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1

Band structure built from oligomer calculations  

Science.gov (United States)

A method to build accurate band structures of polymers from oligomer calculations has been developed. This method relies on systematic procedures for (i) assigning k values, (2) eliminating strongly localized molecular orbitals, and (iii) connecting bands across the entire Brillouin zone. Illustrative calculations are carried out at the HF/STO-3G level for trans-polyacetylene (PA), poly(para-phenylene) (PPP), and water chains. More stringent tests at several different levels are reported for polydiacetylene/polybutatriene.

Pomogaeva, Anna; Kirtman, Bernard; Gu, Feng Long; Aoki, Yoriko

2008-02-01

2

Debye-Hueckel theory for spin ice at low temperature  

International Nuclear Information System (INIS)

At low temperatures, spin ice is populated by a finite density of magnetic monopoles--pointlike topological defects with a mutual magnetic Coulomb interaction. We discuss the properties of the resulting magnetic Coulomb liquid in the framework of Debye-Hueckel theory, for which we provide a detailed context-specific account. We discuss both thermodynamical and dynamical signatures and compare Debye-Hueckel theory to experiment as well as numerics, including data for specific heat and AC susceptibility. We also evaluate the entropic Coulomb interaction that is present in addition to the magnetic one and show that it is quantitatively unimportant in the current compounds. Finally, we address the role of bound monopole anti-monopole pairs and derive an expression for the monopole mobility.

3

Behavior of molecules on interstellar grains: Application of the Langevin equation and iterative extended Hueckel  

International Nuclear Information System (INIS)

The Langevin equation was used to explore an adsorbate desorption mechanism. Calculations were performed using iterative extended Hueckel on a silica model site with various small adsorbates, e.g., H, CH, OH, NO, CO. It was found that barriers to free traversal from one site to another are substantial (approx.3-10 eV). A bootstrap desorption mechanism for some molecules in the process of forming at a site also became apparent from the calculations. The desorption mechanisms appear to be somewhat balanced by a counterforce--the attraction of sites for the newly desorbed molecule. The order of attraction to a silica grain site for the diatomic moleceules considered was OH>CH>CO>NO, when these entites were sufficiently distant. The nature of the silica grain and that of the ''cold'' desorption mechanism, when considered together, suggest that the abundance of very small grain might be less common than anticipated

4

Behavior of molecules on interstellar grains - Application of the Langevin equation and iterative extended Hueckel  

Science.gov (United States)

The Langevin equation was used to explore an adsorbate desorption mechanism. Calculations were performed using iterative extended Hueckel on a silica model site with various small adsorbates, e.g., H, CH, OH, NO, CO. It was found that barriers to free traversal from one site to another are substantial (about 3-10 eV). A bootstrap desorption mechanism for some molecules in the process of forming at a site also became apparent from the calculations. The desorption mechanisms appear to be somewhat balanced by a counterforce - the attraction of sites for the newly desorbed molecule. The order of attraction to a silica grain site for the diatomic molecules considered was OH greater than CH greater than CO greater than NO, when these entities were sufficiently distant. The nature of the silica grain and that of the 'cold' desorption mechanism, when considered together, suggest that the abundance of very small grains might be less common than anticipated.

Aronowitz, S.; Chang, S.

1980-01-01

5

Energy Band Calculations for Maximally Even Superlattices  

Science.gov (United States)

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

Krantz, Richard; Byrd, Jason

2007-03-01

6

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

7

First-principles electronic-band calculations on organic conductors  

Directory of Open Access Journals (Sweden)

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

Shoji Ishibashi

2009-01-01

8

Impact ionisation rate calculations in wide band gap semiconductors  

International Nuclear Information System (INIS)

Calculations of band-to-band impact ionisation rates performed in the semi-classical Fermi's Golden Rule approximation are presented here for the semiconductors GaAs, In0.53Ga0.47As and Si0.5Ge0.5 at 300K. The crystal band structure is calculated using the empirical pseudopotential method. To increase the speed with which band structure data at arbitrary k-vectors can be obtained, an interpolation scheme has been developed. Energies are quadratically interpolated on adapted meshes designed to ensure accuracy is uniform throughout the Brillouin zone, and pseudowavefunctions are quadratically interpolated on a regular mesh. Matrix elements are calculated from the pseudowavefunctions, and include the terms commonly neglected in calculations for narrow band gap materials and an isotropic approximation to the full wavevector and frequency dependent dielectric function. The numerical integration of the rate over all distinct energy and wavevector conserving transitions is performed using two different algorithms. Results from each are compared and found to be in good agreement, indicating that the algorithms are reliable. The rates for electrons and holes in each material are calculated as functions of the k-vector of the impacting carriers, and found to be highly anisotropic. Average rates for impacting carriers at a given energy are calculated and fitted to Keldysh-type expressions with higher than quadratic dependence of the rate on energy above threshold being obtained in all cases. The average rates calculated here are compared to results obtained by other workers, with reasonable agreement being obtained for GaAs, and poorer agreement obtained for InGaAs and SiGe. Possible reasons for the disagreement are investigated. The impact ionisation thresholds are examined and k-space and energy distributions of generated carriers are determined. The role of threshold anisotropy, variation in the matrix elements and the shape of the bands in determining characteristics of the rate, particularly the softness of the rate's threshold behaviour are investigated. (author)

9

Relativistic Band Calculation and the Optical Properties of Gold  

DEFF Research Database (Denmark)

The energy band structure of gold is calculated by the relativistic augmented-plane-wave (RAPW) method. A nonrelativistic calculation is also presented, and a comparison between this and the RAPW results demonstrates that the shifts and splittings due to relativistic effects are of the same order of magnitude as the gaps (approximately 1 eV). Various integrated functions, density of states, joint density of states, and energy distributions of joint density of states are derived from the RAPW calculation. These functions are used in an interpretation of photoemission and static reflectance measurements. It is shown that the photoemission results are extremely well described in terms of a model assuming all transitions to be direct whereas a nondirect model fails. The ?2 profile calculated in a crude model assuming constant matrix elements matches well the corresponding experimental results. The calculated interband edge (??i=2.38 eV) agrees with experimental values, and the absorption tail below the interband edge which is found in experimental traces is also contained in the theoretical curve. By means of a calculation of the Fermi surface and the constant-energy-difference surfaces it has been possible to trace out the regions in k? space where the edge and tail transitions occur. It is demonstrated that structure in the static reflection curves are not related to critical points in the band structure. The arguments are supported by calculations of temperature shifts of the critical-point energies and comparison to the observed temperature shifts of the elements of structure in the experimental ?2 function. Such structure may originate in extended rather than localized regions of k? space. In contrast, critical-point transitions show up clearly in modulated reflectance spectra, and all elements of structure are fully accounted for by our band model. The temperature and strain responses in the band structure are determined by performing the RAPW calculation with two lattice constants and estimating the effects ofthe lattice vibrations by means of an OPW-LCAO (linear combination of atomic orbitals) scheme with pseudopotential Fourier constants reduced by the appropriate Debye-Waller factors. The phonon spectrum has been calculated for the latter purpose.

Christensen, N Egede; Seraphin, B. O.

1971-01-01

10

Reduced Bloch mode expansion for periodic media band structure calculations  

CERN Document Server

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

Hussein, Mahmoud I

2008-01-01

11

Diffraction Calculations and Measurements in Millimeter Frequency Band  

Directory of Open Access Journals (Sweden)

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

P. Pechac

2004-09-01

12

Plasmon-pole models affect band gaps in GW calculations  

Science.gov (United States)

Density functional theory calculations have long been known to underestimate the band gaps in semiconductors. Significant improvements have been made by using GW calculations that uses the self energy, defined as the product of the Green function (G) and screened Coulomb exchange (W). However, many approximations are made in the GW method, specifically the plasmon-pole approximation. This approximation replaces the integration necessary to produce W with a simple approximation to the inverse dielectric function. Four different plasmon-pole approximations have been tested using the tight-binding program ABINIT: Godby-Needs, Hybertsen-Louie, von der Linden-Horsch, and Engel-Farid. For many materials, the differences in the GW band gaps for the different plasmon-pole models are negligible, but for systems with localized electrons, the difference can be larger than 1 eV. The plasmon-pole approximation is generally chosen to best agree with experimental data, but this is misleading in that this ignores all of the other approximations used in the GW method. Improvements in plasmon-pole models in GW can only come about by trying to reproduce the results of the numerical integration rather than trying to reproduce experimental results.

Larson, Paul; Wu, Zhigang

2013-03-01

13

Emission bands of phosphorus and calculation of band structure of rare earth phosphides  

International Nuclear Information System (INIS)

The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band

14

Determination of the internal energy of dense ionized matter by a nonlinear Debye-Hueckel theory  

International Nuclear Information System (INIS)

The internal energy of a plasma is studied based on the Debye-Hueckel theory, which was modified in the case of dense plasmas keeping the nonlinear term of the Poisson equation. Numerical solutions are given. The one-dimensional version of the problem is solved analytically. The method is extended to two-component plasmas. The results are in good agreement with Monte-Carlo simulations. (D.Gy.)

15

Band gaps in pseudopotential self-consistent GW calculations  

CERN Document Server

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, confirming conclusions drawn earlier for CaB_6 and YH_3. Iterating the quasi-particle wave functions as well gives rise to an imbalance between the Hartree and Fock potentials and results in bandgaps in far poorer agreement with experiment.

Popa, V A; Kelly, P J

2005-01-01

16

Perturbation expansion of the ground-state energy for the one-dimensional cyclic Hubbard system in the Hueckel limit  

International Nuclear Information System (INIS)

The perturbation expansion coefficients for the ground-state energy of the half-filled one-dimensional Hubbard model with N = 4? + 2, (? = 1,2,...) sites and satisfying cyclic boundary conditions were calculated in the Hueckel limit (U/? ? 0), where ? designates the one-electron hopping or resonance integral, and U, the two-electron on-site Coulomb integral. This was achieved by solving-order by order-the Lieb-Wu equations, a system of transcendental equations that determines the set of quasi-momenta (ki) and spin variable ?? for this model. The exact values for these quantities were found for the N = 6 member ring up to the 20th order in terms of the coupling constant B = U/2?, as well as numerically for 10 ? N ? 50, and the N = 6 Lieb-Wu system was reduced to a system of sextic algebraic equations. These results are compared with those of the infinite system derived analytically by Misurkin and Ovchinnikov. It is further shown how the results of this article can be used for the interpolation by the root of a polynomial. It is demonstrated that a polynomial of relatively small degree provides a very good approximation for the energy in the intermediate coupling region. 20 refs., 3 tabs

17

Rigorous study of the mean field approximation of Debye and Hueckel for Coulomb systems  

International Nuclear Information System (INIS)

The statistical mechanics of a classical charge symmetric Coulomb system is studied in three dimensions in the limit that the plasma parameter (the inverse temperature divided by the Debye length) goes to zero. To make the system stable, a short range interaction, e.g., hard cores is included. This short range interaction is allowed to go to zero as the plasma parameter goes to zero. Debye and Hueckel used a mean field approximation to give a nonrigorous study of Coulomb systems in his limit. For a system with no external charge distribution, it is shown that the pressure, density, and correlation functions are asymptotic to their Debye-Hueckel approximations. These approximations consist of the ideal gas term plus a term of one lower order in the plasma parameter. The main tools are the Sine-Gordon transformation, the Mayer expansion, and some new correlation inequalities. The sine-Gordon transformation and the Mayer expansion are used to express the observables as functional integrals with respect to a Gaussian measure. The correlation inequalities help control these functional integrals

18

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

International Nuclear Information System (INIS)

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

19

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

Science.gov (United States)

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. Project supported by the National Natural Science Foundation of China (Grant No. 60636030).

Yu, Xiu; Gu, Yong-Xian; Wang, Qing; Wei, Xin; Chen, Liang-Hui

2011-03-01

20

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)

 
 
 
 
21

First-principle band calculation of ruthenium for various phases  

CERN Document Server

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

Watanabe, S; Kai, T; Shiiki, K

2000-01-01

22

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)

23

Ab Initio calculation of band gap renormalization in highly excited GaAs  

CERN Document Server

We present ab initio quasiparticle self-energy calculations in crystalline GaAs for cases of intense electronic excitation (~ 10% of valence electrons excited into conduction band), relevant for high-intensity ultra-short pulsed laser experiments. Calculations are performed using an out-of-equilibrium generalization of the GW approximation based on the Keldysh Green's function approach. Our results indicate that while the band gap is a sensitive function of the amount of excitation, it is not possible to induce complete band gap closure in this system by purely electronic means.

Spataru, C D; Louie, S G; Spataru, Catalin D.; Benedict, Lorin X.; Louie, Steven G.

2004-01-01

24

Optical band gap of SrTcO3 from first-principles calculations  

Science.gov (United States)

Although there are intensive studies on technetium oxide SrTcO3 recently, its ground-state band structure has never been given and no consensus on its band gap is obtained. We use the generalized gradient approximation (GGA) with on-site Coulomb corrections (GGA + U) method to study its band structure and the optical band gap. A series of on-site interaction U and J values are employed in the calculations and the concomitant evolutions of the electronic structure, local magnetic moment of technetium (Tc), the exchange constant and the Néel temperature are investigated. The inter-site exchange constant between antiferromagnetic Tc atoms through medium oxygen is found to increase firstly and then decrease with an increasing U, in agreement with the trend obtained by tight-binding method. The appropriate on-site U and J values are calibrated by comparing the calculated local magnetic moment of Tc with the experimental value. It is found that when U = 2.3 eV, J = 0.3 eV are included for Tc 4d in GGA + U calculations, the local magnetic moment of Tc in orthorhombic SrTcO3 is 2.01 ?B, the same as the experimental value obtained at 4 K. The calculated band structure shows that the band gap is a direct band gap with a magnitude of 1.61 eV.

Dai, Cheng-Min; Ma, Chun-Lan

2014-02-01

25

Calculations for the band lineup of strained InxGa1-xN/GaN quantum wells: Effects of strain on the band offsets  

Science.gov (United States)

Band lineup is one of the most important parameters associated with carrier confinement in heterostructures. Relations for computing the band lineups of InxGa1-xN based heterostructures have been developed. The band positions for InxGa1-xN/GaN heterointerfaces are calculated from the equations developed, which directly corelate the positions of the bands with the band gap of InN and strain at the interface. The strains are calculated from the In mole fractions and lattice constants. The parameters implicitly involved are the elastic stiffness constants (C11 and C12), the hydrostatic deformation potential of the conduction band (a'), and the hydrostatic deformation potential (a) and shear deformation potential (b) for the valence band. Computations have been carried out for different reported band gaps of InN. The effects of strain become prominent as the mole fraction of In increases, changing the band offset ratio.

Das, Tapas; Kabi, Sanjib; Biswas, Dipankar

2009-02-01

26

Metal-ceramic adhesion: Synthesis of aluminum and chromium mixed metal oxides and extended Hueckel modeling of metal-metal oxide interfaces  

Energy Technology Data Exchange (ETDEWEB)

Methods of chemical synthesis and theoretical calculation was used to form new materials that have improved adhesion of a thin metal film to a ceramic. Two goals of this investigation were to develop new synthesis of metal-ceramic couples with improved adhesion between the two components and a fundamental understanding of the chemical factors that affect adhesion. Extended Hueckel calculations were performed on a series of Pt- and NiPt-NiO metal-ceramic couples to examine bonding. The calculations showed an 5 fold increase in adhesion energy in NiPt-NiO over Pt-NiO. Bonding across the interface is found to decrease with increased electron donation as interfacially antibonding orbitals are filled. The synthesis of (Al[sub 1[minus]x]Cr[sub x])[sub 2]O[sub 3] mixed metal oxide powders and coatings by sol-gel methodology utilizing three chromium precursors is reported. Thus, Al[Cr(CO)[sub 3]C[sub 5]H[sub 5

Boorse, R.S.

1993-01-01

27

External arguments for the chaotic bands calculation in the Mandelbrot set  

Science.gov (United States)

In this paper we study the chaotic bands of any Mandelbrot set hyperbolic component. We use external arguments in order to identify the hyperbolic components. If we use harmonics as a tool, we can directly calculate the chaotic bands. Indeed, as we clearly show here, the harmonics of the external arguments of a given hyperbolic component (gene) are the external arguments of the last appearance hyperbolic components of the chaotic bands corresponding to the gene. Likewise, we explain some differences in the chaotic region of cardioids and discs.

Pastor, G.; Romera, M.; Alvarez, G.; Montoya, F.

2005-08-01

28

Study of ZrCl by self-consistent band calculation  

Energy Technology Data Exchange (ETDEWEB)

A nonrelativistic self-consistent electronic band structure calculation has been performed on zirconium monochloride using the KKR method. The exchange potential was approximated by the X..cap alpha.. method. The compound contains homoatomic layers in the sequence Cl--Zr--Zr--Cl and has the characteristics of a graphite-like two-dimensional metal. A substantial charge transfer is found toward the metallic layers and away from the loosely bonded halogen layer. There is also significant admixture of Zr-d character within the filled Cl-3p bands. The total density of states is in good agreement with the valence band photoemission results.

Marchiando, J.F.

1979-07-01

29

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)

30

Electronic structure of Ce 5Rh 4Sn 10 from XPS and band structure calculations  

Science.gov (United States)

We present a combined experimental and theoretical study of the electronic structure for the heavy-fermion antiferromagnet Ce5Rh4Sn10 based on X-ray photoemission spectroscopy (XPS) data and ab initio band structure calculations. The Ce core-level XPS spectra point to a stable trivalent configuration of Ce atoms in Ce5Rh4Sn10, consistently with both the magnetic susceptibility data and the results of computational structure optimization. The band structure calculations confirm a magnetic ground state with significant magnetic moments only at the Ce atoms. The qualitatively correct description of Ce3+ in Ce5Rh4Sn10 has been achieved using the LSDA+U approach for the Ce 4f states. The comparison of the theoretical results with experimental XPS valence band spectrum supports their validity. The calculated partial densities of states suggest that there is a variation in binding energy of the occupied 4f states between Ce atoms in nonequivalent crystallographic positions, which is related to the hybridization with Sn states. Finally, the band structure and charge density maps point to the formation of zig-zag chains of the strongly bounded Sn(2), Sn(3) and Rh atoms along the tetragonal axis, whereas Sn(1) shows nearly dispersionless 5s bands.

Gam?a, M.; ?lebarski, A.; Rosner, H.

2008-05-01

31

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

International Nuclear Information System (INIS)

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

32

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

33

SUBBAND STATES IN INVERSION LAYERS FROM SINGLE AND MULTIPLE BAND CALCULATIONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Selfconsistent subband calculations for inversion layers on InSb and HgCdTe are performed using a single (2x2) and a multiple band (8x8) model. We obtain subband separations and Fermi energies that are independent of the models.

Malcher, F.; Ziegler, A.; Ro?ssler, U.; Lommer, G.

1987-01-01

34

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

35

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

36

CsSnX3 (X= Cl, Br, I) band structure calculations by the QSGW method  

Science.gov (United States)

CsSnX3 (X=Cl,Br,I) perovskite compounds are of interest because of their strong photoluminescence and their potential application to solar cells. We present quasiparticle self-consistent GW (QSGW) calculations for the cubic (?-phase) including spin-orbit coupling and study the changes in band structures from the ?-phase to the ?- and ?-phases in LDA. The QSGW gaps are in good agreement with experiment. An analysis of the orbital character of the bands shows that they have an ``inverted'' band structure: the VBM has a non-degenerate s-like character (Sn-s and X-p antibonding), while the (CBM) has Sn-p character. The strongly intra-atomic dipole allowed nature of the direct gap explains the high photoluminescent intensity. The low hole mass indicates high hole mobility in agreement with experiment. The pressure dependence of the gap is found to be anomalous: the band gap decreases when the lattice constant is decreased. Effective masses and the Kohn-Luttinger type Hamiltonian of the CBM are extracted from the band structures and subsequently used to estimate exciton binding energies using our calculated dielectric constants. These indicate a much lower exciton binding energy for CsSnI3 than recently proposed.

Huang, Ling-Yi; Lambrecht, Walter R. L.

2013-03-01

37

Band gap and band parameters of InN from quasiparticle energy calculations based on exact-exchange densityfunctional theory  

International Nuclear Information System (INIS)

Despite significant improvements in the fabrication and quality of InN, the exact values of the InN bandgap and of the band parameters are still controversially discussed. We have therefore performed quasiparticle energy calculations in the G0W0 approximation using as input the bandstructure obtained in the exact-exchange (EXX) approach. In previous studies we showed that this approach systematically provides bandgaps with an accuracy of ?0.1 eV. Employing this approach we find a bandgap of 0.7 eV for wurtzite InN, suggesting an intrinsic value at the lower end of the experimentally observed range. Taking the Burnstein-Moss effect into account, the increase of the apparent gap with increasing electron concentration is in good agreement with the experimentally observed blue shift of the optical absorption edge. Moreover, the concentration dependence of the effective mass, which results from the non-parabolicity of the conduction band, agrees well with recent experimental findings. The upper range of experimentally observed bandgaps is explained in terms of a defect/impurity model based on the charge neutrality level

38

Electronic band structure and magnetic states of zigzag graphene nanoribbons: quantum chemical calculations  

Science.gov (United States)

Quantum-chemical semi-empirical molecular-orbital calculations of zigzag graphene nanoribbons (nzGNRs) were done for the number of zigzag carbon chains n=4 and 10. The antiferromagnetic (AFM) nature of zGNRs' ground state was confirmed. The energy difference between AFM and ferromagnetic (FM) states was calculated, and dimerization patterns of their chemical bond lengths were elucidated. The electron energy band structure calculations show that narrow nanoribbon (4 zGNR) is semiconducting in both AFM and FM states. For wider nanoribbon (10 zGNR), the AFM state is semiconducting (?0.1 eV band gap), whereas the FM state is half-metallic (electrical conduction with only one spin orientation).

Poklonski, Nikolai A.; Kislyakov, Eugene F.; Vyrko, Sergey A.; Bubel', Oleg N.; Ratkevich, Sergey V.

