valence band, and thus a p-type transformation of the system is achieved. When the two kinds of substitution coexist, the acceptor levels are compensated for all cases, which is unfavorable for the p-type transformation of the system.

  19. Synergistic effects on band gap-narrowing in titania by codoping from first-principles calculations

    OpenAIRE

    Long, Run; English, Niall J.

    2010-01-01

    The large intrinsic band gap in TiO2 has hindered severely its potential application for visible-light irradiation. In this study, we have used a passivated approach to modify the band edges of anatase-TiO2 by codoping of X (N, C) with transition metals (TM=W, Re, Os) to extend the absorption edge to longer visible-light wavelengths. It was found that all the codoped systems can narrow the band gap significantly; in particular, (N+W)-codoped systems could serve as remarkably better photocatal...

  20. Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

    2015-04-01

    High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

  1. Band alignment at the CdS/FeS2 interface based on the first-principles calculation

    Science.gov (United States)

    Ichimura, Masaya; Kawai, Shoichi

    2015-03-01

    FeS2 is potentially well-suited for the absorber layer of a thin-film solar cell. Since it usually has p-type conductivity, a pn heterojunction cell can be fabricated by combining it with an n-type material. In this work, the band alignment in the heterostructure based on FeS2 is investigated on the basis of the first-principles calculation. CdS, the most popular buffer-layer material for thin-film solar cells, is selected as the partner in the heterostructure. The results indicate that there is a large conduction band offset (0.65 eV) at the interface, which will hinder the flow of photogenerated electrons from FeS2 to CdS. Thus an n-type material with the conduction band minimum positioned lower than that of CdS will be preferable as the partner in the heterostructure.

  2. Pushing the limits of first-principles electron-phonon calculations: from photoemission kinks to band gaps

    Science.gov (United States)

    Giustino, Feliciano

    2012-02-01

    The electron-phonon interaction is key to some of the most intriguing and technologically important phenomena in condensed matter physics, ranging from superconductivity to charge density waves, electrical resistivity, and thermoelectricity. Starting from the late nineties first-principles calculations of electron-phonon interactions in metals have become increasingly popular, mainly in connection with the study of conventional superconductors and with the interpretation of angle-resolved photoemission experiments. In contrast, progress on first-principles calculations of electron-phonon interactions in insulators has been comparatively slower. This delay is arguably due to the conventional wisdom that the signatures of electron-phonon interactions in semiconductor band structures are so small that they fall within the error bar of the most accurate electronic structure calculations. In order to fill this gap we developed, within the context of state-of-the-art density-functional techniques, a theory proposed by Allen and Heine for calculating the temperature dependence of band gaps in semiconductors [P. B. Allen, V. Heine, J. Phys. C: Solid State Phys. 69, 2305 (1976)]. This methodology allows us to calculate both the temperature dependence of the quasiparticle energies and the renormalization due to zero-point quantum fluctuations. In order to demonstrate this technique an application to the intriguing case of diamond will be discussed [F. Giustino, S. G. Louie, M. L. Cohen, Phys. Rev. Lett. 105, 265501 (2010)]. In this case the calculated temperature dependence of the direct band gap agrees well with spectroscopic ellipsometry data, and the renormalization due to the electron-phonon interaction is found to be spectacularly large (>0.6 eV). This unexpected finding might be only the tip of the iceberg in a research area which remains largely unexplored and which, from a first glimpse, appears rich of surprises.

  3. Comparison of CONDOR, FCI and MAFIA Calculations for a 150MW S-Band Klystron with Measurements

    International Nuclear Information System (INIS)

    To facilitate the design of high power klystrons an investigation into the reliability and accuracy of three modern particle-in-cell codes was performed. A 150 MW S-band klystron for which measurements were available was used for this comparison. The field calculations of the particle-in-cell codes are based on a finite difference time domain scheme, and use a port approximation to speed up the convergence to steady state. However, they differ in many details (e.g. calculation of E, B or A, ?; space charge correction; 2D or 3D modeling of output cavity)

  4. Tight-binding calculations of the band structure and total energies of the various polytypes of silicon carbide

    Science.gov (United States)

    Bernstein, N.; Gotsis, H. J.; Papaconstantopoulos, D. A.; Mehl, M. J.

    2005-02-01

    We present electronic structure and total energy calculations for SiC in a variety of polytype structures using the NRL nonorthogonal tight-binding method. We develop one set of parameters optimized for a combination of electronic and energetic properties using a sp basis, and one optimized for electronic properties using a spd basis. We compute the energies of polytypes with up to 62 atoms per unit cell, and find that the hexagonal wurtzite structure is highest in energy, the 4H structure is lowest in energy, and the cubic zinc-blende structure is in between, in agreement with our linear augmented plane-wave and other calculations. For the sp model we find that the electronic structure of the cubic and hexagonal structures are in good agreement with density-functional theory calculations only for the occupied bands. The spd parametrization optimized for the electronic structure of the zinc-blende and wurtzite structures at the equilibrium volume reproduces nearly perfectly both the valence and conduction bands. The sp tight-binding model also yields elastic constants, phonon frequencies, stacking fault energies, and vacancy formation energies for the cubic structure in good agreement with available experimental and theoretical calculations. Using molecular dynamics simulations we compute the finite-temperature thermal expansion coefficient and atomic mean-square displacements in good agreement with available first-principles calculations.

  5. A new Green's function for the wake potential calculation of the SLAC S-band constant gradient accelerating section

    International Nuclear Information System (INIS)

    The behavior of the longitudinal wake fields excited by a very short bunch in the SLAC S-band constant gradient accelerating structures has been studied. Wake potential calculations were performed for a bunch length of 10?m using the author's code to obtain a numerical solution of Maxwell's equations in the time domain. We have calculated six accelerating sections in the series (60-ft) to find the stationary solution. While analyzing the computational results we have found a new formula for Green's function. Wake potentials, which are calculated using this Green's function are in amazingly good agreement with numerical results over a wide range of bunch lengths. Green's function simplifies the wake potential calculations and can be easily incorporated into the tracking codes. This is very useful for beam dynamics studies of the linear accelerators of LCLS and FACET .

  6. A New Green's Function for the Wake Potential Calculation of the SLAC S-band Constant Gradient Accelerating Section

    International Nuclear Information System (INIS)

    The behavior of the longitudinal wake fields excited by a very short bunch in the SLAC S-band constant gradient accelerating structures has been studied. Wake potential calculations were performed for a bunch length of 10 microns using the author's code to obtain a numerical solution of Maxwell's equations in the time domain. We have calculated six accelerating sections in the series (60-ft) to find the stationary solution. While analyzing the computational results we have found a new formula for the Green's function. Wake potentials, which are calculated using this Green's function are in amazingly good agreement with numerical results over a wide range of bunch lengths. The Green's function simplifies the wake potential calculations and can be easily incorporated into the tracking codes. This is very useful for beam dynamics studies of the linear accelerators of LCLS and FACET.

  7. Calculation of the Hartree-Fock band structure in solid rare gases and ionic compounds - Application to the optical transitions

    International Nuclear Information System (INIS)

    The well-known 'augmented plane waves' method, for the calculation of electronic states in crystals, is first reviewed. A modification of this method in the case of insulators is then described, which treats exchange in the exact Hartree-Fock formulation, without use of the common free-electron approximation. The band structure of several rare gases (Ne, Ar) and ionic compounds (LiF, NaF, KF, LiCl, NaCl, KCl) has been calculated and discussed. The main point is the strong influence of correlation effects which must be taken into account before comparison between calculated and measured optical transitions. Such an improvement is obtained by including a local polarization potential in the one-electron Hamiltonian, leading to a good agreement of the theoretical transitions with the experimental ones. (author)

  8. Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations

    Science.gov (United States)

    Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.

    2014-01-01

    The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N-H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.

  9. Tunneling calculations for GaAs-Al(x)Ga(1-x) as graded band-gap sawtooth superlattices. Thesis

    Science.gov (United States)

    Forrest, Kathrine A.; Meijer, Paul H. E.

    1991-01-01

    Quantum mechanical tunneling calculations for sawtooth (linearly graded band-gap) and step-barrier AlGaAs superlattices were performed by means of a transfer matrix method, within the effective mass approximation. The transmission coefficient and tunneling current versus applied voltage were computed for several representative structures. Particular consideration was given to effective mass variations. The tunneling properties of step and sawtooth superlattices show some qualitative similarities. Both structures exhibit resonant tunneling, however, because they deform differently under applied fields, the J-V curves differ.

  10. Magnetism and superconductivity in C15 compounds from self-consistent band calculations

    International Nuclear Information System (INIS)

    All-atom--all-electron self-consistent semirelativistic linear muffin-tin orbital energy-band studies are reported for TiBe2, ZrZn2 (at ambient and high pressures), the high-T/sub c/ superconductor ZrV2, and the ultralow-T/sub c/ superconductor YAl2. Total and partial (by atom type and l values) density of states, Stoner-like parameters, electron-phonon coupling parameter lambda and superconducting transition temperatures T/sub c/ (determined within the rigid muffin-tin approximation and McMillan's strong coupling theory with and without paramagnon contributions), and their behavior under applied pressure are used to discuss the origin of their observed magnetism and/or superconductivity. From an analysis of the results, we suggest possible high-T/sub c/ superconductivity at high pressure for ZrZn2, and its unlikely occurrence for TiBe2 unless dominant soft phonon modes exist

  11. Intermetallic solid solution Fe1-xCoxGa3: Synthesis, structure, NQR study and electronic band structure calculations

    Science.gov (United States)

    Verchenko, V. Yu.; Likhanov, M. S.; Kirsanova, M. A.; Gippius, A. A.; Tkachev, A. V.; Gervits, N. E.; Galeeva, A. V.; Büttgen, N.; Krätschmer, W.; Lue, C. S.; Okhotnikov, K. S.; Shevelkov, A. V.

    2012-10-01

    Unlimited solid solution Fe1-xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe-Fe and Co-Co dumbbells are preferred to the Fe-Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin-lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF).

  12. A modified band approach for the accurate calculation of online photolysis rates in stratospheric-tropospheric Chemical Transport Models

    Directory of Open Access Journals (Sweden)

    J. E. Williams

    2006-01-01

    Full Text Available Here we present an efficient and accurate method for the online calculation of photolysis rates relevant to both the stratosphere and troposphere for use in global Chemistry Transport Models and General Circulation Models. The method is a modified version of the band model introduced by Landgraf and Crutzen (1998 which has been updated to improve the performance of the approach for solar zenith angles >72° without the use of any implicit parameterisations. For this purpose, additional sets of band parameters have been defined for instances where the incident angle of the light beam is between 72–93°, in conjunction with a scaling component for the far UV region of the spectrum (?=178.6–202.0 nm. For incident angles between 85–93° we introduce a modification for pseudo-sphericity that improves the accuracy of the 2-stream approximation. We show that this modified version of the Practical Improved Flux Method (PIFM is accurate for angles <93° by comparing the resulting height resolved actinic fluxes with a recently developed full spherical reference model. We also show that the modified band method is more accurate than the original, with errors generally being less than ±10% throughout the atmospheric column for a diverse range of chemical species. Moreover, we perform certain sensitivity studies that indicate it is robust and performs well over a wide range of conditions relevant to the atmosphere.

  13. Ab initio calculations of quasiparticle band structure in correlated systems LDA++ approach

    CERN Document Server

    Lichtenstein, A I

    1997-01-01

    We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated d- or f- electrons. The main feature of this approach is the taking into account the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). In the case of strong interactions (U/W>>1 - rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix the band structure problem is formulated as the functional problem on Nmm' for f-electrons and the standard LDA-functional for delocalized electrons. In the case of moderate correlations (U/W=1 metal-insulator regime) we start from the dynamical mean field iterative perturbation scheme (IPS) of G. Kotliar et. al. and also make use of our multiband atomic Green function. Finally for the weak interactions (U/W<1 -transition metals) the self-consistent diagrammatic fluctuation- exchange (FLEX)-approach of N. Bicker...

  14. The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll

    Science.gov (United States)

    Reimers, Jeffrey R.; Cai, Zheng-Li; Kobayashi, Rika; Rätsep, Margus; Freiberg, Arvi; Krausz, Elmars

    2014-10-01

    We recently established a novel assignment of the visible absorption spectrum of chlorophyll-a that sees the two components Qx and Qy of the low-energy Q band as being intrinsically mixed by non-adiabatic coupling. This ended 50 years debate as to the nature of the Q bands, with prior discussion poised only in the language of the Born-Oppenheimer and Condon approximations. The new assignment presents significant ramifications for exciton transport and quantum coherence effects in photosystems. Results from state of the art electronic structure calculations have always been used to justify assignments, but quantitative inaccuracies and systematic failures have historically limited usefulness. We examine the role of CAM-B3LYP time-dependent density-functional theory (TD-DFT) and Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) calculations in first showing that all previous assignments were untenable, in justifying the new assignment, in making some extraordinary predictions that were vindicated by the new assignment, and in then identifying small but significant anomalies in the extensive experimental data record.

  15. The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll

    International Nuclear Information System (INIS)

    We recently established a novel assignment of the visible absorption spectrum of chlorophyll-a that sees the two components Qx and Qy of the low-energy Q band as being intrinsically mixed by non-adiabatic coupling. This ended 50 years debate as to the nature of the Q bands, with prior discussion poised only in the language of the Born-Oppenheimer and Condon approximations. The new assignment presents significant ramifications for exciton transport and quantum coherence effects in photosystems. Results from state of the art electronic structure calculations have always been used to justify assignments, but quantitative inaccuracies and systematic failures have historically limited usefulness. We examine the role of CAM-B3LYP time-dependent density-functional theory (TD-DFT) and Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) calculations in first showing that all previous assignments were untenable, in justifying the new assignment, in making some extraordinary predictions that were vindicated by the new assignment, and in then identifying small but significant anomalies in the extensive experimental data record

  16. Intermetallic solid solution Fe1?xCoxGa3: Synthesis, structure, NQR study and electronic band structure calculations

    International Nuclear Information System (INIS)

    Unlimited solid solution Fe1?xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF). - Graphical abstract: Rate of the nuclear spin–lattice relaxation, 1/T1, observed in the 69Ga NQR experiments for the intermetallic solid solution Fe1?xCoxGa3 is the highest for x=0.25 with the highest calculated density of electronic states at the Fermi level, N(EF); in general, 1/T1 correlates with N2(EF). Highlights: ? Fe1?x1?xCoxGa3 solid solution is prepared in single crystalline form from Ga flux. ? In the crystal structure Fe–Fe and Co–Co dumbbells are preferred to Fe–Co dumbbells. ? Metal-to-semiconductor transition occurs at 069,71Ga NQR spectra efficiently probe local environment of two independent Ga atoms. ? Rate of nuclear spin–lattice relaxation follows squared DOS at the Fermi level.

  17. Electronic band calculation of BaPd2Sb2: Which polymorph is stable?

    International Nuclear Information System (INIS)

    Highlights: •Crystal structure of BaPd2Sb2 is CaBe2Ge2-type. •Fermi surfaces are quasi-2D similar to iron pnictides. •In ThCr2Si2-type structure, Fermi surfaces are 3D. •Magnetic interaction via Pd is to be small. •Superconductivity in BaPd2Sb2 is expected. -- Abstract: Iron-pnictide superconductor (Ba,K)Fe2As2 and nickelate superconductor BaNi2As2 both have the ThCr2Si2-type crystal structure. On the other hand, platinum superconductor SrPt2As2 has the CaBe2Ge2-type crystal structure. We focused on BaPd2Sb2, which contains Pd located between Ni and Pt on the periodic table. We have calculated the electronic structure of BaPd2Sb2 from first-principles, and found that the CaBe2Ge2-type structure is more stable. The Fermi surfaces of BaPd2Sb2 are two-dimensional for the CaBe2Ge2-type structure, and are three-dimensional for the ThCr2Si2-type structure. The calculated D(EF) is 32.1 States/Ry, which is comparable with that in SrPt2As2. These results strongly suggest that superconductivity also occurs in BaPd2Sb2

  18. Inelastic plasmon and inter-band electron-scattering potentials for Si from dielectric matrix calculations

    International Nuclear Information System (INIS)

    Inelastic scattering of electrons in a crystalline environment may be represented by a complex non-hermitian potential. Completed generalised expressions for this inelastic electron scattering potential matrix, including virtual inelastic scattering, are derived for outer-shell electron and plasmon excitations. The relationship between these expressions and the general anisotropic dielectric response matrix of the solid is discussed. These generalised expressions necessarily include the off-diagonal terms representing effects due to departure from translational invariance in the interaction. Results are presented for the diagonal back structure dependent inelastic and virtual inelastic scattering potentials for Si, from a calculation of the inverse dielectric matrix in the random phase approximation. Good agreement is found with experiment as a function of incident energies from 10 eV to 100 keV. Anisotropy effects and hence the interaction de localisation represented by the off-diagonal scattering potential terms, are found to be significant below 1 keV. 38 refs., 2 figs

  19. Calculations of intersection cross-slip activation energies in fcc metals using nudged elastic band method

    Energy Technology Data Exchange (ETDEWEB)

    Rao, S.I., E-mail: satish.rao@wpafb.af.mil [UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894 (United States); Dimiduk, D.M. [Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLM, Wright-Patterson AFB, OH 45433-7817 (United States); Parthasarathy, T.A. [UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894 (United States); El-Awady, J. [Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 (United States); Woodward, C.; Uchic, M.D. [Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLM, Wright-Patterson AFB, OH 45433-7817 (United States)

    2011-11-15

    The nudged elastic band (NEB) method is used to evaluate activation energies for dislocation intersection cross-slip in face-centered cubic (fcc) nickel and copper, to extend our prior work which used an approximate method. In this work we also extend the study by including Hirth locks (HL) in addition to Lomer-Cottrell locks and glide locks (GL). Using atomistic (molecular statics) simulations with embedded atom potentials we evaluated the activation barrier for a dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane when intersecting a 120{sup o} forest dislocation in both Ni and Cu. The initial separation between the screw and the intersecting dislocation on the (1 1 1) glide plane is varied to find a minimum in the activation energy. The NEB method gives energies that are {approx}10% lower than those reported in our prior work. It is estimated that the activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120{sup o} intersection forming GL in Ni and Cu are {approx}0.47 and {approx}0.65 eV, respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are {approx}0.68 and {approx}0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120{sup o} intersection forming HL in Ni and Cu are estimated to be {approx}0.09 and {approx}0.31 eV, respectively. These values are a factor of 3-20 lower than the activation energy for bulk cross-slip in Ni and, a factor of 2-6 lower than the activation energy for cross-slip in Cu estimated by Friedel-Escaig analysis. These results suggest that cross-slip should nucleate preferentially at selected screw dislocation intersections in fcc materials and the activation energies for such mechanisms are also a function of stacking fault energy.

  20. Electronic structures and valence band XPS spectra of BeO and SiC calculated by X? cluster method

    International Nuclear Information System (INIS)

    The DV-X? cluster method has been applied for calculations of the electronic structures and for analysis of valence band XPS spectra of BeO, ?-SiC (Wurutzite type) and ?-SiC (Zinc-blende type). Clusters studied are [Be4O4] for BeO, and [Si4C4] and [Si5C4]sup(0.75+) for ?-SiC and ?-SiC, respectively. The calculation for BeO has yielded the electronic level structure characteristic of an insulating material. For ?-SiC and ?-SiC the level structures can be related well with their semiconducting behavior. The calculated XPS spectrum of ?-SiC is very similler to that of ?-SiC and is in good agreement with the observed one. However, the effective charge on Si atom in ?-SiC obtained is about twice that in ?-SiC (?-SiC : +1.56, ?-SiC : +0.75). The marked difference indicates that ?-SiC is a material more ionic than ?-SiC. (author)

  1. Angular momentum projected multi-cranked configuration mixing for reliable calculation of high-spin rotational bands

    CERN Document Server

    Shimada, Mitsuhiro; Shimizu, Yoshifumi R

    2015-01-01

    By employing the angular momentum projection technique we propose a method to reliably calculate the quantum spectrum of nuclear collective rotation. The method utilizes several cranked mean-field states with different rotational frequencies and they are superposed in the sense of the configuration mixing or the generator coordinate method, after performing the projection; the idea was originally suggested by Peierls-Thouless in 1962. It is found that the spectrum as a result of the configuration mixing does not essentially depend on chosen sets of cranking frequencies if the number of mean-field states utilized in the mixing is larger than a certain small value. We apply this method to three examples employing the Gogny D1S effective interaction and show that it is useful to study high-spin rotational bands by means of the angular momentum projection method.

  2. Electronic band structure and specific features of Sm{sub 2}NiMnO{sub 6} compound: DFT calculation

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A.H. [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic)

    2013-09-15

    The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm{sub 2}NiMnO{sub 6} compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm{sub 2}NiMnO{sub 6} compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (E{sub F}). The calculated density of states at the E{sub F} is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (?) is found to be 3.74, 4.25 and 4.54 mJ/mol K{sup 2} for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed. - Highlights: • The compound is metallic with strong hybridization near the Fermi energy. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of two sheets. • The bonding features are analyzed using the electronic charge density.

  3. Electronic band structure and specific features of Sm2NiMnO6 compound: DFT calculation

    International Nuclear Information System (INIS)

    The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm2NiMnO6 compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm2NiMnO6 compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (EF). The calculated density of states at the EF is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (?) is found to be 3.74, 4.25 and 4.54 mJ/mol K2 for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed. - Highlights: • The compound is metallic with strong hybridization near the Fermi energy. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of two sheets. • The bonding features are analyzed using the electronic charge density

  4. A band Lanczos approach for calculation of vibrational coupled cluster response functions: simultaneous calculation of IR and Raman anharmonic spectra for the complex of pyridine and a silver cation.

    Science.gov (United States)

    Godtliebsen, Ian H; Christiansen, Ove

    2013-07-01

    We describe new methods for the calculation of IR and Raman spectra using vibrational response theory. Using damped linear response functions that incorporate a Lorentzian line-shape function from the outset, it is shown how the calculation of Raman spectra can be carried out through the calculation of a set of vibrational response functions in the same manner as described previously for IR spectra. The necessary set of response functions can be calculated for both vibrational coupled cluster (VCC) and vibrational configuration interaction (VCI) anharmonic vibrational wave-functions. For the efficient and simultaneous calculation of the full set of necessary response functions, a non-hermitian band Lanczos algorithm is implemented for VCC, and a hermitian band Lanczos algorithm is implemented for VCI. It is shown that the simultaneous calculation of several response functions is often advantageous. Sample calculations are presented for pyridine and the complex between pyridine and the silver cation. PMID:23609967

  5. First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb2Cl5

    International Nuclear Information System (INIS)

    Highlights: • Electronic structure of TlPb2Cl5 is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p* states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb2Cl5 is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb2Cl5 are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb2Cl5 using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb2Cl5 is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb2Cl5 is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb2Cl5 compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of a TlPb2Cl5 polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb2Cl5 surface

  6. Band structure of silicene on the zirconium diboride (0001) thin film surface - convergence of experiment and calculations in the one-Si-atom Brillouin zone

    OpenAIRE

    Lee, Chi-cheng; Fleurence, Antoine; Yamada-takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer

    2014-01-01

    So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB$_2$(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part o...

  7. Calculation of the band structure of GdCo2, GdRh2 e GdIr2 by the APW method

    International Nuclear Information System (INIS)

    The band structure of GdCo2, GdRh2, GdIr2 has been calculated by the APW method. A histogram of the density of states is presented for each compound. The bands are transition-metal-like, with s-d hybridization near the Fermi level. The 5d character near the Fermi level increases as one goes from Co to Ir

  8. Finite difference time domain method for calculating the band structure of a 2D photonic crystal and simulating the lensing effect

    International Nuclear Information System (INIS)

    A finite difference time domain method based on regular Yee's algorithm in an orthogonal coordinate system is utilized to calculate the band structure of a two-dimensional square-lattice photonic crystal comprising dielectric cylinders in air background and to simulate the image formation of mentioned structure incorporating the perfectly matched layer boundary condition. By analyzing the photonic band diagram of this system, we find that the frequency region of effective negative refraction exists in the second band in near-infrared domain. In this case, electromagnetic wave propagates with a negative phase velocity and the evanescent waves can be supported to perform higher image resolution

  9. Calculator.

    Science.gov (United States)

    Parma City School District, OH.

    Five activities are presented in this student workbook on using the electronic calculator. Following the directions for using the machine, problems are given on multiplying and dividing, finding percentages, calculating the area of assorted polygons, changing fractions to decimals, and finding squares and square roots. (JH)

  10. Extinction coefficients of CC and CC bands in ethyne and ethene molecules interacting with Cu+ and Ag+ in zeolites--IR studies and quantumchemical DFT calculations.

    Science.gov (United States)

    Kozyra, Pawe?; Góra-Marek, Kinga; Datka, Jerzy

    2015-02-01

    The values of extinction coefficients of CC and CC IR bands of ethyne and ethene interacting with Cu+ and Ag+ in zeolites were determined in quantitative IR experiments and also by quantumchemical DFT calculations with QM/MM method. Both experimental and calculated values were in very good agreement validating the reliability of calculations. The values of extinction coefficients of ethyne and ethene interacting with bare cations and cations embedded in zeolite-like clusters were calculated. The interaction of organic molecules with Cu+ and Ag+ in zeolites ZSM-5 and especially charge transfers between molecule, cation and zeolite framework was also discussed in relation to the values of extinction coefficients. PMID:25307963

  11. Extinction coefficients of Ctbnd C and Cdbnd C bands in ethyne and ethene molecules interacting with Cu+ and Ag+ in zeolites - IR studies and quantumchemical DFT calculations

    Science.gov (United States)

    Kozyra, Pawe?; Góra-Marek, Kinga; Datka, Jerzy

    2015-02-01

    The values of extinction coefficients of Ctbnd C and Cdbnd C IR bands of ethyne and ethene interacting with Cu+ and Ag+ in zeolites were determined in quantitative IR experiments and also by quantumchemical DFT calculations with QM/MM method. Both experimental and calculated values were in very good agreement validating the reliability of calculations. The values of extinction coefficients of ethyne and ethene interacting with bare cations and cations embedded in zeolite-like clusters were calculated. The interaction of organic molecules with Cu+ and Ag+ in zeolites ZSM-5 and especially charge transfers between molecule, cation and zeolite framework was also discussed in relation to the values of extinction coefficients.

  12. Uniaxial stress influence on lattice, band gap and optical properties of n-type ZnO: first-principles calculations

    International Nuclear Information System (INIS)

    The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by first-principles calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0–13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO. (condensed matter: structural, mechanical, and thermal properties)

  13. Venus' and Mars' limb radiance calculations for infrared CO2 bands taking account of local thermodynamical equilibrium breaking

    International Nuclear Information System (INIS)

    Theoretical estimates of limb total band radiance in the vibration-rotation CO2 bands are presented for the first time for both Venus and Mars' atmospheric layers with nonequilibrium population of vibrational CO2 states. The daytime vertical profiles of limb radiance have been obtained in the 1,2; 1,4; 1,6; 2,0; 2,7 and 4,7 and 4,3 ?m bands, and the nighttime ones - in the 4,3 ?m band only. The daytime profiles have a radiance maximum caused by the increase of the vibrational states population with altitude, which is due to sunshine absorption in the infrared CO2 bands. The nighttime profiles reveal an abrupt decrease in the radiance lapse rate with altitude, which is caused by the population maximum of vibrational states due to tropospheric thermal radiation absorption in the 4,3 ?m band

  14. Electronic properties of ZnWO4 based on ab initio FP-LAPW band-structure calculations and X-ray spectroscopy data

    International Nuclear Information System (INIS)

    Total and partial densities of states of the atoms constituting zinc tungstate, ZnWO4, have been calculated using the ab initio full potential linearized augmented plane wave (FP-LAPW) method. The theoretical data reveal that main contributors in the valence band of ZnWO4 are the Zn 3d-, W 5d- and O 2p-like states: the Zn 3d- and W 5d-like states contribute mainly at the bottom, whilst the O 2p-like states at the top of the valence band, with also significant portions of contributions of the above states throughout the whole valence-band region of the tungstate under study. In addition, data of our band-structure FP-LAPW calculations indicate that the conduction band of ZnWO4 is dominated by contributions of the W 5d-like states. To verify the theoretical findings, high-quality inclusion-free ZnWO4 single crystals were specially grown along the [010] direction for the present experimental studies employing the low thermal gradient Czochralski technique. It has been established that, comparison on a common energy scale of the X-ray photoelectron valence-band spectrum and the X-ray emission bands representing the energy distribution of mainly the Zn 3d-, W 5d- and O 2p-like states of ZnWO4 confirm experimentally the present FP-LAPW theoretical data regarding the occupations of the valence band of zinc tungstate. - Graphical abstract: Display Omitted - Highlights: • Total and partial densities of states of the atoms constituting ZnWO4 are calculated. • Zn 3d and W 5d states are dominant contributors at the bottom of the valence band. • Contributions of O 2p states dominate at the top of the valence band. • Bottom of the conduction band is dominated by contributions of W 5d* states. • The theoretical results are confirmed experimentally by X-ray spectroscopy data

  15. Band structure of MoS_2, MoSe_2, and alpha-MoTe_2 Angle-resolved photoelectron spectroscopy and ab-initio calculations

    CERN Document Server

    Böker, T; Müller, A; Janowitz, C; Manzke, R; Voss, D; Krüger, P; Mazur, A I; Pollmann, J; Boeker, Th.

    2001-01-01

    In this work the complete valence-band structure of the molybdenum dichalcogenides MoS_2, MoSe_2, and alpha-MoTe_2 is presented and discussed in comparison. The valence bands have been studied using both angle-resolved photoelectron spectroscopy (ARPES) with synchrotron radiation, as well as, ab-initio band-structure calculations. The ARPES measurements have been carried out in the constant-final-state (CFS) mode. The results of the calculations show in general very good agreement with the experimentally determined valence-band structures allowing for a clear identification of the observed features. The dispersion of the valence bands as a function of the perpendicular component k_perp of the wave vector reveals a decreasing three-dimensional character from MoS_2 to alpha-MoTe_2 which is attributed to an increasing interlayer distance in the three compounds. The effect of this k_perp dispersion on the determination of the exact dispersion of the individual states as a function of k_parallel is discussed. By p...

  16. Calculation of the Thermoelectric Properties of n- and p-Type Lead Telluride Using a Three-Band Model of the Electron Energy Spectrum

    Science.gov (United States)

    Dmitriev, A. V.; Tkacheva, E. S.

    2014-04-01

    In this paper, we study theoretically the thermoelectric properties of n- and p-type PbTe in the wide temperature interval of 300-900 K. A three-band model of the PbTe electron energy spectrum is used in these calculations. The full set of the relevant kinetic characteristics is calculated including the electrical and thermal conductivities, the Seebeck coefficient, and the thermoelectric figure-of-merit. The calculated thermoelectric quantities are in good agreement with the available experimental data.

  17. Experimental study and calculations of nitric oxide absorption in the ?(0,0) and ?(1,0) bands for strong temperature conditions

    International Nuclear Information System (INIS)

    Absorption spectra of nitric oxide in the ?(0,0) and ?(1,0) bands have been measured for hard temperature conditions up to 1700 K in order to validate a model for the simulation of these two bands. The good agreement between experiments and calculations (relative errors of 2-5% for the ?(0,0) band and 10-15% for the ?(1,0) band) consolidates the two important assumptions concerning the intermediate Hund's case between (a) and (b) for the X2? state of the ?(0,0) and ?(1,0) absorption bands and the use of collisional broadening parameters of ?(0,0) to simulate the ?(1,0) band. Using this simulation, a study of the Beer-Lambert law behavior at high temperature has been carried out. With the instrument resolution used for these experiments, it was shown that a correction of the Beer-Lambert law is necessary. To apply this technique for the measurements of NO concentrations inside the combustion chamber of an optical SI engine, a new formulation of the Beer-Lambert law has been introduced, since the modified form proposed in the literature is no longer applicable in the total column range of interest

  18. Experimental study and calculations of nitric oxide absorption in the {gamma}(0,0) and {gamma}(1,0) bands for strong temperature conditions

    Energy Technology Data Exchange (ETDEWEB)

    Trad, H. E-mail: houcem.trad@univ-orleans.frhttp://www.univ-orleans.fr/ESEM/LME; Higelin, P.; Djebaieli-Chaumeix, N.; Mounaim-Rousselle, C

    2005-02-01

    Absorption spectra of nitric oxide in the {gamma}(0,0) and {gamma}(1,0) bands have been measured for hard temperature conditions up to 1700 K in order to validate a model for the simulation of these two bands. The good agreement between experiments and calculations (relative errors of 2-5% for the {gamma}(0,0) band and 10-15% for the {gamma}(1,0) band) consolidates the two important assumptions concerning the intermediate Hund's case between (a) and (b) for the X{sup 2}{pi} state of the {gamma}(0,0) and {gamma}(1,0) absorption bands and the use of collisional broadening parameters of {gamma}(0,0) to simulate the {gamma}(1,0) band. Using this simulation, a study of the Beer-Lambert law behavior at high temperature has been carried out. With the instrument resolution used for these experiments, it was shown that a correction of the Beer-Lambert law is necessary. To apply this technique for the measurements of NO concentrations inside the combustion chamber of an optical SI engine, a new formulation of the Beer-Lambert law has been introduced, since the modified form proposed in the literature is no longer applicable in the total column range of interest.

  19. The Uncertainties of the Calculated Optical Basicity from the Optical Band Gap and the Refractive Index for Some Oxide Glass Systems

    OpenAIRE

    El-Sayed Mostafa

    2005-01-01

    In this study, the uncertainties of the optical basicity calculation based on the optical band gap and the refractive index for two glass systems (K2O-Nb2O5-TeO2, B2O3-Na2O-TeO2), have been estimated. The results benefits are very important in the determination of the optical basicity of binary and ternary glass systems. It has been established that as in the binary glass systems, there is a general trend of increasing the oxide ion polarizability with decreasing the oxide optical band gap an...

  20. First-principles calculation of the band gap of AlxGa1¡-xN and InxGa1¡-xN

    Directory of Open Access Journals (Sweden)

    Roberto N\\u00FA\\u00F1ez-Gonz\\u00E1lez

    2008-01-01

    Full Text Available Ab-initio calculations of the band gap variation of AlxGa1¡xN and InxGa1¡xN ternary compounds were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW method, within the Density Functional Theory (DFT. These nitrides were modeled in their wurtzite structure using the supercell method, for concentrations x = 0, 0.25, 0.50, 0.75 and 1.0. To optimize the cell parameters of the binary compounds we used the PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996 3865 exchange correlation functional. For the band structure calculations, we used both PBE96 and EV93 (Engel et al., Phys. Rev. B 47 (1993 13164 exchange correlation functionals. We considered experimental and calculated (with PBE96 lattice parameters to work out the electronic properties. We found that the fundamental gap is direct in all compounds. The calculation with EV93 functional gives a better band gap estimation for binary nitrides. The bowing parameter was also estimated obtaining the values b = 0.74 eV for AlxGa1¡xN and b = 2.12 eV for InxGa1¡xN.

  1. Dielectric-dependent screened Hartree-Fock exchange potential and Slater-formula with Coulomb-hole interaction for energy band structure calculations

    Science.gov (United States)

    Shimazaki, Tomomi; Nakajima, Takahito

    2014-09-01

    We previously reported a screened Hartree-Fock (HF) exchange potential for energy band structure calculations [T. Shimazaki and Y. Asai, J. Chem. Phys. 130, 164702 (2009); T. Shimazaki and Y. Asai, J. Chem. Phys. 132, 224105 (2010)]. In this paper, we discuss the Coulomb-hole (COH) interaction and screened Slater-formula and determine the energy band diagrams of several semiconductors, such as diamond, silicon, AlAs, AlP, GaAs, GaP, and InP, based on the screened HF exchange potential and Slater-formula with COH interaction, to demonstrate the adequacy of those theoretical concepts. The screened HF exchange potential and Slater-formula are derived from a simplified dielectric function and, therefore, include the dielectric constant in their expressions. We also present a self-consistent calculation technique to automatically determine the dielectric constant, which is incorporated into each self-consistent field step.

  2. Electronic band structure calculations on thin films of the L21 full Heusler alloys X2YSi (X, Y = Mn, Fe, and Co): Toward spintronic materials

    International Nuclear Information System (INIS)

    To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn2FeSi, Fe2MnSi, Fe2FeSi, Fe2CoSi, and Co2FeSi) with an L21 structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co2FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed. - Highlights: ? Electronic band structure calculations of L21 full Heusler alloy thin films. ? Spintronic materials. ? Electronic properties dependency on layer thickness.

  3. Dependence of band gap bowing of epitaxial InxGa1-xN on composition, strain and ordering effects by first-principles calculations

    International Nuclear Information System (INIS)

    The band gap of InxGa1-xN alloys does not only depend on the In composition, but also on the strain state and the ordering of In atoms. We performed a theoretical study to disentangle the different effects. According to our results, the band gaps of InxGa1-xN alloys show parabolic behavior in compressive regions and linear dependence in the tensile regions. We further find a universal bowing behavior in InxGa1-xN alloys for the whole In content range under constant relative strain. Inhomogeneous In distributions lead to a narrower band gap, but are energetically unfavorable. Based on the calculated results, an interpolating form for the band gap as a function of ordering, biaxial strain and chemical content for InxGa1-xN alloys is suggested. Our results provide guidance to determine the band gaps of InxGa1-xN alloys under real experiment conditions.

  4. Electronic structure and optical absorption bands of the U center in alkaline earth fluorides calculated by the SCF-MSX? method

    International Nuclear Information System (INIS)

    The self-consistent-field multiple-scattering method in the X? approximation is used to calculate the electronic structure and the optical transition energies of the U center in CaF2, SrF2 and BaF2. The very good agreement obtained between the experimental and theoretical results concerning the optical bands indicates that the scheme used is convenient to treat this type of defect

  5. Real-space finite-difference calculation method of generalized Bloch wave functions and complex band structures with reduced computational cost

    Science.gov (United States)

    Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan

    2014-07-01

    Generalized Bloch wave functions of bulk structures, which are composed of not only propagating waves but also decaying and growing evanescent waves, are known to be essential for defining the open boundary conditions in the calculations of the electronic surface states and scattering wave functions of surface and junction structures. Electronic complex band structures being derived from the generalized Bloch wave functions are also essential for studying bound states of the surface and junction structures, which do not appear in conventional band structures. We present a novel calculation method to obtain the generalized Bloch wave functions of periodic bulk structures by solving a generalized eigenvalue problem, whose dimension is drastically reduced in comparison with the conventional generalized eigenvalue problem derived by Fujimoto and Hirose [Phys. Rev. B 67, 195315 (2003)], 10.1103/PhysRevB.67.195315. The generalized eigenvalue problem derived in this work is even mathematically equivalent to the conventional one, and, thus, we reduce computational cost for solving the eigenvalue problem considerably without any approximation and losing the strictness of the formulations. To exhibit the performance of the present method, we demonstrate practical calculations of electronic complex band structures and electron transport properties of Al and Cu nanoscale systems. Moreover, employing atom-structured electrodes and jellium-approximated ones for both of the Al and Si monatomic chains, we investigate how much the electron transport properties are unphysically affected by the jellium parts.

  6. Real-space finite-difference calculation method of generalized Bloch wave functions and complex band structures with reduced computational cost.

    Science.gov (United States)

    Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan

    2014-07-01

    Generalized Bloch wave functions of bulk structures, which are composed of not only propagating waves but also decaying and growing evanescent waves, are known to be essential for defining the open boundary conditions in the calculations of the electronic surface states and scattering wave functions of surface and junction structures. Electronic complex band structures being derived from the generalized Bloch wave functions are also essential for studying bound states of the surface and junction structures, which do not appear in conventional band structures. We present a novel calculation method to obtain the generalized Bloch wave functions of periodic bulk structures by solving a generalized eigenvalue problem, whose dimension is drastically reduced in comparison with the conventional generalized eigenvalue problem derived by Fujimoto and Hirose [Phys. Rev. B 67, 195315 (2003)]. The generalized eigenvalue problem derived in this work is even mathematically equivalent to the conventional one, and, thus, we reduce computational cost for solving the eigenvalue problem considerably without any approximation and losing the strictness of the formulations. To exhibit the performance of the present method, we demonstrate practical calculations of electronic complex band structures and electron transport properties of Al and Cu nanoscale systems. Moreover, employing atom-structured electrodes and jellium-approximated ones for both of the Al and Si monatomic chains, we investigate how much the electron transport properties are unphysically affected by the jellium parts. PMID:25122409

  7. Band gap narrowing in nitrogen-doped La2Ti2O7 predicted by density-functional theory calculations.

    Science.gov (United States)

    Zhang, Junying; Dang, Wenqiang; Ao, Zhimin; Cushing, Scott K; Wu, Nianqiang

    2015-04-14

    In order to reveal the origin of enhanced photocatalytic activity of N-doped La2Ti2O7 in both the visible light and ultraviolet light regions, its electronic structure has been studied using spin-polarized conventional density functional theory (DFT) and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid approach. The results show that the deep localized states are formed in the forbidden band when nitrogen solely substitutes for oxygen. Introducing the interstitial Ti atom into the N-doped La2Ti2O7 photocatalyst still causes the formation of a localized energy state. Two nitrogen substitutions co-exist stably with one oxygen vacancy, creating a continuum energy band just above the valence band maximum. The formation of a continuum band instead of mid-gap states can extend the light absorption to the visible light region without increasing the charge recombination, explaining the enhanced visible light performance without deteriorating the ultraviolet light photocatalytic activity. PMID:25751702

  8. Rain Rate-Radar Reflectivity Relationship for Drop Size Distribution and Rain Attenuation Calculation of Ku Band Signals

    OpenAIRE

    Govardhani.Immadi; Kotamraju, Sarat K.; Habibulla Khan; Venkata Narayana, M.

