WorldWideScience
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

Relativistically parameterized extended Hueckel calculations. 3. Structure and bonding for some compounds of uranium and other heavy elements  

International Nuclear Information System (INIS)

The relativistically parameterized extended Hueckel molecular orbital method REX is used to explore the effects of relativity upon molecular orbital energies and compositions. The uranium compounds studied are UO22+, UO2Cl42-, UF6, UCl6, UCl4, U(BH4)4, and U(C8H8)2. Other heavy element compounds studied are MI3 (M = La, Gd, Lu), PoH2, (eka)PoH2, I3-, AtI2-, and RnF2. Relativistic orbital energy parameters and atomic orbital exponents are presented as supplementary material for all elements with Z = 1 to 120 together with corresponding nonrelativistic values for all elements with Z = 1 to 100. It is concluded that the REX method provides semiquantitative estimates of spin-orbit splittings and relativistic bonding effects for compounds of heavy elements

3

Charge Oscillations in Debye-Hueckel Theory  

OpenAIRE

The recent generalized Debye-Hueckel (GDH) theory is applied to the calculation of the charge-charge correlation function G_{ZZ}(r). The resulting expression satisfies both (i) the charge neutrality condition and (ii) the Stillinger-Lovett second-moment condition for all T and rho_N, the overall ion density, and (iii) exhibits charge oscillations for densities above a "Kirkwood line" in the (rho_N,T) plane. This corrects the normally assumed DH correlations, and, when combin...

Lee, Benjamin P.; Fisher, Michael E.

1997-01-01

4

Modified Iterative Extended Hueckel. 1: Theory  

Science.gov (United States)

Iterative Extended Huekel is modified by inclusion of explicit effective internuclear and electronic interactions. The one electron energies are shown to obey a variational principle because of the form of the effective electronic interactions. The modifications permit mimicking of aspects of valence bond theory with the additional feature that the energies associated with valence bond type structures are explicitly calculated. In turn, a hybrid molecular, orbital valence, bond scheme is introduced which incorporates variant total molecular electronic density distributions similar to the way that Iterative Extended Hueckel incorporates atoms.

Aronowitz, S.

1980-01-01

5

Hueckel spectrum for large carbon fullerenes and tubes  

International Nuclear Information System (INIS)

Very large carbon fullerenes and tubes have almost everywhere the structure of a planar hexagonal lattice. The spectrum of such a Hueckel Hamiltonian is obtained in closed form in the present paper, for the case where single and double bonds have the same Hueckel couplings. For the case where single and double bonds have different Hueckel couplings, the problem is treated for some specific bond arrangements. ((orig.))

6

Debye-Hueckel-Bjerrum theory for charged colloids  

OpenAIRE

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...

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

1998-01-01

7

Analysis of the polarized optical excitations by electronic band structure calculations : organic suprconductor {beta}'(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}.  

Energy Technology Data Exchange (ETDEWEB)

The room temperature polarized optical conductivity of the superconducting salt {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} was analyzed by calculating its electronic band structure using the extended Hueckel tight binding method. The electronic band structure obtained with double-zeta orbitals is consistent with the observed optical properties. The optical transitions in the energy region of 0-0.75 eV are intraband transitions associated with the bands that result from the highest-occupied molecular orbitals of the BEDT-TTF molecules. The optical conductivity is much stronger along the interstack direction (b-axis direction) than along the direction perpendicular to it throughout the energy region of 0-0.75 eV. This anisotropy is readily accounted for by the band dispersion relations calculated for the wave vector directions parallel to the b* and a* directions. Polarized optical conductivity provides indirect information about the anisotropy of band dispersion relations.

Koo, H.-J.; Whangbo, M.-H.; Dong, J.; Olejniczak, I.; Musfeldt, J. L.; Schlueter, J. A.; Geiser, U.; North Carolina State Univ.; State Univ. of New York at Binghamton

1999-01-01

8

Band Gap Calculations on Low Band Gap Squaric Acid Derived Polymers  

Science.gov (United States)

The band gaps of some fully conjugated polymers derived from the condensation reactions of aromatic ring systems with squaric acid are presented. The method of calculation is based on the singlet-triplet energy difference extrapolated to infinite chain length. This method accounts for correlation induced orbital relaxation not incuded in Hartree-Fock crystal orbital calculations. Band gaps are estimated to be as low as 0.5eV for these potential conducting polymers.

Yeates, A. T.; Dudis, D. S.; Duan, X.; Kawai, R.

1996-03-01

9

Neutrino flux calculations for the AGS narrow band beam  

International Nuclear Information System (INIS)

Presented are results of calculations of nu/sub ?/ fluxes in the AGS neutrino beam with the new dichromatic horn. The wide band beam nu/sub ?/, as well as the nu/sub e/ backgrounds, are discussed. The nu/sub e//nu/sub ?/ ratio is about 8 x 10-3. The possible sources and magnitudes of uncertainties are discussed. Finally, the calculated fluxes are compared with beam measurements

10

Elementary energy bands in band structure calculations of some wide-bandgap crystals  

Science.gov (United States)

Semiconducting Tl3AsS4 crystal was chosen as an example to show that its valence band is composed of the elementary energy bands. Their topology and symmetry obtained in the empty-lattice approximation is confirmed by ab initio band structure calculations. It was shown that these elementary energy bands correspond to the Wyckoff position c in a unit cell. Earlier predictions that the largest electron density distribution is focused in the vicinity of this position, similarly to the case of YAlO3 and SbSI crystals, is confirmed. A conclusion on the common topology and symmetry of the elementary energy bands in electronic and phonon spectra is presented.

Sznajder, M.; Bercha, D. M.; Rushchanskii, K. Z.

2004-01-01

11

Hueckel model for metal clusters: Ground states and low energy isomers  

International Nuclear Information System (INIS)

Hueckel model with one s-electron per atom is used to study the geometries and electronic structures of clusters of 9 to 22 atoms. Two different optimization schemes for obtaining the ground states are used; (i) minimization of an approximate Hueckel ground state energy starting from a random geometry and (ii) simulated annealing. Both methods give similar and new ground state geometries for clusters with 10 to 14 atoms. All clusters with more than 10 atoms will be distorted if the bond distance is allowed to vary ±5.5%. The ground states of clusters with atoms 10, 11, 12, and 14 are found to have the N=9 cluster as the basic building block, whereas the N=13 cluster is a distorted cuboctahedron. As a general trend, the deformation of clusters increases from atom number 8 to 14 and shrinks again from 15 to 20 atoms, in accordance with jellium model results

12

Density Fluctuations in an Electrolyte from Generalized Debye-Hueckel Theory  

OpenAIRE

Near-critical thermodynamics in the hard-sphere (1,1) electrolyte is well described, at a classical level, by Debye-Hueckel (DH) theory with (+,-) ion pairing and dipolar-pair-ionic-fluid coupling. But DH-based theories do not address density fluctuations. Here density correlations are obtained by functional differentiation of DH theory generalized to {\\it non}-uniform densities of various species. The correlation length $\\xi$ diverges universally at low density $\\rho$ as $(...

Lee, Benjamin P.; Fisher, Michael E.

1996-01-01

13

Calculation of band structure in (101)-biaxially strained Si  

Science.gov (United States)

The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of (101)-biaxially strained Si on relaxed Si1- X Ge X alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys (?4) splitting from the [0±10] valley (?2) constitute the conduction band (CB) edge, that valence band (VB) edge degeneracy is partially lifted and that the electron mass is unaltered under strain while the hole mass decreases in the [100] and [010] directions. In addition, the fitted dependences of CB splitting energy, VB splitting energy and indirect bandgap on X are all linear.

Song, Jianjun; Zhang, Heming; Hu, Huiyong; Fu, Qiang

2009-04-01

14

Band gaps in pseudopotential self-consistent GW calculations  

OpenAIRE

For materials which are incorrectly predicted by density functional theory to be metallic, an iterative procedure must be adopted in order to perform GW calculations. In this paper we test two iterative schemes based on the quasi-particle and pseudopotential approximations for a number of inorganic semiconductors whose electronic structures are well known from experiment. Iterating just the quasi-particle energies yields a systematic, but modest overestimate of the band gaps...

Popa, V. A.; Brocks, G.; Kelly, P. J.

2005-01-01

15

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

International Nuclear Information System (INIS)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients Vrvec Grvec G'(rvec k) which can be decomposed into terms, each being quadratic in rvec k and multiplied by a function of (rvec G-rvec G'), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe2, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry's method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. copyright 1997 The American Physical Society

16

The correlated-k coefficients calculated by random band models  

Science.gov (United States)

The correlated-k coefficient for the cumulative distribution of the absorption coefficient in random band models is calculated with a computationally efficient algorithm based on a numerical inverse Laplace transform. A scaling transformation is introduced to partially eliminate the ill-conditioned behavior around the singularity point. In the region very close to the singularity, an analytic expression for the k coefficient derived for the Malkmus model is used to match the whole solution. The algorithm yields accurate k coefficients with a maximum error for a few percent. When applied to the random band model with an S exp -1-beta-tailed line-intensity distribution and a Voigt line profile, the algorithm yields a maximum error in the escape function of less than 3 percent in comparison with line-by-line integrations. The algorithm is sufficiently general to be applicable to a variety of radiative transfer problems in planetary atmospheres.

Zhu, Xun

1992-03-01

17

Calculations of dislocation mobility using nudged elastic band method and first principles DFT calculations  

OpenAIRE

Abstract We present a new technique which makes it possible to determine mobility properties of dislocations with first principles accuracy without having to apply corrections for the influence of boundary conditions. The Nudged Elastic Band method is used together with periodic boundary conditions and all dislocations included in the simulated cell are coherently displaced during the calculations. The method is applied to the displacement of a non-dissociated shuffle screw disl...

Pizzagalli, Laurent; Beauchamp, Pierre; Jo?nsson, Hannes

2007-01-01

18

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)

19

Elementary energy bands in ab initio calculations of the YAlO3 and SbSI crystal band structure  

Science.gov (United States)

The local density approximation has been implemented to determine the band structure of orthorhombic crystals YAlO3 (YAP) and SbSI. The topology of the valence band structures was analyzed. It has been demonstrated that Zak's elementary energy bands in the band structure are distinguishable on the basis of the empty-lattice approximation. The calculated electron density distribution of YAP and SbSI crystals is related to particular Wyckoff positions. Moreover, there is a direct correspondence between the obtained elementary energy bands and the aforementioned Wyckoff positions characterized by electron density distribution.

Bercha, D. M.; Rushchanskii, K. Z.; Sznajder, M.; Matkovskii, A.; Potera, P.

2002-11-01

20

Band structure calculations of Pt and Pt3Ti  

International Nuclear Information System (INIS)

Linearized augmented plane wave (LAPW) calculations of the Pt and Pt3Ti bulk electron structures are presented. We emphasis on hybridization, charge transfer effects and the impact on chemisorption properties densities of states (DOS) and novel band-structures are also provided. The delocalized character of free electron states documents itself by sp-orbitals largely unaffected by alloy formation i.e. the Pt and Ti projected sp-densities are similar and also akin to the distribution of sp-states for pure platinum. The strong Pt-Ti interaction comes from d and f orbitals with a significantly lowered Pt d center-of-mass for the alloy and an intense Ti d structure above the Fermi level. The f-projected density of states gives two narrow peaks: a Ti peak below the Fermi level and an unoccupied Pt peak near Ef. Together the d and f interactions result in a much lowered DOS(Ef). Our results are of direct relevance for adsorption systems modelling titania supported platinum, a well known catalyst for CO hydrogenation. The ordered alloy, Pt3Ti, forms in the industrial catalyst under reducing conditions at elevated temperatures, a phenomenon related to the strong metal support interaction (SMSI) effect in catalysis, and much work has addressed special adsorption sites for enhanced methanation rates. (orig.)

21

Optical properties of novel intermediate band indium thiospinel materials by quantum mechanical calculations  

OpenAIRE

In this work we present quantum mechanic calculations using the Density Functional Theory for several transition metal substituted octahedral thiospinels derivatives of the In2S3 and MgIn2S4 compounds. The calculations predict that these materials will have a partially filled band inside the band-gap of the aforementioned semiconductors and due to that can be proposed as a novel class of high efficiency photovoltaic materials for intermediate band solar cells. The new band enables absorption ...

Wahno?n Benarroch, Perla; Aguilera Bonet, Irene; Palacios Clemente, Pablo; Sa?nchez Noriega, Kefre?n; Conesa, Jose Carlos

2009-01-01

22

Energy band calculation of amorphous indium tin oxide films on polyethylene terephthalate substrate with indirect transition  

International Nuclear Information System (INIS)

Amorphous indium tin oxide films were grown on a polyethylene terephthalate substrate by RF-magnetron sputtering. The energy band, which contained not only the width of the optical band but also detailed information about the Fermi level (Ef) and mobility edge (Ec'), was calculated according to the theory of amorphous semiconductors with the experimental parameters of transmittance and electrical conductivity. Furthermore, the calculated energy band can be used to effectively explain both the variation of electrical conductivity and the weak absorption at the wavelength range of 750-800 nm in our experiment. An indirect transition was also clearly observed in our samples during the calculation of the optical energy band.

23

Electronic band structure of a type-II ‘W’ quantum well calculated by an eight-band k · p model  

International Nuclear Information System (INIS)

In this paper, we present an investigation of type-II ‘W’ quantum wells for the InAs/Ga1?xInxSb/AlSb family, where ‘W’ denotes the conduction profile of the material. We focus our attention on using the eight-band k · p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period—AlSb/InAs/Ga1?xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1?xInxSb layer and the alloy composition in Ga1?xInxSb separately. In the last part, in order to compare the eight-band k · p model, we recalculate the conduction bands of the ‘W’ structure using the one-band k · p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained. (general)

24

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

Science.gov (United States)

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.

Hristov, Alexander

2009-08-15

25

BoltzTraP. A Code for Calculating Band-structure Dependent Quantities  

Energy Technology Data Exchange (ETDEWEB)

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.

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

2006-01-01

26

BoltzTraP. A code for calculating band-structure dependent quantities  

OpenAIRE

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.

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

2006-01-01

27

Calculation of the energy band structures in semiconductors by RAPW method  

International Nuclear Information System (INIS)

To calculate the energy band structures in semiconductors using the relativistic augmented plane wave method, atomic potential and charge density are needed, which are calculated by self-consistent method. Wave function for one electron is determined by solving the Dirac equation with the Hartree-Fock equation based on the slater's exchange potential. The results of calculation for Cu+1 are given. (Author)

28

Certain electronic structure parameters calculated in a two-band approximation for zirconium carbonitrides  

International Nuclear Information System (INIS)

X-ray spectra of the ZrC-ZrN solid solution valence band are obtained. Transfer properties and their temperature dependence are studied. They serve as basis for calculating main electronic structure parameters in terms of a two-band model of degenerate electrons and undegenerate holes. The energy equality of C and N atoms in interstitial octa-pores and an additive pattern of the band structure variations when carbon is replaced by nitrogen are shown

29

Photonic band calculation in the form of $k(\\omega)$ including evanescent waves  

OpenAIRE

We give a general method to calculate photonic band structure in the form of wave number $k$ as a function of frequency $\\omega$, which is required whenever we want to calculate signal intensity related with photonic band structure. This method is based on the fact that the elements of the coefficient matrix for the plane wave expansion of the Maxwell equations contain wave number up to the second order, which allows us to rewrite the original eigenvalue equation for $\\omega...

Cho, Kikuo; Ushida, Jun; Bamba, Motoaki

2003-01-01

30

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)

31

Electronic structure analysis of UIr using soft x-ray photoemission spectroscopy and band calculation  

Energy Technology Data Exchange (ETDEWEB)

Uranium ferromagnet UIr is well-known to a pressure-induced superconductor without an inversion symmetry. In order to clarify the U 5f states of ferromagnetically-ordered UIr below T{sub c} {approx} 46 K and at ambient pressure, we observed 5f-sensitive soft X-ray photoemission spectra (SXPES), and calculated the band structure by a relativistic LAPW method in a local-spin density approximation. The temperature-dependent angle-integrated SXPES near the Fermi energy show a definite energy-shift of the band structures below and above T{sub c}. The exchange splitting of the 5f bands seems to be consistent with an itinerant band picture like Stoner model. Furthermore the angle-resolved SXPES are compared with the theoretical band structure to investigate the relationship between the band shift and the magnetism.

Yamagami, H [Department of Physics, Kyoto Sangyo University, Kyoto 603-8555 (Japan); Ohkochi, T; Fujimori, S-i; Toshimitsu, T; Yasui, A; Okane, T; Saitoh, Y [Synchrotron Radiation Research Center SPring-8, JAEA, Hyogo 679-5148 (Japan); Fujimori, A [Department of Physics, The University of Tokyo, Tokyo (Japan); Haga, Y; Yamamoto, E; Ikeda, S [Advanced Science Research Center, JAEA, Ibaraki 319-1195 (Japan); Onuki, Y, E-mail: yamagami@cc.kyoto-su.ac.j [Graduate School of Science, Osaka University, Osaka 560-0043 (Japan)

2010-01-15

32

Empiric k·p Hamiltonian calculation of the band-to-band photon absorption in semiconductors  

OpenAIRE

The Empiric k·p Hamiltonian method is usually applied to nanostructured semiconductors. In this paper, it is applied to a homogeneous semiconductor in order to check the adequacy of the method. In this case, the solutions of the diagonalized Hamiltonian, as well as the envelope functions, are plane waves. The procedure is applied to the GaAs and the interband absorption coefficients are calculated. They result in reasonable agreement with the measured values, further supporting the adequacy ...

Luque Lo?pez, Antonio; Panchak, A.; Mellor Null, Alexander Virgil; Vlasov, A.; Marti? Vega, Antonio; Andreev, V.

2014-01-01

33

Calculations of ? and ?? band B(E2) transition probabilities within Triaxial Projected Shell Model  

International Nuclear Information System (INIS)

The Triaxial Projected Shell Model (TPSM) provides a unified microscopic description of rotational and multi-phonon vibrational states. We applied the TPSM model with its new capability to calculate B(E2) [1] values in the rare-earth region. The energies of the double-phonon states are reproduced. The calculated B(E2) values agree within an order of magnitude with the experimental ones. The calculations point to the identification of the new K=4+ band in 162Dy as a possible ??-band

34

Empiric k·p Hamiltonian calculation of the band-to-band photon absorption in semiconductors  

Science.gov (United States)

The Empiric k·p Hamiltonian method is usually applied to nanostructured semiconductors. In this paper, it is applied to a homogeneous semiconductor in order to check the adequacy of the method. In this case, the solutions of the diagonalized Hamiltonian, as well as the envelope functions, are plane waves. The procedure is applied to the GaAs and the interband absorption coefficients are calculated. They result in reasonable agreement with the measured values, further supporting the adequacy of the Empiric k·p Hamiltonian method.

Luque, Antonio; Panchak, Aleksandr; Mellor, Alexander; Vlasov, Alexey; Martí, Antonio; Andreev, Viatcheslav

2015-01-01

35

Calculation of semiconductor band gaps with the M06-L density functional  

Science.gov (United States)

The performance of the M06-L density functional has been tested for band gaps in seven semiconductors plus diamond and MgO. Comparison with the local spin density approximation (LSDA), Becke-Lee-Yang-Parr (BLYP), Perdew-Burke-Eernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and Heyd-Scuseria-Ernzerhof (HSE) functionals shows that M06-L has improved performance for calculating band gaps as compared to other local functionals, but it is less accurate than the screened hybrid HSE functional for band gaps.

Zhao, Yan; Truhlar, Donald G.

2009-02-01

36

Emergence of rotational bands in ab initio no-core configuration interaction calculations  

CERN Document Server

Rotational bands have been observed to emerge in ab initio no-core configuration interaction (NCCI) calculations for p-shell nuclei, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. We investigate the ab initio emergence of nuclear rotation in the Be isotopes, focusing on 9Be for illustration, and make use of basis extrapolation methods to obtain ab initio predictions of rotational band parameters for comparison with experiment. We find robust signatures for rotational motion, which reproduce both qualitative and quantitative features of the experimentally observed bands.

Caprio, M A; Vary, J P; Smith, R

2015-01-01

37

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)

38

Eight-band calculations of strained InAs/GaAs quantum dots compared with one, four, and six-band approximations  

OpenAIRE

The electronic structure of pyramidal shaped InAs/GaAs quantum dots is calculated using an eight-band strain dependent $\\bf k\\cdot p$ Hamiltonian. The influence of strain on band energies and the conduction-band effective mass are examined. Single particle bound-state energies and exciton binding energies are computed as functions of island size. The eight-band results are compared with those for one, four and six bands, and with results from a one-band approximation in whic...

Pryor, Craig

1997-01-01

39

Diagonalization of large matrices in pseudopotential band-structure calculations: Dual-space formalism  

International Nuclear Information System (INIS)

Combining iterative methods of calculating the eigenvectors of a Hermitian matrix with a matrix-multiplication technique using the fast-Fourier-transform algorithm, we present an efficient method of performing total-energy and band-structure calculations in crystals with the plane-wave local-pseudopotential formalism. The method can be viewed as a dual-space formalism where part of the calculations is performed in momentum space and another part in coordinate space. Significant savings in both computer time and memory are obtained. Results of calculations for molecular hydrogen with matrix sizes as large as 7200 are presented as an example

40

XPS valence band spectra and theoretical calculations for investigations on thiogermanate and thiosilicate glasses  

International Nuclear Information System (INIS)

This paper reports on investigations of thiogermanate and thiosilicate crystals and glasses by means of XPS valence band spectra and theoretical calculations (FLAPW method). The calculations were achieved on three crystallized phases GeS2, Na2GeS3 and SiS2 and valence band spectra (visualization of the occupied electronic density of states) were precisely interpreted through modulated density of states and charge density maps. This information was used to go further in the structural investigations of some thiogermanate and thiosilicate glasses. In sodium thiogermanates, an increase in Ge-Ge bonds was revealed as the modifier content (Na2S) increases. In thiosilicates, the evolution of the valence spectra according to the nature of the alkaline atoms (Li, Na) has been interpreted as changes in the local connectivity of units (edge or corner sharing tetrahedra). This study exhibits the potentialities of valence band spectra to provide information on glassy systems

41

Debye-Hueckel solution for steady electro-osmotic flow of a micropolar fluid in a cylindrical microcapillary  

CERN Document Server

Analytic expressions for the speed, flux, microrotation, stress, and couple stress in a micropolar fluid exhibiting steady, symmetric and one-dimensional electro-osmotic flow in a uniform cylindrical microcapillary were derived under the constraint of the Debye-Hueckel approximation, which is applicable when the cross-sectional radius of the microcapillary exceeds the Debye length, provided that the zeta potential is sufficiently small in magnitude. As the aciculate particles in a micropolar fluid can rotate without translation, micropolarity influences fluid speed, fluid flux, and one of the two non-zero components of the stress tensor. The axial speed in a micropolar fluid intensifies as the radius increases. The stress tensor is confined to the region near the wall of the microcapillary but the couple stress tensor is uniform across the cross-section.

Siddiqui, Abuzar A

2011-01-01

42

Band structure calculations for dilute nitride quantum wells under compressive or tensile strain  

Energy Technology Data Exchange (ETDEWEB)

We have calculated the band structure of InGaAsN/GaAs(N)/GaAs compressively strained quantum wells (QW) emitting at 1.3 {mu}m using the band anticrossing model and an eight-band kp Hamiltonian. The calculated interband optical transition energies have been compared to the experimental ones deduced from photocurrent, photoluminescence and excitation of photoluminescence spectroscopy experiments and measured laser characteristics extracted from the recent literature. Because of the high compressive strain in the QW, strain-compensated structures may be required in order to grow stable multiple QWs; in view of this we have studied the band structure of InGaAsN/GaAsP/GaAs QWs emitting at 1.3 {mu}m. Dilute nitride structures also offer the possibility of growing tensile strained QW lasers on InP substrate emitting in the 1.55 {mu}m emission wavelength range. In order to evaluate the potentialities of such structures we have determined the band characteristics of InGaAsN/InGaAsP/InP heterostructures with a TM polarized fundamental transition.

Carrere, H [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Marie, X [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Barrau, J [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Amand, T [LNMO-INSA, 135 avenue de Rangueil, 31077 Toulouse cedex 4 (France); Bouzid, S Ben [LPN, Route de Nozay, 91460 Marcoussis (France); Sallet, V [LPN, Route de Nozay, 91460 Marcoussis (France); Harmand, J-C [LPN, Route de Nozay, 91460 Marcoussis (France)

2004-08-11

43

Band structure calculations for dilute nitride quantum wells under compressive or tensile strain  

International Nuclear Information System (INIS)

We have calculated the band structure of InGaAsN/GaAs(N)/GaAs compressively strained quantum wells (QW) emitting at 1.3 ?m using the band anticrossing model and an eight-band kp Hamiltonian. The calculated interband optical transition energies have been compared to the experimental ones deduced from photocurrent, photoluminescence and excitation of photoluminescence spectroscopy experiments and measured laser characteristics extracted from the recent literature. Because of the high compressive strain in the QW, strain-compensated structures may be required in order to grow stable multiple QWs; in view of this we have studied the band structure of InGaAsN/GaAsP/GaAs QWs emitting at 1.3 ?m. Dilute nitride structures also offer the possibility of growing tensile strained QW lasers on InP substrate emitting in the 1.55 ?m emission wavelength range. In order to evaluate the potentialities of such structures we have determined the band characteristics of InGaAsN/InGaAsP/InP heterostructures with a TM polarized fundamental transition

44

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)

45

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

46

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

International Nuclear Information System (INIS)

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.

47

BoltzTraP. A code for calculating band-structure dependent quantities  

Science.gov (United States)

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.

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

2006-07-01

48

Calculations of transmission functions in the infrared CO2 and O3 bands  

Science.gov (United States)

An efficient method for computing the transmission function in the 15-micron CO2 and the 9.6-micron O3 bands is presented. An inhomogeneous atmospheric path is treated as homogeneous by applying simple pressure and temperature scaling approximations. The transmission functions are then derived from small precomputed tables. Because the atmospheric cooling rate is primarily contributed from adjacent layers, the simple scaling approximations can be used to accurately compute transmission functions in both the middle and lower atmosphere. Applying the parameterization to vastly different atmospheric conditions, the difference with line-by-line calculations is small. In the region between 0.01 mbar and the earth's surface, the cooling rate difference is less than 0.3 C/d in the 15-micron CO2 band and less than 0.1 C/d in the 9.6-micron O3 band.

Chou, Ming-Dah; Kouvaris, Louis

1991-01-01

49

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

CERN Document Server

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.

Kokabi, Alireza; Khorasani, Sina; Fardmanesh, Mehdi

2011-01-01

50

Full-band-structure calculation of Shockley-Read-Hall recombination rates in InAs  

Science.gov (United States)

We report a calculational procedure to obtain the rate of electron-hole recombination, mediated by the Shockley-Read-Hall (SRH) mechanism. Our method uses a combination of first-principles calculations and accurate empirical band structures. First, we use ab initio calculations to identify the point defects, their densities and energy levels in the gap. Then we parametrize the tight-binding interaction between defect and the host atoms in a Green's function approach to obtain the defect levels as identified by the first-principles calculations. Finally, the resulting tight-binding Hamiltonian is used to obtain the dipole matrix element between the conduction and valence band states, mediated through the defect levels in the gap, in second-order perturbation theory. The states are integrated over the entire Brillioun zone, subject to energy and momentum conservation, to obtain the limiting lifetimes of the carriers. This method is applied to study the minority carrier lifetimes in n-doped InAs. The calculated effective lifetimes that include Auger and SRH recombinations as functions of temperature agree reasonably well with experiment. Our calculation of lifetimes in 3.5×1016 and 2.0×1016cm-3 n-doped InAs indicate that SRH is dominant at low temperatures and that the lifetimes vary between 10-8 and 10-7 s.

Krishnamurthy, Srinivasan; Berding, M. A.

2001-07-01

51

Theoretical Calculations of Infrared Bands of CH3+ and CH5+  

International Nuclear Information System (INIS)

Existing theoretical calculations predict that infrared spectra of the two most fundamental reactive carbo-ions, methyl cation CH3+ with D3h symmetry and protonated methyl cation CH5+ with Cs(I), Cs(II), and C2v symmetries, appear together in the 7-?m region corresponding to the C-H bending modes. Vibrational band profiles of CH3+ and CH5+ have been compared by ab initio calculation methods that use the basis sets of MP2/aug-cc-pVTZ and CCSD(T)/cc-pVTZ. Our results indicate that the bands of rotation-vibration transitions of CH3+ and CH5+ should overlap not only in the 3-?m region corresponding to the C-H stretching modes but also in the 7-?m region corresponding to the C-H bending modes. Five band intensities of CH5+ among fifteen vibrational transitions between 6 and 8 ?m region are stronger than those of the v2 and v4 bands in CH3+. Ultimate near degeneracy of the two bending vibrations v2 and v4 of CH3+ along with the stronger intensities of CH5+ in the three hydrogen scrambling structures may cause extreme complications in the analysis of the high-resolution carbo-ion spectra in the 7-?m region

52

Photonic band calculation in the form of $k(\\omega)$ including evanescent waves  

CERN Document Server

We give a general method to calculate photonic band structure in the form of wave number $k$ as a function of frequency $\\omega$, which is required whenever we want to calculate signal intensity related with photonic band structure. This method is based on the fact that the elements of the coefficient matrix for the plane wave expansion of the Maxwell equations contain wave number up to the second order, which allows us to rewrite the original eigenvalue equation for $\\omega^2$ into that for wave number. This method is much better, especially for complex wave numbers, than the transfer matrix method of Pendry, which gives the eigenvalues in the form of exp$[ikd]$ . As a simplest example, we show a comparison of $\\omega(k)$ and $k(\\omega)$ for a model of intersecting square rods.

Cho, K; Bamba, M; Cho, Kikuo; Ushida, Jun; Bamba, Motoaki

2003-01-01

53

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

OpenAIRE

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 lineshapes 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 atomistic first-principles simulations.

Lu?, Jing-tao; Christensen, Rasmus B.; Foti, Giuseppe; Frederiksen, Thomas; Gunst, Tue; Brandbyge, Mads

2013-01-01

54

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

DEFF Research Database (Denmark)

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.

Lu, Jing Tao; Christensen, Rasmus Bjerregaard

2014-01-01

55

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

Science.gov (United States)

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.

Lü, Jing-Tao; Christensen, Rasmus B.; Foti, Giuseppe; Frederiksen, Thomas; Gunst, Tue; Brandbyge, Mads

2014-02-01

56

A Mathematical Solution to the Theoretical Band Gap Underestimation: Predictive Calculations of Properties of Semiconductors  

Science.gov (United States)

Most density functional theory (DFT) calculations find band gaps that are 30-50 percent smaller than the experimental ones, as illustrated in this presentation that recalls some popular explanations of this band gap problem, i.e., self-interaction effects and derivative discontinuities of the exchange correlation energy. A survey of the increasingly numerous approaches aimed at resolving the theoretical underestimation follows these explanations. These approaches include the Green function and screened Coulomb approximation (GWA), time dependent density functional theory (TDDFT), the exact exchange and screened exchange methods, and the use of local density approximation (LDA) potentials plus additional potentials located at atomic sites. Using the Rayleigh theorem, we describe a basis set and variational effect inherently associated with calculations that employ a linear combination of atomic orbitals (LCAO) in a variational approach of the Rayleigh-Ritz type. This description concomitantly shows a source of large underestimation errors in calculated band gaps, i.e., an often dramatic lowering of some unoccupied energies on account of the Rayleigh theorem as opposed to the Hamiltonian. We present the Bagayoko, Zhao, and Williams (BZW) method [Phys. Rev. B 60, 1563 (1999); PRB 74, 245214 (2006); and PRB 76, 037101 (2007)] that follows from the description of the aforementioned effect and that leads (a) to DFT and LDA calculated band gaps of semiconductors in agreement with experiment and (b) theoretical predictions of band gaps that are confirmed by experiment. Unlike most calculations, BZW computations solve, self-consistently, a system of two coupled equations. DFT-BZW calculated effective masses and optical properties (dielectric functions) also agree with measurements. We illustrate ten years of success of the BZW method with its results for GaN, C, Si, 3C-SIC, 4H-SiC, ZnO, AlAs, Ge, ZnSe, w-InN, InAs, and AlN. We conclude with a request to revisit beliefs relative to actual limitations of DFT and of schemes purporting to correct it or to go beyond it.