2012-01-01

39

Discrete-variational Dirac-Slater calculations on the valence band XPS for ?-uranium metal  

International Nuclear Information System (INIS)

We have performed relativistic molecular orbital calculations for the valence band structure of ?-uranium metal, using the discrete-variational Dirac-Slater (DV-DS) method. We have used a U9 model cluster for the calculation of the bulk electronic structure of ?-uranium metal. The calculated valence X-ray photoelectron spectrum (XPS) which is obtained from the U9 model cluster agrees well with the experimental spectrum. The peaks in the experimental spectrum are assigned to atomic components on the basis of the partial density of states (pDOS) for uranium atomic orbitals (AOs)

40

Band calculations for 4f systems based on the dynamical mean field theory  

International Nuclear Information System (INIS)

Recent band calculations for Ce compounds based on the dynamical mean field theory (DMFT) are reported. The auxiliary impurity problem has been solved by a method named NCAf2vc, which includes the correct exchange process of the f1?f0, f2 virtual excitation, the crystalline field splitting (CFS), and the spin-orbit interaction (SOI) of the self-energy. These are necessary features in the quantitative band theory for Ce compounds. The results of applications on Ce metal and Ce-monopnictides are presented

 
 
 
 
41

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

42

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

43

Relativistic Band-Structure Calculations for CeTIn$_5$(T=Ir and Co)  

CERN Document Server

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn$_5$ (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 $4f$ 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 superconductivity in CeTIn$_5$ 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$_5$ by including $f$-$f$ and $p$-$p$ hoppings as well as $f$-$p$ hybridization, whic...

Maehira, T; Ueda, K; Hasegawa, A

2002-01-01

44

Numerical extraction of de Haas - van Alphen frequencies from calculated band energies  

CERN Document Server

A new algorithm for extracting de Haas - van Alphen frequencies, effective masses, and electronic density of states contributions from calculated band energies is presented. The algorithm creates an interpolated k-space "super cell", which is broken into slices perpendicular to the desired magnetic field direction. Fermi surface orbits are located within each slice, and de Haas - van Alphen frequencies, effective masses and density of states contributions are calculated. Orbits are then matched across slices, and extremal orbits determined. This technique has been successful in locating extremal orbits not previously noticed in the complicated topology of existing UPt3 band-structure data; these new orbits agree with experimental de Haas - van Alphen measurements on this material, and solidify the case for a fully-itinerant model of UPt3.

Rourke, P M C

2008-01-01

45

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

46

Proper Generalized Decomposition applied to linear acoustic: A new tool for broad band calculation  

Science.gov (United States)

The calculation of the acoustic response of systems in frequency bands is becoming increasingly important in simulation-based engineering design. This is particularly true in medium-frequency bands, where the response is very sensitive to the frequency. Some standard techniques for addressing these problems present a frequency dependent formulation and may involve fixed-frequency calculations at many different frequencies. In this paper, we propose a new technique which combines the Variational Theory of Complex Rays (VTCR) with Proper Generalized Decomposition (PGD) and does not require the resolution of acoustic problems at many frequencies. In this approach, the VTCR is used to find an approximate solution of a medium-frequency acoustic problem using only a few degrees of freedom (DOFs). Then, PGD is used to find a representation of the approximate solution which is separated between two variables, the wave propagation direction and the frequency. A relevant numerical example is used to present the strategy and illustrate its applicability for frequency band calculations.

Barbarulo, Andrea; Ladevèze, Pierre; Riou, Hervé; Kovalevsky, Louis

2014-05-01

47

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

Energy Technology Data Exchange (ETDEWEB)

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

Popescu, V.; Zunger, A.

2012-02-15

48

Multivalence-band calculation of the excitonic dielectric function for hexagonal GaN  

International Nuclear Information System (INIS)

The complex dielectric function of hexagonal gallium nitride (?-GaN) is obtained from a numerical solution of the excitonic Schrödinger equation taking into account the full 6 × 6 valence-band structure. The valence-band parametrization includes anisotropy, nonparabolicity, and the coupling of angular-momentum eigenstates. Spectra of excitonic eigenfunctions are obtained from a time-dependent initial-value problem, which is solved via an exponential split-operator method. In particular, we calculate the dielectric function and the reflectivity of a-plane GaN with polarization vectors parallel and perpendicular to the c-axis of the crystal. The simulated reflection spectra are in excellent agreement with recent experimental data and allow the unambiguous identification of the experimentally observed excitonic resonances. The binding energies of the FXA, FXB, and FXC excitons found in our calculation differ by up to 27%, depending on the chosen parameter set. An important consequence of this observation is that the experimentally observed splittings of the excitons cannot be used for the parametrization of the valence band near the ?-point, but need to be corrected by the differences of the binding energies. This is of general relevance for all spectroscopic measurements in semiconductors with a wide bandgap. (paper)

49

Multivalence-band calculation of the excitonic dielectric function for hexagonal GaN.  

Science.gov (United States)

The complex dielectric function of hexagonal gallium nitride (?-GaN) is obtained from a numerical solution of the excitonic Schrödinger equation taking into account the full 6 × 6 valence-band structure. The valence-band parametrization includes anisotropy, nonparabolicity, and the coupling of angular-momentum eigenstates. Spectra of excitonic eigenfunctions are obtained from a time-dependent initial-value problem, which is solved via an exponential split-operator method. In particular, we calculate the dielectric function and the reflectivity of a-plane GaN with polarization vectors parallel and perpendicular to the c-axis of the crystal. The simulated reflection spectra are in excellent agreement with recent experimental data and allow the unambiguous identification of the experimentally observed excitonic resonances. The binding energies of the FXA, FXB, and FXC excitons found in our calculation differ by up to 27%, depending on the chosen parameter set. An important consequence of this observation is that the experimentally observed splittings of the excitons cannot be used for the parametrization of the valence band near the ?-point, but need to be corrected by the differences of the binding energies. This is of general relevance for all spectroscopic measurements in semiconductors with a wide bandgap. PMID:23567664

Lenk, Steve; Schwarz, Felix; Goldhahn, Rüdiger; Runge, Erich

2013-05-01

50

Improved Plane-Wave Expansion Method for Band Structure Calculation of Metal Photonic Crystal  

International Nuclear Information System (INIS)

We combine Cartesian coordinates and polar coordinates wave number eigenvalue equations based on the plane-wave expansion (PWE) method to calculate and optimize the band structures of the two-dimensional (2D) metal photonic crystals (PhCs). Compared with the traditional PWE methods for metal PhCs, the band structures can be calculated directly in our method and no further procedures are needed to handle the folded band structures. With this method, we optimize the large gap-midgap ratio of the 2D square lattice of square metal rods and circular metal rods. The TM gap-midgap ratio of the 2D square lattice of square metal rods reaches 7.6246% with the side length L=0.71a with a being the lattice constant. The TM gap-midgap ratio of the 2D square lattice of circular metal rods reaches 16.3934% with radius R=0.45a. Our method can be easily used in both square lattice and triangular lattice directly. (fundamental areas of phenomenology(including applications))

51

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

52

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

International Nuclear Information System (INIS)

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

53

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

54

Electronic Structure of CeRhIn$_{5}$ dHvA and Energy Band Calculations  

CERN Document Server

The de Haas - van Alphen effect and energy band calculations are used to study angular dependent extremal areas and effective masses of the Fermi surface of the highly correlated antiferromagnetic material CeRhIn$_5$. The agreement between experiment and theory is reasonable for the areas measured with the field applied along the (100) axis of the tetragonal structure, but disagree in size for the areas observed for the field applied along the (001) axis where the antiferromagnetic spin alignment is occurring. Detailed comparisons between experiment and theory are given.

Hall, D; Murphy, T; Tozer, S; Miller-Ricci, E; Peabody, L; Li, C Q H; Alver, U; Goodrich, R G; Sarrao, J L; Pagliuso, P G; Wills, J M; Fisk, Z; Hall, Donavan; Miller-Ricci, Eliza; Peabody, Lydia; Li, Charis Q H

2000-01-01

55

Fundamental characteristics of a new Hg3TeCl4 crystal obtained by means of the elementary energy bands concept based on AB INITIO band structure calculations  

International Nuclear Information System (INIS)

Ab initio band structure calculations of the orthorhombic Hg3TeCl4 crystals of the symmetry D2h15 were performed and the topology of its valence band was analyzed in the framework of the elementary energy bands concepts. The effective masses of charge carriers were estimated. It was demonstrated that the anisotropy of the effective mass tensor components does not coincide with the mechanical one of the Hg3TeCl4 crystal. A possible reason of this fact was proposed.

56

SGFM applied to the calculation of surface band structure of V  

International Nuclear Information System (INIS)

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

57

Comment on ''Laboratory measurements and theoretical calculations of O2 A-band electric quadrupole transitions''  

International Nuclear Information System (INIS)

D. A. Long et al.[Phys. Rev. A 80, 042513 (2009)] recently reported accurate measurements on the ultraweak electric quadrupole (E2) transitions in the O2 A band. They also presented elegant theoretical calculation of the line intensities based on Hund's case (b) formulation. However, their theoretical elucidation fails to relate to a highly relevant previous work by Balasubramanian and Narayanan [Acta Phys. Hung 74, 341 (1994)] in which closed-form expressions for the E2 branch line strengths for the eight possible rotational branches of the b1?g+-X3?g- transition, in intermediate coupling, are derived. The complete equivalence of the two methods is proven through direct calculation. A second point of concern is that the magnetic dipole (M1) transition moment M1 = 0.0687 ?B deduced by Long et al. from the previously measured transition intensities is ?2.7 times the ab initio value of 0.0255 ?B computed by Minaev et al.[Chem. Phys. 208, 299 (1996)]. Since the latter reproduces closely the measured Einstein's spontaneous emission coefficient of the A band, this large discrepancy is intriguing.

58

Nitrogen-broadened lineshapes in the oxygen A-band: Experimental results and theoretical calculations  

Science.gov (United States)

We report measurements for N 2-broadening, pressure-shift and line mixing coefficients for 55 oxygen transitions in the A-band retrieved using a multispectrum fitting technique. Nineteen laboratory absorption spectra were recorded at 0.02 cm -1 resolution using a multi-pass absorption cell with path length of 1636.9 cm and the IFS 120 Fourier transform spectrometer located at Justus-Liebig-University in Giessen, Germany. The total sample pressures ranged from 8.8 to 3004.5 Torr with oxygen volume mixing ratios in nitrogen ranging between 0.057 and 0.62. An Exponential Power Gap (EPG) scaling law was used to calculate the N 2-broadening and N 2-line mixing coefficients. The line broadening and shift coefficients for the A-band of oxygen self-perturbed and perturbed by N 2 are modeled using semiclassical calculations based on the Robert-Bonamy formalism and two intermolecular potentials. These potentials involve electrostatic contributions including the hexadecapole moment of the molecules and (a) a simple dispersion contribution with one adjustable parameter to fit the broadening coefficients or (b) the atom-atom Lennard-Jones model without such adjustable parameters. The first potential leads to very weak broadening coefficients for high J transitions whereas the second potential gives much more improved results at medium and large J values, in reasonable agreement with the experimental data. For the line shifts which mainly arise in our calculation from the electronic state dependence of the isotropic potential, their general trends with increasing J values can be well predicted, especially from the first potential. From the theoretical results, we have derived air-broadening and air-induced shift coefficients with an agreement comparable to that obtained for O 2-O 2 and O 2-N 2.

Predoi-Cross, Adriana; Holladay, Christopher; Heung, Henry; Bouanich, Jean-Pierre; Mellau, Georg Ch.; Keller, Reimund; Hurtmans, Daniel R.

2008-09-01

59

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2014-03-31

60

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)

 
 
 
 
61

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

International Nuclear Information System (INIS)

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

62

Electronic band structure of lanthanum bromide and strontium iodide from many-body perturbation theory calculations  

Science.gov (United States)

Rare-earth based scintillators represent a challenging class of scintillator materials due to pronounced spin-orbit coupling and subtle interactions between d and f states that cannot be reproduced by standard electronic structure methods such as density functional theory. In this contribution we present a detailed investigation of the electronic band structure of LaBr3 using the quasi-particle self-consistent GW (QPscGW) method. This parameter-free approach is shown to yield an excellent description of the electronic structure of LaBr3. Specifically we reproduce the correct level ordering and spacing of the 4f and 5d states, which are inverted with respect to the free La atom, the band gap as well as the spin-orbit splitting of La-derived states. We furthermore present electronic structure calculations using G0W0 for the important scintillator material SrI2. We explicitly take into account spin-orbit coupling at all levels of the theory. Our results demonstrate the applicability and reliability of the GW approach for rare-earth halides and complex halides. They furthermore provide an excellent starting point for investigating the electronic structure of rare-earth dopants such as Ce and Er.

Aberg, Daniel; Ehart, Paul; Sadigh, Babak

2012-02-01

63

Band calculations of the GPA high-pressure effects on the heavy lanthanide metals  

International Nuclear Information System (INIS)

Jackson's group and Mito's group have performed the systematic studies for the GPa high-pressure effects on the magnetic properties of the heavy lanthanide elements. They found that the Curie temperatures decrease linearly with increasing pressure and the magnetic signals disappear at around 9.0 GPa for Gd, 7.5 GPa for Tb, 7.4 GPa for Dy and 11.0 GPa for Ho. With the Anderson's point of view, the results of our band calculation conclude that some part of the decreasing of the bulk magnetization of Gd by pressure is caused by the narrowing of the bandwidth of itinerant s, d hybridized conduction electrons and the broadening of the bandwidth of localized f-orbital electrons

64

Band calculations of the GPA high-pressure effects on the heavy lanthanide metals  

Science.gov (United States)

Jackson's group and Mito's group have performed the systematic studies for the GPa high-pressure effects on the magnetic properties of the heavy lanthanide elements. They found that the Curie temperatures decrease linearly with increasing pressure and the magnetic signals disappear at around 9.0 GPa for Gd, 7.5 GPa for Tb, 7.4 GPa for Dy and 11.0 GPa for Ho. With the Anderson's point of view, the results of our band calculation conclude that some part of the decreasing of the bulk magnetization of Gd by pressure is caused by the narrowing of the bandwidth of itinerant s, d hybridized conduction electrons and the broadening of the bandwidth of localized f-orbital electrons.

Tokita, M.; Zenmyo, K.; Mito, M.; Matsumoto, K.; Takeda, K.

2007-03-01

65

Techniques for calculation of the band structure and low-energy secondary electron spectroscopy of iridium  

International Nuclear Information System (INIS)

Fine structure (FS) of the secondary electron emission spectrum (SEMS) os iridium perpendicular to (111) surface and of the total current spectrum (TCS) of Ir polycrystal was interpreted theoretically. The calculations took account of the energy dependence of the energy band level expansion, the electron-electron and the electron-plasmon contributions into distribution function of nonequilibrium electrons current isotopic component from the electrons scattered within the surface. SEMS and TCS FS was shown to result mainly from the electron structure of the terminal state. The elaborated technique enabled to separate the volume effect in SEMS and TCS from the surface ones. Dependence of SEMS and TCS FS on the geometrical structure and the degree of crystal ordering was proved. In that case, moderation of FS intensity served as a measure of defectiveness within a specimen near-the-surface range

66

Antiferromagnetic band structure of La2CuO4: Becke- 3-Lee-Yang-Parr calculations  

Science.gov (United States)

Using the Becke-3-Lee-Yang-Parr (B3LYP) functional, we have performed band-structure calculations on the high-temperature superconductor parent compound, La2CuO4. Under the restricted spin formalism (??=??), B3LYP band structure agrees well with the standard local-density approximation (LDA) band structure. It is metallic with a single Cu x2-y2/O p? band crossing the Fermi level. Under the unrestricted spin formalism (?????), the B3LYP band structure has a spin-polarized antiferromagnetic solution with a band gap of 2.0 eV, agreeing well with experiment. This state is 0.52 eV (per formula unit) lower than that calculated under the restricted spin formalism. The apparent high energy of the spin-restricted state is attributed to an overestimate of on-site Coulomb repulsion, which is corrected in the unrestricted spin calculations. The stabilization of the total energy with spin polarization arises primarily from the stabilization of the x2-y2 band, such that the character of the eigenstates at the top of the valence band in the antiferromagnetic state becomes a strong mixture of Cu x2-y2/O p? and Cu z2/O' pz. Since the Hohenberg-Kohn theorem requires the spin-restricted and spin-unrestricted calculations to give identical ground-state energies and total spatial densities for the exact functionals, this large disparity in energy reflects the inadequacy of current functionals for describing the cuprates. This calls into question the use of band structures based on current restricted spin-density functionals (including LDA) as a basis for single-band theories of superconductivity in these materials.

Perry, Jason K.; Tahir-Kheli, Jamil; Goddard, William A.

2001-04-01

67

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

Science.gov (United States)

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.

Andrzejewski, Janusz

2013-09-01

68

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

69

Voltage effect in PTCR ceramics: Calculation by the method of tilted energy band  

International Nuclear Information System (INIS)

A numerical model for the calculation of the electrical characteristics of donor-doped BaTiO3 semiconducting ceramics is suggested. This paper established a differential equation about electron level on the base of Poisson equation, and solved the equation with Runge-Kutta method. Under extra electric field, electrical characteristics have been calculated by the method of tilted energy band. We have quantitatively computed the positive temperature coefficient of resistivity (PTCR) behavior of donor-doped BaTiO3 semiconducting ceramics and its voltage effect, and further obtained non-linear current-voltage characteristics with different grain sizes at different temperature. The results pointed out that the resistance jumping is reduced with increasing electric field applied; current and voltage relation follows Ohm's law below Curie temperature, and exhibits strong non-linear above Curie temperature; the non-linear coefficient shows a maximum value at temperature the resistivity reaches maximum and with grain size closed to depletion region width. The results are compared with experimental data.

70

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

International Nuclear Information System (INIS)

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

71

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-11-15

72

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-05-15

73

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

Science.gov (United States)

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

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

2014-10-01

74

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

75

Calculation of wakefields in a 17 GHz beam-driven photonic band-gap accelerator structure  

Science.gov (United States)

We present the theoretical analysis and computer simulation of the wakefields in a 17 GHz photonic band-gap (PBG) structure for accelerator applications. Using the commercial code CST Particle Studio, the fundamental accelerating mode and dipole modes are excited by passing an 18 MeV electron beam through a seven-cell traveling-wave PBG structure. The characteristics of the longitudinal and transverse wakefields, wake potential spectrum, dipole mode distribution, and their quality factors are calculated and analyzed theoretically. Unlike in conventional disk-loaded waveguide (DLW) structures, three dipole modes (TM11-like, TM12-like, and TM13-like) are excited in the PBG structure with comparable initial amplitudes. These modes are separated by less than 4 GHz in frequency and are damped quickly due to low radiative Q factors. Simulations verify that a PBG structure provides wakefield damping relative to a DLW structure. Simulations were done with both single-bunch excitation to determine the frequency spectrum of the wakefields and multibunch excitation to compare to wakefield measurements taken at MIT using a 17 GHz bunch train. These simulation results will guide the design of next-generation high-gradient accelerator PBG structures.

Hu, Min; Munroe, Brian J.; Shapiro, Michael A.; Temkin, Richard J.

2013-02-01

76

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

77

Band structure of the solid state - interpretation of the nature of the chemical bond in some transition metal compounds in terms of energy band structure calculations  

International Nuclear Information System (INIS)

The nature of chemical binding for some transition metal compounds (ScN, ScO, TiC, TiN, Tio, VC, VN, VO) with NaCl structure is discussed in terms of energy band structure calculations. The discussion is based on the wave functions and energy eigenvalues, as calculated by the 'Quasi self sonsistent APW method' as well as on the energy eigen values and eigen vectors resulting from the Slater-Koster LCAO-Tight binding interpolation scheme. The LCAO-TB l-like partial density of states can be used to analyse the valence bands. This analysis shows, that the deepest valence band has predominantly s-character. The following bands, which can be derived in essence from the atomic 2p states of the of the non metal are characterized not only by the partial p-like density of states but also by a substantial contribution from the d-like partial density of states, which is decreasing going from a particular Carbide to the corresponding Oxide. For the valence bands, which can be associated with the atomic 3d states of the metal, the density of states exhibits besides the partial d-density of states small contributions from the partial p-like density of states. The decomposition of the d-like partial density of states into an esub(g)-like and a tsub(2g)-like contribution is discussed. By analyzing the APW crystal wave functions the partial l-like charges inside each atomic sphere can be obtained. If the APW total charges within the atomic spheres are compared with the charges of a hyeres are compared with the charges of a hypothetical crystal, which correspond to a superposition of the charge densities of the neutral atoms, a transfer of electrons from the metal to the non-metal sphere is found for all compounds under investigation. (orig.)

78

Calculation of optical band gaps of a-Si:H thin films by ellipsometry and UV-Vis spectrophotometry  

Science.gov (United States)

Hydrogenated amorphous silicon (a-Si:H) thin films doped with Phosphorus (P) and Nitrogen (N) were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The optical band gaps of the thin films obtained through either changing the gas pressure (P-doped only) or adulterating nitrogen concentration (with fixed P content) were investigated by means of Ellipsometric and Ultraviolet-Visible (UV-Vis) spectroscopy, respectively. Tauc formula was used in calculating the optical band gaps of the thin films in both methods. The results show that Ellipsometry and UV-Vis spectrophotometry can be applied in the research of the optical properties of a-Si:H thin films experimentally. Both methods reflect the variation law of the optical band gaps caused by CVD process parameters, i.e., the optical band gap of the a-Si:H thin films is increased with the rise of the gas pressure or the nitrogen concentration respectively. The difference in optical band gaps of the doped a-Si:H thin films calculated by Ellipsometry or UV-Vis spectrophotometry are not so great that they both can be used to measure the optical band gaps of the thin films in practical applications.

Qiu, Yijiao; Li, Wei; Wu, Maoyang; Fu, Junwei; Jiang, Yadong

2010-10-01

79

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

80

Band gap engineering of early transition-metal-doped anatase TiO2: first principles calculations.  

Science.gov (United States)

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

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

2014-10-21

 
 
 
 
81

Systematic two-band model calculations of the GMR effect with metallic and non-metallic spacers and with impurities  

International Nuclear Information System (INIS)

By a semi-empirical 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 an 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 non-metallic spacers in the ballistic limit

82

Systematic two-band model calculations of the GMR effect with metallic and non-metallic spacers and with impurities  

Energy Technology Data Exchange (ETDEWEB)

By a semi-empirical 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 an 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 non-metallic spacers in the ballistic limit.