    2014-01-01

    With the increased demand for long distance Tele communication day by day, satellite communication system was developed. Satellite communications utilize L, C, Ku and Ka bands of frequency to fulfil all the requirements. Utilization of higher frequencies causes severe attenuation due to rain. Rain attenuation is noticeable for frequencies above 10ghz. Amount of attenuation depends on whether the operating wave length is comparable with rain drop diameter or not. In this paper the main focus i...

  9. Measurements and calculations of ethylene line-broadening by argon in the ?7 band at room temperature

    OpenAIRE

    Nguyen, Linh; Blanquet, Ghislain; Buldyreva, Jeanna; Lepe?re, Muriel

    2008-01-01

    Abstract Argon broadening coefficients are measured for 32 vibrotational lines in the ?7 band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3? J ? 19, 0? Ka ? 4, 2 ? Kc ? 19 in the P, Q and R branches are located in the spectral range 919-1023 cm-1. The fitting of experimental line shapes with Rautian profile provides the collisional widths slightly larger than those derived from Voigt profile. The in...

  10. Calculation of band offsets in Cd1-xXxTe alloys, X = Zn, Mg, Hg and Mn and magnetic effects in CdMnTe

    International Nuclear Information System (INIS)

    Highlights: ? The conduction and valence band offsets of the pseudo-morphically strained Cd1-xXxTe layer on relaxed Cd1-yXyTe substrate, are investigated for X = Zn, Mg, Hg and Mn in the entire range 0 ? x,y ? 1. ? For Cd1-xMnxTe diluted magnetic semiconductors, the exchange interactions are determined in the order to take into account magnetic effect. ? The conduction and valence band offsets of Cd1-xMnxTe/CdTe interface are calculated in the whole range of Mn composition x and for magnetic field values equal to 0 and 5 T. - Abstract: Due to the large variety of properties offered by the telluride binaries CdTe, ZnTe, MgTe, HgTe and MnTe as well as their mixed ternary alloys, an accurate knowledge of their electronic band parameters is crucial. These materials have been extensively studied but, some points bearing on several properties have never previously reported or are still not clear. In this paper, we report results on the conduction and valence band offsets of the pseudo-morphically strained Cd1-xXxTe layer on relaxed Cd1-yXyTe substrate, X = Zn, Hg, Mg and Mn. Based on the Van Der Walle model, calculations have been performed for the all range of material and substrate 0 ? x,y ? 1. These discontinuities have not yet calculated for X = Mg, Mn or Hg in the all range 0 ? x,y ? 1. For the CdMnTe diluted magnetic semnTe diluted magnetic semiconductor which we focus more interest due to its considerable current interest for applications, calculations have been done without and with correction taking into account magnetic effect of magnesium ions Mn2+. It is found that the introduction of only a few percent of Mn into CdTe provides a unique opportunity to combine two important fields in physics, semiconductivity and magnetism. We can take advantage both of possibility of applications in solid-state lasers and exceptional magnetic properties offered by this magnetic diluted semiconductor. This study presents important quantities that are required to model quantum structures and offers a fast and inexpensive way to check device designs and processes.

  11. Tunneling calculations for GaAs-Al(x)Ga(1-x)As graded band-gap sawtooth superlattices

    Science.gov (United States)

    Forrest, Kathrine; Meijer, Paul H. E.

    1990-01-01

    The transmission resonance spectra and tunneling current-voltage characteristics for direct conduction band electrons in sawtooth GaAs-Al(x)Ga(1-x)As superlattices are computed. Only direct-gap interfaces are considered. It is found that sawtooth superlattices exhibit resonant tunneling similar to that in step superlattices, manifested by correlation of peaks and regions of negative differential resistance in the current-voltage curves with transmission resonances. The Stark shift of the resonances of step-barrier superlattices is a linear function of the field, whereas in sawtooth superlattices under strong fields the shift is not a simple function of the field. This follows from the different ways in which the two structures deform under uniform electric fields: the sawtooth deforms into a staircase, at which field strength all barriers to tunneling are eradicated. The step-barrier superlattice always presents some barrier to tunneling, no matter how high the electric field strength.

  12. Rain Rate-Radar Reflectivity Relationship for Drop Size Distribution and Rain Attenuation Calculation of Ku Band Signals

    Directory of Open Access Journals (Sweden)

    Govardhani.Immadi

    2014-05-01

    Full Text Available With the increased demand for long distance Tele communication day by day, satellite communication system was developed. Satellite communications utilize L, C, Ku and Ka bands of frequency to fulfil all the requirements. Utilization of higher frequencies causes severe attenuation due to rain. Rain attenuation is noticeable for frequencies above 10ghz. Amount of attenuation depends on whether the operating wave length is comparable with rain drop diameter or not. In this paper the main focus is on drop size distribution using empirical methods, especially Marshall and Palmer distributions. Empirical methods deal with power law relation between the rain rate(mm/h and radar reflectivity(dBz. Finally it is discussed about the rain rate variation, radar reflectivity, drop size distribution, that is made for two rain events at K L University, Vijayawada on 4th September 2013 and on 18 th August 2013.

  13. On the importance of constrained atomic relaxations in the Nudged Elastic Band calculations of the Peierls barriers of dislocations

    CERN Document Server

    Gröger, R

    2011-01-01

    We demonstrate that the straightforward application of the Nudged Elastic Band (NEB) method does not determine the correct Peierls barrier of 1/2 screw dislocations in BCC metals. Although this method guarantees that the states (images) of the system are distributed uniformly along the minimum energy path, it does not imply that the dislocation positions are distributed uniformly along this path. In fact, clustering of dislocation positions near potential minima occurs which leads to an overestimate of both the slope of the Peierls barrier and the Peierls stress. We propose a modification in which the NEB method is applied only to a small number of degrees of freedom that determine the position of the dislocation, while all other coordinates of atoms are relaxed by molecular statics as in any atomistic study. This modified NEB method with relaxations gives the Peierls barrier that increases smoothly with the dislocation position and the corresponding Peierls stress agrees well with that evaluated by the direc...

  14. Calculated band structures and optical properties of lead chalcogenides PbX (X=S, Se, Te) under hydrostatic pressure

    Energy Technology Data Exchange (ETDEWEB)

    Rached, D.; Rabah, M.; Benkhettou, N.; Driz, M.; Soudini, B

    2003-09-01

    The hydrostatic pressure dependence of the principal energy gaps and of the optical properties of PbX (X=S, Se, and Te) has been calculated with the use of the self-consistent full-potential linear muffin-tin orbital method. The local density approximation and density functional theory are applied. Structural properties such as the equilibrium lattice constants, the bulk modulus, and its pressure derivatives were calculated for lead chalcogenides in the rock salt structure (NaCl). We have found that the results of the structural properties calculations are in agreement with those of ab initio and experimental data. In the rock salt structure, the pressure dependence of the energy gaps of these compounds is overestimated compared to the available experimental data. However, for the same structure, the comparison of our results with those of ab initio calculations shows good agreement. On the other hand, the effect of the applied pressure is clearly seen in the optical response spectrum, especially near the energy transition regions.

  15. Calculated band structures and optical properties of lead chalcogenides PbX (X=S, Se, Te) under hydrostatic pressure

    International Nuclear Information System (INIS)

    The hydrostatic pressure dependence of the principal energy gaps and of the optical properties of PbX (X=S, Se, and Te) has been calculated with the use of the self-consistent full-potential linear muffin-tin orbital method. The local density approximation and density functional theory are applied. Structural properties such as the equilibrium lattice constants, the bulk modulus, and its pressure derivatives were calculated for lead chalcogenides in the rock salt structure (NaCl). We have found that the results of the structural properties calculations are in agreement with those of ab initio and experimental data. In the rock salt structure, the pressure dependence of the energy gaps of these compounds is overestimated compared to the available experimental data. However, for the same structure, the comparison of our results with those of ab initio calculations shows good agreement. On the other hand, the effect of the applied pressure is clearly seen in the optical response spectrum, especially near the energy transition regions

  16. A modified band approach for the accurate calculation of on-line photolysis rates in stratospheric-tropospheric Chemical Transport Models

    Directory of Open Access Journals (Sweden)

    J. E. Williams

    2006-05-01

    Full Text Available Here we present an efficient and accurate method for the online calculation of photolysis rates relevant to both the stratosphere and troposphere for use in global Chemistry Transport Models. The method is a modified version of the band model introduced by Landgraf and Crutzen (1998 which has been updated to improve the performance of the approach for solar zenith angles >75° without the use of any implicit parameterisations. For this purpose, additional sets of band parameters have been defined for instances where the incident angle of the light beam is between 75–93°, in conjunction with a scaling component for the far UV region of the spectrum (?=176.6–202.0 nm. For incident angles between 85–93° we introduce a modification for pseudo-sphericity that improves the accuracy of the 2-stream approximation. We show that this modified version of PIFM is accurate for angles <93° by comparing the resulting height resolved actinic fluxes with a recently developed full spherical reference model. We also show that the modified band method is more accurate than the original, with errors generally being ±10% throughout the atmospheric column for a diverse range of chemical species. Moreover, we perform certain sensitivity studies that indicate it is robust and performs well over a wide range of conditions relevant to the atmosphere.

  17. Penetration of solar irradiance in the Schumann-Runge bands of O2 - A comparison of balloon-borne measurements and calculations

    Science.gov (United States)

    Frederick, J. E.; Hudson, R. D.; Mentall, J. E.

    Measurements of the attenuated solar irradiance made from the STRATCOM VIII balloon are compared with calculated values of the solar irradiance reaching the 40 km level for a solar zenith angle of 66.18 deg. The ability of theory to match intensity maxima which correspond to the cross section minima between the bands is investigated. The comparisons show that model results are too small by a factor of 1.8 between 199 and 22 nm, which is attributed to a systematic calibration offset between the balloon data and the irradiances of Bruckner et al. (1976). A large disagreement between the observed and calculated intensities at peaks H and I results from an error in the cross sections used in current aeronomic work.

  18. The density of states and band gap of liquid water by sequential Monte Carlo/Quantum mechanics calculations

    Scientific Electronic Library Online (English)

    P. Cabral do, Couto; R. C., Guedes; B. J. Costa, Cabral.

    2004-03-01

    Full Text Available SciELO Brazil | Language: English Abstract in english Electronic properties of liquid water were investigated by sequential Monte Carlo/Quantum mechanics calculations. The density of states (DOS) and HOMO-LUMO gap (E G) of liquid water have been determined by Hartree-Fock and Density Functional Theory (DFT) calculations. The quantum mechanical calculat [...] ions were carried out over uncorrelated supermolecular structures generated by the Monte Carlo simulations. The DFT calculations were performed with a modified B3LYP exchange-correlation functional proposed by Abu-Awwad and Politzer which was parametrized to reproduce valence orbital energies in agreement with experimental ionization potentials of the water molecule. We have analyzed the dependence of the DOS and HOMO-LUMO gap on the number of water molecules and on surface effects. Our prediction for E G is 6:5 ± 0:5 eV in good agreement with a recent experimental prediction of 6.9 eV.

  19. Band structure of silicene on zirconium diboride (0001) thin-film surface: Convergence of experiment and calculations in the one-Si-atom Brillouin zone

    Science.gov (United States)

    Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer

    2014-08-01

    So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB2(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle Green's function follows the spectral weight observed in ARPES spectra. By additionally varying the in-plane lattice constant, the results of density functional theory calculations and ARPES data obtained in a wide energy range converge into the "planarlike" phase and provide the orbital character of electronic states in the vicinity of the Fermi level. It is anticipated that the choice of a smaller commensurate unit cell for the representation of the electronic structure will be useful for the study of epitaxial two-dimensional materials on various substrates in general.

  20. Synthesis and photonic band calculations of NCP face-centered cubic photonic crystals of TiO2 hollow spheres.

    Science.gov (United States)

    Zhu, Yong-zheng; Cao, Yan-ling; Li, Zhi-hui; Ding, Juan; Liu, Jun-song; Chi, Yuan-bin

    2007-02-01

    With the help of self-assembly, thermal sintering, selective etching techniques and sol-gel process, the non-close packed (ncp) face-centered cubic (fcc) photonic crystals of titanium dioxide (TiO2) hollow spheres connected by TiO2 cylindrical tubes have been fabricated using silica template. The photonic bandgap calculations indicate that the ncp structure of TiO2 hollow spheres was easier to open the pseudogaps than close packed system at the lowest energy. PMID:17097102

  1. Electric field gradients, isomer shifts and hyperfine fields from band structure calculations in NiI2

    International Nuclear Information System (INIS)

    NiI2 undergoes an isostructural phase transition under pressure from an insulating antiferromagnetic state to a metallic but nonmagnetic state. We investigate this transition with the full-potential linearized augmented plane wave (LAPW) method within the density functional theory using the generalized gradient approximation (GGA), which provides an improved description of exchange and correlation effects. Once the electron density is calculated self-consistently with high accuracy, quantities such as electric field gradients, isomer shifts or hyperfine fields can easily be obtained from that density. Using this approach we study the change of the iodine hyperfine parameters during the pressure induced metallization of NiI2. In general, good agreement between theory and experiment is found, and insight is gained by an analysis of the theoretical data indicating the physical origin of the measured quantities. (orig.)

  2. Combining GW calculations with exact-exchange density-functional theory: An analysis of valence-band photoemission for compound semiconductors

    CERN Document Server

    Rinke, P; Neugebauer, J; Freysoldt, C; Scheffler, M; Rinke, Patrick; Qteish, Abdallah; Neugebauer, Joerg; Freysoldt, Christoph; Scheffler, Matthias

    2005-01-01

    We report quasiparticle-energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group-III-nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridisation compared to t...

  3. Phonon anharmonicity of phonon band gap effect of scheelite PbWO4 studied by Raman spectrometry and first-principles calculations

    Science.gov (United States)

    Suda, Jun; Kamishima, Osamu; Kawamura, Jun-ichi; Hattori, Takeshi; Omiya, Manabu

    2014-08-01

    The phonon-dispersions of PbWO4 crystal are calculated using the first-principles calculations. Polarized Raman spectra in the PbWO4 were measured in the temperature range from 4 K to 280 K, and the temperature dependence of the linewidth of the Eg (193 cm-1) and Ag (906 cm-1) Raman modes was analyzed using both the first-principles calculations and lattice perturbative approach. We found that the different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the PDOS (one-phonon density of states) resulting in different anharmonic interactions. The ratio of up-conversion TDOS (temperature-weighted two-phonon density of states) to down-conversion TDOS for Eg mode (193 cm-1) is more than that for Ag (906 cm-1). Therefore, the linewidths for the Eg mode (193 cm-1) may be varied with increasing temperature by comparison with those of the Ag (906 cm-1).

  4. Density-functional band-structure calculations for La-, Y-, and Sc-filled CoP3-based skutterudite structures

    International Nuclear Information System (INIS)

    The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P3 skutterudite structures are promising materials for thermoelectric applications

  5. Consideration of the band-gap tunability of BaSi2 by alloying with Ca or Sr based on the electronic structure calculations

    International Nuclear Information System (INIS)

    The electronic structures and total energies of BaSi2-SrSi2 and BaSi2-CaSi2 systems have been calculated using the first-principle pseudopotential method to clarify the band gap tunability of BaSi2 by alloying with Sr or Ca. From an energetic consideration of the compounds where all the BaI sites or all the BaII sites of the BaSi2 lattice are preferentially replaced by Sr or Ca, it is expected that the BaI site will be preferentially replaced by Sr rather than the BaII sites. Compounds where all the BaII sites are replaced by Sr or all the BaII or all the BaI sites are replaced by Ca are energetically unfavorable compared to the undissolved system of BaSi2 and SrSi2 or CaSi2. The effect of the addition of Sr or Ca into the BaSi2 lattice on the gap value is different depending on the replaced sites of Ba. The replacement of BaI site by Sr will broaden the band gap of BaSi2, which is consistent with the observed results

  6. Spectra calculations in central and wing regions of CO2 IR bands between 10 and 20 ?m. II. Atmospheric solar occultation spectra

    International Nuclear Information System (INIS)

    The theoretical approach based on the Energy Corrected Sudden Approximation presented in the previous companion paper is used in order to account for line-mixing effects in infrared bands of CO2. Its performance, which was demonstrated using laboratory spectra is confirmed here by considering atmospheric transmission in the 10-14 ?m region. Comparisons are made between forward calculations of atmospheric transmission spectra and values measured using two different solar occultation experiments based on high resolution Fourier transform instruments. The results demonstrate that neglecting line-mixing and using a Voigt model can lead to a very large overestimation of absorption that may extend over more than 300 cm-1 in the wing of the CO2 ?2 band. They also demonstrate the capability of our model to represent accurately the absorption in the entire region for a variety of atmospheric paths. Among positive consequences of the quality of the model, the possibility of retrieving amounts of (heavy) trace gases with weak and broad absorption features is demonstrated

  7. Valence band electronic structure of Nd1?xYxMnO3 using X-ray absorption, photoemission and GGA + U calculations

    International Nuclear Information System (INIS)

    Highlights: •Decrease in the occupancy of Mn 3d orbitals with doping. •Greater splitting of the eg orbitals due to the increased Jahn–Teller distortion with doping. •Decrease in O 2p–Mn 3d charge transfer character with doping. •Increase in charge transfer energy and band gap with doping. •Calculations hint a subtle change from a charge transfer to Mott–Hubbard type insulator with doping. -- Abstract: The electronic structures of Nd1?xYxMnO3 (x = 0–0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L3,2- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L3,2-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn–Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x = 0.5 composition with respect to x = 0 suggest a subtle change from a charge transfer to Mott

  8. Intermetallic solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3}: Synthesis, structure, NQR study and electronic band structure calculations

    Energy Technology Data Exchange (ETDEWEB)

    Verchenko, V.Yu.; Likhanov, M.S.; Kirsanova, M.A. [Department of Chemistry, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Gippius, A.A; Tkachev, A.V.; Gervits, N.E. [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); A.V. Shubnikov Institute of Crystallography, Moscow 119333 (Russian Federation); Galeeva, A.V. [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Buettgen, N.; Kraetschmer, W. [Institut fuer Physik, University of Augsburg, Augsburg D-86135 (Germany); Lue, C.S. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Okhotnikov, K.S. [Materials and Environmental Chemistry, Stockholm University, Stockholm (Sweden); Shevelkov, A.V., E-mail: shev@inorg.chem.msu.ru [Department of Chemistry, Lomonosov Moscow State University, Moscow 119991 (Russian Federation)

    2012-10-15

    Unlimited solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3} was prepared from Ga flux. Its crystal structure was refined for Fe{sub 0.5}Co{sub 0.5}Ga{sub 3} (P4{sub 2}/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and {sup 69,71}Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe-Fe and Co-Co dumbbells are preferred to the Fe-Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin-lattice relaxation shows that the rate of the relaxation, 1/T{sub 1}, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N{sup 2}(E{sub F}). - Graphical abstract: Rate of the nuclear spin-lattice relaxation, 1/T{sub 1}, observed in the {sup 69}Ga NQR experiments for the intermetallic solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3} is the highest for x=0.25 with the highest calculated density of electronic states at the Fermi level, N(E{sub F}); in general, 1/T{sub 1} correlates with N{sup 2}(E{sub F}). Highlights: Black-Right-Pointing-Pointer Fe{sub 1-x}Co{sub x}Ga{sub 3} solid solution is prepared in single crystalline form from Ga flux. Black-Right-Pointing-Pointer In the crystal structure Fe-Fe and Co-Co dumbbells are preferred to Fe-Co dumbbells. Black-Right-Pointing-Pointer Metal-to-semiconductor transition occurs at 0

  9. Q-Band single-crystal EPR study and molecular orbital calculations of [(C 6H 5) 4As][Re VINCl 4/Re VOCl 4

    Science.gov (United States)

    Voigt, A.; Abram, U.; Böttcher, R.; Richter, U.; Reinhold, J.; Kirmse, R.

    2000-03-01

    A Q-band single-crystal EPR study of tetraphenylarsoniumtetrachloro-nitridorhenate(VI), [(C 6H 5) 4As][Re VINCl 4], diamagnetically diluted by the isoelectronic oxorhenate(V) complex is reported. The EPR spectra are typical of an ion with 5d 1 ( S=1/2) configuration and are influenced by large rhenium hyperfine coupling constants and nuclear quadrupole interactions. They are characterized by well-resolved 185,187Re hyperfine patterns with almost equal spacings and the occurrence of "forbidden" transitions ( ?mI=±1, ?mI=±2). The 185,187Re hyperfine parameters as well as the data obtained from density functional theory (DFT) and the extended Hückel theory (EHT) molecular orbital calculations are used to analyze the spin density distribution in the system under study. Thereby, the negative sign found for the spin density at the nitrogen from DFT is mainly determined by spin polarization. In addition, both MO methods are used to calculate the electric field gradient being responsible for the 185,187Re nuclear quadrupole coupling.

  10. Optimization of the Jastrow factor using the random-phase approximation and a similarity-transformed Hamiltonian: Application to band-structure calculation for some semiconductors and insulators

    Energy Technology Data Exchange (ETDEWEB)

    Ochi, Masayuki, E-mail: ochi@cms.phys.s.u-tokyo.ac.jp [Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Sodeyama, Keitaro [Elements Strategy Initiative for Catalysis and Batteries, Kyoto University, Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245 (Japan); WPI International Center for Materials Nanoarchitectonics, National Institute for Material Science, Tsukuba, Ibaraki 305-0044 (Japan); Tsuneyuki, Shinji [Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Institute for Solid State Physics, Kashiwa, Chiba 277-8581 (Japan)

    2014-02-21

    Based on the random-phase approximation and the transcorrelated (TC) method, we optimize the Jastrow factor together with one-electron orbitals in the Slater determinant in the correlated wave function with a new scheme for periodic systems. The TC method is one of the promising wave function theories for first-principles electronic structure calculation, where the many-body wave function is approximated as a product of a Slater determinant and a Jastrow factor, and the Hamiltonian is similarity-transformed by the Jastrow factor. Using this similarity-transformed Hamiltonian, we can optimize the one-electron orbitals without evaluating 3N-dimensional integrations for the N-electron system. In contrast, optimization of the Jastrow factor within the framework of the TC method is computationally much more expensive and has not been performed for solid-state calculations before. In this study, we also benefit from the similarity-transformation in optimizing the Jastrow factor. Our optimization scheme is tested in applications to some solids from narrow-gap semiconductors to wide-gap insulators, and it is verified that the band gap of a wide-gap insulator and the lattice constants of some solids are improved by this optimization with reasonable computational cost.

  11. Optimization of the Jastrow factor using the random-phase approximation and a similarity-transformed Hamiltonian: Application to band-structure calculation for some semiconductors and insulators

    International Nuclear Information System (INIS)

    Based on the random-phase approximation and the transcorrelated (TC) method, we optimize the Jastrow factor together with one-electron orbitals in the Slater determinant in the correlated wave function with a new scheme for periodic systems. The TC method is one of the promising wave function theories for first-principles electronic structure calculation, where the many-body wave function is approximated as a product of a Slater determinant and a Jastrow factor, and the Hamiltonian is similarity-transformed by the Jastrow factor. Using this similarity-transformed Hamiltonian, we can optimize the one-electron orbitals without evaluating 3N-dimensional integrations for the N-electron system. In contrast, optimization of the Jastrow factor within the framework of the TC method is computationally much more expensive and has not been performed for solid-state calculations before. In this study, we also benefit from the similarity-transformation in optimizing the Jastrow factor. Our optimization scheme is tested in applications to some solids from narrow-gap semiconductors to wide-gap insulators, and it is verified that the band gap of a wide-gap insulator and the lattice constants of some solids are improved by this optimization with reasonable computational cost

  12. First-principles calculation of the band gap of Al xGa1-xN and In xGa1-x N

    Scientific Electronic Library Online (English)

    Roberto, Núñez-González; Armando, Reyes-Serrato; Alvaro, Posada-Amarillas; Donald H, Galván.

    2008-11-01

    Full Text Available SciELO Mexico | Language: English Abstract in spanish En este trabajo se realizaron cálculos de primeros principios de la variación del ancho de banda prohibido en los compuestos ternarios Al xGa1-xN e In xGa1-x N, utilizando el Método Linealizado de Ondas Planas Aumentadas con Potencial Completo (FLAPW), dentro del marco de la Teoría del Funcional de [...] la Densidad (DFT). Los nitruros fueron modelados en una estructura tipo wurzita utilizando el método de supercelda, y considerando las concentraciones x = 0, 0.25, 0.50, 0.75 y 1.0. Para la optimización de los parámetros de red se utilizó el potencial de correlación-intercambio PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996) 3865). Para el cálculo de la estructura de bandas de energía se utilizaron los funcionales PBE96 y EV93 (Engel et al., Phys. Rev. B 47 (1993) 13164). Se consideraron parámetros de red experimentales y calculados (con PBE96) para los cálculos de las propiedades electrónicas. Nuestros cálculos indican que la banda prohibida fundamental es directa en estos compuestos. Los cálculos con el funcional EV93 dan como resultado una mejor estimación de los anchos de las bandas prohibidas de los compuestos binarios. Calculamos el parámetro de curvatura, obteniendo los valores b = 0.74 eV para Al xGa1-xN y b = 2.12 eV para In xGa1-x N. Abstract in english Ab-initio calculations of the band gap variation of Al xGa1-xN and In xGa1-x N ternary compounds were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method, within the Density Functional Theory (DFT). These nitrides were modeled in their wurtzite structure using the su [...] percell method, for concentrations x = 0, 0.25, 0.50, 0.75 and 1.0. To optimize the cell parameters of the binary compounds we used the PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996) 3865) exchange-correlation functional. For the band structure calculations, we used both PBE96 and EV93 (Engel et al., Phys. Rev. B 47 (1993) 13164) exchange-correlation functionals. We considered experimental and calculated (with PBE96) lattice parameters to work out the electronic properties. We found that the fundamental gap is direct in all compounds. The calculation with EV93 functional gives a better band gap estimation for binary nitrides. The bowing parameter was also estimated obtaining the values b = 0.74 eV for Al xGa1-xN and b = 2.12 eV for In xGa1-x N.

  13. Photodissociation of water. II. Wave packet calculations for the photofragmentation of H2O and D2O in the B˜ band

    Science.gov (United States)

    van Harrevelt, Rob; van Hemert, Marc C.

    2000-04-01

    A complete three-dimensional quantum mechanical description of the photodissociation of water in the B˜ band, starting from its rotational ground state, is presented. In order to include B˜-X˜ vibronic coupling and the B˜-Ã Renner-Teller coupling, diabatic electronic states have been constructed from adiabatic electronic states and matrix elements of the electronic angular momentum operators, following the procedure developed by A. J. Dobbyn and P. J. Knowles [Mol. Phys. 91, 1107 (1997)], using the ab initio results discussed in the preceding paper. The dynamics is studied using wave packet methods, and the evolution of the time-dependent wave function is discussed in detail. Results for the H2O and D2O absorption spectra, OH(A)/OH(X) and OD(A)/OD(X) branching ratios, and rovibrational distributions of the OH and OD fragments are presented and compared with available experimental data. The present theoretical results agree at least qualitatively with the experiments. The calculations show that the absorption spectrum and the product state distributions are strongly influenced by long-lived resonances on the adiabatic B˜ state. It is also shown that molecular rotation plays an important role in the photofragmentation process, due to both the Renner-Teller B˜-X˜ mixing, and the strong effect of out-of-plane molecular rotations (K>0) on the dynamics at near linear HOH and HHO geometries.

  14. Measurements and Theoretical Calculations of N2-broadening and N2-shift Coefficients in the v2 band of CH3D

    Science.gov (United States)

    Predoi-Cross, A.; Hambrook, Kyle; Brawley-Tremblay, Marco; Bouanich, J. P.; Smith, Mary Ann H.

    2006-01-01

    In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the v2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm(exp -1) resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH3D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N2 pressure- broadening coefficients of 368 v2 transitions with quantum numbers as high as J"= 20 and K = 16, where K" = K' equivalent to K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported N2-induced pressure-shift coefficients vary from about 0.0003 to 0.0094 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J", and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J", J", and J" + 1 in the (sup Q)P-, (sup Q)Q-, and (sup Q)R-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressureshift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N2-pressure shifts whose vibrational contribution is derived from parameters fitted in the (sup Q)Q-branch of self-induced shifts of CH3D, are also in reasonable agreement with the scattered experimental data (20% in most cases).

  15. Semiclassical calculations of half-widths and line shifts for transitions in the 30012?00001 and 30013?00001 bands of CO2 II: Collisions with O2 and air

    International Nuclear Information System (INIS)

    The complex Robert-Bonamy (CRB) formalism was used to calculate the half-width, its temperature dependence, and the line shift for CO2 for transitions in the 30012?00001 and 30013?00001 bands with O2 as the perturbing gas. The calculations were done for rotational quantum numbers from J=0 to J=120 with no ad hoc scaling of the line shape equations. The intermolecular potential parameters are adjusted on accurate experimental measurements of the half-widths, its temperature dependence, and the pressure-induced line shifts so that a single intermolecular potential reproduces all three parameters. Using the results of this work and previous results for N2-broadening, air-broadening line shape parameters were also determined. The comparison of the CRB calculations with the experimental data available in the literature for the three line shape coefficients demonstrates the quality of the present calculations for the both bands under study.

  16. Band Calculations for Ce Compounds with AuCu$_{3}$-type Crystal Structure on the basis of Dynamical Mean Field Theory I. CePd$_{3}$ and CeRh$_{3}$

    OpenAIRE

    Sakai, Osamu

    2010-01-01

    Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem was solved by a method named NCA$f^{2}$vc (noncrossing approximation including the $f^{2}$ state as a vertex correction). The calculations take into account the crystal-field splitting, the spin-orbit interaction, and the correct exchange process of the $f^{1} \\rightarrow f^{0},f^{2}$ virtual excitat...

  17. The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

    Science.gov (United States)

    Rubio-Lago, L.; García-Vela, A.; Arregui, A.; Amaral, G. A.; Bañares, L.

    2009-11-01

    The photodissociation of methyl iodide at different wavelengths in the red edge of the A-band (286-333 nm) has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the methyl fragment in the vibrational ground state (? =0). The kinetic energy distributions (KED) of the produced CH3(? =0) fragments show a vibrational structure, both in the I(P23/2) and I?(P21/2) channels, due to the contribution to the overall process of initial vibrational excitation in the ?3(C-I) mode of the parent CH3I. The structures observed in the KEDs shift toward upper vibrational excited levels of CH3I when the photolysis wavelength is increased. The I(P23/2)/I?(P21/2) branching ratios, photofragment anisotropies, and the contribution of vibrational excitation of the parent CH3I are explained in terms of the contribution of the three excited surfaces involved in the photodissociation process, Q30, Q11, and Q31, as well as the probability of nonadiabatic curve crossing Q11?Q30. The experimental results are compared with multisurface wave packet calculations carried out using the available ab initio potential energy surfaces, transition moments, and nonadiabatic couplings, employing a reduced dimensionality (pseudotriatomic) model. A general qualitative good agreement has been found between theory and experiment, the most important discrepancies being in the I(P23/2)/[I(P23/2)+I?(P21/2)] branching ratios. Inaccuracies of the available potential energy surfaces are the main reason for the discrepancies.

  18. Calculation of equilibria at elevated temperatures using the MINTEQ geochemical code

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R.W.

    1988-12-01

    Coefficients and equations for calculating mineral hydrolysis constants, solubility products and formation constants for 60 minerals and 57 aqueous species in the 13 component thermodynamic system K/sub 2/O-Na/sub 2/O-CaO-MgO-FeO-Al/sub 2/O/sub 3/-SiO/sub 2/-CO/sub 2/-H/sub 2/O-HF-HCl-H/sub 2/S-H/sub 2/SO/sub 4/ are presented in a format suitable for inclusion in the MINTEQ computer code. The temperature functions presented for minerals are based on the MINTEQ data base at 25/degree/C and the integration of analytical heat capacity power functions. This approach ensures that the temperature functions join smoothly with the low-temperature data base. A new subroutine, DEBYE, was added to MINTEQ that is used to calculate the theoretical Debye-Hueckel parameters A and B as a function of temperature. In addition, this subroutine also calculates a universal value of the extended Debye-Hueckel parameter, b/sub i/, as a function of temperature. The coefficients and equations provide the capability to use MINTEQ to more accurately calculate water/rock equilibrium for temperatures of up to 250/degree/C, and in dilute, low-sulfate, near neutral groundwaters to 300/degree/C. 52 refs., 1 fig., 6 tabs.

  19. Magnetic rotation (MR) band crossing in N=78 odd-Z nuclei: Tilted axis cranking (TAC) calculations to explore the role of nucleons

    International Nuclear Information System (INIS)

    Magnetic Rotation (MR) band crossing is studied systematically in N=78 isotones (La, Pr, Pm and Eu) using Tilted Axis Cranking (TAC) model. The observables such as I(¯h) vs ¯h?, excitation energy E(MeV) vs spin I(¯h), and the B(M1)/B(E2) vs I(¯h) were considered to pinpoint MR crossing in these nuclei. The results of tilted axis cranking were compared with these experimental observables. The B(M1) and B(E2) values were also reported and used to understand the crossing behaviour of these MR bands. The systematic evolution of this phenomenon in N=78 odd-Z istotones leads to understand the role of nucleons in MR band crossing

  20. Ultrawide Band Electromagnetic Pulses

    International Science & Technology Center (ISTC)

    Development of New Calculation-Theoretical and Metrologic Approaches in Technology of Ultrawide Band Electromagnetic Pulses, Elaboration and Investigation of Standard Field-Forming Systems of Subnanosecond Pulse Field

  1. The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

    OpenAIRE

    Rubio Lago, L.; Garci?a Vela, Alberto; Arregui, A.; Amaral, G. A.; Ban?ares, Luis

    2009-01-01

    The photodissociation of methyl iodide at different wavelengths in the red edge of the A-band (286–333 nm) has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the methyl fragment in the vibrational ground state (=0). The kinetic energy distributions (KED) of the produced CH3(=0) fragments show a vibrational structure, both in the I(2P3/2) and I*(2P1/2) channels, due to the contribution to the overall process of initial vibrational...

  2. Real-structure effects: Band gaps of Mg_xZn_{1-x}O, Cd_xZn_{1-x}O, and n-type ZnO from ab-initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Schleife, A; Bechstedt, F

    2012-02-15

    Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical-absorption spectra (including excitonic effects) for several transparent conducting oxides. We discuss HSE+G{sub 0}W{sub 0} results for band structures, fundamental band gaps, and effective electron masses of MgO, ZnO, CdO, SnO{sub 2}, SnO, In{sub 2}O{sub 3}, and SiO{sub 2}. The Bethe-Salpeter equation is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE+G{sub 0}W{sub 0} approach and the solution of the Bethe-Salpeter equation are very well-suited to describe the electronic structure and the optical properties of various transparent conducting oxides in good agreement with experiment.

  3. Resolution of near-infrared spectral data from distillation of binary mixtures and calculation of band boundaries of feasible solutions for species profiles

    Energy Technology Data Exchange (ETDEWEB)

    Kompany-Zareh, Mohsen; Vasighi, Mahdi (Institute for Advanced Studies in Basic Sciences, Zanjan - Iran)

    2008-02-15

    In this work, mean centering, ordinary and incomplete rank annihilation based methods were applied to estimate concentration profiles (g/mL) and pure spectra of components from an evolutionary near infrared spectral data for successive condensates from distillation process of binary mixtures. Constraints such as non-negativity, selectivity of some spectral regions and density of condensates were applied during the resolution of some series of data. Fixed size moving window evolving factor analysis (FSMWEFA) and orthogonal projection analysis (OPA) were the applied chemometrics methods for assigning the selective regions. No pure spectrum from any of components or calibration samples was necessary for performing the analysis. Three binary mixtures containing toluene:n-hexane, toluene:cyclohexene and toluene:ethanol were investigated using the proposed method. Band boundaries of feasible solutions for pure absorption spectra and species concentration profiles for the mixture of components were successfully estimated in presence of high spectral overlap. In the first case the solution was unique, but in the second and third distillations a number of acceptable solutions were obtained as band boundaries. (author)

  4. Spectra calculations in central and wing regions of CO2 IR bands between 10 and 20 ?m. III: atmospheric emission spectra

    International Nuclear Information System (INIS)

    A theoretical model for the prediction of CO2 absorption in both central and wing regions of infrared absorption bands was presented in the companion paper I. It correctly accounts for line-mixing effects and was validated by comparisons with laboratory spectra in the 600-1000 cm-1 region. This quality was confirmed using atmospheric transmissions measured by solar occultation experiments in the second paper. The present work completes these studies by now considering atmospheric emission in the 10-20 ?m range. Comparisons are made between computed atmospheric radiances and measurements obtained using four different Fourier transform experiments collecting spectra for nadir, up-looking, as well as limb (from balloon and satellite) geometries. Our results confirm that using a Voigt model can lead to very large errors that affect the spectrum more than 300 cm-1 away from the center of the CO2 ?2 band. They also demonstrate the capability of our model to represent accurately the radiances in the entire region for a variety of atmospheric paths. This success opens interesting perspectives for the sounding of pressure and temperature profiles, particularly at low altitudes. Another benefit of the quality of the model should be an increased accuracy in the retrieval of atmospheric state parameters from broad features in the measured spectra (clouds, aerosols, heavy trace gases)

  5. Calculation of band offsets in Cd{sub 1-x}X{sub x}Te alloys, X = Zn, Mg, Hg and Mn and magnetic effects in CdMnTe

    Energy Technology Data Exchange (ETDEWEB)

    Abdi-Ben Nasrallah, S., E-mail: samiaabdi@myway.com [Unite de Recherche de Physique des Solides, Departement de Physique, Faculte des Sciences de Monastir, 5019 Monastir (Tunisia); Mnasri, S.; Sfina, N. [Unite de Recherche de Physique des Solides, Departement de Physique, Faculte des Sciences de Monastir, 5019 Monastir (Tunisia); Bouarissa, N. [Department of Physics, Faculty of Science, King Khalid University, Abha, PO Box 9004 (Saudi Arabia); Said, M. [Unite de Recherche de Physique des Solides, Departement de Physique, Faculte des Sciences de Monastir, 5019 Monastir (Tunisia)

    2011-07-21

    Highlights: > The conduction and valence band offsets of the pseudo-morphically strained Cd{sub 1-x}X{sub x}Te layer on relaxed Cd{sub 1-y}X{sub y}Te substrate, are investigated for X = Zn, Mg, Hg and Mn in the entire range 0 {<=} x,y {<=} 1. > For Cd{sub 1-x}Mn{sub x}Te diluted magnetic semiconductors, the exchange interactions are determined in the order to take into account magnetic effect. > The conduction and valence band offsets of Cd{sub 1-x}Mn{sub x}Te/CdTe interface are calculated in the whole range of Mn composition x and for magnetic field values equal to 0 and 5 T. - Abstract: Due to the large variety of properties offered by the telluride binaries CdTe, ZnTe, MgTe, HgTe and MnTe as well as their mixed ternary alloys, an accurate knowledge of their electronic band parameters is crucial. These materials have been extensively studied but, some points bearing on several properties have never previously reported or are still not clear. In this paper, we report results on the conduction and valence band offsets of the pseudo-morphically strained Cd{sub 1-x}X{sub x}Te layer on relaxed Cd{sub 1-y}X{sub y}Te substrate, X = Zn, Hg, Mg and Mn. Based on the Van Der Walle model, calculations have been performed for the all range of material and substrate 0 {<=} x,y {<=} 1. These discontinuities have not yet calculated for X = Mg, Mn or Hg in the all range 0 {<=} x,y {<=} 1. For the CdMnTe diluted magnetic semiconductor which we focus more interest due to its considerable current interest for applications, calculations have been done without and with correction taking into account magnetic effect of magnesium ions Mn{sup 2+}. It is found that the introduction of only a few percent of Mn into CdTe provides a unique opportunity to combine two important fields in physics, semiconductivity and magnetism. We can take advantage both of possibility of applications in solid-state lasers and exceptional magnetic properties offered by this magnetic diluted semiconductor. This study presents important quantities that are required to model quantum structures and offers a fast and inexpensive way to check device designs and processes.

  6. Chemical trends of the band gaps of idealized crystal of semiconducting silicon clathrates, M8Si38A8 (M = Na, K, Rb, Cs; A = Ga, Al, In), predicted by first-principle pseudopotential calculations

    International Nuclear Information System (INIS)

    Research highlights: ? This paper reports the results of electronic structural calculations of Si clathrate, M8Si38Ga8 (M: the encapsulated guest alkali atom; Na, K, Rb, and Cs). ? All of them are found to be indirect semiconductors with the calculated gaps (Eg) from 0.45 to 0.89 eV, which should be compared to the calculated gap of 0.65 eV of crystalline Si with the diamond structure. The gaps become wider with the promotion to the heavier guest alkali atoms and the reasons of gap widening are discussed using the calculated dependence of Eg on the cell-volume of guest-free silicon clathrate (Si46). Effect of the substitutional elements in the clathrate framework (Al and In in place of Ga) was also discussed. - Abstract: We have calculated the band structures of Si clathrate, M8Si38Ga8 (M = Na, K, Rb, and Cs), using the density-functional theory under the generalized gradient corrected local density approximation, where M is the encapsulated guest alkali atom. They are found to be indirect semiconductors with the calculated gaps (Eg) from 0.45 to 0.89 eV, which should be compared to the calculated gap of 0.65 eV of crystalline Si with the diamond structure. The gaps become wider with the promotion to the heavier guest alkali atoms and the reasons of gap widening are discussed using the calculated dependence of Eg on the cell-volume of guest-free/sub> on the cell-volume of guest-free silicon clathrate (Si46). Effect of the substitutional elements in the clathrate framework (Al and In in place of Ga) was also discussed.