Bagayoko, Diola

2008-03-01

57

Electron-phonon interaction in transition metals. Results of relativistic APW band structure calculations  

Energy Technology Data Exchange (ETDEWEB)

The Hopfield parameter eta of the electron-phonon coupling is calculated for twelve transition metals (Rh, Pd, Ag, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au) in the rigid muffin-tin approximation. Using relativistic APW band structure data and a generalized Gaspari-Gyorffy formula the influence of relativistic effects is completely taken into account. It is found that eta may be calculated in remarkably good approximation using spin-weighted averages of phase shifts and density matrix coefficients. The theoretical results for the electron-phonon parameter lambda and the electronic specific heat are compared with the experimental data.

John, W.; Nemoshkalenko, V.V.; Antonov, V.N.; Antonov, V.N.

1984-01-01

58

Rigid muffin-tin calculations of superconducting parameters in d- and f-band metals  

International Nuclear Information System (INIS)

We present a brief review of calculations of superconducting parameters within the widely used rigid muffin-tin (RMT) approximation. The systems which are discussed are the Group V bcc transitional elements, transition-metal carbides and nitrides. Nb-based A15 compounds, hydrides and f-band metals. Where experimental information on ?2(?)F(?) is available, we compare the first frequency moment, which is independent of the lattice vibrational spectrum, directly with the theoretical calculation to assess the accuracy of the RMT ansatz. The ability of the RMT approach to predict trends correctly is also surveyed. (orig.)

59

Band structure mapping and calculations of CuInS2(001)  

International Nuclear Information System (INIS)

The ternary compound semiconductor CuInS2 is used as an absorber material for thin film solar cells. A better understanding of the detailed electronic structure might lead to an improvement of the junction properties with respect to the still limited photo voltage of the present devices. We report on band structure mapping via ARUPS on thin epitaxial layers of CuInS2(001) prepared on sulfur passivated GaAs(100). To have a better control on the deposition process we introduced a MOMBE type deposition with an organic sulfur precursor. Samples were prepared and precharacterized in a dedicated UHV deposition and analysis system. ARUPS measurements were conducted at the beamline TGM7 at BESSY II. We discuss the experimentally determined band structure in comparison to recent augmented spherical wave (ASW) calculations as based on density functional theory and the local density approximation (LDA). Beside earlier calculations presented by Zunger for some high symmetry directions along ? perpendicular to our calculations include for ? parallel the experimental parameters of an ARUPS experiment thus allowing a direct comparison with our experimentally derived data rather than an idealistic run on the boundary of the Brillouin-zone. Additionally we derive the effective mass from the valence band curvature

60

Isotopic selectivity calculations for multi-step photoionization of calcium atoms using narrow-band lasers  

Energy Technology Data Exchange (ETDEWEB)

Isotopic selectivity calculations are carried out for minor calcium isotopes against the major isotope {sup 40}Ca for the single-resonance two-step and double-resonance three-step photoionization schemes with narrow-band lasers by using spectral simulation (SS) and modified spectrum (MS) approaches. The results of these calculations are compared with the density matrix (DM) results reported in the literature. It is noted that the values of isotopic selectivity from the SS approach do not agree with those from the DM approach whereas the MS approach, considering hole burning in the Doppler-broadened atomic spectrum, predicts selectivity values which are in good agreement with the DM results. It is argued that one can adequately use the simple MS approach rather than the complex DM approach for the calculation of isotopic selectivity of multi-step photoionization with single-frequency lasers. (author)

Pulhani, A.K.; Suri, B.M.; Gupta, G.P. [Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai (India)]. E-mail: gpgupta@apsara.barc.ernet.in

2002-09-14

61

A Hartree-Fock ab initio band-structure calculation employing Wannier-type orbitals  

CERN Document Server

An ab initio Wannier-function-based approach to electronic ground-state calculations for crystalline solids is outlined. In the framework of the linear combination of atomic orbitals method the infinite character of the solid is rigorously taken into account. The Hartree-Fock ground-state energy, cohesive energy, lattice constant and bulk modulus are calculated in a fully ab initio manner as it is demonstrated for sodium chloride, NaCl, using basis sets close to the Hartree-Fock limit. It is demonstrated that the Hartree-Fock band-structure can easily be recovered with the current approach and agrees with the one obtained from a more conventional Bloch-orbital-based calculation. It is argued that the advantage of the present approach lies in its capability to include electron correlation effects for crystalline insulators by means of well-established quantum chemical procedures.

Albrecht, M; Dolg, M; Fulde, P; Stoll, H; Albrecht, Martin; Shukla, Alok; Dolg, Michael; Fulde, Peter; Stoll, Hermann

1998-01-01

62

Band structure calculations for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates  

CERN Document Server

Electronic band structures for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates are calculated using linear muffin-tin orbital method within the local density approximation. It is found that barium states strongly contribute to the density of states at the Fermi level and thus can influence the transport properties of the compounds. A sharp peak of the density of states is found just at the Fermi level. It is also shown that the shifting of barium atoms toward experimentally deduced split positions in Ba$_{6}$Ge$_{25}$ produces a splitting of this peak which may therefore be interpreted as a band Jahn-Teller effect. If the locking of the barium atoms at the observed structural phase transition is assumed, this reduction of the density of states at the Fermi level can qualitatively account for the experimentally observed decrease of the magnetic susceptibility and electrical resistivity at the phase transition.

Zerec, I; Thalmeier, P; Grin, Y; Zerec, Ivica; Yaresko, Alexander; Thalmeier, Peter; Grin, Yuri

2002-01-01

63

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

64

Compton profiles and band structure calculations of CdS and CdTe  

International Nuclear Information System (INIS)

In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci 137Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

65

Compton profiles and band structure calculations of CdS and CdTe  

Energy Technology Data Exchange (ETDEWEB)

In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci {sup 137}Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Heda, N.L.; Mathur, S.; Ahuja, B.L. [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur, Rajasthan (India); Sharma, B.K. [Department of Physics, University of Rajasthan, Jaipur (India)

2007-03-15

66

Band structure calculations for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates  

OpenAIRE

Electronic band structures for Ba$_{6}$Ge$_{25}$ and Ba$_{4}$Na$_{2}$Ge$_{25}$ clathrates are calculated using linear muffin-tin orbital method within the local density approximation. It is found that barium states strongly contribute to the density of states at the Fermi level and thus can influence the transport properties of the compounds. A sharp peak of the density of states is found just at the Fermi level. It is also shown that the shifting of barium atoms toward expe...

Zerec, Ivica; Yaresko, Alexander; Thalmeier, Peter; Grin, Yuri

2002-01-01

67

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

Energy Technology Data Exchange (ETDEWEB)

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.

Minar, J. [Department Chemie und Biochemie, Physikalische Chemie, Universitaet Muenchen, Butenandtstr. 5-13, D-81377 Munich (Germany)]. E-mail: jan.minar@cup.uni-muenchen.de; Chadov, S. [Department Chemie und Biochemie, Physikalische Chemie, Universitaet Muenchen, Butenandtstr. 5-13, D-81377 Munich (Germany); Ebert, H. [Department Chemie und Biochemie, Physikalische Chemie, Universitaet Muenchen, Butenandtstr. 5-13, D-81377 Munich (Germany); Chioncel, L. [Institut fuer Theoretische Physik - Computational Physics, Technische Universitaet Graz, A-8010 Graz (Austria); Lichtenstein, A. [Institut fuer theoretische Physik, Universitaet Hamburg, 20355 Hamburg (Germany); De Nadai, C. [European Synchrotron Radiation Facility, BoIte Postale 220, 38043 Grenoble Cedex (France); Brookes, N.B. [European Synchrotron Radiation Facility, BoIte Postale 220, 38043 Grenoble Cedex (France)

2005-07-21

68

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

69

Calculation of intrinsic damping in half metals  

Science.gov (United States)

The extended Hueckel tight binding method in combination with Kambersky's torque correlation model [1] is used to calculate the precessional magnetization relaxation in half-metallic systems. In Kambersky's model damping is described by a combination of spin-flip excitations and orbital excitations. An analytical expression of the transition matrix element which represents scattering events within a single band (intraband) and between different bands (interband) respectively [2] can be obtained within the TB scheme, which enables a better understanding of the damping mechanisms in half-metallic structures. Due to the absence of spin-flip scattering in half-metallic systems, the Gilbert damping rate of half-metals is expected to be much smaller than that of metals. Using this approach we calculated the damping for different half-metallic structures. The minimum intrinisic relaxation rate ? was calculated to be, 3.2 MHz, 1.1 MHz, 0.13 MHz, for the Heusler structures Co2MnGe , Co2MnSi and the Rutile structure CrO2 respectively. The damping rates for these half-metallic materials are much lower than that of bcc Fe, as we anticipated from the analytical analysis. References: [1] V. Kambersky, Czech. J. Phys. B 26, 1366 (1976). [2] K. Gilmore, Y.U. Idzerda and M.D. Stiles, Phys. Rev. Lett. 99, 027204 (2007).

Liu, Chunsheng; Mewes, Claudia K. A.; Chshiev, Mairbek; Mewes, Tim; Butler, William H.

2009-03-01

70

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

71

Calculation of the Band Gap Energy and Study of Cross Luminescence in Alkaline-Earth Dihalide Crystals  

Science.gov (United States)

The band gap energy as well as the possibility of cross luminescence processesin alkaline-earth dihalide crystals have been calculated using the ab initio Perturbed-Ion (PI) model.The gap is calculated in several ways: as adifference between one-electron energy eigenvalues and as adifference between total energies of appropriate electronic states of thecrystal, both at the HF level and with inclusion of Coulomb correlation effects.In order to study the possibility of ocurrence of cross luminescence in thesematerials, the energy differencebetween the valence band and the outermost core band for somerepresentative crystals has been calculated.Both calculated band gap energies and cross luminescence predictions comparevery well with the available experimental and theoretical results.

Aguado, Andrés; Ayuela, Andrés; López, José; Alonso, Julio

1999-08-01

72

Calculation of the Band Gap Energy and Study of Cross Luminescence in Alkaline-Earth Dihalide Crystals  

CERN Document Server

The band gap energy as well as the possibility of cross luminescence processes in alkaline-earth dihalide crystals have been calculated using the ab initio Perturbed-Ion (PI) model. The gap is calculated in several ways: as a difference between one-electron energy eigenvalues and as a difference between total energies of appropriate electronic states of the crystal, both at the HF level and with inclusion of Coulomb correlation effects. In order to study the possibility of ocurrence of cross luminescence in these materials, the energy difference between the valence band and the upmost core band for some representative crystals has been calculated. Both calculated band gap energies and cross luminescence predictions compare very well with the available experimental results.

Aguado, A; López, J M; Alonso, J A; Aguado, Andres; Ayuela, Andres; Lopez, Jose M.; Alonso, Julio A.

1999-01-01

73

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

CERN Document Server

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.

Maris, P; Vary, J P

2014-01-01

74

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

75

First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2  

International Nuclear Information System (INIS)

The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density functional theory with the full-potential linearized-augmented-plane-wave method. New occupied bands are found between the band gaps of both Ag-doped rutile and anatase TiO2. The formation of these new bands can be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption. (condensed matter: electronicstructure, electrical, magnetic, and opticalproperties)

76

On optimizing Jacobi–Davidson method for calculating eigenvalues in low dimensional structures using eight band k · p model  

International Nuclear Information System (INIS)

The paper presents two ways of improving the Jacobi–Davidson method for calculating the eigenvalues and eigenvectors described by eight-band k · p model for quantum dots and other low dimensional structures. First, the method is extended by the application of time reversal symmetry operator. This extension allows efficient calculations of the twofold degeneracy present in the multiband k · p model and other interior eigenvalues. Second, the preconditioner for the indefinite matrix which comes from the discretization of the eight band k · p Hamiltonian is presented. The construction of this preconditioner is based on physical considerations about energy band structure in the k · p model. On the basis of two real examples, it is shown that the preconditioner can significantly shorten the time needed to calculate the interior eigenvalues, despite the fact that the memory usage of the preconditioner and Hamiltionian is comparable. Finally, some technical details for implementing the eight band k · p Hamiltonian and the eigensolver are provided

77

Range-Separation Density-Fitting Band Structure Calculation with Gaussian Auxiliary Function  

Science.gov (United States)

In this paper, we discuss a range-separation density-fitting method for obtaining the electronic band structure. The formalism is based on Gaussian orbital basis functions. The Hartree term and the nuclear attractive term are divided into long- and short-range contributions by using the error and complementary error functions, respectively. The long-range Hartree term is evaluated through a density-fitting procedure based on Gaussian auxiliary functions, where the net charge neutrality of electrons and atomic nuclei in the unit cell is ensured by Lagrange multipliers. We implemented a first-principles program code based on the methodology, and demonstrate calculation results, using semi-local density functional theory (DFT) functionals, the Hartree–Fock, and hybrid DFT methods. We also discuss the efficiency and accuracy of the methodology.

Shimazaki, Tomomi; Kosugi, Taichi; Nakajima, Takahito

2014-05-01

78

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

Science.gov (United States)

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 of the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). It allows us to consider such correlation effects as the non-Fermi-step form of the distribution function, the enhancement of the effective mass including Kondo resonances,'' the appearance of the satellites in the electron spectra, etc. To specify the form of the self-energy, it is useful to distinguish (according to the ratio of the on-site Coulomb energy U to the bandwidth W) three regimes-strong, moderate, and weak correlations. 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 nmm' the band-structure problem is formulated as the functional problem on nmm' for f electrons and the standard local-denisty-approximation functional for delocalized electrons. In the case of moderate correlations (U/W~1-metal-insulator regime, Kondo systems) we start from the d=? dynamical mean-field iterative perturbation scheme of Kotliar and co-workers and also make use of our multiband atomic Green function for constrained nmm'. Finally for the weak interactions (U/WBickers and Scalapino is generalized to the realistic multiband case. We present two-band, two-dimensional model calculations for all three regimes. A realistic calculation in the Hubbard-I scheme with the exact solution of the on-site multielectron problem for f(d) shells was performed for mixed-valence 4f compound TmSe, and for the classical Mott insulator NiO.

Lichtenstein, A. I.; Katsnelson, M. I.

1998-03-01

79

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

Science.gov (United States)

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.

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

1993-07-01

80

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

CERN Document Server

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...

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

81

The calculation of ground wave attenuation in the HF band using program WAGNER  

Science.gov (United States)

Computational test results from a double precision version of the FORTRAN program WAGNER are presented. The potential value of this integral equation technique is its purported ability to model propagation losses over two-dimensional paths through irregular and inhomogeneous terrain. However the numerical integration algorithm can be affected by poor convergence and inaccuracy, particularly at frequencies above the MF band. We have investigated these properties in terms of selected key parameters and have derived empirical criteria governing convergence and physical accuracy. We find that calculations of basic transmission loss using WAGNER are subject to significant limitations at HF frequencies as the terrain becomes irregular and as the conductivity and dielectric constant of the ground both become smaller. On the other hand, the shadow loss due to an obstacle may be reliably calculated by WAGNER on the assumption that shadow loss is independent of ground electrical constants, thus permitting the use of dummy values of conductivity and dielectric constant to ensure that the physical accuracy criterion is satisfied.

Thomas, R. M.; Zollo, A. O.

1987-12-01

82

Relativistic embedding method: The transfer matrix, complex band structures, transport, and surface calculations  

Science.gov (United States)

We develop the relativistic embedding method for electronic-structure studies. An expression for the transfer matrix is derived in terms of the Green’s function of the Dirac equation, and we outline its evaluation within the relativistic embedding framework. The transfer matrix is used to find the complex band structure and an embedding potential that can replace a semi-infinite substrate in ab initio electronic-structure calculations. We show that this embedding potential may be used to define an operator that gives the current flowing across a surface; the eigenstates of which define channel functions for conductance studies, and which enable the derivation of a relativistic generalization of the known expression for the conductance across a nanodevice connected to leads. Finally, the application of the embedding potential in relativistic electronic-structure studies is illustrated using an electronlike basis to solve the surface-embedded Dirac equation for Au(111). A calculation with a single layer of atoms within the embedded volume correctly predicts the magnitude of the Rashba-type splitting of the zone center surface state.

James, M.; Crampin, S.

2010-04-01

83

Relativistic band-structure calculations for CeTIn sub 5 (T=Ir and Co) and analysis of the energy bands by using tight-binding method  

CERN Document Server

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn sub 5 (T=Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Ce 4 f and In 5 p states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when we attempt to understand magnetism and superconductively in CeTIn sub 5 from the microscopic viewpoint, the energy bands obtained in the RLAPW method are too complicated to analyze the system by further including electron correlations. Thus, it is necessary to prepare a more simplified model, keeping correctly the essential characters of the energy bands obtained in the band-structure calculation. For the purpose, we construct a tight-binding model for CeTIn sub 5 by including f-f and p-p hoppings as well as f-p hybridization, which are ex...

Maehira, T; Ueda, K; Hasegawa, A

2003-01-01

84

Calculation and spectroscopy of the Landau band structure at a thin and atomically precise tunneling barrier  

CERN Document Server

Two laterally adjacent quantum Hall systems separated by an extended barrier of a thickness on the order of the magnetic length possess a complex Landau band structure in the vicinity of the line junction. The energy dispersion is obtained from an exact quantum-mechanical calculation of the single electron eigenstates for the coupled system by representing the wave functions as a superposition of parabolic cylinder functions. For orbit centers approaching the barrier, the separation of two subsequent Landau levels is reduced from the cyclotron energy to gaps which are much smaller. The position of the anticrossings increases on the scale of the cyclotron energy as the magnetic field is raised. In order to experimentally investigate a particular gap at different field strengths but under constant filling factor, a GaAs/AlGaAs heterostructure with a 52 Angstrom thick tunneling barrier and a gate electrode for inducing the two-dimensional electron systems was fabricated by the cleaved edge overgrowth method. The...

Habl, M; Wegscheider, W; Bichler, M; Abstreiter, G; Habl, Matthias; Reinwald, Matthias; Wegscheider, Werner; Bichler, Max; Abstreiter, Gerhard

2006-01-01

85

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

Directory of Open Access Journals (Sweden)

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

O. Funk

86

Calculation of photonic band-gap of one dimensional photonic crystal  

International Nuclear Information System (INIS)

Photonic crystal is a composite dielectric with periodic modulation of refractive index that brings about unique photonic band-gap effect by which light could be totally reflected on the surface of such material regardless of any incident angle or mode. Many applications based on this mechanism have been developed and introduced into new waveguides. Such band-gap effect could be understood by investigating the optical performance of one dimensional photonic crystal. In this paper, the principle of band-gap effect of one dimension photonic crystal is firstly explained by Bragg reflection, the band-gap centre is obtained; then the modelling of band-gap of one dimension photonic crystal is conducted as well, the result is in agreement with the Bragg results and shows that the centre of photonic band-gap shifts to larger wavelength with higher refractive index (RI) ratio or dimension ratio between the two component dielectrics, but the involved boundary condition in simulation leads to higher onset RI ratio (3.5) responsible for the presence of photonic band-gap. This work would be useful to the design and fabrication of photonic crystal devices.

87

Packing structures and periodic band calculations on DPO (2,5-dipicryl-1,3,4-oxadiazole).  

Science.gov (United States)

Molecular mechanics (MM) method with Compass and Dreiding force fields is used to predict molecular packing for DPO among the 7 most possible space groups (P2(1)/c, P-1, P2(1)2(1)2(1), P2(1), Pbca, C2/c, and Pna2(1)), respectively. Then, periodic band calculations are performed on the predicted crystals using the DFT-GGA-RPBE method. Obtained density of state (DOS) shows that C-O, CN-O(2) and N-N bonds are possibly the trigger bond during thermolysis. Band gap (DeltaE(g)) equals 1.33 eV, which shows DPO with higher sensitivity. Periodic calculation results are consistent well with that drawn from bond dissociation energy calculations on gas molecule. PMID:19419814

Wang, Gui-xiang; Shi, Chun-hong; Gong, Xue-dong; Zhu, Wei-hua; Xiao, He-ming

2009-09-30

88

Theoretical calculation of self-broadening coefficients for the ?5 band of methyl chloride at various temperatures  

Science.gov (United States)

Self-broadening coefficients of transitions belonging to the ?5 band of methyl chloride have been calculated using a semi-classical model based on the Anderson-Tsao-Curnutte (ATC) theory, including some improvements proposed by Robert and Bonamy. The calculations show the predominance of the dipole-dipole interaction. To better match the experimental measurements performed at room temperature in our previous work, a cut-off of the intermolecular distance has been used. The rotational J and K dependencies of the calculated self-broadening coefficients have been clearly observed and are consistent with our previous measurements.

Barbouchi Ramchani, A.; Jacquemart, D.; Dhib, M.; Aroui, H.

2014-02-01

89

Improved cache performance in Monte Carlo transport calculations using energy banding  

Science.gov (United States)

We present an energy banding algorithm for Monte Carlo (MC) neutral particle transport simulations which depend on large cross section lookup tables. In MC codes, read-only cross section data tables are accessed frequently, exhibit poor locality, and are typically too much large to fit in fast memory. Thus, performance is often limited by long latencies to RAM, or by off-node communication latencies when the data footprint is very large and must be decomposed on a distributed memory machine. The proposed energy banding algorithm allows maximal temporal reuse of data in band sizes that can flexibly accommodate different architectural features. The energy banding algorithm is general and has a number of benefits compared to the traditional approach. In the present analysis we explore its potential to achieve improvements in time-to-solution on modern cache-based architectures.

Siegel, A.; Smith, K.; Felker, K.; Romano, P.; Forget, B.; Beckman, P.

2014-04-01

90

Empirical calculations for ground state band level energies of 76Kr and 74Se nuclei  

International Nuclear Information System (INIS)

The neutron deficient nuclei 76Kr and 74Se (N=40) in the mass region A=80 exhibit interesting properties like shape coexistence, triaxiality, large quadrupole deformation patterns, strong upbends in kinetic moment of inertia of yrast bands and complex band structure. The spectroscopy of these nuclei is of special interest because both the proton and neutron shells are partially filled which results in large deformation in the ground state

91

Symmetry Aspects of the Band Structure and Motion Equations Applied in Calculating the Cyclotron Frequency of Electrons in Metals  

Directory of Open Access Journals (Sweden)

Full Text Available Cyclotron frequency of a crystal electron is, in general, not an easily accessible parameter. Nevertheless, its calculation can be simplified when the symmetry properties of the band structure and those of the motion equations in the magnetic field are simultaneously taken into account. In effect, a combined symmetry of the electron Hamiltonian and that of the Lorentz equation provide us with a non-linear oscillator problem of high symmetry. In the next step, the kinetic energy of the oscillator can be separated from the whole of electron energy and applied in a new kind of calculation of the cyclotron frequency which is much more simple than before. In consequence, a detailed approach to the electron circulation, also in more complex band structures, becomes a relatively easy task. For different crystal lattices of cubic symmetry taken as examples the cyclotron frequency of the present and a former method are compared numerically giving the same results.

Stanislaw Olszewski

2011-08-01

92

Systematic Two-band Model Calculations of the GMR Effect with Metallic and Nonmetallic Spacers and with Impurities  

CERN Document Server

By an accurate Green's function method we calculate resistances and the corresponding Giant Magneto-Resistance effects (GMR) of two metallic ferromagnetic films separated by different spacers, metallic and non-metallic ones, in a simplified model on a sc lattice, in CPP and CIP geometries (i.e. current perpendicular or parallel to the planes), without impurities, or with interface- or bulk impurities. The electronic structure of the systems is approximated by two hybridized orbitals per atom, to mimic s-bands and d-bands and their hybridization. We show that such calculations usually give rough estimates only, but of the correct order of magnitude; in particular, the predictions on the impurity effects depend strongly on the model parameters. One of our main results is the prediction of huge CPP-GMR effects for {\\it non-metallic} spacers in the ballistic limit.

Gebele, O; Krey, U; Krompiewski, S

1999-01-01

93

The band gaps of Lamb waves in a ribbed plate: A semi-analytical calculation approach  

Science.gov (United States)

In this paper a semi-analytical method is proposed to investigate the transmission band gaps of Lamb waves through repetitive structures in a waveguide. For a unit cell the scattering matrix is obtained by the Lamb mode matching technique at each artificially sliced interface and then substituted into the Bloch theorem to solve the eigenproblem incurred by cell repetition. The method is implemented on a ribbed plate. The band gaps in the dispersion curves are confirmed by the dips of Lamb wave transmission coefficients, and attributed to the coupled vibrations of Lamb modes in different sliced sections of the unit cell.

Feng, Feilong; Lin, Shuyu

2014-01-01

94

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

Science.gov (United States)

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.

Giustino, Feliciano

2012-02-01

95

Band-structure parameters by genetic algorithm  

International Nuclear Information System (INIS)

A genetic algorithm has been used to solve a complex multidimensional parameter-fitting problem. We will focus on the parameters of an empirical tight-binding Hamiltonian. The method is used to approximate the electronic energy band structure if energy values are known for a few wave vectors of high symmetry. Compared to the usual manual procedure this method is more accurate and automatic. This approach, based on the extended Hueckel theory (EHT), has provided a list of EHT parameters for IV-IV and III-V semiconductors with zinc-blende structure and helped us to find a symmetry in the EHT. copyright 1996 The American Physical Society

96

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)

97

Band alignment and local structure of CIGS alloys from combining X-ray absorption spectroscopy and ab initio calculations  

OpenAIRE

Structural and electronic properties of Cu(In,Ga)S2 (CIGS) alloys as a function of the In/Ga ratio are studied by combining near edge X-ray absorption fine structure and extended X-ray absorption fine structure spectroscopy with density functional theory calculations. While the S absorption edge shifts with the change of the In/Ga ratio, consistently with the corresponding variation of the band gap, the edges of the other elements are largely independent of composition. Our calculations repro...

Sarmiento-pe?rez, Rafael; Botti, Silvana; Schnohr, Claudia S.; Lauermann, Iver; Rubio Secades, A?ngel; Johnson, Benjamin

2014-01-01

98

A method for calculating wide band electromagnetic interference from power line corona  

International Nuclear Information System (INIS)

An algorithm for calculating electromagnetic interference from power line corona for a range of frequencies from 100 kHz to 30 MHz is demonstrated. It can be used for calculations at any distance or direction from the line. The algorithm incorporates an existing generation function which has been optimized by comparison to long term electromagnetic interference measurements

99

Band-gap corrected density functional theory calculations for InAs/GaSb type II superlattices  

Science.gov (United States)

We performed pseudopotential based density functional theory (DFT) calculations for GaSb/InAs type II superlattices (T2SLs), with bandgap errors from the local density approximation mitigated by applying an empirical method to correct the bulk bandgaps. Specifically, this work (1) compared the calculated bandgaps with experimental data and non-self-consistent atomistic methods; (2) calculated the T2SL band structures with varying structural parameters; (3) investigated the interfacial effects associated with the no-common-atom heterostructure; and (4) studied the strain effect due to lattice mismatch between the two components. This work demonstrates the feasibility of applying the DFT method to more exotic heterostructures and defect problems related to this material system.

Wang, Jianwei; Zhang, Yong

2014-12-01

100

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)

101

Band calculation of the effect of magnetic impurity atoms on the properties of superconductors  

International Nuclear Information System (INIS)

Magnetic impurity atoms scatter the conduction electrons of a host metal because of the exchange interaction. The phase shifts caused by this scattering are calculated from a crude model for conduction electrons with spin parallel or antiparallel to the spin of the impurity atom, for various alloy systems of interest (Cr, Mn, Fe, Co, and Ni in Al, Zn, Nb, In, Sn, Tl, and Pb). From the calculated phase shifts, the expected depression in the host metal's superconducting transition temperature is calculated, and the results are compared with experimental data. Partial waves beyond s waves are found to be essential; in fact, the p- and d-wave scattering dominate the s-wave scattering in many cases. The superconducting electronic density of states can also be calculated from the phase shifts, and good agreement with our results has been found with tunneling data obtained by Tsang and Ginsberg for In-Mn alloys

102

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

Science.gov (United States)

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. PMID:24410219

Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

2014-01-01

103

Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction  

International Nuclear Information System (INIS)

We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chose as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of strain are studied by looking at the variation of the VBO versus the in plane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed. (author). 25 refs, 3 figs, 5 tabs

104

Polarized optical reflectance and electronic band structure of ?'-NaV2O5  

International Nuclear Information System (INIS)

We report polarized optical reflectance studies of ?'-NaV2O5 between 0.5 and 6 eV as a function of temperature (T) and magnetic field (H). The electronic excitations and their polarization dependence are interpreted according to our extended Hueckel tight-binding polarized band structure calculations. Strong bands near 1 eV in both chain and rung directions are attributed to V d?d transitions. Charge transfer excitations are estimated to begin near 3.3 eV and have significant strength at 4.4 eV and above. The reflectance ratios, ?R(T)=R(T)/R(T=4 K), measured at H=0 and 28 T, reveal broad polarization-dependent changes through the low temperature transition, Tc. Integrated intensities of ?R features exhibit a second-order transition at 36 K in zero field and at 33±1 K in high field, consistent with a spin-Peierls aspect to the phase transition. (c) 1999 The American Physical Society

105

Sulfur-doping of rutile-titanium dioxide by ion implantation: Photocurrent spectroscopy and first-principles band calculation studies  

International Nuclear Information System (INIS)

Sulfur (S)-doped titanium dioxide (TiO2) was synthesized by ion implantation and subsequent thermal annealing. The S ions were implanted into the single crystals of rutile TiO2 at a fluence of 8x1015 ions/cm2. According to the results of Rutherford backscattering spectroscopy and ion channeling analysis, the irradiation damage recovered by annealing at 600 deg. C in air. In the annealed crystal, the S atoms occupied oxygen sites for form Ti-S bonds, as confirmed by x-ray photoelectron spectroscopy. Compared to the pure TiO2, a photocurrent was observed in the lower-energy regions for the S-doped TiO2. Based on the theoretical analyses by the first-principles band calculations using the full potential linearized augmented plane-wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the band gap narrowing in the S-doped TiO2. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm (<2.9 eV)

106

Measurements and calculations of Ar-broadening and -shifting parameters of water vapor transitions of ?1+?2+?3 band  

Science.gov (United States)

The water vapor line broadening and shifting for 94 lines in the ?1+?2+?3 band induced by argon pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm-1 and in a wide pressure range of Ar. The calculations of the broadening coefficients ? and ? were performed in the framework of the semi-classical method. The intermolecular potential was taken as the sum of pair potentials which, in turn, were modeled by the Lennard-Jones potentials. Optimal sets of potential parameters given the best discrepancy of measured broadening coefficients are found. The influence of the rotational dependence of an intermolecular potential and its repulsive part on the calculated coefficients ? and ? is discussed.

Petrova, T. M.; Solodov, A. M.; Solodov, A. A.; Starikov, V. I.

2014-11-01

107

Electronic Band Calculation of LaTSb2 (T=Cu,Ag,Au)  

Science.gov (United States)

The series of compounds LaTSb2 (T=Cu,Ag,Au) show various electronic properties. In this paper we have calculated the electronic structure of LaTSb2 from first-principles. The obtained Fermi surfaces of LaAgSb2 show strong two-dimensionality, which well agrees with the results of de Haas - van Alphen experiment. On the other hand, one of the Fermi surface of LaCuSb2 show three-dimensionality. LaAuSb2 has the intermediate properties. These different Fermi surfaces may cause the occurrence of the charge density wave (CDW) in LaAgSb2 and LaAuSb2, and no occurrence of the CDW in LaCuSb2. The conduction electrons are mainly due to Sb-5p electrons, while La-d and T-d electrons also have considerable contribution. The calculated electronic specific heat coefficient well agrees with the experimental results. The energy dispersion curve shows some Dirac points in the case of scalar-relativistic calculation, but these Dirac points are disappeared when we take the spin-orbit interaction into account.

Hase, I.; Yanagisawa, T.

108

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

CERN Document Server

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...