Gebele, O. E-mail: gebele@tu-harburg.de; Boehm, M. E-mail: mboehm@wila-verlag.de; Krey, U. E-mail: uwe.krey@physik.uni-regensburg.de; Krompiewski, S. E-mail: stefan.krompiewski@ifmpan.poznan.pl

2000-06-01

83

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

84

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

85

Time Dependent Density Functional Theory Calculations of Large Compact PAH Cations: Implications for the Diffuse Interstellar Bands  

Science.gov (United States)

We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)

2002-01-01

86

Quantum confinement effect in armchair graphene nanoribbons: Effect of strain on band gap modulation studied using first-principles calculations  

Science.gov (United States)

The quantum confinement effect may play an important role in the gap modulation of armchair graphene nanoribbons (AGNRs) under strain. Using the phase accumulation model, we have investigated the energy-dependent phase shift ?(?) at the ? point of AGNRs under various strains using first-principles calculation. The calculation results show that although the energy dispersion of the phase shift is modified by strain, the phase shift near the Fermi level is close to 0.75?, indicating that strain has little effect near that energy level. We can approximate the energy-dependent phase shift by a constant, ?(?)=0.75?, for AGNRs under various x strains. Due to the structural similarity between AGNRs and zigzag carbon nanotubes (ZCNTs), the electronic properties of AGNRs should be similar to those of ZCNTs. The quantization condition of the wave vector of ZCNTs governed by the periodic boundary condition along the circumference direction is similar to that of AGNRs except that the phase shift is equal to zero, ? (?)=0. Using the zone-folding (ZF) method, we can calculate the band gap of any strained AGNR (ZCNT) from the phase shift ?=0.75? (?=0) and the electronic structure of the strained graphene. The AGNR shows a zigzag behavior of the dependence of the band gap on strain which is very similar to the ZCNT. The zigzag patterns are significantly shifted by different phase shifts. The peak value of the band gap and the period of the pattern decreases as the width of the ribbon increases. For a given AGNR, the peak value and the period of the pattern increase as the strain increases. A flattening of the peaks appears at the strain where the maximum band gap occurs due to large compressive strain. All these observations can be understood easily from our ZF calculations. The agreement between our model and real local-density approximation calculations indicates that our model can provide an efficient and accurate method to estimate the band gap of AGNRs and ZCNTs under strain, and therefore can provide a better understanding of the effect of quantum confinement on the electronic properties of AGNRs.

Loh, Siow Mean; Huang, Yu-Hui; Lin, Ken-Ming; Su, W. S.; Wu, B. R.; Leung, T. C.

2014-07-01

87

Calculated hydroxyl A2 sigma --> X2 pi (0, 0) band emission rate factors applicable to atmospheric spectroscopy  

Science.gov (United States)

A calculation of the A2 sigma --> X2 pi (0, 0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant fluorescence in the terrestrial atmosphere is presented in this paper. The most accurate available line parameters have been used. Special consideration has been given to the solar input flux because of its highly structured Fraunhofer spectrum. The calculation for the OH atmospheric emission rate factor in the solar resonant fluorescent case is described in detail with examples and intermediate results. Results of this calculation of OH emission rate factors for individual rotational lines are on average 30% lower than the values obtained in an earlier work.

Cageao, R. P.; Ha, Y. L.; Jiang, Y.; Morgan, M. F.; Yung, Y. L.; Sander, S. P.

1997-01-01

88

First-principles calculations of the optical band-gaps of Zn xCd 1- xO alloys  

Science.gov (United States)

Using first-principles calculations, we investigated the structural and electronic properties of two binaries: ZnO in wurtzite structure and CdO in wurtzite and rock-salt structures. In addition several compositions with various ordered structures of Zn xCd 1- xO alloys were studied within the theory of order-disorder transformation. The full potential linearized augmented plane wave method was used and the d orbitals of Zn and Cd were included in the valence bands. In this investigation of alloying ZnO with CdO, the fundamental band-gap of the alloys is shown to be direct and to decrease versus the Cd composition.

Rozale, H.; Bouhafs, B.; Ruterana, P.

2007-07-01

89

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

90

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

Energy Technology Data Exchange (ETDEWEB)

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.

Appalakondaiah, S.; Vaitheeswaran, G., E-mail: gvaithee@gmail.com [Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Hyderabad 500 046, Andhra Pradesh (India); Lebègue, S. [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France)

2014-01-07

91

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

International Nuclear Information System (INIS)

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

92

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

93

Density functional calculation of band-parameters for boron nitride at normal and high pressures  

International Nuclear Information System (INIS)

The present work employs the total-energy pseudopotential technique within the framework of the density-functional theory with both the local-density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional so as to calculate the structural, electronic, chemical bonding and elastic properties of BN in the zinc-blende structure at normal and high pressures. The results are generally in good agreement with the available experimental data. We found that in many cases (except may be for elastic constants) the GGA improves agreement with experiment. The calculations showed that the transition pressure for BN from the zinc-blende phase to the rocksalt phase is much smaller than previously reported theoretical values

94

Density functional calculation of band-parameters for boron nitride at normal and high pressures  

Energy Technology Data Exchange (ETDEWEB)

The present work employs the total-energy pseudopotential technique within the framework of the density-functional theory with both the local-density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional so as to calculate the structural, electronic, chemical bonding and elastic properties of BN in the zinc-blende structure at normal and high pressures. The results are generally in good agreement with the available experimental data. We found that in many cases (except may be for elastic constants) the GGA improves agreement with experiment. The calculations showed that the transition pressure for BN from the zinc-blende phase to the rocksalt phase is much smaller than previously reported theoretical values.

Saib, S. [Physics Department, Faculty of Science and Engineering, University of M' sila, 28000 M' sila (Algeria); Bouarissa, N. [Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha (Saudi Arabia)], E-mail: N_Bouarissa@yahoo.fr

2008-01-10

95

An improved treatment of overlapping absorption bands based on the correlated k distribution model for thermal infrared radiative transfer calculations  

International Nuclear Information System (INIS)

This paper discusses several schemes for handling gaseous overlapping bands in the context of the correlated k distribution model (CKD). Commonly used methods are generally based on certain spectral correlation assumptions; thus they are either less accurate or less efficient and rarely apply to all overlapping bands. We propose a new treatment, which we developed from the traditional absorber amount weighted scheme and improved for application to various bands. This approach is quite efficient for treating the gaseous mixture as if it were a 'single gas.' Numerical experiments demonstrate that the new scheme achieves high accuracy with a fast operating speed. To validate the new scheme, we conducted spectrally integrated calculations and sensitivity experiments in the thermal infrared region. Compared to line-by-line integration results, errors in cooling rates were less than 0.2 K/day below 70 Km and rose to 1 K/day from above 70 Km up to 100 Km; flux differences did not exceed 0.8 W/m2 at any altitude. Changes in CO2 and H2O concentrations slightly influenced the accuracy of the results.

96

Constrained nudged elastic band calculation of the Peierls barrier with atomic relaxations  

International Nuclear Information System (INIS)

We demonstrate that the straightforward application of the nudged elastic band (NEB) method does not determine the correct Peierls barrier of 1/2?1 1 1? 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 direct application of stress in the atomistic modeling of the dislocation glide. (paper)

97

Calculation of absorption in the microwindows of the 4.3-micron CO2 band from an ECS scaling analysis  

Science.gov (United States)

Line coupling induced by collisions leads to drastic modifications of the absorption profile in the microwindows of the self- and N2-broadened nu(3) CO2 fundamental vibration-rotation band. Calculations of these modifications have been performed by using the energy-corrected sudden (ECS) scaling law. Linewidths have been inverted to obtain effective rotation-translation basis rate constants and to deduce R-R, P-P and R-P line couplings. The characteristics of these couplings are presented and discussed. Calculated ECS profiles in the microwindows are compared with experimental data and also with previous results based on a statistical fitting law. The ECS approach is particularly suitable for practical infrared spectroscopic applications including line-coupling effects.

Boissoles, J.; Boulet, C.; Bonamy, L.; Robert, D.

1989-12-01

98

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

99

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

100

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

 
 
 
 
101

Electronic band calculation of BaPd2Sb2: Which polymorph is stable?  

Science.gov (United States)

Iron-pnictide superconductor (Ba,K)Fe2As2 and nickelate superconductor BaNi2As2 both have the ThCr2Si2-type crystal structure. On the other hand, platinum superconductor SrPt2As2 has the CaBe2Ge2-type crystal structure. We focused on BaPd2Sb2, which contains Pd located between Ni and Pt on the periodic table. We have calculated the electronic structure of BaPd2Sb2 from first-principles, and found that the CaBe2Ge2-type structure is more stable. The Fermi surfaces of BaPd2Sb2 are two-dimensional for the CaBe2Ge2-type structure, and are three-dimensional for the ThCr2Si2-type structure. The calculated D(EF) is 32.1 States/Ry, which is comparable with that in SrPt2As2. These results strongly suggest that superconductivity also occurs in BaPd2Sb2.

Hase, I.; Yanagisawa, T.

2013-11-01

102

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

International Nuclear Information System (INIS)

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 120o 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 ?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 120o intersection forming GL in Ni and Cu are ?0.47 and ?0.65 eV, respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are ?0.68 and ?0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120o intersection forming HL in Ni and Cu are estimated to be ?0.09 and ?0.31 eV, respectively. These values are a ctively. 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.

103

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

104

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

105

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.)

106

Direct calculation of valence-band Auger emission: Spin polarization of Auger electrons from a potassium (110) surface  

Science.gov (United States)

We report calculations on spin-polarized Auger electron emission from the valence band of a potassium (110) film. In treating this process we use an N-electron scheme that is based on a generalized version of density-functional theory. The transition rate is determined by explicitly evaluating the transition matrix elements that contain the four states involved. The core and valence states are obtained from a self-consistent full-potential linearized augmented plane wave calculation on a K(110) multilayer. In the experiments that the present calculations refer to, the particular oriented core-hole state is created by photoexcitation using circularly polarized light. The observed energy spectrum and the angular dependence of the spin polarization of the emitted Auger electrons can be simply related to the character of the spinor-hole state. We compare our results for normal incidence of the light to the pertinent experiments on the Auger spin polarization referenced to the spin of the incoming photons. The results are in fair agreement with each other.

Yuan, Jianmin; Fritsche, L.; Noffke, J.

1997-10-01

107

The electronic structure of MoO2. Comparison of photoemission spectroscopy, macroscopic measurements and band-structure calculations  

International Nuclear Information System (INIS)

In this work the electronic properties and the surface structure of the transition metal oxide MoO2 are examined. The interest in MoO2 is due to its close structural relationship to VO2 which is controversially discussed in literature. Different cuts through the Fermi body of MoO2 and the band dispersion along selected directions of high symmetry were measured by angular resolved photoemission spectroscopy (ARUPS). A comparison of the ARUPS results to existing LDA calculations and Shubnikov de Haas measurements shows a good qualitative agreement of experiment an theory. A quantitative comparison reveals discrepancies between the LDA calculations and the experimental findings. These variations can be interpreted in terms of non-negligible many body effects, which are insufficiently incorporated by the LDA calculations. The order of the single crystal surfaces of MoO2 was examined by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). It is shown that the preparation of the surface crucially controls its atomic structure. Dependent on the mode of preparation different surface reconstructions exist, which in turn clearly modify the electronic structure

108

IOS and ECS line coupling calculation for the CO-He system - Influence on the vibration-rotation band shapes  

Science.gov (United States)

Line coupling coefficients resulting from rotational excitation of CO perturbed by He are computed within the infinite order sudden approximation (IOSA) and within the energy corrected sudden approximation (ECSA). The influence of this line coupling on the 1-0 CO-He vibration-rotation band shape is then computed for the case of weakly overlapping lines in the 292-78 K temperature range. The IOS and ECS results differ only at 78 K by a weak amount at high frequencies. Comparison with an additive superposition of Lorentzian lines shows strong modifications in the troughs between the lines. These calculated modifications are in excellent quantitative agreement with recent experimental data for all the temperatures considered. The applicability of previous approaches to CO-He system, based on either the strong collision model or exponential energy gap law, is also discussed.

Boissoles, J.; Boulet, C.; Robert, D.; Green, S.

1987-01-01

109

IOS and ECS line coupling calculation for the CO-He system - Influence on the vibration-rotation band shapes  

Science.gov (United States)

Line coupling coefficients resulting from rotational excitation of CO perturbed by He are computed within the infinite order sudden approximation (IOSA) and within the energy corrected sudden approximation (ECSA). The influence of this line coupling on the 1-0 CO-He vibration-rotation band shape is then computed for the case of weakly overlapping lines in the 292-78 K temperature range. The IOS and ECS results differ only at 78 K by a weak amount at high frequencies. Comparison with an additive superposition of Lorentzian lines shows strong modifications in the troughs between the lines. These calculated modifications are in excellent quantitative agreement with recent experimental data for all the temperatures considered. The applicability of previous approaches to CO-He system, based on either the strong collision model or exponential energy gap law, is also discussed.

Boissoles, J.; Boulet, C.; Robert, D.; Green, S.

1987-09-01

110

Optical polarization in columnar InAs/GaAs quantum dots: 8-band k?p calculations  

Science.gov (United States)

We have theoretically studied the optical polarization in columnar InAs/GaAs quantum dots (QDs), in which the self-assembled QDs are vertically stacked with no interdot spacing. The model structure of the columnar QDs consists of truncated-cone-shaped InAs QDs with the stacking-layer numbers (SLNs) of 1, 3, 5, 7, and 9. We used the valence-force-field model to calculate the strain distribution. We find that the biaxial strain in the middle layers of the columnar QDs decreases with increasing SLN and becomes negative for SLN=9 . This is due to the condition that the vertical lattice constant of InAs in these layers has to match that of the side GaAs. By using the strain-dependent 8-band k?p theory for the electronic states, we calculated the transverse-electric (TE)- and transverse-magnetic (TM)-mode intensities for the electron-hole transitions. The piezoelectric effect is included in the calculations. For SLN=1 and 3, only the TE-mode transition occurs. With increasing SLN beyond 3, the TM-mode intensity increases while the TE-mode one decreases. Consequently, when SLN changes from 7 to 9, the dominant polarization character changes from the TE mode to the TM mode. This dominant polarization change is attributed to the increase of the light-hole character in the wave function of the ground hole state, which is the consequence of the negative biaxial strain in the middle layers for SLN=9 . The change in the optical polarization calculated in this study is in good agreement with the photoluminescence experiment reported by Kita [Jpn. J. Appl. Phys., Part 2 41, L1143 (2002)].

Saito, Toshio; Ebe, Hiroji; Arakawa, Yasuhiko; Kakitsuka, Takaaki; Sugawara, Mitsuru

2008-05-01

111

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

Science.gov (United States)

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 consistent with the experimental observation.

Aizawa, H.; Kuroki, K.; Yasuzuka, S.; Yamada, J.

2012-11-01

112

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

113

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

114

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

Science.gov (United States)

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

Rafiee Dastjerdi, S.; Ghanaatshoar, M.

2013-08-01

115

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

International Nuclear Information System (INIS)

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

116

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

International Nuclear Information System (INIS)

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

117

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

118

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

119

Calculation of the total energy per unit cell and of the band structures of the five nucleotide base stacks using the local-density approximation  

Science.gov (United States)

All-electron first-principles total energy electronic structure calculations were carried out for single chains of four nucleotide base stacks (composed of adenine, thymine, guanine, and cytosine, respectively) in the DNA B conformation (3.36 Å stacking distance and 36° screw angle ?) using the local-density approximation (LDA) within a helical band structure approach. A uracil stack was also computed in the DNA B conformation and compared with the results obtained for the four DNA base stacks. The total energies per unit cell as a function of the stacking distance (at fixed screw angle ?=36°) and of the screw angle (at d=3.36 Å) show in most cases rather good agreement with the experiment. As expected with LDA calculations, the band gaps were underestimated by nearly 50% compared to experimentally suggested values. Finally, some suggestions are given for the improvement of the band structures of the nucleotide base stacks.

Zhang, M.-L.; Miao, M. S.; Van Doren, V. E.; Ladik, J. J.; Mintmire, J. W.

1999-11-01

120

Calculation of the Total Energy per Unit Cell and of the Band Structures of the Five Nucleotide Base Stacks Using the Local Density Approximation (LDA)  

Science.gov (United States)

All-electron first-principles total energy electronic structure calculations were carried out for single chains of four nucleotide base stacks (composed of adenine, thymine, guanine, and cytosine, respectively) in the DNA B conformation (3.36Åstacking distance and 36 deg screw angle) using the local-density approximation within a helical band structure approach. A uracil stack was also computed in the DNA B conformation and compared with the results obtained for the four DNA base stacks. The total energies per unit cell as a function of the stacking distance (at fixed screw angle =36 deg) and of the screw angle (at d=3.36Åshow in most cases rather good agreement with the experiment. As expected with LDA calculations, the band gaps were underestimated by nearly 50some suggestions are given for the improvement of the band structures of the nucleotide base stacks.

Zhang, Ming-Liang; Miao, Mao Sheng; van Doren, Victor. E.; J. J. Ladik Collaboration; J. W. Mintmire Collaboration

2000-03-01

 
 
 
 
121

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

International Nuclear Information System (INIS)

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

122

Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction  

International Nuclear Information System (INIS)

The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP

123

Energy spectrum and structure of thin pseudomorphic InAs quantum wells in an AlAs matrix: Photoluminescence spectra and band-structure calculations  

Science.gov (United States)

The energy spectrum of thin pseudomorphic InAs quantum wells (QWs) in an AlAs matrix has been studied by steady-state and transient photoluminescence (PL) and calculation. It has been found that the PL spectra of the QWs consist of intense lines related to a no-phonon excitonic transition accompanied by its phonon replicas. The band alignment in the QWs is shown to be of type I, with the lowest conduction band states belonging to the indirect XXY minimum.

Shamirzaev, Timur S.; Gilinsky, Alexanser M.; Kalagin, Alexanser K.; Nenashev, Alexey V.; Zhuravlev, Konstantin S.

2007-10-01

124

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

125

Absorption cross section of ozone isotopologues calculated with the multiconfiguration time-dependent hartree (MCTDH) method: I. The Hartley and Huggins bands.  

Science.gov (United States)

The absorption cross sections of 18 isotopologues of the ozone molecule have been calculated in the range of the Hartley-Huggins bands (27000-55000 cm(-1)). All 18 possible ozone isotopologues made with (16)O, (17)O, and (18)O have been considered, with emphasis on those of geophysics interest like (16)O(3) (17)O(16)O(2), (16)O(17)O(16)O, (18)O(16)O(2), and (16)O(18)O(16)O. We have used the MCTDH algorithm to propagate wavepackets. As an initial wavepacket, we took the vibrational ground state multiplied by the transition dipole moment surface. The cross sections have been obtained from the autocorrelation function of this wavepacket. Only two potential energy surfaces (PESs) and the corresponding transition dipole moment are involved in the calculation. The dissociating R state has been omitted. The calculations have been performed only for J = 0. The comparison with the experimental absorption cross sections of (16)O(3) and (18)O(3) has been performed after an empirical smoothing which mimics the rotational envelop. The isotopologue dependence of the cross sections of 18 isotopologues can be split into two energy ranges, (a) from 27000 to 32000 cm(-1), the Huggins band, which is highly structured, and (b) from 32000 to 55000 cm(-1), the main part of the cross section which has a bell shape, the Hartley band. This bell-shaped envelop has been characterized by a new analytic model depending on only four parameters, amplitude, center, width, and asymmetry. The isotopologue dependence of these parameters reveals the tiny differences between the absorption cross sections of the various isotopologues. In contrast to the smooth shape of the Hartley band, the Huggins band exhibits pronounced vibrational structures and therefore shows large isotopologue differences which may induce a significant isotopologue dependence of the ozone photodissociation rates under actinic flux. PMID:20583798

Ndengué, Steve Alexandre; Gatti, Fabien; Schinke, Reinhard; Meyer, Hans-Dieter; Jost, Rémy

2010-09-16

126

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.

127

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.

128

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

129

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

Energy Technology Data Exchange (ETDEWEB)

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

Novokhatski, A,; /SLAC

2012-02-17

130

Model Calculations of Solar Spectral Irradiance in the 3.7 Micron Band for Earth Remote Sensing Applications  

Science.gov (United States)

Since the launch of the first Advanced Very High Resolution Radiometer (AVHRR) instrument aboard TIROS-N, measurements in the 3.7 micron atmospheric window have been exploited for use in cloud detection and screening, cloud thermodynamic phase and surface snow/ice discrimination, and quantitative cloud particle size retrievals. The utility of the band has led to the incorporation of similar channels on a number of existing satellite imagers and future operational imagers. Daytime observations in the band include both reflected solar and thermal emission energy. Since 3.7 micron channels are calibrated to a radiance scale (via onboard blackbodies), knowledge of the top-of-atmosphere solar irradiance in the spectral region is required to infer reflectance. Despite the ubiquity of 3.7 micron channels, absolute solar spectral irradiance data comes from either a single measurement campaign (Thekaekara et al. 1969) or synthetic spectra. In this study, we compare historical 3.7 micron band spectral irradiance data sets with the recent semi-empirical solar model of the quiet-Sun by Fontenla et al. (2006). The model has expected uncertainties of about 2 % in the 3.7 pm spectral region. We find that channel-averaged spectral irradiances using the observations reported by Thekaekara et al. are 3.2-4.1% greater than those derived from the Fontenla et al. model for MODIS and AVHRR instrument bandpasses; the Kurucz spectrum (1995) as included in the MODTRAN4 distribution, gives channel-averaged irradiances 1.2-1.5 % smaller than the Fontenla model. For the MODIS instrument, these solar irradiance uncertainties result in cloud microphysical retrievals uncertainties comparable with other fundamental reflectance error sources.

Platnick, Steven; Fontenla, Juan M.

2006-01-01

131

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

132

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

Science.gov (United States)

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

Forrest, Kathrine; Meijer, Paul H. E.