  7. Photonic band gap materials

    Science.gov (United States)

    Cassagne, D.

    Photonic band gap materials Photonic band gap materials are periodic dielectric structures that control the propagation of electromagnetic waves. We describe the plane wave method, which allows to calculate the band structures of photonic crystals. By symmetry analysis and a perturbative approach, we predict the appearance of the low energy photonic band gaps of hexagonal structures. We propose new two-dimensional structures called graphite and boron nitride. Using a transfer matrix method, we calculate the transmission of the graphite structure and we show the crucial role of the coupling with external modes. We study the appearance of allowed modes in the photonic band gap by the introduction of localized defects in the periodicity. Finally, we discuss the properties of opals formed by self-organized silica microspheres, which are very promising for the fabrication of three-dimensional photonic crystals. Les matériaux à bandes interdites photoniques sont des structures diélectriques périodiques qui contrôlent la propagation des ondes électromagnétiques. Nous décrivons la méthode des ondes planes qui permet de calculer les structures de bandes des cristaux photoniques. Par une analyse de la symétrie et une approche perturbative, nous précisons les conditions d'existence des bandes interdites de basse énergie. Nous proposons de nouvelles structures bidimensionnelles appelées graphite et nitrure de bore. Grâce à une méthode de matrices de transfert, nous calculons la transmission de la structure graphite et nous mettons en évidence le rôle fondamental du couplage avec les modes extérieurs. Nous étudions l'apparition de modes permis dans la bande interdite grâce à l'introduction de défauts dans la périodicité. Enfin, nous discutons les propriétés des opales constituées de micro-billes de silice auto-organisées, qui sont très prometteuses pour la fabrication de cristaux photoniques tridimensionnels.

  8. Electronic structure of Cu1-xNixRh2S4 and CuRh2Se4: Band-structure calculations, x-ray photoemission, and fluorescence measurements

    International Nuclear Information System (INIS)

    The electronic structure of spinel-type Cu1-xNixRh2S4 (x=0.0, 0.1, 0.3, 0.5, 1.0) and CuRh2Se4 compounds has been studied by means of x-ray photoelectron (XPS) and fluorescent spectroscopy. Cu L3, Ni L3, S L2,3, and Se M2,3 x-ray emission spectra (XES) were measured near thresholds at Beamline 8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES measurements of the constituent atoms of these compounds, reduced to the same binding energy scale, are found to be in excellent agreement with XPS valence bands. The calculated XES spectra which include dipole matrix elements show that the partial density of states reproduce experimental spectra quite well. States near the Fermi level (EF) have strong Rh d and S(Se) p character in all compounds. In NiRh2S4 the Ni 3d states contribute strongly at EF, whereas in both Cu compounds the Cu 3d bands are only ?1 eV wide and centered ?2.5 eV below EF, leaving very little 3d character at EF. The density of states at the Fermi level is less in NiRh2S4 than in CuRh2S4. This difference may contribute to the observed decrease, as a function of Ni concentration, in the superconducting transition temperature in Cu1-xNixRh2S4. The density of states of the ordered. The density of states of the ordered alloy Cu0.5Ni0.5Rh2S4 shows behavior that is more ''split-band''-like than ''rigid-band''-like. (c) 2000 The American Physical Society

  9. Electronic band structure and optical properties of titanium oxyphosphates Li0.50Co0.25TiO(PO4) single crystals: An ab-initio calculations

    International Nuclear Information System (INIS)

    From the refined atomic positions obtained by Belmal et al. (2004) using X-ray diffraction for Li0.50Co0.25TiO(PO4), we have performed a structural optimization by minimizing the forces acting on the atoms keeping the lattice parameters fixed at the experimental values. With this relaxed (optimized) geometry we have performed a comprehensive theoretical study of electronic properties and dispersion of the linear optical susceptibilities using the full potential linear augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) exchange-correlation potential was applied. In addition, the Engel-Vosko generalized gradient approximation (EVGGA) was used for comparison with GGA because it is known that EVGGA approach yields better band splitting compared to the GGA. We have calculated the band structure, and the total and partial densities of states. The electron charge densities and the bonding properties were analyzed and discussed. The complex dielectric optical susceptibilities were discussed in detail. - Graphical abstract: It is shown that P is tetrahedrally coordinated by four O ions. Highlights: ? Comprehensive theoretical study of electronic and optical properties was performed. ? Using X-ray diffraction data we have performed a structural optimization. ? The electron charge densities and the bonding properties were analyzed and discussed. ? Fermi surface was analyzed since it is useful for predictind since it is useful for predicting thermal, magnetic, and optical properties. ? The density of states at EF and the electronic specific heat coefficient were calculated.

  10. Interplay between structural, magnetic properties and calculated band structures of (EDT-TTF){sub 2}[M(DMIT){sub 2}]{sub 2} where M = Ni, Pd

    Energy Technology Data Exchange (ETDEWEB)

    Doublet, M.L. [Lab. de Chimie Theorique, Univ. de Paris Sud, 91 Orsay (France); Canadell, E. [Lab. de Chimie Theorique, Univ. de Paris Sud, 91 Orsay (France); Garreau, B. [Lab. de Chimie de Coordination du CNRS, 31 Toulouse (France); Legros, J.P. [Lab. de Chimie de Coordination du CNRS, 31 Toulouse (France); Pouget, J.P. [Lab. de Physique des Solides, Univ. de Paris-Sud, 91 Orsay (France); Brossard, L. [Lab. de Physique des Solides, INSA, 31 Toulouse (France)

    1995-03-15

    The resistivity hump which characterizes the 50 K metal-metal transition in (EDT-TTF){sub 2}[Pd(dmit){sub 2}]{sub 2} is shown to be associated with the condensation of a charge density wave ground state, as deduced from SQUID susceptibility and X-ray diffuse scattering measurements. Comparison between the observed CDW wavevector and the nesting properties of the calculated Fermi surfaces as a function of the electron transfer suggests that the charge transfer is approximately +3/4. (orig.)

  11. Theoretical calculations of the optical band positions and zero-field splitting 2D for Cr{sup 3+} ions in fluoride garnet Na{sub 3}Li{sub 3}In{sub 2}F{sub 12}

    Energy Technology Data Exchange (ETDEWEB)

    Mei, Yang [School of Physics and Electronic Engineering, Mianyang Normal University, Mianyang 621000 (China); Research Center of Laser Fusion, CAEP, Mianyang 621900 (China); Zheng, Wen-Chen, E-mail: zhengwc1@163.com [Department of Material Science, Sichuan University, Chengdu 610064 (China); Zhang, Lin [Research Center of Laser Fusion, CAEP, Mianyang 621900 (China)

    2013-12-15

    Five optical band positions and one EPR zero-field splitting 2D for Cr{sup 3+} ions at the trigonally-distorted octahedral In{sup 3+} site in fluoride garnet Na{sub 3}Li{sub 3}In{sub 2}F{sub 12} are calculated together from the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model, where the contributions from both the spin–orbit parameters of central d{sup n} ion and ligand ion are contained. The calculated results are in reasonable agreement with the experimental values. The calculations show that similar to the bonding length (i. e., metal-ligand distance) R, the bonding angle ? (between the direction of R and C{sub 3} axis) is different from the corresponding one in the host crystal Na{sub 3}Li{sub 3}In{sub 2}F{sub 12} because of the size mismatching substitution. It appears that the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model is effective in the unified calculation of optical spectra and EPR zero-field splitting for d{sup 3} ions in crystals.

  12. Comparison of trajectory models in calculations of N2-broadened half-widths and N2-induced line shifts for the rotational band of H216O and comparison with measurements

    International Nuclear Information System (INIS)

    In this work, Complex Robert-Bonamy calculations of half-widths and line shifts were done for N2-broadening of water for 1639 transitions in the rotational band using two models for the trajectories. The first is a model correct to second order in time, the Robert-Bonamy parabolic approximation. The second is the solution of Hamilton's equations. Both models use the isotropic part of the atom-atom potential to determine the trajectories. The present calculations used an intermolecular potential expanded to 20th order to assure the convergence of the half-widths and line shifts. The aim of the study is to assess if the difference in the half-widths and line shifts determined from the two trajectory models is greater than the accuracy requirements of the spectroscopic and remote sensing communities. The results of the calculations are compared with measurements of the half-widths and line shifts. It is shown that the effects of the trajectory model greatly exceed the needs of current remote sensing measurements and that line shape parameters calculated using trajectories determined by solving Hamilton's equations agree better with measurement.

  13. Comparison of Trajectory Models in Calculations of N2-broadened Half-widths and N2-induced Line Shifts for the Rotational Band of H2O-16 and Comparison with Measurements

    Science.gov (United States)

    Lamouroux, J.; Gamache, R. R.; Laraia, A. L.; Ma, Q.; Tipping, R. H.

    2012-01-01

    In this work, Complex Robert-Bonamy calculations of half-widths and line shifts were done for N2-broadening of water for 1639 transitions in the rotational band using two models for the trajectories. The first is a model correct to second order in time, the Robert-Bonamy parabolic approximation. The second is the solution of Hamilton's equations. Both models use the isotropic part of the atom-atom potential to determine the trajectories. The present calculations used an intermolecular potential expanded to 20th order to assure the convergence of the half-widths and line shifts. The aim of the study is to assess if the difference in the half-widths and line shifts determined from the two trajectory models is greater than the accuracy requirements of the spectroscopic and remote sensing communities. The results of the calculations are compared with measurements of the half-widths and line shifts. It is shown that the effects of the trajectory model greatly exceed the needs of current remote sensing measurements and that line shape parameters calculated using trajectories determined by solving Hamilton's equations agree better with measurement.

  14. Room-temperature Broadening and Pressure-shift Coefficients in the nu(exp 2) Band of CH3D-O2: Measurements and Semi-classical Calculations

    Science.gov (United States)

    Predoi-Cross, Adriana; Hambrook, Kyle; Brawley-Tremblay, Shannon; Bouanich, Jean-Pierre; Devi, V. Malathy; Smith, Mary Ann H.

    2006-01-01

    We report measured Lorentz O2-broadening and O2-induced pressure-shift coefficients of CH3D in the nu(exp 2) fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm(exp 1) resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH3D volume mixing ratios of 0.012 in oxygen. We report measurements for O2 pressure-broadening coefficients of 320 nu(exp 2) transitions with quantum numbers as high as J0(sup w) = 17 and K = 14, where K(sup w) = K' is equivalent to K (for a parallel band). The measured O2-broadening coefficients range from 0.0153 to 0.0645 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported O2-induced pressure-shift coefficients vary from about -0.0017 to -0.0068 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J(sup W), and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J(sup W), J(sup W), and J(sup w) + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O2-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m| vibrational contribution are either derived from parameters fitted in the QQ-branch of selfinduced shifts of CH3D or those obtained from pressure shifts induced by Xe in the nu(sup 3) band of CH3D are in reasonable agreement with the scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation).

  15. Electronic band structure of new “122” pnictogen-free superconductor SrPd 2Ge 2 as compared with SrNi 2Ge 2 and SrNi 2As 2 from first principles calculations

    Science.gov (United States)

    Shein, I. R.; Ivanovskii, A. L.

    2010-08-01

    Very recently the new low-temperature ( TC?3 K) superconductor (SC) SrPd 2Ge 2 has been reported. This compound is isostructural with curently intensively studied group of so-called “122” SCs (based on tetragonal AM 2Pn 2 phases, where A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we have studied the electronic structure of new SC SrPd 2Ge 2. The band structure, total and partial densities of states and Fermi surface topology for SrPd 2Ge 2 are evaluated and discussed in comparison with those of isostructural SrNi 2Ge 2 and SrNi 2As 2 phases.

  16. Electronic band structure of new '122' pnictogen-free superconductor SrPd2Ge2 as compared with SrNi2Ge2 and SrNi2As2 from first principles calculations

    International Nuclear Information System (INIS)

    Very recently the new low-temperature (TC?3 K) superconductor (SC) SrPd2Ge2 has been reported. This compound is isostructural with currently intensively studied group of so-called '122' SCs (based on tetragonal AM2Pn2 phases, where A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we have studied the electronic structure of new SC SrPd2Ge2. The band structure, total and partial densities of states and Fermi surface topology for SrPd2Ge2 are evaluated and discussed in comparison with those of isostructural SrNi2Ge2 and SrNi2As2 phases.

  17. Electronic energy bands

    International Nuclear Information System (INIS)

    In this chapter the progress in electronic-band structure calculations is discussed of layered materials which include iodides of group IIB and IVA elements, vanadium oxide, zirconium chloride and bromide, scandium chloride and platinum telluride. 298 refs.; 136 figs.; 29 tabs

  18. Semiclassical calculations of half-widths and line shifts for transitions in the 30012?00001 and 30013?00001 bands of CO2, I: Collisions with N2

    International Nuclear Information System (INIS)

    Calculations of the half-width, its temperature dependence, and the line shift are made for the rotational states J=0-120 for two of the Fermi-tetrad bands (30012?00001 and 30013?00001) of CO2 perturbed by N2. The calculations employ the semi-classical complex Robert-Bonamy method with no ad hoc scaling, J-dependent or otherwise, and an intermolecular potential (IP) comprised of an electrostatic part, an atom-atom part, and an isotropic London dispersion part. The averaging over the impact parameter b and relative speed v are explicitly carried out. Many interesting features about CO2 as the radiating molecule are elucidated. Effects of the trajectory model, the order of the expansion of the atom-atom component of the potential, and the inclusion of the imaginary terms are studied. It is shown that the results are very sensitive to the intermolecular potential. The final IP parameters give results that demonstrate excellent agreement with measurement for the three line shape parameters studied in this work.

  19. Band crossing in 172HF

    International Nuclear Information System (INIS)

    The use of a multiplicity filter to enhance the observation of high spin states following the 160Gd(16O,4n)172Hf reaction has enabled the yrast band to be seen up to spin 22+. The energy of the 22+ ? 20+ transition is consistent with that predicted recently in a band crossing calculation. (Author)

  20. Chemically induced compaction bands in geomaterials

    Science.gov (United States)

    Stefanou, Ioannis; Sulem, Jean

    2013-04-01

    Compaction bands play an important role in oil production and may provide useful information on various geological processes. Various mechanisms can be involved at different scales: the micro scale (e.g. the grain scale), the meso scale (e.g. the Representative Element Volume) and the macro scale (e.g. the structure). Moreover, hydro-chemo-mechanical couplings might play an important role in triggering instabilities in the form of compaction bands. Compaction bands can be seen as an instability of the underneath mathematical problem leading to localization of deformation [1,2,3]. Here we explore the conditions of compaction banding in quartz-based geomaterials by considering the effect of chemical dissolution and precipitation [4,5]. In due course of the loading process grain crushing affects the residual strength, the porosity and the permeability of the material. Moreover, at the micro-level, grain crushing results in an increase of the grain specific surface, which accelerates the dissolution [6]. Consequently, the silica is removed more rapidly from the grain skeleton and the overall mechanical properties are degraded due to chemical factors. The proposed model accounts for these phenomena. In particular, the diffusion of the diluted in the water silica is considered through the mass balance equation of the porous medium. The reduction of the mechanical strength of the material is described through a macroscopic failure criterion with chemical softening. The grain size reduction is related to the total energy input [7]. A grain size and porosity dependent permeability law is adopted. These degradation mechanisms are coupled with the dissolution/precipitation reaction kinetics. The obtained hydro-chemo-mechanical model is used to investigate the conditions, the material parameters and the chemical factors inducing compaction bands formation. References [1] J.W. Rudnicki, and J.R. Rice. "Conditions for the Localization of Deformation in Pressure-sensitive Dilatant Materials." Journal of the Mechanics and Physics of Solids 23.6 (1975): 371-394. [2] I. Vardoulakis and J. Sulem: Bifurcation analysis in geomechanics. Blackie. 1995. [3] J.W. Rudnicki, "Conditions for Compaction and Shear Bands in a Transversely Isotropic Material." International Journal of Solids and Structures 39.13-14 (2002): 3741-3756. [4] L.-B. Hu and T. Hueckel. "Coupled Chemo-mechanics of Intergranular Contact: Toward a Three-scale Model." Computers and Geotechnics 34.4 (2007): 306-327. [5] R. Nova, R. Castellanza, and C. Tamagnini. "A Constitutive Model for Bonded Geomaterials Subject to Mechanical And/or Chemical Degradation." International Journal for Numerical and Analytical Methods in Geomechanics 27.9 (2003): 705-732. [6] J.D. Rimstidt and H.L. Barnes. "The Kinetics of Silica-water Reactions." Geochimica et Cosmochimica Acta 44.11 (1980): 1683-1699. [7] P.V. Lade, J.A. Yamamuro and P.A. Bopp "Significance of Particle Crushing in Granular Materials." Journal of Geotechnical Engineering, 122.4 (1996): 309-316.

  1. Quasirelativistic band structure of bismuth telluride

    International Nuclear Information System (INIS)

    The band structure of bismuth telluride belonging to the group of the Asub(2)Ssup(5)BsUb(3)-type crystals with the Dsub(3d)sup(5) symmetry is under consideration. The Bi2Te3 band structure was calculated using the Pauli equation pseudopotential method. Calculation results are presented for the Brillouin zone symmetric points. The energy bands are classified according to their symmetry. The evailable basic parameters of the bismuth telluride band structure are compared with the result of other paper. Analysis of the calculated band structure shows that there is some difference of the band behaviour in the direction perpendicular to quintet (GITAL, KA, XU) layers that of bands lying in the quintet plane (other Brillouin zone directions). In the first case the energy band dispersion is well below than that in the second case. This fact conforms with a lower current carrier mobility in the direction perpendicular to the layers, as compared to other crystal directions

  2. Calculation of attenuation by rain using the DAH model and diameter of antennas for the Ka Band in Mexico; Calculo de atenuacion por lluvia usando el modelo DAH y diametro de antena para Banda Ka en Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Landeros-Ayala, S.; Neri-Vela, R; Cruz-Sanchez, H.; Hernandez-Bautista, H. [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)

    2002-03-01

    In the last years, the peak in the demand of satellite communication service has caused the saturation in the use of the frequencies corresponding to the band, Cand Ku. Due to this, the engineers have looked for viable alternatives, in order to satisfy the current requisition, as well as the future demand, for which a considerable increment is expected. One of these alternatives is the use of the Ka Band (20Hz/30Hz), that is why the importance of studying the propagation effects that are experienced at these frequencies, especially the attenuation effect by rain, as in this case, where it is significant. The present article has the purpose to describe the use of the Modelo DAH (whose authors are Asoka Dissanayake, Jeremy Allnutt and Fatim Haidara), mixed with the global maps of distribution of rain by Crane, for the calculation of the attenuation by rain in satellite communication systems operated in the Ka Band. Besides, antenna diameters for the systems of communications in Ka Band in different locations of the Mexican Republic, using for it the attenuation margins for rain obtained through the Modelo DAH, and using as references the characteristics of the ANIK F2 satellite and a terrestrial station VSAT, are proposed. [Spanish] En los ultimos anos, el auge en la demanda de servicios de comunicacion por satelite ha provocado la saturacion en los uso de la frecuencia correspondientes a las bandas C y Ku. Debido a esta razon, se han buscado alternativas viables para poder satisfacer la demanda actual, asi como la demanda futura, para la cual se espera un incremento considerable. Una de estas alternativas es el uso de Banda Ka (20Hz/30Hz), de ahi la importancia del estudio sobre los efectos de programacion que se experimentan a esta frecuencia, en especial, el efecto de atencion por lluvias, ya que sen este caso resulta ser significativa. El presente articulo tiene como finalidad describir el uso del Modelo DAH (cuyos autores son Asoka Dissanayake, Jeremy Allnutt y Fatim Haidara), combinado con los mapas globales de distribucion de lluvia de Crane, para el calculo de la atencion por lluvia en sistema de comunicacion por satelite que operen en la Banda Ka. Ademas, se proponen diametros de antena para los sistemas de comunicaciones en Banda Ka en diferentes localidades de la Republica Mexicana, empleando para ello, los margenes de atencion por lluvia obtenidos a trav del Modelo DAH, y usando como referencia las caracteristicas del satelite de comunicaciones ANIK F2 y de una estacion terrena VSAT.Se muestra una fig. de la atenuacion por lluvia a 27.5 gHz y de los diametros de antena para banda Ka en Mexico. Se da una tabla de la atenuacion por lluvia a 29.5 GHz y a 20.2 GHz.

  3. Energy band structure of osmium

    International Nuclear Information System (INIS)

    The energy band structure of hexagonal-close-packed osmium metal has been calculated using non-relativistic Augmented Plane Wave (APW) method. The muffin-tin potential is computed using Liberman's atomic charge densities and Kohn-Sham exchange approximation. The density of states and heat capacity are calculated and compared with experimental data. The results are compared with earlier theoretical calculations of Jepson et al and Iyakutti et al. (author)

  4. Candidate chiral bands in 198Tl

    International Nuclear Information System (INIS)

    High-spin states in 198Tl were studied using the 197Au(?, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast ?h9/2 x ?i13/2-1 band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality. (orig.)

  5. Band structure of boron doped carbon nanotubes

    OpenAIRE

    Wirtz, Ludger; Rubio Secades, A?ngel

    2003-01-01

    We present {\\it ab initio} and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a lowering of the Fermi energy into the valence band, a regular, periodic distribution of the p-dopants leads to the formation of a dispersive ``acceptor''-like band in the band gap of the undoped tube. This comes from the superposition of acceptor levels at the boron atoms...

  6. Silicon nanowire band gap modification

    OpenAIRE

    Nolan, Michael; O Callaghan, Sean; Fagas, Giorgos; Greer, James C.; Frauenheim, Thomas

    2010-01-01

    Band gap modification for small-diameter (1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-sect...

  7. Band crossings in 128Ba

    International Nuclear Information System (INIS)

    Excited states of 128Ba have been studied by in beam ?-ray and conversion electron spectroscopy using the 118Sn(13C,3n)128Ba reaction. 28 new levels were found, 16 spin and parity assignments were made and 4 new bands were identified. The low-lying two-quasiparticle bands were compared with cranked shell model calculations. The low-lying collective levels are discussed in the framework of the interacting boson model. (orig.)

  8. Tuning the structural and physical properties of Cr2Ti3Se8 by lithium intercalation: a study of the magnetic properties, investigation of ion mobility with NMR spectroscopy and electronic band structure calculations.

    Science.gov (United States)

    Wontcheu, Joseph; Bensch, Wolfgang; Wilkening, Martin; Heitjans, Paul; Indris, Sylvio; Sideris, Paul; Grey, Clare P; Mankovsky, Sergiy; Ebert, Hubert

    2008-01-01

    The room temperature intercalation of Cr2Ti3Se8 with butyl lithium yields a phase mixture of the starting material and of the new trigonal phase with composition Li0.4Cr0.5Ti0.75Se2. The phase pure fully intercalated trigonal phase is obtained at elevated temperature (80 degrees C) with the final composition Li0.62Cr0.5Ti0.75Se2. The line profile analysis (LPA) of the powder patterns shows that pronounced strain occurs in the intercalated material. The deintercalation of the material is realized by treatment of the fully intercalated sample with distilled water leading to the composition Li0.15Cr0.5Ti0.75Se2. The intercalation is accompanied by an electron transfer from the guest Li to the host material, and as a consequence significant changes of the interatomic distances are observed. The local environment and the dynamics of the Li+ ions in the fully intercalated sample were studied with 7Li magic angle spinning (MAS) NMR investigations. These reveal different environments of transition metal neighbors for the Li sites and a high mobility of the Li ions. Magnetic measurements show that in the pristine material antiferromagnetic interactions are dominating (theta = -113.5 K) with no long-range order at low temperatures. The magnetic ground state is characterized by a spin-glass behavior. With increasing Li content the antiferromagnetic character vanishes progressively, and the fully intercalated phase exhibits a positive Weiss constant (theta = 12 K) indicating dominating ferromagnetic exchange interactions; i.e., the magnetic properties can be significantly altered by lithiation. The interpretation of our experimental findings is supported by the results of accompanying band structure calculations done within the framework of local spin density functional theory. These demonstrate in particular the role of the charge transfer between the constituents as a function of the Li concentration and its impact on the exchange coupling. PMID:18076171

  9. Molecular orbital calculations on the Th-Ni interaction in Th(eta5-C5H5)2(?-PH2)2Ni(CO)2

    International Nuclear Information System (INIS)

    Organometallic chemists continue to search for new types of bonding and the relatively unexplored chemistry of the f-block elements presents inviting possibilities. Stimulated by the recent observation of a short Th-Ni separation in Th(eta5-C5(CH3)5)2(?-PPh2)2Ni(CO)2, extended Hueckel calculations have been performed to clarify the nature of the proposed metal-metal interaction. Two principal sources of Th-Ni interaction are discernible: first is the filled-filled repulsion between the d-levels of the Ni fragment and the symmetrized combinations of 3a1 and 1b1 PH2 orbitals; and second is between the filled d levels of Ni(CO)2 and the many empty levels of Cp2Th(PH2)2 that are centered on Th. 5 references, 2 figures

  10. Band-limited power flow into enclosures

    Science.gov (United States)

    Pope, L. D.; Wilby, J. F.

    1977-01-01

    Equations for the band-limited power flow to a cavity in the low-frequency regime are derived. The total power to cavity is obtained by summing separate calculations of the power from structural modes resonant in the band and power from structural modes resonant below the band. High-frequency relations compatible with the usual statistical energy analysis and generalized to include other excitations in addition to diffuse fields are also provided.

  11. Multiple band interactions in 131Nd

    International Nuclear Information System (INIS)

    High-spin states in 131Nd were populated in the reaction 94Mo(40Ca,2pn) at a beam energy of 180 MeV. Over 170 new transitions were placed in a level scheme that consists of seven rotational structures. The bands were given configuration assignments based on their B(M1)/B(E2) ratios (for the strongly coupled bands), aligned angular momentum, observed band crossings, and signature splitting. Several quasiparticle alignments were observed in the bands and compared with predictions from the cranked shell model. Three-band mixing calculations were performed in order to interpret the low-spin interaction observed in the [411]1/2 band. An examination of the signature splitting for the [541]1/2 bands in 129,131,133Nd revealed information regarding the parentage of the orbital as well as a signature inversion at higher spin. (c) 2000 The American Physical Society

  12. Multiple band interactions in {sup 131}Nd

    Energy Technology Data Exchange (ETDEWEB)

    Hartley, D. J. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Reviol, W. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Riedinger, L. L. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Balabanski, D. L. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Jin, H. Q. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Smith, B. H. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Zeidan, O. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Zhang, Jing-ye [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States); Galindo-Uribarri, A. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Sarantites, D. G. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States)] (and others)

    2000-04-01

    High-spin states in {sup 131}Nd were populated in the reaction {sup 94}Mo({sup 40}Ca,2pn) at a beam energy of 180 MeV. Over 170 new transitions were placed in a level scheme that consists of seven rotational structures. The bands were given configuration assignments based on their B(M1)/B(E2) ratios (for the strongly coupled bands), aligned angular momentum, observed band crossings, and signature splitting. Several quasiparticle alignments were observed in the bands and compared with predictions from the cranked shell model. Three-band mixing calculations were performed in order to interpret the low-spin interaction observed in the [411]1/2 band. An examination of the signature splitting for the [541]1/2 bands in {sup 129,131,133}Nd revealed information regarding the parentage of the orbital as well as a signature inversion at higher spin. (c) 2000 The American Physical Society.

  13. Multiple band interactions in 131Nd

    Science.gov (United States)

    Hartley, D. J.; Reviol, W.; Riedinger, L. L.; Balabanski, D. L.; Jin, H. Q.; Smith, B. H.; Zeidan, O.; Zhang, Jing-Ye; Galindo-Uribarri, A.; Sarantites, D. G.; Lafosse, D. R.; Wilson, J. N.; Mullins, S. M.

    2000-04-01

    High-spin states in 131Nd were populated in the reaction 94Mo(40Ca,2pn) at a beam energy of 180 MeV. Over 170 new transitions were placed in a level scheme that consists of seven rotational structures. The bands were given configuration assignments based on their B(M1)/B(E2) ratios (for the strongly coupled bands), aligned angular momentum, observed band crossings, and signature splitting. Several quasiparticle alignments were observed in the bands and compared with predictions from the cranked shell model. Three-band mixing calculations were performed in order to interpret the low-spin interaction observed in the [411]1/2 band. An examination of the signature splitting for the [541]1/2 bands in 129,131,133Nd revealed information regarding the parentage of the orbital as well as a signature inversion at higher spin.

  14. Cranked Skyrme-Hartree-Fock calculation for superdeformed and hyperdeformed rotational bands in N=Z nuclei from sup 3 sup 2 S to sup 4 sup 8 Cr

    CERN Document Server

    Inakura, T; Yamagami, M; Matsuyanagi, K

    2002-01-01

    With the use of the symmetry-unrestricted cranked Skyrme-Hartree-Fock method in the three-dimensional coordinate-mesh representation, we have carried out a systematic theoretical search for the superdeformed and hyperdeformed rotational bands in the mass A=30-50 region. Along the N=Z line, we have found superdeformed solutions in sup 3 sup 2 S, sup 3 sup 6 Ar, sup 4 sup 0 Ca, sup 4 sup 4 Ti, and hyperdeformed solutions in sup 3 sup 6 Ar, sup 4 sup 0 Ca, sup 4 sup 4 Ti, sup 4 sup 8 Cr. The superdeformed band in sup 4 sup 0 Ca is found to be extremely soft against both the axially symmetric (Y sub 3 sub 0) and asymmetric (Y sub 3 sub 1) octupole deformations. An interesting role of symmetry breaking in the mean field is pointed out.

  15. Comparison of line-by-line and Curtis matrix calculations for the vibrational temperatures and radiative cooling of the CO2 15 micrometer bands in the middle and upper atmosphere

    Science.gov (United States)

    Lopez-Puertas, M.; Wintersteiner, P. P.; Picard, R. H.; Winick, J. R.; Sharma, R. D.

    1994-10-01

    A comparison of the iterative line-by-line RAD, and the inverse modified Curtis matrix (MCM) non-local thermodynamic equilibrium (LTE) models has been undertaken with the purpose of studying the effect of radiative transfer algorithms on the non-LTE populations of the CO2(nu(sub 2)) levels and on the 15 micrometer radiative cooling rates produced by the bands originating from them. The comparison has been carried out for a large range of model input parameters which include CO2 strong and weak 15 micrometer bands, extreme atmospheric temperature structures, a large altitude interval (40-160 km), and extreme values for kinetic parameters. A good general agreement for the populations and cooling rates for all bands and conditions is found. The model differences for the vibrational temperatures and cooling rates are generally smaller than 2 K and 0.5 K/day, respectively. This result is in contrast with the large differences found when compared with some previous non-LTE models.

  16. Rotational bands in 238U

    Science.gov (United States)

    Ward, D.; Andrews, H. R.; Ball, G. C.; Galindo-Uribarri, A.; Janzen, V. P.; Nakatsukasa, T.; Radford, D. C.; Drake, T. E.; DeGraaf, J.; Pilotte, S.; Shimizu, Y. R.

    1996-02-01

    A thick foil of 238U was bombarded with 209Bi beams at 1130 and 1330 MeV, delivered by the TASCC facility at Chalk River Laboratories. Gamma-ray spectroscopy of states populated in multiple Coulomb excitation was performed with the 8? spectrometer, an instrument comprising 20 Compton-suppressed HPGe detectors and 71 BGO ball elements. The event trigger required that 3 BGO elements and 2 HPGe detectors fire in coincidence. The experiment achieved a high degree of sensitivity, the weakest rotational band observed had about 0.16% intensity of the ground state rotational band. Several bands were observed to high spin for the first time, including the ?-vibrational band (spin 27 +) and the octupole bands with K = 0 (spin 31 -), K = 1 (spin 28 -) and K = 2 (spin 25 -). Results for positive and negative parity vibrational bands are compared with cranked RPA calculations. Although this theory can explain some features of the data, many puzzling aspects remain to be explored.

  17. Band head spin and moment of inertia for super deformed rotational bands using the VMI model

    International Nuclear Information System (INIS)

    Nearly all the super-deformed bands (SD) have been observed with hanging transitions, as a result only the ?-ray energies are known with no firm spin parity assignments. Knowledge of the spin-parities is very crucial for their configuration assignments and for complete theoretical understanding of the SD bands. The VMI model has been applied to calculate the lowest spin (and hence the K-value) and also the gamma energies for the SD bands. The calculated band head spin is compared with other theoretical estimates available in the literature

  18. A simple theoretical approach to calculate the electrical conductivity of nonideal copper plasma

    International Nuclear Information System (INIS)

    A simple theoretical approach to calculate the electrical conductivity of partially ionized nonideal copper plasma is introduced. The densities of plasma species are calculated, to machine accuracy, including electronic excitation and allowing for high ionization states up to the atomic number of the element. Depression of ionization energies is taken into account using an interpolation formula that is valid over a wide range of densities. The formula yields the results of the Debye-Hueckel and the ion-sphere models at the limiting boundaries of low and high densities, respectively. The nonideal Coulomb logarithm is represented by an analytic wide-range formula supplemented by a specially tailored cutoff parameter. Effects of excluding excited and high ionization states on the calculation of ionization equilibrium and electrical conductivity of copper are investigated and assessed. Computational results of the electrical conductivity are compared with results from other theoretical models and available experimental measurements and showed reasonable agreement. A discussion about the choice of the ion-sphere radius is included and concerns about thermodynamic inconsistency when using the modified nonideal Saha equations are discussed and cleared

  19. Prolate-oblate band mixing and new bands in 182Hg

    International Nuclear Information System (INIS)

    In-beam ?-ray spectroscopic studies of 182Hg have revealed five new bands. The 2+ state of the prolate band has been identified at an energy of 548.6 keV and is higher than in 184Hg. A two parameter band mixing calculation results in an interaction energy of 83 keV between the prolate 2+ and the oblate 2+ states. Several additional new bands are seen including some which are interpreted as quadrupole vibrational bands built on the excited prolate minimum

  20. Come Join the Band

    Science.gov (United States)

    Olson, Cathy Applefeld

    2011-01-01

    A growing number of students in Blue Springs, Missouri, are joining the band, drawn by a band director who emphasizes caring and inclusiveness. In the four years since Melissia Goff arrived at Blue Springs High School, the school's extensive band program has swelled. The marching band alone has gone from 100 to 185 participants. Also under Goff's…

  1. Triaxial superdeformed bands in 86Zr

    International Nuclear Information System (INIS)

    Four new superdeformed bands have been found in the nucleus 86Zr. The good agreement between experiment and configuration-dependent shell correction calculations suggests that three of the bands have triaxial superdeformed shapes. Such unique features in mass A?80 superdeformed bands have been predicted, but not observed experimentally until now. A fourth band in 86Zr is interesting due to a fairly constant and unusually high dynamic moment of inertia. Possible interpretations of this structure are discussed. copyright 1998 The American Physical Society

  2. Triaxial superdeformed bands in {sup 86}Zr

    Energy Technology Data Exchange (ETDEWEB)

    Sarantites, D.G.; LaFosse, D.R.; Devlin, M.; Lerma, F. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Wood, V.Q.; Saladin, J.X.; Winchell, D.F. [Physics Department, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Baktash, C.; Yu, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Fallon, P.; Lee, I.Y.; Macchiavelli, A.O.; MacLeod, R.W. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Afanasjev, A.V.; Ragnarsson, I. [Department of Mathematical Physics, Lund Institute of Technology, Box 118, S-22100 Lund (Sweden)

    1998-01-01

    Four new superdeformed bands have been found in the nucleus {sup 86}Zr. The good agreement between experiment and configuration-dependent shell correction calculations suggests that three of the bands have triaxial superdeformed shapes. Such unique features in mass A{approximately}80 superdeformed bands have been predicted, but not observed experimentally until now. A fourth band in {sup 86}Zr is interesting due to a fairly constant and unusually high dynamic moment of inertia. Possible interpretations of this structure are discussed. {copyright} {ital 1998} {ital The American Physical Society}

  3. Candidate chiral bands in {sup 198}Tl

    Energy Technology Data Exchange (ETDEWEB)

    Lawrie, E.A.; Lawrie, J.J.; Bark, R.A.; Mullins, S.M.; Murray, S.H.T. [Themba LABS, Somerset West (South Africa); Vymers, P.A.; Maliage, S.M.; Masiteng, P.L.; Ramashidzha, T.M.; Sharpey-Schafer, J.F.; Shirinda, O. [Themba LABS, Somerset West (South Africa); University of the Western Cape, Bellville (South Africa); Vieu, Ch.; Schueck, C. [CNRS - IN2P3, Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, Orsay (France); Lindsay, R. [University of the Western Cape, Bellville (South Africa); Mabala, G.K. [Themba LABS, Somerset West (South Africa); University of Cape Town, Department of Physics, Rondebosch (South Africa); Ragnarsson, I. [Lund University, Division of Mathematical Physics, LHT, Lund (Sweden)

    2010-07-15

    High-spin states in {sup 198}Tl were studied using the {sup 197}Au({alpha}, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast {pi}h{sub 9/2} x {nu}i{sub 13/2}{sup -1} band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality. (orig.)

  4. Topological aspects of band theory

    Science.gov (United States)

    Soluyanov, Alexey A.

    Band theory has proven to be one of the most successful developments in condensed matter theory. It is the basis of our current understanding of crystalline solids, describing complex electronic behavior in terms of a single quasi-particle that moves in some effective field of the crystal lattice environment and other particles. In recent years topological and geometrical considerations opened a fundamentally new branch of research in band theory. One of the major advances in this field came with the realization that insulating band structures can be classified according to the values of some topological invariants associated with the occupied single-particle states. Insulators that correspond to non-trivial values of these topological invariants realize new states of matter with properties drastically different from those attributed to an ordinary insulator. In this work we address questions that arise in the context of band theory in the presence of topologically non-trivial bands. Part of the thesis is aimed at the actual determination of the presence of non-trivial band topology. We develop a method to distinguish an ordinary insulator from a topological one in the presence of time-reversal symmetry. The method is implemented within the density functional theory framework and is illustrated with applications to real materials in ab initio calculations. Another question considered in this work is that of a real-space representation of topological insulators, and in particular, the construction of Wannier functions - localized real-space wavefunctions. Wannier functions form one of the most powerful tools in band theory, and it is very important to understand how to implement Wannier function techniques in the presence of topological bands. In some cases bands with non-trivial topology do not allow for the construction of exponentially localized Wannier functions. While previous work has shown that in the presence of time-reversal symmetry such a construction should be possible in principle, it has remained unclear how to do it in practice. We present an explicit construction of a Wannier representation for a particular model of a time-reversal invariant topological insulator. This construction is very different from the one used for ordinary band insulators. We then proceed to develop a procedure that allows for such a construction in the general case, without any reference to a particular model. Our work provides a basis for extending Wannier function techniques to topologically non-trivial band structures.

  5. Electronic structure of the valence band of II--VI wide band gap semiconductor interfaces

    OpenAIRE

    Olguin, D.; Baquero, R.

    1996-01-01

    In this work we present the electronic band structure for (001)--CdTe interfaces with some other II--VI zinc blende semiconductors. We assume ideal interfaces. We use tight binding Hamiltonians with an orthogonal basis ($s p^3 s^*$). We make use of the well--known Surface Green's Function Matching method to calculate the interface band structure. In our calculation the dominion of the interface is constituted by four atomic layers. We consider here anion--anion interfaces on...

  6. Spectral band selection for classification of soil organic matter content

    Science.gov (United States)

    Henderson, Tracey L.; Szilagyi, Andrea; Baumgardner, Marion F.; Chen, Chih-Chien Thomas; Landgrebe, David A.

    1989-01-01

    This paper describes the spectral-band-selection (SBS) algorithm of Chen and Landgrebe (1987, 1988, and 1989) and uses the algorithm to classify the organic matter content in the earth's surface soil. The effectiveness of the algorithm was evaluated comparing the results of classification of the soil organic matter using SBS bands with those obtained using Landsat MSS bands and TM bands, showing that the algorithm was successful in finding important spectral bands for classification of organic matter content. Using the calculated bands, the probabilities of correct classification for climate-stratified data were found to range from 0.910 to 0.980.

  7. Super deformed bands in A 180 mass region

    International Nuclear Information System (INIS)

    In this work a re-investigation of deformed bands in the mass region A?180, was carried out, making use of the available experimental data of both W and Os even-even isotopes. Discussing the back bending phenomenon in all isotopes understudy, and searching for a second back bending, to declare the presence of the so-called tilted super band. Band crossing was also discussed and the average moment of inertia was calculated. At last the hint of Makito about tilted band was also declared in the frame work of rotational band. Also the staggering of gamma vibrational band was also discussed

  8. Isentropic versus isothermal energy bands in rotating nuclei

    International Nuclear Information System (INIS)

    Should energy bands in heated rotating nuclei be calculated at constant entropy or constant temperature. For Hamilton's equation ? = dE/dI to be satisfied, the first law of thermodynamics requires that each energy band E(I) follow a path of constant entropy. Isentropic energy bands are calculated for the two-level model in the finite-temperature HFB cranking approximation. The Maxwell relations connecting thermal and rotational variables are derived. (orig.)

  9. Multiple triaxial bands in 138Nd

    Science.gov (United States)

    Petrache, C. M.; Ragnarsson, I.; Ma, Hai-Liang; Leguillon, R.; Zerrouki, T.; Bazzacco, D.; Lunardi, S.