Lichtenstein, A I

1997-01-01

109

Eight-band k ?p calculations of the composition contrast effect on the linear polarization properties of columnar quantum dots  

Science.gov (United States)

We present eight-band k ?p calculations of the electronic and polarization properties of columnar InzGa1-zAs quantum dots (CQD) with high aspect ratio embedded in an InxGa1-xAs/GaAs quantum well. Our model accounts for the linear strain effects, linear piezoelectricity, and spin-orbit interaction. We calculate the relative intensities of transverse-magnetic (TM) and transverse-electric (TE) linear polarized light emitted from the edge of the semiconductor wafer as a function of the two main factors affecting the heavy hole—light hole valence band mixing and hence, the polarization dependent selection rules for the optical transitions, namely, (i) the composition contrast z /x between the dot material and the surrounding well and (ii) the dot aspect ratio. The numerical results show that the former is the main driving parameter for tuning the polarization properties. This is explained by analyzing the biaxial strain in the CQD, based on which it is possible to predict the TM to TE intensity ratio. The conclusions are supported by analytical considerations of the strain in the dots. Finally, we present the compositional and geometrical conditions to achieve polarization independent emission from InGaAs/GaAs CQDs.

Andrzejewski, Janusz; Sek, Grzegorz; O'Reilly, Eoin; Fiore, Andrea; Misiewicz, Jan

2010-04-01

110

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

111

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

Science.gov (United States)

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.

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

2014-10-01

112

Conduction properties of the organic superconductor ?-(BEDT-TTF)2Cu(NCS)2 based on Hubbard-unrestricted-Hartree-Fock band calculations  

Science.gov (United States)

The organic superconductor ?-(BEDT-TTF)2Cu(NCS)2 (with Tc=10.4 K) possesses a number of puzzling electronic properties, including the temperature dependence of resistivity, magnetic susceptibility, and Hall coefficient. To provide a basis for understanding these properties, we carried out band calculations using the two-dimensional Hubbard model with the unrestricted-Hartree-Fock theory. The electron transfer hopping interactions are from ab initio calculations. For a Hubbard parameter of UCoul~0.6775 eV, the calculated results give good agreement with Shubnikov-de Haas and magnetic breakdown experiments. The calculations lead to a two-band semimetal with a momentum gap separating the electron and hole bands. The anomalous experimental observations are explained in terms of BEDT-TTF related phonons coupling these two bands. These results also provide a framework for describing the conduction properties of similar BEDT-TTF crystals. This approach should also be useful for other organic conductors.

Demiralp, Ersan; Goddard, William A., III

1997-11-01

113

Further improvements in program to calculate electronic properties of narrow band gap materials  

Science.gov (United States)

The tasks that we have accomplished are discussed. An extra task was a calculation comparing electron mobilities in Mercury Manganese Telluride with Mercury Cadmium Telluride given in 1H. We then list the reports and papers produced and follow that with either abstracts or the papers themselves. In one key paper we obtain good results between experiment and theory in Mercury Zinc Telluride and also find it typically has mobilities competitive with Mercury Cadmium Telluride. In the Appendix we have a relatively complete set of references.

Patterson, James D.

1992-01-01

114

Metal-ceramic interface adhesion: Band structure calculations on Pt-NiO couples  

Energy Technology Data Exchange (ETDEWEB)

A problem of critical technological importance and fundamental scientific interest in materials science and materials engineering is that of adhesion between metals and ceramics. metal-ceramic adhesion is important to such industrial areas as microelectronics, catalysts, protective coatings for metals and metal-ceramic composite materials. Under certain annealing conditions Pt-NiO couples form NiPt intermetallic layers at the interface. It has been suggested that an observed 4-fold increase in the ultimate shear strength of the interface upon inclusion of a 1-nm-thick NiPt interlayer is caused by metal-oxygen bonding at the interface. Extended Huckel calculations, within the tight-binding formalism, have been performed on a series of Pt- and NiPt-NiO metal-ceramic couples to elucidate the nature of the bonding at these interfaces. the calculations showed an approximately 5-fold increase in adhesion energy in NiPt-NiO over Pt-NiO. This attributed to the more efficient electron donating capability of nickel compared to that of platinum. Bonding across the interface is found to decrease with increased electron donation as interfacially antibonding orbitals are filled. Theoretical reasons for the eventual mechanical failure in the oxide component are adduced. 25 refs., 7 figs., 3 tabs.

Boorse, R.S.; Burlitch, J.M.; Hoffmann, R.; Alemany, P. (Cornell Univ., Ithaca, NY (United States))

1993-04-01

115

Band structure calculations of CuAlO2, CuGaO2, CuInO2 and CuCrO2 by screened exchange  

OpenAIRE

We report density functional theory (DFT) band structure calculations on the transparent conducting oxides CuAlO2, CuGaO2, CuInO2 and CuCrO2. The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard local density approximation (LDA) and generalized gradient approximation (GGA) approaches. We show that the resulting electronic band gaps compare well with experimental values and previous quasiparticle calculations and sh...

Gillen, Roland; Robertson, John

2011-01-01

116

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

117

Band-structure and optical-transition parameters of wurtzite MgO,ZnO, and CdO from quasiparticle calculations  

International Nuclear Information System (INIS)

We use Hedin's GW framework to compute quasiparticle bands for group-II monoxides in wurtzite (wz) structure. Modern hybrid density functional theory is applied to compute the starting electronic structure for the solution of the quasiparticle equation. We derive band parameters and effective masses for the three uppermost valence bands as well as the lowest conduction band including spin-orbit coupling. Optical transition matrix elements and exciton binding energies are also calculated. In addition to the prediction of parameters for wz-MgO and wz-CdO we discuss the chemical trend. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

118

Study of SO2 line parameters with a quantum cascade laser spectrometer around 1090cm-1: Comparison with calculations of the ?1 and ?1+?2-?2 bands of 32SO2 and the ?1 band of 34SO2  

International Nuclear Information System (INIS)

SO2 spectra have been recorded with a quantum cascade laser spectrometer at 9?m. Line positions, line strengths and self-broadening coefficients of 42 lines have been precisely determined. All these parameters have shown some discrepancies with those of the HITRAN database. Moreover several lines found in this study were not present in this database. In order to have a complete line list of transitions of SO2 appearing into the recorded spectra, we have performed a new calculation of the ?1 band of 32SO2, the ?1+?2-?2 band of 32SO2 and the ?1 band of 34SO2. This new calculation demonstrates a considerable improvement of the calculations of synthetic spectra of SO2. These new calculations improve the positions (up to 0.03cm-1), the intensities (up to 30%) and the self-broadening coefficients (up to 100%) of the ?1 band of 32SO2 with respect to HITRAN database and permit to obtain a complete set of data for the ?1+?2-?2 band of 32SO2 and the ?1 band of 34SO2 where the positions and strengths are in very good agreement with experimental data

119

Generating function approach to the calculation of spectral band shapes of free-base chlorin including Duschinsky and Herzberg-Teller effects.  

Science.gov (United States)

A generating function approach to the calculation of spectral band shapes including Duschinsky and Herzberg-Teller effects is proposed and applied to the computation of the free-base chlorin Q absorption bands, using molecular geometries and normal vibrations obtained by density functional theory computations. The results clearly show that non-Condon effects can significantly affect the relative intensities of the weakest Q(y) and, to a lesser extent, Q(x) bands. The proposed approach is extremely powerful and can be used in the cases where the molecular size makes the direct calculation of Franck-Condon integrals by recurrence formulas prohibitive. PMID:22978703

Borrelli, Raffaele; Capobianco, Amedeo; Peluso, Andrea

2012-10-11

120

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

OpenAIRE

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 agr...

Boeker, Th; Severin, R.; Mueller, A.; Janowitz, C.; Manzke, R.; Voss, D.; Krueger, P.; Mazur, A.; Pollmann, J.

2001-01-01

121

Surface alloying in the Sn/Ni(111) system studied by synchrotron radiation photoelectron valence band spectroscopy and ab-initio density of states calculations  

International Nuclear Information System (INIS)

Photoelectron spectroscopy using synchrotron radiation and ab-initio electronic structure calculations were used in order to describe the fine structure of the valence band in the Sn/Ni(111) system. The characteristic contributions of each metal in the valence band photoemission spectra obtained with a photon energy of 80 eV and their changes upon the formation of the (?3 x ?3)R30o Sn/Ni(111) surface alloy were also born out in the calculated density-of-states curves in fair agreement with the experiments. The Sn-Ni interaction leads to a considerable broadening of the valence band width at the bimetallic surfaces

122

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)

123

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

Science.gov (United States)

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.

Reshak, A. H.; Azam, Sikander

2013-09-01

124

Crystal structure of Ca (Al H4 )2 predicted from density-functional band-structure calculations  

Science.gov (United States)

Calcium alanate [Ca(AlH4)2] is a candidate material for high-density reversible solid-state hydrogen storage that thus far has been scarcely studied. This paper presents a scheme for solving the crystal structure of a compound based on only a few model structures from similar compounds and employs this to predict the crystal structure and electronic structure of Ca(AlH4)2 . By deliberately breaking the symmetry of the model structures down to P1 , local minima may be avoided, and thus the number of required input models is smaller. Density-functional band-structure calculations within the generalized gradient approximation were used in the structural minimizations. The most stable structure was based on Ca(BaF4)2 and was in the orthorhombic space group Pbca with lattice constants a=1337 , b=928 , and c=891pm . The electronic density of states reveals an insulator with a band gap of around 4eV .

Løvvik, O. M.

2005-04-01

125

Magnetic properties and band structure calculations of YCo2-xMx with M=Cr, Ti  

International Nuclear Information System (INIS)

The YCo2-xMx systems with M = Cr, Ti form solid solutions having MgCu2 -type structure in the composition range x ? 0.4 for M = Cr and x ? 0.2 for M = Ti. Magnetic measurements were performed in the temperature range 4 K - 700 K and fields up to 7 T. At low temperatures, the magnetic susceptibilities, for compounds with Ti, follow a linear T2 dependence. At temperatures higher than a characteristic value T*, a Curie-Weiss type behavior is evidenced. Similar behavior, at high temperatures, was evidenced in YCo2-xCrx system. The experimental data were analysed in spin fluctuation model. Band structure calculations were also performed. The magnetic susceptibilities, at 4 K of YCo2-xTix, as well as their temperature coefficients, in the low temperature range, are reasonable described by using the computed density of states. (orig.)

126

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

127

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)

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

Godtliebsen, Ian H; Christiansen, Ove

2013-07-01

128

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

129

First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb{sub 2}Cl{sub 5}  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Electronic structure of TlPb{sub 2}Cl{sub 5} is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p{sup *} states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb{sub 2}Cl{sub 5} is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb{sub 2}Cl{sub 5} are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb{sub 2}Cl{sub 5} using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb{sub 2}Cl{sub 5} 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 TlPb{sub 2}Cl{sub 5} is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb{sub 2}Cl{sub 5} 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{sup +} ion-irradiated surfaces of a TlPb{sub 2}Cl{sub 5} polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb{sub 2}Cl{sub 5} surface.

Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Bekenev, V.L.; Denysyuk, N.M. [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Parasyuk, O.V. [Department of Inorganic and Physical Chemistry, Eastern European National University, 13 Voli Avenue, Lutsk 43025 (Ukraine); Fedorchuk, A.O. [Department of Inorganic and Organic Chemistry, Lviv National University of Veterinary Medicine and Biotechnologies, Pekarska St., 50, 79010 Lviv (Ukraine)

2014-01-05

130

First-principles calculation of the band offset at BaO/BaTiO$_3$ and SrO/SrTiO$_3$ interfaces  

OpenAIRE

We report first-principles density-functional pseudopotential calculations on the atomic structures, electronic properties, and band offsets of BaO/BaTiO$_3$ and SrO/SrTiO$_3$ nanosized heterojunctions grown on top of a silicon substrate. The density of states at the junction does not reveal any electronic induced interface states. A dominant perovskite character is found at the interface layer. The tunability of the band offset with the strain conditions imposed by the subs...

Junquera, Javier; Zimmer, Magali; Ordejon, Pablo; Ghosez, Philippe

2002-01-01

131

Band gap engineering of (N, Si)-codoped TiO2 from hybrid density functional theory calculations  

International Nuclear Information System (INIS)

We have investigated systematically the influence on electronic properties of anatase-TiO2 of codoping by N and Si at different concentrations using Heyd-Scuseria-Ernzerhof (HSE06) hybrid density functional theory calculations. The optimized total energy shows that TiO2 codoping by N and Si favours a configuration of two substitutional N atoms located at two adjacent O sites, with one substitutional Si atom at their neighbouring Ti site. We show that N-Si codoping can harvest longer-wavelength visible-light than either those of N and Si monodoping, owing to the contribution from N 2p in the ‘forbidden gap’ and Si 3s-3p at the tail of the conduction band. Increasing the N doping concentration leads to a larger extent of gap narrowing, which is directly related to coupling between N atoms. Our results suggest that double-hole coupling plays a key role in similar systems to obtain high visible-light photoactivity in TiO2-based photocatalysts. (paper)

132

Electronic bands and excited states of III-V semiconductor polytypes with screened-exchange density functional calculations  

Energy Technology Data Exchange (ETDEWEB)

The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal Al{sub x}Ga{sub 1?x}P and Al{sub x}Ga{sub 1?x}As alloys, respectively, leads to a direct transition with a gap energy of ?2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials.

Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori [Department of Physics Engineering, Mie University, 1577 Kurima-Machiya, Tsu 514-8507 (Japan); Freeman, Arthur J. [Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208 (United States)

2014-03-31

133

Electronic bands and excited states of III-V semiconductor polytypes with screened-exchange density functional calculations  

Science.gov (United States)

The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal AlxGa1-xP and AlxGa1-xAs alloys, respectively, leads to a direct transition with a gap energy of ˜2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials.

Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori; Freeman, Arthur J.

2014-03-01

134

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)

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

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

2015-02-01

135

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)

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.

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

2015-02-01

136

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)

137

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

138

Conduction properties of the organic superconductor ?-(BEDT-TTF)2Cu(NCS)2 based on Hubbard endash unrestricted-Hartree-Fock band calculations  

International Nuclear Information System (INIS)

The organic superconductor ?-(BEDT-TTF)2Cu(NCS)2 (with Tc=10.4K) possesses a number of puzzling electronic properties, including the temperature dependence of resistivity, magnetic susceptibility, and Hall coefficient. To provide a basis for understanding these properties, we carried out band calculations using the two-dimensional Hubbard model with the unrestricted-Hartree-Fock theory. The electron transfer hopping interactions are from ab initio calculations. For a Hubbard parameter of UCoul?0.6775eV, the calculated results give good agreement with Shubnikov-de Haas and magnetic breakdown experiments. The calculations lead to a two-band semimetal with a momentum gap separating the electron and hole bands. The anomalous experimental observations are explained in terms of BEDT-TTF related phonons coupling these two bands. These results also provide a framework for describing the conduction properties of similar BEDT-TTF crystals. This approach should also be useful for other organic conductors. copyright 1997 The American Physical Society

139

Model construction and superconductivity analysis of organic conductors ?-(BDA-TTP)2MF6 (M = P, As, Sb and Ta) based on first-principles band calculation  

International Nuclear Information System (INIS)

We perform a first-principles band calculation for a group of quasi-two-dimensional organic conductors ?-(BDA-TTP)2MF6 (M = P, As, Sb and Ta). The ab-initio calculation shows that the density of states is correlated with the bandwidth of the singly occupied (highest) molecular orbital, while it is not necessarily correlated with the unit-cell volume. The direction of the major axis of the cross section of the Fermi surface lies in the ?–B-direction, which differs from that obtained by the extended Hückel calculation. Then, we construct a tight-binding model which accurately reproduces the ab-initio band structure. The obtained transfer energies give a smaller dimerization than in the extended Hückel band. As to the difference in the anisotropy of the Fermi surface, the transfer energies along the inter-stacking direction are smaller than those obtained in the extended Hückel calculation. Assuming spin-fluctuation-mediated superconductivity, we apply random phase approximation to a two-band Hubbard model. This two-band Hubbard model is composed of the tight-binding model derived from the first-principles band structure and an on-site (intra-molecule) repulsive interaction taken as a variable parameter. The obtained superconducting gap changes sign four times along the Fermi surface like in a d-wave gap, and the nodal direction is different from that obtained in the extended Hückel model. Anion dependence of Tc is qualitatively cf Tc is qualitatively consistent with the experimental observation. (paper)

140

Band Offsets at the ZnO/Cu2ZnSnS4 Interface Based on the First Principles Calculation  

Science.gov (United States)

Cu2ZnSnS4 (CZTS) is attracting much attention recently as an absorber layer material in a heterojunction solar cell. We evaluate the valence band offset ?Ev at the ZnO/CZTS heterojunction interface by calculating the local density of states for each atom in the heterostructure supercell by the first-principles method. ?Ev is in the range of 0.8-1.3 eV, depending on the interface anion-atom species and the lattice constraint condition. The conduction band minimum of CZTS is predicted to be lower than that of ZnO.

Bao, Wujisiguleng; Ichimura, Masaya

2013-06-01

141

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

Directory of Open Access Journals (Sweden)

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.

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

2008-01-01

142

Energy Band Structure and Optical Response Function of Icosahedral B12As2: A Spectroscopic Ellipsometry and First-principles Calculational Study  

Energy Technology Data Exchange (ETDEWEB)

An experimental and theoretical study on the dielectric-response function of icosahedral B{sub 12}As{sub 2} in the spectral region between 1.24 and 9.8 eV is presented. Comprehensive experimental information on the energy band structure from the analysis of features in the optical dispersion was complemented by spin-orbit first-principles calculations. The lowest indirect band gap width is 3.2 eV; the two lowest direct interband transitions are at 3.46 and 3.9 eV. High-energy critical points are assigned to specific electron transitions in the Brillouin zone and their dimensionality was determined. The static dielectric constant of B{sub 12}As{sub 2} is uniaxially anisotropic with values of 7.84 and 9.02 for polarization perpendicular and parallel to the trigonal axis. Hole and electron effective masses are derived from the band dispersions.

Bakalova, S.; Gong, Y; Cobet, C; Esser, N; Zhang, Y; Edgar, J; Zhang, Y; Dudley, M; Kuball, M

2010-01-01

143

Energy band structure and optical response function of icosahedral B12As2 : A spectroscopic ellipsometry and first-principles calculational study  

Science.gov (United States)

An experimental and theoretical study on the dielectric-response function of icosahedral B12As2 in the spectral region between 1.24 and 9.8 eV is presented. Comprehensive experimental information on the energy band structure from the analysis of features in the optical dispersion was complemented by spin-orbit first-principles calculations. The lowest indirect band gap width is 3.2 eV; the two lowest direct interband transitions are at 3.46 and 3.9 eV. High-energy critical points are assigned to specific electron transitions in the Brillouin zone and their dimensionality was determined. The static dielectric constant of B12As2 is uniaxially anisotropic with values of 7.84 and 9.02 for polarization perpendicular and parallel to the trigonal axis. Hole and electron effective masses are derived from the band dispersions.

Bakalova, S.; Gong, Y.; Cobet, C.; Esser, N.; Zhang, Y.; Edgar, J. H.; Zhang, Y.; Dudley, M.; Kuball, M.

2010-02-01

144

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.

145

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

Science.gov (United States)

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. PMID:25240347

Shimazaki, Tomomi; Nakajima, Takahito

2014-09-21

146

Electronic bands, Fermi surface, and elastic properties of new 4.2 K superconductor SrPtAs with a honeycomb structure from first principles calculations  

International Nuclear Information System (INIS)

New 4.2 K superconductor SrPtAs with a honeycomb structure. Electronic bands, Fermi surface, elastic properties. Predictions from first principles calculations. Comparison with the related layered superconductor SrPt2As2. The hexagonal phase SrPtAs (s.g. P6/mmm; no. 194) with a honeycomb lattice structure was recently declared as a new low-temperature (TC ? 4.2 K) superconductor. Here, by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt2As2.

147

Electronic structure of SrPt4Ge12: a study by soft x-ray photoelectron spectroscopy and band structure calculations  

International Nuclear Information System (INIS)

We present a comparative study of the electronic structure of the superconducting skutterudite SrPt4Ge12 by means of soft X-ray photoelectron spectroscopy and full potential band structure calculations. Excellent agreement between the measured and the calculated valence spectra is observed, confirming the picture of rather localized, low lying Pt 5d states compared to Pt metal. This implicates that the states at the Fermi level stem predominantly from Ge 4p electrons. An analysis of the chemical bonding in SrPt4Ge12 based on the electron localizability indicator is given.

148

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

Science.gov (United States)

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.

Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan

2014-07-01

149

Pseudo-potential band structure calculation of InSb ultra-thin films and its application to assess the n-metal-oxide-semiconductor transistor performance  

International Nuclear Information System (INIS)

The band structure of InSb thin films with (1?0?0) surface orientation is calculated using the empirical pseudopotential method (EPM) to evaluate the performance of nanoscale devices using a InSb substrate. Contrary to the predictions by simple effective mass approximation methods (EMA), our calculation reveals that the ? valley is still the lowest lying conduction valley. Based on EPM calculations, we obtained the important electronic structure and transport parameters, such as effective mass and valley energy minimum, of InSb thin film as a function of the film thickness. Our calculations reveal that the 'effective mass' of ?-valley electrons increases with the scaling down of the film thickness. We also provide an assessment of nanoscale InSb thin film devices using a non-equilibrium Green's function under the effective mass framework in the ballistic regime

150

What is the best DFT functional for vibronic calculations? A comparison of the calculated vibronic structure of the S1-S0 transition of phenylacetylene with cavity ringdown band intensities.  

Science.gov (United States)

The sensitivity of vibronic calculations to electronic structure methods and basis sets is explored and compared to accurate relative intensities of the vibrational bands of phenylacetylene in the S(1)(A(1)B(2)) ? S(0)(X(1)A(1)) transition. To provide a better measure of vibrational band intensities, the spectrum was recorded by cavity ringdown absorption spectroscopy up to energies of 2000 cm(-1) above the band origin in a slit jet sample. The sample rotational temperature was estimated to be about 30 K, but the vibrational temperature was higher, permitting the assignment of many vibrational hot bands. The vibronic structure of the electronic transition was simulated using a combination of time-dependent density functional theory (TD-DFT) electronic structure codes, Franck-Condon integral calculations, and a second-order vibronic model developed previously [Johnson, P. M.; Xu, H. F.; Sears, T. J. J. Chem. Phys. 2006, 125, 164331]. The density functional theory (DFT) functionals B3LYP, CAM-B3LYP, and LC-BLYP were explored. The long-range-corrected functionals, CAM-B3LYP and LC-BLYP, produced better values for the equilibrium geometry transition moment, but overemphasized the vibronic coupling for some normal modes, while B3LYP provided better-balanced vibronic coupling but a poor equilibrium transition moment. Enlarging the basis set made very little difference. The cavity ringdown measurements show that earlier intensities derived from resonance-enhanced multiphoton ionization (REMPI) spectra have relative intensity errors. PMID:22616733

Lopez, Gary V; Chang, Chih-Hsuan; Johnson, Philip M; Hall, Gregory E; Sears, Trevor J; Markiewicz, Beatrice; Milan, Mariana; Teslja, Alexey

2012-06-28

151

Energy band structure calculations of Ga{sub x}In{sub 1?x}P alloys under the influence of temperature and pressure  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Effect of temperature of Ga{sub x}In{sub 1?x}P alloy was calculated. •Effect of hydrostatic pressure of Ga{sub x}In{sub 1?x}P alloy was calculated. •Refractive index and high frequency dielectric constant were studied. •Good agreement between our results and published data was obtained. -- Abstract: This work is concerned with the dependence of the electronic energy band structures for Ga{sub x}In{sub 1?x}P alloys on temperature and pressure. The calculations are based on local empirical pseudo-potential method (EPM) coupled with the virtual crystal approximation (VCA) which incorporates compositional disorder as an effective potential. The direct and indirect energy band gaps of the considered alloys have been determined over entire composition parameter, x from 0 to 1, temperature from T = 0 K to 500 K and pressure from P=0Kbar to 120 Kbar. In addition, the refractive index and dielectric constant of the considered alloys under the effect of composition, temperature and pressure have also been studied. The ternary alloys Ga{sub x}In{sub 1?x}P is bordered by two binary compounds GaP and InP which have been studied recently by our group. Comparison of the calculated results with the experimental and published data showed good agreement.

Degheidy, Abdel Razik; Elwakil, Sayed Abdel Aty; Elkenany, Elkenany Brens, E-mail: kena@mans.edu.eg

2013-10-15

152

The accurate calculation of the band gap of liquid water by means of GW corrections applied to plane-wave density functional theory molecular dynamics simulations.  

Science.gov (United States)

Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For simulations of phase transformations and chemical reactions in water or aqueous solutions whereby an accurate description of the electronic structure is required, we suggest to use these advanced GW corrections in combination with the statistical analysis of quantum mechanical MD simulations. PMID:25388568

Fang, Changming; Li, Wun-Fan; Koster, Rik S; Klimeš, Ji?í; van Blaaderen, Alfons; van Huis, Marijn A

2014-12-01

153

A novel approach to calculation of the second-order nonlinear optical susceptibilities of organic crystals based on energy-band theory  

Science.gov (United States)

The second-order nonlinear optical susceptibilities in five organic crystals are studied based on the EHMO band-structure method. The crystals studied included m-aminophenol, urea, m-dinitrobenzene, POM [3-methyl-4-nitropyridine-1-oxide] and m-nitroaniline. The ?cell tensor components for a unit cell of crystals are calculated by the sum-over-states method. Results are presented for the density of states and second-order nonlinear optical coefficients d(2)(0), which are compared with other existing calculations and experimental data. The overall agreement of our calculations with available data is quite satisfactory. Moreover, the effect of the interactions between neighboring unit cells on the hyperpolarizability tensor components of ?cell is examined and analyzed. The results show that the procedure developed in this work provides a new insight into the second-order susceptibilities of organic molecular crystals, which is important in molecular engineering.

Zhu, Xiao-Lei; You, Xiao-Zeng; Zhang, Yong

2000-04-01

154

Rotational bands in 235U comparison with rotor-plus-quasiparticle calculations using H.F. orbitals  

International Nuclear Information System (INIS)

235U was Coulomb excited with 84Kr beams of 370 and 450 Mev. Observed energy levels are tabulated. Then the spectrum of 235U was determined from self-consistent calculations of the neighboring even-even core nuclei 234U and 236U within a rotor-plus-quasi-particle approach. The calculations reproduced the trends of the experimental low-energy spectrum quite well; this fact confirms the rotational nature of 235U. 1 figure, 2 tables

155

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 and increasing the refractive index of the glass samples. Also it has been found that the uncertainty of the optical basicity estimation is around ±5 to ±15%. Some tables have been reported to help us predict the method used to determine the optical basicity for a glass system accurately.

El-Sayed Mostafa

2005-01-01

156

Semiclassical calculations of half-widths and line shifts for transitions in the 30012?00001 and 30013?00001 bands of CO2. III: Self collisions  

International Nuclear Information System (INIS)

This paper is the third in a series devoted to accurate semi-empirical calculations of pressure-broadened half-widths, pressure-induced line shifts, and the temperature dependence of the half-widths of carbon dioxide. In this work complex Robert-Bonamy (CRB) calculations were made for transitions in two of the Fermi-tetrad bands for self-collisions, i.e. the CO2-CO2 system. The intermolecular potential (IP) was adjusted to match measurements of the half-width, its temperature dependence, and the line shift. It is shown that small changes in the parameters describing the IP lead to noticeable changes in the line shape parameters and that it is possible to find a set of IP parameters, which, when used in the CRB formalism, yield half-widths, their temperature dependence, and line shifts in excellent agreement with measurement. This work demonstrates that this agreement can be obtained if the atom-atom potential is expanded to high order and rank (here 20 4 4), the real and imaginary (S1 and Im(S2)) components are retained, and the determination of the trajectories is made by solving Hamilton's equations. It was found that the temperature dependence of the half-width is sensitive to the range of temperatures used in the fit and that the vibrational dependence of the line shape parameters for these two bands is very small. Databases of the half-width, its temperature dependence, and the line shift for the atmospheres of Venus (2line shift for the atmospheres of Venus (296-700 K fit range for the temperature exponents of the half-widths) and Mars (125-296 K fit range for the temperature exponents of the half-widths) are provided. The calculations are compared with the measured data for the bands under study.

157

Electronic band structure, Fermi surface, and elastic properties of new 4.2K superconductor SrPtAs from first-principles calculations  

OpenAIRE

The hexagonal phase SrPtAs (s.g. P6/mmm; #194) with a honeycomb lattice structure very recently was declared as a new low-temperature (TC ~ 4.2K) superconductor. Here by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with th...

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

2011-01-01

158

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

OpenAIRE

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-el...

Rinke, Patrick; Qteish, Abdallah; Neugebauer, Joerg; Freysoldt, Christoph; Scheffler, Matthias

2005-01-01

159

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

CERN Document Server

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...

Gröger, R

2011-01-01

160

Stability and band gaps of InGaAs, BGaAs, and BInGaAs alloys: Density-functional supercell calculations  

International Nuclear Information System (INIS)

The influence of arrangement and content of substituents (B, In) in BGaAs, InGaAs, and BInGaAs alloys on the stabilities and band gaps is investigated using density-functional supercell calculations. The stability of ternary alloys decreases from InGaAs over BGaAs to GaAsN. Typical substituent structures show the following stability order: isolated substituents - [110] chains - clusters - twisted [111] chains - (200/211) arrangements (most stable). This is valid for both the In- and B-poor as well as the In- and B-rich alloys. From the fact that grown InGaAs provides a different gap than the most stable arrangement one can conclude that other structures (isolated indium atoms or InmAs clusters) are formed during the growth. Simultaneous substitutions (BInGaAs) of larger (In) and smaller (B) atoms prefer arrangements in larger distances (220) for isovalent boron substitution and in In-B bonds for antisite boron substitution. The high degree boron antisite substitution induces partially occupied acceptor bands which lead to a strong reduction of the band gap in comparison to the isovalent substitution. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

161

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

Science.gov (United States)

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).

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

2014-08-01

162

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

CERN Document Server

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...

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

2005-01-01

163

Absorption intensities of rovibronic transitions in the A-band of 16O2: Analysis and calculation of magnetic dipole and electric quadrupole contributions  

Science.gov (United States)

The recently measured magnetic dipole (M1) absorption intensities of rovibronic transitions in the A-band (b?g+1-X?g-3, 030 band) of 16O2 are theoretically analyzed employing a model in which the b?g+1:X?g-3 mutual perturbations are treated to a sufficient degree of accuracy. Effects of rotational perturbations became manifest in the data analysis and rovibronic correction parameters are needed to reconcile theory and experiment. At a subtle level there is evidence of Herman-Wallis (HW) type effect arising from vibration-rotation interaction in the b and X states. The functional form for the HW correction factor is arrived at from first principles. The final calculations reproduce the measured intensities to fraction of a percent, well within the measurement accuracy. The present analysis leads to the value 0,0=0.02679(4) ?B for the M1 transition moment, and the spontaneous emission rate (Einstein-A coefficient) ?0,0=0.0874 s-1. For the sake of completeness, the electric quadrupole (E2) contribution to the observed intensities is also quantitatively assessed.

Balasubramanian, T. K.; Mishra, Adya P.; Kshirsagar, R. J.

2014-01-01

164

RPC Calculations for K-forbidden Transitions in 183W, Evidence for Large Inertial Parameter Connected with High-lying Rotational Bands  

International Nuclear Information System (INIS)

Recent measurements have shown that the transitions deexciting the 453 keV 7/2- level in 183W to the K = 1/2- and 3/2- bands are strongly retarded. The data for B(M1) and B(E2) are analyzed in terms of the RPC model (rotation + particle motion + coupling). With the ?K = 1 (Coriolis) coupling, the K-forbidden M1-transitions proceed via admixtures of high-lying 5/2- bands. A reasonable and unambiguous fit to the data is obtained by varying the strength of the coupling. Allowing for various uncertainties and corrections, one finds that the inertial parameter (the inverse of the coupling constant, i. e. 2J(2?)2/(?)2 may have values between roughly 1 and 3 times the rigid rotator value of 2J(2?)2/(?)2, thus being unexpectedly large. Calculations with the ?K=2 coupling were also performed and turn out not to give better agreement with experiment

165

RPC Calculations for K-forbidden Transitions in {sup 183}W, Evidence for Large Inertial Parameter Connected with High-lying Rotational Bands  

Energy Technology Data Exchange (ETDEWEB)

Recent measurements have shown that the transitions deexciting the 453 keV 7/2{sup -} level in {sup 183}W to the K = 1/2{sup -} and 3/2{sup -} bands are strongly retarded. The data for B(M1) and B(E2) are analyzed in terms of the RPC model (rotation + particle motion + coupling). With the {delta}K = 1 (Coriolis) coupling, the K-forbidden M1-transitions proceed via admixtures of high-lying 5/2{sup -} bands. A reasonable and unambiguous fit to the data is obtained by varying the strength of the coupling. Allowing for various uncertainties and corrections, one finds that the inertial parameter (the inverse of the coupling constant, i. e. 2J(2{pi}){sup 2}/({Dirac_h}){sup 2} may have values between roughly 1 and 3 times the rigid rotator value of 2J(2{pi}){sup 2}/({Dirac_h}){sup 2}, thus being unexpectedly large. Calculations with the {delta}K=2 coupling were also performed and turn out not to give better agreement with experiment.