1990-01-01

133

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

134

Photolysis rate coefficients in the upper atmosphere: Effect of line by line calculations of the O2 absorption cross section in the Schumann Runge bands  

Science.gov (United States)

A line by line (LBL) method to calculate highly resolved O2 absorption cross sections in the Schumann Runge (SR) bands region was developed and integrated in the widely used Tropospheric Ultraviolet Visible (TUV) model to calculate accurate photolysis rate coefficients (J values) in the upper atmosphere at both small and large solar zenith angles (SZA). In order to obtain the O2 cross section between 49,000 and 57,000 cm-1, an algorithm which considers the position, strength, and half width of each spectral line was used. Every transition was calculated by using the HIgh-resolution TRANsmission molecular absorption database (HITRAN) and a Voigt profile. The temperature dependence of both the strength and the half widths was considered within the range of temperatures characteristic of the US standard atmosphere, although the results show a very good agreement also at 79 K. The cross section calculation was carried out on a 0.5 cm-1 grid and the contributions from all the lines lying at ±500 cm-1 were considered for every wavelength. Both the SR and the Herzberg continuums were included. By coupling the LBL method to the TUV model, full radiative transfer calculations that compute J values including Rayleigh scattering at high altitudes and large SZA can now be done. Thus, the J values calculations were performed for altitudes from 0 to 120 km and for SZA up to 89°. The results show, in the J case, differences of more than ±10% (e.g. at 96 km and 30°) when compared against the last version of the TUV model (4.4), which uses the Koppers and Murtagh parameterization for the O2 cross section. Consequently, the J values of species with cross sections overlapping the SR band region show variable differences at lower altitudes. Although many species have been analyzed, the results for only four of them (O2, N2O, HNO3, CFC12) are presented. Due to the fact that the HNO3 absorption cross section extends up to 350 nm this molecule was used to verify the consistency of the new TUV LBL at lower altitudes. Thus, it shows differences up to 5.7% at 21 km but 0% in the troposphere. Because of the more accurate consideration of the Rayleigh scattering the distribution of the actinic flux in its direct and diffuse components (in the SR bands wavelength interval) is also modified.

Fernández, Rafael P.; Palancar, Gustavo G.; Madronich, Sasha; Toselli, Beatriz M.

2007-03-01

135

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

Science.gov (United States)

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

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

136

Elastic moduli of copper: Electronic structure contributions from pseudopotentials and full-potential linear muffin-tin orbital band structure calculations  

Energy Technology Data Exchange (ETDEWEB)

The elastic moduli of copper have been determined from the electronic structure by using an empty core pseudopotential model and first-principles full-potential linear muffin-tin orbital (FPLMTO) band calculations. General second order stress-strain coefficients are determined from strain derivatives of the total energy. The pseudo-potential model includes d-state interactions and results in an effective pair-wise interaction between ions. In terms of the pair-wise interaction and its derivatives, formulas for the second order elastic constants are given. FPLMTO calculations are presented for the total energy and its derivatives of Cu based on a self consistent local density functional Hamiltonian with no shape approximation to the potential. Pseudopotential and FPLMTO results for the elastic moduli and their pressure derivatives are compared at pressures of zero and one Mbar. 13 refs., 9 figs., 6 tabs.

Straub, G.K.; Wills, J.M.

1989-11-01

137

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

Science.gov (United States)

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

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

2014-08-01

138

Electronic band calculation of BaPd{sub 2}Sb{sub 2}: Which polymorph is stable?  

Energy Technology Data Exchange (ETDEWEB)

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

Hase, I., E-mail: i.hase@aist.go.jp; Yanagisawa, T.

2013-11-15

139

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

140

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

 
 
 
 
141

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

142

Electronic structure of CeRhSn2 and LaRhSn2 from x-ray photoemission spectroscopy and band structure calculations  

Science.gov (United States)

We report on the electronic structure and magnetic properties of the Kondo lattice system CeRhSn2 and of the reference compound LaRhSn2. The Ce 3d and 4d x-ray photoemission spectroscopy (XPS) data point to a stable configuration of the Ce 4f shell in CeRhSn2. The ac magnetic susceptibility measurements reveal two magnetic transitions for CeRhSn2 at temperatures TC1?4 K and TC2?3 K. The temperature dependences of the ac susceptibility show also broad maxima at about 17 and 15 K for CeRhSn2 and LaRhSn2, respectively. Such features hint at spin fluctuations on Rh atoms. To get detailed insight into the electronic structure of both CeRhSn2 and LaRhSn2 we perform ab initio band structure calculations within the local (spin) density approximation (L(S)DA) and using the LSDA+U approach to account for the strong Coulomb interactions within the Ce 4f shell. The LSDA+U approximation gives qualitatively the correct physical picture of Ce3+ in CeRhSn2. The reliability of the theoretical results is confirmed by the comparison of the calculated XPS valence band spectra with experimental data. A Fermi surface analysis shows that there are some parallel sections of the sheets, which could generate 'nesting' instabilities. These nesting features might be responsible for the spin fluctuations suggested by the ac susceptibility measurements.

Gam?a, M.; ?lebarski, A.; Rosner, H.

2008-01-01

143

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 charg

144

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2014-02-21

145

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

146

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.  

Science.gov (United States)

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. PMID:24559343

Ochi, Masayuki; Sodeyama, Keitaro; Tsuneyuki, Shinji

2014-02-21

147

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

148

Interacting boson fermion-fermion model calculation of the ? h11/2 ?? h11/2 doublet bands in 134 Pr  

Science.gov (United States)

The interacting boson fermion-fermion model is employed in the analysis of the positive-parity doublet bands in 134 Pr . It is shown that stable triaxial deformation gives rise to the experimentally observed crossing between the yrast and yrare bands built on the ? h11/2 ?? h11/2 configuration. The collective structure of the yrast band is basically built on the ground-state band of the triaxial core, whereas the collective structure of the yrare band is predominantly based on the ? band of the core. The mixing between the two bands increases with angular momentum. A constant energy spacing between the two lowest positive-parity bands is predicted in other odd-odd N=75 nuclei with ? -soft potential energy surfaces.

Brant, S.; Vretenar, D.; Ventura, A.

2004-01-01

149

Interacting boson fermion-fermion model calculation of the ?h11/2-?h11/2 doublet bands in 134Pr  

International Nuclear Information System (INIS)

The interacting boson fermion-fermion model is employed in the analysis of the positive-parity doublet bands in 134Pr. It is shown that stable triaxial deformation gives rise to the experimentally observed crossing between the yrast and yrare bands built on the ?h11/2-?h11/2 configuration. The collective structure of the yrast band is basically built on the ground-state band of the triaxial core, whereas the collective structure of the yrare band is predominantly based on the ? band of the core. The mixing between the two bands increases with angular momentum. A constant energy spacing between the two lowest positive-parity bands is predicted in other odd-odd N=75 nuclei with ?-soft potential energy surfaces

150

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

151

Band calculations for Ce compounds with AuCu3-type crystal structure on the basis of dynamical mean field theory. 1. CePd3 and CeRh3  

International Nuclear Information System (INIS)

Band calculations for Ce compounds with the AuCu3-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem was solved by a method named NCA f2vc (noncrossing approximation including the f2 state as a vertex correction). The calculations take into account the crystal-field splitting, the spin-orbit interaction, and the correct exchange process of the f1 ? f0, f2 virtual excitation. These are necessary features in the quantitative band theory for Ce compounds and in the calculation of their excitation spectra. The results of applying the calculation to CePd3 and CeRh3 are presented as the first in a series of papers. The experimental results of the photoemission spectrum (PES), the inverse PES, the angle-resolved PES, and the magnetic excitation spectra were reasonably reproduced by the first-principles DMFT band calculation. At low temperatures, the Fermi surface (FS) structure of CePd3 is similar to that of the band obtained by the local density approximation. It gradually changes into a form that is similar to the FS of LaPd3 as the temperature increases, since the 4f band shifts to the high-energy side and the lifetime broadening becomes large. (author)

152

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

153

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

154

Verification of Hume-Rothery electron concentration rule in Cu5 Zn8 and Cu9 Al4 ? brasses by ab initio FLAPW band calculations  

Science.gov (United States)

Both Cu5Zn8 and Cu9Al4 ? brasses containing 52 atoms in its cubic cell have been recognized as a typical Hume-Rothery alloy phase, since these structurally complex compounds are stabilized at the same electron concentration of 1.61 electrons per atom in spite of different amounts of solute elements Zn and Al involved. Both compounds are found to possess the pseudogap at the Fermi level. Its origin has been studied by performing the full-potential linearized augmented plane-wave (FLAPW) band calculations to lay a firm foundation on the empirical Hume-Rothery electron concentration rule in a straightforward way. This was accomplished through the study of the Fourier coefficient in the plane-wave expansion of the FLAPW wave function in the intermediate region outside the muffin-tin potential for states near the Fermi level. It is concluded that electrons contributing to forming the pseudogap resonate with crystal planes associated with {330} and {411} zones and give rise to standing waves for both Cu5Zn8 and Cu9Al4 ? brasses. This clearly explains why these two compounds having different solute concentrations are stabilized at the same e/a value of 1.61.

Asahi, R.; Sato, H.; Takeuchi, T.; Mizutani, U.

2005-04-01

155

Inversion and tunneling in aziridine and aziridine-N-d. Gas-phase nuclear magnetic resonance band shape analysis and model calculations of the isotope effect  

International Nuclear Information System (INIS)

The inversion barriers in aziridine and aziridine-N-d were measured in the gas phase by NMR total band shape analysis. The isotope effect on the inversion barrier may be described by the following parameters (at 650C): ??G2+(= ?G2+/sub D/ - ?G2+/sub H/) = 0.57 +- 0.07 kcal/mol, ??H2+ = 2.1 +- 1.2 kcal/mol, ??S2+ = 4.8 +- 3.6 cal/( mol K), and k/sub H//k/sub D/ equals 2.34. Model calculations of the isotope effect, including complete vibrational analyses of the two isotopic species, are able to reproduce the experimental data only if tunneling is taken into account. Reaction coordinate frequencies of parallel?2+/sub H/parallel = 1050 +- 50 cm-1 and parallel?2+/sub D/ parallel = 800 +- 40 cm-1 for the protium and deuterium compounds, respectively, were estimated, and the barrier height, corrected for zero-point energy differences between initial and transition states (and thus comparable with theoretical inversion barriers obtained by molecular orbital methods), was found to be 19.1 kcal/mol

156

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

157

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

158

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.)

159

Calculations of electronic structure, elastic properties for YxGa1?xN and band offsets of YxGa1?xN/ScyGa1?yN heterointerfaces  

International Nuclear Information System (INIS)

Using the pseudopotential scheme under the virtual crystal approximation combined with the Harrison bond-orbital model, we report a theoretical investigation of the electronic and elastic properties of YxGa1?xN ternary alloys in the zinc-blende structure. Besides, band offsets calculations for pseudomorphically strained YxGa1?xN/ScyGa1?yN interfaces have been performed on the basis of the model solid theory. Our results agree generally well with the available experimental and previously published theoretical data. The composition dependence of the selected features of YxGa1?xN such as energy band gaps, effective masses, elastic constants, bulk modulus, shear modulus, internal strain parameter, and valence and conduction band offsets has been examined. To the author's best knowledge, there had been no reported work on these properties for the material under load

160

Quasi-two-dimensional Fermi surfaces in the flat antiferromagnetic Brillouin zone of NpRhGa5 studied by dHvA experiments and energy band calculations  

International Nuclear Information System (INIS)

We succeeded in growing a high-quality single crystal of NpRhGa5 by the Ga-flux method and observed the de Haas-van Alphen oscillation in the antiferromagnetic state. Four kinds of nearly cylindrical Fermi surfaces, which correspond to main Fermi surfaces, were clearly detected. These quasi-two-dimensional Fermi surfaces are formed in the flat antiferromagnetic Brillouin zone and are well explained on the basis of spin- and orbital-polarized LAPW energy band calculations. The cyclotron masses are moderately enhanced, ranging from 8.1 to 11.7 m0, which are approximately four times larger than the corresponding band masses. This is the first case where the 5f-itinerant band model is applicable to a neptunium magnetic compound. (letter to the editor)

 
 
 
 
161

Quasi-two-dimensional Fermi surfaces in the flat antiferromagnetic Brillouin zone of NpRhGa{sub 5} studied by dHvA experiments and energy band calculations  

Energy Technology Data Exchange (ETDEWEB)

We succeeded in growing a high-quality single crystal of NpRhGa{sub 5} by the Ga-flux method and observed the de Haas-van Alphen oscillation in the antiferromagnetic state. Four kinds of nearly cylindrical Fermi surfaces, which correspond to main Fermi surfaces, were clearly detected. These quasi-two-dimensional Fermi surfaces are formed in the flat antiferromagnetic Brillouin zone and are well explained on the basis of spin- and orbital-polarized LAPW energy band calculations. The cyclotron masses are moderately enhanced, ranging from 8.1 to 11.7 m{sub 0}, which are approximately four times larger than the corresponding band masses. This is the first case where the 5f-itinerant band model is applicable to a neptunium magnetic compound. (letter to the editor)

Aoki, Dai [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamagami, Hiroshi [Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555 (Japan); Homma, Yoshiya [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Shiokawa, Yoshinobu [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamamoto, Etsuji [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Nakamura, Akio [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Haga, Yoshinori [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Settai, Rikio [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Onuki, Yoshichika [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)

2005-05-04

162

Energy bands and optical properties of HgTe and CdTe calculated on the basis of the tight-binding model with spin-orbit interaction  

International Nuclear Information System (INIS)

It is shown that inclusion of spin-orbit interaction and omission of the usual two-center approximation in the second neighbour Slater-Koster tight-binding method leads to an improved interpolation formula for the energy bands of II-VI semiconducting compounds such as CdTe. Due to the inclusion of spin-orbit interaction it is possible to obtain the inverted band structure of HgTe. Reflectivity spectra are computed in fairly good agreement with experiment, up to 5 eV. A detailed discussion of critical points contributed to E1, E1 + ?1 and E2 maxima is carried out. Moreover, the local properties near the GAMMA point (e.g. effective mass, g factor, Kane's matrix element P, nonparabolicity, warping) of the valence and conduction bands are found to be in excellent agreement with experimental data. (author)

163

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

Science.gov (United States)

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.

Kumar, Suresh

2014-08-01

164

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

165

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

166

Particular relative positions of low energy levels in the h/sub 11/2/ band structure of /sup 119/Xe experiment and IBFA calculations  

CERN Document Server

The level ordering of the lowest members in the h/sub 11/2/ band structure of /sup 119/Xe is discussed and compared with those of xenon isotopes and isotones. A description is given in terms of the interacting boson fermion model. (5 refs).

Gizon, J; Crawford, J; Cunningham, M A; Gizon, A

1981-01-01

167

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for CdxZn1-xSe  

International Nuclear Information System (INIS)

Compound semiconductor alloys of the type AxB1-xC 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 sp3 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 talk, we concentrate on bulk CdxZn1-xSe 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 CdxZn1-xSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on CdxZn1-xSe nanowires reported in the literature.

168

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for Cd{sub x}Zn{sub 1-x}Se  

Energy Technology Data Exchange (ETDEWEB)

Compound semiconductor alloys of the type A{sub x}B{sub 1-x}C 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 sp{sup 3} 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 talk, we concentrate on bulk Cd{sub x}Zn{sub 1-x}Se 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 Cd{sub x}Zn{sub 1-x}Se layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on Cd{sub x}Zn{sub 1-x}Se nanowires reported in the literature.

Mourad, Daniel; Czycholl, Gerd [Institut fuer Theoretische Physik, Universitaet Bremen (Germany); Kruse, Carsten; Klembt, Sebastian; Retzlaff, Reiner; Hommel, Detlef [Institut fuer Festkoerperphysik, Universitaet Bremen (Germany); Gartner, Mariuca; Anastasescu, Mihai [Institute fuer Physikalische Chemie ' ' Ilie Murgulescu' ' , Rumaenische Akademie (Romania)

2011-07-01

169

First-principles calculations of the phase diagrams and band gaps in CuInSe2-CuGaSe2 and CuInSe2-CuAlSe2 pseudobinary systems  

Science.gov (United States)

The phase diagrams and band gaps in CuInSe2-CuGaSe2 (CIS-CGS) and CuInSe2-CuAlSe2 (CIS-CAS) pseudobinary systems are determined using a combination of first-principles calculations based on a hybrid Hartree-Fock density functional approach, cluster expansion, and Monte Carlo simulations. The CIS-CGS and CIS-CAS systems show phase-separation critical temperatures of 420 and 460 K, respectively. For both CuIn1-xGaxSe2 (CIGS) and CuIn1-xAlxSe2 (CIAS) alloys, the dependence of the band gaps on the temperature before quench is suggested to be small through the analysis of atomic configurational effects. The band gaps are generally close to those at the ideal disorder state and exhibit nearly quadratic composition dependences, i.e., band bowing. Composition-dependent bowing behavior is identified for CIAS, with a stronger bowing in a higher CAS composition range.

Kumagai, Yu; Soda, Yoshito; Oba, Fumiyasu; Seko, Atsuto; Tanaka, Isao

2012-01-01

170

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

171

Mental Calculation Methods Used by 11-Year-Olds in Different Attainment Bands: A Reanalysis of Data from the 1987 APU Survey in the UK.  

Science.gov (United States)

Reanalyzes data obtained in 1987 on mental calculation strategies used by 11-year-olds in England, Wales, and Northern Ireland. Classifies mental strategies developed in the past decade in international research. Compares frequency and effectiveness of the strategies used by pupils of different levels of attainment. Discusses basic arithmetic…

Foxman, Derek; Beishuizen, Meindert

2002-01-01

172

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-07-21

173

Band Interaction between Chiral Doublet Bands  

International Nuclear Information System (INIS)

Band interaction between the chiral doublet bands based on ?h11/2 vh?111/2 configuration is investigated in the particle rotor model with different triaxial deformation ?. The variation of chiral partner states with ? values is understood qualitatively based on the basic picture of two interaction levels, which is confirmed further by the calculated overlap integral of wave functions at different ? values. It is found that the interaction strengths of chiral partner states are obviously different for odd spins and even ones. (nuclear physics)

174

Field theoretic calculation of the surface tension for a model electrolyte system  

International Nuclear Information System (INIS)

We carry out the calculation of the surface tension for a model electrolyte to first order in a cumulant expansion about a free-field theory equivalent to the Debye-Hueckel approximation. In contrast with previous calculations, the surface tension is calculated directly without recourse to integrating thermodynamic relations. The system considered is a monovalent electrolyte with a region at the interface, of width h, from which the ionic species are excluded. In the case where the external dielectric constant ?0 is smaller than the electrolyte solution's dielectric constant ? we show that the calculation at this order can be fully regularized. In the case where h is taken to be zero the Onsager-Samaras limiting law for the excess surface tension of dilute electrolyte solutions is recovered, with corrections coming from a nonzero value of ?0/?

175

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

International Nuclear Information System (INIS)

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

176

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

177

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

178

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

179

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.

180

The interaction strength between bands in 166Yb nucleus  

International Nuclear Information System (INIS)

In this article the interactions strength between super band (s-band) and the ground band (g-band) s-, ?-band and ?-band are calculated. Also the interaction strength ?- and ?-bands is calculated. The unperturbed energy states for g-, ?- and ?-bands are predicted by variable moment of inertia model (VMI) and the s-band is considered as pure rotational one. The calculations of the interaction strength between bands are performed in the frame work of the two-levels approach. The predicted values of the interaction strength is in good agreement with experimental and other theoretical one. (author). 10 refs., 1 fig., 2 tabs

 
 
 
 
181

A calculation of the position of the quasi-? and quasi-? bands for the transitional nucleus 154Dy with Monte Carlo methods  

International Nuclear Information System (INIS)

A calculation of the excitation energy of the 0+ states and of the 2+ states is performed using Monte Carlo methods for the nucleus 154Dy. The Hamiltonian is assumed to be a monopole+quadrupole pairing+quadrupole with the parameters fixed by the spectroscopic Monte Carlo method so as to reproduce the experimental excitation energies of the yrast states up to J 8 within the 50-82 and 82-126 proton and neutron major shells. The resulting Hamiltonian has been diagonalized in the J = 0 and J = 2 subspaces using the quantum Monte Carlo method. The size of the basis is fixed by comparing the yrast energies obtained with the basis-independent spectroscopic Monte Carlo method, and those obtained with the quantum Monte Carlo method. The excitation energy of the 0+2 is much higher than the experimental value. The structure of the 0+2,3 and of the 2+2,3 eigenstates is discussed in terms of fluctuating intrinsic states and resolved in terms of the deformation variables. (brief report)

182

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| 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

183

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

184

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

185

Methyl vinyl ketone in the gas phase, investigated by electron diffraction, infrared band contour analysis and microwave spectroscopy, supplemented with ab-initio calculations of geometries and force fields  

Science.gov (United States)

The structure of methyl vinyl ketone was studied by the analysis of gas phase electron diffraction, microwave and infrared (IR) data, including band profiles. The experimental data are supplemented with vibrational constraints taken from force-field calculations at the 4-21G ab-initio level and with geometrical constraints arising from molecular mechanics (MMP 1 force field), and geometry relaxed 4-21G and 4-21G** ab-initio calculations. An independent vibrational analysis was performed leading to an assignment of the IR frequencies. A contour analysis allowed unequivocal identification of the ?(C?O) band centres and shapes of the two conformers. All data are in accord with the gas phase consisting of ap and sp conformers, at room temperature in the ratio ap : sp = 80 : 20. An enthalpy difference of ? H = 1.07(10) kcal mol -1 was obtained. A rationalization of why microwave spectroscopy failed to detect the sp conformer was found in the direction and magnitude of its dipole moment as well as in the value of its partition function. The experimental data favour the ab-initio constrained geometrical model, the MMP1 based model could be rejected on statistical grounds. Furthermore, the data are in accord with planar heavy atom skeletons for both the ap and sp forms. Subject to the ab-initio constraints, the internal coordinates ( rg distances, r0? angles) were refined to: C?O 1.219 Å; C?C 1.336 Å; C( sp2)?C( sp2) 1.494 Å; C( sp2)?C( sp3) 1.520 Å; 1.089 Å; 1.109 Å; C?C?C( ap) 125.0°; C?C?C( sp) 120.6°; C( sp2)?C(O)?C( sp3)( ap) 118.9°; C( sp2)?C(O)?C( sp3)( sp) 116.1°.

De Smedt, J.; Vanhouteghem, F.; Van Alsenoy, C.; Geise, H. J.; van der Veken, B.; Coppens, P.

1989-04-01

186

Band crossings in 170Os  

International Nuclear Information System (INIS)

Excited states in the neutron-deficient nucleus 170Os were identified up to spin (24+) in the yrast band and to spin (23-) in the lowest negative-parity band. Deformation systematics implied by the 2+ state energies for the very light osmium isotopes are compared with theory. Band-crossing frequencies, alignments and alignment gains are compared with cranked shell-model calculations. Deformation changes are required to obtain detailed agreement. A three-band mixing approach is invoked to explain the low-spin yrast anomaly in 172Os and to reproduce the yrast band in 170Os. The excitation energy of the postulated 'intruder' band in 170Os and 172Os is deduced. (orig.)