    2015-02-01

    High-spin states in 138Nd were investigated by using the 48Ca+94Zr reaction and ? -ray coincidences were acquired with the GASP spectrometer. A rich level scheme was developed including 14 new bands of quadrupole transitions at very high spins. Linking transitions connecting 11 high-spin bands to low-energy states have been observed. Calculations based on the cranked Nilsson-Strutinsky formalism have been used to assign configurations to the observed bands. The main result of these calculations is that all 14 bands exhibit a stable triaxial deformation up to the highest observed spins, giving strong support to the existence of a triaxial minimum with normal deformation and positive asymmetry parameter in nuclei with a few holes in the N =82 shell closure.

  10. DSAM lifetime measurements in the yrast band of 131La and the chiral bands in 132La

    International Nuclear Information System (INIS)

    Lifetimes of the h11/2 decoupled band in 131La and supposed chiral bands in odd-odd 132La have been measured using the Doppler Shift Attenuation method. The properties of all bands have been calculated in terms of the Core Quasi Particle Coupling and Core Particle Hole Coupling models by using in both cases the same phenomenological core of 130Ba. A new band in 132La has been found. (author)

  11. Multiple band crossing in 164Er

    International Nuclear Information System (INIS)

    The present measurements on 164Er give the first evidence for higher superbands and also the first example of intersections between the ? band and these superbands. A beam of 69.6-MeV 18O ions bombarded a metallic neodymium foil enriched to 96% in mass 150. The resulting level scheme for the positive-parity states is presented. The ground-state rotational band up to spin 22+, the yrast sequence up to 24+, and both the odd- and even-spin members of the ?-vibrational band up to 21+ are seen. The plot of the experimental excitation energies vs I clearly shows several intersecting rotational bands. A calculation was made using typical parameters to illustrate the general features predicted for 164Er by the rotation-alignment model. The correspondence between experiment and theory is indeed striking. The interaction between the intersecting bands is most clearly illustrated in a backbending plot of the data. 3 figures

  12. Bayesian Calculator

    Science.gov (United States)

    Birnbaum, Michael H.

    This page, created by Michael H. Birnbaum of Fullerton University, uses Bayes' Theorem to calculate the probability of a hypothesis given a datum. An example about cancer is given to help users understand Bayes' Theorem and the calculator. This page is a great representation of conditional probability. Detailed instructions are provided on proper use of the calculator.

  13. Collective bands in neutron-rich 104Mo nucleus

    International Nuclear Information System (INIS)

    Levels in the neutron-rich 104Mo nucleus have been investigated by observing prompt ?-rays from the spontaneous fission of 252Cf with the Gamma sphere detector array. The ground-state band, the one-phonon and the two-phonon ?-vibrational bands as well as a quasiparticle band have been confirmed and expanded with spin up to 14?. Other two side bands probably built on new quasiparticle states are identified. The possible configurations for the quasiparticle bands are discussed. Two of the quasiparticle bands show larger moments of inertia and may have pair-free characteristics. The levels of the ground-state band, the one-phonon ?-band and the two-phonon ?-band calculated from a general collective model are in close agreement with the experimental data

  14. Electronic energy band structure of osmium metal

    International Nuclear Information System (INIS)

    The non-relativistic energy band calculation of osmium metal with Kolin-Sham exchange gives fairly well the relative positions of different peaks in the density of states curve. In order to have a good agreement with the electronic specific heat and conduction band peak positions with respect to the Fermi energy, the Fermi energy is to be shifted to the higher energy side. Results are compared with earlier theoretical and experimental data

  15. Multiple band structures in 191Hg

    International Nuclear Information System (INIS)

    The level structure of the nucleus 191Hg has been considerably extended from previous studies by using the 160Gd(36S, 5n) reaction in conjunction with an array of Compton-suppressed germanium detectors. A series of 13 different level sequences has been established in addition to three superdeformed bands. A majority of the band structures can be understood in cranked shell model calculations assuming on oblate collective nuclear shape. There is some evidence for the onset of triaxiality. Finally, two bands of single-particle character have been found. They are interpreted as being associated with a prolate non-collective shape (?=-120deg). (orig.)

  16. Electronic band structure of beryllium oxide

    CERN Document Server

    Sashin, V A; Kheifets, A S; Ford, M J

    2003-01-01

    The energy-momentum resolved valence band structure of beryllium oxide has been measured by electron momentum spectroscopy (EMS). Band dispersions, bandwidths and intervalence bandgap, electron momentum density (EMD) and density of occupied states have been extracted from the EMS data. The experimental results are compared with band structure calculations performed within the full potential linear muffin-tin orbital approximation. Our experimental bandwidths of 2.1 +- 0.2 and 4.8 +- 0.3 eV for the oxygen s and p bands, respectively, are in accord with theoretical predictions, as is the s-band EMD after background subtraction. Contrary to the calculations, however, the measured p-band EMD shows large intensity at the GAMMA point. The measured full valence bandwidth of 19.4 +- 0.3 eV is at least 1.4 eV larger than the theory. The experiment also finds a significantly higher value for the p-to-s-band EMD ratio in a broad momentum range compared to the theory.

  17. Highly deformed Bands in 175Hf

    International Nuclear Information System (INIS)

    Two high-spin regularly spaced rotational bands with large dynamical moments of inertia have been identified in 175Hf with the Gammasphere spectrometer. These new bands are very similar to the previously identified triaxial superdeformed bands in the hafnium nuclei. However, the new bands in 175Hf have been linked into the known level scheme and thereby provide the first firm spin assignments for these structures in this region. In order to understand the new bands, theoretical calculations have been performed based on the ULTIMATE CRANKER code. The new bands in 175Hf are deduced to be built upon highly deformed structures. No experimental evidence for triaxiality was established and this work suggests that the structure of the so-called 'triaxial' superdeformed bands in the Hf nuclei may be quite different from those identified in the lighter mass Lu nuclei. Since the two highly deformed bands in 175Hf are associated with different deformations, this work also identifies the role of the intruder orbits in polarizing the nuclear shape

  18. Highly deformed Bands in 175 Hf

    Science.gov (United States)

    Scholes, D. T.; Cullen, D. M.; Kondev, F. G.; Janssens, R. V.; Carpenter, M. P.; Hartley, D. J.; Djongolov, M. K.; Sletten, G.; Hagemann, G.; Wheldon, C.; Walker, P. M.; Abu Saleem, K.; Ahmad, I.; Balabanski, D. L.; Chowdhury, P.; Danchev, M.; Dracoulis, G. D.; El-Masri, H. M.; Goon, J.; Heinz, A.; Kaye, R. A.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Moore, E. F.; Riedinger, L. L.; Riley, M. A.; Seweryniak, D.; Shestakova, I.; Wiedenhöver, I.; Zeidan, O.; Zhang, Jing-Ye

    2004-11-01

    Two high-spin regularly spaced rotational bands with large dynamical moments of inertia have been identified in 175 Hf with the Gammasphere spectrometer. These new bands are very similar to the previously identified triaxial superdeformed bands in the hafnium nuclei. However, the new bands in 175 Hf have been linked into the known level scheme and thereby provide the first firm spin assignments for these structures in this region. In order to understand the new bands, theoretical calculations have been performed based on the ULTIMATE CRANKER code. The new bands in 175 Hf are deduced to be built upon highly deformed structures. No experimental evidence for triaxiality was established and this work suggests that the structure of the so-called “triaxial” superdeformed bands in the Hf nuclei may be quite different from those identified in the lighter mass Lu nuclei. Since the two highly deformed bands in 175 Hf are associated with different deformations, this work also identifies the role of the intruder orbits in polarizing the nuclear shape.

  19. Adaptive Confidence Bands

    OpenAIRE

    Genovese, Christopher R.; Wasserman, Larry

    2007-01-01

    We show that there do not exist adaptive confidence bands for curve estimation except under very restrictive assumptions. We propose instead to construct adaptive bands that cover a surrogate function f^\\star which is close to, but simpler than, f. The surrogate captures the significant features in f. We establish lower bounds on the width for any confidence band for f^\\star and construct a procedure that comes within a small constant factor of attaining the lower bound for ...

  20. Investigation of chiral bands in {sup 106}Ag

    Energy Technology Data Exchange (ETDEWEB)

    Lieder, Evgenia [Themba LABS, Somerset West (South Africa); FhG, INT, Euskirchen (Germany); Lieder, Rainer; Bark, Rob; Lawrie, Elena; Lawrie, Kobus; Ntshangase, Sifiso; Mullins, Simon; Papka, Paul; Kheswa, Ntombi [Themba LABS, Somerset West (South Africa); Meng, Jie [PhS, PKU, Beijing (China); PhS, BUAA, Beijing (China); Qi, Bin [SDU, Weihai (China); Zhang, Shuangquan; Li, Zhipan [PhS, PKU, Beijing (China)

    2010-07-01

    Dipole bands in {sup 106}Ag have been studied with the {gamma}-detector array AFRODITE at iThemba LABS, South Africa. A {sup 96}Zr({sup 14}N,4n){sup 106}Ag reaction at a beam energy of 71 MeV has been used. The three previously known negative-parity bands in {sup 106}Ag have been extended. Bands 1 and 2 were proposed to be chiral partner bands. However, in view of the present results, bands 2 and 3 seem to be better candidates for chiral partner bands since their staggering parameters, B(M1)/B(E2) ratios, kinematic moments of inertia and quasiparticle alignments agree much better than those of bands 1 and 2. Triaxial relativistic mean field (RMF) and particle-rotor model (PRM) calculations support this interpretation. In the potential energy surface of {sup 106}Ag, obtained in RMF calculations, two minima have been found in the {beta}{sub 2}-{gamma} plane. Based on PRM calculations using the deformation parameters of the two minima and a {nu}h{sub 11/2} x {pi}g{sup -1}{sub 9/2} particle-hole configuration, bands 2 and 3 may represent partners with chiral vibration at {gamma}{approx}12degree. Band 1, located in the other minimum, may be a magnetic dipole band or the partner of a second pair of chiral bands.

  1. Electronic band structure of new '122' pnictogen-free superconductor SrPd{sub 2}Ge{sub 2} as compared with SrNi{sub 2}Ge{sub 2} and SrNi{sub 2}As{sub 2} from first principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Shein, I.R. [Institute of Solid State Chemistry, Ural Division, Russian Academy of Sciences, Pervomaiskaya St. 91, Ekaterinburg 620990 (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.r [Institute of Solid State Chemistry, Ural Division, Russian Academy of Sciences, Pervomaiskaya St. 91, Ekaterinburg 620990 (Russian Federation)

    2010-08-15

    Very recently the new low-temperature (T{sub C{approx}}3 K) superconductor (SC) SrPd{sub 2}Ge{sub 2} has been reported. This compound is isostructural with currently intensively studied group of so-called '122' SCs (based on tetragonal AM{sub 2}Pn{sub 2} phases, where A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we have studied the electronic structure of new SC SrPd{sub 2}Ge{sub 2}. The band structure, total and partial densities of states and Fermi surface topology for SrPd{sub 2}Ge{sub 2} are evaluated and discussed in comparison with those of isostructural SrNi{sub 2}Ge{sub 2} and SrNi{sub 2}As{sub 2} phases.

  2. Wide Band to ''Double Band'' upgrade

    International Nuclear Information System (INIS)

    The Wide Band beam currently uses electrons obtained from secondary photon conversions to produce the photon beam incident on the experimental targets. By transporting the positrons produced in these conversions as well as the electrons it is possible to almost double the number of photons delivered to the experiments per primary beam proton. 11 figs

  3. Flat bands in the Weaire-Thorpe model and silicene

    Science.gov (United States)

    Hatsugai, Y.; Shiraishi, K.; Aoki, H.

    2015-02-01

    In order to analytically capture and identify peculiarities in the electronic structure of silicene, the Weaire-Thorpe (WT) model, a standard model for treating three-dimensional (3D) silicon, is applied to silicene with a buckled 2D structure. In the original WT model for four hybridized sp3 orbitals on each atom along with inter-atom hopping, the band structure can be systematically examined in 3D, where flat (dispersionless) bands exist as well. For examining silicene, here we re-formulate the WT model in terms of the overlapping molecular-orbital (MO) method which enables us to describe flat bands away from the electron-hole symmetric point. The overlapping MO formalism indeed enables us to reveal an important difference: while in 3D the dipersive bands with cones are sandwiched by doubly-degenerate flat bands, in 2D the dipersive bands with cones are sandwiched by triply-degenerate and non-degenerate (nearly) flat bands, which is consistent with the original band calculation by Takeda and Shiraishi. Thus there emerges a picture for why the whole band structure of silicene comprises a pair of dispersive bands with Dirac cones with each of the bands touching a nearly flat (narrow) band at ?. We can also recognize that, for band engineering, the bonds perpendicular to the atomic plane are crucial, and that ferromagnetism or structural instabilities are expected if we can shift the chemical potential close to the flat bands.

  4. BTU Calculator

    Science.gov (United States)

    A calculator that estimates the heating needs of a room, a combination of rooms, or an entire home. Enter the length and width of the area to be heated and select the climate and insulation factors from the pop-up boxes. A Java version of this calculator is also available.

  5. CO Cameron band and CO2+ UV doublet emissions in the dayglow of Venus: Role of CO in the Cameron band production

    OpenAIRE

    Bhardwaj, Anil; Jain, Sonal Kumar

    2013-01-01

    Present study deals with the model calculations of CO Cameron band and CO2+ ultraviolet doublet emissions in the dayglow of Venus. The overhead and limb intensities of CO Cameron band and CO2+ UV doublet emissions are calculated for low, moderate, and high solar activity conditions. Using updated cross sections, the impact of dierent e-CO cross section for Cameron band production is estimated. The electron impact on CO is the major source mechanism of Cameron band, followed ...

  6. Progressive Band Selection

    Science.gov (United States)

    Fisher, Kevin; Chang, Chein-I

    2009-01-01

    Progressive band selection (PBS) reduces spectral redundancy without significant loss of information, thereby reducing hyperspectral image data volume and processing time. Used onboard a spacecraft, it can also reduce image downlink time. PBS prioritizes an image's spectral bands according to priority scores that measure their significance to a specific application. Then it uses one of three methods to select an appropriate number of the most useful bands. Key challenges for PBS include selecting an appropriate criterion to generate band priority scores, and determining how many bands should be retained in the reduced image. The image's Virtual Dimensionality (VD), once computed, is a reasonable estimate of the latter. We describe the major design details of PBS and test PBS in a land classification experiment.

  7. MEMS Calculator

    Science.gov (United States)

    SRD 166 MEMS Calculator (Web, free access)   This MEMS Calculator determines the following thin film properties from data taken with an optical interferometer or comparable instrument: a) residual strain from fixed-fixed beams, b) strain gradient from cantilevers, c) step heights or thicknesses from step-height test structures, and d) in-plane lengths or deflections. Then, residual stress and stress gradient calculations can be made after an optical vibrometer or comparable instrument is used to obtain Young's modulus from resonating cantilevers or fixed-fixed beams. In addition, wafer bond strength is determined from micro-chevron test structures using a material test machine.

  8. Deformed intruder bands in 113Sn

    Science.gov (United States)

    Sears, J. M.; Gundel, S. E.; Fossan, D. B.; Lafosse, D. R.; Vaska, P.; Degraaf, J.; Drake, T. E.; Janzen, V. P.; Radford, D. C.; Droste, Ch.; Morek, T.; Garg, U.; Lamkin, K.; Naguleswaran, S.; Smith, G.; Walpe, J. C.; Kaczarowski, R.; Afanasjev, A. V.; Ragnarsson, I.

    1998-09-01

    High-spin states in the odd-A 113Sn nucleus have been investigated with the 100Mo(18O, 5n) reaction at 94 MeV using the Chalk River 8? array. Three decoupled (?I=2) rotational bands extending to spins I in the range (63/2-69/2)? have been identified and connected to known low-lying states. Experimental observations for the most extended band have been interpreted as evidence for smooth band termination. Theoretical calculations performed within a configuration-dependent shell-correction approach suggest that all three bands are built upon deformed two-particle-two-hole proton excitations across the Z=50 shell gap.

  9. New results on the superdeformed {sup 196}Pb nucleus: The decay of the excited bands to the yrast band

    Energy Technology Data Exchange (ETDEWEB)

    Bouneau, S.; Azaiez, F.; Duprat, J. [IPN, Orsay (France)] [and others

    1996-12-31

    The study of the superdeformed (SD) {sup 196}Pb nucleus has been revisited using the EUROGAM phase 2 spectrometer. In addition to the known yrast and two lowest excited SD bands, a third excited SD band has been seen. All of the three excited bands were found to decay to the yrast SD band through, presumably, E1 transitions, allowing relative spin and excitation energy assignments. Comparisons with calculations using the random-phase approximation suggest that all three excited bands can be interpreted as octupole vibrational structures.

  10. Position and Confidence Limits of an Extremum: The Determination of the Absorption Maximum in Wide Bands.

    Science.gov (United States)

    Heilbronner, Edgar

    1979-01-01

    Discusses the determination of the position of the absorption maximum in wide bands as well as the confidence limits for such calculations. A simple method, suited for pocket calculators, for the numerical evaluation of these calculations is presented. (BB)

  11. Higher Dipole Bands in the NLC Accelerating Structure

    CERN Document Server

    Adolphsen, C E; Dolgashev, V A; Ko, K; Li, Z; Miller, R

    2000-01-01

    We show that scattering matrix calculations for dipole modes between 23-43 GHz for the 206 cell detuned structure (DS) are consistent with finite element calculations and results of the uncoupled model. In particular, the rms sum wake for these bands is comparable to that of the first dipole band. We also show that for RDDS1 uncoupled wakefield calculations for higher bands are consistent with measurements. In particular, a clear 26 GHz signal in the short range wake is found in both results.

  12. Braille Calculator

    Directory of Open Access Journals (Sweden)

    Yoshit V. Gidh

    2013-02-01

    Full Text Available A thorough grounding in mathematics enhances educational and occupational opportunities for all people, whether sighted or visually impaired. In day-to-day routines, a practical understanding of mathematics allows a person to function more successfully and independently.? Access to, and doing mathematics, is one of the biggest obstacles for blind students in school and at the university. Our Braille Calculator will present new approaches to offering blind students better access to math, to provide new tools for doing math. In this report, the basic problems and solutions to the problem are discussed as a means of laying the groundwork for our Braille Calculator. Many aspects and concepts of mathematics are visual and spatial in nature. Students who are blind or visually impaired, and their teachers, now have standards which are closely aligned with those used for sighted students. Braille mathematics standards are essential to ensure that functionally blind students become literate in mathematics. However for complex engineering and statistical calculations even sighted students have to depend on Calculator. So we came up with an idea of Braille Calculator

  13. Decay of superdeformed bands

    International Nuclear Information System (INIS)

    One of the major challenges in the study of superdeformation is to directly connect the large number of superdeformed bands now known to the yrast states. In this way, excitation energies, spins and parities can be assigned to the levels in the second well which is essential to establish the collective and single-particle components of these bands. This paper will review some of the progress which has been made to understand the decay of superdeformed bands using the new arrays including the measurement of the total decay spectrum and the establishment of direct one-step decays from the superdeformed band to the yrast line in 194Hg. 42 refs., 5 figs

  14. Variationally-optimized muffin-tin potentials for band calculations

    International Nuclear Information System (INIS)

    A method is suggested to determine the best local periodic crystal potential V(r) by minimizing the Hartree-Fock expectation value of the energy. The explicit form of the integral equation for the local exchange potential is obtained for the special case of the Muffin-tin aproximation. (author)

  15. Distribution Free Prediction Bands

    OpenAIRE

    Lei, Jing; Wasserman, Larry

    2012-01-01

    We study distribution free, nonparametric prediction bands with a special focus on their finite sample behavior. First we investigate and develop different notions of finite sample coverage guarantees. Then we give a new prediction band estimator by combining the idea of "conformal prediction" (Vovk et al. 2009) with nonparametric conditional density estimation. The proposed estimator, called COPS (Conformal Optimized Prediction Set), always has finite sample guarantee in a ...

  16. De Haas-van Alphen effect and LMTO band structure of LaSn3

    International Nuclear Information System (INIS)

    Results of de Haas-van Alphen experiments in the intermetallic compound LaSn3 can be explained by a linear muffin-tin orbital band structure calculation without involving the f bands of lanthanum. (author)

  17. Coriolis mixing of the octupole vibrational bands in 156Gd

    International Nuclear Information System (INIS)

    Coriolis mixing of negative parity states in 156Gd nucleus is considered within the framework of a phenomenological model. Energy spectrum and ratios of effective probabilities of E1-transitions from the levels of octupole bands are described. Possibilities of E1-transitions from K?=2--band states are discussed; intraband E2-transitions in K?=0--, 1-- and 2--bands are calculated. 16 refs., 2 figs., 4 tabs

  18. Analytical results for random band matrices with preferential basis

    CERN Document Server

    Frahm, K M

    1995-01-01

    Using the supersymmetry method we analytically calculate the local density of states, the localiztion length, the generalized inverse participation ratios, and the distribution function of eigenvector components for the superposition of a random band matrix with a strongly fluctuating diagonal matrix. In this way we extend previously known results for ordinary band matrices to the class of random band matrices with preferential basis. Our analytical results are in good agreement with (but more general than) recent numerical findings by Jacquod and Shepelyansky.

  19. Edge Configurational Effect on Band Gaps in Graphene Nanoribbons

    OpenAIRE

    Deepika; Kumar, T. J. Dhilip; Shukla, Alok; Kumar, Rakesh

    2014-01-01

    In this Letter, we put forward a resolution to the prolonged ambiguity in energy band gaps between theory and experiments of fabricated graphene nanoribbons (GNRs). Band structure calculations using density functional theory are performed on oxygen passivated GNRs supercells of customized edge configurations without disturbing the inherent sp2 hybridization of carbon atoms. Direct band gaps are observed for both zigzag and armchair GNRs, consistent with the experimental repo...

  20. Optical band-gap determination of nanostructured WO3 film

    OpenAIRE

    Gonzalez-borrero, P. P.; Sato, F.; Medina, A. N.; Baesso, M. L.; Bento, A. C.; Baldissera, G.; Persson, C.; Niklasson, Gunnar A.; Granqvist, Claes Go?ran; Da Silva, A. Ferreira

    2010-01-01

    The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green's function approach using the projector augmented wa...

  1. Band structure of SnTe studied by Photoemission Spectroscopy

    OpenAIRE

    Littlewood, P. B.; Mihaila, B.; Schulze, R. K.; Safarik, D. J.; Gubernatis, J. E.; Bostwick, A.; Rotenberg, E.; Opeil, C. P.; Durakiewicz, T.; Smith, J. L.; Lashley, J. C.

    2010-01-01

    We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe, and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p-bands. Our study reveals the conjectured complex Fermi surface structure near the L-points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering is...

  2. The triaxial superdeformed bands in {sup 163}Lu

    Energy Technology Data Exchange (ETDEWEB)

    Sugawara-Tanabe, Kazuko [Otsuma Women' s University, Tama, Tokyo (Japan); Tanabe, Kosai [Saitama University, Dept. of Physics, Saitama (Japan)

    2002-12-01

    Triaxial superdeformed bands in {sup 163}Lu are analysed by applying the Holstein-Primakoff transformation both to the total and single-particle angular momenta. Quite good agreements with the experimental values are reproduced in the energy difference between two superdeformed bands as a function of angular momentum, and also in the ratio of E2 transitions among these bands. The results coming from the exact diagonalization of the particle plus rotor Hamiltonian are compared with the approximate calculation. (author)

  3. Inflation Calculator

    Science.gov (United States)

    Friedman, S. Morgan.

    This simple inflation calculator uses the Consumer Price Index to adjust any given amount of money, from 1800 to 1998. Creator S. Morgan Friedman uses data from the Historical Statistics of the United States for statistics predating 1975 and the annual Statistics Abstracts of the United States for data from 1975 to 1998. Links to other online inflation information are also included.

  4. Mercury Calculator

    Science.gov (United States)

    WGBH Educational Foundation

    2010-12-23

    This interactive calculator produced by Teachers' Domain helps you determine the mercury levels in various types of fish, and enables you to make more informed choices about which fish are safe to eat and which should be avoided or eaten infrequently.

  5. Electronic band structure of CdF2

    International Nuclear Information System (INIS)

    Energy distribution curves (EDC) of electrons photoemitted (h?1 = 21.22 eV and h?2 = 40.8 eV) from the valence band (F-2p) and the Cd 4d band of a CdF2 crystal are measured and the valence and conduction band structures are calculated using the local empirical pseudopotential method (EPM). Comparison of the measured and calculated data show that the three main maxima measured in the valence band correspond well to the maxima in X5, L3, and X5 obtained in the calculated histogram of the valence band density of states. The influence of the final-state structure on the position of peaks in the valence band is not observed on EDCs obtained for both, h?1 and h?2 photoemission exciting energies. For Cd 4d band the wide splitting of 1.46 eV is obtained only for h?1 = 21.22 eV while it is not obtained on EDC for h?2 = 40.8 eV. This Cd 4d band splitting may be caused by the influence of the final density-of-states maximum obtained in conduction band in X1-point. The results obtained are compared with reflectivity data available in the literature. (author)

  6. Electronic structure of the valence band of the II--VI wide band gap binary/ternary alloy interfaces

    OpenAIRE

    Olguin, D.; Baquero, R.

    1996-01-01

    We present an electronic structure calculation of the valence band for some II--VI binary/ternary alloy interfaces. We use the empirical tight-binding method and the surface Green's function matching method. For the ternary alloys we use our previously set Hamiltonians they describe well the band gap change with composition obtained experimentally. At the interface domain, we find three non-dispersive and two interface states besides the known bulk bands. The non-dispersive ...

  7. Quantum properties of optical field in photonic band gap structures.

    Science.gov (United States)

    Severini, S; Sibilia, C; Bertolotti, M; Scalora, M; Bowden, C

    2001-10-22

    A theoretical analysis of the quantum behaviour of radiation field's propagation in photonic band gaps structures is performed. In these initial calculations we consider linear inhomogeneous and nondispersive media. PMID:19424363

  8. Photonic band structure and omnidirectional band gap in anisotropic superlattice

    International Nuclear Information System (INIS)

    We investigate theoretically the photonic band structure of one-dimensional superlattice (SL) composed of alternating anisotropic layers with their principal axis oriented at arbitrary directions. The dispersion relation of order two is calculated analytically by using the 4 x 4 matrix method which is based on boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector kparallel (parallel to the layers), the dispersion curves (frequency ?) versus kB (where kB is the Bloch wave vector of the periodic system along the axis of the superlattice) is illustrated. Specific applications of these results are given for the case of biaxial superlattice. With an appropriate choice of the superlattice parameters, we show that it is possible to realise, for these coupled electromagnetic waves, an absolute (or omnidirectional) band gap of width depending on the anisotropic parameters of the media forming the SL. (author)

  9. Properties of octupole-vibrational bands in the 160Dy nucleus

    Science.gov (United States)

    Usmanov, P. N.; Solnyshkin, A. A.; Vdovin, A. I.; Salikhbaev, U. S.

    2014-11-01

    The mixing of octupole-vibrational bands in the 160Dy nucleus is analyzed within a phenomenological model that involves Coriolis coupling. The energies of levels in the bands, the reduced probabilities for E1 transitions from the octupole-vibrational bands to the ground-state and ? bands, and the ratios of the reduced probabilities for these transitions to the neighboring levels of the ground-state band are calculated. Satisfactory agreement with available experimental data is reached.

  10. Electronic band structure of helical iodine chains

    Energy Technology Data Exchange (ETDEWEB)

    Rybkovskiy, Dmitry [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation); Moscow State Institute of Radio Engineering, Electronics and Automation (Technical University), 78 Vernadskogo Prospect, 119454 Moscow (Russian Federation); Osadchy, Alexander; Obraztsova, Elena [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation)

    2012-12-15

    The electronic band structure of helical iodine chains was calculated within the empirical tight binding approach. The screw symmetry of the system was used to reduce the size of the problem to a single atom with four atomic orbitals. The overlap parameters were fitted to reproduce the DFT results for a linear iodine chain. The obtained results for helical chains have shown the energy band splitting due to the overlap between p orbitals introduced by the structure twisting. The splitting magnitude depends on the pitch of the helix. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Band Structure of New ReFeAsO Superconductors

    Directory of Open Access Journals (Sweden)

    Hyun-Tak Kim

    2013-05-01

    Full Text Available We investigate the band structure of Fe-based superconductors using the first-principle method of density-functional theory. We calculated the band structure and the density of states at the Fermi level for ReFeAsO (Re = Sm, Er superconductors. Our calculations indicate that the maximum critical superconducting transition temperature Tc will be observed for compounds with Sm and Er at 55 and 46 K, respectively.

  12. Nano Calculators

    OpenAIRE

    Venkatesh Kumaran, P.

    2007-01-01

    The whole circuit is obtained from the sun through a molecule called "Rhodopsin and bacteriorhodopsin". These molecules have the capability of trapping and storing energy from the sun light. These molecules are placed on the outer surface of the calculator to trap the energy and store it themselves for latter usage. The thickness of the whole circuit measures less than 300nm.The top layer is made up of layer which will show the different keys and a display unit. "Molecules a...

  13. Calculator thermometer

    International Nuclear Information System (INIS)

    An inexpensive substitution for calibrated thermocouples, linearizing electronics, and the NBS thermocouple tables is obtained through the use of a hand-held calculator. Automatic offset corrections and interpolations to an output temperature are possible in a one button operation beginning with voltmeter EMF. The inverse operation is also given. Appropriate constants have been found for the Cu-constantan, iron-constantan, and chromel-alumel thermocouples

  14. Braille Calculator

    OpenAIRE

    Gidh, Yoshit V.; Latey, Mahesh S.; Arpita Roy, Kunal Shah; Savita Ingle

    2013-01-01

    A thorough grounding in mathematics enhances educational and occupational opportunities for all people, whether sighted or visually impaired. In day-to-day routines, a practical understanding of mathematics allows a person to function more successfully and independently.? Access to, and doing mathematics, is one of the biggest obstacles for blind students in school and at the university. Our Braille Calculator will present new approaches to offering blind students better access to math, to ...

  15. Broken Calculator

    Science.gov (United States)

    Mandy Barrow

    2008-01-01

    This interactive applet helps students develop fluency and flexibility with numbers. At each of 6 difficulty levels the user is presented with 8 target numbers and a partial set of keys on a basic calculator (does not follow order of operations). The goal is to use the given keys to make as many of the target numbers as possible within the 3-minute time limit. Some levels include memory keys.

  16. Strain-Induced Band Profile of Stacked InAs/GaAs Quantum Dots

    Directory of Open Access Journals (Sweden)

    Worasak SUKKABOT

    2014-05-01

    Full Text Available The strain distribution and band profile in triply stacked InAs/GaAs quantum dots with dot spacing of 0.0 - 6.0 nm was calculated. The continuum elasticity theory for strain distribution and 8-band k.p theory for band structure was used. The use of the k.p method to calculate band structure with and without including the effects of strain is reported. The calculated results show the importance of strain effect on the confinement potential of the band structure for triply stacked InAs/GaAs quantum dots.doi:10.14456/WJST.2014.18

  17. Unified Theory of Charge Transport in Wide-Band and Narrow-Band Semiconductors

    Science.gov (United States)

    Ortmann, Frank; Bechstedt, Friedhelm; Hannewald, Karsten

    2009-03-01

    The charge carrier mobility is often calculated within one of the two limiting cases: wide bands or narrow bands. In the case of wide-band systems, usually pure band transport is assumed along with a calculated relaxation time. In contrast, for narrow-band materials, hopping is usually considered prevalent and the interaction with lattice vibrations is described within the polaron concept. In this talk, we will present a unified approach to the description of charge transport based upon the Kubo formalism applied to a Holstein Hamiltonian. As a result, we obtain an analytical formula for the temperature dependence and anisotropy of the mobility describing a seamless transition from band transport at low temperatures to hopping transport at high temperatures. The results are illustrated for naphthalene crystals and a comparison to previous approaches [1,2] is made. [3pt] [1] V.M. Kenkre, Phys. Lett. A 305, 443 (2002)[0pt] [2] K. Hannewald and P.A. Bobbert, Phys. Rev. B 69, 075212 (2004)

  18. Banded transformer cores

    Science.gov (United States)

    Mclyman, C. W. T. (inventor)

    1974-01-01

    A banded transformer core formed by positioning a pair of mated, similar core halves on a supporting pedestal. The core halves are encircled with a strap, selectively applying tension whereby a compressive force is applied to the core edge for reducing the innate air gap. A dc magnetic field is employed in supporting the core halves during initial phases of the banding operation, while an ac magnetic field subsequently is employed for detecting dimension changes occurring in the air gaps as tension is applied to the strap.

  19. Ultra wide band antennas

    CERN Document Server

    Begaud, Xavier

    2013-01-01

    Ultra Wide Band Technology (UWB) has reached a level of maturity that allows us to offer wireless links with either high or low data rates. These wireless links are frequently associated with a location capability for which ultimate accuracy varies with the inverse of the frequency bandwidth. Using time or frequency domain waveforms, they are currently the subject of international standards facilitating their commercial implementation. Drawing up a complete state of the art, Ultra Wide Band Antennas is aimed at students, engineers and researchers and presents a summary of internationally recog

  20. Effect of size of silica microspheres on photonic band gap

    Energy Technology Data Exchange (ETDEWEB)

    Dhiman, N., E-mail: naresh20dhiman@gmail.com; Sharma, A., E-mail: naresh20dhiman@gmail.com; Gathania, A. K. [Department of Physics, National Institute of Technology, Hamirpu-177005, Himachal Pradesh (India); Singh, B. P. [Department of Physics, Indian Institute of Technology Bombay Powai, Mumbai-400076 (India)

    2014-04-24

    In present work photonic crystals of different size of silica microspheres have been fabricated. The optical properties of these developed photonic crystals have been studied using UV-visible spectroscopy. UV-visible spectroscopy shows that they have photonic band gap that can be tuned in visible and infrared regime by changing the size of silica microspheres. The photonic band gap structures of these photonic crystals have been calculated using MIT photonic band gap package. It also reveals that with the increase in size of silica microspheres the photonic band gap shifts to lower energy region.

  1. Two-quasiparticle bands in ^174Hf studied with Gammasphere

    Science.gov (United States)

    Djongolov, M. K.; Riedinger, L. L.; Bingham, C. R.; Danchev, M.; Goon, J.; Zhang, Jing-Ye; Hartley, D. J.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Kondev, F. G.; Lauritsen, T.; Moore, E. F.; Hagemann, G.; Sletten, G.; Aguilar, A.; Riley, M. A.; Chowdhury, P.; Mukherjee, G.; Ngijoi-Yogo, E.; Tandel, S. K.; Cullen, D. M.; Dracoulis, G. D.; Kaye, R. A.; Laird, R. W.; McClain, B.

    2004-10-01

    We performed recently a high-statistics experiment on rotational bands in ^174Hf using Gammasphere located at Argonne National Laboratory. The enhanced statistics from this thin-target experiment allowed the discovery of a new low-K band in this nucleus and an extension of previously known side bands towards 50 hbar. This induced a new overview of the orbital couplings available in this nucleus at low energies. We will discuss the physics of two-quasiparticle bands in ^174Hf using TRS calculations and comparison with available data from adjacent odd-A nuclei.

  2. Photoperiod Calculator

    Science.gov (United States)

    Lammi, Jarmo J.

    Jarmo Lammi has developed this simple, easy-to-use tool that provides information useful for teaching and research purposes. Users select a day, month, location (city or latitude and longitude) and time-of-day, and then submit their entry. The Calculator then generates the following information: latitude and longitude for the city/location, declination of the sun, height of sun at noon that day, daylength, and time of sunrise and sunset. This is a useful tool for ecological research and teaching.

  3. DUAL BAND MONOPOLE ANTENNA DESIGN

    Directory of Open Access Journals (Sweden)

    P. Jithu

    2013-06-01

    Full Text Available The WLAN and Bluetooth applications become popular in mobile devices, integrating GSM and ISM bands operation in one compact antenna, can reduce the size of mobile devices. Recently, lot many investigations are carried out in designing a dual band antennas with operating frequencies in GSM band and in ISM band for mobile devices. Printed monopoles are under this investigation. In this paper, dual-band printed monopoles are presented to operate at GSM band i.e. 900 MHz and ISM band i.e. 2.4 GHz. We intend to observe the antenna characteristics on the network analyzer and verify the theoretical results with the practical ones.

  4. DUAL BAND MONOPOLE ANTENNA DESIGN

    OpenAIRE

    Jithu, P.; Paul, A.; Pithadia, V.; Misquitta, R.; Khot, U. P.

    2013-01-01

    The WLAN and Bluetooth applications become popular in mobile devices, integrating GSM and ISM bands operation in one compact antenna, can reduce the size of mobile devices. Recently, lot many investigations are carried out in designing a dual band antennas with operating frequencies in GSM band and in ISM band for mobile devices. Printed monopoles are under this investigation. In this paper, dual-band printed monopoles are presented to operate at GSM band i.e. 900 MHz and ISM band i.e. 2.4 GH...

  5. Band structure and electronic properties of transition metal hydrides

    International Nuclear Information System (INIS)

    A calculation of band structures, densities of states, and Fermi surfaces for 3d-element hybrides is made. The results of this calculation are compared with the APW calculation by Switendick and the experimental measured values of electronic specific heat, magnetic susceptibility, and optical absorptivity. By using the Gaspari-Gyorffy theory values of the electron-phonon coupling constant and Tsub(c) are calculated. High critical temperatures of superconductivity are predicted for chromium and nickel dihydrides. (author)

  6. Small Quadrupole Deformation for the Dipole Bands in 112In

    CERN Document Server

    Trivedi, T; Sethi, J; Saha, S; Kumar, S; Naik, Z; Parkar, V V; Naidu, B S; Deo, A Y; Raghav, A; Joshi, P K; Jain, H C; Sihotra, S; Mehta, D; Jain, A K; Choudhury, D; Negi, D; Roy, S; Chattopadhyay, S; Singh, A K; Singh, P; Biswas, D C; Bhowmik, R K; Muralithar, S; Singh, R P; Kumar, R; Rani, K

    2012-01-01

    High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\\sim$ 20$\\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations.

  7. Reverberation reduction by sub-band unmasking

    Science.gov (United States)

    Libbey, Brad; Rogers, Peter

    2002-05-01

    Reverberation reduces the intelligibility of speech recorded in rooms. Signal processing algorithms attempt to reduce this reverberation such that the speech not only sounds less reverberant, but is more intelligible. Historically, these techniques are based on calculations of the room impulse response, on arrays of two or more microphones, noise cancellation, or cepstral techniques. The new technique assumes that the intelligibility loss is due to overlap masking of reverberant tails of speech. The algorithm looks at sub-bands and identifies those that mask adjacent bands. When this occurs in conjunction with a decaying envelope the decay rate is increased. Thus, the masked band has a greater chance of being heard. Intelligibility results for the processed speech will be presented.

  8. Rubber Band newton Scale

    Science.gov (United States)

    Don Rathjen

    2009-01-01

    In this activity, learners make a simple spring-like scale using a rubber band instead of a spring, and calibrate the scale in newtons (N). Learners will gain an understanding of and familiarity with the newton as a unit of force, and use the scale to weigh common objects.

  9. Rubber Band Boat

    Science.gov (United States)

    Watsonville Environmental Science Workshop

    2011-01-01

    In this activity, learners build styrofoam boats powered by twisted rubber bands. Use this activity to introduce learners to potential energy, kinetic energy, Newton's Laws of Motion, rotational motion, and density. Note: a drill is required for this activity, and is not included in the cost of materials.

  10. Rubber Band Racer

    Science.gov (United States)

    Watsonville Environmental Science Workshop

    2011-01-01

    In this activity, learners construct speedy vehicles made out of paper plates and powered by twisted rubber bands. This toy is an excellent demonstration of potential and kinetic energy and how things move. This project can also be used to help learners understand Newton's Laws of Motion and friction. Activity guide has detailed step-by-step instructions, illustrations, and focus questions.

  11. Rubber Band Car

    Science.gov (United States)

    WGBH

    2010-01-01

    In this design challenge activity, learners build a car that can travel at least four feet using rubber band power and use the design process to debug problems. Learners can follow up this activity with the "Motorized Car" and "Customized Car" activities in the Leader Notes guide.