Malmskog, S.G. [AB Atomenergi, Nykoeping (Sweden); Wahlborn, S. [Div. of Theore tical Physics, Royal Inst. of Technology Stockholm (Sweden)

1967-09-15

166

Characterization of the Fermi surface of BEDT-TTF4[Hg2Cl6].PhCl by electronic band structure calculations  

International Nuclear Information System (INIS)

Tight-binding band structure calculations for the room temperature structure of BEDT-TTF4[Hg2Cl6]-PhCl show the existence of closed electron and hole Fermi surfaces, in agreement with the 2D metallic conductivity of this salt. It is shown that these closed Fermi surfaces result from the hybridization of two hidden 1D Fermi surfaces. However, our study also shows that a transition associated with either a usual or a hidden nesting type mechanism is unlikely. This explains why this salt retains its metallic properties without any resistivity anomaly down to 1.3 K. Our study suggests that BEDT-TTF4[Hg2Cl6]-PhCl is somewhat anisotropic 2D semimetal and should exhibit Shubnikov-de Haas oscillations corresponding to a cross-sectional area of approximately 13% of the first Brillouin zone. (orig.)

167

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

168

Investigation of high-k materials RScO{sub 3}(R=Sm,Gd,Dy) by XPS and band structure calculations  

Energy Technology Data Exchange (ETDEWEB)

There has been considerable interest in high-k-dielectrics rare earth oxides as replacement for SiO{sub 2} in advanced field-effect transistors (FETs). Promising candidates are the perovskites SmScO{sub 3}, GdScO{sub 3} and DyScO{sub 3}. A tendency towards antiferromagnetic ordering at low temperatures is observed for the high magnetic moments at rare earth atoms. We analyse the electronic structure of the single crystalline samples by means of X-ray photoelectron spectroscopy and firstprinciples theory. The electronic structure calculations are performed with the augmented plane waves method (WIEN2k code) of the density functional theory, taking into account the spin-orbit interaction and orbital-dependent potential (LDA+U). The calculated positions of the main features in the valence band agree with the XPS data, the underlying chemical bonding can be analysed in detail. Small differences in the electronic structure, resulting in different stability of ferro and antiferromagnetic configurations, are discussed.

Raekers, M.; Bartkowski, S.; Neumann, M. [Universitaet Osnabrueck, Fachbereich Physik, Osnabrueck (Germany); Kuepper, K.; Zhou, S.; Potzger, K. [FZ Dresden- Rossendorf, Dresden (Germany); Postnikov, A. [Universite Paul Verlaine, Metz (France); Uecker, R. [IKZ, Berlin (Germany)

2007-07-01

169

Spectral characterization, optical band gap calculations and DNA binding of some binuclear Schiff-base metal complexes derived from 2-amino-ethanoic acid and acetylacetone  

Science.gov (United States)

Bi-nuclear metal complexes derived from the reaction of Cu(II), Co(II), Ni(II) and Zn(II) acetates with the Schiff-base ligand (H2L) resulted from the condensation of 2-amino-ethanoic acid (glycine) and acetylacetone have been synthesized and characterized by elemental analyses, Raman spectra, FT-IR, ES-MS, UV-Vis., 1H NMR, ESR, thermal analyses (TG, DTG and DTA) and magnetic measurements. The results showed that, the Schiff base ligand can bind two metal ions in the same time. It coordinates to the first metal ion as mono-negative bi-dentate through azomethine nitrogen and enolic carbonyl after deprotonation. At the same time, it binds to the second metal ion via carboxylate oxygen after deprotonation. The thermodynamic parameters E?, ?H?, ?G? and ?S? have been calculated by Coats-Redfern (CR) and Horowitz-Metzger (HM) methods. The optical band gaps of the isolated complexes have been calculated from absorption spectra and the results indicated semi-conducting nature of the investigated complexes. The interactions between the copper (II) complex and calf thymus DNA (CT-DNA) have been studied by UV spectra. The results confirm that the Cu(II) complex binds to CT-DNA.

Hussien, Mostafa A.; Nawar, Nagwa; Radwan, Fatima M.; Hosny, Nasser Mohammed

2015-01-01

170

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

171

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

Scientific Electronic Library Online (English)

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.

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

2008-11-01

172

Crystal and electronic band structures of homologous compounds ZnkIn2Ok+3 by Rietveld analysis and first-principle calculation  

International Nuclear Information System (INIS)

Crystal structure of homologous compounds, Zn3In2O6, Zn4In2O7, Zn5In2O8, Zn7In2O10, and In2O3 were refined by X-ray Rietveld analysis. Band structures of the homologous compounds were evaluated by first-principle calculation (Cambridge Serial Total Energy Package, CASTEP), using the structural data obtained from the Rietveld analysis. According to the results of CASTEP calculations, a sharp cut-off at the Fermi level could be observed when In3+ preferentially occupies the tetrahedral site (Zn3In2O6(4)) or the trigonal bipyramid site (Zn3In2O6(5)) in the (InZnk)Ok+1+ layers. The cut-off at the Fermi level could not be observed when In3+ and Zn2+ are totally disordered at these sites. Electronic structure calculation suggested that Zn3In2O6(4) is a good conductor and that Zn3In2O6(5) is a poor conductor. Results of geometry optimization indicate that the formation enthalpy of Zn3In2O6(4) was lower than that of Zn3In2O6(5). Considering the electronic structure and the formation enthalpy, Zn3In2O6(4) in which In3+ in tb>6(4) in which In3+ in the (InZnk)Ok+1+ layer occupies the tetrahedral site preferentially, is likely to be the favored structure

173

Efficient and automatic calculation of optical band shapes and resonance Raman spectra for larger molecules within the independent mode displaced harmonic oscillator model  

Science.gov (United States)

In this work, an improved method for the efficient automatic simulation of optical band shapes and resonance Raman (rR) intensities within the "independent mode displaced harmonic oscillator" is described. Despite the relative simplicity of this model, it is able to account for the intensity distribution in absorption (ABS), fluorescence, and rR spectra corresponding to strongly dipole allowed electronic transitions with high accuracy. In order to include temperature-induced effects, we propose a simple extension of the time dependent wavepacket formalism developed by Heller which enables one to derive analytical expressions for the intensities of hot bands in ABS and rR spectra from the dependence of the wavepacket evolution on its initial coordinate. We have also greatly optimized the computational procedures for numerical integration of complicated oscillating integrals. This is important for efficient simulations of higher-order rR spectra and excitation profiles, as well as for the fitting of experimental spectra of large molecules. In particular, the multimode damping mechanism is taken into account for efficient reduction of the upper time limit in the numerical integration. Excited state energy gradient as well as excited state geometry optimization calculations are employed in order to determine excited state dimensionless normal coordinate displacements. The gradient techniques are highly cost-effective provided that analytical excited state derivatives with respect to nuclear displacements are available. Through comparison with experimental spectra of some representative molecules, we illustrate that the gradient techniques can even outperform the geometry optimization method if the harmonic approximation becomes inadequate.

Petrenko, Taras; Neese, Frank

2012-12-01

174

The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity  

Directory of Open Access Journals (Sweden)

Full Text Available A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species and the parameterizations adopted for improving the description of scattering and absorption by clouds and aerosols. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone changes by ±5% in the seasonal mean mixing ratios throughout the troposphere, which induces changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by ~5% and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.

J. E. Williams

2011-09-01

175

The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity  

Directory of Open Access Journals (Sweden)

Full Text Available A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species, the aerosol climatology which is adopted and the parameterizations adopted for improving the description of scattering and absorption by clouds. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone (O3 changes by ±10% in the seasonal mean mixing ratios throughout the troposphere, especially over land. These changes and the perturbations in the photolysis rate of O3 induce changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by ~5 % and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.

J. E. Williams

2012-01-01

176

Cathode catalysts for fuel cell development: A theoretical study based on band structure calculations for tungsten nitride and cobalt tungsten nitrides  

International Nuclear Information System (INIS)

Band structure calculations were performed for tungsten nitride, cobalt tungsten nitrides, and platinum slabs. The major requirements for the development of a superior cathode catalyst are: (1) that the Fermi level of the cathode catalyst is close to the energy level of the lowest unoccupied molecular orbital of O2, the lowest unoccupied atomic orbital of an oxygen atom, and the lowest unoccupied atomic orbital of a hydrogen atom so that they can readily interact with one another; and (2) that the cathode catalysts have smaller ?E value which represent the difference between the Fermi level and the peak position of the density of states of the Op orbital of O2 adsorbed on the catalyst. The active site structures of cobalt tungsten nitrides for activation of the oxygen reduction reaction were found to have the surface structure of Co-O-Co, which lowered the unoccupied orbital of the oxygen atom to approximately that of the Fermi level. However, this structure concomitantly lowered the Fermi level, which resulted in an increase in ?E. Consequently, the optimal cathode catalyst regarding the surface conformation contains a Co-O-Co structure that is dispersed on the surface of the cobalt tungsten nitride. The cobalt tungsten oxynitride exhibited a catalytic activity for the oxygen reduction reaction. A linear dependence is observed between the ?E and the oxygen reduction reaction offset potentials of the tungsten nitride, cobalt tungsteof the tungsten nitride, cobalt tungsten nitride, cobalt tungsten oxynitride, and platinum.

177

Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations  

Science.gov (United States)

A combined experimental-theoretical study of optically pumped nuclear magnetic resonance (OPNMR) has been performed in a GaAs /A l0.1G a0.9As quantum well film epoxy bonded to a Si substrate with thermally induced biaxial strain. The photon energy dependence of the Ga OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from the electronic structure and differential absorption to spin-up and spin-down states of the electron conduction band using a modified k .p model based on the Pidgeon-Brown model. Comparison of theory with experiment facilitated the assignment of features in the OPNMR energy dependence to specific interband Landau level transitions. The results provide insight into how effects of strain and quantum confinement are manifested in optical nuclear polarization in semiconductors.

Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R.

2014-10-01

178

Magnetic properties and band structure calculations of YCo{sub 2-x}M{sub x} with M=Cr, Ti  

Energy Technology Data Exchange (ETDEWEB)

The YCo{sub 2-x}M{sub x} systems with M = Cr, Ti form solid solutions having MgCu{sub 2} -type structure in the composition range x {<=} 0.4 for M = Cr and x {<=} 0.2 for M = Ti. Magnetic measurements were performed in the temperature range 4 K - 700 K and fields up to 7 T. At low temperatures, the magnetic susceptibilities, for compounds with Ti, follow a linear T{sup 2} dependence. At temperatures higher than a characteristic value T{sup *}, a Curie-Weiss type behavior is evidenced. Similar behavior, at high temperatures, was evidenced in YCo{sub 2-x}Cr{sub x} system. The experimental data were analysed in spin fluctuation model. Band structure calculations were also performed. The magnetic susceptibilities, at 4 K of YCo{sub 2-x}Ti{sub x}, as well as their temperature coefficients, in the low temperature range, are reasonable described by using the computed density of states. (orig.)

Tetean, R.; Burzo, E.; Sarkoezi, Z.; Chioncel, L.; Garlea, O. [Babes-Bolyai Univ., Cluj-Napoca (Romania). Faculty of Physics

2001-07-01

179

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

Science.gov (United States)

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).

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

2006-01-01

180

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.

181

Crystallographic and magnetic structure of SrCoO2.5 brownmillerite: Neutron study coupled with band-structure calculations  

Science.gov (United States)

A study of the crystallographic and magnetic structure of SrCoO2.5 with a brownmillerite-type structure has been carried out from neutron powder-diffraction (NPD) measurements at temperatures ranging from 10 to 623 K, across the Néel temperature (TN=537K) of this antiferromagnetic oxide. The study has been complemented with differential scanning calorimeter (DSC), dc susceptibility and magnetization measurements. Although the refinement of the crystal structure from NPD data is possible in the orthorhombic Pnma and Ima2 space groups, the support of ab-initio band-structure calculations has allowed us to select, without ambiguity, the Ima2 space group as the ground state for SrCoO2.5 brownmillerite. In Ima2 the crystallographic structure of SrCoO2.5 is described as layers of corner-sharing Co1O6 octahedra alternating along the a axis with layers of vertex-sharing Co2O4 tetrahedra, conforming chains running along the [0 0 1] direction. The magnetic structure below TN=537K is G -type with the magnetic moments directed along the c axis. This magnetic arrangement is stable from TN down to 10 K. At T=10K , the magnetic moment values for Co1 and Co2 atoms are 3.12(13)?B and 2.88(14)?B , respectively, compatible with a Co2+? state, where ? stands for a ligand hole. The magnetic susceptibility curves show, below 200 K, a divergence of zero-field cooling and field cooling curves, displaying broad maxima which are interpreted as due to the presence of ferromagnetic clusters embedded into an antiferromagnetic matrix. These inhomogeneities are inherent to the synthesis process, by quenching microcrystalline samples of SrCoO3-x composition from high temperature, where cubic, ferromagnetic perovskites have been identified by diffraction methods.

Muñoz, A.; de La Calle, C.; Alonso, J. A.; Botta, P. M.; Pardo, V.; Baldomir, D.; Rivas, J.

2008-08-01

182

The hsub(11/2) negative-parity band structures in sup(119,121)Xe. Comparison between experimental and IBFA calculations  

International Nuclear Information System (INIS)

Systematics of strongly excited collective bands in transitional nuclei have been established from intensive in-beam studies. They show typical trends of level orderings and level spacings directly related to the structure of the nuclei. The paper reports on results concerning the h 11/2 band in 121Xe (N = 67) and 119Xe (N = 65) for which the Fermi energy is below the 7/2- orbital i.e. in a region where the transition from ?I = 1 rotational-like to ?I = 2 decoupled bands occurs. (U.K.)

183

Calculation of equilibria at elevated temperatures using the MINTEQ geochemical code  

Energy Technology Data Exchange (ETDEWEB)

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.

Smith, R.W.

1988-12-01

184

Role of p-d and s-d interactions in the electronic structure and band gap of Zn1-xMxO (M=Cr, Mn, Fe, Co, Ni, and Cu): Photoelectron and optical spectroscopy and first-principles band structure calculations  

Science.gov (United States)

We report an investigation on the effect of p-d and s-d interactions in the electronic structure, and especially in the band-gap value, of wurtzite wide-gap diluted magnetic semiconductors Zn1-xMxO (M=Cr, Mn, Fe, Co, Ni, Cu). Thin films prepared by pulsed laser deposition are investigated by means of optical absorption at low-temperature and photoelectron spectroscopy. Pure wurzite phase is shown to be maintained for Co and Mn concentrations up to 25% and for Cr up to 10%, while in the case of Fe, Ni, and Cu, other phases are present for concentrations higher than 5, 2, and 1%, respectively. The band gap of the Zn1-xMxO alloy increases at a rate of 9, 22, 4, and 23 meV/%M for M=Cr, Mn, Fe, and Co, respectively, and decreases at a rate of about -14 and -10 meV/%M for M=Ni and Cu. Photoelectron spectroscopy of the Zn1-xMxO valence band for M=Mn and Co shows that the emergence of the transition metal-related photoemission peak is clearly correlated to a larger binding energy of the O 2p valence-band peaks. A simple model of p-d and s-d interaction is proposed in which the decrease of Zn 3d electron density below the valence band and the increase of M 3d electron density for M=Cr to Co lead to higher binding energies of the valence-band maximum and, thus, to a larger band gap. In contrast, for Ni and Cu the 3d electrons lie below the valence-band maximum and push it to lower binding energies, thus decreasing the band gap. This simple model is basically confirmed by first-principles density functional theory band structure calculations. Detailed analyses of the band structures and densities of states show that the p-d interaction leads to an increase of the band gap for M=Mn to Co but a decrease for M=Ni and Cu. They also suggest that the s-d interaction plays the major role or contributes as much as the p-d interaction in leading to the increase of the band gap for M=Cr and Mn, respectively.

Gilliland, S. J.; Sans, J. A.; Sánchez-Royo, J. F.; Almonacid, G.; García-Domene, B.; Segura, A.; Tobias, G.; Canadell, E.

2012-10-01

185

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

186

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

187

Cranked Skyrme-Hartree-Fock calculation for superdeformed and hyperdeformed rotational bands in N=Z nuclei from 32S to 48Cr  

CERN Document Server

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 32S, 36Ar, 40Ca, 44Ti, and hyperdeformed solutions in 36Ar, 40Ca, 44Ti, 48Cr. The superdeformed band in 40Ca is found to be extremely soft against both the axially symmteric (Y30) and asymmetric (Y31) octupole deformations. An interesting role of symmetry breaking in the mean field is pointed out.

Inakura, T; Yamagami, M; Matsuyanagi, K

2002-01-01

188

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for CdZnSe  

CERN Document Server

Compound semiconductor alloys of the type ABC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present paper, we concentrate on bulk CdZnSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdZnSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on catalytically grown CdZnSe nanowires reported in the ...

Mourad, Daniel; Klembt, Sebastian; Retzlaff, Reiner; Gartner, Mariuca; Anastasescu, Mihai; Hommel, Detlef; Czycholl, Gerd

2010-01-01

189

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)

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.

Schleife, A; Bechstedt, F

2012-02-15

190

Characterisation of the Fermi surface and phase transitions of (BEDO-TTF)2 ReO4·(H2O) by physical property measurements and electronic band structure calculations  

OpenAIRE

The electronic properties of the organic superconductor (BEDO-TTF)2 ReO4·(H2O) were investigated by temperature dependent resistivity, ESR, Hall effect and magnetoresistance measurements. Shubnikov-de Haas (SdH) oscillations were observed in magnetic fields up to 24 T in the temperature range 0.5 K to 4.2 K. The electronic band structure of (BEDO-TTF)2 ReO4·(H2O) was calculated by employing the extended Hückel tight binding method on the basis of its room temperature crystal structure. The...

Kahlich, Siegfried; Schweitzer, Dieter; Rovira, Concepcio; Paradis, Jeffrey A.; Whangbo, Myung-hwan; Heinen, Ilsabe; Keller, Heimo J.; Nuber, Bernhard; Bele, Petra; Brunner, Hermann; Shibaeva, Rimma P.

1994-01-01

191

Standardization of methods of calculating the weighting functions on the basis of the parameters of the fine structure of the absorption bands of atmospheric gases  

Science.gov (United States)

Point 7 of a list of works conducted by the USSR in accordance with the Joint Soviet-American Research Program on improving methods of heat probes from satellites is discussed. Numerous calculations of transmission functions, along with tables are enclosed.

1978-01-01

192

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.

193

Collective bands in 68Se  

International Nuclear Information System (INIS)

The collective bands of the N = Z nucleus 68Se are studied within our deformed configuration mixing shell model based on Hartree–Fock states. The configuration space consists of the spherical single particle orbits 1p3/2, 0f5/2, 1p1/2 and 0g9/2 with 56Ni as the inert core. A modified Kuo interaction for this basis space has been used in our calculation. The calculated ground band, K = 2+ excited band and the K = 5- excited band agree reasonably well with the experiment. Our calculation shows that the ground band is essentially of oblate shape and the excited K = 2+ band is of prolate shape. This is in agreement with the conclusions drawn from the recent experimental analysis. (author)

194

Theoretical calculations of the optical band positions and zero-field splitting 2D for Cr3+ ions in fluoride garnet Na3Li3In2F12  

International Nuclear Information System (INIS)

Five optical band positions and one EPR zero-field splitting 2D for Cr3+ ions at the trigonally-distorted octahedral In3+ site in fluoride garnet Na3Li3In2F12 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 dn 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 C3 axis) is different from the corresponding one in the host crystal Na3Li3In2F12 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 d3 ions in crystals

195

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.

196

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)

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.

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

2012-01-01

197

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)

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.

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

198

Electronic band structure and Fermi surface of new 3.7 K superconductor LiCu2P2 from first-principles calculations  

International Nuclear Information System (INIS)

Research highlights: ? New ThCr2Si2-like 3.7 K superconductor LiCu2P2 was recently discovered. ? Electronic structure and Fermi surface of this phase were examined by FLAPW-GGA. ? We found that LiCu2P2 may be classified as a (p + d) metal. ? The Fermi surface of LiCu2P2 contains disconnected electronic- and hole-like pockets. ? The bonding for LiCu2P2 is highly anisotropic and includes mixed covalent-ionic bonds. - Abstract: By means of the first-principles calculations, we have studied the structural, electronic properties and the Fermi surface (FS) of the newly discovered ThCr2Si2-like iron- and arsenic-free 3.7 K superconductor LiCu2P2. Our studies showed that LiCu2P2 is an unusual 'intermediate' system, which may be classified as a (p + d) metal, unlike the majority of 122 phases, which are d or sp metals. Unlike FeAs 122 phases having a typical cylinder-like (2D) FS topology, the Fermi surface of LiCu2P2 adopts a 3D-like two-sheet topology formed by disconnected electronic-like and hole-like pockets. The picture of inter-atomic bonding for LiCu2P2 is highly anisotropic and includes mixed covalent-ionic bonds Cu-P (inside [Cu2P2] blocks), direct P-P bonds (between the adjacent [Cu2P2] blocks) to2P2] blocks) together with ionic bonds owing to Li ? [Cu2P2] charge transfer.

199

ELECTRONIC BAND STRUCTURE OF THE ORDERED Zn0.5Cd0.5Se ALLOY CALCULATED BY THE SEMI-EMPIRICAL TIGHT-BINDING METHOD CONSIDERING SECOND-NEAREST NEIGHBOR  

Directory of Open Access Journals (Sweden)

Full Text Available Usually, semiconductor ternary alloys are studied via a pseudo-binary approach in which the semiconductoris described like a crystalline array were the cation/anion sub-lattice consist of a random distribution of thecationic/anionic atoms. However, in the case of reported III-V and II-VI artificial structures, in which anordering of either the cations or the anions of the respective fcc sub-lattice is involved, a pseudo-binaryapproach can no longer be employed, an atomistic point of view, which takes into account the localstructure, must be used to study the electronic and optical properties of these artificial semiconductoralloys. In particular, the ordered Zn0.5Cd0.5Se alloy has to be described as a crystal with the simple-tetragonalBravais lattice with a composition equal to the zincblende random ternary alloy. The change of symmetryproperties of the tetragonal alloy, in relation to the cubic alloy, results mainly in two effects: i reduction ofthe banned gap, and ii crystal field cleavage of the valence band maximum. In this work, the electronicband structure of the ordered Zn0.5Cd0.5Se alloy is calculated using a second nearest neighbor semi-empiricaltight binding method. Also, it is compared with the electronic band structure obtained by FP-LAPW (fullpotentiallinearized augmented-plane wave method.

Juan Carlos Salcedo-Reyes

2008-09-01

200

Electronic band structure, Fermi surface and elastic properties of polymorphs of new 5.2K iron-free superconductor SrPt2As2 from first principles calculations  

OpenAIRE

By means of the first-principles calculations, we have studied in details the structural, elastic and electronic properties of the new tetragonal CaBe2Ge2-type 5.2K superconductor SrPt2As2 in comparison with two hypothetical SrPt2As2 polymorphs with ThCr2Si2-type structures which differ by atomic configurations of [Pt2As2] (or [Pt2As2]) blocks. We have found that CaBe2Ge2-type SrPt2As2 is a quite unique system with complicated 2D-3D character of near-Fermi bands, and the "in...

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

2011-01-01

201

Valence band electronic structure of Nd{sub 1?x}Y{sub x}MnO{sub 3} using X-ray absorption, photoemission and GGA + U calculations  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Decrease in the occupancy of Mn 3d orbitals with doping. •Greater splitting of the e{sub g} 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 Nd{sub 1?x}Y{sub x}MnO{sub 3} (x = 0–0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L{sub 3,2}- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L{sub 3,2}-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–Hubbard type insulator.

Balasubramanian, Padmanabhan, E-mail: padmanabhan@iopb.res.in [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); Institute of Physics, Bhubaneshwar 751005 (India); Nair, Harikrishnan S. [J?lich Center for Neutron Sciences, Forschungszentrum J?lich, Outstation at FRM II, LichtenberGstr. 1, Garching 85747 (Germany); Tsai, H.M. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Bhattacharjee, S. [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Liu, M.T. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); Yadav, Ruchika [Department of Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore 560012 (India); Chiou, J.W. [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Lin, H.J.; Pi, T.W. [National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Tsai, M.H. [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Elizabeth, Suja [Department of Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore 560012 (India); Pao, C.W.; Wang, B.Y.; Chuang, C.H.; Pong, W.F. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China)

2013-08-15

202

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)

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| <= 12 values (11.3% for the first calculation and 8.1% for the second calculation). The O2-pressure shifts whose 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).

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

2006-01-01

203

Band Together!  

Science.gov (United States)

After nearly a decade as band director at St. James High School in St. James, Missouri, Derek Limback knows that the key to building a successful program is putting the program itself above everything else. Limback strives to augment not only his students' musical prowess, but also their leadership skills. Key to his philosophy is instilling a…

Olson, Cathy Applefeld

2011-01-01

204

Chemically induced compaction bands in geomaterials  

Science.gov (United States)

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.

Stefanou, Ioannis; Sulem, Jean

2013-04-01

205

CHEMEOS: A New Chemical-Picture-Based Model for Plasma Equation-of-State Calculations  

International Nuclear Information System (INIS)

We present the results of a new plasma equation-of-state (EOS) model currently under development at the Atomic and Optical Theory Group (T-4) in Los Alamos. This model is based on the chemical picture of the plasma and uses the free-energy-minimization technique and the occupation-probability formalism. The model is constructed as a combination of ideal and non-ideal contributions to the total Helmholtz free energy of the plasma including the effects of plasma microfields, strong coupling, and the hard-sphere description of the finite sizes of atomic species with bound electrons. These types of models have been recognized as a convenient and computationally inexpensive tool for modeling of local-thermal-equilibrium (LTE) plasmas for a broad range of temperatures and densities, We calculate the thermodynamic characteristics of the plasma (such as pressure and internal energy), and populations and occupation probabilities of atomic bound states. In addition to a smooth truncation of partition functions necessary for extracting ion populations from the system of Saha-type equations, the occupation probabilities can also be used for the merging of Rydberg line series into their associated bound-free edges.In the low-density, high-temperature regimes the plasma effects are adequately described by the Debye-Hueckel model and its corresponding contribution to the total Helmholtz free energy of the plasma. In strongly-coupled plasmas, however, the Debye-Hueckel approximation however, the Debye-Hueckel approximation is no longer appropriate. In order to extend the validity of our EOS model to strongly-coupled plasmas while maintaining the analytic nature of our model, we adopt fits to the plasma free energy based on hypernetted-chain and Monte Carlo simulations. Our results for hydrogen are compared to other theoretical models. Hydrogen has been selected as a test-case on which improvements in EOS physics are benchmarked before analogous upgrades are included for any element in the EOS part of the new Los Alamos opacity code ATOMIC

206

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)

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.

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

2002-03-01

207

Elementary energy bands in the band structure of the narrow-band-gap semiconductor CdSb  

Science.gov (United States)

Based upon the example of a narrow band gap covalent CdSb crystal (D2h16) , it is shown that a spatial electron density distribution in the unit cell is related to the Zak’s elementary energy bands creating the valence band and to the corresponding Wyckoff positions. A role of particular electronic states in the creation of the elementary energy bands was analyzed by conducting ab initio band structure calculations of CdSb. The investigations of the topology of the elementrary energy bands allows one to predict the nature of chemical bondings in rhombic crystals.

Bercha, D. M.; Slipukhina, I. V.; Sznajder, M.; Rushchanskii, K. Z.

2004-12-01

208

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.)

209

Band structures in 129Cs  

International Nuclear Information System (INIS)

The 122Sn(11B,4n) fusion-evaporation reaction at Elab=60 MeV was used to populate excited states in 129Cs, and the deexcitations were investigated using in-beam ?-ray spectroscopic techniques. The level scheme of 129Cs is established up to ?8 MeV excitation energy and 47/2 h spin. The observed band structures are interpreted for their configurations in the framework of cranking model calculations and systematic of the neighboring 55Cs isotopes. A negative-parity ?I=1 coupled band has been assigned the ?h11/2 x ?(h11/2)2 configuration as solution of the tilted-axis cranking, which coexists with the ?h11/2 yrast band resulting from the principal-axis cranking. A new band has been identified as a ?-vibrational band built on the ?h11/2 orbital. A pair of strongly coupled positive-parity bands exhibiting similar features have been assigned different unpaired three-quasiparticle configurations involving the ?h11/2 x ?h11/2 component. The previously identified unfavored signature partners of the ?d5/2 and ?g7/2 bands are reassigned as ? vibrations of the core coupled to the ?g7/2 single-particle configuration, and the favored signature of the ?d5/2 band, respectively.

210

Collective band structure in 66Zn  

International Nuclear Information System (INIS)

The collective nature of states in 66Zn has been studied by carrying out a deformed configuration mixing shell model calculation in 1psub(3/2)0fsub(5/2)1psub(1/2)0gsub(9/2) model space. An effective interaction obtained for this space by Kuo has been used. The collective structure for 2 positive-parity bands and 5 negative-parity bands is identified. A qualitative understanding of the backbending at the J = 6+ state in the yrast positive-parity band is given in terms of the band crossing of the ground-state band and the more deformed excited band arising from 2p2h excitation to the gsub(9/2) orbit. Several high-spin members of the observed bands as well as in-band E2 transition strengths have been predicted. (orig.)

211

Calculation and tunneling spectroscopy of the Landau band structure of two laterally coupled quantum Hall systems with adjustable Fermi level (German Title: Berechnung und Tunnelspektroskopie der Landau-Bandstruktur zweier lateral gekoppelter Quanten-Hall-Systeme mit variablem Fermi-Niveau)  

Science.gov (United States)

In the presence of a perpendicular magnetic field, the quasi-free charge carriers of a two-dimensional electron system condense in equidistant and numerously degenerated Landau levels. Variations of the electrostatic potential locally lift the degeneracy and, therefore, cause the formation of Landau bands. A complex Landau band structure exists in the scope of a tunneling barrier which separates two laterally adjacent electron systems. In the case of weak coupling, the band structure may be described approximately as a superposition of the mirror-inverted dispersions of both subsystems with Landau band gaps lifting the degeneracy at the crossing points. The tunneling current through the barrier becomes maximum when the Fermi level coincides with one of the anticrossings. The first part of this thesis presents a method for calculating the Landau band structure of a quantum Hall system with an unidirectional and piecewise constant potential modulation. In the second part, the knowledge of the energy eigenstates is the prerequisite for the analysis of the magnetic field dependent conductance traces of two laterally coupled electron systems. In the scope of the effective mass approximation, the Schrödinger equation is solved for a 2D-electron which resides both in the parabolic magnetic confinement potential and the piecewise constant conduction band offset of an intrinsic semiconductor heterostructure. The exact solution is possible by using an ansatz with parabolic cylinder functions. After discussing the generic properties of the energy spectrum and the corresponding wave functions, a dedicated algorithm for solving the continuity conditions at the heterojunctions is presented for a system consisting of three domains of constant potential. The numerical method yields the Landau band structure in the scope of a tunneling barrier (biased or not) or a rectangular potential well (quantum wire). Generally, the algorithm is applicable for any harmonic oscillator which is superimposed by a two-step potential. For this thesis, two laterally adjacent electron systems separated by a 52 Angstrom thick barrier have been realized in the GaAs/AlGaAs material system by using the technique of cleaved-edge overgrowth (CEO). In comparison to former experiments with modulation-doped electron films (Kang et al., Nature 403, 59 (2000)), the sample design is characterized by a gate electrode which allows for the investigation of a certain Landau band gap at different magnetic fields by adjusting the Fermi level in a suitable way. Instead of preparing several samples for the spectroscopy of the same anticrossing at different barrier widths, the effective shape of the barrier (in units of the magnetic length and the cyclotron energy) may be varied as a function of the magnetic field. The circumvention of the unavoidable fluctuations between successive growth processes is necessary if the small effect of the magnetic shift of the band gaps on the scale of the cyclotron energy or quantum interferences due to random tunneling centers in the barrier are investigated by varying the electron density. For a rising magnetic field, the calculated band structures show an increase of the band gaps on the scale of the cyclotron energy. This effect is confirmed experimentally by a shift of the conductance peaks on the scale of the filling factor towards greater values. At high gate voltages an internal bias builds up due to leakage currents through the barrier of the second growth step. The corresponding distortion of the band structure is observed as a shift of the conductance peaks towards lower filling factors. The tunneling current is not only determined by the band structure and the Fermi level, but it is also substantially affected by randomly spread defects in the barrier which are responsible for a locally enhanced tunnel probability. When the lowest Landau level is completely filled, Aharonov-Bohm (AB) oscillations between opposite edge channels appear due to interference via the tunneling centers. Using the energy eigenfunctions of the interfering

Habl, Matthias

2007-03-01

212

Congenital Constriction Band Syndrome  

Directory of Open Access Journals (Sweden)

Full Text Available Congenital constriction bands are anomalous bands that encircle a digit or an extremity. Congenitalconstriction band syndrome is rare condition and is mostly associated with other musculoskeletaldisorders.We report such a rare experience.