187

Band crossing in 170Os  

International Nuclear Information System (INIS)

Excited states in the neutron-deficient nucleus 170Os were identified up to spin (24+) in the yrast band and to spin (23-) in the lowest negative-parity band. Deformation systematics implied by the 2+ state energies for the very light osmium isotopes are compared with theory. Band-crossing frequencies, alignments and alignment gains are compared with cranked shell model calculations. Deformation changes are required to obtain detailed agreement. A three-band mixing approach is invoked to explain the low spin yrast anomaly in 172Os and to reproduce the yrast band in 170Os. The excitation energy of the postulated intruder band in 1700s and 172Os is deduced

188

Band structures of zirconium hydrides  

International Nuclear Information System (INIS)

The band structures of zirconium hydride compounds are calculated using the APW method. By comparing the bands for a hypothetical f.c.c. compound ZrH0 with f.c.c. ZrH2 (corresponding to the delta-phase), it is shown that the hydrogen atoms give rise to a new 'bonding' band below the Fermi level. The band structures of two interstitial hydrogen h.c.p. compounds ZrHsub(0.5) and ZrH (?-phase) are also calculated. For ZrHsub(0.5)with two Zr atoms and one H atom in the primitive unit cell no new bands are formed. For ZrH with two Zr atoms and two H atoms in the primitive unit cell a new band is formed just below the Fermi level but the band structure is similar to that of ZrHsub(0.5) and ?-Zr with the Fermi level raised. Estimates of the total energies show that the band structure contributions favour formation of f.c.c. ZrH2 (corresponding to the delta-phase) over an interstitial ?-phase, as is observed experimentally. (author)

189

Energy band structure of osmium  

International Nuclear Information System (INIS)

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

190

Calculation of anisotropy constants  

Science.gov (United States)

Accurate calculation is made for the anistropy constants for Ni, Co and Fe metals by using Gilat and Raubenheimer's method in d band model. The obtained result is in agreement with the experimental result. Additionally, the anisotropy constants for Ni-based alloys, Co-based alloys and Gd metal are calculated.

Mori, Nobuo; Ukai, Takeshi; Ohtsuka, Shuji

1983-02-01

191

Band-limited power flow into enclosures  

Science.gov (United States)

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

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

1977-01-01

192

First triaxial superdeformed band in 170Hf  

International Nuclear Information System (INIS)

First evidence is presented for triaxial superdeformation in 170Hf. High-spin states in this nucleus have been investigated in a ?-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.)

193

Multiple band interactions in 131Nd  

International Nuclear Information System (INIS)

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

194

Multiple band interactions in {sup 131}Nd  

Energy Technology Data Exchange (ETDEWEB)

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

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

2000-04-01

195

Superdeformed bands in {sup 145}Gd  

Energy Technology Data Exchange (ETDEWEB)

The dynamic moments of inertia of the superdeformed bands in {sup 145}Gd have been analysed in the framework of cranked Woods-Saxon-Strutinski model. Special attention was given for the observed in experiment band crossing region. The calculated moments of inertia describe fairly well the measured data. 4 refs, 2 figs.

Rzaca-Urban, T. [Warsaw Univ., Inst. of Experimental Physics, Warsaw (Poland); Lieder, R.M.; Utzelmann, S.; Gast, W.; Jaeger, H.M. [Forschungszentrum Juelich GmbH, Inst. fuer Kernphysik, Juelich (Germany); Georgiev, A. [Forschungszentrum Juelich GmbH, Inst. fuer Kernphysik, Juelich (Germany)]|[Bulgarian Academy of Sciences, Sofia (Bulgaria); Bazacco, D.; Lunardi, S.; Menegazzo, R.; Rossi-Alvarez, C. [Istituto Nazionale di Fisica Nucleare, Padua (Italy); Angelis, G. de.; Napoli, D.R.; Vedovato, G. [Istituto Nazionale di Fisica Nucleare, Legnaro (Italy); Wyss, R. [Royal Inst. of Technology, Dept. of Plasma Physics, Stockholm (Sweden)

1996-12-31

196

Band structure of superlattice with ?-like potential  

International Nuclear Information System (INIS)

Band structure of superlattice with ?-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

197

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

CERN Document Server

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

Inakura, T; Yamagami, M; Matsuyanagi, K

2002-01-01

198

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

International Nuclear Information System (INIS)

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

199

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

200

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

 
 
 
 
201

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

202

Band structure in adaptive curvilinear coordinates  

International Nuclear Information System (INIS)

The recently introduced adaptive-coordinate electronic-structure formalism is extended to finite Bloch wave vectors to permit band-structure calculations and more accurate Brillouin-zone sampling in structural energy calculations. Coordinates adapted to minimize the energy of the occupied states are shown to yield an accurate band structure for diamond far up into the conduction bands by comparison with linear augmented plane-wave results. Adaptive coordinate results for the structural properties and charge density of diamond are also reported

203

Calculation of magnetostriction constants  

Science.gov (United States)

The magnetostriction constants h1 and h2 for Ni and Fe metals and the anisotropy constants K1 and K2 for Fe metal are calculated on the basis of the approximate d bands obtained by Deegan's prescription, by using Gilat-Raubenheimer's method. The obtained results are compared with the experimental ones.

Tatebayashi, T.; Ohtsuka, S.; Ukai, T.; Mori, N.

1986-02-01

204

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

International Nuclear Information System (INIS)

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

205

Super deformed bands in A 180 mass region  

International Nuclear Information System (INIS)

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

206

Computational search for direct band gap silicon crystals  

Science.gov (United States)

Due to its abundance, silicon is the preferred solar-cell material despite the fact that current silicon materials have indirect band gaps. Although the band gap properties of silicon have been studied intensively, until now, no direct band gap silicon-based material has been found or suggested. We report here the discovery of direct band gap silicon crystals. By using conformational space annealing, we optimize various crystal structures containing multiple (10 to 20) silicon atoms per unit cell so that their electronic structures become direct band gap. Through first-principles calculations, we identify many direct and quasidirect band gap crystal structures, which exhibit excellent photovoltaic efficiency.

Lee, In-Ho; Lee, Jooyoung; Oh, Young Jun; Kim, Sunghyun; Chang, K. J.

2014-09-01

207

Spectral band selection for classification of soil organic matter content  

Science.gov (United States)

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

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

1989-01-01

208

Identification of the Brillouin zone planes in the Hume-Rothery matching rule and their role in the formation of the pseudogap from ab initio band calculations for the Al-Mg-Zn 1/1-1/1-1/1 approximant  

Science.gov (United States)

The Hume-Rothery matching rule has been widely used for many years as a practically useful guide to search for new quasicrystals and their approximants. In this work, we have performed the linear muffin-tin orbital atomic-sphere approximation band calculations for the nearly-free-electron-like Al30Mg40Zn30 1/1-1/1-1/1 approximant. It is shown that highly degenerate free-electron states in the vicinity of the center of (543), (710), and (550) planes, whose reciprocal lattice vectors well coincide with the Fermi diameter 2kF in the extended zone scheme, are all reduced to the regions centered at the point N corresponding to the center of the (110) zone planes in the reduced-zone scheme and that the lifting of these degenerate states leads to the sizable pseudogap at the Fermi level, thereby lowering the electronic energy in this system. This is, to our knowledge the first attempt to identify the Brillouin zone planes in the empirical Hume-Rothery rule and to extract their role in the formation of the pseudogap from ab initio band calculations.

Sato, Hirokazu; Takeuchi, Tsunehiro; Mizutani, Uichiro

2001-09-01

209

Excited superdeformed band in 142Sm identical to 146Gd  

International Nuclear Information System (INIS)

A study of superdeformation in the nucleus 142Sm has revealed a superdeformed band, which is isospectral for ?-ray energies above ?1 MeV with a 146Gd band. The relative alignment of these bands is compared to Hartree-Fock calculations. This second case of A?150 2p2n isospectrality is discussed in terms of specific orbitals which are often associated with identical bands

210

Bulk band gaps in divalent hexaborides  

Energy Technology Data Exchange (ETDEWEB)

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.

Denlinger, Jonathan; Clack, Jules A.; Allen, James W.; Gweon, Gey-Hong; Poirier, Derek M.; Olson, Cliff G.; Sarrao, John L.; Bianchi, Andrea D.; Fisk, Zachary

2002-08-01

211

Conduction bands in the filled skutterudites  

International Nuclear Information System (INIS)

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

212

Multiple band crossing in 164Er  

International Nuclear Information System (INIS)

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

213

Electronic energy band structure of osmium metal  

International Nuclear Information System (INIS)

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

214

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)

215

Q?band loop?gap resonator  

International Nuclear Information System (INIS)

The upper frequency for loop?gap resonators intended for use in electron?spin?resonance spectroscopy has been extended to Q band (35 GHz). A practical structure is described containing sample support, frequency tuning, and variable coupling. A typical sample volume is 39 nL. High?energy densities (15 GW?1/2) were achieved. As found previously at X band, Q?band loop?gap resonators permit observation of the dispersion with minimal demodulation of phase noise originating in the klystron. Theoretical calculations of the resonant frequency, Q, and the filling factor are found to be in good agreement with experiment

216

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

217

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

218

Energy bands and mass enhancement in yttrium  

International Nuclear Information System (INIS)

The electronic structure of Y has been calculated with the linear Muffin-Tin-Orbital method including the relativistic effects. The energy eigenvalues were determined at 392 points in the irreducible zone, with a local-density potential. The energy bands were also calculated with a non-self-consistent potential constructed from a superposition of atomic charge densities. These potentials gave rise to significantly different s-band positions, but the separation between the p- and d-bands was almost identical in the two cases. Since the state-density at the Fermi level has an s-component of only about 1% the Fermi surfaces in the two cases are very similar. The comparison between the measured and calculated Fermi-surface areas and masses is tabulated. It was concluded that the discrepancies were due to the calculated p-band lying too high relative to the d-band; when this was lowered artificially better agreement was obtained. The overall mass enhancement of the electrons at the Fermi surface in Y is considerably larger than for most other hcp transition metals. This may be due to magnetic effects. (U.K.)

219

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

220

Band Structure and Electrical Conductivity in Semiconductors  

Science.gov (United States)

In this experiment, we will, 1. understand how conductivity in semiconductors depends on carrier concentration and mobility, and how these depend on temperature, 2. distinguish between intrinsic and extrinsic temperature regimes and identify the applicable temperature range from an examination of measured data, 3. appreciate and utilize the advantages of the four-probe resistance measurement technique, 4. calculate the energy band gap for doped Si and pure Ge, 5. calculate the temperature dependent coefficient of the majority carriers, 6. through experimental realizations, appreciate a physical understanding of the band gap structure of semiconductors.

Khalid, Asma; Anwar, Muhammad S.; Zia, Wasif

2012-07-08

 
 
 
 
221

Photonic band structure and omnidirectional band gap in anisotropic superlattice  

Energy Technology Data Exchange (ETDEWEB)

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

Ouchani, N.; Bria, D.; Nougaoui, A. [Laboratoire de Dynamique et d' Optique des Materiaux, Departement de Physique, Faculte des Sciences, Universite Mohamed I, B.P. 524, 60000 Oujda (Morocco); Djafari-Rouhani, B. [Laboratoire de Dynamique et Structure des Materiaux Moleculaires, UMR CNRS 8024, UFR de Physique, Universite de Lille 1, 59655 Villeneuve d' Ascq (France)

2006-06-15

222

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

223

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.

224

Electronic properties and chemical bonding of orthorhombic chromium carbide  

Energy Technology Data Exchange (ETDEWEB)

The electronic properties of an orthorhombic phase of chromium carbide are calculated by the extended Hueckel tight-binding method. We found in this phase similar trends in band structure and total and p-d orbital projected DOS with respect to other crystalline phases calculated previously. The bonding nature is analyzed in terms of the crystal orbital overlap population (COOP). The results show a high degree of metal-non-metal hybridized states contributing to the metallic nature of bonding. (orig.)

Posada-Amarillas, A. [Sonora Univ., Hermosillo (Mexico). Dept. de Investigacion en Fisica; Galvan, D.H.; Avalos-Borja, M. [UNAM, Ensenada, B.C. (Mexico). Centro de Ciencias de la Materia Condensada; Castillon, F.F. [UNAM, Ensenada, B.C. (Mexico). Centro de Ciencias de la Materia Condensada; Sonora Univ., Hermosillo (Mexico). Dept. de Investigacion en Polimeros y Materiales

2002-02-01

225

Investigation of chiral bands in {sup 106}Ag  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-01

226

Bolus calculators.  

Science.gov (United States)

Matching meal insulin to carbohydrate intake, blood glucose, and activity level is recommended in type 1 diabetes management. Calculating an appropriate insulin bolus size several times per day is, however, challenging and resource demanding. Accordingly, there is a need for bolus calculators to support patients in insulin treatment decisions. Currently, bolus calculators are available integrated in insulin pumps, as stand-alone devices and in the form of software applications that can be downloaded to, for example, smartphones. Functionality and complexity of bolus calculators vary greatly, and the few handfuls of published bolus calculator studies are heterogeneous with regard to study design, intervention, duration, and outcome measures. Furthermore, many factors unrelated to the specific device affect outcomes from bolus calculator use and therefore bolus calculator study comparisons should be conducted cautiously. Despite these reservations, there seems to be increasing evidence that bolus calculators may improve glycemic control and treatment satisfaction in patients who use the devices actively and as intended. PMID:24876436

Schmidt, Signe; Nørgaard, Kirsten

2014-09-01

227

Bayesian Calculator  

Science.gov (United States)

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

Birnbaum, Michael H.

2009-01-15

228

Band termination in 123I  

International Nuclear Information System (INIS)

High-spin states in the nucleus 123I were populated by the 110Pd(16O, p4n) reaction at 75 MeV. ?-ray energies, intensities, ?-? coincidences, and directional correlation ratios were measured. The rotational band built on the ?h11/2 single-particle state was extended to spin I=35/2-; at higher spin the level spacings and the feeding pattern were found to become irregular, indicating a sudden change of structure. The 39/2- state and a higher-lying 43/2- level were interpreted as aligned oblate states, in line with the systematics of the lighter odd-A iodine isotopes. Total Routhian surface calculations were performed and were found to support the occurrence of a band termination. Higher-lying levels that feed the h11/2 band were identified, reaching spin I?47/2 and an excitation energy of about 9 MeV. copyright 1997 The American Physical Society

229

Band offsets and heterostructures of two-dimensional semiconductors  

Science.gov (United States)

The band offsets and heterostructures of monolayer and few-layer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) are investigated from first principles calculations. The band alignments between different MX2 monolayers are calculated using the vacuum level as reference, and a simple model is proposed to explain the observed chemical trends. Some of the monolayers and their heterostructures show band alignments suitable for potential applications in spontaneous water splitting, photovoltaics, and optoelectronics. The strong dependence of the band offset on the number of layers also implicates a possible way of patterning quantum structures with thickness engineering.

Kang, Jun; Tongay, Sefaattin; Zhou, Jian; Li, Jingbo; Wu, Junqiao

2013-01-01

230

Prolate and oblate rotational bands in 136Sm  

International Nuclear Information System (INIS)

Six rotational bands have been established in 136Sm following heavy-ion induced reactions carried out at the Nuclear Structure Facility, Daresbury. The yrast band has been observed up to 1? = (24+) and undergoes three band-crossings. A band was observed built on the low-lying 2+ gamma-vibrational state, in addition to two negative parity sidebands built on two-quasiproton excitations. A dipole band showing the characteristics of collective oblate rotation was also established. The results are discussed in terms of total Routhian surface and cranked Woods-Saxon model calculations. (author)

231

Detailed band structure of Chevrel phases  

International Nuclear Information System (INIS)

We have performed full band-structure calculations for several Chevrel phases. The conduction band is esub(g)-like throughout most of the Brillouin zone, but near the centre we find strong tsub(1u) character. The tsub(1u)(esub(u)) state is a Mo-X intercluster pd? antibond and its occupancy decreases as we proceed from the 24- to the 20-electron compounds. This explains the observed decrease of the intercluster distance, it leads to non rigid-band behaviour, and it may be a source of strong electron-phonon coupling to low-frequency, external modes. Moreover, the esub(g)-tsub(1u) mixing gives rise to critical-field anisotropy. The 22-electron compounds BaMo6S8 and EuMo6S8 with half-filled esub(g)-bands are found to be semimetallic or semiconducting in their low-temperature phase. (orig.)

232

Rotational bands in [sup 107]Cd  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in [sup 107]Cd were populated by the reaction [sup 94]Zr([sup 17]O, 4n) at 80 MeV and their decay was studied by [gamma]-spectroscopic methods using the NORDBALL multi-detector array. The experiment included [gamma]-ray yields, [gamma][gamma]-coincidences and [gamma]-ray angular correlation measurements. Rotational bands were observed up to spin 39-/2 and (51+/2) in the negative- and positive-parity bands, respectively. Calculations of total routhian surfaces and quasi-particle routhians have been performed and are used for assigning quasiparticle configurations to the bands. In the g[sub 7/2] neutron band, a h[sub 11/2] neutron alignment is observed. A large signature splitting is expected in the [nu]g[sub 7/2] band before the band crossing. For the band built on a single [nu]h[sub 11/2] quasiparticle, an alignment of either g[sub 7/2] or h[sub 11/2] neutrons is proposed. Shape change effects are discussed. (orig.).

Jerrestam, D. (Uppsala Univ., Nykoeping (Sweden) Niels Bohr Inst., Roskilde (Denmark)); Liden, F. (Physics Dept., Schuster Lab., Manchester Univ. (United Kingdom)); Gizon, J.; Barneoud, D. (Inst. des Sciences Nucleaires, Joseph Fourier Univ., 38 - Grenoble (France)); Hildingsson, L.; Klamra, W.; Lindblad, T. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden)); Wyss, R. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden) Royal Inst. of Tech., Physics Dept., Stockholm (Sweden)); Kownacki, J. (Inst. of Experimental Physics, Warsaw Univ. (Poland)); Nyberg, J. (Niels Bohr Inst., Roskilde (Denmark))

1992-08-17

233

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

234

Bands and Coulomb effects in 50Cr  

Science.gov (United States)

Experimental evidence for the coexistence of states with different K? value was found in 50Cr. The bandcrossing of the K=0+ ground state band with a K=10+ one is confirmed. Large scale shell model calculations could explain all of the observed experimental features and in particular the known experimental Coulomb energy differences in the mirror pair 50Fe-50Cr.

Brandolini, F.; Sanchez-Solano, J.; Lenzi, S. M.; Medina, N. H.; Poves, A.; Ur, C. A.; Bazzacco, D.; de Angelis, G.; de Poli, M.; Farnea, E.; Gadea, A.; Napoli, D. R.; Rossi-Alvarez, C.

2002-08-01

235

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)

236

BTU Calculator  

Science.gov (United States)

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

2007-03-27

237

Band structure of 118Xe  

International Nuclear Information System (INIS)

High spin states of 118Xe have been investigated by means of ? ray spectroscopy using the 92Mo(29Si,2pn) at a bombarding energy of 110 MeV. Several new side bands as well as the yrast band were established. A band crossing between the ground state and super bands was observed at ??c = 0.39 MeV. A negative parity band with two quasi particle excitation, and a quasi ? band were also identified. (orig.)

238

Configuration structure of superdeformed bands in A?190 mass region  

International Nuclear Information System (INIS)

Using the particle-number conservation method for treating the cranked shell model with pairing interaction, the authors systematically investigate the variations of the moments of inertia, the angular moment alignment and the signature splitting with rotational frequencies for superdeformed bands in the A?190 mass region. According to our calculated results, the authors provide a global description of the configuration structure of superdeformed bands in the A?190 mass region. Most superdeformed bands are located at the strong-coupling orbits, such as neutron [512]5/2, [624]9/2. A few superdeformed bands lie on high j orbits, i.e., neutron [761]3/2, [752]5/2. Our calculated configuration assignments give a satisfactorily explanation to the general behavior, the anomalous change and the band crossing of superdeformed bands in the A?190 mass region. (authors)

239

A new type of band crossing at large deformation  

Science.gov (United States)

A detailed study of the positive parity yrast and yrare rotational bands in 77Rb is presented. Using the reaction 40Ca( 40Ca, 3 p) and the EUROGAM I spectrometer, ??? coincidences enabled us to follow both bands over a large spin range and to measure many E2 strengths. The moments of inertia and transition quadrupole moments indicate that a more deformed band ( ?2 ? 0.38) is crossed by a less deformed one ( ?2 ? 0.29). Since the yrare band starts at the extremely low spin value of I = {9}/{2}, the conventional band crossing mechanism of two aligning high- j quasiparticles is excluded. The frequency-dependent equilibrium shapes were calculated with Nilsson-Strutinsky type calculations using a diabatic tracing of configurations near the neutron Fermi level. This is the first observation of such a band crossing.

Harder, A.; Dönau, F.; Lieb, K. P.; Cunningham, R. A.; Gelletly, W.; Gross, C. J.; Hannachi, F.; Kabadiyski, M. K.; Roth, H. A.; Rudolph, D.; Simpson, J.; Skeppstedt, Ö.; Varley, B. J.; Warner, D. D.

1996-02-01

240

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)

 
 
 
 
241

Band structure of W and Mo by empirical pseudopotential method  

Science.gov (United States)

The empirical pseudopotential method (EPM) is used to calculate the band structure of tungsten and molybdenum. Agreement between the calculated reflectivity, density of states, density of states at the Fermi surface and location of the Fermi surface from this study and experimental measurements and previous calculations is good. Also the charge distribution shows the proper topological distribution of charge for a bcc crystal.

Sridhar, C. G.; Whiting, E. E.

1977-01-01

242

Collective bands in 106Ag and 107Ag  

International Nuclear Information System (INIS)

The nuclei 106Ag and 107Ag have been studied using 80 MeV 17O ions impinging on 94Zr. The ?-rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using ?-ray yields, ?? coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands. ((orig.))