  12. Multi-Band-SWIFT.

    Science.gov (United States)

    Idiyatullin, Djaudat; Corum, Curtis A; Garwood, Michael

    2015-02-01

    A useful extension to SWIFT (SWeep Imaging with Fourier Transformation) utilizing sidebands of the excitation pulse is introduced. This MRI method, called Multi-Band-SWIFT, achieves much higher bandwidth than standard SWIFT by using multiple segmented excitations (bands) of the field of view. A description of the general idea and variants of the pulse sequence are presented. From simulations and semi-phenomenological theory, estimations of power deposition and signal-to-noise ratio are made. MB-SWIFT and ZTE (zero-TE) sequences are compared based on images of a phantom and human mandible. Multi-Band-SWIFT provides a bridge between SWIFT and ZTE sequences and allows greatly increased excitation and acquisition bandwidths relative to standard SWIFT for the same hardware switching parameters and requires less peak amplitude of the radiofrequency field (or greater flip angle at same peak amplitude) as compared to ZTE. Multi-Band-SWIFT appears to be an attractive extension of SWIFT for certain musculoskeletal and other medical imaging applications, as well as for imaging materials. PMID:25557859

  13. Wide band devices

    International Nuclear Information System (INIS)

    Several methods helping to utilize the neutron spectra emitted by pulsed neutron sources with better efficiency are considered (e.g. supermirror neutron guides, multidetectors, wide band polarizers and the method of pseudostatistical modulation). The present status of proposed approaches are reviewed. (author) 7 figs., 6 refs

  14. Linear methods in band theory

    DEFF Research Database (Denmark)

    Andersen, O. Krogh

    1975-01-01

    Two approximate methods for solving the band-structure problem in an efficient and physically transparent way are presented and discussed in detail. The variational principle for the one-electron Hamiltonian is used in both schemes, and the trial functions are linear combinations of energy-independent augmented plane waves (APW) and muffin-tin orbitals (MTO), respectively. The secular equations are therefore eigenvalue equations, linear in energy. The trial functions are defined with respect to a muffin-tin (MT) potential and the energy bands depend on the potential in the spheres through potential parameters which describe the energy dependence of the logarithmic derivatives. Inside the spheres, the energy-independent APW is that linear combination of an exact solution, at the arbitrary but fixed energy E?, and its energy derivative which matches continuously and differentiably onto the plane-wave part in the interstitial region. The energies obtained with the linear-APW method for the MT potential have errors of order (E-Ev)4. Similarly, the energy-independent MTO is that linear combination which matches onto that solution of the Laplace equation in the interstitial region which is regular at infinity. The energies obtained with the linear-MTO method have additional errors of order (E-Vmtz)2, arising from the interstitial region where the potential is Vmtz. The linear-APW (LAPW) method combines desirable features of the APW and OPW methods; it can treat d bands, the energy dependence of its pseudopotential is linear and, owing to the smoothness of the energy-independent APW at the spheres, non-MT contributions to the potential are included principally through their Fourier components. The linear-MTO (LMTO) method is particularly suited for closely packed structures and it combines desirable features of Korringa-Kohn-Rostoker, linear-combination-of-atomic-orbitals, and cellular methods; the secular matrix is linear in energy, the overlap integrals factorize as potential parameters and structure constants, the latter are canonical in the sense that they neither depend on the energy nor the cell volume and they specify the boundary conditions on a single MT or atomic sphere in the most convenient way. This method is very well suited for self-consistent calculations. The empty-lattice test is applied to the linear-MTO method and the free-electron energy bands are accurately reproduced. Finally, it is shown how relativistic effects may be included in both the LAPW and LMTO methods.

  15. Calculator calculus

    CERN Document Server

    McCarty, George

    1982-01-01

    How THIS BOOK DIFFERS This book is about the calculus. What distinguishes it, however, from other books is that it uses the pocket calculator to illustrate the theory. A computation that requires hours of labor when done by hand with tables is quite inappropriate as an example or exercise in a beginning calculus course. But that same computation can become a delicate illustration of the theory when the student does it in seconds on his calculator. t Furthermore, the student's own personal involvement and easy accomplishment give hi~ reassurance and en­ couragement. The machine is like a microscope, and its magnification is a hundred millionfold. We shall be interested in limits, and no stage of numerical approximation proves anything about the limit. However, the derivative of fex) = 67.SgX, for instance, acquires real meaning when a student first appreciates its values as numbers, as limits of 10 100 1000 t A quick example is 1.1 , 1.01 , 1.001 , •••• Another example is t = 0.1, 0.01, in the functio...

  16. Reliability calculations

    International Nuclear Information System (INIS)

    Risk and reliability analysis is increasingly being used in evaluations of plant safety and plant reliability. The analysis can be performed either during the design process or during the operation time, with the purpose to improve the safety or the reliability. Due to plant complexity and safety and availability requirements, sophisticated tools, which are flexible and efficient, are needed. Such tools have been developed in the last 20 years and they have to be continuously refined to meet the growing requirements. Two different areas of application were analysed. In structural reliability probabilistic approaches have been introduced in some cases for the calculation of the reliability of structures or components. A new computer program has been developed based upon numerical integration in several variables. In systems reliability Monte Carlo simulation programs are used especially in analysis of very complex systems. In order to increase the applicability of the programs variance reduction techniques can be applied to speed up the calculation process. Variance reduction techniques have been studied and procedures for implementation of importance sampling are suggested. (author)

  17. The ASTROSAT/UVIT Exposure Time Calculator

    Science.gov (United States)

    Leahy, D.

    2014-05-01

    ASTROSAT is India's broad-spectral-band astronomy satellite. The Ultraviolet Imaging Telescope (UVIT) on ASTROSAT provides UV and optical (120 to 550 nm) coverage. The UVIT exposure time calculator was developed to enable planning of observations with the UVIT instrument of various astronomical sources of UV radiation. Here, the UVIT exposure time calculator is described.

  18. Infrared spectroscopy of electronic bands in bilayer graphene

    International Nuclear Information System (INIS)

    We present infrared spectra (0.1-1 eV) of electrostatically gated bilayer graphene as a function of doping and compare it with tight-binding calculations. All major spectral features corresponding to the expected interband transitions are identified in the spectra: a strong peak due to transitions between parallel split-off bands and two onset-like features due to transitions between valence and conduction bands. A strong gate voltage dependence of these structures and a significant electron-hole asymmetry are observed that we use to extract several band parameters. The structures related to the gate-induced band gap are less pronounced in the experiment than predicted by the tight-binding model that uses parameters obtained from previous experiments on graphite and recent self-consistent band-gap calculations

  19. An innovative band-to-band tunneling analytical model and implications in compact modeling of tunneling-based devices

    Science.gov (United States)

    De Michielis, L.; Da?tekin, N.; Biswas, A.; Lattanzio, L.; Selmi, L.; Luisier, M.; Riel, H.; Ionescu, A. M.

    2013-09-01

    In this paper, an analytical band-to-band tunneling model is proposed, validated by means of drift-diffusion simulation and comparison with experimental data, implemented in Verilog-A, and finally proven with SPICE simulator through simulation of circuits featuring tunneling diodes. The p-n junction current calculation starts from a non-local Band-to-Band tunneling theory including the electron-phonon interaction and therefore it is particularly suited for indirect semiconductor materials such as silicon- or germanium-based interband tunneling devices.

  20. MRO Ka-Band Demonstration

    Science.gov (United States)

    Shambayati, Shervin

    2006-01-01

    This viewgraph presentation reviews the Mars Reconnaissance Orbiter use of the Ka-band. Due to lack of spectrum at X-band (8.41 GHz) NASA is switching to Ka-band (32 GHz) for its Deep Space Missions. This is 50 MHz bandwidth at X-band vs. 500 MHz at Ka-band. Weather events cause a greater degradation for the Ka-band link. Therefore, the Ka-band needs to be operated in a different manner than the X-band. The Ka-band achieves a maximum average capacity at a lower weather reliability than X-band (80 to 90% for Ka-band vs. 95% for X-band). Studies have been done to suggest different methods of operation for Ka-band. The Mars Reconnaissance Orbiter (MRO) will allow us to evaluate the proposed methods of operations for the Ka-band The MRO is the first spacecraft to have a fully functioning independent Ka-band downlink stream.

  1. Occlusion calculator.

    Science.gov (United States)

    Bansal, Abhishek; Hiremath, Anand; Aluckal, Eby

    2015-01-01

    Start with end in mind' is a popular cliché in orthodontics. This aptly applies to the therapeutic occlusion the orthodontist strives to achieve. Predicting the post treatment occlusion is an essential component of treatment planning. When no extractions or symmetric extractions are done predicting the final occlusion is somewhat easy. Prediction is challenging when we do unconventional and/or asymmetric extractions. To aid this decision Kesling proposed the 'Kesling Setup'. Though it serves the purpose acceptably; it is time, energy and money consuming. We have developed a model which can help us visualize the final occlusion in matter of seconds. Although this model is primarily intended for orthodontic postgraduate teaching, it can be of considerable use even to a seasoned orthodontist. The regular use of "Orthodontic Calculator" in our department is a testimony to its usefulness. PMID:25738101

  2. Structures calculation

    International Nuclear Information System (INIS)

    Structures calculation is a research and applications field in permanent evolution thanks to the development of more and more performing computer tools for the modeling and the numerical simulation of complex structures taking into account the behaviour of more and more sophisticated materials. The aim of the Computational Structural Mechanics Association (CSMA) is to develop technical and scientific exchanges between industrial and research partners. This colloquium, organized every 2 years comprises 4 general conferences and 125 communications. Five papers were selected for INIS. Three of them deal with the dynamical modeling of the vibrational behaviour of reactor core components (fuel assemblies and control rod clusters), one concerns the load resistance of multi-perforated metal structures like steam generator tube plates or turbine blades, and the last paper concerns the humidity stability of composite materials used in particle detectors. (J.S.)

  3. Elucidating the stop bands of structurally colored systems through recursion

    CERN Document Server

    Amir, Ariel

    2012-01-01

    Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...

  4. Cluster structure and deformed bands in the 38Ar nucleus

    International Nuclear Information System (INIS)

    The structure of the 38Ar nucleus is investigated by the 34S+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K?=0+ band is found to be predominantly 34S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states

  5. Enhancement of phononic band gaps in ternary/binary structure

    Energy Technology Data Exchange (ETDEWEB)

    Aly, Arafa H., E-mail: arafa16@yahoo.com [Physics department, Faculty of sciences, Beni-suef University, Beni Suef 62111 (Egypt); Mehaney, Ahmed [Physics department, Faculty of sciences, Beni-suef University, Beni Suef 62111 (Egypt)

    2012-11-01

    Based on the transfer matrix method (TMM) and Bloch theory, the interaction of elastic waves (normal incidence) with 1D phononic crystal had been studied. The transfer matrix method was obtained for both longitudinal and transverse waves by applying the continuity conditions between the consecutive unit cells. Dispersion relations are calculated and plotted for both binary and ternary structures. Also we have investigated the corresponding effects on the band gaps values for the two types of phononic crystals. Furthermore, it can be observed that the complete band gaps are located in the common frequency stop-band regions. Numerical simulations are performed to investigate the effect of different thickness ratios inside each unit cell on the band gap values, as well as unit cells thickness on the central band gap frequency. These phononic band gap materials can be used as a filter for elastic waves at different frequencies values.

  6. Graphene Nano ribbon Conductance Model in Parabolic Band Structure

    International Nuclear Information System (INIS)

    Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nano ribbon (GNR) with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel

  7. Identification of triaxial strongly deformed bands in 164Hf

    Science.gov (United States)

    Marsh, J. C.; Ma, W. C.; Hagemann, G. B.; Janssens, R. V. F.; Bengtsson, R.; Ryde, H.; Carpenter, M. P.; Gürdal, G.; Hartley, D. J.; Hoffman, C. R.; Ijaz, Q. A.; Kondev, F. G.; Lauritsen, T.; Mukhopadhyay, S.; Riedinger, L. L.; Yadav, R. B.; Zhu, S.

    2013-10-01

    Two new rotational bands of distinct character have been identified in 164Hf. They are suggested to correspond to the long-anticipated triaxial strongly deformed (TSD) bands predicted by theoretical studies. The bands have been linked to known states, and the level spins and energies could be determined. The bands are also substantially stronger in intensity and are located at lower spins than the previously observed TSD bands in 168Hf, hereby making 164Hf the best even-even system so far for the study of TSD structures in the A˜160 mass region. Cranking calculations based on the modified-oscillator model suggest that the bands are associated with four-quasiparticle configurations that involve high-j intruder (i13/2)2 proton orbitals.

  8. Edge configurational effect on band gaps in graphene nanoribbons

    Science.gov (United States)

    Deepika, Kumar, T. J. Dhilip; Shukla, Alok; Kumar, Rakesh

    2015-03-01

    In this article, we put forward a resolution to the prolonged ambiguity in energy band gaps between theory and experiments of fabricated graphene nanoribbons (GNRs). Band structure calculations using density functional theory are performed on oxygen-passivated GNR supercells of customized edge configurations without disturbing the inherent s p2 hybridization of carbon atoms. Direct band gaps are observed for both zigzag and armchair GNRs, consistent with the experimental reports. In addition, we provide an explanation of the experimentally observed scattered band gap values of GNRs as a function of width in a crystallographic orientation on the basis of edge configurations. We conclude that edge configurations of GNRs significantly contribute to band gap formation in addition to its width for a given crystallographic orientation and will play a crucial role in band gap engineering of GNRs for future research on fabrication of nanoelectronic devices.

  9. Computing Band Structures in Undergraduate Solid State

    Science.gov (United States)

    Hasbun, Javier

    2011-03-01

    Understanding band structures is quite challenging for undergraduate solid state physics students. Calculating the band structures is even more difficult. However, using the techniques developed earlier [1], and which were applied to the simple cubic structures, it is possible to extend them to semiconducting systems in a simple way. The idea is to employ the 8-band model concept of Harrison's Hamiltonian approach [2] to model and parametrize the bands. The method also uses the system's band structure's Green's function and employs the k-space Brillouin-zone ray approach [3] combined with a complex integration method [4] to obtain the density of states. The number of occupied electron states up to a certain energy is obtained using Romberg's method and example results will be shown. [1] Javier Hasbun (J42.00013) http://meetings.aps.org/Meeting/MAR10/Event/119248 [2] S. Froyen, and W. A. Harrison, Phys. Rev. B Vol. 20, 2420 (1979). [3] An-Ban Chen, Phys. Rev. B, Vol. 16, 3291 (1977). [4] Javier Hasbun http://meetings.aps.org/link/BAPS.2009.MAR.L29.12

  10. Ab Initio Calculations of Oxosulfatovanadates

    DEFF Research Database (Denmark)

    FrØberg, Torben; Johansen, Helge

    1996-01-01

    Restricted Hartree-Fock and multi-configurational self-consistent-field calculations together with secondorder perturbation theory have been used to study the geometry, the electron density, and the electronicspectrum of (VO2SO4)-. A bidentate sulphate attachment to vanadium was found to be stable with anO-V-O angle of 72.5 degrees . The calculated spectrum shows bands in reasonable agreement with anexperimental spectrum which has been attributed to (VO2SO4)-. The geometry and the electron density fortwo binuclear vanadium complexes proposed as intermediates in the vanadium catalyzed SO2 oxidationhave further been studied.

  11. TDRS Ku band gateway

    Science.gov (United States)

    Collins, Cynthia; Lecha, Javier; Principe, Caleb M.; Ross, Douglas

    1987-01-01

    The Wideband Transport Frame Formatter (WTFF) is the tracking and data relay satellite (TDRS) ku-band return link gateway. The WTFF system is a multiplexing device developed to process and downlink the high rate data generated by a wide variety of users. The WTFF is designed to frame and format high data rate user channels into transport frames and multiplex according to a predefined schedule into two bit streams that are compatible with TDRS Ku I and Q band service. The combined data rate will be 300 Mbps. The WTFF will service up to eight input channels generating data in the range of 10 to 150 Mbps. In addition to these input channels, audio data will be accepted by the WTFF system and inserted in the downlink. A second function of the WTFF is to provide telecommunication coding as assigned to each virtual channel to ensure a given quality of service.

  12. AMNIOTIC BAND SYNDROME

    Directory of Open Access Journals (Sweden)

    Jovana ?or?evi?

    2009-04-01

    Full Text Available Amniotic band syndrome (ABS is a set of congenital malformations attributed to amniotic bands that entangle fetal parts during intrauterine life, which results in a broad spectrum of anatomic disturbances - ranging from minor constriction rings and lymphedema of the digits to complex, bizarre multiple congenital anomalies incompatible with life. ABS is not very often, but should be considered in every newborn with congenital anomalies, especially defects of extremities and/or body walls. ABS can be diagnosed prenatally by ultrasound; otherwise, the defects are seen after birth. Child's karyotyping is of great importance, in order to avoid misdiagnosis and incorrect information of recurrence risk. A team of specialists should be included in the treatment and follow-up of children with ABS, according to individual needs of every single patient.The aim of this paper is to point out diagnostic and therapeutic approaches in newborns with ABS trough the report of two cases.

  13. Photonic Band Gap

    Science.gov (United States)

    Ho, Seng-Tiong

    Created by Boyang Liu and Professor Seng-Tiong Ho at Northwestern University, and presented by the NanoEd Resource Portal, this site covers the concept of the photonic band gap. Here, visitors will find a basic description of the concept, ideas of how to incorporate it into classroom activities, and a user's manual to walk students step-by-step through the concept. There is also a link to an interactive simulation (the link is labeled Open Visualization), which allows students to adjust the wavelength and color of the light source, particle size, and incident angle to view changes to the photonic band gap. This is a thorough and useful resource for any nanotechnology classroom.

  14. Rotational band 111Sn

    International Nuclear Information System (INIS)

    Partial level scheme of the neutron deficient 111Sn isotope is established upto an excitation energy of about 9 MeV and I? = 43/2- from ?-rays following 103Rh(12C,p3n) reaction. Clear evidence for the existence of a negative parity rotational band above I? = 23/2-, most probably based on 3p-2h configuration, is obtained. (orig.)

  15. Spectral electron momentum density calculation in graphite

    International Nuclear Information System (INIS)

    The linear muffin-tin orbital method has been used to calculate energy-momentum distribution of valence electrons in graphite along major symmetry directions and as the spherical average over the irreducible wedge of the Brillouin zone. These data bridge the gap between existing band structure calculations and emerging electron momentum spectroscopy of solids. The calculation has been validated by comparison to the most accurate experimental data on the highly oriented laser annealed carbon films. 14 refs., 1 tab., 4 figs

  16. Multiple band structure and band termination in 157Ho

    International Nuclear Information System (INIS)

    Rotational bands of 157Ho have been populated via the 124Sn(37Cl, 4n) reaction at beam energies of 155 and 165 MeV. Gamma-ray spectroscopy was performed using the 8? spectrometer at Chalk River. Many rotational bands have been observed for the first time. A detailed level scheme is presented, containing approximately 380 transitions, and the quasiparticle structure of the various bands is discussed. Band termination has been observed in the yrast states. For strongly coupled bands, B(M1)/B(E2) transition strength ratios are extracted and compared with previous measurements and theoretical expectations. Branching ratios for out-of-band E2 transitions are analysed to extract band mixing interaction strengths. Implications for rotational damping are considered. The interaction at the first backbend in the ground bands is found to be strongly signature dependent; this is evidence for a signature-dependent triaxial shape of the nucleus. (orig.)

  17. Band structure of Gd2Ni2Al15 intermetallic compound

    International Nuclear Information System (INIS)

    The results of band structure calculation of the Gd2Ni2Al15 intermetallic compound by the augmented plane wave method are presented. It was found that the positions of nickel 3d bands and gadolinium 4f bands are the same which explains the magnetic moment value of the nickel atom in this compound about 1.6 ?/sub B/

  18. A narrow conduction band in YBa2Cu3O7 - ?

    International Nuclear Information System (INIS)

    LDA band-structure calculations of YBa2Cu3O7 - ? show wide bands (of several eV) spanning Ef. The authors discuss how experiments especially transport measurements, contradict this and indicate the presence of a narrow conduction band (about a tenth of an eV wide)

  19. Absorption spectrum and assignment of the Chappuis band of ozone

    International Nuclear Information System (INIS)

    New global diabatic potential energy surfaces of the electronic states 1B1 and 1A2 of ozone and the non-adiabatic coupling surface between them are constructed from electronic structure calculations. These surfaces are used to study the visible photodissociation in the Chappuis band by means of quantum mechanical calculations. The calculated absorption spectrum and its absolute intensity are in good agreement with the experimental results. A vibrational assignment of the diffuse structures in the Chappuis band system is proposed on the basis of the nodal structures of the underlying resonance states

  20. Correlation effects in the valence bands of ferromagnetic semiconductor EuS

    CERN Document Server

    Sharma, A

    2005-01-01

    We present a many body analysis of the multi-band Kondo lattice model. The study is then combined with the first principles TB-LMTO band structure calculations, in order to investigate the temperature dependent correlation effects in the 3$\\textit{p}$ valence bands of the ferromagnetic semiconductor EuS. Some of the physical properties of interest like the quasi-particle density of states (Q-DOS), spectral density (SD) and quasi-particle band structure (Q-BS) are calculated and discussed. Therewith, we propose a spin resolved ARPES of the valence bands of EuS to be performed.

  1. Variations in the wide band and narrow band beams for NuMI

    International Nuclear Information System (INIS)

    This paper is directed at studies related to using the main injector at Fermilab to generate neutrino beams. The note describes two studies that have been done on variations of the reference beams. The first suggests a method to reduce the low-energy tail of the narrow band beam (NBB); the second addresses possibilities for minimizing the far/near variations in the spectra for the wide band beam (WBB). Both of these are studied with NUADA (Long Baseline) and are meant to give guidance for GEANT calculations that would be able to answer whether the suggested ideas are in fact improvements, once all the complex processes are included

  2. Hofstadter butterflies for flat bands

    OpenAIRE

    Aoki, Hideo; Ando, Masato; Matsumura, Hajime

    1996-01-01

    Hofstadter's diagram, or the energy spectrum against the magnetic field in tight-binding systems, is obtained for the models having flat (dispersionless) one-electron band(s) that have originally been proposed for itinerant spin ferromagnetism. Magnetic fields preserve those flat bands that arise from a topological reason, while dispersions emerge in a singular manner for the flat bands arising from interference, implying an anomalous orbital magnetism.

  3. Coulomb (or strong) correlation effects in the band structure of Eu2O3

    International Nuclear Information System (INIS)

    Two band-structure calculations of Eu2O3 are performed, one of them in the metallic phase and the other in the semiconducting phase; the difference between the corresponding band Hamiltonians is the occupation potential U(r) that includes the Coulomb correlation effects. On both phases, the 4f occupied bands are mixed with the 2p bands; this fact broadens these 4f bands so that its calculation is possible in this complex crystal lattice T/sub h/7. In the semiconducting band structure, the 4f empty bands are localized in the d-zone energy showing (4f, 5d) hybridization that produces a broadening still greater than for the 4f occupied bands. The semiconducting gap is GAMMA1+ - H1-and its value is 3.7 eV. (author)

  4. Magnetized plasma photonic crystals band gap

    Science.gov (United States)

    Ataei, Elahe; Sharifian, Mehdi; Bidoki, Najmeh Zare; Bidoki

    2014-08-01

    In this paper, the effect of the magnetic field on one-dimensional plasma photonic crystal band gaps is studied. The one-dimensional fourfold plasma photonic crystal is applied that contains four periodic layers of different materials, namely plasma1-MgF2-plasma2-glass in one unit cell. Based on the principle of Kronig-Penney's model, dispersion relation for such a structure is obtained. The equations for effective dielectric functions of these two modes are theoretically deduced, and dispersion relations for transverse electric (TE) and transverse magnetic (TM) waves are calculated. At first, the main band gap width increases by applying the exterior magnetic field. Subsequently, the frequency region of this main band gap transfers completely toward higher frequencies. There is a particular upper limit for the magnitude of the magnetic field above which increasing the exterior magnetic field strength doesn't have any significant influence on the dispersion function behavior. (With an increase in incident angle up to ?1 = 66°, the width of photonic band gap (PBG) changes for both TM/TE polarization.) With an increase in incident angle up to ?1 = 66°, the width of PBG decreases for TM polarization and the width of PBG increases for TE polarization, but it increases with further increasing of the incident angle from ?1 = 66° to 89° for both TE- and TM-polarizations. Also, it has been observed that the width of the photonic band gaps changes rapidly by relative difference of the two-plasma frequency. Results show the existence of several photonic band gaps that their frequency and dispersion magnitude can be controlled by the exterior magnetic field, incident angle, and two plasma frequencies. The result of this research would provide theoretical instructions for designing filters, microcavities, fibers, etc.

  5. Quadrupole collective correlations and termination of the superdeformed bands in mercury

    International Nuclear Information System (INIS)

    Fully self-consistent Generator Coordinate Method calculations have been performed on a basis of quadrupole constrained Hartree-Fock plus BCS wave functions for the five even mercury isotopes 190-198 Hg. The GCM results support conclusions drawn from previous HF+BCS calculations. The predicted evolution of superdeformed band head (shape isomer) properties as a function of the neutron number is consistent with the data. Using calculated transition matrix elements, we evaluate in-band versus out-of-band quadrupole decay and explain the sudden termination of the superdeformed band

  6. 4H-SiC band structure investigated by surface photovoltage spectroscopy

    International Nuclear Information System (INIS)

    The conduction and valence band structure of high-purity 4H-SiC epilayers have been studied by surface photovoltage spectroscopy (SPS). A comparison between defect-free and single-layer stacking fault affected areas is reported. Electronic transitions, determined by SPS, are in good agreement with ab initio calculations. Electronic transitions and changes in band occupation have been observed in stacking fault rich areas below the band gap. Moreover, stacking faults induce the presence of a split-off band below the conduction band and a modification of the electron density of states in the conduction band always at the M point.

  7. Transport properties of one-dimensional, disordered two-band systems

    OpenAIRE

    Garcia, Martin E.; Llois, Ana Maria; Balseiro, C. A.; Weissmann, Mariana

    1986-01-01

    We have studied the transport properties of disordered one-dimensional two-band systems. The model includes a narrow d band hybridised with an s band. The Landauer formula was used in the case of a very narrow d band or in the case of short chains. The results were compared with the localisation length of the wavefunctions calculated by the transfer matrix method, which allows the use of very lang chains, and an excellent agreement was obtained.

  8. Electronic band structure of La 4Sb 3 and La 4Bi 3

    Science.gov (United States)

    Takegahara, Katsuhiko; Harima, Hisatomo; Kasuya, Tadao

    1985-10-01

    The self-consistent APW band calculations for La 4Sb 3 and La 4Bi 3 have been done. A narrow gap appears between the conduction bands derived dominantly from the La d states and the valence bands derived mostly from the p states of pnictogens mixed with the La d states. In Sm 4Bi 3 the 4f level is expected to be in this gap, but closes to the bottom of conduction band.

  9. Anatomical and biomechanical evaluation of the tension band technique in patellar fractures

    OpenAIRE

    Baran, Onder; Manisali, Metin; Cecen, Berivan

    2008-01-01

    Tension band wiring for patellar fractures is common, but some recent reports refer to disadvantages of this approach. Our anatomical and biomechanical study focused on use of tension band techniques in patellar fractures. The anatomy of the patella and tendon insertion was examined with knee magnetic resonance imaging (MRI) and correlated with the technical requirements of the tension band. Tension band wiring over tendinous tissue was simulated and calculated with a cyclic biomechanical tes...

  10. Deformed bands in odd-A 1f sub(7/2) shell nuclei

    International Nuclear Information System (INIS)

    The properties of the rotation-like bands in 45Sc, 45Ti, 51Cr and 53Fe have been studied via (?, p?) and (?, n?) reactions. The decrease of the collectivity is observed in the K sup(?) = 3/2+ band in 45Sc. In 53Fe, the band structure of the K sup(?) = 1/2- band is lost for J >= 11/2- in agr eement with a recent shell-model calculation. (author)

  11. Self-consistent treatment of v-groove quantum wire band structure in no parabolic approximation

    Directory of Open Access Journals (Sweden)

    Crnjanski Jasna V.

    2004-01-01

    Full Text Available The self-consistent no parabolic calculation of a V-groove-quantum-wire (VQWR band structure is presented. A comparison with the parabolic flat-band model of VQWR shows that both, the self-consistency and the nonparabolicity shift sub band edges, in some cases even in the opposite directions. These shifts indicate that for an accurate description of inter sub band absorption, both effects have to be taken into the account.

  12. On the band offset in PbTe-PbEuSeTe quantum wells

    International Nuclear Information System (INIS)

    The influence of the experimental uncertainties in carrier density and effective mass on the theoretical determination of the band offset in PbTe-PbEuSeTe quantum wells is analyzed in the framework of the two-band Dimmock model. It is shown that these uncertainties could lead to a large indetermination of the calculated band offset and that two different values of the band offset are compatible with the experimental data. (author). 11 refs, 2 figs

  13. The Oxygen a Band

    Science.gov (United States)

    Benner, D. Chris; Devi, V. Malathy; Hoo, Jiajun; Hodges, Joseph; Long, David A.; Sung, Keeyoon; Drouin, Brian; Okumura, Mitchio; Bui, Thinh Quoc; Rupasinghe, Priyanka

    2014-06-01

    The oxygen A band is used for numerous atmospheric experiments, but spectral line parameters that sufficiently describe the spectrum to the level required by OCO2 and other high precision/accuracy experiments are lacking. Fourier transform spectra from the Jet Propulsion Laboratory and cavity ring down spectra from the National Institute of Standards and Technology were fitted simultaneously using the William and Mary multispectrum nonlinear least squares fitting technique into a single solution including the entire band. In addition, photoacoustic spectra already available from the California Institute of Technology will be added to the solution. The three types of spectrometers are complementary allowing the strengths of each to fill in the weaknesses of the others. With this technique line positions, intensities, widths, shifts, line mixing, Dicke narrowing, temperature dependences and collision induced absorption have been obtained in a single physically consistent fit. D. Chris Benner, C. P. Rinsland, V. M. Devi, M. A. H. Smith, and D. Atkins, JQSRT 1995;53:705-21. Part of the research described in this paper was performed at The College of William and Mary, the, Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration and the Jet Propulsion Laboratory. Support for the National Institute of Standards and Technology was provided by the NIST Greenhouse Gas Measurements and Climate Research Program and a NIST Innovations in Measurement Science (IMS) award.

  14. Energy Properties of rotational bands of 170-174Yb isotopes

    Science.gov (United States)

    Okhunov, Abdurahim A.; Al-Sammarrae, Anwer A. M.; Turaeva, G.

    2014-11-01

    Accounting for Coriolis mixing of experimentally known rotational bands non-adiabatic effects in energy of low-lying excited states are investigated, within phenomenological model. The Calculations for isotopes 170,172,174,176yb, are carried out. The energy and wave function structure of excited states are calculated. The finding reveals that the bands mixing has been found to have considerable impact on the wave function of low-lying states 0+ and 2+ bands.

  15. Effect of Bond Alternation on Electronic Energy Band Structure of Armchair Carbon Nanotubes

    Science.gov (United States)

    Phong, Tran Cong; Hieu, Nguyen Ngoc

    The influence of the bond alternation on electronic energy band structure of armchair carbon nanotubes is studied by the tight-binding approximation. It is shown that the armchair carbon nanotubes at ground state with Kekule structure open small band gap at the Fermi level. Dependence of energy band gap of armchair carbon nanotubes with Kekule structure on their radius is considered and numerically calculated. The numerical calculations are applied to the (n, n) carbon nanotubes with n = 5, 6, 7, 8.

  16. Dipole bands in high spin states of 57135La78

    International Nuclear Information System (INIS)

    High spin states of 135La have been investigated using the reaction 128Te(11B,4n)135La at a beam energy of 50.5 MeV. Two negative parity dipole bands (?I = 1) have been established. Crossover E2 transitions have been observed for the first time in one of the dipole bands. For the Tilted Axis Cranking (TAC) calculations, a three-quasiparticle (3qp) configuration ?(h11/2)1??(h11/2)?2 and a five-quasiparticle (5qp) configuration ?(h11/2)1(g7/2/d5/2)2??(h11/2)?2 have been taken for the two negative parity dipole bands. The comparison of experimental observables with TAC calculations supports the configuration assignments for both the dipole bands

  17. Electron band theory 1952-1962

    International Nuclear Information System (INIS)

    Work undertaken by the Theoretical Physics Division between 1952 and 1965 to obtain an understanding of electrons in metals, with uranium and the actinides and the structurally-important transition metals as the main targets is examined. A main result of that period was a conviction that the majority of the physical properties of all metals, except the 4f rare-earth series and the actinides beyond uranium, were dominated by band effects which could be described well enough for most purposes by simple one-electron calculations with simple self-consistent fields. The period from 1960 on showed increasingly clearly the necessity of incorporating relativistic spin-orbit coupling terms in the heavy metals, and some 'local exchange field' correction to the fields close to nuclei. The problems of the non-local interaction of spins - highly important for alloy theory and for antiferromagnetic instability -required the evolution of computers large enough to produce wave-functions at all wave-vectors for all bands so that the susceptibility at arbitrary wave-vector could be computed. This work has not proved to be very illuminating so far, and much interest again focusses today on heuristic arguments that give qualitative descriptions of band structures, such as canonical d-bands to account for crystal structure. (UK)

  18. Collective ?-vibrational bands in 165Ho and 167Er

    International Nuclear Information System (INIS)

    The nuclear structures of 165Ho and 167Er have been investigated by means of Coulomb excitation. These nuclei excited at moderate spins exhibit ?-vibrational bands with K?=(11)/(2)-, (3)/(2)- in 165Ho and K?=(11)/(2)+ in 167Er. The ?-vibrational bands in 165Ho are found to be isospectral;having very nearly identical in-band ?-ray energies. Gamma-ray branching ratios are analysed to extract information on collectivity andCoriolis mixing. Experimental results are compared with calculations performed with the cranked shell model+RPA+particle-vibration coupling and by invoking the generalized intensity relations (GIR) in the unified model scheme. Although this model explains many features of the data, puzzling aspects such as identical transition energies for the bands in 165Ho remain unexplained. The role of the K quantum number in identical bands is discussed. (orig.)

  19. Systematic description of superdeformed bands in the mass-190 region

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Yang; Guidry, M. [Oak Ridge National Lab., TN (United States)]|[Univ. of Tennessee, Knoxville, TN (United States); Zhang, Jing-ye [Univ. of Tennessee, Knoxville, TN (United States)

    1996-12-31

    Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. The authors calculation of electromagnetic properties and pairing correlations provides an understanding of the observed gradual increase of dynamical moments of inertia with angular momentum observed in many bands in this mass region.

  20. Interlayer Exchange Coupling Mediated by Valence Band Electrons

    OpenAIRE

    Blinowski, J.; Kacman, P.

    2000-01-01

    The interlayer exchange coupling mediated by valence band electrons in all-semiconductor IV-VI magnetic/nonmagnetic superlattices is studied theoretically. A 3D tight-binding model, accounting for the band and magnetic structure of the constituent superlattice components is used to calculate the spin-dependent part of the total electronic energy. The antiferromagnetic coupling between ferromagnetic layers in EuS/PbS superlattices is obtained, in agreement with the experiment...

  1. Electronic valence band structure of V2O5

    International Nuclear Information System (INIS)

    We present high-resolution ARPES measurements of V2O5 single crystals carried out with synchrotron radiation and He I resonance lamp. The obtained experimentally band structure in k parallel is compared with calculations, e.g. The aging behavior of different bands with time is studied. The degradation of the surface due to the high reactivity is discussed referring to the previous reported experimental work.

  2. Plate wave stop-bands in periodically poled lithium niobate.

    Science.gov (United States)

    Ostrovskii, I V; Klymko, V A; Nadtochiy, A B

    2009-04-01

    The dispersion curves of four lowest plate acoustic waves (PAWs) in the ZX cut of a periodically poled lithium niobate (PPLN) wafer are computed numerically and investigated experimentally. Experiment is in agreement with simulated dispersion curves. Calculations and measurements reveal the stop-bands in the dispersion curves of the PAW modes in PPLN despite a wafer that has uniform mechanical properties. At a specific wave number, within the frequencies of the stop-bands, the acoustic modes do not propagate. PMID:19354350

  3. Nuclear field theory treatment of K not= 0 rotational bands

    International Nuclear Information System (INIS)

    The properties of the lowest members of K not= 0 rotational bands are described as anharmonic vibrational bands. The anharmonicity is calculated by the method called Nuclear Field Theory (particle-vibration coupling). It is shown to be important not to truncate the diagrammatic expansion at a fixed number of vertices. Instead, the way in which the diagrams depend on the number of degrees of freedom participating is used to guide the truncation. (orig.)

  4. Band transport model for discotic liquid crystals

    Science.gov (United States)

    Lever, L. J.; Kelsall, R. W.; Bushby, R. J.

    2005-07-01

    A theoretical model is presented for charge transport in discotic liquid crystals in which a charge is delocalized over more than one lattice site. As such, charge transport is via a banded conduction process in a narrow bandwidth system and takes place over coherent lengths of a few molecules. The coherent lengths are disrupted by the geometrical disorder of the system and are treated as being terminated by quantum tunnel barriers. The transmission probabilities at these barriers have been calculated as a function of the charge carrier energy. Phononic interactions are also considered and the charge carrier scattering rates are calculated for intermolecular and intramolecular vibrations. The results of the calculations have been used to develop a Monte Carlo simulation of the charge transport model. Simulated data are presented and used to discuss the nature of the tunnel barriers required to reproduce experimental data. We find that the model successfully reproduces experimental time of flight data including temperature dependence.

  5. Band alignment of SnS/Zn(O,S) heterojunctions in SnS thin film solar cells

    OpenAIRE

    Sun, Leizhi; Haight, Richard; Sinsermsuksakul, Prasert; Bok Kim, Sang; Park, Helen Hejin; Gordon, Roy Gerald

    2013-01-01

    Band alignment is critical to the performance of heterojunction thin film solar cells. In this letter, we report band alignment studies of SnS/Zn(O,S) heterojunctions with various compositions of Zn(O,S). Valence band offsets (VBOs) are measured by femtosecond laser pump/probe ultraviolet photoelectron spectroscopy (fs-UPS) from which conduction band offsets (CBOs) are calculated by combining with band gaps obtained by optical transmission/reflection measurements. The SnS/Zn(O,S) heterojuncti...

  6. In-Band and Inter-Band B(E2) Values within the Triaxial Projected Shell Model

    CERN Document Server

    Boutachkov, P; Sun, Y; Sheikh-Javid, A; Frauendorf, S

    2002-01-01

    The Triaxial Projected Shell Model (TPSM) has been successful in providing a microscopic description of the energies of multi-phonon vibrational bands in deformed nuclei. We report here on an extension of the TPSM to allow, for the first time, calculations of B(E2) values connecting gamma- and gamma-gamma-vibrational bands and the ground state band. The method is applied to 166,168Er. It is shown that most of the existing B(E2) data can be reproduced rather well, thus strongly supporting the classification of these states as gamma-vibrational states. However, significant differences between the data and the calculation are seen in those B(E2) values which involve odd-spin states of the gamma-band. Understanding these discrepancies requires accurate experimental measurements and perhaps further improvements of the TPSM.

  7. Morphologies of three-dimensional shear bands in granular media

    CERN Document Server

    Fazekas, S; Kertész, J; Wolf, D E

    2005-01-01

    Using three-dimensional Distinct Element Method with spherical particles we simulated shear band formation of granular materials in axisymmetric triaxial shear test. The calculated three-dimensinoal shear band morphologies are in good agreement with those found experimentally. We observed spontaneous symmetry braking strain localization provided it was allowed by the boundaries. If the symmetry was enforced, we found strain hardening. We discuss the formation mechanism of shear bands in the light of our observations and compare our results with high resolution NMR experiments.

  8. Transition temperature of two-band superconductors with Anderson impurities

    International Nuclear Information System (INIS)

    The influence of impurities on the superconducting transition temperature of two-band superconductors containing Anderson impurities is investigated. It is found that the concentration-dependent transition temperature shows typical departures from the formula for a single-band superconductor. These departures occur because of the interband scattering of conduction electrons on impurities. The calculations reveal clearly that in the presence of impurities the effective pairing interaction becomes coupling-parameter dependent, giving rise to a new pair-weakening mechanism. Analytic results for T/sub c/ on the basis of this simple two-band model are presented

  9. Band-edge lasers based on randomly mixed photonic crystals.

    Science.gov (United States)

    Kim, Sunghwan; Yoon, Sungjoon; Seok, Hyojun; Lee, Jeongkug; Jeon, Heonsu

    2010-04-12

    By employing two-dimensional InGaAsP photonic band-edge lasers, we have experimentally demonstrated that a random mixture of two different photonic crystals (PCs) possesses a new band structure that is intermediate to that of the two host PCs. The photonic band-edges shift monotonically, but with a strong bowing effect, as the mixed PC system is systematically transformed from one PC to the other. The experimental observations are in excellent agreement with finite-difference time-domain simulations and model calculations based on virtual-crystal approximation with compositional disorder effect included. PMID:20588609

  10. A new construction algorithm of narrow-band function for artificial history simulation method based on narrow-band superposition

    International Nuclear Information System (INIS)

    In this paper, a new type of narrow-band function is proposed for the artificial history simulation method based on narrow-band superposition, which aims to meet the needs of both fitting of the target response spectrum and envelop of the power spectral density. The new narrow-band function is based on the normal distribution function and trigonometric functions. Its band width can be controlled and it decays rapidly on both sides. While the target response spectrum is fitted by superimposing the new narrow-band time history, the power spectral density is enveloped by modifying the Fourier amplitude spectrum locally. The numerical example demonstrates that not only the artificial time history generated by this algorithm reaches high matching precision to the target response spectrum, but also the corresponding calculated power spectrum envelopes the target power spectrum. (authors)

  11. Two-Dimensional Ferroelectric Photonic Crystals: Optics and Band Structure

    CERN Document Server

    Simsek, Sevket; Ozbay, Ekmel

    2013-01-01

    In this report we present an investigation of the optical properties and band structure calculations for the photonic structures based on the functional materials- ferroelectrics. A theoretical approach to the optical properties of the 2D and 3D photonic crystals which yields further insight in the phenomenon of the reflection from different families of lattice planes in relation to the presence of photonic gaps or photonic bands. We calculate the photonic bands and optical properties of LiNbO3 based photonic crystals. Calculations of reflection and transmission spectra show the features correspond to the onset of diffraction, as well as to additional reflectance structures at large values of the angle of incidence.

  12. Bulk band structure of Bi2Te3

    Science.gov (United States)

    Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco; de Carvalho, Vagner Eustáquio; Ladeira, Luiz Orlando; Teixeira, Nayara Gomes; Soares, Edmar Avellar; Friedrich, Christoph; Blügel, Stefan; Hofmann, Philip

    2014-08-01

    The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators.

  13. Bulk band structure of Bi2Te3

    DEFF Research Database (Denmark)

    Michiardi, Matteo; Aguilera, Irene

    2014-01-01

    The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators.