Rajesh Gupta, Fareed Malik, Rishabh Gupta, M.A.Basit, Dara Singh

2008-04-01

213

Amniotic constriction bands  

Science.gov (United States)

Pseudo-ainhum; Streeter's dysplasia; Amniotic band sequence; Amniotic band syndrome ... Amniotic constriction bands are caused by damage to a part of the placenta called the amnion. The placenta carries ...

214

Band Structures of the Nucleus 129Cs  

International Nuclear Information System (INIS)

High-spin states in 129Cs are populated via the 122Sn (11B, 4n) reaction at beam energies of 55 and 60 MeV. Two additional bands are placed in the level scheme and the previously known bands are extended to higher spins. The results are compared to the cranked shell model calculations and to the systematics of the adjacent Cs isotpoes. One of the new bands is interpreted as the ?-vibrational band built on the ?h11/2 orbital. The possible configuration for another new band is discussed. Upbend caused by (vh11/2)2 alignment is observed both in the favored and unfavored sequences of the ?h11/2 configuration. The band based on the ?g7/2 configuration at low spins forks around spin 17/2, and the two different S-bands are attributed to (vh11/2) and (?h11/2)2 rotational alignments, respectively

215

Band structure and electron level population in plane channeling  

International Nuclear Information System (INIS)

The method of band structure calculation of electrons moving in a plane channel is proposed. The energy band structure for the channel (110) in silicon and tungsten is calculated. It is shown that at 20 MeV the bands degenerate into the levels. The band population is investigated depending on electron energy and monocrystal angle of incidence. Population inversion is the greatest at angles of incidence not exceeding the Bragg angle

216

Band Structure and Effective Masses of ZnMgO  

OpenAIRE

We analyze the influence of the Mg concentration on several important properties of the band structure of ZnMgO alloys in wurtzite structure using ab initio calculations. For this purpose, the band structure for finite concentrations is defined in terms of the Bloch spectral density, which can be calculated within the coherent potential approximation. We investigate the concentration dependence of the band gap and the crystal-field splitting of the valence bands. The effecti...

Franz, Christian; Giar, Marcel; Heinemann, Markus; Czerner, Michael; Heiliger, Christian

2013-01-01

217

Come Join the Band  

Science.gov (United States)

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…

Olson, Cathy Applefeld

2011-01-01

218

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

219

Reinvestigation of Collective Bands in 107Tc  

International Nuclear Information System (INIS)

The high spin states of a neutron-rich 107Tc nucleus are reinvestigated by observing prompt ?-rays from the spontaneous fission of 252Cf. The previous level scheme is updated. A collective band based on the ?5/2? [303] orbital is confirmed and extended. Inconsistencies in the configuration assignments for a type of positive parity bands of odd-A 105,107,109Tc in the previous reports are clarified according to the g factor calculations. A new band based on the 1499.5 keV level in 107Tc is proposed as a two-phonon ?-vibrational band

220

Band structure of boron doped carbon nanotubes  

CERN Document Server

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 with the delocalized carbon $\\pi$-orbitals. Irregular (random) boron-doping leads to a high concentration of hybrids of acceptor and unoccupied carbon states above the Fermi edge.

Wirtz, L; Wirtz, Ludger; Rubio, Angel

2003-01-01

221

Band structures in 99Rh  

Science.gov (United States)

Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at {{E}_{lab}}=120\\;MeV and the de-excitations were investigated through in-beam ?-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the \\pi {{p}_{1/2}} and \\pi {{g}_{9/2}} configurations. The \\Delta I = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the \\pi {{g}_{9/2}}\\otimes \

Kumar, S.; Singh, V.; Singh, K.; Sihotra, S.; Singh, N.; Goswamy, J.; Malik, S. S.; Ragnarsson, I.; Trivedi, T.; Singh, R. P.; Muralithar, S.; Kumar, R.; Bhowmik, R. K.; Palit, R.; Bharti, A.; Mehta, D.

2014-10-01

222

Direct band gap silicon allotropes.  

Science.gov (United States)

Elemental silicon has a large impact on the economy of the modern world and is of fundamental importance in the technological field, particularly in solar cell industry. The great demand of society for new clean energy and the shortcomings of the current silicon solar cells are calling for new materials that can make full use of the solar power. In this paper, six metastable allotropes of silicon with direct or quasidirect band gaps of 0.39-1.25 eV are predicted by ab initio calculations at ambient pressure. Five of them possess band gaps within the optimal range for high converting efficiency from solar energy to electric power and also have better optical properties than the Si-I phase. These Si structures with different band gaps could be applied to multiple p-n junction photovoltaic modules. PMID:24971657

Wang, Qianqian; Xu, Bo; Sun, Jian; Liu, Hanyu; Zhao, Zhisheng; Yu, Dongli; Fan, Changzeng; He, Julong

2014-07-16

223

Collective Band Structures and Identification of One-Phonon and Two-Phonon ?-Vibrational Bands in 109Tc  

International Nuclear Information System (INIS)

The high spin states of the neutron-rich 109Tc nucleus are reinvestigated by observing prompt ?-rays from the spontaneous fission of 252Cf. The previously known yrast band based on the 7/2+ state is updated. A side band built on the 11/2+ state is expanded and a new band based on the 15/2+ state is identified. Band crossing in the yrast band occurs around ?? ? 0.36MeV. This band crossing is associated with the alignment of two h11/2 neutrons according to the cranked shell model calculations. The band based on the 11/2+ state is proposed as a candidate for the one-phonon ?-vibrational band, and the band built on the 15/2+ state is proposed as a candidate for the two-phonon ?-vibrational band. Other characteristics for the observed bands are discussed. (nuclear physics)

224

Band structure in 77,79Sr  

International Nuclear Information System (INIS)

We have investigated the structure of the collective bands in 77,79Sr within our deformed configuration mixing (DCM) shell model based on Hartree-Fock states. In our model, the single particle orbits 1p3/2, 0f5/2, 1p1/2 and 0g9/2 are taken as the configuration space with 56Ni as the core. A modified Kuo interaction for this basis space is used in our calculation. The different levels are classified into collective bands on the basis of the B(E2) values among them. The calculated collective bands and the B(E2) values are compared with available experimental data. Our calculation is able to reproduce the identical bands observed in 77Sr, 78Sr and 78Rb. (author)

225

Frustration phenomena in Josephson point contacts between single-band and three-band superconductors  

OpenAIRE

Within the formalism of Usadel equations the Josephson effect in dirty point contacts between single-band and three-band superconductors is investigated. The general expression for the Josephson current, which is valid for arbitrary temperatures, is obtained. We calculate current-phase relations for very low temperature and in the vicinity of the critical temperature. For three-band superconductors with broken time-reversal symmetry (BTRS) point contacts undergo frustration ...

Yerin, Y. S.; Omelyanchouk, A. N.

2014-01-01

226

Systematic Study of Electronic Phases, Band Gaps and Band Overlaps of Bismuth Antimony Nanowires  

OpenAIRE

We have developed an iterative one dimensional model to study the narrow band-gap and the associated non-parabolic dispersion relations for bismuth antimony nanowires. An analytical approximation has also been developed. Based on the general model, we have developed, we have calculated and analyzed the electronic phase diagrams and the band-gap/band-overlap map for bismuth antimony nanowires, as a function of stoichiometry, growth orientation, and wire width.

Tang, Shuang; Dresselhaus, Mildred

2013-01-01

227

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

OpenAIRE

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...

Olguin, D.; Baquero, R.

1996-01-01

228

Quasiparticle band-edge energy and band offsets of monolayer of molybdenum and tungsten chalcogenide  

OpenAIRE

We report the quasiparticle energy of monolayer of molybdenum and tungsten dichalcogenides, MX2 (M=Mo, W; X=S, Se, Te). Beyond calculating bandgaps, we have achieved converged absolute band energies relative to the vacuum level. Compared with the results from other approaches, the GW calculation reveals substantially larger bandgaps and different absolute band energies because of enhanced many-electron effects. Interestingly, our fully-converged quasiparticle energies ratify...

Liang, Yufeng; Huang, Shouting; Soklaski, Ryan; Yang, Li

2013-01-01

229

Relative intensity calculations for nitrous oxide.  

Science.gov (United States)

A tabulation of calculated rotational line intensities, relative to the integrated intensity of a vibration-rotation band, is given for Sigma-Sigma, Pi-Sigma, Sigma-Pi, Pi-Pi, and Delta-Pi transitions of nitrous oxide. These calculations were made for temperatures of 250 K and 300 K. A summary of band-intensity measurements is also presented.

Young, L. D. G.

1972-01-01

230

Ground States Rotational Band in Deformed e-e Nuclei  

CERN Document Server

In the frame work of the hydrodynamical model, a new model of the ground state rotational bands of deformed e-e nuclei is developed by introducing the variable moment of inertia, and the effect of beta- and gamma- vibrational bands. The model is applied to calculate the energies of the ground state band of 158Dy. The results of our calculations are in close agreement with data compared with other existing models.

Kelabi, M E; Singh, V; Kelabi, Mohamed E.; Singh, Vikram

2005-01-01

231

Bulk band gaps in divalent hexaborides  

International Nuclear Information System (INIS)

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for proper inclusion of many-body effects in quasi-particle band calculations

232

Conduction bands in the filled skutterudites  

Science.gov (United States)

Some filled skutterudite compounds have recently been found to exhibit very interesting properties: a metal-insulator transition (PrRu4P12), an antiferroquadrupole ordering and heavy-fermion behaviour under magnetic fields (PrFe4P12) and a new class of heavy-fermion superconductivity (PrOs4Sb12). Such varied and interesting physical properties are thought to reflect the Fermi surface properties. Band structure calculations have revealed the characteristics of the conduction bands. The main conduction band consisting of p orbitals of pnictogen surrounding the rare-earth ions has a nesting property, and strongly hybridizes with one of 4f electrons. One of the other conduction bands does not have mixing matrix elements with 4f electrons, resulting in the unique band structure in CeOs4Sb12.

Harima, Hisatomo; Takegahara, Katsuhiko

2003-07-01

233

Properties of terminating bands in nuclei  

International Nuclear Information System (INIS)

General properties of terminating bands are briefly reviewed and exemplified on the observed high-spin properties of 158Er and 156Er. The very similar features of the positive parity high-spin spectra of the N=88 isotones of Dy, Er and Yb are pointed out and discussed. The possibility of estimate B(E2)-values in terminating bands from measured feeding times is explored. The spin contribution from different orbitals is calculated in terminating bands as well as more collective bands. One aim is to get some idea of the interaction between different configurations and to this end we also consider a single-j shell model. The limits of terminating bands in the yrast region when the number of valence nucleons increases is discussed. The usefulness of these results when planning future experimental studies is considered. (orig.)

234

Crystal structure, electronic structure, and thermoelectric properties of AuTlSb: A new pyrite superstructure  

International Nuclear Information System (INIS)

The ternary compound AuTlSb adopts a new structure type in the orthorhombic space group Pna21 with lattice constants a = 6.5507(8) A, b 14.2871(18) A, c = 6.5254(9) A. The structure contains Au atoms octahedrally coordinated to Sb-Sb and Tl-Tl dimers, and can be viewed as an ordered superstructure of AuSb2 (pyrite). In addition to the synthesis and crystal structure of AuTlSb, we report extended Hueckel band structure calculations and bonding analysis, as well as electrical resistivity and thermopower measurements between 80 K and 300 K. For comparison, we include the results from extended Hueckel calculations on the parent structure AuSb2. The band structure calculations predict AuTlSb to be metallic, which is in agreement with the transport properties measurements

235

Crystal structure, electronic structure, and thermoelectric properties of AuTlSb: A new pyrite superstructure  

Energy Technology Data Exchange (ETDEWEB)

The ternary compound AuTlSb adopts a new structure type in the orthorhombic space group Pna2{sub 1} with lattice constants a = 6.5507(8) A, b 14.2871(18) A, c = 6.5254(9) A. The structure contains Au atoms octahedrally coordinated to Sb-Sb and Tl-Tl dimers, and can be viewed as an ordered superstructure of AuSb{sub 2} (pyrite). In addition to the synthesis and crystal structure of AuTlSb, we report extended Hueckel band structure calculations and bonding analysis, as well as electrical resistivity and thermopower measurements between 80 K and 300 K. For comparison, we include the results from extended Hueckel calculations on the parent structure AuSb{sub 2}. The band structure calculations predict AuTlSb to be metallic, which is in agreement with the transport properties measurements.

McGuire, Michael A. [Department of Physics, Clark Hall, Cornell University, Ithaca, NY 14853 (United States); Reynolds, Thomas K. [Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853 (United States); DiSalvo, Francis J. [Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853 (United States)]. E-mail: fjd3@cornell.edu

2006-11-30

236

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)

237

Luminosity calculation  

International Nuclear Information System (INIS)

The luminosity of the Tevatron collider was calculated. The data used for the calculation are the flying wire transverse beam profile and the SBD bunch profile. For the 900 GeV/c mini beta runs, the calculation was compared to the CDF luminosity monitor. The ratio of the calculation and C:BOLUMP is 0.95. 1 ref., 9 figs., 4 tabs

238

Superconducting instability in 3 band metallic nanotubes  

OpenAIRE

Motivated by recent experiments on small radius nanotubes, we study the superconducting instabilities of cylindrical (5,0) nanotubes. According to band structure calculations, thesenanotubes possess three bands at the Fermi energy. Using a fermionic renormalization group approach and a careful bosonization treatment,we consider the effect of different attractive interactions, mediated by phonons, within the Luttinger Liquid framework. We particularly focus on a superconduct...

Carpentier, David; Orignac, Edmond

2006-01-01

239

Superconductivity in W{sub 5}SiB{sub 2} with the T{sub 2}-phase structure studied by the specific heat measurement and band structure calculation  

Energy Technology Data Exchange (ETDEWEB)

The new superconductor W{sub 5}SiB{sub 2} with the T{sub 2}-phase. H{sub C2} (0) is estimated in greater detail. W{sub 5}SiB{sub 2} can be described within the conventional framework of BCS theory. W d-orbital plays an important role for the superconductivity. The superconducting state of W{sub 5}SiB{sub 2} with the T{sub 2}-phase structure has been investigated by a specific heat measurement and a density of state calculation. The estimated {Delta}C{sub p}/{gamma}T{sub c} and 2{Delta}(0)/k{sub B}T{sub c} values are 1.49 and 3.32, which are close to 1.43 and 3.53 within the weak coupling regime. The electronic specific heat data clearly indicates the absence of gap nodes in the superconducting order parameter, suggesting an isotropic s-wave superconductor. From the density of state calculations, we found that W d-orbital plays an important role for the superconductivity in W{sub 5}SiB{sub 2}.

Fukuma, M., E-mail: fukuma.0816@phys.aoyama.ac.jp [Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe 5-10-1, Chuo-ku, Sagamihara-shi, Kanagawa 229-8558 (Japan); Kawashima, K.; Maruyama, M.; Akimitsu, J. [Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe 5-10-1, Chuo-ku, Sagamihara-shi, Kanagawa 229-8558 (Japan)

2011-11-15

240

Multiple band structures of 131Cs  

International Nuclear Information System (INIS)

Excited states in 131Cs were investigated through in-beam ?-ray spectroscopic techniques following its population in the 124Sn(11B, 4n) fusion-evaporation reaction at a beam energy of 46 MeV. The previously known level scheme has been substantially extended up to ?9 MeV excitation energy and 49/2(?/2?) spin with the addition of seven new band structures. The present level scheme consisting of 15 bands exhibits a variety of collective features in this nucleus at intermediate spin. The excitation energies of the observed levels in different bands and the corresponding ratios of transition strengths, i.e., B(M1)/B(E2), have been compared with the results of projected deformed Hartree-Fock calculations based on various quasiparticle configurations. A strongly coupled band has been reassigned a high-K three-quasiparticle ?h11/2 x ?(h11/2d3/2) configuration based on the properties of this band and that of its new coupled side band. The configurations of these bands are also discussed in the framework of tilted-axis cranking model calculations and the systematics of the odd-A Cs isotopes. Additional three energetically closely placed coupled bands have been assigned different unpaired three-quasiparticle configurations. ?-vibrational bands coupled to the ?h11/2 and ?g7/2 single-particle configurations have been reported in this nucleus. Observation of new E1 transitions linkingn of new E1 transitions linking the opposite-parity ?h11/2 and ?d5/2 bands provides fingerprints of possible octupole correlations

241

Electronic band structure of beryllium oxide  

International Nuclear Information System (INIS)

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 ? 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

242

Electronic band structure of beryllium oxide  

CERN Document Server

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.

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

2003-01-01

243

Band structure parameters of the nitrides: The origin of the small band gap of InN  

CERN Document Server

Using a band-structure method that includes the correction to the band gap error in the local density approximation (LDA), we study the chemical trends of the band gap variation in III-V semiconductors and predict that the band gap for InN is 0.8 +/- 0.1 eV, which is much smaller than previous experimental value of approx. 1.9 eV. The unusually small band gap for InN is explained in terms of the high electronegativity of nitrogen and consequently the small band gap deformation potential of InN. The possible origin of the measured large band gaps is discussed in terms of the non-parabolicity of the bands and the Moss-Burstein shift. Based on the error analysis of our LDA calculation and available experimental data we have compiled the recommended band structure parameters for wurtzite AlN, GaN and InN.

Wei, S H; Wei, Su-Huai; Carrier, Pierre

2004-01-01

244

Adaptive Confidence Bands  

OpenAIRE

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 ...

Genovese, Christopher R.; Wasserman, Larry

2007-01-01

245

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

OpenAIRE

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 t...

Ramires, Aline; Continentino, Mucio A.

2010-01-01

246

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

247

Chiral bands in 105Rh  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The 105Rh nucleus has been studied by in-beam gamma spectroscopy with the heavy-ion fusion-evaporation reaction 100Mo(11B, 02ngamma) at 43 MeV. A rich variety of structures was observed at high and low spin, using gamma - gamma - t and gamma - gamma - particle coincidences a [...] nd directional correlation ratios. Four magnetic dipole bands have also been observed at high spin. Two of them are nearly degenerate in excitation energy and could be chiral partners, as predicted by Tilted Axis Cranking calculations.

J.A., Alcántara-Núñez; J.R.B., Oliveira; E.W., Cybulska; N.H., Medina; M.N., Rao; R.V., Ribas; M.A., Rizzutto; W.A., Seale; F., Falla-Sotelo; K.T., Wiedemann; V.I., Dimitrov; S., Frauendorf.

2004-09-01

248

Born Effective Charges of Barium Titanate band by band decomposition and sensitivity to structural features  

CERN Document Server

The Born effective charge tensors of Barium Titanate have been calculated for each of its 4 phases. Large effective charges of Ti and O, also predicted by shell model calculations and made plausible by a simplified model, reflect the partial covalent character of the chemical bond. A band by band decomposition confirms that orbital hybridization is not restricted to Ti and O atoms but also involves Ba which appears more covalent than generally assumed. Our calculations reveal a strong dependence of the effective charges on the atomic positions contrasting with a relative insensitivity on isotropic volume changes.

Ghosez, P; Lambin, P; Michenaud, J P; Ghosez, Ph.; Lambin, Ph.

1994-01-01

249

Singing with the Band  

Science.gov (United States)

Usually band, orchestra, and choir directors work independently. However, the authors--one a choral director, the other a band director--have learned that making music together makes friends. Not only can ensemble directors get along, but joint concerts may be just the way to help students see how music can reach the heart. Combined instrumental…

Altman, Timothy Meyer; Wright, Gary K.

2012-01-01

250

Stretch Band Exercise Program  

Science.gov (United States)

This article discusses how to use stretch bands for improving total body fitness and quality of life. A stretch band exercise program offers a versatile and inexpensive option to motivate participants to exercise. The authors suggest practical exercises that can be used in physical education to improve or maintain muscular strength and endurance,…

Skirka, Nicholas; Hume, Donald

2007-01-01

251

Progressive Band Selection  

Science.gov (United States)

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.

Fisher, Kevin; Chang, Chein-I

2009-01-01

252

Electronic band structure of lithium, sodium and potassium fluorides  

International Nuclear Information System (INIS)

A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good

253

Electronic band structure of transparent conductor. Nb-doped anatase TiO2  

International Nuclear Information System (INIS)

We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements. The band calculations revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form a d-nature condition band, without impurity states in the in-gap region, resulting in high carrier density exceeding 1021 cm-3 and excellent optical transparency in the visible region. Furthermore, we confirmed that the results of valence band and core-level photoemission measurements are consistent with prediction by the present band calculations. (author)

254

LHC Bellows Impedance Calculations  

CERN Document Server

To compensate for thermal expansion the LHC ring has to accommodate about 2500 bellows which, together with beam position monitors, are the main contributors to the LHC broad-band impedance budget. In order to reduce this impedance to an acceptable value the bellows have to be shielded. In this paper we compare different designs proposed for the bellows and calculate their transverse and longitudinal wakefields and impedances. Owing to the 3D geometry of the bellows, the code MAFIA was used for the wakefield calculations; when possible the MAFIA results were compared to those obtained with ABCI. The results presented in this paper indicate that the latest bellows design, in which shielding is provided by sprung fingers which can slide along the beam screen, has impedances smaller tha those previously estimated according to a rather conservative scaling of SSC calculations and LEP measurements. Several failure modes, such as missing fingers and imperfect RF contact, have also been studied.

Dyachkov, M

1997-01-01

255

The surface band structure of W(112)  

International Nuclear Information System (INIS)

Both the experimental and theoretical band structure of the W(112) surface are presented, with the theoretical band structure calculated by the film-LAPW (linearized augmented plane waves) method. The results permit one to compare the W(112) and Mo(112) band structures and illuminate the similarities. It is found that for the W(112) surface the main photoemission features combine contributions from both the surface and bulk, as has been previously noted for Mo(112). The main differences between the electronic structures of the furrowed W(112) and Mo(112) surfaces are seen in the width of occupied bands. The differences are attributed to the extent of localization of valence 4d and 5s electrons in Mo and 5d and 6s electrons in W. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

256

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1996-12-31

257

Photonic band gap in thin wire metamaterials.  

Science.gov (United States)

We investigate the band structure of a class of photonic crystals made from only thin wires. Using a different method, we demonstrate that a complete photonic band gap is possible for such materials. Band gap materials normally consist of space filling dielectric or metal, whereas thin wires occupy a very small fraction of the volume. We show that this is related to the large increase in scattering at the Brillouin zone boundary. The method we developed brings together the calculation techniques in three different fields. The first is the calculation of scattering from periodic, tilted antennas, which we improve upon. The second is the standard technique for frequency selective surface design. The third is obtained directly from low energy electron diffraction theory. Good agreements with experiments for left handed materials, negative materials, and frequency selective surfaces are demonstrated. PMID:18517551

Hock, Kai Meng

2008-03-01

258

Multi bunch dynamics in detuned x-band structures  

International Nuclear Information System (INIS)

The multi bunch dynamics of a 2 x 250 GeV version of the JLC is studied. The rf-properties of detuned x-band tubes are calculated with the Computer codes URMEL and MAFIA. The dispersion curve found with these codes is compared with an equivalent circuit model. The calculation of the dipole mode loss parameters is investigated in detail. Tracking calculations are used to investigate the misalignment tolerances for detuned x-band structures. Also tilted x-band tubes are considered. (author)

259

Level density calculation for deformed nuclei  

International Nuclear Information System (INIS)

Level densities for the rare earth and actinide nuclei have been calculated using a modified version of the Ericson formalism. The assumption was made, that K (the projection of J on the symmetry axis of the nucleus) is a good quantum number in the compound nucleus. Individual level densities for the different (K,J) values of the compound nucleus formed by low energy neutron interactions were calculated. The results show good agreement with the interpretation of recent results obtained on U-235 in this laboratory. Using the above calculations it is also possible to infer from the measured level densities the locations of the band heads of different K bands in the compound nucleus. The results also indicate that the K bands responsible for the level densities exclude the ground state rotational band. Levels built on the higher lying ? and ? vibrational bands and their composites are sufficient in number to explain the observed level densities. 4 tables

260

Laparoscopic adjustable gastric banding.  

Science.gov (United States)

The introduction of laparoscopic adjustable silicone gastric banding (LASGB) has recently revolutionized gastric restrictive procedures in the treatment of morbid obesity. We analysed the short and long term results of this minimally invasive bariatric procedure. A total of 652 patients with a body mass of (median) 45 kg/m(2) were treated. There were only minor preoperative incidents. One patient died more than one month after the procedure. Early postoperative complications included 2 gastric perforations caused by a nasogastric tube and one early slipping of the band. Late complications occurred in 7% of the patients: 25 patients suffered a pouch dilation, 2 patients had gastric erosion by the band; 18 patients had port complications requiring reoperation. Loss of excess weight was 62% at 2 years. Laparoscopic adjustable gastric banding is a safe and effective treatment for morbid obesity. The most frequent complication is pouch dilation. Further study is warranted for the evaluation of long term results. PMID:12152153

Cadière, G B; Himpens, J; Hainaux, B; Gaudissart, Q; Favretti, S; Segato, G

2002-06-01

261

Band Topology or Geometry?  

OpenAIRE

The study of topology of energy bands in solid has always been interesting and fruitful. Historically, Thouless et al proposed the TKNN number or Chern number of the energy bands to explain the quantization of Hall conductance in the integer quantum Hall effect. Recently, Z2 topological insulators have been intensively studied and similarly topological crystalline insulators are proposed.These materials exhibit nontrivial charge or spin transport properties that is due to th...

Wu, Yi-dong

2011-01-01

262

Amniotic band syndrome.  

OpenAIRE

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. AB...

Jovana ?or?evi?; Branislav Jovanovi?; Marina ?or?evi?; Gordana Trifunovi?; Velimir Kosti?; Jelena Radovi?; Lidija Popovi?

1983-01-01

263

Photonic band structure for a superconductor-dielectric superlattice  

International Nuclear Information System (INIS)

The photonic band structure in the transversal electric mode for a one-dimensional superconductor-dielectric superlattice is theoretically calculated. By using the Abeles theory for a stratified medium, we first calculate the transmittance spectrum from which all the possible bands can be directly seen. Then we calculate the real photonic band structure based on the transcendental equation derived from the transfer matrix method and Bloch theorem. The band structure is shown to be strongly consistent with the transmittance spectrum. We finally study the three lowest band gaps as a function of penetration of superconductor, permittivity of dielectric, and angle of incidence, respectively. The optical properties in a superconductor-dielectric superlattice thus are well disclosed

264

Superdeformed band in asymmetric N > Z nucleus 40Ar  

International Nuclear Information System (INIS)

A rotational band with five cascade ?-ray transitions was newly found in 40Ar. The deduced transition quadrupole moment of 1.45-0.31+0.49 eb has demonstrated this band as having a superdeformed shape of ?2 - 0.5. The structure of the band was discussed in the framework of cranked Hartree-Fock-Bogoliubov calculations and the assignment of multiparticle-multihole configuration has been made. (author)

265

First triaxial superdeformed band in {sup 170}Hf  

Energy Technology Data Exchange (ETDEWEB)

First evidence is presented for triaxial superdeformation in {sup 170}Hf. High-spin states in this nucleus have been investigated in a {gamma}-ray coincidence measurement using the EUROBALL spectrometer array. A new band was discovered which has moments of inertia that are very similar to the ones of triaxial superdeformed bands in neighbouring Hf and Lu nuclei. The intensities with which these bands are populated are different from what may be expected from calculated potential-energy minima. (orig.)

Neusser, A.; Huebel, H.; Bringel, P.; Domscheit, J.; Mergel, E.; Nenoff, N.; Singh, A.K. [Helmholtz-Institut fuer Strahlen- und Kernphysik, Universitaet Bonn, Nussallee 14-16, D-53115 Bonn (Germany); Hagemann, G.B.; Jensen, D.R. [Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark); Bhattacharya, S. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064 (India); Curien, D.; Dorvaux, O. [Institut de Recherches Subatomiques, 23 Rue du Loess, F-67037 Strasbourg (France); Hannachi, F.; Lopez-Martens, A. [Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, F-91405 Orsay Campus (France)

2002-12-01

266

Analytical results for random band matrices with preferential basis  

CERN Document Server

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.

Frahm, K M

1995-01-01

267

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.

268

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)

269

Weak morphology dependent valence band structure of boron nitride  

Science.gov (United States)

We report a hard X-ray photoelectron spectroscopy (HX-PES) investigation on valence band structure of Boron Nitrides (BN) having different morphologies, including nanosheets, nanotubes, and micro-sized particles. Very weak morphology/valence band structure dependence was observed. For each case, the B-N ?-band overlapping with ?-band between 0 to -12.5 eV and the s-band below -15 eV were identified. No obvious morphology-induced band shifts and intensity variations were observed. First-principles calculations based on density functional theory were performed and the results were compared with the experimental data. This theoretical analysis well explains the weak morphology dependent valence band spectra of BN nanomaterials obtained during HX-PES measurements.

Zhi, Chunyi; Ueda, Shigenori; Zeng, Haibo; Wang, Xuebin; Tian, Wei; Wang, Xi; Bando, Yoshio; Golberg, Dmitri

2013-08-01

270

Chaotic Calculations.  

Science.gov (United States)

Uses chaos theory to investigate the nonlinear phenomenon of population growth fluctuation. Illustrates the use of computers and computer programs to make calculations in a nonlinear difference equation system. (MDH)

Chenery, Gordon

1991-01-01

271

Exploring the origin of degenerate doublet bands in $^{106}$Ag  

CERN Document Server

The electromagnetic transition probabilities of the excited levels for the two nearly degenerate bands of $^{106}$Ag have been measured using the Doppler Shift Attenuation Method. A comparison with the calculated values using triaxial projected shell model approach indicates that these bands originate from two different quasi-particle configurations but constructed from the same mean-field deformation.

Rather, N; Chattopadhyay, S; Roy, S; Rajbanshi, S; Gowsami, A; Bhat, G H; Sheikh, J A; Palit, R; Pal, S; Saha, S; Sethi, J; Biswas, S; Singh, P; Jain, H C

2013-01-01

272

Study of titanium oxide bands in red giant spectra  

International Nuclear Information System (INIS)

The effect of model atmosphere parameters Tsub(eff) and lg g on theoretical intensities of TiO bands is examined. A comparison of the observed and calculated intensity drops at the selected TiO ?-system band heads shows a resonable accordance

273

Quantitative band mapping of crystals from resonant inelastic X-ray scattering  

Energy Technology Data Exchange (ETDEWEB)

Using measurements of resonant inelastic X-ray scattering (RIXS) spectra and k-momentum conservation, quantitative site and symmetry projected band mapping is realized for broad sp-band materials Si and BP. It is shown that agreement between experimental and calculated band dispersion for Si and BP is observed only if Si 3d and P 3d states are taken into account in the band structure calculations.