243

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

244

Loss of solutions in shear banding fluids in shear banding fluids driven by second normal stress differences  

CERN Document Server

Edge fracture occurs frequently in non-Newtonian fluids. A similar instability has often been reported at the free surface of fluids undergoing shear banding, and leads to expulsion of the sample. In this paper the distortion of the free surface of such a shear banding fluid is calculated by balancing the surface tension against the second normal stresses induced in the two shear bands, and simultaneously requiring a continuous and smooth meniscus. We show that wormlike micelles typically retain meniscus integrity when shear banding, but in some cases can lose integrity for a range of average applied shear rates during which one expects shear banding. This meniscus fracture would lead to ejection of the sample as the shear banding region is swept through. We further show that entangled polymer solutions are expected to display a propensity for fracture, because of their much larger second normal stresses. These calculations are consistent with available data in the literature. We also estimate the meniscus di...

Skorski, Stanislav

2011-01-01

245

Photonic band structure and omnidirectional band gap in anisotropic superlattice  

International Nuclear Information System (INIS)

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

246

Distribution Free Prediction Bands  

CERN Document Server

We study distribution free, nonparametric prediction bands with a special focus on their finite sample behavior. First we investigate and develop different notions of finite sample coverage guarantees. Then we give a new prediction band estimator by combining the idea of "conformal prediction" (Vovk et al. 2009) with nonparametric conditional density estimation. The proposed estimator, called COPS (Conformal Optimized Prediction Set), always has finite sample guarantee in a stronger sense than the original conformal prediction estimator. Under regularity conditions the estimator converges to an oracle band at a minimax optimal rate. A fast approximation algorithm and a data driven method for selecting the bandwidth are developed. The method is illustrated first in simulated data. Then, an application shows that the proposed method gives desirable prediction intervals in an automatic way, as compared to the classical linear regression modeling.

Lei, Jing

2012-01-01

247

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

248

Hellas Banded Terrain  

Science.gov (United States)

16 June 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the banded southeastern floor of the giant impact basin, Hellas. Hellas Planitia is a large and varied region. In southeastern Hellas, banded terrain is fairly common. The pattern probably results from erosion of layered sediment that was subsequently covered by a mantling material. This mantling material later was eroded and roughened the terrain somewhat. This image is located near 41.1oS, 275.6oW. The picture covers an area about 3 km (1.9 mi) across; sunlight illuminates the scene from the upper left.

2004-01-01

249

Dimensional Reduction of Hyperspectral Image DataUsing Band Clustering and Selection Based on Statistical Characteristics of Band Images  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper an approach for the dimensionalityreduction of the hyperspectral image data using the method ofband selection based on the statistical measures is introduced.The spread hyperspectral image data is measured in each bandand the calculated bands are clustered using the K-meansclustering technique. The K-means clustering of bands isperformed in such a way that the intra-cluster variance is keptminimize and the inter-cluster variance maximum. Theoptimal number of band selection is do...

Muhammad Sohaib; Ihsan-Ul-Haq; Qaiser Mushtaq

2013-01-01

250

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

251

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

252

Rubber Band Car  

Science.gov (United States)

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

Wgbh

2010-01-01

253

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

254

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

255

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

256

DUAL BAND MONOPOLE ANTENNA DESIGN  

Directory of Open Access Journals (Sweden)

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

P. Jithu

2013-06-01

257

Band Gaps and Single Scattering of Phononic Crystal  

Directory of Open Access Journals (Sweden)

Full Text Available A method is introduced to study the transmission and scattering properties of acoustic waves in two–dimen- sional phononic band gap (PBG materials. First, it is used to calculate the transmission coefficients of PBG samples. Second, the transmitted power is calculated based on the far field approach. We have also calcu- lated the scattering cross section, the results indicate that phononic band gap appear in frequency regions between two well separated resonance states.

Xiaoyi Huang

2011-12-01

258

Band Structure of New ReFeAsO Superconductors  

Directory of Open Access Journals (Sweden)

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

Hyun-Tak Kim

2013-05-01

259

Braille Calculator  

Directory of Open Access Journals (Sweden)

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

Yoshit V. Gidh

2013-02-01

260

Linear methods in band theory  

DEFF Research Database (Denmark)

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

1975-01-01

 
 
 
 
261

MRO Ka-Band Demonstration  

Science.gov (United States)

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

Shambayati, Shervin

2006-01-01

262

Multiple superdeformed bands in Sr, Y, and Zr nuclei  

International Nuclear Information System (INIS)

Multiple superdeformed bands in the nuclei 80-83Sr, 82-84Y, and 83,84Zr have been studied in a backed-target experiment using the Gammasphere and Microball detector arrays. For 15 bands in these nuclei, average transition quadrupole moments (Qt) have been measured accurately. Among those are two pairs of 'isospectral' bands and the Qt values obtained in each case are nearly identical. The measured Qt values and dynamical moments of inertia place stringent conditions on configuration assignments for the bands obtained from mean field calculations

263

Avoided Band Crossing in Locally Periodic Elastic Rods  

CERN Document Server

Avoided band crossings have been studied theoretically and it has been shown that they can provide a tunning of the metal-insulator transition. Here we present an experimental example of an avoided band crossing for a classical undulatory system: torsional waves in locally periodic rods. To excite and detect the torsional waves, an electromagnetic-acoustic transducer for low-frequencies that we have recently developed, is used. Calculations performed using the transfer matrix method agree with the experimental measurements. In the observed avoided band crossing one level, which is a border-induced bulk level, moves from one band to the next.

Méndez-Sánchez, R A; Flores, J

2005-01-01

264

Gutzwiller theory of band magnetism in LaOFeAs  

International Nuclear Information System (INIS)

For the iron pnictide LaOFeAs we investigate multi-band Hubbard models which are assumed to capture the relevant physics. In our calculations, we employ the Gutzwiller variational theory which is a genuine many particle approach. We will present results both on the paramagnetic and antiferromagnetic phases of our model systems. These results show that a five band-model is not adequate to capture the relevant physics in LaOFeAs. However, our results for the eight band-model which includes the arsenic 4p bands reproduce the experimental data, especially the small magnetic moment, for a broad parameter regime.

265

Effect of size of silica microspheres on photonic band gap  

International Nuclear Information System (INIS)

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

266

Gutzwiller theory of band magnetism in LaOFeAs  

Energy Technology Data Exchange (ETDEWEB)

For the iron pnictide LaOFeAs we investigate multi-band Hubbard models which are assumed to capture the relevant physics. In our calculations, we employ the Gutzwiller variational theory which is a genuine many particle approach. We will present results both on the paramagnetic and antiferromagnetic phases of our model systems. These results show that a five band-model is not adequate to capture the relevant physics in LaOFeAs. However, our results for the eight band-model which includes the arsenic 4p bands reproduce the experimental data, especially the small magnetic moment, for a broad parameter regime.

Schickling, Tobias; Gebhard, Florian [Fachbereich Physik, Philipps Universitaet, D-35037 Marburg (Germany); Buenemann, Joerg [Institut fuer Physik, BTU Cottbus, D-03013 Cottbus (Germany); Boeri, Lilia; Andersen, Ole K. [Max Planck Institute for Solid State Research, D-70569 Stuttgart (Germany); Weber, Werner [Fakultaet Physik, TU Dortmund, D-44221 Dortmund (Germany)

2012-07-01

267

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

268

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

269

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

270

Correlated band structure of 3d2 vanadates  

International Nuclear Information System (INIS)

We study the correlated band structure and the momentum-resolved spectra for 3d2 vanadates, like La O3 and YVO3, using a combination of a first-principles technique and dynamical mean-field theory with a Monte Carlo impurity solver. The self-energy for the effective 3d bands is calculated using maximum-entropy spectral analysis of the Monte Carlo results and a self-consistent procedure. We use this self-energy to calculate the full momentum-resolved spectrum and the correlated band structure, which we compare to available spectroscopy experimental results. We also discuss the effects of the lattice distortions and chemistry

271

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

272

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)

273

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

Science.gov (United States)

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

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

2013-09-01

274

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

275

Nuclear band structure at very high spin  

International Nuclear Information System (INIS)

Complete text of publication follows. The description of nuclear high spin bands in terms of the configuration constrained cranked Nilsson-Strutinsky (CNS) approach will be discussed. Pairing is neglected in these calculations, making it possible to get a simple understanding of the different configurations. Examples from different mass regions show very good agreement between calculations and experiment in many cases making it possible to assign detailed configurations. In this assignment, the fact that the configurations have well-defined maximum spin values is very important, independently of if the bands really terminate or not. Going to lower spin values, the detailed understanding at high spin should be very helpful when trying to understand the structure in the regime where different configurations are more mixed. (author)

276

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

277

Enhancement of phononic band gaps in ternary/binary structure  

International Nuclear Information System (INIS)

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

278

Cluster structure and deformed bands in the 38Ar nucleus  

International Nuclear Information System (INIS)

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

279

Calculation Software  

Science.gov (United States)

MathSoft Plus 5.0 is a calculation software package for electrical engineers and computer scientists who need advanced math functionality. It incorporates SmartMath, an expert system that determines a strategy for solving difficult mathematical problems. SmartMath was the result of the integration into Mathcad of CLIPS, a NASA-developed shell for creating expert systems. By using CLIPS, MathSoft, Inc. was able to save the time and money involved in writing the original program.

1994-01-01

280

Burnout calculation  

International Nuclear Information System (INIS)

Reviewed is the effect of heat flux of different system parameters on critical density in order to give an initial view on the value of several parameters. A thorough analysis of different equations is carried out to calculate burnout is steam-water flows in uniformly heated tubes, annular, and rectangular channels and rod bundles. Effect of heat flux density distribution and flux twisting on burnout and storage determination according to burnout are commended

 
 
 
 
281

Broken Calculator  

Science.gov (United States)

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

Barrow, Mandy

2008-01-01

282

Braille Calculator  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2013-01-01

283

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

284

Shears band in the 105Sn nucleus  

International Nuclear Information System (INIS)

The structure of 105Sn has been investigated through the 50Cr(58Ni,2pn) reaction at a beam energy of 210 MeV. In addition to an extension of the spherical level scheme, a regular sequence of dipole transitions has been found. The experimental results are in agreement with the prediction of tilted axis cranking calculations, which satisfactorily explain the properties of the band. (orig.). With 2 figs

285

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.

286

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

287

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)

288

Electronic structures of narrow-band materials  

International Nuclear Information System (INIS)

This thesis investigates the electronic structures of narrow-band actinide, rare earth, and transition metal materials, using the experimental techniques of photoemission (PES) and inverse photoemission (BIS) spectroscopy. Narrow-band materials exhibit many interesting phenomena such as mixed-valence, heavy-fermion properties, and high temperature superconductivity. This is primarily due to the correlated narrow band electrons and their interaction with conduction or valence band electrons. The theoretical characterization of the electronic structures of a many body system is the spectral weight of the single particle Green's function. The spectral weight of narrow band electrons is determined by measuring the PES/BIS spectrum, the spectrum to remove and add electrons. For Ce compounds, the impurity Anderson Hamiltonian can describe both the ground state properties and the 4f spectrum. In this description, the low-energy properties are determined by a low-energy scale set by the Kondo temperature, which characterizes spin fluctuations. To make a detailed test of this picture, the Ce 3d and 4f spectra are measured and analyzed using this model for Ce(Ru1-xRhx)3B2 and CeCu2Si2. The spectral change during the ?-? phase transition of Ce0.7Th0.3 has been analyzed. The Yb 4f spectrum of YbAl3 is measured and analyzed by applying the impurity Anderson Hamiltonian calculations for Ce to Yb with an electron-hole mapping. The author has studied the 4f spectra of heavy-fermion compounds, YbXCu4, with X = Ag, Au, and Pd. The 5f spectra of uranium materials do not resemble the Ce 4f spectra, in having much more f-weight around EF. However, the measured 5f width of the heavy fermion uranium materials exceeds the 5f width obtained from the local density functional calculations

289

The ASTROSAT/UVIT Exposure Time Calculator  

Science.gov (United States)

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

Leahy, D.

2014-05-01

290

47 CFR 61.47 - Adjustments to the SBI; pricing bands.  

Science.gov (United States)

...Adjustments to the SBI; pricing bands. 61.47...Adjustments to the SBI; pricing bands. ...calculate an SBI value for each affected...services that are added to existing...initialized at a value of 100, corresponding...restructuring. (e) Pricing bands shall...

2010-10-01

291

Octupole bands of Gd isotopes  

International Nuclear Information System (INIS)

Excited states in 154,156,158,160Gd have been populated through the multiple coulomb excitation process by 32S, 48Ti, 58Ni ions. The ground band, ?-band and octupole K?=0- band were extended to I?=16+, (12+), and (11-) state respectively in 160Gd. The octupole K?=1- band was extended to I?=9- state in 158Gd. Excitation cross sections of individual levels relative to that of the I?=4+ state in the ground band in each nucleus were compared with the simulation by the computer code GOSIA within the framework of the pure rotational model. From these comparisons the matrix elements for both intra-band and inter-band transitions were deduced. (orig.)

292

Correlation effects in the valence bands of ferromagnetic semiconductor EuS  

CERN Document Server

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

Sharma, A

2005-01-01

293

Relativistic Band Structure and Fermi Surface of PdTe2 by the LMTO Method  

DEFF Research Database (Denmark)

The energy bands of the trigonal layer compound PdTe2 have been calculated, using the relativistic linear muffin-tin orbitals method. The bandstructure is separated into three distinct regions with low-lying Te 5s bands, conduction bands formed by Pd 4d and Te 5p states, and high-lying bands formed by Pd 5p, Te 6s and Te 5d states. Density of states and joint density of states have been calculated from the bands determined over the appropriate irreducible zone. The Fermi surface consists of two closed sheets in band 11 and band 13, and sheets in band 12 connected to one another by tubes. The results allow an explanation of most of the de Haas-van Alphen frequencies observed previously.

Skriver, Hans Lomholt

1977-01-01

294

Validity of the rigid band approximation in the study of the thermopower of narrow band gap semiconductors  

Science.gov (United States)

Theoretical studies of thermoelectric properties using ab initio electronic structure calculations help not only to understand existing experimental data but also to predict new materials which can be potentially good thermoelectrics. However, in these studies it is inevitable to employ some approximations. It is therefore important to verify their reliability. To this end, we have investigated the validity of the rigid band approximation (RBA), commonly used in calculating the thermopower (S) in doped (sometimes heavily) narrow band gap semiconductors. We have considered two important systems: half-Heusler HfCoSb and PbTe. We calculate band structures of pure and doped systems [using quasiperiodic approximation (QPA)] by employing the density-functional method. We then use Boltzmann transport theory to calculate the thermopower using both RBA and the band structure with QPA. We find that band structures do not change significantly when isovalent impurities are present excepting in specific cases. However, charged impurities (relevant to the doping case) providing carriers can change the host band structure appreciably. We find that impurities in general remove existing degeneracies which tend to reduce the RBA value of ?S?. The reduction is significant in both HfCoSb and PbTe when charged defects are present.

Lee, Mal-Soon; Mahanti, S. D.

2012-04-01

295

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)

296

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.

297

Hybrid Functional Studies on Impurity-Concentration-Controlled Band Engineering of Chalcogen-Hyperdoped Silicon  

Science.gov (United States)

We employ the hybrid functional method to study the impurity-concentration-controlled band engineering of chalcogen-hyperdoped silicon. The variations of defect band width and distance to the conduction band with increasing impurity concentration are given, in which at very low concentration, the reasonable depths of defect states and the energy gap compared with the experiments indicate the good accuracy of hybrid functional calculations for the band structures. For S- and Se-doped silicon, the critical concentrations for the merging of defect and conduction bands are obtained. At the key concentrations related to the insulator-to-metal transition, the characteristics of band structures are discussed.

Shao, Hezhu; Liang, Cong; Zhu, Zhen; Ning, Bo-Yuan; Dong, Xiao; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

2013-08-01

298

Double crossing of the ground rotational band and super band  

Energy Technology Data Exchange (ETDEWEB)

We suggest that the crossing of the ground rotational band by a second rotational-aligned band may in fact be a double crossing. From extrapolations of the rotational energy formula, we show that one could expect such a second crossing around I approx. = 30 in /sup 158/Er. This provides an alternative explanation in terms of a double band crossing for the second discontinuity recently observed in the moment of inertia about I = 28 in /sup 158/Er.

Peker, L.K.; Hamilton, J.H.

1978-03-20

299

Double crossing of the ground rotational band and super band  

International Nuclear Information System (INIS)

We suggest that the crossing of the ground rotational band by a second rotational-aligned band may in fact be a double crossing. From extrapolations of the rotational energy formula, we show that one could expect such a second crossing around I approx. = 30 in 158Er. This provides an alternative explanation in terms of a double band crossing for the second discontinuity recently observed in the moment of inertia about I = 28 in 158Er

300

Dipole bands in high spin states of 57135La78  

Science.gov (United States)

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.

Garg, Ritika; Kumar, S.; Saxena, Mansi; Goyal, Savi; Siwal, Davinder; Verma, S.; Palit, R.; Saha, Sudipta; Sethi, J.; Sharma, Sushil K.; Trivedi, T.; Jadav, S. K.; Donthi, R.; Naidu, B. S.; Mandal, S.

2014-08-01

 
 
 
 
301

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

302

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Baran, Onder; Manisali, Metin; Cecen, Berivan

2009-01-01

303

Band transport model for discotic liquid crystals  

Science.gov (United States)

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

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

2005-07-01

304

High-spin band structure in 166Yb  

International Nuclear Information System (INIS)

High-spin states in 166Yb have been studied via the 154Sm (16O,4n)166Yb reaction with 80 Mev 16O ions from the NBI tandem accelerator. ?-? coincidence data were accumulated with an array of four Ge(Li) and four NaI(Tl) detectors to favour high multiplicity events. Totally about 3 x 108 events were accumulated in the coincidence experiment. Measurements of the angular distribution of the ?-radiation and the conversion coefficients were furthermore performed. Four weakly populated side bands are observed besides the yrast cascade which is followed up to its 24+ member. The ground state band has thus been identified to its 18+ state, while the crossing Stockholm band becomes the yrast band from its 16+ member. The S-band is established from its 12+ state. The observed level energies and transition rates are well reproduced in calculations within the particle rotor model. (author)

305

Statistical decay out of the super-deformed yrast bands?  

International Nuclear Information System (INIS)

The experimental data on super-deformed yrast bands in 132Ce, 152Dy, 192Hg are used to calculate the parameters of transmission coefficient through the potential energy barrier between states of two deformations. It is found that the simplest form of transmission coefficient, together with the standard expressions for transition strengths, allow to reproduce the experimental intensity of super-deformed bands reasonably well. 2 figs., 8 refs. (author)

306

Development of S-band traveling wave RF window  

International Nuclear Information System (INIS)

A cold model of a traveling-wave-in-ceramic (TWC) type S-band (2856MHz) RF window was designed and fabricated. The ceramic in the RF window has the same dimensions as those used in S-band pillbox type windows. The impedance matching between the rectangular waveguide and the cylindrical waveguide was adjusted with irises located on the boundary. The dimensions of the window were determined by calculations using the simulation code HFSS. (author)

307

Prompt Proton Decay and Deformed Bands in 56Ni  

International Nuclear Information System (INIS)

High-spin states in the doubly magic N=Z nucleus 56Ni have been investigated with three fusion-evaporation reaction experiments. New ?-ray transitions are added, and a confirmation of a previously suggested prompt proton decay from a rotational band in 56Ni into the ground state of 55Co is presented. The rotational bands in 56Ni are discussed within the framework of cranked Nilsson-Strutinsky calculations

308

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

309

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

310

The electronic band structure of CoS2  

International Nuclear Information System (INIS)

Angle-resolved and energy-dependent photoemission was used to study the band structure of paramagnetic CoS2 from high-quality single-crystal samples. A strongly dispersing hybridized Co-S band is identified along the ?-X line. Fermi level crossings are also analysed along this line, and the results are interpreted using band structure calculations. The Fermi level crossings are very sensitive to the separation in the S-S dimer, and it is suggested that the half-metallic gap in CoS2 may be controlled by the bonding-antibonding splitting in this dimer, rather than by exchange splitting on the Co atoms

311

Vibronic instabilities in a system with nonrigid electron bands  

Science.gov (United States)

The vibronic dynamical lattice destabilization of a gapped two-band system with moving upper band bottom is investigated in one, two and three dimensions. The second order electron energy renormalization leading to possible destabilization has been calculated for various characteristic physical dispositions. The position of the chemical potential in the upper band near the gap edge promotes the destabilization. The dimensionality of the system does not change the general trends in the behavior of the destabilization. However, in low dimensional cases the chemical potential entering the singularity in the density of states enhances the speed of destabilization rapidly.

Veende, Kadri

2014-06-01

312

Gutzwiller theory of band magnetism in LaOFeAs.  

Science.gov (United States)

We use the Gutzwiller variational theory to calculate the ground-state phase diagram and quasiparticle bands of LaOFeAs. The Fe3d-As4p Wannier-orbital basis obtained from density-functional theory defines the band part of our eight-band Hubbard model. The full atomic interaction between the electrons in the iron orbitals is parametrized by the Hubbard interaction U and an average Hund's-rule interaction J. We reproduce the experimentally observed small ordered magnetic moment over a large region of (U,J) parameter space. The magnetically ordered phase is a stripe spin-density wave of quasiparticles. PMID:22400768

Schickling, Tobias; Gebhard, Florian; Bünemann, Jörg; Boeri, Lilia; Andersen, Ole K; Weber, Werner

2012-01-20

313

High-spin intruder band in $^{107}$In  

CERN Document Server

High-spin states in the neutron deficient nucleus $^{107}$In were studied via the $^{58}$Ni($^{52}$Cr, 3p) reaction. In-beam $\\gamma$ rays were measured using the JUROGAM detector array. A rotational cascade consisting of ten $\\gamma$-ray transitions which decays to the 19/2$^{+}$ level at 2.002 MeV was observed. The band exhibits the features typical for smooth terminating bands which also appear in rotational bands of heavier nuclei in the A$\\sim$100 region. The results are compared with Total Routhian Surface and Cranked Nilsson-Strutinsky calculations.