  14. A model for shear-band formation and high-explosive initiation in a hydrodynamics code

    Energy Technology Data Exchange (ETDEWEB)

    Kerrisk, J.F.

    1996-03-01

    This report describes work in progress to develop a shear band model for MESA-2D. The object of this work is (1) to predict the formation of shear bands and their temperature in high explosive (HE) during a MESA-2D calculation, (2) to then assess whether the HE would initiate, and (3) to allow a detonation wave initiated from a shear band to propagate. This requires developing a model that uses average cell data to estimate the size and temperature of narrow region (generally much narrower than the cell size) that is undergoing shear within the cell. The shear band temperature (rather than the average cell temperature) can be used to calculate the flow stress of the material in the cell or to calculate heat generation from reactive materials. Modifications have been made to MESA-2D to calculate shear band size and temperature, and to initiate HE detonation when conditions warrant. Two models have been used for shear-band size and temperature calculation, one based on an independent estimate of the shear band width and a second based on the temperature distribution around the shear band. Both models have been tested for calculations in which shear band formation occurs in steel. A comparison of the measured and calculated local temperature rise in a shear band has been made. A model for estimating the time to initiation of the HE based on the type of HE and the temperature distribution in a shear band has also been added to MESA-2D. Calculations of conditions needed to initiate HE in projectile-impact tests have been done and compared with experimental data. Further work is d to test the model.

  15. Band-Structure of Thallium by the LMTO Method

    DEFF Research Database (Denmark)

    Holtham, P. M.; Jan, J. P.

    1977-01-01

    The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s and p bands for the HCP structure. Energy bands have been evaluated both with and without spin-orbit coupling which is particularly large in thallium. Energy bands close to the Fermi level were found to be mainly 6p like in character. The 6s states lay below the 6p bands and were separated from them by an energy gap. The 6d and 7s bands were found to be far above the Fermi level and the 5d states were found to be far below it. Fermi surface properties and the electronic specific heat are computed and compared with experiment. The joint density of states has also been computed and is in reasonable agreement with experimental optical properties.

  16. Superdeformed bands in 153Ho

    International Nuclear Information System (INIS)

    In a recent experiment carried out with the EUROGAM PHASE II ?-ray spectrometer three new superdeformed (SD) bands have been established in 153Ho. The properties of these SD bands are discussed in terms of proton particle-hole excitations and are compared to the SD bands in the adjacent nuclei. This is the first observation of SD structures in a Z = 67 nucleus. (author)

  17. Superdeformed band in 154Dy

    International Nuclear Information System (INIS)

    A superdeformed band has been found in the 154Dy (N=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of 152Dy and the transition energies are similar to those of an excited superdeformed band in 153Dy. It is proposed that the two valence neutrons above the N=86 shell gap occupy the deformation-driving [514]9/2 orbital

  18. A theoretical approach to the design of reduced band gap noncorrosive electrodes for photoelectrochemical solar cells

    International Nuclear Information System (INIS)

    Preliminary results from our charge self-consistent LCAO band structure (CSCBS) calculations with Bloch sums as the basis reveal that a noncorrosive reduced band gap electrode for photoelectrochemical solar cells may be produced from a (1:1) mixture of ?-PbO2 and TiO2 (both rutile). The band gaps for the constituents (?-PbO2 and TiO2) and the 1:1 mixture are calculated and a detailed characterization of the valence and the conduction bands is undertaken to offer a possible mechanism for the reduction of the band gap of the mixture. The band gap for the perovskite PbTiO3 is also calculated to offer a guideline for selecting from the competing pathways to the fabrication of noncorrosive photoelectrochemical electrodes

  19. Small Quadrupole Deformation for the Dipole Bands in 112In

    OpenAIRE

    Trivedi, T.; Palit, R.; Sethi, J.; Saha, S.; Kumar, S.; Naik, Z.; Parkar, V. V.; Naidu, B. S.; Deo, A. Y.; Raghav, A.; Joshi, P. K.; Jain, H. C.; Sihotra, S.; Mehta, D.; Jain, A. K.

    2012-01-01

    High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\\sim$ 20$\\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calcul...

  20. M-Band Graphic Equalizer

    OpenAIRE

    Mallikarjuna Rao, Dr P.; Prof. Ch.Srinivasa Kumar

    2011-01-01

    This paper deals with the concept of filter banks. Filter banks are a group of band-pass filters connected in parallel. Each parallel connection forms a channel for different frequency-bands present in the input signal. The output of the filter bank is formed by merging these channels. The main theme behind the use of filter banksis to boost or attenuate different individual bands of frequencies present in a signal, without affecting other bands. There are several ways of realizing an filter ...

  1. Ground state band and quasi ?-band structure in 104Ru

    International Nuclear Information System (INIS)

    The odd-even staggering effect in quasi ?-band is considered most sensitive phenomenon in nuclear spectroscopy that carries information about the variable symmetry in the transitional region. The authors managed the deviation of model estimates of energy levels in 104Ru from that of respective experimental ones restricted to 13% in 2+ level of quasi ?-band

  2. Single Band Helical Antenna in Axial Mode

    Directory of Open Access Journals (Sweden)

    Parminder Singh

    2012-11-01

    Full Text Available Helical antennas have been widely used in a various useful applications, due to their low weight and low profile conformability, easy and cheap realization.Radiation properties of this antenna are examined both theoretically and experimentally. In this paper, an attempt has been made to investigate new helical antenna structure for Applications. CST MWS Software is used for the simulation and design calculations of the helical antennas. The axial ratio, return loss, VSWR, Directivity, gain, radiation pattern is evaluated. Using CST MWS simulation software proposed antenna is designed/simulated and optimized. The antenna exhibits a single band from 0 GHz to 3 GHz for GPS and several satellite applications

  3. Superdeformed bands of odd nuclei in A=190 region in the quasiparticle picture

    International Nuclear Information System (INIS)

    Properties of the superdeformed (SD) bands of 195Pb and 193Hg have been studied by the cranked Hartree-Fock-Bogoliubov method. The calculations reproduce the flat behavior of the dynamical moment of inertia of two of the SD bands of 195Pb measured recently. Possible configuration assignments for the observed bands 3 and 4 of 195Pb are discussed. The two interacting SD bands of 193Hg have also been calculated. The analysis confirms the superiority of a density-dependent pairing force over a seniority pairing interaction. (author)

  4. Superdeformed bands of odd nuclei in A=190 region in the quasiparticle picture

    Energy Technology Data Exchange (ETDEWEB)

    Terasaki, J.; Flocard, H. [Paris-11 Univ., 91 - Orsay (France). Inst. de Physique Nucleaire; Heenen, P.H. [Brussels Univ. (Belgium). Service de Physique Nucleare Therorique; Bonche, P. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Service de Physique Theorique

    1996-07-01

    Properties of the superdeformed (SD) bands of {sup 195}Pb and {sup 193}Hg have been studied by the cranked Hartree-Fock-Bogoliubov method. The calculations reproduce the flat behavior of the dynamical moment of inertia of two of the SD bands of {sup 195}Pb measured recently. Possible configuration assignments for the observed bands 3 and 4 of {sup 195}Pb are discussed. The two interacting SD bands of {sup 193}Hg have also been calculated. The analysis confirms the superiority of a density-dependent pairing force over a seniority pairing interaction. (author). 25 refs.

  5. Spectral absorption coefficients for the fundamental and first overtone vibration-rotation bands of CN

    Science.gov (United States)

    Bailey, W. L.

    1977-01-01

    A previous measurement of the transition moment of the fundamental vibration-rotation band of CN is combined with theoretical calculations of relative vibrational transition probabilities in order to compute absorption coefficients for the CN fundamental and first-overtone bands. Line strengths for 121 lines in each branch of all fundamental and first-overtone bands with upper-transition states not greater than 6 are calculated for temperatures of 2000, 3000, and 4000 K; these line strengths are presented as averaged over 8-kayser intervals. The relative vibrational transition moments are placed on an absolute scale, and the wavenumbers of the band origins and heads are given

  6. HENRY'S LAW CALCULATOR

    Science.gov (United States)

    On-Site was developed to provide modelers and model reviewers with prepackaged tools ("calculators") for performing site assessment calculations. The philosophy behind OnSite is that the convenience of the prepackaged calculators helps provide consistency for simple calculations,...

  7. Band crossings in 86Zr

    International Nuclear Information System (INIS)

    The level scheme of 86Zr has been investigated experimentally and theoretically. Band crossings due to g/sub 9/2/ protons and neutrons as well as the second backbend in the yrast line have been observed. The triaxial cranked shell model has been applied in order to study the quasiparticle content of different bands and to determine the underlying nuclear shape

  8. Decoupling, band forking, and deformation

    International Nuclear Information System (INIS)

    From extensive in-beam ?-ray studies of odd-mass and odd-odd Re isotopes, the authors have elucidated properties of many decoupled (open-quotes Kclose quotes = 1/2) and doubly decoupled (1/2 circle-times 1/2) bands. Such ?I = 2 bands are the most intensely populated in a variety of heavy-ion induced reactions. They suffer extreme coriolis distortions and exhibit complex alignment patterns, but from them much can be deduced about the deformation-driving properties of the p and n states involved. In several odd-mass isotopes, and most clearly in 175Re, a second, weakly populated ?I = 2 band feeds into the decoupled band around I = 17/2-. At times this band has been interpreted as a 1/2+[660] band, but such is unlikely because of the necessarily slow, hindered E1 interband transitions required. The authors find it more likely that this band is an alternate, higher-deformation backbending sequence associated with the decoupled band itself-this would account for its similar population patterns in reactions involving projectiles with widely differing masses. Multiple decouplings of this type may also lead to extreme deformations, perhaps even superdeformation

  9. The Moral Ends of Band

    Science.gov (United States)

    Allsup, Randall Everett

    2012-01-01

    This article provides a theoretical framework through which to reimagine and revitalize contemporary music education practices, using the large ensemble paradigm called "band" as the primary unit of analysis. Literature suggests that band places too much emphasis on teacher control and external measures of validation. Critics propose replacing…

  10. Decay pathways and rotational properties of strongly deformed bands in ^168Hf

    Science.gov (United States)

    Ma, W. C.; Yadav, R. B.; Amro, H.; Varmette, P. G.; Zhang, Y. C.; Hagemann, G. B.; Herskind, B.; Schmidt, K. A.; Sletten, G.; Carpenter, M.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Bracco, A.; Frattini, S.; Million, B.; Domscheit, J.; Hubel, H.; Hartley, D. J.; Riedinger, L. L.; Odegard, S. W.; Siem, S.

    2008-04-01

    Three strongly deformed bands were observed previously in ^168 Hf [1] and proposed as candidates of triaxial strongly deformed (TSD) bands. However, none of the bands was linked to known levels. Without the knowledge of level spins, parities, and excitation energies, it was difficult to gain a clear understanding of these bands. We have performed an extensive spectroscopic analysis for the ?-ray coincidence data obtained from a Gammasphere experiment at ANL. The decay pathways of TSD2 band to low-spin structures have been established, and the approximate spin values of levels in TSD1 band obtained. A detailed comparison of experimental properties of these bands and theoretical calculations, as well as the intrinsic configurations of the bands will be discussed. Work supported by U.S. DOE grant DE-FG02-95ER40939. [1] H. Amro et al., Physics Letters B 506 (2001) 39-44.

  11. Gaia broad band photometry

    Science.gov (United States)

    Jordi, C.; Gebran, M.; Carrasco, J. M.; de Bruijne, J.; Voss, H.; Fabricius, C.; Knude, J.; Vallenari, A.; Kohley, R.; Mora, A.

    2010-11-01

    Aims: The scientific community needs to be prepared to analyse the data from Gaia, one of the most ambitious ESA space missions, which is to be launched in 2012. The purpose of this paper is to provide data and tools to predict how Gaia photometry is expected to be. To do so, we provide relationships among colours involving Gaia magnitudes (white light G, blue GBP, red GRP and GRVS bands) and colours from other commonly used photometric systems (Johnson-Cousins, Sloan Digital Sky Survey, Hipparcos and Tycho). Methods: The most up-to-date information from industrial partners has been used to define the nominal passbands, and based on the BaSeL3.1 stellar spectral energy distribution library, relationships were obtained for stars with different reddening values, ranges of temperatures, surface gravities and metallicities. Results: The transformations involving Gaia and Johnson-Cousins V - IC and Sloan DSS g - z colours have the lowest residuals. A polynomial expression for the relation between the effective temperature and the colour GBP - GRP was derived for stars with Teff ? 4500 K. For stars with Teff Gaia passbands have been used to compute tracks and isochrones using the Padova and BASTI models. Finally, the performances of the predicted Gaia magnitudes have been estimated according to the magnitude and the celestial coordinates of the star. Conclusions: The provided dependencies among colours can be used for planning scientific exploitation of Gaia data, performing simulations of the Gaia-like sky, planning ground-based complementary observations and for building catalogues with auxiliary data for the Gaia data processing and validation. Tables 11-13 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/523/A48

  12. Dual-band infrared camera

    Science.gov (United States)

    Vogel, H.; Schlemmer, H.

    2005-10-01

    Every year, numerous accidents happen on European roads due to bad visibility (fog, night, heavy rain). Similarly, the dramatic aviation accidents of year 2001 in Milan and Zurich have reminded us that aviation safety is equally affected by reduced visibility. A dual-band thermal imager was developed in order to raise human situation awareness under conditions of reduced visibility especially in the automotive and aeronautical context but also for all transportation or surveillance tasks. The chosen wavelength bands are the Short Wave Infrared SWIR and the Long Wave Infrared LWIR band which are less obscured by reduced visibility conditions than the visible band. Furthermore, our field tests clearly show that the two different spectral bands very often contain complementary information. Pyramidal fusion is used to integrate complementary and redundant features of the multi-spectral images into a fused image which can be displayed on a monitor to provide more and better information for the driver or pilot.

  13. Modeling charged defects inside density functional theory band gaps

    Science.gov (United States)

    Schultz, Peter A.; Edwards, Arthur H.

    2014-05-01

    Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn-Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn-Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn-Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem.

  14. Modeling charged defects inside density functional theory band gaps

    International Nuclear Information System (INIS)

    Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem

  15. Description of the Triaxial Strongly Deformed Bands in 160,161Tm and 163Tm

    International Nuclear Information System (INIS)

    Properties of the triaxial strongly deformed (TSD) bands of 160,161Tm and 163Tm are investigated systematically within the supersymmetry scheme including many-body interactions and a perturbation possessing SO(5)(or SU(5)) symmetry on the rotational symmetry. Quantitatively good results of the ?-ray energies, the dynamical moments of inertia and the spin of the TSD bands in 160,161Tm and 163Tm are obtained. The calculation shows that competition between the pairing and anti-pairing effects exist in these TSD bands. Meanwhile, the SU(3) symmetry in TSD bands is broken more seriously than that in superdeformed bands. (nuclear physics)

  16. Identification of the unfavored N=7 superdeformed band in 191Hg

    International Nuclear Information System (INIS)

    A new superdeformed band has been identified in 191Hg bringing the total number of bands observed in this nucleus to four. The new band has properties similar to those of a superdeformed band reported recently in 193Hg. Both bands are believed to be built on the unfavored signature of the j15/2 intruder configuration. Comparisons between the data and cranked Woods-Saxon calculations highlight the strengths and weaknesses of theory in describing high-N orbitals at large deformation

  17. Optical And Thermoelectrical Studies On Band Edge Structure Of SnTe

    Science.gov (United States)

    Ishida, A.; Tsuchiya, T.; Takaoka, S.

    2011-12-01

    Optical transmission properties and Seebeck coefficient of SnTe were measured to study the energy band edge structures of the SnTe. Burstein-Moss effect in the optical transmission spectra was very small owing to a bumped band edge structure with a large band-edge density of states. The optical transmission spectra were simulated assuming the bumped band edge structure. Dependence of Seebeck coefficient on the carrier concentration was also calculated theoretically assuming the band edge structure. Experimental Seebeck coefficient of SnTe with relatively small hole concentration increased significantly and agreed well with the theoretical value.

  18. Information retrieval from wide-band meteorological data - An example

    Science.gov (United States)

    Adelfang, S. I.; Smith, O. E.

    1983-01-01

    The methods proposed by Smith and Adelfang (1981) and Smith et al. (1982) are used to calculate probabilities over rectangles and sectors of the gust magnitude-gust length plane; probabilities over the same regions are also calculated from the observed distributions and a comparison is also presented to demonstrate the accuracy of the statistical model. These and other statistical results are calculated from samples of Jimsphere wind profiles at Cape Canaveral. The results are presented for a variety of wavelength bands, altitudes, and seasons. It is shown that wind perturbations observed in Jimsphere wind profiles in various wavelength bands can be analyzed by using digital filters. The relationship between gust magnitude and gust length is modeled with the bivariate gamma distribution. It is pointed out that application of the model to calculate probabilities over specific areas of the gust magnitude-gust length plane can be useful in aerospace design.

  19. Compact Dual Band Microstrip Antenna for Ku-Band Application

    OpenAIRE

    Islam, M. T.; Misran, N.; Mobashsher, A. T.

    2010-01-01

    A new design of dual band compact microstrip antenna is proposed for Ku-band applications. Dual band is achieved using three pairs of thin slits from the sides of a rectangular patch and feeding with a microstrip feedline. The antenna has a compact structure and the total size is 9.50 by 10 by 0.254 mm. The result shows that the return loss of -23.83 dB is achieved at the first resonant frequency of 12.54 GHz and -14.04 dB is obtained at the second resonant frequency of 14.15 GHz. The antenna...

  20. ?I=4 Bifurcation in Identical Superdeformed Bands

    International Nuclear Information System (INIS)

    ?I=4 bifurcation has been observed in two superdeformed bands, the newly discovered yrast superdeformed band of 148Eu, and a previously known excited band in 148Gd. Both of these bands have moments of inertia that are identical to the yrast band of 149Gd, the first superdeformed band in which this bifurcation was observed. This first observation of ?I=4 bifurcation in identical superdeformed bands provides a crucial test of recent models. copyright 1997 The American Physical Society

  1. Band gap engineering strategy via polarization rotation in perovskite ferroelectrics

    International Nuclear Information System (INIS)

    We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2?eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics

  2. Optically induced coherent intra-band dynamics in disordered semiconductors

    CERN Document Server

    Schlichenmaier, C; Meier, T; Thomas, P; Koch, S W

    2002-01-01

    On the basis of a tight-binding model for a strongly disordered semiconductor with correlated conduction- and valence band disorder a new coherent dynamical intra-band effect is analyzed. For systems that are excited by two, specially designed ultrashort light-pulse sequences delayed by tau relatively to each other echo-like phenomena are predicted to occur. In addition to the inter-band photon echo which shows up at exactly t=2*tau relative to the first pulse, the system responds with two spontaneous intra-band current pulses preceding and following the appearance of the photon echo. The temporal splitting depends on the electron-hole mass ratio. Calculating the population relaxation rate due to Coulomb scattering, it is concluded that the predicted new dynamical effect should be experimentally observable in an interacting and strongly disordered system, such as the Quantum-Coulomb-Glass.

  3. Effective three-band structure in Fe-based superconductors

    Science.gov (United States)

    Möckli, David; de Mello, E. V. L.

    2015-01-01

    We present self-consistent calculations of the multi-gap structure measured in some Fe-based superconductors. These materials are known to have structural disorder in real space and a multi-gap structure due to the 3d Fe orbitals contributing to a complex Fermi surface topology with hole and electron pockets. Different experiments identify three s-wave–like superconducting gaps with a single critical temperature (T_c) . We investigate the temperature dependence of these gaps by a multi-band Bogoliubov-de Gennes theory at different pockets in the presence of effective hybridizations between some bands and an attractive temperature-dependent intra-band interaction. We show that this approach reproduces the three observed gaps and single Tc in different compounds of Ba1?xKxFe2As2, providing some insights into the inter-band interactions.

  4. Electronic structure of periodic curved surfaces -- topological band structure

    CERN Document Server

    Aoki, H; Takeda, D; Morise, H

    2001-01-01

    Electronic band structure for electrons bound on periodic minimal surfaces is differential-geometrically formulated and numerically calculated. We focus on minimal surfaces because they are not only mathematically elegant (with the surface characterized completely in terms of "navels") but represent the topology of real systems such as zeolites and negative-curvature fullerene. The band structure turns out to be primarily determined by the topology of the surface, i.e., how the wavefunction interferes on a multiply-connected surface, so that the bands are little affected by the way in which we confine the electrons on the surface (thin-slab limit or zero thickness from the outset). Another curiosity is that different minimal surfaces connected by the Bonnet transformation (such as Schwarz's P- and D-surfaces) possess one-to-one correspondence in their band energies at Brillouin zone boundaries.

  5. Band structure of SnTe studied by photoemission spectroscopy.

    Science.gov (United States)

    Littlewood, P B; Mihaila, B; Schulze, R K; Safarik, D J; Gubernatis, J E; Bostwick, A; Rotenberg, E; Opeil, C P; Durakiewicz, T; Smith, J L; Lashley, J C

    2010-08-20

    We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p bands. Our study reveals the conjectured complex Fermi surface structure near the L points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering issues about the electronic structure. The chemical potential at the crystal surface is found to be 0.5 eV below the gap, corresponding to a carrier density of p=1.14 × 10(21)? cm(-3) or 7.2 × 10(-2) holes per unit cell. At a temperature below the cubic-rhombohedral structural transition a small shift in spectral energy of the valance band is found, in agreement with model predictions. PMID:20868120

  6. Band-gap engineering in fluorographene nanoribbons under uniaxial strain

    International Nuclear Information System (INIS)

    Based on extensive first-principles calculations, we report the structural and electronic properties of fluorinated graphene, i.e., fluorographene nanoribbons (FGNRs) under uniaxial strain. Our results indicate that the FGNRs are semiconductors with wide direct band gaps regardless of their edge structures. Moreover, the band gap of FGNR can be effectively modulated nonlinearly with the applied uniaxial elastic strain, where the band gap value increases first and then reduces when the applied strain changes from ?10.0% to 10.0%. This abnormal behavior mainly originates from the electronic structures of valence and conduction band edges, which is quite different from previously reported linear behavior on graphene nanoribbon. Our results imply the great potential applications of FGNRs in the optical electronics

  7. Shape coexistence and band crossings in 174 Pt

    Science.gov (United States)

    Goon, J. Tm.; Hartley, D. J.; Riedinger, L. L.; Carpenter, M. P.; Kondev, F. G.; Janssens, R. V.; Abu Saleem, K. H.; Ahmad, I.; Amro, H.; Cizewski, J. A.; Davids, C. N.; Danchev, M.; Khoo, T. L.; Heinz, A.; Lauritsen, T.; Ma, W. C.; Poli, G. L.; Ressler, J.; Reviol, W.; Seweryniak, D.; Smith, M. B.; Wiedenhöver, I.; Zhang, Jing-Ye

    2004-07-01

    High-spin states in 174 Pt were populated via the 92 Mo ( 84 Sr ,2p ) and 92 Mo ( 84 Sr ,2p2n ) reactions. The ground-state band has been extended from I=14 to 24 (tentatively 26) and a new side band is observed up to a spin of 21 (tentatively 23). A low-frequency crossing is observed in the latter band at a rotational frequency that is similar to that seen in the ground-state band. The first and second i13/2 neutron alignments are also observed in 174 Pt . Surprisingly, these crossings occur at approximately the same frequency. Total Routhian surface and cranked shell model calculations are used in an attempt to understand this behavior.

  8. Shape coexistence and band crossings in 174Pt

    International Nuclear Information System (INIS)

    High-spin states in 174Pt were populated via the 92Mo(84Sr,2p) and 92Mo(84Sr,2p2n) reactions. The ground-state band has been extended from I=14 to 24 (tentatively 26) and a new side band is observed up to a spin of 21 (tentatively 23). A low-frequency crossing is observed in the latter band at a rotational frequency that is similar to that seen in the ground-state band. The first and second i13/2 neutron alignments are also observed in 174Pt. Surprisingly, these crossings occur at approximately the same frequency. Total Routhian surface and cranked shell model calculations are used in an attempt to understand this behavior

  9. Study of intruder band in 112Sn

    International Nuclear Information System (INIS)

    Excited states of the positive-parity intruder band in 112Sn, populated in the 100Mo(20Ne,?4n) reaction at a beam energy of 136 MeV, have been studied. The band has been observed up to 11570.0 keV with spin (24+). Mean lifetimes have been measured for six states up to the 22+, 10335.1 keV level and an upper limit of the lifetime has been estimated for the 11570.0 keV (24+) state. The B(E2) values, derived from the present lifetime results, correspond to a moderate quadrupole deformation of ?2?0.18 for states with spin J?>=12+, and the decrease in B(E2) for the 14+->12+ transition is consistent with a ?(h11/2)2 alignment at ??0.35 MeV, predicted by a cranked shell-model calculation. Total Routhian surface calculations predict a triaxial shape following the alignment

  10. Ranging Property of the Dual-Band Band Limited Signal (DBBLS

    Directory of Open Access Journals (Sweden)

    KOVAR, P.

    2012-08-01

    Full Text Available The Dual-Band Band Limited Signal (DBBLS is a signal with its power spectral density consisting of two separate lobes. Signals that can be considered as DBBLS are for example signals with BOC, AltBOC modulation, signals modulated on two close carriers and many other signals, which are used in modern satellite navigation systems. This signal advantage is its excellent ranging property. The parted power spectral density enables processing the DBBLS as a single wideband signal in single-channel receiver or as two narrow band signals in two-channel receiver. The signal processing of the ranging signals is based on the calculation of the cross-correlation function, which can be calculated from the signal measured by the two-channel receiver by the derived method more efficiently than from the whole signal. The two-channel processing has nearly optimal performance, but the hardware and computation complexity is much lower. The developed method can by applied, for instance, for the processing of the Galileo E5 signal or pair of the Compass L1 signals.

  11. Band crossing in Shears band of $^{108}$Cd

    CERN Document Server

    Roy, Santosh; Pal, S; Chattopadhyay, S; Bhattacharya, S; Goswami, A; Jain, H C; Joshi, P K; Bhowmik, R K; Kumar, R; Muralithar, S; Singh, R P; Madhavan, N; Rao, P V Madhusudhana

    2010-01-01

    The level lifetimes have been measured for a Shears band of $^{108}$Cd which exhibits bandcrossing. The observed level energies and B(M1) rates have been successfully described by a semi-classical geometric model based on shear mechanism. In this geometric model, the bandcrossing in Shears band has been described as the reopening of the angle between the blades of a shear.

  12. The effective air absorption coefficient for predicting reverberation time in full octave bands.

    Science.gov (United States)

    Wenmaekers, R H C; Hak, C C J M; Hornikx, M C J

    2014-12-01

    A substantial amount of research has been devoted to producing a calculation model for air absorption for pure tones. However, most statistical and geometrical room acoustic prediction models calculate the reverberation time in full octave bands in accordance with ISO 3382-1 (International Organization for Standardization, 2009). So far, the available methods that allow calculation of air absorption in octave bands have not been investigated for room acoustic applications. In this paper, the effect of air absorption on octave band reverberation time calculations is investigated based on calculations. It is found that the approximation method, as described in the standard ANSI S1.26 (American National Standards Institute, 1995), fails to estimate accurate decay curves for full octave bands. In this paper, a method is used to calculate the energy decay curve in rooms based on a summation of pure tones within the band. From this decay curve, which is found to be slightly concave upwards, T20 and T30 can be determined. For different conditions, an effective intensity attenuation coefficient mB ;eff for the full octave bands has been calculated. This mB ;eff can be used for reverberation time calculations, if results are to be compared with T20 or T30 measurements. Also, guidelines are given for the air absorption correction of decay curves, measured in a scale model. PMID:25480055

  13. Coffee ring deposition in bands

    Science.gov (United States)

    Mandre, Shreyas; Wu, Ning; Aizenberg, Joanna; Mahadevan, Lakshminarayanan

    2010-11-01

    Microscopic particles suspended in a liquid are transported and deposited at a contact line, as the contact line recedes due to evaporation. A particle layer of uniform thickness is deposited if the particle concentration is above a threshold; below this threshold the deposit forms periodic bands oriented parallel to the contact line. We present a model for the formation of these bands based on evaporation leading to the breakup of the thin liquid film near the contact line. The threshold results from a competition between evaporation speed and deposition speed. Using this model, we predict the thickness and length of the bands, making the control of patterned deposition possible.

  14. Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2012-01-01

    InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5 the band gap closes and the systems become “metallic”. These effects are related to the existence of the built-in electric fields that strongly influence valence- and conduction-band profiles and thus determine effective band gap and emission energies of the superlattices. Varying the widths of the quantum wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.

  15. Recent advances of ab initio calculations in condensed matter physics

    International Nuclear Information System (INIS)

    Recent advances of ab initio calculations in condensed matter physics are presented, with regard to the following eight issues. 1.Two ways of thought in static density functional theory; 2.Functional forms in solid state theory; 3.Time dependent density functional theory and density matrix functional theory; 4.Calculations of band structure in semiconductors:band gap and band order; 5.f electrons and strong correlated metals; 6.Mott insulators; 7.Noncovalent (weak)interactions; 8.Wave function based research. Some background knowledge is presented also. (authors)

  16. Band theoretical study of the Fermi surface of CeB6

    International Nuclear Information System (INIS)

    Fully relativistic band structure calculations have been performed for CeB6 and preliminary results are presented. The Fermi surface is obtained and the dHvA frequency of the ? orbit is calculated. A good quantitative agreement with the experimental results suggests the importance of including both the spin-polarisation and spin-orbit coupling in the calculations. ((orig.))

  17. Electronic energy band parameters of CsCl evaluated on core Bloch states and plane waves

    International Nuclear Information System (INIS)

    Electronic energy bands of CsCl crystal have been calculated within the mixed basis approach with using the core Bloch states and plane waves. The calculated energy parameters of the crystal are in the satisfactory agreement with the experimental data obtained from the analysis of the core-valence luminescence spectra. The obtained results form a base for calculation of CVL spectra parameters

  18. Acoustic band gaps of the woodpile sonic crystal with the simple cubic lattice

    International Nuclear Information System (INIS)

    This study theoretically and experimentally investigates the acoustic band gap of a three-dimensional woodpile sonic crystal. Such crystals are built by blocks or rods that are orthogonally stacked together. The adjacent layers are perpendicular to each other. The woodpile structure is embedded in air background. Their band structures and transmission spectra are calculated using the finite element method with a periodic boundary condition. The dependence of the band gap on the width of the stacked rods is discussed. The deaf bands in the band structure are observed by comparing with the calculated transmission spectra. The experimental transmission spectra for the ?-X and ?-X' directions are also presented. The calculated results are compared with the experimental results.

  19. 'Pudding mold'-type band as an origin of large thermopower in ?-type organic conductors

    International Nuclear Information System (INIS)

    We study the origin of the large thermopower in quasi-two-dimensional ?-type organic conductor, ?-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y (y?0.875), from the view point of a 'pudding mold'-type band structure. We calculate the electronic band structure using an ab initio band calculation package, and obtain a tight binding model fit to the ab initio band structure. Using the model and Boltzmann's equation approach, we calculate the temperature dependence of the Seebeck coefficient. We conclude that the peculiar band structure is the origin of the large Seebeck coefficient and the appearance of the maximum value at a certain temperature.

  20. Acoustic band gaps of the woodpile sonic crystal with the simple cubic lattice

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Liang-Yu; Chen, Lien-Wen, E-mail: chenlw@mail.ncku.edu.t [Department of Mechanical Engineering, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2011-02-02

    This study theoretically and experimentally investigates the acoustic band gap of a three-dimensional woodpile sonic crystal. Such crystals are built by blocks or rods that are orthogonally stacked together. The adjacent layers are perpendicular to each other. The woodpile structure is embedded in air background. Their band structures and transmission spectra are calculated using the finite element method with a periodic boundary condition. The dependence of the band gap on the width of the stacked rods is discussed. The deaf bands in the band structure are observed by comparing with the calculated transmission spectra. The experimental transmission spectra for the {Gamma}-X and {Gamma}-X' directions are also presented. The calculated results are compared with the experimental results.

  1. Superdeformed bands in 130Ce

    International Nuclear Information System (INIS)

    Four superdeformed bands have been assigned to 130Ce following a high-statistics ?-ray study using the EUROGAM II spectrometer. The strongest band exhibits two distinct backbends which, in one scenario, may be interpreted as crossings between high-j N = 6 neutron orbitals (?i13/2) and low-j N = 4 orbitals (?d3/2) in an unpaired system. (author)

  2. Superdeformed bands in 153Ho

    International Nuclear Information System (INIS)

    In a recent experiment performed with the EUROGAM II ?-ray spectrometer three superdeformed (SD) bands have been established in 153Ho. The properties of these bands are discussed in terms of single-particle proton excitations and are compared with respect to the SD magic nucleus 152Dy. These results represent the first observation of SD structures in a holmium nucleus and provide further information on the proton orbitals lying above the Z=66 shell gap. copyright 1997 The American Physical Society

  3. Ultraviolet bands of potassium dimer

    International Nuclear Information System (INIS)

    The ultraviolet band spectra of potassium dimer have been investigated. The studies were performed in absorption in the second order of a 3.4 m Ebert spectrograph with a reciprocal dispersion of 2.6 A/mm. A number of new bands in the electronic states G and H not previously reported have been observed. The vibrational analysis is performed and molecular constants are evaluated. (author)

  4. Band structure from random interactions

    OpenAIRE

    Bijker, R.; Frank, A.

    1999-01-01

    The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P)=0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally ...

  5. Narrow-Band Microwave Filters

    Directory of Open Access Journals (Sweden)

    A.V. Strizhachenko

    2010-01-01

    Full Text Available Original design of the narrow-band compact filters based on the high-quality waveguide-dielectric resonator with anisotropic materials has been presented in this work. Designed filters satisfy the contradictory requirements: they provide the narrow frequency band (0.05 ÷ 0.1 % of the main frequency f0 and the low initial losses ?0 ? 1 dB.

  6. Band structure in 84Sr

    International Nuclear Information System (INIS)

    Excited levels in 84Sr have been populated in the reactions 76Ge (12C, 4n) and 81Br (6Li,3n). Singles and coincidence gamma-ray spectra as well as angular distributions were measured. Lifetimes were measured by the recoil-distance method. The positive parity levels were sorted out into four bands; the existence of at least two negative parity bands was established. The properties of 84Sr were compared to those of neighbouring nuclei

  7. BAND STRUCTURE IN 84Sr

    OpenAIRE

    Dewald, A.; Kaup, U.; Gast, W.; Gelberg, A.; Schuh, H. -w; Zell, K.; Brentano, Von

    1980-01-01

    Excited levels in 84Sr have been populated in the reactions 76Ge (12C, 4n) and 81Br (6Li,3n). Singles and coincidence gamma-ray spectra as well as angular distributions were measured. Lifetimes were measured by the recoil-distance method. The positive parity levels were sorted out into four bands ; the existence of at least two negative parity bands was established. The properties of 84Sr were compared to those of neighbouring nuclei.

  8. Electronic Structure and Valence Band Spectra of Bi4Ti3O12

    OpenAIRE

    Postnikov, A. V.; Bartkowski, St; Mersch, F.; Neumann, M.; Kurmaev, E. Z.; Cherkashenko, V. M.; Nemnonov, S. N.; Galakhov, V. R.

    1995-01-01

    The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.

  9. Application of Hyperspectral Band Elimiation Technique to PVT Images of Composite Structures

    OpenAIRE

    Mahmoud Zaki Iskandarani

    2012-01-01

    A new approach to NDT of composite structures using Band Elimination of the analyzed image index by Hyperspectral image analysis approach is presented and discussed. The matrix Band Elimination technique allows the monitoring and analysis of a components structure based on Filtering of bands and correlation between sequentially pulsed thermal images and their indices. The technique produces several matrices resulting from frame deviation and pixel redistribution calculations for intelligent c...

  10. Mixed state of a dirty two-band superconductor application to MgB_2

    CERN Document Server

    Koshelev, A E

    2003-01-01

    We investigate the vortex state in a two-band superconductor with strong intraband and weak interband electronic scattering rates. Coupled Usadel equations are solved numerically and the distributions of the pair potentials and local densities of states are calculated for two bands at different values of magnetic fields. The existence of two distinct length scales corresponding to different bands is demonstrated. The results provide qualitative interpretation of recent STM experiments on vortex structure imaging in MgB_2.

  11. New Band Structures in Neutron-Rich Mo and Ru Isotopes

    Science.gov (United States)

    Hamilton, J. H.; Luo, Y. X.; Zhu, S. J.; Rasmussen, J. O.; Ramayya, A. V.; Goodin, C.; Li, K.; Hwang, J. K.; Liu, S.; Almehed, D.; Frauendorf, S.; Dimitrov, V.; Zhang, Jing-Ye; Che, X. L.; Jang, Z.; Stefanescu, I.; Gelberg, A.; Ter-Akopian, G. M.; Daniel, A. V.; Lee, I. Y.; Ding, H.-B.; Xu, R. Q.; Wang, J.-G.; Xu, Q.; Stoyer, M. A.; Donangelo, R.; Stone, N. J.

    2009-03-01

    Rotational bands in 110,112Ru and 108Mo have been investigated by means of gamma -gamma -gamma and gamma -gamma (theta ) coincidences of prompt gamma rays emitted in the spontaneous fission of 252Cf. New Delta I = 1 negative parity doublet bands are found. These bands in 110,112Ru and 108Mo have all the properties expected for chiral vibrations. Microscopic calculations that combine the TAC mean-field with random phase approximation support this interpretation.

  12. New Band Structures in Neutron-Rich Mo and Ru Isotopes

    International Nuclear Information System (INIS)

    Rotational bands in 110,112Ru and 108Mo have been investigated by means of ?-?-? and ?-?(?) coincidences of prompt ? rays emitted in the spontaneous fission of 252Cf. New ?I = 1 negative parity doublet bands are found. These bands in 110,112Ru and 108Mo have all the properties expected for chiral vibrations. Microscopic calculations that combine the TAC mean-field with random phase approximation support this interpretation. (author)

  13. Identification of a possible proton two-quasiparticle band in 158Sm

    Science.gov (United States)

    Wang, E. H.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Brewer, N. T.; Luo, Y. X.; Rasmussen, J. O.; Zhu, S. J.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.

    2014-12-01

    High-spin states in neutron-rich 158Sm have been reinvestigated by measuring the prompt ? rays emitted in the spontaneous fission of 252Cf . A new negative-parity band has been established up to spin 12. By comparison with the theoretical calculations, a two-quasiparticle state with ? 5 /2 [532 ] ? ? 5 /2 [413 ] configuration has been proposed for the band head. The systematics of the two-quasiparticle states and bands in this region are discussed.

  14. Dosimetry of narrow band UVB treatments

    International Nuclear Information System (INIS)

    Full text: For many years psoriasis has been treated with broad band UVB lamps. These lamps have a bell shaped spectrum which peaks at 305 nm and extends from 280 nm to 350 nm. However research with monochromatic UV radiation has shown that wavelengths between 300 nm and 320 nm are the most efficacious for clearing psoriasis while wavelengths below 305 nm are most effective for producing the undesirable side effect of erythema (sunburn). In response to these findings Philips developed a narrow band UVB tube in which a large fraction of the output was confined to a narrow peak (bandwidth 2.5 nm) situated at 311 nm. Christchurch Hospital replaced broad band UVB with narrow band treatments in August 1995 and as this required UV exposures to be substantially increased new protocols had to be developed. Three aspects needed to be addressed. These were translating the dose from broad band to narrow band for current patients, determining the initial dose for new patients and developing a formula for increasing subsequent exposures to both types of patient. To translate doses the spectral irradiance (?W/cm2/nm) that would fall on the patient was measured in both the old broad band and the new narrow band treatment units and from this UV doses were calculated. All doses were expressed in mJ/cm2 of unweighted UV over the range 250 nm to 400 nm. The erythemal effectiveness of the two units were compared by using the CIE 1987 curve to express doses in terms CIE 1987 curve to express doses in terms of the equivalent exposure of monochromatic 297 nm radiation. It was found that an exposure of 3.96 mJ/cm2 from the broad band FS40 tubes and 12.79 mJ/cm2 from the narrow band TL/01 tubes were both equivalent to 1.00 mJ/cm2 of monochromatic 297 nm radiation so when transferring patients all broad band doses needed to be increased by a factor of 3.2. Before transferring any patients this factor was confirmed by conducting two minimal erythema dose (MED) tests on a normal subject, one in each unit. For new patients a narrow band treatment schedule has been developed which is based on the patient' s MED. Before commencing treatments the patient is given an MED test using untanned skin on the inner surface of the forearm. The initial dose is 70% of the MED and each subsequent exposure is increased by a constant increment, namely 21.4% of the initial dose. This progression continues until the dose reaches three times the MED at which time it is held constant. Treatments are given twice per week up to a maximum of 30 treatments or until the psoriasis clears. If mild erythema occurs the next treatment is held at the previous dose while for more severe erythema it is missed entirely. This schedule is similar to the one in use at The Royal Victoria Infirmary, Newcastle upon Tyne, but with two minor exceptions. In Newcastle the increments are larger (on average 45% of the initial dose) but they only occur once a week. The transfer from broad band to narrow band was accomplished successfully without any incidence of erythema. After four months experience the 31 patients who were currently following the MED based protocol were reviewed. The lowest MED measured was 500 mJ/cm2 while the highest (three in number) exceeded 1110 mJ/cm2. Eleven of the patients exhibited erythema at some point in their treatment but it was only necessary to reduce the dose increment in one case. Of the remaining 20 patients, 13 who showed poor clearing of their psoriasis were placed on a dose schedules in which the dose increments were increased by between 20 % to 33%. In view of the fact almost equal numbers of patients received too large or too small a dose the schedule can be considered to be a good compromise

  15. Band loss by nestling mourning doves

    Science.gov (United States)

    Kaczynski, C.F.; Kiel, W.H.