Sokolov, A.V.; Finkelstein, L.D.; Kurmaev, E.Z.; Shin, S.; Karimov, P.F.; Skorikov, N.A.; Postnikov, A.V. E-mail: apostnik@uos.de

2004-07-01

274

Nontrivial topological states on a Möbius band  

Science.gov (United States)

In the field of topological insulators, the topological properties of quantum states in samples with simple geometries, such as a cylinder or a ribbon, have been classified and understood during the past decade. Here we extend these studies to a Möbius band and argue that its lack of orientability prevents a smooth global definition of parity-odd quantities such as pseudovectors. In particular, the Chern number, the topological invariant for the quantum Hall effect, lies in this class. The definition of spin on the Möbius band translates into the idea of the orientable double cover, an analogy used to explain the possibility of having the quantum spin Hall effect on the Möbius band. We also provide symmetry arguments to show the possible lattice structures and Hamiltonian terms for which topological states may exist in a Möbius band, and we locate our systems in the classification of topological states. Then, we propose a method to calculate Möbius dispersions from those of the cylinder, and we show the results for a honeycomb and a kagome Möbius band with different types of edge termination. Although the quantum spin Hall effect may occur in these systems when intrinsic spin-orbit coupling is present, the quantum Hall effect is more intricate and requires the presence of a domain wall in the sample. We propose an experimental setup which could allow for the realization of the elusive quantum Hall effect in a Möbius band.

Beugeling, W.; Quelle, A.; Morais Smith, C.

2014-06-01

275

Band structure of A2B6 compounds  

International Nuclear Information System (INIS)

The band structure of the ZnS, ZnSe, ZnTe, CdS, CdSe and CdTe compounds of the sphalerite modification with provision for the s-, p-, d- states is calculated by the modified method of orthogonalized plane waves (MOPW). The calculation is carried out to find out the nature of interaction between the d electrons of a metal and s, p electrons of a nonmetal. The effect of the Zn and Cd d-states on the energy characteristics of the whole band spectrum of halcogenides of these metals is analyzed in detail. All the compounds under investigation, except CdTe, have the valent d band of the metal higher than the s band of the nonmetal. The first G sub(1c)-d band energy transition corresponds to 13.6-14.0 eV. The energy gaps between the 5s points of the Te band and the lower band of the conductivity band are following Gsub(1c)-Xsub(1v)-11.8 eV, Gsub(1c)-Lsub(1v)-12.1eV, 13.0 eV. The rest experimentally observed CdTe transitions in the > 10 eV range are interpreted as transitions between the Te 5s band and the lower zone of the conductivity band

276

Quantum properties of optical field in photonic band gap structures  

OpenAIRE

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. (C) 2001 Optical Society of America.

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

2001-01-01

277

New materials for intermediate band photovoltaic cells. A theoretical and experimental approach  

OpenAIRE

Density functional theory calculations of certain transition-metal doped semiconductors show a partially occupied relatively narrow band located between valence band and conduction band. These novel systems, containing the metallic band, are called intermediate-band materials. They have enhanced optoelectronic properties which allow an increase in solar energy conversion efficiency of conventional solar cells. We previously proposed III-V, chalcopyrite and sulfide derived compounds show...

Wahno?n Benarroch, Perla; Palacios Clemente, Pablo; Aguilera Bonet, Irene; Semino?vski Pe?rez, Yohanna; Conesa, Jose Carlos; Lucena, Raquel

2010-01-01

278

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

Directory of Open Access Journals (Sweden)

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

Worasak SUKKABOT

2014-05-01

279

Banded transformer cores  

Science.gov (United States)

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.

Mclyman, C. W. T. (inventor)

1974-01-01

280

Ultra wide band antennas  

CERN Document Server

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

Begaud, Xavier

2013-01-01

281

Flat band ferromagnetism without connectivity conditions in the flat band  

OpenAIRE

It is known that a system which exhibits a half filled lowest flat band and the localized one-particle Wannier states on the flat band satisfy the connectivity conditions, is always ferromagnetic. Without the connectivity conditions on the flat band, the system is non-magnetic. We show that this is not always true. The reason is connected to a peculiar behavior of the band situated just above the flat band.

Gulacsi, Miklos; Kovacs, Gyorgy; Gulacsi, Zsolt

2014-01-01

282

Strain-tunable band gap of hydrogenated bilayer graphene  

International Nuclear Information System (INIS)

First-principles calculations have been utilized to investigate the biaxial strain-dependent electronic properties of fully hydrogenated bilayer graphene. It has been found that after complete hydrogenation, bilayer graphene exhibits semiconducting characteristics with a wide direct band gap. The band gap can be tuned continuously by the biaxial strain. Furthermore, compressive strain can induce the semiconductor-to-metal transition of this hydrogenated system. The origin of the strain-tunable band gap is discussed. The present study suggests the possibility of tuning the band gap of fully hydrogenated bilayer graphene by using mechanical strain and may provide a promising approach for the fabrication of electromechanical devices based on bilayer graphene.

283

Micromechanics of slip bands on a free surface  

Science.gov (United States)

A micromechanics analysis for the formation and propagation of slip bands on the free surface of a polycrystal under monotonic loading is presented. For the growth of slip bands, the analysis satisfies the conditions of both equilibrium and displacement continuity, as well as the relation between slip and the resolved shear stress throughout the polycrystal. Numerical calculations show how the microstress field causes the concentration of plastic deformation in discrete sliding bands and give results which are in good qualitative agreement with known slip band observations on aluminum single crystals.

Lin, S. R.; Lin, T. H.

1976-01-01

284

Photonic band structure of highly deformable, self-assembling systems  

CERN Document Server

We calculate the photonic band structure at normal incidence of highly deformable, self-assembling systems - cholesteric elastomers subjected to external stress. Cholesterics display brilliant reflection and lasing owing to gaps in their photonic band structure. The band structure of cholesteric elastomers varies sensitively with strain, showing new gaps opening up and shifting in frequency. A novel prediction of a total band gap is made, and is expected to occur in the vicinity of the previously observed de Vries bandgap, which is only for one polarisation.

Bermel, P A; Bermel, Peter A.; Warner, Mark

2001-01-01

285

Wobbling motion in the multi-bands crossing region  

OpenAIRE

The backbending in the A=180 mass region is expected to be caused by multi-bands crossing between low-K (g- and s-bands) and high-K bands. % We analyze a mechanism of coupling of these bands in terms of a dynamical treatment for nuclear rotations, i.e., the wobbling motion. The wobbling states are produced through the generator coordinate method after angular momentum projection, in which the intrinsic states are constructed through the 2d-cranked HFB calculations.

Oi, Makito; Ansari, Ahmad; Horibata, Takatoshi; Onishi, Naoki

1998-01-01

286

Numerical calculations  

International Nuclear Information System (INIS)

While the analytical solutions of the equations of motion can be useful in the effort to develop new general concepts for the application of quadrupole fields, they have been replaced by numerical methods when specific calculations or computer simulations are required. Such methods have involved either numerical integration or the use of matrices. Numerical calculation of ion trajectories using point-by-point integration of the Mathieu equation has been extensively applied to determining ion trajectories in all types of quadrupole devices and has contributed a great deal to the understanding of their performance. One limitation of numerical integration is the necessity to repeat the calculation for each combination of an initial position and an initial velocity. Calculations can be scaled when there is an initial displacement but no initial velocity (or vice versa) as, for example, with an ion beam entering the mass filter parallel to the instrument (z) axis. However, such a beam is unlikely in a real case when fringing fields are present. A second limitation has been the cost of making detailed computer simulations for rf fields consisting of a sufficient number of rf cycles. For these reasons, newly developed techniques using matrix methods with analyses based on phase-space dynamics are now replacing numerical integration. (Auth.)

287

Mercury Calculator  

Science.gov (United States)

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.

Foundation, Wgbh E.

2010-12-23

288

Calculation Nation  

Science.gov (United States)

This web site, which is part of the NCTM Illuminations project, allows students to challenge themselves or opponents from anywhere in the world by playing games that are organized around content from the upper elementary and middle grades math curriculum. The games allow students to learn about fractions, factors, multiples, symmetry, as well as practice important skills like basic multiplication and calculating area.

2011-01-01

289

Rubber Band newton Scale  

Science.gov (United States)

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.

Rathjen, Don

2009-01-01

290

Band taut sutured manifolds  

CERN Document Server

Attaching a 2-handle to a genus two or greater boundary component of a 3-manifold is a natural generalization of Dehn filling a torus boundary component. We prove that there is an interesting relationship between an essential surface in a sutured 3-manifold, the number of intersections between the boundary of the surface and one of the sutures, and the cocore of the 2-handle in the manifold after attaching a 2-handle along the suture. We use this result to show that tunnels for tunnel number one knots or links in any 3-manifold can be isotoped to lie on a branched surface corresponding to a certain taut sutured manifold hierarchy of the knot or link exterior. In a subsequent paper, we use the theorem to prove that band sums satisfy the cabling conjecture, and to give new proofs that unknotting number one knots are prime and that genus is superadditive under band sum. To prove the theorem, we introduce band taut sutured manifolds and prove the existence of band taut sutured manifolds.

Taylor, Scott A

2011-01-01

291

Rubber Band Thermodynamics  

Science.gov (United States)

In this demonstration, learners explore the thermal properties of rubber. Learners investigate whether a rubber band contracts or expands when heated. Learners discover that when rubber is heated it behaves differently than most familiar materials. Most materials expand when they are heated, but rubber contracts.

2012-04-09

292

Amniotic band syndrome.  

Science.gov (United States)

Amniotic band syndrome is an uncommon congenital disorder without any genetic or hereditary disposition. It involves fetal entrapment in strands of amniotic tissue and causes an array of deletions and deformations. Primary treatment is plastic and reconstructive surgery after birth with in utero fetal surgery also coming in vogue. PMID:24426485

Shetty, Prathvi; Menezes, Leo Theobald; Tauro, Leo Francis; Diddigi, Kumar Arun

2013-10-01

293

Configuration assignment to ground state rotational band of 184Au  

International Nuclear Information System (INIS)

Recently, the rotational level scheme of 184Au has been investigated by means of in-beam ? -ray spectroscopy techniques. On the basis of a comparison of the measured and calculated B(M1)/B(E2) ratios, Li et al. suggested a highly mixed character for the ground state two quasiparticle (2qp) rotational band of 184Au. In this paper, the configuration assignment to ground state band of 184Au is revisited in terms of Two Quasi-Particle Rotor Model (TQPRM) calculations. Our results further strengthen the earlier proposed configuration assignments to this band

294

Structure of various K bands in 178Hf  

International Nuclear Information System (INIS)

Many bands of states are now known experimentally in the nucleus 178Hf. These bands seem to have K as a good quantum number and some of the band-heads are isomers. The structure of this nucleus has been studied by doing Hartree-Fock calculation using a ''modified surface delta interaction'' with one active ma or shell for each of protons and neutrons and with 132Sn as the core. There is axial symmetry in the calculation, but no time-reversal symmetry for the K/O bands. Solutions obtained are K = 0+, 8- and 24- with prolate deformation and a K = 0+ intrinsic state with oblate deformation. Considering the prolate Hartree-Fock solutions and particle-hole excitations across their Fermi surfaces, it has been possible to obtain the bands seen experimentally. The isomerism of the bands can be explained by the microscopic calculation. Two K = 16+ bands, one band with two unpaired protons and two unpaired neutrons, and the other with four unpaired neutrons are obtained. (auth.)

295

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)

296

ELECTRONIC BAND STRUCTURE AND PHOTOEMISSION : A REVIEW AND PROJECTION  

OpenAIRE

A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types : (i) ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations ; (ii) surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby ; (iii)...

Falicov, L.

1987-01-01

297

Quasiparticle band structure of antiferromagnetic Eu Te  

International Nuclear Information System (INIS)

The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor Eu Te is derived by use of a combination of a many-body model procedure with a tight-binding-'linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d-f model for a single band electron ('test electron') being exchange coupled to the anti ferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d-f model are taken from a TB-LMTO calculation for paramagnetic Eu Te. The d-f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice-quasiparticle band structure (S-QBS) and sublattice-quasiparticle density of states (S-QDOS) of the unoccupied 5 d-6 s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles ('magnetic polarons') are worked out in detail. The temperature dependence of the S-QDOS and S-QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from TN to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5 d-6 s) spin exchange processes between (5 d-6 s) conduction band electrons and localized 4 f moments. (author)

298

Calculator thermometer  

Energy Technology Data Exchange (ETDEWEB)

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.

Huray, P. G.; Nave, S. E.

1979-01-01

299

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

300

Search for positive parity bands in 117Xe  

International Nuclear Information System (INIS)

Excited states of 117Xe were populated via the reaction 28Si+92Mo at 100-120MeV. More than 40 new ?-transitions and three new positive parity bands have been observed by means of in-beam ?-ray spectroscopy. The previously known ?h11/2 bands were confirmed, and the ?g7/2 favored band was extended up to 47/2+ in which two bandcrossings have been observed at h?=0.33 and 0.44MeV, respectively. The band structures have been discussed by means of TRS and CSM calculations. A newly observed rotational band consisting of five ?-transitions has been considered as the ?h11/2 band of 117Cs. ((orig.))

301

Elucidating the stop bands of structurally colored systems through recursion  

CERN Document Server

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...

Amir, Ariel

2012-01-01

302

Susceptibilities for first principles band structures  

Science.gov (United States)

We present a parallel implementation of a new method for calculating the unenhanced susceptibility proposed by us recently. Our implementation uses the first principles LMTO band structure within the tight binding approach as input to calculate the joint density of states. The susceptibility is then obtained by integrating over the product of the joint density of states and a Lindhard function. Our program, which has a simple friendly user interface, runs on the PC with a quadputer board, a Meiko Surface running CSTools powered either by T800 or i860 compute boards and the Intel iPSC/860 hypercube in Daresbury. Our method incorporates the troublesome matrix elements naturally and our results on Pd and Ni show that the decrease in ?( q) as we go away from the Brillouin zone centre is due mainly to the matrix elements rather than to the band energies.

Crockford, D. J.; Yeung, W.

1993-04-01

303

Structure of positive-parity yrast band in sup 8 sup 0 Br 27.50.+e; 21.10.Re; 21.10.Tg; NUCLEAR REACTION 76 Ge( 7 Li, 3n); Enriched targets; E = 32 MeV; Measured E gamma,I gamma,gamma-gamma-t; DCO ratios; Doppler shifts; 80 Br; Deduced levels; J pi; (E2); band structure; Comparison with cranked-shell model calculations  

CERN Document Server

The states of the positive-parity yrast band in sup 8 sup 0 Br have been investigated using the sup 7 sup 6 Ge( sup 7 Li, 3n gamma ) reaction at a beam energy of 32 MeV. The band has been extended up to 4450 keV with a spin of (14 sup + ). Unambiguous spin assignments are made for states up to 2944.0 keV and gamma -ray multipole mixing ratios are determined for several DELTA J=1 transitions. Lifetimes studies for the 10 sup + , 11 sup + and 12 sup + states provide an estimate of the quadrupole deformation in this band. Cranking model analysis of the experimental data reveals a signature inversion at a spin of 12 Planck constant and a probable neutron alignment at Planck constant omega approx 0.7 MeV. The results are discussed within the framework of the systematics of similar bands in the lighter Br isotopes and the cranked-shell model. In addition, a new positive-parity and two negative-parity sequences have been identified.

Ray, I; Bhattacharya, S; Saha-Sarkar, M; Muralithar, S; Singh, R P; Bhowmik, R K

2000-01-01

304

Mach bands in mammography.  

Science.gov (United States)

The radiologic appearance of tissue surrounding a tumor often influences the characterization of a cancerous lesion. An example is the radiolucent halo that is sometimes seen around breast cancers. Mammograms of 108 malignant tumors (74 scirrhous tumors, 17 partially scirrhous nodular tumors, and 17 nodular tumors) and eight benign tumors that showed peritumoral fat were retrospectively evaluated. All the scirrhous and partially scirrhous nodular cancers were more or less surrounded by a 5-10-mm-wide hyperlucent halo; this corona sign was also found in 14 nodular cancers. The halo sign, a hyperleucent 1-mm band, was observed around all benign lesions and immediately adjacent to sharply delineated cancers. These radiologic findings are an optical illusion (Mach band, background contrast effect). Densitometric measures and isoluminous analysis did not demonstrate the presence of a true hyperlucent zone. PMID:2843941

Gordenne, W H; Malchair, F L

1988-10-01

305

Photonic Band Gap  

Science.gov (United States)

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.

Ho, Seng-Tiong

306

AMNIOTIC BAND SYNDROME  

Directory of Open Access Journals (Sweden)

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.

Jovana ?or?evi?

2009-04-01

307

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.)

308

Banded electromagnetic stator core  

Science.gov (United States)

A stator core for an electromagnetic pump includes a plurality of circumferentially adjoining groups of flat laminations disposed about a common centerline axis and collectively defining a central bore and a discontinuous outer perimeter, with adjacent groups diverging radially outwardly to form V-shaped gaps. An annular band surrounds the groups and is predeterminedly tensioned to clamp together the laminations, and has a predetermined flexibility in a radial direction to form substantially straight bridge sections between the adjacent groups. 5 figures.

Fanning, A.W.; Gonzales, A.A.; Patel, M.R.; Olich, E.E.

1994-04-05

309

Photoperiod Calculator  

Science.gov (United States)

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.

Lammi, Jarmo J.

1999-01-01

310

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)

311

Line shape of light absorption of surface band-to-band electron transitions  

International Nuclear Information System (INIS)

The surface bands existence have been experimentally confirmed for the most of facets of semiconductors (Si(III), Ge(III), GaAs(1OO) and others) by photoelectron spectroscopy. It is assumed that the electron transitions from the lowest donor-like band to the higher acceptor-like band are influenced by external radiation and the energy absorption probability depends on the absorption surface properties. The bands narrow enough with beforehand electron energy dispersions are considered as a function of quasimomenta in each of them. Electron wave functions contain only momenta along the surface. The probability transitions calculation is carried out according to standard formulas including primary electrons dispersion probability on the states of the lowest band ?(kII) as a function of KII. The summation with the pulse conservation law accounting is fulfilled over all final states. Besides it is supposed that the electrons are thermalized and their interactions with the thermostat might be also accounted with the help of a phenomenological parameter ?. As a result of the calculations the line-shape of absorption expressed through the transition probability is found to depend essentially on the correlation of the following three parameters: the phenomenological parameter ?, the band-width difference of the two considered bands ?L L2-L1 and the temperature of crystal. From the physical point of view the case when ? L >> 3 ?int of view the case when ? L >> 3 ? is the most interesting. In this case the form of absorption curves at fixed ?L in broad temperature interval changes weakly whereas at fixed T and increasing ?L it is changed considerably (from Lorentz to bell-like). (author)

312

Remote Sensing Interactive: Band Combination  

Science.gov (United States)

Band Combination is one of a number of interactive tools being developed to illustrate basic remote sensing concepts. Here, the user is able to experiment with RGB bands on three different image modes: MODIS, ASTER and LANDSAT.

313

Hyperspectral bands prediction based on inter-band spectral correlation structure  

Science.gov (United States)

Hyperspectral imaging has been widely studied in many applications; notably in climate changes, vegetation, and desert studies. However, such kind of imaging brings a huge amount of data, which requires transmission, processing, and storage resources for both airborne and spaceborne imaging. Compression of hyperspectral data cubes is an effective solution for these problems. Lossless compression of the hyperspectral data usually results in low compression ratio, which may not meet the available resources; on the other hand, lossy compression may give the desired ratio, but with a significant degradation effect on object identification performance of the hyperspectral data. Moreover, most hyperspectral data compression techniques exploits the similarities in spectral dimensions; which requires bands reordering or regrouping, to make use of the spectral redundancy. In this paper, we analyze the spectral cross correlation between bands for AVIRIS and Hyperion hyperspectral data; spectral cross correlation matrix is calculated, assessing the strength of the spectral matrix, we propose new technique to find highly correlated groups of bands in the hyperspectral data cube based on "inter band correlation square", and finally, we propose a new technique of band regrouping based on correlation values weights for different group of bands as network of correlation.

Ahmed, Ayman M.; Sharkawy, Mohamed El.; Elramly, Salwa H.

2013-02-01

314

Bandcrossing of magnetic rotation bands in 137Pr  

International Nuclear Information System (INIS)

The odd mass nucleus 137Pr has been studied to high spins in order to investigate the magnetic rotation phenomenon in mass 130 region using the 122Sn(19F,4n)137Pr reaction at a beam energy of 80 MeV. A known ?I=1 band has been extended to J?=47/2- with the addition of three new transitions. Directional Correlation of Oriented Nuclei (DCO) ratios and linear polarization measurements have been performed to assign the multipolarities of gamma transitions and the spins and parities of the energy levels in this band, now established as the M1 band. The combination of M1 transitions along with cross over E2 transitions have been observed in this band for the first time. The experimentally deduced B(M1)/B(E2) ratios show a decrease with increasing spin after band-crossing suggesting magnetic rotation. TAC calculations for the 3qp: ?h11/2 x ?(h11/2)-2 configuration reproduce the experimental observations in the lower spin part of the ?I=1 band and the 5qp: ?h11/2(g7/2)2 x ?(h11/2)-2 configuration reproduces the ?I=1 band at higher spins; the crossing of the bands based on the two configuration leads to a back-bending also. Theoretical calculations also support a magnetic rotation nature for both the configurations

315

Viscoelastic shear banding in foam  

OpenAIRE

Shear banding is an important feature of flow in complex fluids. Essentially, shear bands refer to the coexistence of flowing and non-flowing regions in driven material. Understanding the possible sources of shear banding has important implications for a wide range of flow applications. In this regard, quasi-two dimensional flow offers a unique opportunity to study competing factors that result in shear bands. One proposal is the competition between intrinsic dissipation and...

Krishan, Kapilanjan; Dennin, Michael

2008-01-01

316

Probability Calculator  

Science.gov (United States)

This tool lets you calculate the probability that a random variable X is in a specified range, for a variety of probability distributions for X: the normal distribution, the binomial distribution with parameters n and p, the chi-square distribution, the exponential distribution, the geometric distribution, the hypergeometric distribution, the negative binomial distribution, the Poisson distribution, and Student's t-distribution. The first choice box lets you select a probability distribution. Depending on the distribution you select, text areas will appear for you to enter the values of the parameters of the distribution. Parameters that are probabilities (e.g., the chance of success in each trial for a binomial distribution) can be entered either as decimal numbers between 0 and 1, or as percentages. If you enter a probability as a percentage, be sure to include the percent sign (%) after the number.

Stark, Philip B.

317

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.)

318

The narrow pass band filter of tunable 1D phononic crystals with a dielectric elastomer layer  

International Nuclear Information System (INIS)

In this paper, we study the defect bands of a 1D phononic crystal consisting of aluminum (Al) and polymethyl methacrylate (PMMA) layers with a dielectric elastomer (DE) defect layer. The plane wave expansion (PWE) method and supercell calculation are used to calculate the band structure and the defect bands. The transmission spectra are obtained using the finite element method (FEM). Since the thickness of the dielectric elastomer defect layer is controlled by applying an electric voltage, the frequencies of the defect bands can be tuned. A narrow pass band filter can be developed and designed by using the dielectric elastomer

319

Broad band waveguide spectrometer  

Science.gov (United States)

A spectrometer for analyzing a sample of material utilizing a broad band source of electromagnetic radiation and a detector. The spectrometer employs a waveguide possessing an entry and an exit for the electromagnetic radiation emanating from the source. The waveguide further includes a surface between the entry and exit portions which permits interaction between the electromagnetic radiation passing through the wave guide and a sample material. A tapered portion forms a part of the entry of the wave guide and couples the electromagnetic radiation emanating from the source to the waveguide. The electromagnetic radiation passing from the exit of the waveguide is captured and directed to a detector for analysis.

Goldman, Don S. (Folsom, CA)

1995-01-01

320

Semiconductors bonds and bands  

CERN Document Server

As we settle into this second decade of the twenty-first century, it is evident that the advances in micro-electronics have truly revolutionized our day-to-day lifestyle. The technology is built upon semiconductors, materials in which the band gap has been engineered for special values suitable to the particular application. This book, written specifically for a one semester course for graduate students, provides a thorough understanding of the key solid state physics of semiconductors. It describes how quantum mechanics gives semiconductors unique properties that enabled the micro-electronics revolution, and sustain the ever-growing importance of this revolution.

Ferry, David K

2013-01-01

321

Ab Initio Calculations of Oxosulfatovanadates  

DEFF Research Database (Denmark)

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.

FrØberg, Torben; Johansen, Helge

1996-01-01

322

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)

323

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

324

Calculation of Gilbert damping in ferromagnetic ?lms  

OpenAIRE

The Gilbert damping constant in the phenomenological Landau-Lifshitz-Gilbert equation which describes the dynamics of magnetization, is calculated for Fe, Co and Ni bulk ferromagnets, Co ?lms and Co/Pd bilayers within a nine-band tight-binding model with spin-orbit coupling included. The calculational effciency is remarkably improved by introducing ?nite temperature into the electronic occupation factors and subsequent summation over the Matsubara frequencies. The calculated dependence of...

Edwards D. M.; Cinal M.; Barati E.; Umerski A.

2013-01-01

325

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.

326

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

327

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

Directory of Open Access Journals (Sweden)

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.

Crnjanski Jasna V.

2004-01-01

328

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

OpenAIRE

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.

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

1986-01-01

329

Theory of two-photon absorption by exciton states in cubic semiconductors with degenerate valence bands  

International Nuclear Information System (INIS)

The coefficient of the absorption of two polarized photons is calculated for direct band gap semiconductors with degenerate valence bands. Wannier-Mott exciton states are included in both the intermediate and final states. Numerical calculations are performed for ZnSe and are compared with Sondergeld's experimental and theoretical results. (author). 11 refs, 2 tabs

330

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)

331

A Multi-band Wavelet Watermarking Scheme  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents a new multi-band wavelet watermarking scheme. Compared with conventional watermarking schemes implemented in two-band wavelet domain, by incorporating the principal component analysis (PCA technique the proposed blind watermarking in the multi-band wavelet domain can achieve higher perceptual transparency and stronger robustness. Specifically, the developed watermarking scheme can successfully resist common signal processing such as JPEG compression with quality factor as low as 15, and some geometric distortions such as cropping (cropped by 50\\%. In addition, the proposed multi-band wavelet based watermarking scheme can be parameterized, thus resulting in more security. That is, an attacker may not be able to detect the embedded watermark if the attacker does not know the parameter. Different from many other watermarking schemes, in which the watermark detection threshold is chosen empirically, the false positive rate of the proposed watermarking scheme can be calculated analytically so that watermark detection threshold can be chosen based solely on the targeted false positive.

Xiangui Kang

2008-03-01

332

Quasiparticle band gaps of boron nitride nanoribbons  

Science.gov (United States)

We present a systematic study on the quasiparticle band gaps of armchair boron nitride nanoribbons (ABNNRs) as a function of the ribbon width, using a first-principles many-body approach based on the GW approximation. Because of the quasi-one-dimensional nature of ABNNRs, the enhanced Coulomb interaction effects and the reduced screening greatly influence the quasiparticle band gaps, giving rise to the GW correction in a range 2.5-3.0 eV. A comparative study on the edge structures of ABNNRs reveals that the band gaps of the hydrogen-terminated ABNNRs are direct and have apparent family dependence, while those of the bare ABNNRs are indirect and have no family dependence. This is consistent with the conclusion obtained by density functional theory (DFT) within the local-density approximation. Our GW calculations validate the qualitative correctness of the DFT study on BNNRs, together with the demonstration of the necessity of many-body approaches for quantitative understanding of quasiparticle band gaps.

Hu, Chunping; Ogura, Ryo; Onoda, Nobuhito; Konabe, Satoru; Watanabe, Kazuyuki

2012-06-01

333

Band gap prediction for composition-tunable alloyed semiconductor nanocrystals  

Science.gov (United States)

Size and composition-dependences of band gap energies are important properties for nanocrystal semiconductors, and have attracted extensive attentions for the last two decades. In this letter, a simple method of band gap prediction for nanocrystal alloys is developed. The band gaps of II-VI semiconductor homogeneous alloys with zinc blende and wurtzite structure, such as zb-(ZnS)x(CdS)1-x, zb-(CdS)x(CdSe)1-x, zb-(ZnSe)x(CdSe)1-x, w-(ZnS)x(CdS)1-x, w-(ZnSe)x(CdSe)1-x, and w-(CdSe)x(CdTe)1-x nanocrystal alloys, are calculated. The calculated results are in good agreement with the available experimental data. It provides insights into the effects of structure, size, and composition on the band gap.

Gao, Lihua; Gao, Faming

2013-07-01

334

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

335

Zone folding effect in Raman G-band intensity of twisted bilayer graphene  

OpenAIRE

The G-band Raman intensity is calculated for twisted bilayer graphene as a function of laser excitation energy based on the extended tight binding method. Here we explicitly consider the electron-photon and electron-phonon matrix elements of twisted bilayer graphene to calculate the resonance Raman intensity. The G-band Raman intensity is sensitive to the laser excitation energy and the twisting angle between the layers as a result of folding the electronic energy band structure. The Van Hove...

Dresselhaus, Mildred; Sato, Kentaro; Saito, Riichiro; Cong, Chunxiao; Yu, Ting

2012-01-01

336

Valence bands spin splitting in GaAs/AlGaAs quantum wells  

Science.gov (United States)

A quantitative comparison between different model calculations of valence band states in GaAs/AlGaAs heterostructures is presented. We demonstrate that a 14-band k.p Hamiltonian using a completely new parameterization based on fits of the tight-binding band structure leads to energy dispersion relations in excellent agreement with experiment, whereas previous parameterizations result in significant deviations. The relevance of the present results to the calculation of spin-related phenomena is discussed.

Nguyen-Quang, T.; Jancu, J.-M.; Voisin, P.

2006-08-01

337

Band Population Measurements in a Purely Optical Dark Lattice  

CERN Document Server

We create a dark optical lattice structure using a blue detuned laser field coupling an atomic ground state of total angular momentum F simultaneously to two excited states with angular momenta F and F-1, or F and F+1. The atoms are trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest energy band which is only weakly coupled to the light field. The populations of the two lowest energy bands reaches 70%. Kinetic energies on the order of the recoil energy are obtained by adiabatically reducing the optical potential. The band populations are directly mapped on free particle momentum intervals by this adiabatic release. In an experiment with subrecoil momentum resolution we measure the band populations and find good absolute agreement with the theoretically calculated steady state band populations.

Sander, F; Hänsch, T W; Stecher, H; Ritsch, H; Sander, Frank; Esslinger, Tilman; Hansch, Theodor W.; Stecher, Herwig; Ritsch, Helmut

1996-01-01

338

Valence Band X-Ray Emission Spectra of Compressed Germanium  

International Nuclear Information System (INIS)

We report measurements of the valence band width in compressed Ge determined from x-ray emission spectra below the Ge K edge. The width of the valence band does not show any pressure dependence in the semiconducting diamond-type structure of Ge below 10 GPa. On the other hand, in the metallic ?-Sn phase above 10 GPa the valence band width increases under compression. Density-functional calculations show an increasing valence band width under compression both in the semiconducting phase (contrary to experiment) and in the metallic ?-Sn phase of Ge (in agreement with observed pressure-induced broadening). The pressure-independent valence band width in the semiconducting phase of Ge appears to require theoretical advances beyond the density-functional theory or the GW approximation

339

Does an ??+ rotational band exist in 8Be  

International Nuclear Information System (INIS)

For 8Be it is well known that the ground state rotational band can be interpreted in terms of an ??-molecule. Recently, an additional rotational band consisting of ??+-molecules and starting around Esub(x) approximately 20 MeV was predicted in 8Be by refined cluster model calculations. As ? and ?+ are not identical bosons, negative parity states (1-, 3-) are members of this band too. Its moment of inertia is predicted to be roughly twice as large as the one of the ground state band of 8Be. In connection with the speculations that the famous 12C-12C resonances may be understood, in a model which includes the ?+ the existance of this band and its interpretation is of considerable interest. Experimentally such states can be reached through the p+7Li, d+6Li and the ?+? channel. (Auth.)