Ideguchi, E; Ganio?lu, E; Hadinia, B; Lagergren, K; Bäck, T; Johnson, A; Wyss, R; Eeckhaudt, S; Grahn, T; Greenlees, P; Julin, R; Juutinen, S; Kettunen, H; Leino, M; Leppanen, A -P; Nieminen, P; Nyman, M; Pakarinen, J; Rahkila, P; Scholey, C; Uusitalo, J; Joss, D T; Paul, E S; Wiseman, D R; Wadsworth, R; Afanasjev, A V; Ragnarsson, I

2010-01-01

314

Collective bands in [sup 106]Ag and [sup 107]Ag  

Energy Technology Data Exchange (ETDEWEB)

The nuclei [sup 106]Ag and [sup 107]Ag have been studied using 80 MeV [sup 17]O ions impinging on [sup 94]Zr. The [gamma]-rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using [gamma]-ray yields, [gamma][gamma] coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands. ((orig.))

Jerrestam, Dan (Department of Neutron Research, Uppsala University, Studsvik, S-611 82 Nykoeping (Sweden)); Klamra, W. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Gizon, J. (Institut des Sciences Nucleaires, IN2P3-CNRS/Universite Joseph Fourier, 53 avenue des Martyrs, F-38026 Grenoble cedex (France)); Liden, F. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Hildingsson, L. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Kownacki, J. (Institute of Experimental Physics, University of Warsaw, Warsaw (Poland)); Lindblad, T. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Nyberg, J. (The Niels Bohr Institute, Risoe, DK-4000 Roskilde (Denmark))

1994-09-26

315

Strain modulated band gap of edge passivated armchair graphene nanoribbons  

CERN Document Server

First principles calculations were performed to study strain effects on band gap of armchair graphene nanoribbons (AGNRs)with different edge passivation, including H, O, and OH group. The band gap of the H-passivated AGNRs shows a nearly periodic zigzag variation under strain. For O and OH passivation, the zigzag patterns are significantly shifted by a modified quantum confinement due to the edges. In addition, the band gap of the O-passivated AGNRs experiences a direct-to-indirect transition with sufficient tensile strain (~5%). The indirect gap reduces to zero with further increased strain.

Peng, Xihong

2011-01-01

316

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

International Nuclear Information System (INIS)

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

317

Two-Dimensional Ferroelectric Photonic Crystals: Optics and Band Structure  

CERN Document Server

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

Simsek, Sevket; Ozbay, Ekmel

2013-01-01

318

Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent.

Ling, Chen, E-mail: chen.ling@tema.toyota.com; Zhou, Li Qin; Banerjee, Debasish; Jia, Hongfei

2014-01-25

319

High Temperature Spectrum for ?3 Band of Carbon Dioxide  

International Nuclear Information System (INIS)

The total internal partition sums (TIPS) are calculated at the temperature up to 6000 K for 12C16O2. Using the calculated partition functions, we produce the line intensities of ?3 band of 12C16O2 at several high temperatures. The results show that the calculated line intensities are in very good agreement with those of HITRAN database at the temperature up to 3000 K, which provides a strong support for the calculations of TIPS and line intensities at high temperature. Then the calculation is extended to further high temperature, and the simulated spectra of ?3 band of 12C16O2 at 5000 and 6000 K are reported.

320

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

 
 
 
 
321

A Study of Higher-Band Dipole Wakefields in X-Band Accelerating Structures for the G/NLC  

International Nuclear Information System (INIS)

The X-band linacs for the G/NLC (Global/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series. The present accelerating structures are 60 cm in length and incorporate damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield, frequencies of adjacent structures are interleaved. Limited analysis has been done previously on the higher order dipole bands. Here, we calculate the contribution of higher order bands of interleaved structures to the wakefield. Beam dynamics issues are also studied

322

Band properties of the transitional nucleus 187Pt  

International Nuclear Information System (INIS)

High-spin states in 187Pt have been studied experimentally using the 173Yb(18O, 4n) reaction at beam energies of 78 and 85 MeV. The previously known bands based on the ?i13/2,?7/2-[503], and ?i13/22?j configurations have been extended to high-spin states, and new rotational bands associated with the ?3/2-[512] and ?1/2-[521] Nilsson orbits have been identified. The total Routhian surface calculations indicate that the transitional nucleus 187Pt is very soft with respect to ? and ? deformations. The band properties, such as level spacings, band crossing frequencies, alignment gains, and signature splittings, have been compared with the systematics observed in neighboring nuclei and have been interpreted within the framework of the cranked shell model. The rotational bands show different band crossing frequencies, which can be explained by the alignment either of i13/2 neutrons or of h9/2 protons. Importantly, evidence is presented for a ?h9/2 alignment at very low frequency in the ?7/2-[503] band. The proton nature of the band crossing is strongly suggested by comparing the measured B(M1;I?I-1)/B(E2;I?I-2) ratios with the theoretical values from the semiclassical Doenau and Frauendof approach

323

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.

Skriver, Hans Lomholt

1977-01-01

324

Yrare bands of 121Xe  

International Nuclear Information System (INIS)

High-spin states in 121Xe have been studied via the 109Ag (16O,p3n)121Xe reaction at a beam energy of 80 MeV. Several rotational bands based on one- and three-quasiparticle excitations have been established. Among them, an unfavoured yrare rotational band with unfavoured signature has been newly identified. (orig.)

325

Band crossings in 86Zr  

International Nuclear Information System (INIS)

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

326

Valence-band photoemission intensities in thorium dioxide  

International Nuclear Information System (INIS)

Resonant photoemission spectra of the O 2p-derived valence band of insulating ThO2 are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5d core-level threshold energies (85 ? hv ? 120 eV), resonance is greatest at the bottom of the O 2p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2p states and Th 6d. (author)

327

Description of the candidate chiral doublet bands in 98Tc  

International Nuclear Information System (INIS)

The candidate chiral doublet bands in 98Tc with configuration ?g9/2 ? ?h11/2 are studied theoretically for the first time via the triaxial particle rotor model. The main properties of the doublet bands including the energy spectra and electromagnetic transitions are calculated for different triaxiality parameter ?, and the data in 98Tc can be well described by the calculations with ? = 38°. Based on the analysis of angular momentum components, it is found that the chiral rotational geometry in 98Tc deviates from the ideal chiral picture. (authors)

328

Rotational and vibrational bands in 108Pd  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The 108Pd nucleus has been studied with the 100Mo(11B, p2ngamma) reaction at 43 MeV incident energy. gamma -gamma - t, gamma -gamma - charged particle coincidences and directional correlation ratios were measured using the gamma spectrometer formed by four Compton suppressed HPGe detectors and a 4pi [...] charged-particle ancillary detector system. The struture of the bands was interpreted within the framework of the cranked shell model and total Routhian 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.

1005-10-01

329

Isotope dependence of band gap in semiconductors  

Science.gov (United States)

Recently, carrier confinement was observed in diamond superlattice consisting of pure ^12C and ^13C layers. This interesting phenomenon comes from large isotope dependence of fundamental gap width in diamond. To understand this carrier confinement and design related nanodevices, we investigate the effect of electron-phonon couplings on quasiparticle energies in semiconductors composed of carbon and other light elements using first-principles methods based on the density functional theory. The calculated isotope dependence as well as temperature dependence of band gap in diamond is found to agree well with the experiment. We also discuss the isotope dependence in binary compounds such as boron nitride and silicon carbide.

Koretsune, Takashi; Saito, Susumu

2012-02-01

330

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

331

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

332

Quadrupole moment measurements for strongly deformed bands in ^171,172Hf  

Science.gov (United States)

A lifetime measurement using the DSAM technique has been performed at Gammasphere to study the nature of strongly deformed bands in ^171,172Hf [1]. The measured quadrupole moments, ˜9.5 b for Band ED in ^171Hf, and ˜13.5 b for Band SD1 in ^172Hf, support our previous interpretation that Band ED is associated with near-prolate shape and an enhanced deformation w.r.t. the normal deformed bands, and the Band SD1 has a superdeformed shape with little triaxiality, contrary to the cranking calculations with the Ultimate Cranker code. The calculations successfully predicted the existence of triaxial strongly deformed (TSD) structures in Lu isotopes, but the predicted TSD bands in Hf isotopes remain elusive apart from the one in ^168Hf. [1] Y. C. Zhang et al., Phys. Rev. C 76, 064321 (2007).

Mukhopadhyay, S.; Ma, W. C.; Yadav, R. B.; Marsh, J.; Ijaz, Q. A.; Cullen, D. M.; Riedinger, L. L.; Hartley, D. J.; Lakshmi, S.; Hota, S. S.; Chowdhury, P.; Chiara, C. J.; Toh, Y.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Kondev, F. G.; Lauritsen, T.; Zhu, S.

2010-11-01

333

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

International Nuclear Information System (INIS)

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

334

Plasmon dispersion and quasiparticle band structures for noble metals  

International Nuclear Information System (INIS)

Full text: In density-functional theory the Kohn-Sham eigenvalues cannot be interpreted as excitation energies, but band structures are often qualitatively correct and can be used as a starting point for perturbation-theoretical treatments. The GW approximation for the electronic self-energy is a particularly successful method for accurate quantitative band-structure calculations. The screened interaction W incorporates local field effects from the inversion of the dielectric matrix determined in the Random Phase Approximation. The inverted dielectric matrix combined with non-local empirical pseudopotentials also yields adequately calculated low energy excited state properties of materials. Dielectric calculations based on the pseudo-wavefunctions and energy band structure within a plasmon picture determine mean free path lengths and Fourier components of the inelastic scattering potential. Efficient band structures simulate ballistic transport effects in copper and surface state changes with strain during silver epitaxial film growth on silicon, but care must be taken with convergence, in order to obtain good agreement with first principle calculations and experimental values. Comparisons are made with recent LDA and GW calculations for silver

335

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

336

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

337

Population of rotational bands in superheavy nuclei  

Directory of Open Access Journals (Sweden)

Full Text Available Using the statistical approach, we study the population of ground-state rotational bands of superheavy nuclei produced in the fusion-evaporation reactions 208Pb(48Ca, 2n254No, 206Pb(48Ca, 2n252No, and 204Hg(48Ca, 2n250Fm. We calculate relative intensities of E2-transitions between the rotational states and entry spin distributions of the residual nuclei, evaporation residue cross sections, and excitation functions for these reactions. Fermi-gas model is used for the calculation of level density, and damping of shell effects both with excitation energy and angular momentum is taking into account. The results are in a good agreement with the experiment data.

Antonenko N.V.

2012-02-01

338

Band offsets in cubic GaN/AlN superlattices - Theory and experiment  

Energy Technology Data Exchange (ETDEWEB)

The presently unknown band offset in non-polar cubic GaN/AlN superlattices has been investigated by intersubband and interband spectroscopy as well as ab-initio calculations. On the one hand, the conduction band offset has been determined from the comparison of the measured transition energies with model calculations within the effective mass approximation. On the other hand, the valence and conduction band offset has been accurately simulated by calculating many body corrections within the GW approximation on top of hybrid-functional density functional theory (DFT) calculations. A conduction band offset of (1.4{+-}0.1) eV and a valence band offset of (0.5{+-}0.1) eV has been thus obtained as a result of both approaches.

Landmann, Marc; Mietze, Christian; Rauls, Eva; Lischka, Klaus; As, Donat J.; Schmidt, Wolf Gero [Universitaet Paderborn (Germany)

2011-07-01

339

Comparison of RESRAD with hand calculations  

International Nuclear Information System (INIS)

This report is a continuation of an earlier comparison done with two other computer programs, GENII and PATHRAE. The dose calculations by the two programs were compared with each other and with hand calculations. These band calculations have now been compared with RESRAD Version 5.41 to examine the use of standard models and parameters in this computer program. The hand calculations disclosed a significant computational error in RESRAD. The Pu-241 ingestion doses are five orders of magnitude too small. In addition, the external doses from some nuclides differ greatly from expected values. Both of these deficiencies have been corrected in later versions of RESRAD

340

Coffee ring deposition in bands  

Science.gov (United States)

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

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

2010-11-01

 
 
 
 
341

Fluid depletion in shear bands  

CERN Document Server

How does pore liquid reconfigure within shear bands in wet granular media? Conventional wisdom predicts that liquid is drawn into dilating granular media. We, however, find a depletion of liquid in shear bands despite increased porosity due to dilatancy. This apparent paradox is resolved by a microscale model for liquid transport at low liquid contents induced by rupture and reconfiguration of individual liquid bridges. Measured liquid content profiles show macroscopic depletion bands similar to results of numerical simulations. We derive a modified diffusion description for rupture-induced liquid migration.

Mani, Roman; Or, Dani; Herrmann, Hans J

2012-01-01

342

Triaxial superdeformed and normal-deformed high-spin band structures in 170Hf  

International Nuclear Information System (INIS)

The high-spin structure of 170Hf was investigated using the EUROBALL spectrometer. The previously known level scheme was extended in the low-spin region as well as to higher spins, and several new bands were discovered. In particular, two bands were identified which show the characteristics of triaxial superdeformation. One of these bands is strongly populated, and its excitation energy and spins are established. Configuration assignments are made to the normal-deformed bands based on comparisons of their properties with cranked shell model calculations. The results for the very high spin states provide important input for such calculations

343

NUCLEAR PHYSICS: Description of Properties of Triaxial Superdeformed Bands in Odd-A Lu Isotopes  

Science.gov (United States)

Properties of the triaxial superdeformed (TSD) bands of odd-A Lu isotopes are investigated systematically within the supersymmetry scheme including many-body interactions and a perturbation possessing the SO(5) (or SU(5)) symmetry on the rotational symmetry. Quantitatively good results of the ?-ray energies, the dynamical moments of inertia and the spin of the TSD bands in odd-A Lu isotopes are obtained. The calculation shows that the competition between the pairing and anti-pairing effects exists in these TSD bands. Meanwhile, the SU(3) symmetry in TSD bands are broken more seriously than in superdeformed (SD) bands.

Zhang, Da-Li; Li, Jin-Bo; Cao, Hong-Ping

2010-01-01

344

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

International Nuclear Information System (INIS)

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

345

Determination of xenon valence and conduction bands by spin-polarized photoemission  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using circularly polarized synchrotron radiation and spin-resolved photoemission, we have studied the valence and conduction bands of Xe(111) up to about 18 eV above the valence-band maximum. Direct information about the symmetry of bands and their hybridization is provided by photoelectron spin polarization. Our data also prove the existence of a gap in the unoccupied bands above the fundamental gap. A comparison of our data with calculated band structures shows the importance of an energy-d...

Kessler, B.; Eyers, A.; Horn, K.; Mu?ller, Norbert; Schmiedeskamp, G.; Scho?nhense, G.; Heinzmann, Ulrich

1987-01-01

346

Determination of xenon valence and conduction bands by spin-polarized photoemission  

Science.gov (United States)

Using circularly polarized synchrotron radiation and spin-resolved photoemission, we have studied the valence and conduction bands of Xe(111) up to about 18 eV above the valence-band maximum. Direct information about the symmetry of bands and their hybridization is provided by photoelectron spin polarization. Our data also prove the existence of a gap in the unoccupied bands above the fundamental gap. A comparison of our data with calculated band structures shows the importance of an energy-dependent self-energy correction.

Kessler, B.; Eyers, A.; Horn, K.; Müller, N.; Schmiedeskamp, B.; Schönhense, G.; Heinzmann, U.

1987-07-01

347

Study of intruder band in 112Sn  

International Nuclear Information System (INIS)

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

348

Band gap engineering strategy via polarization rotation in perovskite ferroelectrics  

International Nuclear Information System (INIS)

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

349

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

350

Optically induced coherent intra-band dynamics in disordered semiconductors  

CERN Document Server

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

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

2002-01-01

351

Band gap engineering strategy via polarization rotation in perovskite ferroelectrics  

Science.gov (United States)

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; Grinberg, Ilya; Rappe, Andrew M.

2014-04-01

352

Band-gap engineering in fluorographene nanoribbons under uniaxial strain  

International Nuclear Information System (INIS)

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

353

Formal Verification of Air Traffic Conflict Prevention Bands Algorithms  

Science.gov (United States)

In air traffic management, a pairwise conflict is a predicted loss of separation between two aircraft, referred to as the ownship and the intruder. A conflict prevention bands system computes ranges of maneuvers for the ownship that characterize regions in the airspace that are either conflict-free or 'don't go' zones that the ownship has to avoid. Conflict prevention bands are surprisingly difficult to define and analyze. Errors in the calculation of prevention bands may result in incorrect separation assurance information being displayed to pilots or air traffic controllers. This paper presents provably correct 3-dimensional prevention bands algorithms for ranges of track angle; ground speed, and vertical speed maneuvers. The algorithms have been mechanically verified in the Prototype Verification System (PVS). The verification presented in this paper extends in a non-trivial way that of previously published 2-dimensional algorithms.

Narkawicz, Anthony J.; Munoz, Cesar A.; Dowek, Gilles

2010-01-01

354

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

355

Lasing at the band edges of plasmonic lattices  

CERN Document Server

We report room temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback lasers, a central question is how the underlying band structure from which lasing emerges is modified by both the much stronger scattering and the disadvantageous loss of metal. We use spectrally resolved back-focal plane imaging to measure the wavelength- and angle dependence of emission below and above threshold, thereby mapping the band structure. We find that for silver particles, the band structure is strongly modified compared to dielectric reference DFB lasers, since the strong scattering gives large stop gaps. In contrast, gold particles scatter weakly and absorb strongly, so that thresholds are higher, but the band structure is not strongly modified. The experimental findings are supported by finite element and fourier modal method calculations of the...

Schokker, A Hinke

2014-01-01

356

Infrared radiation parameterizations for the minor CO2 bands and for several CFC bands in the window region  

Science.gov (United States)

Fast and accurate parameterizations have been developed for the transmission functions of the CO2 9.4- and 10.4-micron bands, as well as the CFC-11, CFC-12, and CFC-22 bands located in the 8-12-micron region. The parameterizations are based on line-by-line calculations of transmission functions for the CO2 bands and on high spectral resolution laboratory measurements of the absorption coefficients for the CFC bands. Also developed are the parameterizations for the H2O transmission functions for the corresponding spectral bands. Compared to the high-resolution calculations, fluxes at the tropopause computed with the parameterizations are accurate to within 10 percent when overlapping of gas absorptions within a band is taken into account. For individual gas absorption, the accuracy is of order 0-2 percent. The climatic effects of these trace gases have been studied using a zonally averaged multilayer energy balance model, which includes seasonal cycles and a simplified deep ocean. With the trace gas abundances taken to follow the Intergovernmental Panel on Climate Change Low Emissions 'B' scenario, the transient response of the surface temperature is simulated for the period 1900-2060.

Kratz, David P.; Chou, Ming-Dah; Yan, Michael M.-H.

1993-01-01

357

Flexural wave propagation in beams with periodically attached vibration absorbers: Band-gap behavior and band formation mechanisms  

Science.gov (United States)

This paper is concerned with flexural wave propagation and vibration transmission in beams with periodically attached vibration absorbers. Such periodic systems feature unique wave filtering characteristics that can find applications in the control of wave propagation in flexural beam structures. The study is performed by using an exact analytical approach based on a combination of the spectral element method and periodic structure theory. Both infinite and finite periodic structures are considered. An explicit expression is provided for the calculation of propagation constants and thus the complex band structures, and it is further developed to examine the effects of various system parameters on the band-gap behavior, including the position, width and wave attenuation performance of all the band gaps. The band formation mechanisms of such periodic systems are explained via both derivations and physical models, yielding explicit equations to enable the prediction of all the band edge frequencies in an exact manner without the need to calculate propagation constants. Based on these equations, explicit formulas are further derived to determine the conditions for the transition and near-coupling between local resonance and Bragg scattering, each being a unique band-gap opening mechanism.

Xiao, Yong; Wen, Jihong; Yu, Dianlong; Wen, Xisen

2013-02-01

358

Performance Analysis of IIR Digital Band Stop Filter  

Directory of Open Access Journals (Sweden)

Full Text Available IIR Band-stop filter is recursive in nature i.e. the present output sample depends on the past input sample, past output samples and the present input samples. If the past and present inputs and output are varied the resulting present output will be changed. The Band-stop filter rejects one band of frequency and allows all other frequency band to pass. In this paper, the performance analysis of Band-stop filter is done using the Modified Analog-to-Digital Mapping technique and simulated in Matlab7. The response of the filter can be modified by changing the value of the components. The coefficients that are essentially required to design a IIR Digital Band-stop filter, are also calculated using the above mentioned algorithm and finally the magnitude response and the stability of the filter are determined using Matlab7 with satisfying results. The pole-zero plot of a system, filter in this case, determines the stability of the predesigned IIR Band-stop filter.

Subhadeep Chakraborty, Abhirup Patra

2013-05-01

359

Anomalous electromagnetically induced transparency in photonic-band-gap materials  

International Nuclear Information System (INIS)

The phenomenon of electromagnetically induced transparency has been studied when a four-level atom is located in a photonic band gap material. Quantum interference is introduced by driving the two upper levels of the atom with a strong pump laser field. The top level and one of the ground levels are coupled by a weak probe laser field and absorption takes place between these two states. The susceptibility due to the absorption for this transition has been calculated by using the master equation method in linear response theory. Numerical simulations are performed for the real and imaginary parts of the susceptibility for a photonic band gap material whose gap-midgap ratio is 21%. It is found that when resonance frequencies lie within the band, the medium becomes transparent under the action of the strong pump laser field. More interesting results are found when one of the resonance frequencies lies at the band edge and within the band gap. When the resonance frequency lies at the band edge, the medium becomes nontransparent even under a strong pump laser field. On the other hand, when the resonance frequency lies within the band gap, the medium becomes transparent even under a weak pump laser field. In summary, we found that the medium can be transformed from the transparent state to the nontransparent state just by changing the location of the resonance frequency. We call these two effects anomalous electromagnetically induced transparency

360

CNDO/S calculation electron structure of hexagonal boron nitride  

International Nuclear Information System (INIS)

Reliability of semiempiric CNDO/S method was studied, using as an example calculations of simple clusters of hexagonal BN, for which experimental data are known and band and cluster calculations are made. A satisfactory coincidence of forbidden zone width, calculated and experimentally obtained, is confirmed

 
 
 
 
361

BandMusic PDF Library  

Science.gov (United States)

A summer band concert in a white gazebo is always a highlight of small town life. The BandMusic PDF Library might just inspire such a musical gathering, as they offer up hundreds of pieces of band music at no charge. On their homepage, visitors can find Featured Content, such as the complete score for the Bacchanal from Samson and Delilah and the band music transcription of Verdi's Luisa Miller. Moving along, visitors can use the Search the Library link to look for pieces of interest, or they can just browse around by title, genre, composer, publisher, year, or keyword. Also, the Wish List contains items that the site is looking for, and perhaps a kind visitor can provide them with access to a copy so that others might enjoy said work.