    1963-01-01

    Nestling mourning doves (Zenaidura macroura) were banded and checked for band loss prior to fledging at Parchman, Mississippi, during the months of June-August, 1960. Three hundred seventy-seven nestlings 4-6 days of age were banded, 117 with size 3 bands, 120 with size 3A bands, and 140 with size 3A bands secured by Dalzoflex tape. Two hundred twenty nestlings 7-9 days of age were banded, 114 with size 3 bands and 106 with size 3A bands. In the 4- to 6-day age group, 66.3 percent of the size 3A bands were lost. This was a statistically significant departure from the 7.7 percent loss of size 3 bands. No taped bands were lost. However, predators ate 13.8 percent of the nestlings with taped bands and significantly fewer of the nestlings banded without tape. In the 4- to 6-day age group, percentages of nestlings known to be available for band recovery at 9 days or older were: size 3, 69.2 percent; size 3A with tape, 59.0 percent; size 3A, 25.8 percent. In the 7-to 9-day age group, there was a 3.3 percent loss of size 3A bands and no loss of size 3 bands. The minimum age at which nestlings were banded without subsequent loss of bands was 6 days for size 3 and 8 days for size 3A.

  16. Comparing C- and L-band SAR images for sea ice motion estimation

    Science.gov (United States)

    Lehtiranta, J.; Siiriä, S.; Karvonen, J.

    2015-02-01

    Pairs of consecutive C-band synthetic-aperture radar (SAR) images are routinely used for sea ice motion estimation. The L-band radar has a fundamentally different character, as its longer wavelength penetrates deeper into sea ice. L-band SAR provides information on the seasonal sea ice inner structure in addition to the surface roughness that dominates C-band images. This is especially useful in the Baltic Sea, which lacks multiyear ice and icebergs, known to be confusing targets for L-band sea ice classification. In this work, L-band SAR images are investigated for sea ice motion estimation using the well-established maximal cross-correlation (MCC) approach. This work provides the first comparison of L-band and C-band SAR images for the purpose of motion estimation. The cross-correlation calculations are hardware accelerated using new OpenCL-based source code, which is made available through the author's web site. It is found that L-band images are preferable for motion estimation over C-band images. It is also shown that motion estimation is possible between a C-band and an L-band image using the maximal cross-correlation technique.

  17. Fluctuations in a superconducting quantum critical point of multi-band metals

    CERN Document Server

    Ramires, Aline

    2011-01-01

    In multi-band metals quasi-particles arising from different atomic orbitals coexist at a common Fermi surface. Superconductivity in these materials may appear due to interactions within a band (intra-band) or among the distinct metallic bands (inter-band). Here we consider the suppression of superconductivity in the intra-band case due to hybridization. The fluctuations at the superconducting quantum critical point (SQCP) are obtained calculating the response of the system to a fictitious space and time dependent field, which couples to the superconducting order parameter. The appearance of superconductivity is related to the divergence of a generalized susceptibility. For a single band superconductor this coincides with the \\textit{Thouless criterion}. For fixed chemical potential and large hybridization, the superconducting state has many features in common with breached pair superconductivity with unpaired electrons at the Fermi surface. The T=0 phase transition from the superconductor to the normal state ...

  18. Hubbard-U band-structure methods

    DEFF Research Database (Denmark)

    Albers, R.C.; Christensen, Niels Egede

    2009-01-01

    The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many-body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations are inconsistent with what the calculations actually do. Although many of these calculations are often treated as essentially first-principles calculations, in fact, we argue that they should be viewed from an entirely different point of view, namely, as based on phenomenological many-body corrections to band-structure theory. Alternatively, it may also be considered that they are just based on a Hubbard model that is more complex than the simple one- or few-band models traditionally used in many-body theories of solids.

  19. Triaxial shape coexistence and new aligned band in 178Os

    International Nuclear Information System (INIS)

    High spin states in 178Os were studied by means of 165Ho(20Ne,p6n)178Os fusion evaporation reaction at a beam energy of 150 MeV, using a clover detector array. Several new transitions belonging to 178Os were placed in a level scheme and a new aligned rotational band was observed in addition to earlier known bands. Spin-parity assignments for most of the proposed levels were made using the deduced directional correlation orientation and polarization measurements for the de-exciting transitions. Experimental results are compared with the projected angular momentum deformed Hartree-Fock model calculations and cranked Woods-Saxon model calculations. This nucleus is predicted to be prolate deformed in the ground state but the ?-softness at higher excitation is revealed by the cranked Woods-Saxon model and the geometrical asymmetric model calculations.

  20. Acoustic band pinning in the phononic crystal plates of anti-symmetric structure

    International Nuclear Information System (INIS)

    Acoustic bands are studied numerically for a Lamb wave propagating in an anti-symmetric structure of a one-dimensional periodic plate by using the method of supercell plane-wave expansion. The results show that all the bands are pinned in pairs at the Brillouin zone boundary as long as the anti-symmetry remains and acoustic band gaps (ABGs) only appear between certain bands. In order to reveal the relationship between the band pinning and the anti-symmetry, the method of eigenmode analysis is introduced to calculate the displacement fields of different plate structures. Further, the method of harmony response analysis is employed to calculate the reference spectra to verify the accuracy of numerical calculations of acoustic band map, and both the locations and widths of ABGs in the acoustic band map are in good agreement with those of the reference spectra. The investigations show that the pinning effect is very sensitive to the anti-symmetry of periodic plates, and by introducing different types of breakages, more ABGs or narrow pass bands will appear, which is meaningful in band gap engineering. (condensed matter: structural, mechanical, and thermal properties)

  1. Quasiparticle bands of the two-dimensional Hubbard model

    Science.gov (United States)

    Zhou, Yu; Fedro, A. J.; Bowen, S. P.; Koelling, D. D.; Leung, T. C.; Harmon, B. N.; Sinha, S. K.

    1991-11-01

    We present a mean-field calculation of the two-dimensional single-band Hubbard model based on a Mori-projection-operator formalism. Various physical properties including the energy, effective hopping matrix element, local moment, momentum distribution function, and Fermi surface are calculated. The results are compared with those of the Hubbard-I approximation, the four-boson mean-field theory of Kotliar and Rockenstein (SBMF), and quantum Monte Carlo simulations. Systematic improvement over the Hubbard-I approximation is seen, and good agreements are obtained between our calculation and the SBMF theory.

  2. Angle-resolved photoemission study and first principles calculation of the electronic structure of GaTe

    OpenAIRE

    Sanchez-royo, J. F.; Pellicer-porres, J.; Segura, A.; Munoz-sanjose, V.; Tobias, G.; Ordejon, P.; Canadell, E.; Huttel, Y.

    2001-01-01

    The electronic band structure of GaTe has been calculated by numerical atomic orbitals density-functional theory, in the local density approximation. In addition, the valence-band dispersion along various directions of the GaTe Brillouin zone has been determined experimentally by angle-resolved photoelectron spectroscopy. Along these directions, the calculated valence-band structure is in good concordance with the valence-band dispersion obtained by these measurements. It ha...

  3. Rotational band structure of intruder configurations: success and limitations of the Cranked Shell Model

    International Nuclear Information System (INIS)

    Rotational bands built on intruder configurations are discussed within the Cranked Shell Model. The experimental observed alignment pattern occurring in these bands cannot be accounted for by standard mean field calculations. The discrepancy between theory and experiment is traced back to the fact that the neutron-proton interaction is only partly and indirectly included in the standard mean field approach

  4. Spin determination of superdeformed bands, A-190 and A-150 regions

    International Nuclear Information System (INIS)

    Methods for theoretical determination of the spin of superdeformed bands (SDB) are briefly reviewed. an energy spectrum formula expanded in powers of I(I+1) for SDB is proposed and applied to the bands in A-190 and A-150 regions. Results of calculations are compared and discussed

  5. Electronic band structure of ferro-pnictide superconductors from ARPES experiment

    OpenAIRE

    Kordyuk, A. A.; Zabolotnyy, V. B.; Evtushinsky, D. V.; Yaresko, A. N.; Buechner, B.; Borisenko, S. V.

    2011-01-01

    ARPES experiments on iron based superconductors show that the differences between the measured and calculated electronic band structures look insignificant but can be crucial for understanding of the mechanism of high temperature superconductivity. Here we focus on those differences for 111 and 122 compounds and discuss the observed correlation of the experimental band structure with the superconductivity.

  6. Structure of collective bands in deformed nuclei from the microscopic point of view

    International Nuclear Information System (INIS)

    Many body calculations with two nucleon residual interactions show that properties of rotational bands up to moderate spins can be explained by a microscopic theory consistent with many low energy nuclear properties. The prospects are good for explaining very high spin bands on the same basis. (orig.)

  7. Three parameter approach to solvent effects on ion-pair charge-transfer bands

    Energy Technology Data Exchange (ETDEWEB)

    Hennig, H.; Billing, R.; Benedix, R.

    1986-01-01

    Solvent effects on the position of ion-pair charge-transfer absorption bands are described using a three parameter approach. The values of calculated coefficients are discussed considering specific and non-specific interactions.

  8. Electron energy loss studies of the valence band density of states of scandium

    International Nuclear Information System (INIS)

    Electron energy loss spectroscopy of the scandium (0001) surface has indicated both core level and valence band excitation loss structure. Comparison to theoretically calculated bulk densities of states for scandium shows good agreement with the experimental results. (author)

  9. Band gap modulation of functionalized metal-organic frameworks.

    Science.gov (United States)

    Musho, Terence; Li, Jiangtan; Wu, Nianqiang

    2014-11-21

    Metal-organic frameworks (MOFs) have been envisioned as alternatives to planar metallic catalysts for solar-to-fuel conversion. This is a direct result of their porous structure and the ability to tailor their optical absorption properties. This study investigates the band gap modulation of Zr-UiO-66 MOFs from both the computational and experimental points of view for three linker designs that include benzenedicarboxylate (BDC), BDC-NO2, and BDC-NH2. Emphasis in this study was aimed at understanding the influence of the bonding between the aromatic ring and the functional group. A ground state density functional theory (DFT) calculation was carried out to investigate the projected density of states and the origins of the modulation. A time-dependent density functional theory (TDDFT) calculation of the hydrogen terminated linkers confirmed the modulation and accounted for the electron charge transfer providing comparable optical band gap predictions to experimental results. Computational results confirmed the hybridization of the carbon-nitrogen bond in conjunction with the donor state resulting from the NH2 functionalization. The NO2 functionalization resulted in an acceptor configuration with marginal modification to the valence band maximum. The largest modulation was BDC-NH2 with a band gap of 2.75 eV, followed by BDC-NO2 with a band gap of 2.93 eV and BDC with a band gap of 3.76 eV. The electron effective mass was predicted from the band structure to be 8.9 me for all MOF designs. PMID:25269595

  10. High-spin properties of 164Er in the multiple band crossing region

    International Nuclear Information System (INIS)

    High-spin states in 164Er have been studied by using the 150Nd(18O,4n?) and 164Dy(?,4n?) reactions and by multiple Coulomb excitation with 136Xe ions. Several positive-parity bands are excited, and two negative-parity bands have been identified. The previously reported backbending behavior of the yrast sequence is demonstrated to result from the intersection of the ground band (seen to spin 22+) with an even-spin ''superband'' observed from spins 12+ to 24+. The odd-spin yrast superband and the second lowest even-spin superband also have been observed. All the superbands have moments of inertia appreciably larger than the ground band. The observed intersection of these multiple superbands with the ? band produces different backbending behavior and a staggering of the energies of the odd- and even-spin members of the ? band. B(E2) values for transitions below and through the band intersection regions of both the ground band and ? bands have been deduced from multiple Coulomb excitation yields. In addition, lifetimes have been measured for the ground band by the Doppler-broadened line-shape technique. The level energies and B(E2) values are consistent with weak interaction matrix elements ( approx. = 45 keV) between the intersecting bands. The B(E2) values of the unperturbed band are found to obey the simple rigid-rotor relationship. The 7- negative-parity band exhibp>- negative-parity band exhibits a normal rotational sequence, while the 5- band exhibits a large odd-even staggering and a larger moment of inertia. Two-quasiparticle-plus-rotor model calculations indicate strong rotation alignment and reproduce the observed properties of the high-spin states for both the positive- and negative-parity bands in 164Er

  11. Band alignment of semiconductors from density-functional theory and many-body perturbation theory

    Science.gov (United States)

    Hinuma, Yoyo; Grüneis, Andreas; Kresse, Georg; Oba, Fumiyasu

    2014-10-01

    The band lineup, or alignment, of semiconductors is investigated via first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT). Twenty-one semiconductors including C, Si, and Ge in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, and GaN and ZnO in the wurtzite structure are considered in view of their fundamental and technological importance. Band alignments are determined using the valence and conduction band offsets from heterointerface calculations, the ionization potential (IP) and electron affinity (EA) from surface calculations, and the valence band maximum and conduction band minimum relative to the branch point energy, or charge neutrality level, from bulk calculations. The performance of various approximations to DFT and MBPT, namely the Perdew-Burke-Ernzerhof (PBE) semilocal functional, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, and the GW approximation with and without vertex corrections in the screened Coulomb interaction, is assessed using the GW?1 approximation as a reference, where first-order vertex corrections are included in the self-energy. The experimental IPs, EAs, and band offsets are well reproduced by GW?1 for most of the semiconductor surfaces and heterointerfaces considered in this study. The PBE and HSE functionals show sizable errors in the IPs and EAs, in particular for group II-VI semiconductors with wide band gaps, but are much better in the prediction of relative band positions or band offsets due to error cancellation. The performance of the GW approximation is almost on par with GW?1 as far as relative band positions are concerned. The band alignments based on average interfacial band offsets for all pairs of 17 semiconductors and branch point energies agree with explicitly calculated interfacial band offsets with small mean absolute errors of both ˜0.1eV, indicating a good overall transitivity of the band offsets. The alignment based on IPs from selected nonpolar surfaces performs comparably well in the prediction of band offsets at most of the considered interfaces. The maximum errors are, however, as large as 0.3, 0.4, and 0.7 eV for the alignments based on the average band offsets, branch point energies, and IPs, respectively. This margin of error should be taken into account when performing materials screening using these alignments.

  12. Band offsets and band bending at heterovalent semiconductor interfaces

    Science.gov (United States)

    Frey, A.; Bass, U.; Mahapatra, S.; Schumacher, C.; Geurts, J.; Brunner, K.

    2010-11-01

    We present a comprehensive study of band offsets and band bending at heterovalent semiconductor heterointerfaces. A perfectly abrupt heterovalent interface is usually thermodynamically unstable, and atomic intermixing of materials with different numbers of valence electrons causes large variations in band offsets and local doping density, depending on the spatial arrangement of atoms at the interface. The studied prototypical II-VI/III-V semiconductor interfaces are n -doped ZnSe/GaAs (001) heterostructures with varied composition profiles close to the interface, which were realized by molecular-beam epitaxy with different amounts of Zn or Se predeposited on n -GaAs prior to n -ZnSe layer growth. The samples are characterized by temperature-dependent electrical transport across the interface, electrochemical capacitance-voltage profiling, Raman spectroscopy, and high-resolution x-ray diffraction. We find that the potential barrier in the conduction band at a Zn-rich n -ZnSe/ n -GaAs interface is as high as 550 meV and it gradually decreases with Se predeposition down to about 70 meV. A large depletion region at the heterointerface, about 50 nm wide, is assigned to significant intermixing of acceptor-type atoms, resulting in an effective electron deficit of 1.5×1013cm-2 . The depletion width and the acceptor density around the interface are nearly independent from the growth start procedure. Se predeposition, however, partially shifts the depletion region at the heterointerface from GaAs into ZnSe, compared to Zn predeposition. The results are discussed on the basis of a band-bending model accounting for variable band offsets, interface state density and atomic interdiffusion profiles depending on growth start.

  13. The U-band Galaxy Luminosity Function of Nearby Clusters

    CERN Document Server

    Christlein, D; Zabludoff, A I

    2004-01-01

    Despite the great potential of the U-band galaxy luminosity function (GLF) to constrain the history of star formation in clusters, to clarify the question of variations of the GLF across filter bands, to provide a baseline for comparisons to high-redshift studies of the cluster GLF, and to estimate the contribution of bound systems of galaxies to the extragalactic near-UV background, determinations have so far been hampered by the generally low efficiency of detectors in the U-band and by the difficulty of constructing both deep and wide surveys. In this paper, we present U-band GLFs of three nearby, rich clusters to a limit of M_U=-17.5 (M*_U+2). Our analysis is based on a combination of separate spectroscopic and R-band and U-band photometric surveys. For this purpose, we have developed a new maximum-likelihood algorithm for calculating the luminosity function that is particularly useful for reconstructing the galaxy distribution function in multi-dimensional spaces (e.g., the number of galaxies as a simult...

  14. Single-Band and Dual-Band Infrared Detectors

    Science.gov (United States)

    Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor); Soibel, Alexander (Inventor); Nguyen, Jean (Inventor); Khoshakhlagh, Arezou (Inventor)

    2015-01-01

    Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed.

  15. Two-dimensional angular-correlation-of-annihilation-radiation study of ?-(BEDT-TTF)2Cu(NCS)2

    International Nuclear Information System (INIS)

    We report the two-dimensional angular-correlation-of-annihilation-radiation measurement of the e+e- (pair) momentum distribution in the organic superconductor ?-(BEDT-TTF)2Cu(NCS)2. Our data, when compared with tight-binding (Hueckel) electronic-band calculations, show features consistent with predicted Fermi surfaces. The structure around Z in our spectrum supports the results from earlier de Haas--van Alphen and Shubnikov--de Haas measurements. In addition, our data show features consistent with the predicted open Fermi surface that runs nearly parallel to YM

  16. High resolution electronic spectroscopy of vibrationally hot bands of benzimidazole.

    Science.gov (United States)

    Brand, Christian; Rolf, Josefin; Wilke, Martin; Schmitt, Michael

    2013-12-01

    Rotationally resolved electronic spectra of seven vibrationally excited bands in the electronic spectrum of benzimidazole have been measured and analyzed. From the vibrational contributions to the rotational constants, an assignment of the hot bands could be made on the basis of anharmonic corrections to the harmonic normal modes and by using the information contained in the Duschinsky matrix calculated by second order coupled cluster (CC2) theory. Fluorescence emission and (hot) absorption spectra of benzimidazole from Jalviste and Treshchalov [Chem. Phys. 1993, 172, 325] have been simulated using Franck-Condon integrals obtained from CC2 optimized geometries and Hessians. PMID:24261704

  17. Resonant fluorescence emission from the Ge and Cu valence band

    Science.gov (United States)

    Kaprolat, A.; Schülke, W.

    Working out the calculation of the double differential scattering cross section for resonantly excited X-ray emission from valence bands, one ends up [7] with a law of momentum conservation, combining Bloch-k-vectors of the envolved electrons and the incoming and outgoing photon. This leads to a rich structure of the fluorescence line that reveals properties of the underlying electronic band structure. First experiments in the hard X-ray region on Ge and Cu are presented, showing, that momentum conservation in the resonant absorption-emission process holds.

  18. C-Band LINAC for a race track microtron

    OpenAIRE

    Carrillo Barrera, David Manuel

    2010-01-01

    The general aim of this thesis is to do the radiofrequency (RF) design of a 2 MeV C-Band linac for a RTM, the mechanical design and thermo mechanical calculations and to follow the machining procedure. Afterwards, a test bench has to be designed so the RF cold measurements may be carried out. In addition, the process of brazing of accelerating cavities will be studied. The novelty of this thesis arises from the fact that C-band linac was never used before in RTM. Specific of...

  19. Limitations to band gap tuning in nitride semiconductor alloys

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2010-01-01

    Relations between the band gaps of nitride alloys and their lattice parameters are presented and limits to tuning of the fundamental gap in nitride semiconductors are set by combining a large number of experimental data with ab initio theoretical calculations. Large band gap bowings obtained theoretically for GaxAl1-xN, InxGa1-xN, and InxAl1-xN for uniform as well as clustered arrangements of the cation atoms are considered in the theoretical analysis. It is shown that indium plays a particular role in nitride alloys being responsible for most of the observed effects.

  20. Triaxial strongly deformed bands in 160,161Tm

    International Nuclear Information System (INIS)

    High-spin states in 160,161Tm were populated using the 128Te(37Cl, 5n and 4n) reactions at a beam energy of 170 MeV. Emitted ? rays were detected in the Gammasphere spectrometer. Two rotational bands with high moments of inertia were discovered, one assigned to 160Tm, while the other tentatively assigned to 161Tm. These sequences display features similar to bands observed in neighboring Er, Tm, Yb, and Lu nuclei which have been discussed in terms of triaxial strongly deformed structures. Cranked Nilsson Strutinsky calculations have been performed that predict well-deformed triaxial shapes at high spin in 160,161Tm

  1. Triaxial strongly deformed bands in Tm160,161

    Science.gov (United States)

    Teal, C.; Lagergren, K.; Aguilar, A.; Hartley, D. J.; Riley, M. A.; Simpson, J.; Carpenter, M. P.; Garg, U.; Janssens, R. V. F.; Joss, D. T.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; Wang, X.; Zhu, S.; Ragnarsson, I.

    2008-07-01

    High-spin states in Tm160,161 were populated using the Te128(Cl37, 5n and 4n) reactions at a beam energy of 170 MeV. Emitted ? rays were detected in the Gammasphere spectrometer. Two rotational bands with high moments of inertia were discovered, one assigned to Tm160, while the other tentatively assigned to Tm161. These sequences display features similar to bands observed in neighboring Er, Tm, Yb, and Lu nuclei which have been discussed in terms of triaxial strongly deformed structures. Cranked Nilsson Strutinsky calculations have been performed that predict well-deformed triaxial shapes at high spin in Tm160,161.

  2. Density functionals from many-body perturbation theory: The band gap for semiconductors and insulators

    OpenAIRE

    Gru?ning, Myrta; Marini, Andrea; Rubio Secades, A?ngel

    2006-01-01

    Theoretically the Kohn-Sham band gap differs from the exact quasiparticle energy gap by the derivative discontinuity of the exchange-correlation functional. In practice for semiconductors and insulators the band gap calculated within any local or semilocal density approximations underestimates severely the experimental energy gap. On the other hand, calculations with an >exact> exchange potential derived from many-body perturbation theory via the optimized effective potential suggest that imp...

  3. Strain induced band gap deformation of H/F passivated graphene and h-BN sheet

    OpenAIRE

    Bhattacharya, A.; Bhattacharya, S.; Das, G. P.

    2011-01-01

    Strain induced band gap deformations of hydrogenated/fluorinated graphene and hexagonal BN sheet have been investigated using first principles density functional calculations. Within harmonic approximation, the deformation is found to be higher for hydrogenated systems than for the fluorinated systems. Interestingly, our calculated band gap deformation for hydrogenated/fluorinated graphene and BN sheets are positive, while those for pristine graphene and BN sheet are found t...

  4. Electron impact excitation of the gamma bands of nitric oxide

    International Nuclear Information System (INIS)

    The excitation of several pronounced ? bands of NO by electron impact was studied from threshold to 1000 eV. A high optical efficiency was achieved by using an ellipsoidal collision chamber with mirrored interior surfaces. The interaction volume viewed was located at one of the foci of the ellipsoid. A 0.25 m double monochromator and single photon counting techniques were employed to monitor molecular band intensities. The optical sensitivity between 2000 and 4000 A was obtained with the molecular branching ratio method by monitoring 1NG CO+, 1NG N+2, 2PG N2 band intensities and suitable progressions in the ? system of NO. Second order effects were avoided by low NO densities (approx.10-1 torr) in the collision chamber. No ionization gauges were used during measurement, thus eliminating the possible dissociation of NO and subsequent formation of N2. Absolute cross sections for ? bands were obtained by normalizing to the 2PG (0,0) band of N2. For this purpose, a known mixture of NO and N2 was prepared in a gas handling manifold using a manometer. For the unambiguously identifiable (0,1), (0,2), (1,0), (1,5), and (2,7) ? bands of NO, the cross sections peaked near 18 eV and had values of 2.2, 1.8, 6.3, 1.3, and 0.57times10-19 cm2, respectively, with a possible error of 25%. The relative peak cross sections agree with calculated band intensities within 20%culated band intensities within 20%

  5. Band shifting for ocean color multi-spectral reflectance data.

    Science.gov (United States)

    Mélin, Frédéric; Sclep, Gert

    2015-02-01

    An approach to perform band shifting applied to multi-spectral ocean remote sensing reflectance RRS values in the visible spectral range is presented. The band-shifting scheme aims at expressing RRS at a wavelength not originally part of the spectrum from data at neighboring bands. The scheme relies on the determination of inherent optical properties (IOPs) by a bio-optical model, the calculation of the IOPs at the target wavelength using the spectral shapes assumed for each IOP, and the operation of the bio-optical model in forward mode to express RRS at the target wavelength. The performance of the band-shifting scheme applied to bands typical of satellite missions is assessed with hyper-spectral data sets obtained from radiative transfer simulations or from field measurements. The relative error ? on the conversion factors from 488 to 490 nm is mostly within 1%. Analogous results are obtained for conversions in the red spectral domain (665, 667 and 670 nm) only for synthetic data sets. The range of ? for conversions between green bands (547, 555 and 560 nm) is within 2% to 5% depending on the data set considered. Similar results are obtained when RRS values are computed at 510 nm from data at 488 and 531 nm. In the case of the assessment with simulated data, all band-shifting operations are characterized by an ? range within 2% for all conversions when the concentration of chlorophyll-a is lower than 1 mg m-3. Applied to satellite data, the band-shifting scheme noticeably improves the agreement between RRS data from different missions. PMID:25836095

  6. X-Band PLL Synthesizer

    Directory of Open Access Journals (Sweden)

    P. Kutin

    2006-04-01

    Full Text Available This paper deals with design and realization of a PLL synthesizer for the microwave X−band. The synthesizer is intended for use as a local oscillator in a K−band downconverter. The design goal was to achieve very low phase noise and spurious free signal with a sufficient power level. For that purpose a low phase noise MMIC VCO was used in phase locked loop. The PLL works at half the output frequency, therefore there is a frequency doubler at the output of the PLL. The output signal from the frequency doubler is filtered by a band-pass filter and finally amplified by a single stage amplifier.

  7. Deformation band formation, characteristics, history

    International Nuclear Information System (INIS)

    Deformation bands (DMB) are crystal slabs that develop slip on systems different from neighbours; they rotate in different directions developing intervening transition boundaries (TB) that rise rapidly in misorientation. In polycrystals, grains divide into DMB, slipping on 2 or 3 systems to provide the 5 required components with minimum energy, as confirmed through OIM boundary misorientations and band rotation poles. TEM exposed the subgrains but seldom TB, except in single crystals as layers of cells. As the TB extend and align into layer bands, the microtextures are similar in cold and hot working. In hot working, TB are quite narrow and able to migrate; at large strains, lengthening and rotating TB (like grain boundaries) are responsible for rapid accumulation of high angle facets of many subgrains. Nevertheless sub-boundaries persist defining steady-state cellular dimensions and flow stress.

  8. Voice over IP Calculator

    Science.gov (United States)

    The Voice over IP Calculator Web site actually consists of four free online tools that can be used to estimate bandwidth requirements and voice paths for a planned VoIP system. The four tools are: Lines and IP Bandwidth Calculator, Erlangs and Bandwidth Calculator, Minutes and Lines Calculator, and Erlangs and Lines Calculator. Each utility is very easy to use, but is mainly intended for experienced IT workers.

  9. Possible Smooth Band Termination in ^123La

    Science.gov (United States)

    Park, H. I.; Hartley, D. J.; Riedinger, L. L.; Zeidan, O.; Zhang, Jing-Ye; Galindo-Uribarri, A.; Carpenter, M. P.; Janssens, R. V. F.; Seweryniak, D.; Devlin, M.; Reviol, W.; Sarantites, D. G.; Dong, B. G.; Ragnarsson, I.

    2002-10-01

    The power of GAMMASPHERE was combined with the selectivity of the MICROBALL in an experiment to investigate rotational structures of near-drip-line nuclei in the La-Nd region. The reaction ^40Ca + ^92Mo was used with a beam energy of 184 MeV. One of the weaker charged-particle channels (2? p), which comprised ˜1.3% of the events recorded, was investigated to study high-spin states in ^123La. Three new decoupled sequences were identified and the previously known structures [1] were significantly extended towards ˜40hbar. It is within this spin region that smooth band termination has been observed in ^127,129La [2]. A minimum in an energy minus a rigid rotor reference plot, which is often attributed to smooth band termination, is in fact observed for the lowest (?,?) = (+,-1/2) configuration. Therefore, cranked Nilsson-Strutinsky calculations were performed and compared with experimental data in order to determine whether the observed sequence is approaching a terminating state. [1] R. Wyss et al., Nucl. Phys. A 503, 244 (1989); [2] R. Wadsworth et al., Phys. Rev. C 62, 034315 (2000).

  10. Shear Banding of Complex Fluids

    CERN Document Server

    Divoux, Thibaut; Manneville, Sébastien; Lerouge, Sandra

    2015-01-01

    Even in simple geometries many complex fluids display non-trivial flow fields, with regions where shear is concentrated. The possibility for such shear banding has been known since several decades, but the recent years have seen an upsurge of studies offering an ever more precise understanding of the phenomenon. The development of new techniques to probe the flow on multiple scales and with increasing spatial and temporal resolution has opened the possibility for a synthesis of the many phenomena that could only have been thought of separately before. In this review, we bring together recent research on shear banding in polymeric and on soft glassy materials, and highlight their similarities and disparities.

  11. Holographic Multi-Band Superconductor

    CERN Document Server

    Huang, Ching-Yu; Maity, Debaprasad

    2011-01-01

    We propose a gravity dual for the holographic superconductor with multi-band carriers. Moreover, the currents of these carriers are unified under a global non-Abelian symmetry, which is dual to the bulk non-Abelian gauge symmetry. We study the phase diagram of our model, and find it qualitatively agrees with the one for the realistic 2-band superconductor, such as MgB2. We also evaluate the holographic conductivities and find the expected mean-field like behaviors in some cases. However, for a wide range of the parameter space, we also find the non-mean-field like behavior with negative conductivities.

  12. ALMA Band 5 Cartridge Performance

    Science.gov (United States)

    Billade, Bhushan; Lapkin, I.; Nystrom, O.; Sundin, E.; Fredrixon, M.; Finger, R.; Rashid, H.; Desmaris, V.; Meledin, D.; Pavolotsky, A.; Belitsky, Victor

    2010-03-01

    Work presented here concerns the design and performance of the ALMA Band 5 cold cartridge, one of the 10 frequency channels of ALMA project, a radio interferometer under construction at Atacama Desert in Chile. The Band 5 cartridge is a dual polarization receiver with the polarization separation performed by orthomode transducer (OMT). For each polarization, Band 5 receiver employs sideband rejection (2SB) scheme based on quadrature layout, with SIS mixers covering 163-211 GHz with 4-8 GHz IF. The LO injection circuitry is integrated with mixer chip and is implemented on the same substrate, resulting in a compact 2SB assembly. Amongst the other ALMA bands, the ALMA Band 5 being the lowest frequency band that uses all cold optics, has the largest mirror. Consequently, ALMA Band 5 mirror along with its support structure leaves very little room for placing OMT, mixers and IF subsystems. The constraints put by the size of cold optics and limited cartridge space, required of us to revise the original 2SB design and adopt a design where all the components like OMT, mixer, IF hybrid, isolators and IF amplifier are directly connected to each other without using any co-ax cables in-between. The IF subsystem uses the space between 4 K and 15 K stage of the cartridge and is thermally connected to 4 K stage. Avoiding co-ax cabling required use of custom designed IF hybrid, furthermore, due to limited cooling capacity at 4 K stage, resistive bias circuitry for the mixers is moved to 15 K stage and the IF hybrid along with an integrated bias-T is implemented using superconducting micro-strip lines. The E-probes for both LO and RF waveguide-to-microstrip transitions are placed perpendicular to the wave direction (back-piece configuration). The RF choke at the end of the probes provides a virtual ground for the RF/LO signal, and the choke is DC grounded to the chassis. The on-chip LO injection is done using a microstrip line directional coupler with slot-line branches in the ground plane. The isolated port of the LO coupler is terminated by floating wideband elliptical termination. The mixer employs two SIS junctions with junction area of 3 ?m2 each, in twin junction configuration, followed by a quarter wave transformer to couple it to the signal probe. A quarter-wave high impedance line on an extra layer of SiO2 is used to extract the IF by separating from RF. At the conference, we plan to present details of the cartridge design and results of the experimental characterization of the ALMA Band 5 cold cartridge.

  13. Multiphonon absorption bands in InP

    International Nuclear Information System (INIS)

    The study of absorption by indium phosphide crystals, caused by interaction between electromagnetic radiation and crystal-lattice vibrational movement has been made. The optical measurements of InP semi-insulating single crystals were carried out under natural light at temperatures of 300 K and 77 K. As a result of measuring transmission spectra and of calculating absorption spectra six heretofore unknown absorption bands have been discovered. An attempt was made to identify all the discovered spectrum features with proper phonon combinations. All the phonon combinations were tabulated and correspond to allowed electric dipole two and three-phonon processes. The results of the investigations outline the importance of optical measurements in order to study the features of the phonon spectrum of indium phosphide - the material forbidding a study using the neutron scattering method

  14. A simplified package for calculating with splines

    Science.gov (United States)

    Smith, P. W.

    1974-01-01

    This package is designed to solve some of the elementary problems of spline interpretation and least squares fit. The subroutines fall into three basic categories. The first category involves computations with a given spline and/or knot sequence; the second category involves routines which calculate the coefficients of splines which perform a certain task (such as interpolation or least squares fit); and the last category is a banded equation solver for specific linear equations.

  15. Analysis of high-temperature thermoelectric properties of p-type CoSb3 within a two-valence-band and two-conduction-band model

    Science.gov (United States)

    Kajikawa, Y.

    2014-05-01

    Experimental data on the thermoelectric properties of p-type CoSb3 reported by Caillat et al. [J. Appl. Phys. 80, 4442 (1996)] have been analyzed, assuming not only a pair of the first valence (v1) and the first conduction (c1) bands but also the second valence (v2) and the second conduction (c2) bands. By taking into account the excitation of carriers into the v2 and the c2 bands, the behavior of the Hall coefficient as well as that of the Seebeck coefficient at high temperatures is well explained. By taking into account the nonparabolicity of the v1 band, the temperature dependence of mobility is well explained with assuming scattering due to acoustic phonons, nonpolar and polar optical phonons, and ionized impurities. Furthermore, various material parameters of CoSb3, such as the band-gap energy, effective masses, and deformation potentials, have been deduced from fitting the calculation to the experimental data on the temperature dependences of the Hall coefficient, the mobility, and the Seebeck coefficient. Among them, the band-gap energy and the effective mass of the v1 band have been corrected from the original values estimated by Caillat et al. In addition, it is shown that the experimental data on the hole-concentration dependences of both the room-temperature Seebeck coefficient and the cyclotron mass are well reproduced by the theoretical calculation using the deduced values for the nonparabolic v1 band.

  16. Quasiparticle band structures and optical properties of magnesium fluoride.

    Science.gov (United States)

    Yi, Zhijun; Jia, Ran

    2012-02-29

    The quasiparticle and optical properties of magnesium fluoride (MgF(2)) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment. PMID:22277330

  17. Dual-Band Tunable Recursive Active Filter

    OpenAIRE

    Segovia Vargas, Daniel; Garci?a Pe?rez, Oscar Alberto; Gonza?lez Posadas, Vicente; Aznar Ballesta, Francisco

    2011-01-01

    This letter presents a novel recursive active filter topology that provides dual-band performance, with independent tuning capability in both bands. The dual-band operation is achieved by using two independent feedback lines. Additionally, linear phase shifters based on left-handed cells are included in these two branches in order to tune the center frequency of both pass bands.

  18. Layer-dependent Band Alignment and Work Function of Few-Layer Phosphorene

    OpenAIRE

    Yongqing Cai; Gang Zhang; Yong-Wei Zhang

    2014-01-01

    Using first-principles calculations, we study the electronic properties of few-layer phosphorene focusing on layer-dependent behavior of band gap, work function and band alignment and carrier effective mass. It is found that few-layer phosphorene shows a robust direct band gap character, and its band gap decreases with the number of layers following a power law. The work function decreases rapidly from monolayer (5.16 eV) to trilayer (4.56 eV), and then slowly upon further i...

  19. Systematic search of candidate chiral bands in odd-odd 122-132Cs isotopes

    International Nuclear Information System (INIS)

    Two nearly degenerate candidate chiral bands have been observed in odd-odd 122-132Cs isotopes. These bands are built on the ?h11/2 (direct x)?h11/2 configuration. Systematic analyses associated with the partner bands are presented. The degree of energy degeneracy, the energy staggering parameter S(I), the B(M1)/B(E2) ratios and the TRS calculations have been deduced for these doublet bands. Systematic comparisons indicate that the odd-odd 126, 128,130Cs isotopes have stable chiral structure at higher spin range. (authors)

  20. Observation of an intermediate band in Sn-doped chalcopyrites with wide-spectrum solar response.

    Science.gov (United States)

    Yang, Chongyin; Qin, Mingsheng; Wang, Yaoming; Wan, Dongyun; Huang, Fuqiang; Lin, Jianhua

    2013-01-01

    Nanostrcutured particles and polycrystalline thin films of Sn-doped chalcopyrite are synthesized by newly-developed methods. Surprisingly, Sn doping introduces a narrow partially filled intermediate band (IB) located ~1.7 eV (CuGaS(2)) and ~0.8 eV (CuInS(2)) above the valance band maximum in the forbidden band gap. Diffuse reflection spectra and photoluminescence spectra reveal extra absorption and emission spectra induced by the IBs, which are further supported by first-principle calculations. Wide spectrum solar response greatly enhances photocatalysis, photovoltaics, and photo-induced hydrogen production due to the intermediate band. PMID:23412565

  1. Decoupled 2-quasiparticle bands and backbending in 174W and 172Hf

    International Nuclear Information System (INIS)

    Negative parity sidebands have been observed to high spin in the N = 100 isotones 174W and 172Hf. Their high and constant moment of inertia, and decay characteristics, identify them as semi-decoupled bands, probably of a configuration involving a psub(3/2) or hsub(9/2) neutron and an isub(13/2) neutron. The character of these bands is used to estimate the properties of the (isub(13/2))2 neutron band responsible for backbending, and through a two-band mixing calculation, the details of backbending. (Author)

  2. About the linewidth of cyclotron resonance in band-gap graphene

    Science.gov (United States)

    Kryuchkov, S. V.; Kukhar', E. I.

    2015-01-01

    The critical amplitude of circularly polarized electromagnetic wave when the hysteresis of cyclotron absorption takes place, was found for band-gap graphene. The dependence of critical amplitude on the gap value and on the relaxation time was investigated. The conditions of applicability of linear theory describing the electromagnetic response of band-gap graphene in a non-zero magnetic field were found. The power of the circularly polarized electromagnetic radiation absorbed by band-gap graphene in the presence of a magnetic field was calculated. The linewidth of cyclotron absorption was shown to be not zero even for pure band-gap graphene.

  3. Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides

    International Nuclear Information System (INIS)

    The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the 'loop of extrema' both in the valence and conduction bands near the center of the cubic Brillouin zone.

  4. Two quasiparticle isomers and bands of 154, 156Nd, 156, 158Sm

    International Nuclear Information System (INIS)

    The decay of a new 3.2 ?, (4-) isomeric state at 1298.0 keV has been observed using ?-ray spectroscopy at the Lohengrin mass spectrometer of the Inst. Laue-Langevin. Prompt ?-ray data from a spontaneous fission experiment have also been analyzed allowing the observation of a collective band on top of this isomeric state, the identification of a new band on top of the previously reported (5-) isomer of 156Nd and the extension of collective bands on top of (5-) isomers of the neighboring 156, 158Sm nuclei. Quasiparticle rotor model calculations correctly predict the energies and decay patterns of these bands. (authors)

  5. Continuum absorption in the 4.3 ?m CO2 band

    Science.gov (United States)

    Klimeshina, Tatyana E.; Rodimova, Olga B.

    2014-11-01

    Factors influencing the determination of the continuum absorption have been assessed, using the 4.3 ?m CO2 band as an example. The local contribution to the total absorption plays a primary role in the case where the continuum absorption is obtained from experiment. The continuum absorption may be found unambiguously from absorption measurements in band wings. For measurements within the bands, the local contribution can be calculated as the difference between the total measured coefficient and the continuum contribution obtained from measurements in band wings.

  6. Quasiparticle band structure and tight-binding model for single- and bilayer black phosphorus

    Science.gov (United States)

    Rudenko, A. N.; Katsnelson, M. I.

    2014-05-01

    By performing ab initio calculations for one- to four-layer black phosphorus within the GW approximation, we obtain a significant difference in the band gap (˜1.5 eV), which is in line with recent experimental data. The results are analyzed in terms of the constructed four-band tight-binding model, which gives accurate descriptions of the mono- and bilayer band structure near the band gap, and reveal an important role of the interlayer hoppings, which are largely responsible for the obtained gap difference.