340

Systematic description of superdeformed bands in the mass-190 region  

Energy Technology Data Exchange (ETDEWEB)

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.

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

341

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.)

342

Nuclear field theory treatment of Knot=0 rotational bands  

International Nuclear Information System (INIS)

The properties of the lowest members of Knot=0 rotational bands are described as anharmonic vibrational bands. The anharmonicity is calculated by the nuclear field theory (particle-vibration coupling) method. 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.)

343

Simulation of narrow band ELF radiation propagation in auroral ionosphere  

International Nuclear Information System (INIS)

Peculiarities of the narrow-band ELF-radiation propagation in the polar ionosphere, generated by auroral electron beams as the Alfven polarization waves, are analyzed by the numerical modeling method. The calculation results make it possible to explain the fact of registering the ELF narrow-band waves and their characteristics, observed in experiments on the low-flying satellites. 13 refs., 4 figs

344

Infrared spectroscopy of electronic bands in bilayer graphene  

OpenAIRE

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 sig...

Kuzmenko, Alexey; Heumen, Erik; Marel, Dirk; Lerch, P.; Blake, P.; Novoselov, K. S.; Geim, A. K.

2008-01-01

345

Band of Brothers  

Science.gov (United States)

With the wealth of allusions to Pearl Harbor in the news this week, this miniseries from HBO focused on World War II is well-timed. Parts one and two of the ten-part Band of Brothers premiered this week, and viewers will find supplemental material here including veterans' stories, a timeline of events related to the war, details on drop zones and paratroopers' uniforms, explanations of the defensive strategies, and more. Flash movies allow viewers to see highlights from the war, pausing where they want more detail. Those who want to pursue their interest in topics further will find pointers to other sites in the Resource Room, which also features chat rooms and message boards. Note that we found the site's navigation not entirely intuitive and the load times quite long even with a high speed connection.

346

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

CERN Document Server

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.

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

2002-01-01

347

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

OpenAIRE

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...

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

2013-01-01

348

Chemically induced compaction bands: Triggering conditions and band thickness  

OpenAIRE

During compaction band formation various mechanisms can be involved at different scales. Mechanical and chemical degradation of the solid skeleton and grain damage are important factors that may trigger instabilities in the form of compaction bands. Here we explore the conditions of compaction band formation in quartz- and carbonate-based geomaterials by considering the effect of chemical dissolution and grain breakage. As the stresses/deformations evolve, the grains of the material break lea...

Stefanou, Ioannis; Sulem, Jean

2014-01-01

349

Normal and superdeformed cluster bands in heavy nuclei  

CERN Document Server

We apply a principle of maximum stability to determine the most favoured core-cluster decompositions of sup 1 sup 9 sup 4 Hg, sup 2 sup 3 sup 6 U and sup 2 sup 4 sup 0 Pu. The results suggest two distinct modes of clusterization for each nucleus, one of which can be associated with the ground state band, and the other with an excited superdeformed band. We compare the calculated properties of these bands with the corresponding data available in all three nuclei.

Buck, B; Horner, M J; Pérez, S M

2000-01-01

350

Unique electronic band structures of hydrogen-terminated silicon nanowires  

International Nuclear Information System (INIS)

Band structure mutation from an indirect to a direct gap is a well-known character of small hydrogen-terminated and silicon nanowires (SiNWs), and suggests the possible emission of silicon. In contrast, we show that hydrogen-terminated SiNWs consistently present indirect band gaps even at an extremely small size, according to our calculations using density functional theory. Interestingly, the band gap of SiNWs shows a quasi-direct feature as the wire size increases, suggesting the possibility of using medium SiNWs in optoelectronic devices. This result also indicates that the electronic structures of SiNWs are strongly orientation dependent

351

Rotational bands and noncollective structures in 85Zr  

International Nuclear Information System (INIS)

The structure of the transitional nucleus 85Zr has been investigated through spectroscopy and lifetime measurements. States up to spins of (45/2)(?/2?) and (39/2)(?/2?) in the positive and negative parity bands, respectively, have been established through ?-? coincidence measurements. The results indicate that there is a competition between collective and noncollective modes of excitation. Two pronounced band crossings have been observed in the positive parity sequence, while none is evident in the negative parity states. The pattern of shape evolution in the positive and negative parity bands is markedly different. The results of the experiments qualitatively corroborate the predictions of total Routhian surface calculations

352

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

CERN Document Server

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 only. We have included the non common either anion or cation (CdTe/ZnSe), common cation (CdTe/CdSe), and common anion (CdTe/ZnTe) cases. We have aligned the top of the the valence band at the whole interface dominion as the boundary condition. The overall conclusion is that the interface is a very rich space where changes in the band structure with respect to the bulk do occur. This is true not only at interfaces with no common atoms but also at the ones with either common cation or anion atoms irrespective to the fact that the common atomic l...

Olguin, D

1996-01-01

353

Bulk band structure of Bi2Te3  

Science.gov (United States)

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.

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

354

Bulk band structure of Bi2Te3  

DEFF Research Database (Denmark)

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.

Michiardi, Matteo; Aguilera, Irene

2014-01-01

355

Ethmocephaly with Amniotic Band Syndrome  

OpenAIRE

Ethmocephaly is the rarest form of holoprosencephaly, which occurs due to an incomplete cleavage of the forebrain. Clinically, the disease presents with a proboscis, hypotelorism, microphthalmos and malformed ears. Amniotic band syndrome is another rare congenital malformation with ring-like constriction bands in the limbs, head, face or trunk. We present a case of ethmocephaly with amniotic band syndrome, which is likely the first of its kind, published in the literature.

Das, Gobinda; Gayen, Sibnath; Bandyopadhyay, Sabyasachi; Das, Debabrata

2012-01-01

356

Ethmocephaly with amniotic band syndrome.  

Science.gov (United States)

Ethmocephaly is the rarest form of holoprosencephaly, which occurs due to an incomplete cleavage of the forebrain. Clinically, the disease presents with a proboscis, hypotelorism, microphthalmos and malformed ears. Amniotic band syndrome is another rare congenital malformation with ring-like constriction bands in the limbs, head, face or trunk. We present a case of ethmocephaly with amniotic band syndrome, which is likely the first of its kind, published in the literature. PMID:23248551

Das, Gobinda; Gayen, Sibnath; Bandyopadhyay, Sabyasachi; Das, Debabrata

2012-10-01

357

Electronic Structure Calculations of Solids Using Density-Functional Method.  

Science.gov (United States)

The electronic structures of the II-VI semiconductors in the Wurtzite structure (ZnO, ZnS, ZnSe, CdS, and CdSe) were calculated within the local-density approximation (LDA) using the linear muffin-tin orbitals (LMTO) method. The cation d states were included in the valence band. The calculation shows that for an accurate measurement of the ground state properties of these compounds the inclusion of the cation d states in the valence band is essential. Next, LDA-LMTO method was used to calculate the electronic structure of the CaF_2/Si(lll) interface. The interface states for three different structural models of the Ca-terminated interface are examined. For each model a pair of two-dimensional interface bands is found. The unoccupied interface band around the zone center is a truly localized band while the occupied interface band is buried below the valence-band maximum. The nature of the two -dimensional interface states is also discussed. Finally, the electron band structures of hexagonal and cubic diamond are calculated. Despite similarity between the two crystal structures, significant differences in the electron bands are found. The lowest gap of hexagonal diamond is found to be 4.5eV, which is 1.1eV smaller than the lowest gap of cubic diamond and is from Gamma to K.

Salehpour, Mohammad Reza

358

Band-Structure of Thallium by the LMTO Method  

DEFF Research Database (Denmark)

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.

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

1977-01-01

359

Rotational bands in odd-A Re and Au nuclei  

International Nuclear Information System (INIS)

High-spin states in 169Re were studied and resulted in the identification of a strongly coupled band based on the 9/2-[514] Nilsson state and a decoupled band built on the 1/2-[541](h9/2) intruder proton orbit. The cranked shell model calculations present configuration-dependent deformations that can explain the different band crossing frequencies. The 9/2-[514] band in 169Re shows the largest signature splitting at low spin among the known odd mass Re isotopes. After the alignment of a pair of i13/2 neutrons, the phase of the splitting is inverted with a significantly reduced amplitude. For the 9/2-[514] bands in light odd-A Re isotopes, the signature splitting of the Routhians and its relation with the signature dependence of M1 transition matrix elements are investigated in connection with the deviation of nuclear shape from axial symmetry, suggesting an appreciable negative ? deformation for the very neutron-deficient odd-A Re isotopes. A rotational band built on the 1/2[660](i13/2) Nilsson orbital has been established for 179Au. Properties of the 1/2[660](i13/2) bands in the odd-A Au nuclei are discussed with an emphasis on the evolution of band head energy and deformation while changing neutron number. (author)

360

Spectra of {gamma} rays feeding superdeformed bands  

Energy Technology Data Exchange (ETDEWEB)

The spectrum of {gamma}rays coincident with SD transitions contains the transitions which populate the SD band. This spectrum can provide information on the feeding mechanism and on the properties (moment of inertia, collectivity) of excited SD states. We used a model we developed to explain the feeding of SD bands, to calculate the spectrum of feeding {gamma}rays. The Monte Carlo simulations take into account the trigger conditions present in our Eurogam experiment. Both experimental and theoretical spectra contain a statistical component and a broad E2 peak (from transitions occurring between excited states in the SD well). There is good resemblance between the measured and calculated spectra although the calculated multiplicity of an E2 bump is low by {approximately}30%. Work is continuing to improve the quality of the fits, which will result in a better understanding of excited SD states. In addition, a model for the last steps, which cool the {gamma} cascade into the SD yrast line, needs to be developed. A strong M1/E2 low-energy component, which we believe is responsible for this cooling, was observed.

Lauritsen, T.; Khoo, T.L.; Henry, R.G. [and others

1995-08-01

361

Feather growth bands and photoperiod  

OpenAIRE

Growth bands are alternate dark/light bands perpendicular to the feather rachis. Previous studies indicate that pairs of dark/light bands are grown every 24 h, with light bands being produced at night, and dark ones during the day. Thus, the dark:light width ratio could reflect the photoperiod under which a feather was grown. We tested this hypothesis by inducing feathers to grow under contrasting photoperiods, using red-legged partridges Alectoris rufa as a model species. We first validated ...

Jovani, Roger; Blas, Julio; Navarro, Carlos; Mougeot, Franc?oise

2011-01-01

362

Scarless platysmaplasty for platysmal bands  

Directory of Open Access Journals (Sweden)

Full Text Available Transection of plastysmal bands has required a surgical approach that leaves scars and limits patient activities for a period of time. The author has developed a simple method to transect the platysmal bands under local anesthesia without resorting to skin incisions. The transection is performed with the use of a Vicryl ® suture that is inserted through the skin, around the platysmal band, and then out through the original entry point. A back and forth motion of the suture cuts through the band.

Shiffman Melvin

2004-01-01

363

Garage Band or GarageBand[R]? Remixing Musical Futures  

Science.gov (United States)

In this paper, I suggest that it is perhaps time to consider the pedagogy of popular music in more extensive terms than conventional rock band practices have to offer. One direction in which this might lead is the expansion of the informal pedagogy based on a "garage band" model to encompass various modes of digital artistry wherever this artistry…

Vakeva, Lauri

2010-01-01

364

Photon drag of carriers in narrow-band semiconductors  

International Nuclear Information System (INIS)

A current of carrier drag by photons in narrow-band semiconductors with cubic symmetry is calculated with allowance for nonsphericity and nonparabolic properties of subzones of the valent zone. The total tensor expression of a photocurrent connected with coefficients characterizing the nonparabolic properties of a light holes subzone and nonsphericity of a heavy holes subzone is obtained using the quantitative Kein model. The results of numerical calculation of the main drag current parameters are presented: components of elementary tensors of temperature, coefficients characterizing nonparabolic properties and also of wave length of incjdent radiation for the Hgsub(1-x)Cdsub(x)Te narrow-band solid solutions

365

Fluorescent chromosome banding in inbred chicken: quinacrine bands, sequential chromomycin and Dapi bands.  

Science.gov (United States)

Highly inbred White Leghorn chickens were used for an investigation of the banding pattern of the macrochromosomes. A standard was set for the Q-bands. GC-specific fluorochrome chromomycin and the AT-specific Dapi were used in a sequential stain. The comparison of these two stains disclosed quantitative differences in the base distribution of the DNA. Factors responsibe for the binding mechanism and the appearance of the bands are discussed. PMID:24247445

Fritschi, S; Stranzinger, G

1985-12-01

366

Single Band Helical Antenna in Axial Mode  

Directory of Open Access Journals (Sweden)

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

Parminder Singh

2012-11-01

367

Characterization of band structure for transverse acoustic phonons in Fibonacci superlattices by a bandedge formalism  

Energy Technology Data Exchange (ETDEWEB)

We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.

Hsueh, W J; Chen, R F; Tang, K Y [Department of Engineering Science, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei 10660, Taiwan (China)], E-mail: hsuehwj@ntu.edu.tw

2008-11-05

368

Characterization of band structure for transverse acoustic phonons in Fibonacci superlattices by a bandedge formalism  

International Nuclear Information System (INIS)

We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.

369

Interband absorption of photons by extended states in intermediate band solar cells  

OpenAIRE

This paper considers sub-bandgap photon absorption in an InAs/GaAs quantum dot matrix. Absorption coefficients are calculated for transitions from the extended states in the valence band to confined states in the conduction band. This completes a previous body of work in which transitions between bound states were calculated. The calculations are based on the empirical k·p Hamiltonian considering the quantum dots as parallelepipeds. The extended states may be only partially extended?in one o...

Luque Lo?pez, Antonio; Mellor Null, Alexander Virgil; Ramiro Gonzalez, In?igo; Antoli?n Ferna?ndez, Elisa; Tobi?as Galicia, Ignacio; Marti? Vega, Antonio

2013-01-01

370

Valence-band satellite in the ferromagnetic nickel: LDA+DMFT study with exact diagonalization  

OpenAIRE

The valence-band spectrum of the ferromagnetic nickel is calculated using the LDA+DMFT method. The auxiliary impurity model emerging in the course of the calculations is discretized and solved with the exact diagonalization, or, more precisely, with the Lanczos method. Particular emphasis is given to spin dependence of the valence-band satellite that is observed around 6 eV below the Fermi level. The calculated satellite is strongly spin polarized in accord with experimental...

Kolorenc, Jindrich; Poteryaev, Alexander I.; Lichtenstein, Alexander I.

2012-01-01

371

Narrow-Band Microwave Filters  

OpenAIRE

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).

Strizhachenko, A. V.; Zvyagintsev, A. A.; Shul’ga, S. N.; Chizhov, V. V.

2010-01-01

372

The Moral Ends of Band  

Science.gov (United States)

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…

Allsup, Randall Everett

2012-01-01

373

Rotational bands in 181Ta  

International Nuclear Information System (INIS)

High-spin states in 181Ta have been studied via the 176Yb(11B,?2n) reaction at 52 MeV using the PEX array and at 57 MeV using the NORDBALL array, with ?-particle detection. The previously known, K?=7/2+ ground state band and K?=9/2- band have been extended to spins 29/2+ and 31/2-, respectively. Two new one-quasiparticle bands, the K?=5/2+ band built on the known 5/2+ isomer and a K?=(1/2-) band have been observed. Two other rotational bands with three-quasiparticle structure, K?=15/2- and (19/2+) with ?7/2[404]?21/2[510]9/2[624] and ?9/2[514]?21/2[510]9/2[624] configurations, respectively, have been newly observed. The half-life of the K?=(19/2+) bandhead which decays to the head of the 15/2- band has been measured to be 140(36) ns. However, transitions from the (19/2+) state to the 15/2- band have not been observed. (orig.)

374

Franck–Condon factors and observed band strength distribution in the vibrational structure of the Ag2 D-X band system  

Directory of Open Access Journals (Sweden)

Full Text Available TPotential curves for the X1Sg+ and D1Su+ states of three diatomic silver isotopomers, 107Ag2, 107Ag109Ag and 109Ag2, were determined from the best available molecular constants by the Rydberg–Klein–Rees method. From these potentials, Franck–Condon factors and band-origin wavenumbers were computed, and the reliability of the obtained values was verified by comparison with the observed band strength distribution and the measured band origin po¬sitions in a previously recorded D-X spectrum. The ratios of the Franck–Con¬don factors to those of corresponding isotopic bands were found to be very close to unity, revealing only a very small isotopic effect on the Franck–Condon factors of Ag2 D-X bands. The isotopic shifts of the calculated band origins agree well with previously measured displacements of band heads.

ANKICA ANTI?-JOVANOVI?

2010-05-01

375

Band anticrossing in dilute nitrides  

Energy Technology Data Exchange (ETDEWEB)

Alloying III-V compounds with small amounts of nitrogen leads to dramatic reduction of the fundamental band-gap energy in the resulting dilute nitride alloys. The effect originates from an anti-crossing interaction between the extended conduction-band states and localized N states. The interaction splits the conduction band into two nonparabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy. The changes in the conduction band structure result in significant increase in electron effective mass and decrease in the electron mobility, and lead to a large enhance of the maximum doping level in GaInNAs doped with group VI donors. In addition, a striking asymmetry in the electrical activation of group IV and group VI donors can be attributed to mutual passivation process through formation of the nearest neighbor group-IV donor nitrogen pairs.

Shan, W.; Yu, K.M.; Walukiewicz, W.; Wu, J.; Ager III, J.W.; Haller, E.E.

2003-12-23

376

Importance of static correlation in the band structure of high-temperature superconductors  

International Nuclear Information System (INIS)

Recently the authors presented a new band structure for La2-xSrxCuO4 and other high-temperature superconductors in which a second narrow band was seen to cross the primary band at the Fermi level. The existence of this second Fermi level band is in complete disagreement with the commonly accepted LDA band structure. Yet it provided a crucial piece of physics which led to an explanation for superconductivity and other unusual phenomena in these materials. In this work, details as to the nature of the failure of conventional methods in deriving the band structure of the cuprates are presented. In particular, a number of chemical analogues describe the problem of static correlation in the band structure calculations and show how this can be corrected with the predictable outcome of a Fermi level band crossing

377

The study of energy bands in neutron-deficient 123,125Ce nuclei  

International Nuclear Information System (INIS)

Theoretical investigation of energy bands of 123,125Ce is performed by applying the projected shell model approach. The present calculation is viewed to reproduce the known experimental data of these nuclei, qualitatively. Not only this, the configurations of diverse bands are also obtained by an analysis of the band diagrams. The low-lying states of the bands are seen to arise from one quasiparticle configuration whereas the high-spin states arise from multi-quasiparticle configurations. The signature partner band of negative parity band is predicted in 123Ce. The ground state bands and relative energies of some bands with respect to them are predicted in 123,125Ce that can be helpful for future experiments

378

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

379

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)

380

Band alignments at the interface of complex oxides  

Science.gov (United States)

The realization of a two-dimensional electron gas at the SrTiO3/LaAlO3 interface has spurred interest in the development of electronic devices based on complex oxides. In the design of such devices it is crucial to know the band alignment at the interface of the different oxides, a key quantity that governs carrier barrier heights and carrier confinement. Reported values for the valence-band alignment at the SrTiO3/LaAlO3 interface vary by more than 1 eV. Using first-principles calculations based on a hybrid functional we calculate the band alignment at the interface between various complex oxides, including the band insulators SrTiO3, SrZrO3, LaAlO3, and LaGaO3 and the Mott insulators GdTiO3 and YTiO3. This choice of materials allows us to analyze the effects of cation size, lattice parameters, band gaps, and lattice orientation on the band alignment.

Bjaalie, Lars; Janotti, Anderson; van de Walle, Chris G.

2013-03-01

381

W-Band Sheet Beam Klystron Simulation  

Energy Technology Data Exchange (ETDEWEB)

With the development of ever higher energy particle accelerators comes the need for compactness and high gradient, which in turn require very high frequency high power rf sources. Recent development work in W-band accelerating techniques has spurred the development of a high-power W-band source. Axisymmetric sources suffer from fundamental power output limitations (P{sub sat} {approx} {lambda}{sup 2}) brought on by the conflicting requirements of small beam sizes and high beam current. The sheet beam klystron allows for an increase in beam current without substantial increase in the beam current density, allowing for reduced cathode current densities and focusing field strengths. Initial simulations of a 20:1 aspect ratio sheet beam/cavity interaction using the 3 dimensional particle-in-cell code Magic3D have demonstrated a 35% beam-power to RF power extraction efficiency. Calculational work and numerical simulations leading to a prototype W-band sheet beam klystron will be presented, together with preliminary cold test structure studies of a proposed RF cavity geometry.

Colby, E.R.; Caryotakis, G.; Fowkes, W.R.; /SLAC; Smithe, D.N.; /Mission Res., Newington

2005-09-12

382

Compact Dual Band Microstrip Antenna for Ku-Band Application  

OpenAIRE

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...

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

2010-01-01

383

Electronic band structures for zinc-blende and wurtzite CdS  

International Nuclear Information System (INIS)

The electronic band structures for zinc-blende and wurtzite CdS are calculated within the local-density approximation with the use of first-principles pseudopotentials. Incorporating the d state into the valence band improves substantially the main-valence-band width, and yields valence-band features in good agreement with experiment. The maximum effect of the d band occurs at GAMMA15 for zinc-blende CdS and at GAMMA1,GAMMA6 for wurtzite CdS. We find that the local-density approximation does not predict accurately the position of localized Cd 4d state

384

Macroscopic optical response and photonic bands  

CERN Document Server

We develop a formalism for the calculation of the macroscopic dielectric response of composite systems made of particles of one material embedded periodically within a matrix of another material, each of which is characterized by a well defined dielectric function. The nature of these dielectric functions is arbitrary, and could correspond to dielectric or conducting, transparent or opaque, absorptive and dispersive materials. The geometry of the particles and the Bravais lattice of the composite are also arbitrary. Our formalism goes beyond the longwavelenght approximation as it fully incorporates retardation effects. We test our formalism through the study the propagation of electromagnetic waves in 2D photonic crystals made of periodic arrays of cylindrical holes in a dispersionless dielectric host. Our macroscopic theory yields a spatially dispersive macroscopic response which allows the calculation of the full photonic band structure of the system, as well as the characterization of its normal modes, upo...

Perez-Huerta, J S; Mendoza, Bernardo S; Mochan, W Luis

2012-01-01

385

Pseudopotential band structure of indium nitride  

International Nuclear Information System (INIS)

The band structure, density of states and the imaginary part of the dielectric function have been calculated for indium nitride by a pseudopotential method. Comparison with published reflectance data permits the identification of principal optical transitions at the GAMMA,M,K, and H symmetry points and we have been able to correct previous transition assignments. The calculated long-wavelength refractive index of 2.88 +- 0.5 compares well with experiment. The material has a direct energy gap at the zone center and the spherically symmetric extrema are well described by scalar effective masses of 0.17m0, 0.5m0 (holes), and 0.12m0 (electrons)

386

Information retrieval from wide-band meteorological data - An example  

Science.gov (United States)

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.

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

1983-01-01

387

Electronic structure of periodic curved surfaces -- topological band structure  

CERN Document Server

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.

Aoki, H; Takeda, D; Morise, H

2001-01-01

388

Analysis of Factors Affecting Log Band Saw Capacity  

Directory of Open Access Journals (Sweden)

Full Text Available The goal of this research was to measure the capacity of the log band saw by monitoring the sawing process per operation for each log and to determine what the influencing factors were and their effect on the technological capacity of the log band saw, based on recorded and processed data. The analysis of the recorded data shows that the processed log volume, whose increase also increases the saw capacity, has the most important effect on log band saw capacity. It is imperative to take into account the volume of logs being processed when calculating the capacity of the log band saw. When monitoring the work of the operator, the use of fixed norms is not recommended and it is imperative that norms are connected to the volume of logs being processed.

Rajka Karan

2009-06-01

389

Multiple triaxial bands and abnormal signature inversion in 7433As  

International Nuclear Information System (INIS)

Excited states of the odd–odd nucleus 74As have been investigated via heavy ion fusion evaporation reaction 70Zn(7Li,3n)74As at beam energy of 30 MeV. The properties of the positive- and the negative- parity bands can be interpreted in terms of the Cranked Nilsson–Strutinsky (CNS) model calculations which show that the observed bands are built on the triaxial deformed shape. The inversion of the favored and unfavored signature branches observed in the positive-parity bands presents at high spins rather than normal signature inversion occurs at low spins. This phenomenon may be explained as the origin of unpaired band crossing in a highly rotating triaxial nucleus.

390

Band-gap engineering in fluorographene nanoribbons under uniaxial strain  

Energy Technology Data Exchange (ETDEWEB)

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.

Zhang, Yan, E-mail: bingbing@mail.ustc.edu.cn, E-mail: liqun@ustc.edu.cn; Li, Qunxiang, E-mail: bingbing@mail.ustc.edu.cn, E-mail: liqun@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2014-01-28

391

Band gap engineering strategy via polarization rotation in perovskite ferroelectrics  

Energy Technology Data Exchange (ETDEWEB)

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.

Wang, Fenggong, E-mail: fenggong@sas.upenn.edu; Grinberg, Ilya; Rappe, Andrew M., E-mail: rappe@sas.upenn.edu [The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104–6323 (United States)

2014-04-14

392

Morphologies of three-dimensional shear bands in granular media.  

Science.gov (United States)

We present numerical results on spontaneous symmetry breaking strain localization in axisymmetric triaxial shear tests of granular materials. We simulated shear band formation using the three-dimensional distinct element method with spherical particles. We demonstrate that the local shear intensity, the angular velocity of the grains, the coordination number, and the local void ratio are correlated and any of them can be used to identify shear bands; however, the latter two are less sensitive. The calculated shear band morphologies are in good agreement with those found experimentally. We show that boundary conditions play an important role. We discuss the formation mechanism of shear bands in the light of our observations and compare the results with experiments. At large strains, with enforced symmetry, we found strain hardening. PMID:17025619

Fazekas, S; Török, J; Kertész, J; Wolf, D E

2006-09-01

393

Bulk Band Structure of Bi$_2$Te$_3$  

OpenAIRE

The bulk band structure of Bi$_2$Te$_3$ 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 ...

Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco; Carvalho, Vagner Eusta?quio; Ladeira, Luiz Orlando; Teixeira, Nayara Gomes; Soares, Edmar Avellar; Friedrich, Chiristoph; Blu?gel, Stefan; Hofmann, Philip

2014-01-01

394

Motion-estimation parallel algorithm based on band matching  

Science.gov (United States)

A new algorithm to compute the motion vector has been developed based on the block-matching approach in which bands are used instead of blocks. The new band-matching algorithm (BDMA) offers better performance than both the fixed size and variable-size block-matching algorithms because it uses less vectors and processes parts of the image instead of the whole image. The BDMA extracts the likely moving objects, forms the image of differences between initial successive frames in an image sequence, divides each 'object' into bands with different sizes, forms a 4 by 4 block around each edge in the band, looks for the type of edges, calculates the different of the textures inside the band, and starts the matching process between frames. Bands are matched according to the number of edges and their type (the type is created and stored using some kind of code-book), and the texture values. Matching results produce a specific vector for the estimated motion. To enhance the performance two independent external memory are employed, they are accessed in parallel. One memory is indexed by the other, one to store the ongoing images, and the second to buffer the bands and results. There sizes and features are adapted to support the application for which the circuit is needed. The new algorithm has been evaluated using several standard video images.

Yazji, Sausan; Bayoumi, Magdy A.; Zavidovique, Bertrand

1997-09-01

395

Compact Dual Band Microstrip Antenna for Ku-Band Application  

Directory of Open Access Journals (Sweden)

Full Text Available 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 gives a stable radiation performance with gain greater than 4 dBi over the frequency band.

M.T. Islam

2010-01-01

396

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

OpenAIRE

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.

Roy, Santosh; Datta, Pradip; 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

397

Reversible Band Gap Engineering in Carbon Nanotubes by Radial Deformation  

CERN Document Server

We present a systematic analysis of the effect of radial deformation on the atomic and electronic structure of zigzag and armchair single wall carbon nanotubes using the first principle plane wave method. The nanotubes were deformed by applying a radial strain, which distorts the circular cross section to an elliptical one. The atomic structure of the nanotubes under this strain are fully optimized, and the electronic structure is calculated self-consistently to determine the response of individual bands to the radial deformation. The band gap of the insulating tube is closed and eventually an insulator-metal transition sets in by the radial strain which is in the elastic range. Using this property a multiple quantum well structure with tunable and reversible electronic structure is formed on an individual nanotube and its band-lineup is determined from first-principles. The elastic energy due to the radial deformation and elastic constants are calculated and compared with classical theories.

Gülseren, O; Ciraci, S; Kilic, C

2002-01-01

398

Band mixing in 29Si and 29P  

International Nuclear Information System (INIS)

The experimental data of the 28Si(?, t)29P and 28Si(?, 3He)29Si reactions at 45 MeV have been analysed in terms of full finite-range coupled-channels calculations. In the calculations, the reaction paths, direct and two step via the inelastic states of the initial and final nuclei have been treated in terms of the finite-range transfer theory. The spectroscopic amplitudes connecting the deformed initial and final nuclei in both the reactions are obtained from Nilsson's model. The data of both the reactions, populating the 1/2+, 3/2+ and 5/2+ states in the K? = 1/2+ band and the 3/2+ and 5/2+ states in the K? = 3/2+ band, are best described by about 20% mixing of between the two bands. The effects of normal Woods-Saxon (WS), squared WS and molecular type of ?-nucleus potentials are also discussed

399

Band structure of 184Ir  

International Nuclear Information System (INIS)

States of 184Ir, excited through several (HI, xn) reactions were studied using in-beam ?-ray and conversion electron spectroscopy techniques. A new high-spin level scheme, comprising three different rotational bands is presented. The negative-parity ?I=1 ground-state band is the most complete example of the semidecoupled ?h9/2x?i13/2 structure, in a prolate deformed situation, known to date. The other two bands are the doubly decoupled ?h9/2x?1/2- [521] and a ?I=1, ?5/2+ [402]x?i13/2 based structure of the compressed type. (orig.)

400

Faithful linear representations of bands  

OpenAIRE

A band is a semigroup consisting of idempotents. It is proved that for any field K and any band S with finitely many components, the semigroup algebra K [S] can be embedded in upper triangular matrices over a commutative K-algebra. The proof of a theorem of Malcev [4, Theorem 10] on embeddability of algebras into matrix algebras over a field is corrected and it is proved that if S = F ? E is a band with two components E, F such that F is an ideal of S and E is finite, then S is a linear sem...

Cedo?, F.

2009-01-01

401

Nonideal anion displacement, band gap variation, and valence band splitting in Cu-In-Se compounds  

International Nuclear Information System (INIS)

Polycrystalline thin films of ternary chalcopyrite CuInSe2 and defect compounds CuIn3Se5 and CuIn5Se8 are prepared in vacuum by three-source coevaporation method. Structural and optical characterizations of the films are done using X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), and optical absorbance spectra measurements. With variation in the composition of CuInSe2, a change over from p-type to n-type conductivity is observed (as noted by the hot probe method). The deformation parameters and the anion displacements are calculated from the X-ray diffraction data, and the cation-anion bond lengths are deduced. The dependence of band gap variation on nonideal anion displacement in the ternary compounds and the effect of Se-p-Cu-d repulsion on band gap are studied. The threefold optical structure observed in the fundamental absorption region of the absorption spectra is analysed to extract the valence band splitting parameters. Hopfields quasi-cubic model adapted for chalcopyrites with tetragonal deformation is used to determine the crystal field splittings and spin orbit splittings, and the linear hybridization model is used to calculate the percentage of d-orbital and p-orbital contribution to hybridization in the compounds under consideration

402

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

Directory of Open Access Journals (Sweden)

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.

KOVAR, P.

2012-08-01

403

Thermal Band Characterization of the LANDSAT-4 Thematic Mapper  

Science.gov (United States)

The initial characterization of the Thematic Mapper (TM) thermal band is reported including gain stability, gain relation to internal calibration, corrections for channel-to-channel and scan direction differences, an approximate comparison to ground truth, and a calculation of noise equivalent temperature difference. Updated calibration information is also presented.