  7. Line parameters for ozone hot bands in the 4.8-micron spectral region

    Science.gov (United States)

    Camy-Peyret, Claude; Flaud, Jean-Marie; Rinsland, Curtis P.; Smith, Mary Ann H.; Devi, V. Malathy

    1990-01-01

    Line positions, intensities, and lower-state energies have been calculated for nine hot bands of (O-16)3 in the 4.8-micron spectral region using improved spectroscopic parameters deduced in recent high-resolution laboratory studies. The good quality of the hot-band parameters has been verified through comparisons of line-by-line simulations with 0.005/cm-resolution laboratory spectra of ozone. The present work and the line parameters calculated for the main bands by Pickett et al. (1988) provide a complete update of ozone spectroscopic parameters in the 4.8 micron region.

  8. Corrugated flat band as an origin of large thermopower in hole doped PtSb2

    Directory of Open Access Journals (Sweden)

    Kouta Mori

    2012-12-01

    Full Text Available The origin of the recently discovered large thermopower in hole-doped PtSb2 is theoretically analyzed based on a model constructed from first principles band calculation. It is found that the valence band dispersion has an overall flatness combined with some local ups and downs, which gives small Fermi surfaces scattered over the entire Brillouin zone. The Seebeck coefficient is calculated using this model, which gives good agreement with the experiment. We conclude that the good thermoelectric property originates from this “corrugated flat band”, where the coexistence of large Seebeck coefficient and large electric conductivity is generally expected.

  9. Decay Heat Calculations for ^235U

    Science.gov (United States)

    Johnson, T. D.; Sonzogni, A.; McCutchan, E.

    2011-10-01

    Following a nuclear reactor shutdown, a major issue is the decay heat due to radioactive decay of fission products and actinides. Contributing to this are light particles (e.g., ?- electrons), heavy particles (e.g., delayed neutrons), and electromagnetic radiation. Sources of uncertainty include probabilities for the formation of specific fission products, and incomplete knowledge of the levels of daughter nuclei. The latter is partially addressed by using Total Absorption Gamma Spectrocopy (TAGS). Earlier calculations are based on older decay schemes and sometimes less precise, mass measurements. In part to facilitate these calculations, the decay sub-library for the Evaluated Nuclear Data File was updated using the Evaluated Nuclear Structure Data Files with the latest mass measurements. The update includes electron conversion coefficients calculated using the Band-Raman Internal Conversion and ``Frozen Orbital'' approximation. The updated library was used in conjunction with available TAGS data to obtain preliminary updated decay heat calculations for ^235U.

  10. Massive band gap variation in layered oxides through cation ordering

    Science.gov (United States)

    Balachandran, Prasanna V.; Rondinelli, James M.

    2015-01-01

    The electronic band gap is a fundamental material parameter requiring control for light harvesting, conversion and transport technologies, including photovoltaics, lasers and sensors. Although traditional methods to tune band gaps rely on chemical alloying, quantum size effects, lattice mismatch or superlattice formation, the spectral variation is often limited to chemical composition or use of epitaxial strain in the LaSrAlO4 Ruddlesden-Popper oxide. First-principles calculations show that ordering electrically charged [LaO]1+ and neutral [SrO]0 monoxide planes imposes internal electric fields in the layered oxides. These fields drive local atomic displacements and bond distortions that control the energy levels at the valence and conduction band edges, providing a path towards electronic structure engineering in complex oxides.

  11. Microscopic study of superdeformed rotational bands in 151 Tb

    International Nuclear Information System (INIS)

    Structure of eight superdeformed bands in the nucleus 151Tb is analyzed using the results of the Hartree-Fock and Woods-Saxon cranking approaches. It is demonstrated that far going similarities between the two approaches exit and predictions related to the structure of rotational bands calculated within the two models are nearly parallel. An interpretation scenario for the structure of the superdeformed bands is presented and predictions related to the exit spins are made. Small but systematic discrepancies between experiment and theory, analyzed in terms of the dynamical moments, J(2), are shown to exist. The pairing correlations taken into account by using the particle-number-projection technique are shown to increase the disagreement. Sources of these systematic discrepancies are discussed - they are most likely related to the yet not optimal parametrization of the nuclear interactions used. (authors)

  12. Microscopic study of superdeformed rotational bands in {sup 151} Tb

    Energy Technology Data Exchange (ETDEWEB)

    El Aouad, N.; Dudek, J.; Li, X.; Luo, W.D.; Molique, H.; Bouguettoucha, A.; Byrski, TH.; Beck, F.; Finck, C.; Kharraja, B. [Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires; Dobaczewski, J. [Warsaw Univ. (Poland); Kharraja, B. [Notre Dame Univ., IN (United States). Dept. of Physics

    1996-12-31

    Structure of eight superdeformed bands in the nucleus {sup 151}Tb is analyzed using the results of the Hartree-Fock and Woods-Saxon cranking approaches. It is demonstrated that far going similarities between the two approaches exit and predictions related to the structure of rotational bands calculated within the two models are nearly parallel. An interpretation scenario for the structure of the superdeformed bands is presented and predictions related to the exit spins are made. Small but systematic discrepancies between experiment and theory, analyzed in terms of the dynamical moments, J{sup (2)}, are shown to exist. The pairing correlations taken into account by using the particle-number-projection technique are shown to increase the disagreement. Sources of these systematic discrepancies are discussed - they are most likely related to the yet not optimal parametrization of the nuclear interactions used. (authors). 60 refs.

  13. Band structure and chemical bond in alkali metal carbonates

    Science.gov (United States)

    Fedorov, I. A.; Zhuravlev, Yu. N.; Korabel'Nikov, D. V.

    2006-10-01

    The band structure, state density, optical functions, and distribution of valence and difference density in alkali-metal carbonates are calculated within the local electron-density functional theory using the method of pseudopotential in the basis of numerical pseudoorbitals. When passing from a lithium cation to a potassium one, the character of hybridization between the crystal sublattices changes to result in an increase in the valence-band width, a decrease in the forbidden-band width, a complication of the structure of state-density spectrum, and a shift of the maxima of optical functions to the low-energy range. It is found that the electron overflow between the ?-and ?-orbitals of crystallographically nonequivalent oxygen atoms can occur in different ways, hence their interaction force with the surrounding atoms is different. The role of cations in stabilization of anion chains resulting from the electron-cloud overlapping in lithium and sodium carbonates is shown.

  14. Atomic Mirror for Wide-Band Scattering of Single Photon

    CERN Document Server

    Chang, Yue; Sun, C P

    2010-01-01

    A resonant two level atom doped in one dimensional waveguide behaves as a mirror, but this single-atom "mirror" can only reflect single photon perfectly at a specific frequency. For a one dimensional coupled-resonator waveguide, we propose to extend the perfect reflection region from a specific frequency to a wide band by placing many atoms individually in the resonators in a finite coordinate region of the waveguide. Such a doped resonator array promises us to control the propagation of a practical photon wave packet with certain momentum distribution instead of a single photon, which is ideally represented by a plane wave with specific momentum. The studies based on the discrete-coordinate scattering theory display that such hybrid structure indeed provides a near-perfect reflection for single photon in a wide band. We also calculated photon group velocity distribution, which shows that the perfect reflection with wide band exactly corresponds to the stopping light region.

  15. Band Structures and Nucleon Alignments in ^173,175W

    Science.gov (United States)

    Guess, C. J.; Tandel, S. K.; Chowdhury, P.; Shirwadkar, U.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Seweryniak, D.; Wang, X.; Zhu, S.; Hartley, D. J.

    2012-10-01

    Spectroscopic study of nuclei in the A˜180 region is essential to better understand regional relationships between Nilsson orbitals. Highly excited rotational states in both nuclei were populated at Argonne National Laboratory via a 230 MeV ^50Ti beam from the ATLAS accelerator incident on a ^128Te target. The Gammasphere array was used to detect ? decays from excited states. Rotational bands built on the level 1/2^-[521], p3/2 in ^173,175W have been extended to spins of 40 and 35 respectively, and bands built on the 7/2^+[633], i13/2 configuration extended to 38 and 27 respectively. New sidebands in ^173W have been observed in all previously-discovered bands. Alignments from i13/2 neutron and h11/2 proton crossings are consistent with predictions of Woods-Saxon cranking calculations. Experimental results and regional systematics will be presented.

  16. The Calculator Reference

    Science.gov (United States)

    Furr, Rick.

    If you remember the days when calculators were as big as today's laptops, then you'll definitely feel nostalgic when you visit the Calculator Reference. Operated by an avid collector of vintage calculators, the site covers Texas Instruments and Hewlett-Packard brands, as well as the pioneering Curta. Several other models are included in the Desktop Calculators section. Even some interesting trivia is given on the site, like why calculator key pads are numbered in a different order than telephone key pads. There are many links to other sites and articles related to classic calculator technology.

  17. Band-engineered SrTiO3 nanowires for visible light photocatalysis

    International Nuclear Information System (INIS)

    We have theoretically investigated the structural, electronic, and optical properties of perovskite SrTiO3 nanowires for use in visible light photocatalytic applications using pseudopotential density-functional theory calculations. The electronic structure calculations show that the band gap is modified in the SrTiO3 nanowires compared with that of the bulk. For TiO2-terminated nanowires, the mid-band states induced by the combination of oxygen and strontium atoms on the surface lead to a shift in the valence band toward the conduction band without interference from the edge of the conduction band, which reduces the band gap. On the contrary, the electronic states induced by the combination of oxygen and strontium atoms on the surface of SrO-terminated nanowires lead to a shift in the conduction band toward the valence band. The calculated optical results indicate that the absorption edge of the nanowires shift towards the red-light region. These theoretical results suggest that perovskite SrTiO3 nanowires are promising candidates for use in visible light photocatalytic processes such as solar-assisted water splitting reactions.

  18. Band-engineered SrTiO{sub 3} nanowires for visible light photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Q.; He, T.; Li, J. L.; Yang, G. W. [State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Optoelectronic and Functional Composite Materials, Nanotechnology Research Center, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong (China)

    2012-11-15

    We have theoretically investigated the structural, electronic, and optical properties of perovskite SrTiO{sub 3} nanowires for use in visible light photocatalytic applications using pseudopotential density-functional theory calculations. The electronic structure calculations show that the band gap is modified in the SrTiO{sub 3} nanowires compared with that of the bulk. For TiO{sub 2}-terminated nanowires, the mid-band states induced by the combination of oxygen and strontium atoms on the surface lead to a shift in the valence band toward the conduction band without interference from the edge of the conduction band, which reduces the band gap. On the contrary, the electronic states induced by the combination of oxygen and strontium atoms on the surface of SrO-terminated nanowires lead to a shift in the conduction band toward the valence band. The calculated optical results indicate that the absorption edge of the nanowires shift towards the red-light region. These theoretical results suggest that perovskite SrTiO{sub 3} nanowires are promising candidates for use in visible light photocatalytic processes such as solar-assisted water splitting reactions.

  19. X-band preamplifier filter

    Science.gov (United States)

    Manshadi, F.

    1986-01-01

    A low-loss bandstop filter designed and developed for the Deep Space Network's 34-meter high-efficiency antennas is described. The filter is used for protection of the X-band traveling wave masers from the 20-kW transmitter signal. A combination of empirical and theoretical techniques was employed as well as computer simulation to verify the design before fabrication.

  20. Band gap ion mass filter

    International Nuclear Information System (INIS)

    Ions in a plasma may be radially separated according to mass using a combination of an axial magnetic field and either a radial or azimuthal electric field. The separation is qualitatively different from that obtained by a plasma centrifuge and the characteristics of confined and unconfined ion orbits are analogous to the phenomenon of band gaps in semiconductors

  1. Wide band data collection system

    Science.gov (United States)

    Turkiewicz, J. M.

    1988-01-01

    The Incorporated Research Institutes for Seismology (IRIS) approached NASA Headquarters in 1986 about the need to collect data daily from seismic stations around the world as part of the Earth Observing System (EOS) mission. A typical IRIS Seismic Station generates 16 Megabytes of data per day when there is seismic activity. The Preliminary Design Parameters of the Wide Band Data Collection System are summarized.

  2. Non-parabolicity of the conduction band of wurtzite GaN

    CERN Document Server

    Syed, S; Wang, Y J; Manfra, M J; Molnar, R J; Stormer, H L

    2003-01-01

    Using cyclotron resonance, we measure the effective mass, $m$*, of electrons in AlGaN/GaN heterostructures with densities, $n_{2D}\\sim 1-6\\times10^{12}$cm$^{-2}$. From our extensive data, we extrapolate a band edge mass of $(0.208\\pm0.002) m_e$. By comparing our $m$* data with the results of a multi-band \\textbf{k.p} calculation we infer that the effect of remote bands is essential in explaining the observed conduction band non-parabolicity (NP). Our calculation of polaron mass corrections -- including finite width and screening - suggests those to be negligible. It implies that the behavior of $m*(n_{2D})$ can be understood solely in terms of NP. Finally, using our NP and polaron corrections, we are able to reduce the large scatter in the published band edge mass values.

  3. Multiphonon difference band absorption in diamond

    Science.gov (United States)

    Thomas, Michael E.

    2011-06-01

    The longwave absorption coefficient of diamond is composed of the two-phonon red wing and multiphonon difference (hot) bands. As temperature increases the difference bands rapidly grow in strength and dominate the absorption. A variation on a multiphonon sum band model is developed for difference bands and applied to a temperature dependent data set on CVD polycrystalline diamond that are 1.54 mm thick. The model can also be used to estimate multiphonon difference band contribution to the refractive index.

  4. Residual stress dependant anisotropic band gap of various (hkl) oriented BaI2 films

    International Nuclear Information System (INIS)

    The thermally evaporated layer structured BaI2 grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48–3.43?eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (?0.071?eV/GPa) found to be significantly higher than that calculated (?0.047?eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass me*=0.66m0 and the hole effective mass mh*=0.53m0 have been determined from the calculated band structure

  5. Reactor core performance calculator

    International Nuclear Information System (INIS)

    Purpose: To simplify the calculation for determining the change in the burn-up degree distribution and the accompanying change in the reactor core performance, as well as improve the rapid responsibity. Constitution: In a case where the reactor core power changes from time t1 to time t2 in a linear functional manner, the reactor core performance at t2 is calculated based on the power distribtuion and the burn-up degree distribution data in the present reactor core status at t1. In this case, since there occurs a large error in one calculation step, the calculation in the power distribution calculator is repeated by a controller. That is, the burn-up degree distribution at t2 is inputted from the memory device to the power distribution calculator to calculate the power distribution at t2 using the inputted value as an estimation value. The calculated value is outputted to a burn-up degree distribution calculator, base on which the burn-up degree distribution at t2 is calculated. The new value thus obtained is compared with the previous value and the calculation is repeated until the difference therebetween satisfies the condition for the converging judgement. Since the calculated value is converged by about several - ten times the calculation speed is increased. (Ikeda, J.)

  6. New Band Structures in Neutron-Rich ^108Mo, and ^108,110,112Ru

    Science.gov (United States)

    Hamilton, J. H.; Luo, Y. X.; Ramayya, A. V.; Goodin, C.; Li, K.; Hwang, J. K.; Liu, S.; Zhu, S. J.; Ding, H.-B.; Che, X. L.; Rasmussen, J. O.; Lee, I. Y.; Almehed, D.; Frauendorf, S.; Dimitrov, V.; Zhang, J. Y.; Stone, N. J.; Ter-Akopian, G. M.; Daniel, A. V.; Stoyer, M. A.; Donangelo, R.; Cole, J. D.

    2008-10-01

    New insights into the structures of ^108Mo, and ^108,110,112Ru are identified in the spontaneous fission of ^252Cf. The 5.7 x 10^11 triples and higher fold prompt gamma coincidences opened up the possibility to see new weakly populated band structures in these nuclei. Two phonon ?-bands that decay only to the one phonon ?-band were discovered in ^108Mo and ^110,112Ru. We discovered in ^108Mo^ and^ 108,110,112Ru ?I=1, doublet bands. Our theoretical calculations indicate ^108Ru is ?-soft and ^110,112Ru are more rigid triaxial nuclei. The non-yrast band in ^108Ru shows an energy level staggering not seen in its yrast partner band nor in ^110,112Ru. This staggering is proposed to be related to its ?-soft shape perturbing its chiral structure. The doublet bands in ^108Mo^ and ^110,112Ru will be shown to have all the properties expected for chiral vibrational bands. Tilted axis cranking calculations for ^110,112Ru stronly support the chiral vibrational interpretation of these bands but do not support their being accidentally degenerate energy doublets built on different configurations.

  7. Band structure of fcc-C60 solid state crystal study

    Directory of Open Access Journals (Sweden)

    S Javanbakht

    2009-09-01

    Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of ? and ? bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.

  8. Band structures extending to very high spin in 126Xe

    International Nuclear Information System (INIS)

    High-spin states in 126Xe have been populated in the 82Se(48Ca,4n)126Xe reaction in two experiments, one at the VIVITRON accelerator in Strasbourg using the Euroball detector array, and a subsequent one with ATLAS at Argonne using the Gammasphere Ge-detector array. Levels and assignments made previously for 126Xe up to I=20 have been confirmed and extended. Four regular bands extending to a spin of almost I=60, which are interpreted as two pairs of signature partners with opposite parity, are identified for the first time. The ? = 0 partner of each pair is connected to the lower-lying levels, whereas the two ? = 1 partners remain floating. A fractional Doppler shift analysis of transitions in the strongest populated (?,?)=(-,0) band provides a value of 5.20.50.4 b for the transition quadrupole moment, which can be related to a minimum in the potential-energy surface calculated by the ULTIMATE CRANKER cranked shell-model code at ??0.35 and ??5 deg. The four lowest bands calculated for this minimum compare well with the two signature pairs experimentally observed over a wide spin range. A sharp upbend at (?/2?)??1170 keV is interpreted as a crossing with a band involving the j15/2 neutron orbital, for which pairing correlations are expected to be totally quenched. The four long bands extend to within ?5 spin units of a crossing with an yrast line defined by calculatline defined by calculated hyperdeformed transitions and will serve as important stepping stones into the spin region beyond 60h for future experiments

  9. Superdeformation in 146Gd: First observation of a band crossing

    International Nuclear Information System (INIS)

    High-spin states of the nucleus 146Gd were populated in a 110Pd(40Ar, 4n) reaction. The emitted ?-radiation was measured using the OSIRIS-spectrometer. A superformed band consisting of 13 discrete transitions was found in 146Gd. From the data obtained in a second experiment, using a backed target, the lifetimes of the states in the SDB have been measured using the DSA-method. An average quadrupolmoment of Q0 = 12 ± 2 eb could be deduced for the band. A band crossing occurs at rotational frequency of ?? = 0.65 MeV. It is for the first time that a crossing could be observed in a superdeformed band. From theoretical calculations a ?62 ?71 configuration with odd spin an odd parity is suggested. The behaviour of the dynamic moment of inertia can be reproduced by cranked Nilsson-model calculations assuming a crossing of the [651 1/2] and [642 5/2] single-neutron levels. (orig.)

  10. Band structure of CdTe under high pressure

    International Nuclear Information System (INIS)

    The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (PM = 1.935 Mbar) and the corresponding reduced volume ((V/V0)M = 0.458) are estimated. Metallization occurs via direct closing of band gap at ? point. (author)

  11. Band Structure and Optical Properties of Ordered AuCu3

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Lengkeek, H. P.

    1979-01-01

    The optical spectra of ordered AuCu3 have been measured at low temperatures by a direct ellipsometric technique. We find several structural elements above the absorption edge as well as in the infrared. The measured spectra are interpreted in terms of the interband absorption calculated from an ab initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement with experiment. The Fermi surface is presented and is found to originate mainly in copper 4s and 4p states.

  12. Predicted photonic band gaps in diamond-lattice crystals built from silicon truncated tetrahedrons

    CERN Document Server

    Woldering, Léon A; Elwenspoek, Miko C

    2011-01-01

    Recently, a silicon micromachining method to produce tetrahedral silicon particles was discovered. In this report, we determine the optical properties of diamond-lattice photonic crystals when assembled from such particles. The optical properties are found using band structure calculations. We show that crystal structures built from such silicon tetrahedra are expected to display small stop gaps. Wide photonic band gaps appear when truncated tetrahedral particles are used to build the photonic crystals. With such truncated tetrahedral particles, a band gap with a width of 23.6% can be achieved, which is more than twice as wide compared to band gaps in self-assembled diamond-lattices of hard-spheres. The width of the band gap is insensitive to small deviations from the optimal amount of truncation. This works paves the way to a new class of silicon diamond-lattice band gap crystals that can be obtained through self-assembly.

  13. Electronic band structures and photovoltaic properties of MWO 4 ( M=Zn, Mg, Ca, Sr) compounds

    Science.gov (United States)

    Kim, Dong Wook; Cho, In-Sun; Shin, Seong Sik; Lee, Sangwook; Noh, Tae Hoon; Kim, Dong Hoe; Jung, Hyun Suk; Hong, Kug Sun

    2011-08-01

    Divalent metal tungstates, MWO 4, with wolframite ( M=Zn and Mg) and scheelite ( M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO 4 and MgWO 4) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO 4 and SrWO 4), which was attributed to their enhanced electron transfer resulting from their appropriate band positions.

  14. Slave-boson theory of the Mott transition in the two-band Hubbard model

    CERN Document Server

    Rügg, A; Pilgram, S; Sigrist, M

    2005-01-01

    We apply the slave-boson approach of Kotliar and Ruckenstein to the two-band Hubbard model with an Ising like Hund's rule coupling and bands of different widths. On the mean-field level of this approach we investigate the Mott transition and observe both separate and joint transitions of the two bands depending on the choice of the inter- and intraorbital Coulomb interaction parameters. The mean-field calculations allow for a simple physical interpretation and can confirm several aspects of previous work. Beside the case of two individually half-filled bands we also examine what happens if the original metallic bands possess fractional filling either due to finite doping or due to a crystal field which relatively shifts the atomic energy levels of the two orbitals. For appropriate values of the interaction and of the crystal field we can observe a a band insulating state and a ferromagnetic metal.

  15. Theory of Band Warping and its Effects on Thermoelectronic Transport Properties

    CERN Document Server

    Mecholsky, Nicholas A; Pegg, Ian L; Fornari, Marco

    2014-01-01

    Optical and transport properties of materials depend heavily upon features of electronic band structures in proximity to energy extrema in the Brillouin zone (BZ). Such features are generally described in terms of multi-dimensional quadratic expansions and corresponding definitions of effective masses. Multi-dimensional expansions, however, are permissible only under strict conditions that are typically violated by degenerate bands and even some non-degenerate bands. Suggestive terms such as "band warping" or "corrugated energy surfaces" have been used to refer to such situations and ad hoc methods have been developed to treat them. While numerical calculations may reflect such features, a complete theory of band warping has not been developed. We develop a generally applicable theory, based on radial expansions, and a corresponding definition of angular effective mass. Our theory also accounts for effects of band non-parabolicity and anisotropy, which hitherto have not been precisely distinguished from, if n...

  16. Cluster structure and deformed bands in the {sup 38}Ar nucleus

    Energy Technology Data Exchange (ETDEWEB)

    Sakuda, T., E-mail: sakuda@cc.miyazaki-u.ac.jp [Department of Physics, University of Miyazaki, Miyazaki 889-2192 (Japan); Ohkubo, S., E-mail: shigeo@cc.u-kochi.ac.jp [Department of Applied Science and Environment, University of Kochi, Kochi 780-8515 (Japan); Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan)

    2013-06-17

    The structure of the {sup 38}Ar nucleus is investigated by the {sup 34}S+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K{sup ?}=0{sup +} band is found to be predominantly {sup 34}S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states.

  17. Band termination and signature crossing observation in some rare-earth nuclei

    International Nuclear Information System (INIS)

    Predictions are very interesting features of moderately high angular momentum configurations as Band Termination, in nuclei with 10-12 valence particles outside the gadolinium 146Gd core. Which are made by core excitation or by promotion as the valence particles to the next shell. General properties of terminating bands are reviewed and exemplified on the observed high-angular momentum properties of 153Ho, 155Ho, 157Ho holmium nuclei. The very similar features are observed in the non-collective ones with N=88 isotones of dysprosium Dy, Erbium Er and tribium Yb nuclei.The spin contribution from different bands is calculated in terminating bands as well as more collective bands. The relation between the level energy minus rigid-rotor rotational energy versus spin for the yrast states is discussed and the plot serves to indicate that something interesting is happing above a certain value of (I). Above this value the nuclei seem to exhibit dominantly band termination behavior

  18. Research on the elastic wave band gaps of curved beam of phononic crystals

    Science.gov (United States)

    Shaogang, Liu; Shidan, Li; Haisheng, Shu; Weiyuan, Wang; Dongyan, Shi; Liqiang, Dong; Hang, Lin; Wei, Liu

    2015-01-01

    Based on wave equations of Timoshenko curved beam, the theoretical derivation and numerical calculation of the behavior of in-plane and out-of-plane wave propagating in curved beam of phononic crystals (CBPC) are carried out using transfer matrix method combined with the Bloch theorem. Finite CBPC is also simulated by FEM method. It is shown that both in-plane and out-of-plane elastic waves band gaps exist in CBPC. Compared with equivalent straight beam of phononic crystals (SBPC), CBPC has some unique characteristics, such as the first complete in-plane band gap, special in-plane coupling band gap, and out-of-plane coupling band gap. In those band gaps, CBPC has a better property of vibration reduction than the equivalent SBPC in some ways. Furthermore, effects of curvature of CBPC on the in-plane and out-of-plane band gaps are discussed.

  19. Narrow-band model for nonequilibrium air plasma radiation

    International Nuclear Information System (INIS)

    A band model is developed for the prediction of radiative transfer in air plasma applications under equilibrium and non-equilibrium conditions. For non-equilibrium applications, the medium is described by rotational-translational and vibrational temperatures but the populations of electronic states can be arbitrary. A specific formulation of the statistical narrow-band (SNB) model is developed for optically thick electronic systems of diatomic molecules when their populations are described by an electronic temperature. Model parameters, deduced from line by line calculations in the Voigt regime, are shown to be also convenient for arbitrary distribution of molecular electronic populations. This model is then complemented to include optically thin electronic systems and the continuum radiation through the simple box model, and line by line calculations for atomic lines. Several tests including equilibrium, non-equilibrium, uniform, and non-uniform conditions show the ability of this hybrid model to provide accurate and efficient solutions for radiative transfer problems in air plasmas.

  20. Balloon Atmospheric Mosaic Measurements (BAMM) IIA Phenomenology And Band Selection

    Science.gov (United States)

    Kassal, T.; Selby, J. E. A.; Waters, R.

    1982-03-01

    A series of line by line source and background infrared simulation calculations have been carried out in the 4.3 m spectral region in order to identify candidate spectral bands for study using balloon and ultimately spaceborne sensors. Source signatures are presented in terms of apparent radiant intensity produced by a volume of hot CO2 located at altitudes ranging from 0 to 20 km as observed from altitudes of 30, 44 and 100 km. Backgrounds, including terrain, clouds and atmospheric emission have been calculated and are presented both spectrally and as inband radiant intensity. A cursory discussion of non-LTE atmospheric emissions occurring above 60 km is presented and the feasibility of looking up from a balloon borne platform to observe these emissions is addressed. A comparison of source and background signatures is given together with a discussion of the band selection process.

  1. Flat-band ferromagnetism in quantum dot superlattices

    CERN Document Server

    Tamura, H; Kimura, T; Takayanagi, H; Tamura, Hiroyuki; Shiraishi, Kenji; Kimura, Takashi; Takayanagi, Hideaki

    2002-01-01

    Possibility of flat-band ferromagnetism in quantum dot arrays is theoretically discussed. By using a quantum dot as a building block, quantum dot superlattices are possible. We consider dot arrays on Lieb and kagome lattices known to exhibit flat band ferromagnetism. By performing an exact diagonalization of the Hubbard Hamiltonian, we calculate the energy difference between the ferromagnetic ground state and the paramagnetic excited state, and discuss the stability of the ferromagnetism against the second nearest neighbor transfer. We calculate the dot-size dependence of the energy difference in a dot model and estimate the transition temperature of the ferromagnetic-paramagnetic transition which is found to be accessible within the present fabrication technology. We point out advantages of semiconductor ferromagnets and suggest other interesting possibilities of electronic properties in quantum dot superlattices.

  2. Flat-band ferromagnetism in quantum dot superlattices

    Science.gov (United States)

    Tamura, Hiroyuki; Shiraishi, Kenji; Kimura, Takashi; Takayanagi, Hideaki

    2002-02-01

    The possibility of flat-band ferromagnetism in quantum dot arrays is theoretically discussed. By using a quantum dot as a building block, quantum dot superlattices are possible. We consider dot arrays on Lieb and kagomé lattices known to exhibit flat-band ferromagnetism. By performing an exact diagonalization of the Hubbard Hamiltonian, we calculate the energy difference between the ferromagnetic ground state and the paramagnetic excited state, and discuss the stability of the ferromagnetism against the second-nearest-neighbor transfer. We calculate the dot-size dependence of the energy difference in a dot model and estimate the transition temperature of the ferromagnetic-paramagnetic transition, which is found to be accessible within the present fabrication technology. We point out advantages of semiconductor ferromagnets and suggest other interesting possibilities of electronic properties in quantum dot superlattices.

  3. Irregularity in K?=8- rotational bands of N =150 isotones

    Science.gov (United States)

    Fu, X. M.; Xu, F. R.; Jiao, C. F.; Liang, W. Y.; Pei, J. C.; Liu, H. L.

    2014-05-01

    Motivated by new experimental spectra in transfermium mass region, we have investigated broken-pair high-K multiparticle excited states and their rotational bands for the N =150 isotones around Z =100, by using the configuration-constrained pairing-deformation-frequency self-consistent total-Routhian-surface (TRS) model. In order to avoid the spurious phase transition encountered in the Bardeen-Copper-Schrieffer (BCS) pairing, the particle-number-conserving method has been employed for pairing calculations. Pairing correlations are remarkably reduced for the rotations of broken-pair multiparticle states. The present configuration-constrained TRS calculations reproduce reasonably existing experimental data. The abnormal feature in the recently observed K?=8- bands of No252 and Fm250 would be associated with configuration mixing.

  4. Table of superdeformed nuclear bands and fission isomers

    International Nuclear Information System (INIS)

    A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in 152Dy was predicted for ?2-0.65. Subsequently, a discrete set of ?-ray transitions in 152DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of ?-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra

  5. Table of superdeformed nuclear bands and fission isomers

    Energy Technology Data Exchange (ETDEWEB)

    Firestone, R.B. [Lawrence Berkeley Lab., CA (United States); Singh, B. [McMaster Univ., Hamilton, ON (Canada)

    1994-06-01

    A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in {sup 152}Dy was predicted for {beta}{sub 2}-0.65. Subsequently, a discrete set of {gamma}-ray transitions in {sup 152}DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of {gamma}-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra.

  6. Rotational band structure of the chiral candidate 134Pr

    International Nuclear Information System (INIS)

    Compete text of publication follows. Pairs of nearly degenerate dipole rotational bands with the same unique-parity configurations are known in several odd-odd nuclei. Such a structure was first studied in 134Pr, and it was considered as manifestation of chiral rotation of the triaxial nucleus. Later, considerably different quadrupole moments were measured for the two bands in this nucleus. This result strongly questioned the chiral interpretation, and new interpretation emerged emphasising the shape difference in the two bands. On the other hand, TRS calculations predict chiral band structure in this nucleus. In order to collect more information on the structure of this key-nucleus among chiral candidates, we studied the rotational bands of 134Pr by in-beam ?-spectroscopic methods. Excited states of 134Pr were populated using the 116Cd(23Na,5n) reaction at a beam energy of 115 MeV and studied using the GAMMASPHERE array. The level scheme of 134Pr was deduced using E?1-E?2-E?3 triple coincidences, which were sorted into Radware cubes. On the basis of the observed ???- coincidence relations several new bands have been identified. One of them is linked to the previous chiral-candidate structure through many M1 and E2 transitions, has the same parity, and the equal-spin levels are nearly degenerate. According to this observation, there are three nearly degenerate ?here are three nearly degenerate ?h11/2?h11/2 bands in 134Pr, what may express a need for rethinking the interpretation of the previous chiral candidate structure.

  7. Shear bands as growing instabilities in viscoanelastic media with memory

    Directory of Open Access Journals (Sweden)

    Marina Dolfin

    2013-09-01

    Full Text Available In this paper we investigate the critical conditions under which a small perturbation in an homogeneous continuum can possibly grows into a shear band instability. In particular, we analyze from a thermodynamical viewpoint the phenomenon of shear bands in viscoanelastic media with memory. It is emphasized, in the scientific literature, that the specific adopted rheology strongly affects the results so that a special attention has to be paid, also for engineering purposes, to the accuracy of the rheological model. Several well-known rheological model (for instance the so called Maxwell or Jeffreys media are particular cases of the general model we adopt in the paper to analyze shear bands. Instability conditions, giving rise to shear bands formation, are obtained by introducing small perturbations around an homogeneous deformation into the system of differential equations governing the problem of homogeneous deformations in the considered continuous medium; as a result a non-homogeneous linear dynamical system is obtained whose stability is analyzed. A research perspective in view of a possible comparison with experimental results is proposed; in particular the simple methodology proposed in the paper should be applied in view of using the phenomenon of the initiation of shear bands to calculate the thermomechanical coefficients of real materials.

  8. Shear band formation in plastic bonded explosive (PBX)

    Energy Technology Data Exchange (ETDEWEB)

    Dey, T.N.; Johnson, J.N.

    1997-07-01

    Adiabatic shear bands can be a source of ignition and lead to detonation. At low to moderate deformation rates, 10-1000/s , two other mechanisms can also give rise to shear bands. These mechanisms are: 1) softening caused by microcracking and 2) a constitutive response with a non-associated flow rule as is observed in granular material such as soil. Brittle behavior at small strains and the granular nature of HMX suggest that PBX-9501 constitutive behavior may be similar to sand. A constitutive model for the first of these mechanisms is studied in a series of calculations. This viscoelastic constitutive model for PBX-9501 softens via a statistical crack model. A sand model is used to provide a non-associated flow rule and detailed results will be reported elsewhere. Both models generate shear band formation at 1-2% strain at nominal strain rates at and below 1000/s. Shear band formation is suppressed at higher strain rates. Both mechanisms may accelerate the formation of adiabatic shear bands.

  9. Superdeformed band at very high spin in 140Nd

    International Nuclear Information System (INIS)

    A new high-spin superdeformed band has been discovered in 60140Nd80. It was populated in the 96Zr(48Ca,4n) reaction and investigated using the EUROBALL ?-ray spectrometer array. The band is observed in the approximate spin range of I=36 to 66. It is associated with shell gaps around Z=60 and at N=80 at large deformation. These gaps produce a pronounced minimum in the calculated total Routhian surfaces at a quadrupole deformation of ?2=0.45. The new band which lies between the high-deformation bands in the A?130 region and the superdeformed bands in A?150 nuclei provides insight into the development of the deformation between these two regions. Two possible configurations are suggested involving four neutrons of i13/2 origin (?64) and either six protons of h11/2/h9/2 origin (?56) or five protons of h11/2/h9/2 and one of i13/2 origin (?5561)

  10. Strain sensitivity of band gaps of Sn-containing semiconductors

    DEFF Research Database (Denmark)

    Li, Hong; Castelli, Ivano Eligio

    2015-01-01

    Tuning of band gaps of semiconductors is a way to optimize materials for applications within photovoltaics or as photocatalysts. One way to achieve this is through applying strain to the materials. We investigate the effect of strain on a range of Sn-containing semiconductors using density functional theory and many-body perturbation theory calculations. We find that the band gaps of bulk Sn oxides with SnO6 octahedra are highly sensitive to volumetric strain. By applying a small isotropic strain of 2% (-2%), a decrease (increase) of band gaps as large as 0.8 to 1.0 eV are obtained. We attribute the ultrahigh strain sensitivity to the pure Sn s-state character of the conduction-band edges. Other Sn-containing compounds may show both increasing and decreasing gaps under tensile strain and we show that the behavior can be understood by analyzing the role of the Sn s states in both the valence and the conduction bands.

  11. Population of rotational bands in superheavy nuclei

    International Nuclear Information System (INIS)

    The spectroscopy of superheavy elements (SHE) is very important for the modern nuclear physics. Comparing the structure predictions of different theoretical models with the experimental data, one can find out their applicability in the region of SHE. This can be very useful for the determination of the next proton magic number beyond Z = 82. Using the statistical approach, we study the population of rotational bands in super-heavy nuclei produced in fusion-evaporation reactions. The reactions 208Pb(48Ca, 2n)254No, 206Pb(48Ca, 2n)252No, and 204Hg(48Ca, 2n)250Fm are considered. The population cross section of state L+ depends on survival of the compound nucleus against fission. The calculated relative intensities of E2-transitions at different spins, which can be compared with the experimental values, are defined by these partial population cross sections. Fermi-gas model is used for the calculation of level densities, and damping of shell effects with excitation energy and angular momentum is taking into account. For more accurate description of the capture process near the Coulomb barrier we use the quantum diffusion approach based on the formalism of reduced density matrix. Taking the same set of parameters, we also describe the excitation functions for these reactions. The results are in a good agreement with the experiment data. Using the parameter of damping of shell effects with angular momentum, we can estimate the moment of inertia of the nucleus at the saddle point

  12. Electronic structure of superconducting gallium-doped germanium from ab-initio calculations

    OpenAIRE

    Lebegue, S.

    2009-01-01

    Using ab-initio calculations, we study the electronic structure of gallium-doped germanium, which was found recently to be a superconductor, with a critical temperature of 0.5 Kelvins, and a particularly low density of Cooper pairs. The calculations of the electronic properties reveal that no sign of an impurity band is observed, and that the Fermi level lies in the valence band of Germanium. Moreover, the calculation of the phonon frequencies shows that a new mode associate...

  13. Full-zone analysis of relativistic spin splitting at band anticrossings: The case of zinc-blende semiconductors

    DEFF Research Database (Denmark)

    Chantis, Athanasios N.; Christensen, Niels Egede

    2010-01-01

    We show that the band spin splitting caused by spin-orbit interaction in crystal structures with no inversion symmetry is strongly influenced by band anticrossing. The splitting is always enhanced for one of the anticrossing bands and suppressed for the other. There are two limiting cases. In the first, the spin splitting is completely suppressed for one of the bands and doubled for the other. In the second, the absolute value of the splitting is markedly enhanced for both bands approaching the magnitude of the hybridization gap. We demonstrate these effects in zinc-blende semiconductors with the help of first-principles GW calculations.

  14. Pressure-induced s-band ferromagnetism in alkali metals

    OpenAIRE

    Pickard, Chris J.; Needs, R. J.

    2011-01-01

    First-principles density-functional-theory calculations show that compression of alkali metals stabilizes open structures with localized interstitial electrons which may exhibit a Stoner-type instability towards ferromagnetism. We find ferromagnetic phases of the lithium-IV-type, simple cubic, and simple hexagonal structures in the heavier alkali metals, which may be described as s-band ferromagnets. We predict that the most stable phases of potassium at low temperatures and...

  15. Complex Band Structures and Decay Length in Polyethylene Chains

    OpenAIRE

    Picaud, Fabien; Smogunov, Alexander; Corso, Andrea Dal; Tosatti, Erio

    2003-01-01

    The complex band structure of an isolated polyethylene chain is calculated within Density Functional Theory (DFT). A plane wave basis and ultrasoft pseudopotentials are used. The results are compared with those obtained via a local basis set. We obtain a gap between the highest occupied molecular orbilar (HOMO) and the antibonding unoccupied molecular orbitals of 9.3 eV and a non-resonant tunneling $\\beta$ parameter of 0.9 per monomer, in reasonable agreement with experiment...

  16. Intruder bands and configuration mixing in lead isotopes

    International Nuclear Information System (INIS)

    A three-configuration mixing calculation is performed in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying 0+ states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the Z=82 shell gap

  17. Tunable band gaps in bilayer graphene-BN heterostructures

    OpenAIRE

    Ramasubramaniam, Ashwin; Naveh, Doron; Towe, Elias

    2010-01-01

    We investigate band-gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV, and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. The calculations suggest that the graphene-boron nitride heterostructures could ...

  18. Itinerant Flat-Band Magnetism in Hydrogenated Carbon Nanotubes

    OpenAIRE

    Yang, Xiaoping; Wu, Gang

    2010-01-01

    We investigate the electronic and magnetic properties of hydrogenated carbon nanotubes using ab initio spin-polarized calculations within both the local density approximation (LDA) and the generalized gradient approximation (GGA). We find that the combination of charge transfer and carbon network distortion makes the spin-polarized flat-band appear in the tube's energy gap. Various spin-dependent ground state properties are predicted with the changes of the radii, the chiral...

  19. Periodic Anderson model with electron-phonon correlated conduction band

    OpenAIRE

    Zhang, Peng; Reis, Peter; Tam, Ka-ming; Jarrell, Mark; Moreno, Juana; Assaad, Fakher; Mcmahan, Andy

    2012-01-01

    This paper reports dynamical mean field calculations for the periodic Anderson model in which the conduction band is coupled to phonons. Motivated in part by recent attention to the role of phonons in the $\\gamma$-$\\alpha$ transition in Ce, this model yields a rich and unexpected phase diagram which is of intrinsic interest. Specifically, above a critical value of the electron-phonon interaction, a first order transition with two coexisting phases develops in the temperature...

  20. The geometry and thickness of deformation-band fault core and its influence on sealing characteristics of deformation-band fault zones

    OpenAIRE

    Shipton, Z. K.; Evans, J. P.; Thompson, L. B.

    2005-01-01

    Deformation-band faults in high-porosity reservoir sandstones commonly contain a fault core of intensely crushed rock surrounding the main slip surfaces. The fault core has a substantially reduced porosity and permeability with respect to both the host rock and individual deformation bands. Although fault core thickness is a large uncertainty in calculations of transmissibility multipliers used to represent faults in single-phase reservoir flow models, few data exist on fault core thickness i...