Lansing, J. C.; Barker, J. L.

1985-01-01

404

Scattering of band carriers by neutral and charged impurities  

OpenAIRE

Mobility of band carriers scattered on donors, partially ionized, partially neutral, is considered in general and calculated for crystals belonging to AIII-BV group. As neutral impurity we have constructed the hydrogen-like model. It is shown that dependence of mobility on temperature is determined by relation between number of ionized and neutral donors and by average energy of electrons.

Bolko, L. I.

2010-01-01

405

A study of higher-band dipole wakefields in X-band accelerating structures for the G/NLC  

CERN Document Server

The X-band linacs for the GLC/NLC (Global Linear Collider/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series [1,2]. The present series of accelerating structures are each 60 cm in length and incorporate both damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield the dipole frequencies of adjacent structures are interleaved. The properties of the first dipole band have been extensively studied. However, limited analysis has been done on the higher order dipole bands. Here, we calculate the contribution of the higher order bands of the interleaved structures to the wakefield using a mode matching computer code [3]. Beam dynamics issues are also studied by tracking the beam through the complete linac using the particle beam tracking code LIAR [4].

Jones, R M

2004-01-01

406

The transverse wakefield calculated by double circuit model  

CERN Document Server

X-band accelerator for multi-bunches has been a new way to produce high luminosity and energy efficiency bunches. As the smaller size and multi-bunches, the wakefield is more severe in X-band accelerator, unless some means of strongly suppressing of the transverse wakefield is adopted in the design of the accelerating structure. To calculate the transverse wakefield of the structure, wakefield calculated through the double circuit model has been demonstrated and its application in the structure designed.

Bin, Yang Xiong

2014-01-01

407

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

DEFF Research Database (Denmark)

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.

Gorczyca, I.; Suski, T.

2012-01-01

408

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

Science.gov (United States)

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

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

2014-12-01

409

First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications  

International Nuclear Information System (INIS)

First-principles calculations of the band offsets between Cu2ZnSnS4 (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.

410

First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications  

Science.gov (United States)

First-principles calculations of the band offsets between Cu2ZnSnS4 (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.

Nagoya, A.; Asahi, R.; Kresse, G.

2011-10-01

411

Fitting the observed PAH bands  

Science.gov (United States)

The interstellar infrared emission spectrum with strong bands near 3.3, 6.2, 7.7, and 11.2 micron is common throughout the Universe. These bands -- often called the Unidentified InfraRed (UIR) bands or Aromatic InfraRed Bands (AIB) -- dominate the mid-IR spectra of most galactic objects and they have been detected in a large number of extragalactic objects. Not only are these features observed in many different objects, there is also significant variability in the spectroscopic details from one object to another and from one region to another within extended sources. Clearly, these spectra contain a wealth of information which reflects the physical conditions in the emission zones and composition of the emitting materials. Many studies have therefore attempted to use these easily observed features as diagnostic tools for various purposes. It is now widely accepted that this spectrum is produced by fluorescent emission from highly vibrationally excited polycyclic aromatic hydrocarbon molecules (PAHs) and closely related species and the features are now often referred to as the PAH emission bands. In this presentation, we use the NASA Ames PAH IR Spectroscopic Database and a simplified model for PAH physics to present a detailed comparison with observations of the UIR bands representing the different characteristic classes of UIR spectra. We find that we can closely reproduce the observed UIR spectra for all classes in the ranges 6--9 micron and 10--14 micron, offering credibility for the hypothesis that the UIR bands are indeed due to the various vibrational modes of PAHs and related species. We will also show how the spectral variations of the PAH bands in different environments can be explained by differences in the size distribution, the charge state and the precise chemical composition of the contributing molecules.

Cami, Jan; Bauschlicher, C.; Peeters, E.; Mattioda, A.; Allamandola, L.

2009-01-01

412

Narrow-Band Microwave Filters  

Directory of Open Access Journals (Sweden)

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.

A.V. Strizhachenko

2010-01-01

413

Multiple-scattering approach to band theory. II. Fast band theory  

International Nuclear Information System (INIS)

The multiple-scattering equations are used to derive a set of band-theory equations that are called the pivoted-multiple-scattering (PMS) equations. The PMS equations are as legitimate a basis for band-theory calculation as the Korringa-Kohn-Rostoker (KKR) equations that are also derived from the multiple-scattering theory. The primary usefulness of the PMS equations is that an approximate expression can be derived from them that gives all the eigenvalues for one k with a single-matrix diagonalization. This expression has the form of a quadratic eigenvalue equation. The usefulness and accuracy of this quadratic KKR formalism is demonstrated by a number of numerical studies

414

Deformation potentials for band-to-band tunneling in silicon and germanium from first principles  

Science.gov (United States)

The deformation potentials for phonon-assisted band-to-band tunneling (BTBT) in silicon and germanium are calculated using a plane-wave density functional theory code. Using hybrid functionals, we obtain: DTA = 4.1 × 108 eV/cm, DTO = 1.2 × 109 eV/cm, and DLO = 2.2 × 109 eV/cm for BTBT in silicon and DTA = 7.8 × 108 eV/cm and DLO = 1.3 × 109 eV/cm for BTBT in germanium. These values agree with experimentally measured values and we explain why in diodes, the TA/TO phonon-assisted BTBT dominates over LO phonon-assisted BTBT despite the larger deformation potential for the latter. We also explain why LO phonon-assisted BTBT can nevertheless dominate in many practical applications.

Vandenberghe, William G.; Fischetti, Massimo V.

2015-01-01

415

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

416

'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.

417

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

418

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.))

419

Graphical comparison of calculated internal conversion coefficients  

International Nuclear Information System (INIS)

Calculated values of the coefficients of internal conversion of gamma rays in the K shell and L1, L2, L3 subshells from published tabulations by Band and Trzhaskovskaya and by Roesel et al. at Data Nucl. Data Tables, 21, 92-514(1978) are compared with values obtained by computer interpolation among tabulated values of Hager and Seltzer Nucl. Data, A4, 1-235(1968). In some cases, agreement among the three calculations is remarkably good, and differences are generally less than 5%. In a few cases, there are differences as large as 20 to 50%, corresponding to the threshold effect described by Roesel et al. The Z-dependent resonance minimum described by Roesel et al. is also observed in the comparison of E1-E4 conversion in the L1 subshell. In several cases (notably M1-M4 conversion in the K shell and L1 subshell), the Band and Roesel calculations show dramatically different dependence on gamma energy and atomic number. For Z = 100, the Band calculation for E4 conversion in the L3 subshell shows irregular behavior at energies below the K-shell binding energy. A few high-quality measurements of internal conversion coefficients (+-5%) would help greatly to establish a basis for choice among the theoretical calculations. 32 figures

420

Calculated Electronic Properties of Zinc Oxide  

Science.gov (United States)

We performed ab-initio, self-consistent calculations of the electronic and related properties of zinc oxide (ZnO). Our computations employed a local density potential and the linear combination of atomic orbital (LCAO) formalism within the Bagayoko, Zhao, and Williams (BZW) procedure. The calculated equilibrium lattice parameters, energy bands, and band gap (3.2 eV) of wurtzite ZnO agree very well with experiment. We discuss optical transitions and other properties and we underscore the predictive capability of local density approximation (LDA) calculations within the BZW procedure. This work was funded in part NASA (Award. No. NCC13-00010 and No. Award No. NCC2-1344.

Bagayoko, D.; Zhao, G. L.; Wang, E. G.

2003-03-01

421

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

OpenAIRE

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...

Mahmoud Zaki Iskandarani

2012-01-01

422

3-Body Scattering (3BS) theory of on-site correlation in narrow band materials  

OpenAIRE

We present the results of a recently developed approach where the interplay between the itinerant and localized character of electrons in narrow band materials is described by adding on-site correlation effects to a first principle band calculation: the single particle band states are treated as mean field solutions of a multi-orbital Hubbard Hamiltonian and the many-body term associated to localized e-e interaction is described in a configuration-interaction scheme. The met...

Manghi, Franca; Rontani, Massimo

1997-01-01

423

Electronic Structure and Valence Band Spectra of Bi4Ti3O12  

OpenAIRE

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.

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

1995-01-01

424

Chemically induced compaction bands: Triggering conditions and band thickness  

Science.gov (United States)

compaction band formation, various mechanisms can be involved at different scales. Mechanical and chemical degradation of the solid skeleton and grain damage are important factors that may trigger instabilities in the form of compaction bands. Here we explore the conditions of compaction band formation in quartz- and carbonate-based geomaterials by considering the effect of chemical dissolution and grain breakage. As the stresses/deformations evolve, the grains of the material break, leading to an increase of their specific surface. Consequently, their dissolution is accelerated and chemical softening is triggered. By accounting for (a) the mass diffusion of the system, (b) a macroscopic failure criterion with dissolution softening, and (c) the reaction kinetics at the microlevel, a model is proposed and the conditions for compaction instabilities are investigated. Distinguishing the microscale (grain level) from the macrolevel (representative elementary volume) and considering the heterogeneous microstructure of the representative elementary volume, it is possible to discuss the thickness and periodicity of compaction bands. Two case studies are investigated. The first one concerns a sandstone rock reservoir which is water flooded and the second one a carbonate rock in which CO2 is injected for storage. It is shown that compaction band instabilities are possible in both cases.

Stefanou, Ioannis; Sulem, Jean

2014-02-01

425

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

CERN Document Server

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 ...

Ramires, Aline

2011-01-01

426

Signature splitting in octupole bands of vibrational and deformed nuclei  

International Nuclear Information System (INIS)

Energy staggering in negative-parity bands is studied in both vibrational and deformed regions. Good agreement is found between empirical signature patterns and those calculated in the IBA. It is shown that the calculations in each region depend essentially on only a single parameter. It is found that each kind of structural region displays unique and characteristic signature behaviour. In ?-soft [O(6)]nuclei the staggering is large and nearly independent of J. Octupole staggering can actually be used as a signature for this symmetry. In deformed regions, signature effects in K=1- bands show a striking singularity as a function of the filling of a shell, which, both experimentally and theoretically, is shown to be due to the crossing and mixing of K=0- and 1- bands. Finally, it is found that, albeit for different reasons in different structural regions, the signature splitting of low-lying negative-parity states in vibrational and deformed regions (K=1- bands) is almost always opposite in phase with that of positive-parity ?-bands: the only exception is at the very beginning of deformed regions. (orig.)

427

Comparison and fit of the two and six band k.p models for the band edge structure of Pbsub(1-x)Snsub(x)Te  

International Nuclear Information System (INIS)

The band edge structure of Pbsub(1-x)Snsub(x)Te is derived in detail using a two band ellipsoidal model and compared with a more rigorous calculation based on six bands. A quantitative comparison is made for two values of the energy gap, corresponding to the cases where x=0 and x=0.17. It was found that, for the occupied states in nondegenerate materials, both models are practically equivalent. Discrepancies may occur only in high degeneracies or deep inversion layers. The agreement between both models was significantly improved by introducing an effective energy gap in the two band model. It is suggested that the use of the effective energy gap may improve the agreement between the two band model and experiment whenever the details of the band edge structure enter the interpretation of the experimental results. (author)

428

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)

429

Evidence for a direct band gap in the topological insulator Bi2Se3 from theory and experiment  

OpenAIRE

Using angle-resolved photoelectron spectroscopy and ab-initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Gamma point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence band maximum is located at the Brillouin center only if many-body effects are included in the calculation...

Nechaev, I. A.; Hatch, R. C.; Bianchi, M.; Guan, D.; Friedrich, C.; Aguilera, I.; Mi, J. L.; Iversen, B. B.; Blu?gel, S.; Hofmann, Ph; Chulkov, E. V.

2012-01-01

430

Triaxial shape coexistence and new aligned band in Os178  

Science.gov (United States)

High spin states in Os178 were studied by means of Ho165(Ne20,p6n)Os178 fusion evaporation reaction at a beam energy of 150 MeV, using a clover detector array. Several new transitions belonging to Os178 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.

Kumar, Rajesh; Govil, I. M.; Dhal, A.; Chaturvedi, L.; Praharaj, C. R.; Rath, A. K.; Kumar, G. Kiran; Basu, S. K.; Chakraborty, A.; Krishichayan; Mukhopadhyay, S.; Pattabiraman, N. S.; Ghugre, S. S.; Sinha, A. K.

2009-11-01

431

All-electron Exact Exchange Treatment of Semiconductors: Effect of Core-valence Interaction on Band-gap and $d$-band Position  

CERN Document Server

Exact exchange (EXX) Kohn-Sham calculations within an all-electron full-potential method are performed on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. Full-potential band-gaps are also not significantly better for $sp$ semiconductors than for insulators, as had been found for pseudopotentials. The locations of $d$-band states, determined using the full-potential EXX method, are in excellent agreement with experiment, irrespective of whether these states are core, semi-core or valence. We conclude that the inclusion of the core-valence interaction is necessary for accurate determination of EXX Kohn-Sham band structures, indicating a possible deficiency in pseudopotential calculations.

Sharma, S; Ambrosch-Draxl, C

2005-01-01

432

Signature splitting and configuration assignments in three-quasiparticle rotational bands  

International Nuclear Information System (INIS)

There are 173 three quasiparticle rotational bands, out of which 38 bands display signature splitting and sometimes a signature inversion also. The observed signature splitting is basically due to the higher order Coriolis coupling and calculation based on particle rotor model (PRM) are in progress

433

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

434

Search for superdeformed bands in {sup 154}Dy  

Energy Technology Data Exchange (ETDEWEB)

The island of superdeformation in the vicinity of the doubly magic {sup 152}Dy yrast superdeformed (SD) band is thought to be well understood in the framework of cranked mean field calculations. In particular, the calculations suggested that in {sup 154}Dy there should be no yrast or near yrast SD minimum in the 40-60 h spin range, where SD bands in this mass region are thought to be {sup 153}Dy nucleus, it is populated. However, with the presence of five SD bands in the neighboring necessary to ascertain if the addition of one single neutron diminishes the importance of shell effects to the extent that superdeformation can no longer be sustained. In an experiment utilizing the increased resolving power of the early implementation phase of Gammasphere, the reaction {sup 122}Sn({sup 36}S,4n) at 165 MeV was employed to populate high spin states in {sup 154}Dy. In a four-day run with 36 detectors, over one billion triple and higher fold coincidence events were recorded. One new SD band was identified and was assigned to {sup 154}Dy. From comparisons with the Im{sup (2)} moments of inertia of the SD bands in {sup 152}Dy and {sup 153}Dy, a configuration based on (514)9/2{sup 2} neutrons coupled to the {sup 152}Dy SD core was proposed. One unexpected and as yet unexplained feature of this new SD band is that the transition energies are almost identical to those of an excited SD band in {sup 153}Dy. It is also worth noting that the feeding of the yrast states is similar to that achieved by the deexcitation from the ensemble of all entry states in the reaction. This observation emphasizes the statistical nature of the decay-out process. A paper reporting these results was accepted for publication.

Nisius, D.; Janssens, R.V.F.; Khoo, T.L. [and others

1995-08-01

435

Spins of superdeformed band in {sup 192}Hg  

Energy Technology Data Exchange (ETDEWEB)

Determination of the spins of SD states is the most important challenge in the study of superdeformation. Knowledge of the spin will provide crucial information on SD bands, in particular on the fascinating phenomenon of bands with identical energies and moments of inertia. Angular distribution coefficients of the {gamma}rays decaying out of the {sup 192}Hg SD band were determined using Eurogam data. These coefficients, as well as the spectral shape and multiplicity of the spectrum, are compared with the results of calculations, thereby providing a check on these calculations. From the measured decay multiplicity and the calculated average spin removed per photon (0.3 h), we deduce the average spin {bar I}{sub decay} removed by the {gamma} rays connecting SD and normal states. The spin I{sub SD} of the SD band from which the decay occurs is given by I{sub SD} = {bar I} decay + {bar I} ND, where {bar I} ND is the average spin removed by the normal yrast states. The state from which the major decay out of the SD band occurs is found to have spin 9.5 {plus_minus} 0.8 h. Since angular momentum is (quantized), this leads to a spin assignment of 9 or 10 h. The latter value is favored since the yrast band in the SD well must have only even spin values. This constitutes the first deduction of spin from data in the mass 150 and 190 regions. The spin of 10 h agrees with the spin which is inferred from a model, using the observed moment of inertia (Im){sup (2)}{omega}.

Lauritsen, T.; Khoo, T.L.; Henry, R.G. [and others

1995-08-01

436

On Eigenvectors of Random Band Matrices with Large Band  

OpenAIRE

We study random, symmetric $N \\times N$ band matrices with a band of size $W$ and Bernoulli random variables as entries. This interpolates between nearest neighbour interaction $W = 1$ and Wigner matrices $W = N$. Eigenvectors are known to be localized for $W \\ll N^{1/8}$, delocalized for $W \\gg N^{4/5}$ and it is conjectured that the transition for the bulk occurs at $W \\sim N^{1/2}$. Eigenvalues in the spectral edge change their behavior at $W \\sim N^{5/6}$ but nothing is ...

Steinerberger, Stefan

2013-01-01

437

Tunneling conductance spectra of a metal/ferromagnet junction within a two-band model  

Energy Technology Data Exchange (ETDEWEB)

We present a theory based on a scattering matrix approach to explain the tunneling spectroscopy of a metal/ferromagnet junction. The isotropic one-band free electron model was used to describe the energy dispersion relation of the electrons in a metal layer, while two-band approximation was used to examine the electronic dispersion relation within the ferromagnetic material. s-band and d-band coupling were considered using the two-band approximation. In this work, interfacial spin-flip scattering was neglected. The energy dispersion and tunneling conductance spectra were calculated to study the effect of the coupling strength between the two bands. With no coupling, the energy band will have the crossing point between the bands. In contrast, a gap is opened up at the crossing points. It was found that the size of the gap depends on the coupling strength. Some kinks occurred in the energy band corresponding to the crossing points. The rich features of conductance spectra occurring in the metallic regime have the effects more significant than those occurring in the tunneling regime. In both regimes the conductance spectrum becomes largest if the effective mass of free electrons in the majority of the bands in the ferromagnetic material is approximately in the same order as that of the free electrons in metals. - Highlights: Black-Right-Pointing-Pointer Tunneling conductance spectra of two-band ferromagnet/superconductor are calculated. Black-Right-Pointing-Pointer s-band and d-band of ferromagnet are mixed. Black-Right-Pointing-Pointer The conductance spectra consist of several kinks, depending on the coupling strength. Black-Right-Pointing-Pointer Two-band ferromagnet model is very essential.

Pasanai, K., E-mail: krisakronmsu@gmail.com [Department of Physics, Faculty of Science, Mahasarakham University, Khamriang Sub-District, Kantarawichai District, Maha Sarakham 44150 (Thailand); Pairor, P. [School of Physics, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000 (Thailand)

2013-02-15

438

Shear Band Formation in Plastic-Bonded Explosives (PBX)  

Science.gov (United States)

Adiabatic shear bands can be a source of ignition and lead to detonation. At low to moderate deformation rates, 10--1000 s-1, two other mechanisms can also give rise to shear bands. These mechanisms are: softening caused by micro-cracking 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 each of these mechanims is studied in a series of calculations. A viscoelastic constitutive model for PBX-9501 softens via a statistical crack model, based on the work of Dienes (1986). A sand model is used to provide a non-associated flow rule. Both models generate shear band formation at 1--2% strain at nominal strain rates at and below 1000 s-1. Shear band formation is suppressed at higher strain rates. The sand model gives qualitative agreement for location and orientation of shear bands observed in a punch experiment. Both mechanisms may accelerate the formation of adiabatic shear bands.

Dey, Thomas N.; Johnson, James N.

1997-07-01

439

New band structures and an unpaired crossing in 78Kr  

International Nuclear Information System (INIS)

High-spin states in 78Kr were studied using the 58Ni(23Na,3p) reaction at 70 MeV and the 58Ni(28Si,?4p) reaction at 130 MeV. Prompt ?-? coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24+ state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. copyright 1999 The American Physical Society

440

Cold versus hot shear banding in bulk metallic glass  

Science.gov (United States)

We present an analysis of the shear-banding dynamics in a bulk metallic glass (BMG), including the temperature rise in the band, the sliding speed of the band, and the time elapsed as well as the step size of the shear offset growth in a stop-and-go cycle. This model analysis quantitatively demonstrates that the major shear band can remain cold and slide in a stick-slip manner. We predict that the shear step (distance covered by a stop-and-go cycle) scales with the sample size and machine stiffness. We also illustrate the conditions when such serrated shear is unsustainable and a hot shear band directly develops in a runaway instability (catastrophe). These findings provide physical insight into the shear-instability processes and offer useful information for improving the plasticity of BMGs. The calculation results are used to explain several intriguing recent experimental observations, including the stick slip of the dominant shear-band and the sample-size effects on the plastic-flow behavior of BMGs.

Cheng, Y. Q.; Han, Z.; Li, Y.; Ma, E.

2009-10-01

441

Optically detecting spin-split bands in semiconductors in magnetic fields  

Science.gov (United States)

We report on combined theoretical and experimental studies of spin-split bands in semiconductors in magnetic fields. We have studied a wide range of systems including: 1) electron and valence band splitting in dilute magnetically doped semiconductors (DMS) systems like InMnAs, 2) electron and valence band splitting in strained InSb/AlInSb heterostructures and 3) valence band splitting in GaAs. The systems have been studied with a variety of experimental techniques including: i) ultra-high magnetic field cyclotron resonance ii) magnetoabsorption and iii) optically pumped NMR (OPNMR). Calculations are based on the 8-band Pidgeon-Brown model generalized to include the effects of the quantum confinement potential as well as pseudomorphic strain at the interfaces and sp-d coupling between magnetic impurities and conduction band electrons and valence band holes. Optical properties are calculated within the golden rule approximation and compared with experiments. Detailed comparison to experiment allows one to accurately determine conduction and valence band parameters including effective masses and g-factors. Results for InMnAs show shifts in the cyclotron resonance peaks with Mn doping. For InSb, we find a sensitive dependence of the elecronic structure on the strain at the pseudomorphic interfaces. For GaAs, we show that OPNMR allows us to spin-resolve the valence bands and that structure in the OPNMR signal is dominated by the weaker light hole to conduction band Landau level transitions.

Pan, X.; Sun, Y.; Saha, D.; Sanders, G. D.; Santos, M. B.; Doezema, R. E.; Hayes, S.; Khodaparast, G.; Munekata, H.; Matsuda, Y. H.; Kono, J.; Stanton, C. J.

2012-10-01

442

Relaxation and cross section effects in valence band photoemission spectroscopy  

International Nuclear Information System (INIS)

Various problems relating to the interpretation of valence band x-ray photoemission (XPS) spectra of solids are discussed. The experiments and calculations reported herein deal with the following questions: (1) To what extent do many-body effects manifest themselves in an XPS valence band spectrum, and thus invalidate a direct comparison between the photoemission energy distribution, I(E), and the density of states, N(E), calculated on the basis of ground-state one-electron theory. (2) The effect of the binding-energy-dependent photoemission cross section on I(E) at XPS energies. (3) In favorable cases indicated by (1) and (2) we examine the effect of the interaction of the crystal field with the apparent spin-orbit splittings of core levels observed in XPS spectra. (4) The use of tight binding band structure calculations to parameterize the electronic band structure from XPS and other data is described. (5) The use of high energy angle-resolved photoemission on oriented single crystals to gain orbital symmetry information is discussed. (6) The evolution of the shape of the photoemission energy distribution (of polycrystalline Cu) as a function of photon energy from 50 less than or equal h ? less than or equal 175 is discussed

443

Thermal emissivity for finite three-dimensional photonic band gap crystals  

OpenAIRE

We discuss the results of computer model for the thermal emissivity of a three-dimensional photonic band gap (PBG) crystal, specifically an inverted opal structure. The thermal emittance for a range of frequencies and angles is calculated.

Stimpson, Andrew J.; Dowling, Jonathan P.

2002-01-01

444

Interband electronic Raman scattering of polarized light in cubic semiconductors with degenerate valence bands  

International Nuclear Information System (INIS)

The cross-sections are calculated for the Raman scattering processes with polarized light in cubic semiconductors where the valence band top is fourfold degenerate ?8. The exciton effect is taken into account. (author). 17 refs

445

Band alignment of semiconductors from density-functional theory and many-body perturbation theory  

Science.gov (United States)

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.

Hinuma, Yoyo; Grüneis, Andreas; Kresse, Georg; Oba, Fumiyasu

2014-10-01

446

Rotational side bands in 160Dy  

International Nuclear Information System (INIS)

The 158Gd(?,2n)160Dy reaction has been used to study rotational side bands in 160Dy. Several negative-parity bands are observed, with several members of K? = 1-, 2- and 40 bands and of a K? = 8- band only the bandhead. A pronounced odd-even staggering of moments of inertia is found for members of the K? = 2- band. Of the positive-parity bands the K? = 2+(?)band, which is seen up to a possible spin of 12 and low-spin members of K? = (O+), (S), and 4+ bands are observed. The mixing between most of the ?-band and S-band members is observed to be smaller than 2% and no evidence for possible anti-alignment of low-spin S-band members with rotation is found. (orig.)

447

Photonic crystal digital alloys and their band structure properties.  

Science.gov (United States)

We investigated semi-disordered photonic crystals (PCs), digital alloys, and made thorough comparisons with their counterparts, random alloys. A set of diamond lattice PC digital alloys operating in a microwave regime were prepared by alternately stacking two kinds of sub-PC systems composed of alumina and silica spheres of the same size. Measured transmission spectra as well as calculated band structures revealed that when the digital alloy period is short, band-gaps of the digital alloys are practically the same as those of the random alloys. This study indicates that the concept of digital alloys holds for photons in PCs as well. PMID:21996867

Lee, Jeongkug; Kim, Dong-Uk; Jeon, Heonsu

2011-09-26

448

Coherent current states in a two-band superconductor  

International Nuclear Information System (INIS)

Homogeneous current states in thin films and Josephson current in superconducting microbridges are studied within the frame of a two-band Ginzburg-Landau theory. By solving the coupled system of equations for two order parameters the depairing current curves and Josephson current-phase relation are calculated foe different values of phenomenological parameters ? and ?. Coefficients ? and ? describe the coupling of order parameters (proximity effect) and their gradients (drag effect), respectively. For define values of parameters the dependence of current j on superfluid momentum q contains local minimum and corresponding bi-stable states. It is shown that the Josephson microbridge from two-band superconductor can demonstrate ?-junction behavior

449

Phase solitons and subgap excitations in two-band superconductors  

Science.gov (United States)

A phase soliton is a topological defect peculiar to two-band superconductors, which is associated with a 2? winding of the relative phase of the two superconducting condensates. I study the quasiparticle spectrum in the presence of a single planar phase soliton. I show that the order-parameter phase variation in each of the bands leads to the existence of subgap states bound to the soliton. Calculation of the soliton energy valid at all temperatures is presented with exact analytical results obtained for a simple soliton model.

Samokhin, K. V.

2012-08-01

450

Topological defects and subgap excitations in two-band superconductors  

Science.gov (United States)

Phase solitons are topological defects peculiar to two-band superconductors, which are associated with a 2? winding of the relative phase of the two superconducting condensates. The order parameter phase variation in each of the bands leads to the quasiparticle bound states whose energies are below the bulk gap. We calculate the single soliton energy as well as the interaction energy of two solitons, at arbitrary temperature. Applications to a similar system -- one or more domain walls in a chiral p-wave superconductor -- are discussed.

Samokhin, Kirill; Przedborski, Michelle

2013-03-01

451

Limitations to band gap tuning in nitride semiconductor alloys  

DEFF Research Database (Denmark)

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.

Gorczyca, I.; Suski, T.

2010-01-01

452

C-Band LINAC for a race track microtron  

OpenAIRE

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...

Carrillo Barrera, David Manuel

2010-01-01

453

Quasiparticle semiconductor band structures including spin-orbit interactions.  

Science.gov (United States)

We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors. PMID:23396813

Malone, Brad D; Cohen, Marvin L

2013-03-13

454

Corrugated flat band as an origin of large thermopower in hole doped PtSb2  

OpenAIRE

The origin of the recently discovered large thermopower in hole-doped PtSb$_2$ 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 ...

Kouta Mori; Hidetomo Usui; Hirofumi Sakakibara; Kazuhiko Kuroki

2012-01-01

455

Band-gap renormalization and optical many-body effects in diluted magnetic semiconductors  

CERN Document Server

We calculate the Coulomb interaction induced many-body band-gap renormalization in a typical diluted magnetic semiconductor Ga_{1-x}Mn_{x}As in the optimally-doped metallic regime as a function of carrier density and temperature. We find a large (~ 0.1 eV) band gap renormalization which is enhanced by the ferromagnetic transition. We also calculate the impurity scattering effect on the gap narrowing.

Zhang, Y; Zhang, Ying

2005-01-01

456

Study of backbending and decoupled bands in a spherical basis formalism  

International Nuclear Information System (INIS)

A study of backbending and decoupled rotational bands is presented in the context of a particle plus rotor model with pairing. The model is first applied to the case of N particles in a single j = 13/2 orbital, coupled to a strongly deformed rotor. Backbending arises in the two-particle case, while no backbend is seen in the twelve-particle case. From these results, backbending apparently arises from the intersection of a mixed low-spin band (mostly J = 0 and 2) with an aligned high-spin band (mostly J = 12). Only one moment of inertia is required to produce the backbend. The odd-N calculation yields decoupled bands for N 7. Overlap integrals with k = 1/2 and k = 13/2 strongly coupled bands are calculated. The calculation is extended to an exact treatment of four particles in the 13/2 orbital. This calculation produces the same backbending mechanism as before except for the fact that the aligned large-J band contains large components with J = 14. At large spin, the calculation produces another backbend, which arises from the alignment of the second pair of particles. The applicability of this result in a real nucleus is discussed in connection with a second yrast discontinuity in 158Er. The use of the lab frame model in the description of real nuclei is demonstrated by the odd-mass Pd calculation. The calculations yield good fits to intraband energy spacings in 101Pd, 103Pd, and 105Pd,d, 103Pd, and 105Pd, and the character (normal or decoupled) of the various bands is well reproduced. The bandheads are less well fit, especially in 105Pd. The model is extended to the even Pd nuclei where a two-quasiparticle calculation is presented for the negative-parity bands in 102Pd. The attempted extension is unsuccessful

457

Strain induced band gap deformation of H/F passivated graphene and h-BN sheet  

OpenAIRE

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...

Bhattacharya, A.; Bhattacharya, S.; Das, G. P.

2011-01-01

458

Plasmon bands in multilayer graphene  

Science.gov (United States)

High-energy collective electronic excitations (plasmons) in freestanding multilayer graphene are studied by momentum-resolved electron energy-loss spectroscopy (EELS). For normal incidence, only the high-energy plasmon band is excited and we measure a blueshift of the ? -plasmon dispersion with increasing thickness. The observed transition between two-dimensional and three-dimensional behavior is explained using a layered-electron-gas (LEG) model. We propose a method to measure all individual plasmon bands by tilting the sample with respect to the electron beam. As a proof of concept, EELS experiments for three-layer graphene are compared with predictions from the LEG model.

Wachsmuth, P.; Hambach, R.; Benner, G.; Kaiser, U.

2014-12-01

459

Holographic Multi-Band Superconductor  

CERN Document Server

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.

Huang, Ching-Yu; Maity, Debaprasad

2011-01-01

460

Calculation of Gilbert damping in ferromagnetic ?lms  

Directory of Open Access Journals (Sweden)

Full Text Available The Gilbert damping constant in the phenomenological Landau-Lifshitz-Gilbert equation which describes the dynamics of magnetization, is calculated for Fe, Co and Ni bulk ferromagnets, Co ?lms and Co/Pd bilayers within a nine-band tight-binding model with spin-orbit coupling included. The calculational effciency is remarkably improved by introducing ?nite temperature into the electronic occupation factors and subsequent summation over the Matsubara frequencies. The calculated dependence of Gilbert damping constant on scattering rate for bulk Fe, Co and Ni is in good agreement with the results of previous ab initio calculations. Calculations are reported for ferromagnetic Co metallic ?lms and Co/Pd bilayers. The dependence of the Gilbert damping constant on Co ?lm thickness, for various scattering rates, is studied and compared with recent experiments.

Edwards D. M.

2013-01-01