362

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

363

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

364

Isogeometric analysis of shear bands  

Science.gov (United States)

Numerical modeling of shear bands present several challenges, primarily due to strain softening, strong nonlinear multiphysics coupling, and steep solution gradients with fine solution features. In general it is not known a priori where a shear band will form or propagate, thus adaptive refinement is sometimes necessary to increase the resolution near the band. In this work we explore the use of isogeometric analysis for shear band problems by constructing and testing several combinations of NURBS elements for a mixed finite element shear band formulation. Owing to the higher order continuity of the NURBS basis, fine solution features such as shear bands can be resolved accurately and efficiently without adaptive refinement. The results are compared to a mixed element formulation with linear functions for displacement and temperature and Pian-Sumihara shape functions for stress. We find that an element based on high order NURBS functions for displacement, temperature and stress, combined with gauss point sampling of the plastic strain leads to attractive results in terms of rate of convergence, accuracy and cpu time. This element is implemented with a -bar strain projection method and is shown to be nearly locking free.

Berger-Vergiat, Luc; McAuliffe, Colin; Waisman, Haim

2014-08-01

365

On spin assignment for yrast band head of 156Tb  

International Nuclear Information System (INIS)

It is obtained by using particle-rotor model of odd-odd nuclei, through theoretical calculation, that the spin assignment for Yrast band head of 156Tb is I0 =3D 8 which is coincident with the conclusion got from systematic analysis of experimental values

366

Birefringence and band structure of CdP2 crystals  

Science.gov (United States)

The spatial dispersion in CdP2 crystals was investigated. The dispersion is positive (nk||?>nk||?) at ?>?0 and negative (nk||?Kramers-Kronig analyses. All features were interpreted as optical transitions on the basis of both theoretical calculations of band structure.

Beril, S. I.; Stamov, I. G.; Syrbu, N. N.; Zalamai, V. V.

2013-08-01

367

Phenomenological analysis of superdeformed bands in the A?150 region  

International Nuclear Information System (INIS)

The deexcitation spins of the superdeformed bands in the A?150 region are determined by using multiple V-shaped plot. The agreement between the calculated and observed transition energies, the kinematic and dynamic moments of inertia is quite well when a correct spin assignment is made

368

Band-edge diagrams for strained III-V semiconductor quantum wells, wires, and dots  

CERN Document Server

We have calculated band-edge energies for most combinations of zincblende AlN, GaN, InN, GaP, GaAs, InP, InAs, GaSb and InSb in which one material is strained to the other. Calculations were done for three different geometries, quantum wells, wires, and dots, and mean effective masses were computed in order to estimate confinement energies. For quantum wells, we have also calculated band-edges for ternary alloys. Energy gaps, including confinement, may be easily and accurately estimated using band energies and a simple effective mass approximation, yielding excellent agreement with experimental results. By calculating all material combinations we have identified novel and interesting material combinations, such as artificial donors, that have not been experimentally realized. The calculations were perfomed using strain-dependent k-dot-p theory and provide a comprehensive overview of band structures for strained heterostructures.

Pryor, C E

2005-01-01

369

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

370

Very Wide Band Absorption of Sunlight Spectra using Titanium Dioxide Particles with Distributed Band Gap  

Directory of Open Access Journals (Sweden)

Full Text Available In this report we proposed an alternative approach to improve the absorption of solar radiation by titanium dioxide (TiO2 particles. We did not dope pure TiO2 with appropriate elements, but we just searched for low-grade (technical grade TiO2 in the market. We assumed low grade TiO2s are those containing dopant atoms of different concentrations and of different elements. By inspecting the UV-Vis spectra of the samples we finally found TiO2 that absorbs nearly all visible spectra (from less than 200 nm to more than 800 nm. By assuming the powder consisted of distributed band gaps, we proposed a simple method for calculating the band gap distribution. We also used the TiO2 for making a prototype of solar cell and for a photocatalys to decompose organic pollutants in water, both are under sunlight illumination.

Mikrajuddin Abdullah

2010-02-01

371

HENRY'S LAW CALCULATOR  

Science.gov (United States)

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

372

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

373

The band structure of BeTe a combined experimental and theoretical study  

CERN Document Server

Using angle-resolved synchrotron-radiation photoemission spectroscopy we have determined the dispersion of the valence bands of BeTe(100) along $\\Gamma X$, i.e. the [100] direction. The measurements are analyzed with the aid of a first-principles calculation of the BeTe bulk band structure as well as of the photoemission peaks as given by the momentum conserving bulk transitions. Taking the calculated unoccupied bands as final states of the photoemission process, we obtain an excellent agreement between experimental and calculated spectra and a clear interpretation of almost all measured bands. In contrast, the free electron approximation for the final states fails to describe the BeTe bulk band structure along $\\Gamma X$ properly.

Nagelstrasser, M; Fischer, F; Litz, T; Waag, A; Fleszar, A; Hanke, W; Steinrück, H P; Landwehr, Gottfried

1998-01-01

374

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

CERN Document Server

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

Koshelev, A E

2003-01-01

375

Two-band second moment model for transition metals and alloys  

International Nuclear Information System (INIS)

A semi-empirical formalism based on the second moment tight-binding approach, considering two bands is presented for deriving interatomic potentials for magnetic d-band materials. It incorporates an empirical local exchange interaction, which accounts for magnetic effects without increasing the computing time required for force evaluation. The consequences of applying a two-band picture to transition metal alloys and transition metal impurities is examined, which combined with evidence from ab initio calculations leads to some surprisingly simplifying conclusions

376

Hubbard-U band-structure methods  

DEFF Research Database (Denmark)

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

Albers, R.C.; Christensen, Niels Egede

2009-01-01

377

Troposcatter at the KU band  

Science.gov (United States)

Troposcatter data were collected with a wideband measurement system for a period of five months spanning parts of the winter, spring, and summer seasons of 1991. The system provided multipath delay measurements with a 2.5 nsec resolution. Measurements of received signal level, Doppler frequency shift and multipath delay spread were obtained on the 161 km troposcatter path from Prospect Hill in Waltham, MA. to Mt. Tug in Lebanon, NH. These observations are the latest in a longer measurement program to characterize the propagation channel for tropospheric scatter communications systems operating at frequencies near 16 GHz (Ku band). Simultaneous observations at 5 GHz (C band) were made during the last month of the observing program to provide calibration and a statistical comparison with earlier observations made using a different Ku band transmission system.

Crane, Robert K.; Wennemyr, Magnus

1994-06-01

378

X-Band PLL Synthesizer  

Directory of Open Access Journals (Sweden)

Full Text Available This paper deals with design and realization of a PLL synthesizer for the microwave X−band. The synthesizer is intended for use as a local oscillator in a K−band downconverter. The design goal was to achieve very low phase noise and spurious free signal with a sufficient power level. For that purpose a low phase noise MMIC VCO was used in phase locked loop. The PLL works at half the output frequency, therefore there is a frequency doubler at the output of the PLL. The output signal from the frequency doubler is filtered by a band-pass filter and finally amplified by a single stage amplifier.

P. Kutin

2006-04-01

379

Rate-Dependent Temperature Increases in Shear Bands of a Bulk-Metallic Glass  

Science.gov (United States)

Using an infrared (IR) camera, we observed in situ the dynamical shear-banding processes of the geometrically constrained specimens of a Zr-based bulk metallic glass in a quasi-static compression at various strain rates, measured the temperature evolutions within the specimens, and calculated the temperature increases in shear bands. Strain-rate-dependent serrated plastic flow is a result of shear-banding operations. The average temperature increases in the specimens are observed during the plastic deformation and their magnitudes are strain rate dependent. The temperature increases in shear bands are related to strain rates. The higher the strain rates, the larger the temperature increases in a shear band. The shear strain in a shear band may be responsible for the strain-rate-dependent temperature increase in a shear band.

Jiang, W. H.; Liao, H. H.; Liu, F. X.; Choo, H.; Liaw, P. K.

2008-08-01

380

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)

 
 
 
 
381

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

382

Band gap modulation of functionalized metal-organic frameworks.  

Science.gov (United States)

Metal-organic frameworks (MOFs) have been envisioned as alternatives to planar metallic catalysts for solar-to-fuel conversion. This is a direct result of their porous structure and the ability to tailor their optical absorption properties. This study investigates the band gap modulation of Zr-UiO-66 MOFs from both the computational and experimental points of view for three linker designs that include benzenedicarboxylate (BDC), BDC-NO2, and BDC-NH2. Emphasis in this study was aimed at understanding the influence of the bonding between the aromatic ring and the functional group. A ground state density functional theory (DFT) calculation was carried out to investigate the projected density of states and the origins of the modulation. A time-dependent density functional theory (TDDFT) calculation of the hydrogen terminated linkers confirmed the modulation and accounted for the electron charge transfer providing comparable optical band gap predictions to experimental results. Computational results confirmed the hybridization of the carbon-nitrogen bond in conjunction with the donor state resulting from the NH2 functionalization. The NO2 functionalization resulted in an acceptor configuration with marginal modification to the valence band maximum. The largest modulation was BDC-NH2 with a band gap of 2.75 eV, followed by BDC-NO2 with a band gap of 2.93 eV and BDC with a band gap of 3.76 eV. The electron effective mass was predicted from the band structure to be 8.9 me for all MOF designs. PMID:25269595

Musho, Terence; Li, Jiangtan; Wu, Nianqiang

2014-11-21

383

Valence band electronic structure of V2O3: identification of V and O bands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a comprehensive study of the photon energy dependence of the valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The analysis of our experimental results, covering an extended photon energy range (20-6000 eV) and combined with GW calculations, allow us to identify the nature of the orbitals contributing to the total spectral weight at different binding energies, and in particular to locate the V 4s at about 8 eV binding energy. From this c...

Papalazarou, E.; Gatti, Matteo; Marsi, M.; Brouet, V.; Iori, F.; Reining, Lucia; Annese, E.; Vobornik, I.; Offi, F.; Fondacaro, A.; Huotari, S.; Lacovig, P.; Tjernberg, O.; Brookes, N. B.; Sacchi, M.

2009-01-01

384

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

385

Rotational bands in the doubly odd nucleus 134Pr  

International Nuclear Information System (INIS)

The band structures of the doubly odd 134Pr nucleus has been investigated via the 119Sn(19F,4n) 134Pr and 110Pd(28Si,p3n)134Pr reactions at beam energies of 87 and 130 MeV, respectively. The three previously known rotational bands based on the ?[541]3/2-(?=±1/2) x ?[514]9/2- and ?[413]5/2+ x ?[514]9/2- configurations have been extended to higher spins. The difference of ?2h in the experimental alignment of the bands based on the signature partners of the [541]3/2- h11/2 proton orbital is discussed in terms of shape coexistence and coupling with the ?-phonon but no consistent interpretation can be found. A new band consisting of quadrupole transitions has also been identified and linked unambiguously to the low-lying levels of the yrast band. Total routhian surface and cranked shell model calculations suggest a (?h11/2)3 x ?[530]1/2- configuration for this band. The experimental ratios of reduced transition probabilities B(M1)/B(E2) of the various rotational structures are compared to the theoretical values obtained from a semiclassical model and from the two-particle plus triaxial-rotor model. (orig.)

386

Multi-band Gutzwiller wave functions for itinerant ferromagnetism  

CERN Document Server

Multi-band Gutzwiller-correlated wave functions reconcile the contrasting concepts of itinerant band electrons versus electrons localized in partially filled atomic shells. The approximate evaluation of these variational ground states becomes exact in the limit of large coordination number. The result allows the identification of quasi-particle band structures for correlated electron systems. As a first application, we summarize a study of itinerant ferromagnetism in a two-band model, thereby elucidating the co-operation of the Coulomb repulsion and the Hund's-rule exchange. Then, we present results of calculations for ferromagnetic nickel, using a realistic 18 spin-orbital basis of 4s, 4p and 3d valence electrons. Good agreement with the experimental ground-state properties of nickel is obtained. In particular, the quasi-particle energy bands agree much better with the photo-emission and Fermi surface data than the band structure obtained from spin-density functional theory. Finally, we present results for t...

Bünemann, J; Weber, W; Buenemann, Joerg; Gebhard, Florian; Weber, Werner

2000-01-01

387

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)

388

ALMA Band 5 Cartridge Performance  

Science.gov (United States)

Work presented here concerns the design and performance of the ALMA Band 5 cold cartridge, one of the 10 frequency channels of ALMA project, a radio interferometer under construction at Atacama Desert in Chile. The Band 5 cartridge is a dual polarization receiver with the polarization separation performed by orthomode transducer (OMT). For each polarization, Band 5 receiver employs sideband rejection (2SB) scheme based on quadrature layout, with SIS mixers covering 163-211 GHz with 4-8 GHz IF. The LO injection circuitry is integrated with mixer chip and is implemented on the same substrate, resulting in a compact 2SB assembly. Amongst the other ALMA bands, the ALMA Band 5 being the lowest frequency band that uses all cold optics, has the largest mirror. Consequently, ALMA Band 5 mirror along with its support structure leaves very little room for placing OMT, mixers and IF subsystems. The constraints put by the size of cold optics and limited cartridge space, required of us to revise the original 2SB design and adopt a design where all the components like OMT, mixer, IF hybrid, isolators and IF amplifier are directly connected to each other without using any co-ax cables in-between. The IF subsystem uses the space between 4 K and 15 K stage of the cartridge and is thermally connected to 4 K stage. Avoiding co-ax cabling required use of custom designed IF hybrid, furthermore, due to limited cooling capacity at 4 K stage, resistive bias circuitry for the mixers is moved to 15 K stage and the IF hybrid along with an integrated bias-T is implemented using superconducting micro-strip lines. The E-probes for both LO and RF waveguide-to-microstrip transitions are placed perpendicular to the wave direction (back-piece configuration). The RF choke at the end of the probes provides a virtual ground for the RF/LO signal, and the choke is DC grounded to the chassis. The on-chip LO injection is done using a microstrip line directional coupler with slot-line branches in the ground plane. The isolated port of the LO coupler is terminated by floating wideband elliptical termination. The mixer employs two SIS junctions with junction area of 3 ?m2 each, in twin junction configuration, followed by a quarter wave transformer to couple it to the signal probe. A quarter-wave high impedance line on an extra layer of SiO2 is used to extract the IF by separating from RF. At the conference, we plan to present details of the cartridge design and results of the experimental characterization of the ALMA Band 5 cold cartridge.

Billade, Bhushan; Lapkin, I.; Nystrom, O.; Sundin, E.; Fredrixon, M.; Finger, R.; Rashid, H.; Desmaris, V.; Meledin, D.; Pavolotsky, A.; Belitsky, Victor

2010-03-01

389

Banded Terrain in East Hellas  

Science.gov (United States)

MGS MOC Release No. MOC2-460, 22 August 2003This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow angle camera image shows banded terrain in easternmost Hellas Planitia, between the distal ends of Dao and Harmakhis valleys. These bands probably indicate the location of eroded, layered bedrock that has been covered by a mantling deposit that, itself, became eroded to form the very small pits and bumps that pervade the region. This picture is located near 41.1oS, 275.0oW. Sunlight illuminates the scene from the left/upper left.

2003-01-01

390

Shear band regularization with peridynamics  

Science.gov (United States)

An extreme form of strain localization, known as shear-banding, is an important phenomenon in many engineering applications and processes especially in high strain-rate settings such as those encountered in ballistic impact. Concrete knowledge and robust computational tools for simulation of shear localization will help to predict these failure modes and optimize designs. It is well known that classical finite-element simulations of shear-banding can produce extremely mesh dependent results. Peridynamics, a non-local theory, is applied in this research to resolve this problem. Peridynamic simulations are compared to finite-element simulation results and show a regularization effect on the strain-localization.

Khan, Md. Imran Hossain

391

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

392

Study of backbending and decoupled bands in a spherical basis formalism  

International Nuclear Information System (INIS)

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

393

QUASIPARTICLE BAND STRUCTURE OF Ce-BASED HEAVY-FERMION COMPOUNDS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the influence on the Fermi surface topology of many-body corrections beyond LDA. A Renormalized Band method is used to calculate the quasiparticle band structures of both CeAl3 and Ce3Al compounds. We discuss the conditions under which the LDA is expected to predict the correct Fermi surface.

Parlebas, J.; Christensen, N.; Runge, E.; Zwicknagl, G.

1988-01-01

394

Phenomenological analysis and determination of spins for super-deformed bands in the mass-190 region  

International Nuclear Information System (INIS)

Fifteen superdeformed bands in seven nuclei of the mass-190 region are analyzed by means of the phenomenological model. An overall and excellent agreement between the calculated and observed spectra E?, kinematic moment of inertia J(1) and dynamic moment of inertia J(2) is obtained for all superdeformed bands in the mass-190 region

395

Recent advances of ab initio calculations in condensed matter physics  

International Nuclear Information System (INIS)

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

396

Asymmetry gap in the electronic band structure of bilayer graphene  

CERN Document Server

A tight binding model is used to calculate the band structure of bilayer graphene in the presence of a potential difference between the layers that opens a gap $\\Delta$ between the conduction and valence bands. In particular, a self consistent Hartree approximation is used to describe imperfect screening of an external gate, employed primarily to control the density $n$ of electrons on the bilayer, resulting in a potential difference between the layers and a density dependent gap $\\Delta (n)$. We discuss the influence of a finite asymmetry gap $\\Delta (0)$ at zero excess density, caused by the screening of an additional transverse electric field, on observations of the quantum Hall effect.

McCann, E

2006-01-01

397

Modification of band structure in intense laser fields  

International Nuclear Information System (INIS)

In the presence of the intense laser field, the Floquet-green's function method has been used for the calculation of the field-modified band structure for a one-dimensional periodic potential. Numerical illustrations show that the energy band structure is strongly modified by the intense laser field (1013-1014 W/cm2 at =780 mn). It is also shown that the laser field creates new laser-induced forbidden gaps, widths of which increase with increasing intensity of radiation. Evaluation of the mean energy spectrum in crystals has been also presented for different intensities of laser field

398

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

399

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

400

C-band wavelength conversion in silicon photonic wire waveguides.  

Science.gov (United States)

We demonstrate C-band wavelength conversion in Si photonic-wire waveguides with submicron cross-section by means of nonresonant, nondegenerate four-wave mixing (FWM) using low-power, cw-laser sources. Our analysis shows that for these deeply scaled Si waveguides, FWM can be observed despite the large phase mismatch imposed by strong waveguide dispersion. The theoretical calculations agree well with proof-of-concept experiments. The nonresonant character of the FWM scheme employed allows to demonstrate frequency tuning of the idler from ~ 20 GHz to > 100 GHz thus covering several C-band DWDM channels. PMID:19495349

Espinola, Richard; Dadap, Jerry; Osgood, Richard; McNab, Sharee; Vlasov, Yurii

2005-05-30

 
 
 
 
401

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

International Nuclear Information System (INIS)

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: ? Tunneling conductance spectra of two-band ferromagnet/superconductor are calculated. ? s-band and d-band of ferromagnet are mixed. ? The conductance spectra consist of several kinks, depending on the coupling strength. ? Two-band ferromagnet model is very essential.

402

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

403

Probing Time-Odd and Tensor Terms of The Skyrme Functional in Superdeformed Bands  

International Nuclear Information System (INIS)

We briefly discuss Hartree Fock Bogoliubov (HFB) plus self consistent cranking calculations for the superdeformed band in 194Hg, using the full Skyrme energy density functional including tensor terms in the p-h channel.

404

Band spectrum based interpretation of superfast luminescence spectra in cesium iodide  

International Nuclear Information System (INIS)

With usage of the cesium iodide calculated band energy spectrum and the simplest representations on the character of energy distribution of highly excited electrons is given and interpretation of experimentally observed spectra of picosecond luminescence

405

Gastric band migration following laparoscopic adjustable gastric banding (LAGB): two cases of endoscopic management using a gastric band cutter  

Science.gov (United States)

Laparoscopic adjustable gastric banding (LAGB) is one of the most frequently used minimally invasive and reversible procedures for the treatment of morbid obesity. Migration of the gastric band into the gastric lumen is a rare late complication of LAGB. Previous attempts at endoscopic removal of migrated bands have included the use of endoscopic scissors, laser ablation and argon plasma coagulation (APC). We report two cases of successful endoscopic management of gastric band migration using a gastric band cutter. PMID:23256012

Hady, Hady Razak; Baniukiewicz, Andrzej; Dabrowski, Andrzej; Kaminski, Fabian; Dadan, Jacek

2011-01-01

406

Gastric band migration following laparoscopic adjustable gastric banding (LAGB): two cases of endoscopic management using a gastric band cutter.  

Science.gov (United States)

Laparoscopic adjustable gastric banding (LAGB) is one of the most frequently used minimally invasive and reversible procedures for the treatment of morbid obesity. Migration of the gastric band into the gastric lumen is a rare late complication of LAGB. Previous attempts at endoscopic removal of migrated bands have included the use of endoscopic scissors, laser ablation and argon plasma coagulation (APC). We report two cases of successful endoscopic management of gastric band migration using a gastric band cutter. PMID:23256012

Rogalski, Pawel; Hady, Hady Razak; Baniukiewicz, Andrzej; D?browski, Andrzej; Kaminski, Fabian; Dadan, Jacek

2012-06-01

407

Isomer ratio calculations using modeled discrete levels  

International Nuclear Information System (INIS)

We have calculated isomer ratios for the 175Lu(n,?), 175Lu(n,2n), 237Np(n,2n), 241Am(n,?), and 243Am(n,?) reactions using modeled level structures in the deformed, odd-odd product nuclei. We find: that the hundreds of discrete levels and their gamma-ray branching ratios provided by the modeling are necessary to achieve agreement with experiment, that many rotational bands must be included in order to obtain a sufficiently representative selection of K quantum numbers, and that the levels of each band must be extended to appropriately high values of angular momentum. 8 references

408

Crossing of shears bands in 196Pb  

International Nuclear Information System (INIS)

High-spin states in 196Pb have been populated using the reaction 170Er(30Si, 4n). The previously observed shear bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin. (orig.)

409

Electron correlations in narrow band systems  

International Nuclear Information System (INIS)

If is studied the effect of the electron correlations in narrow bands, such as d(f) bands in the transition metals (rare earths) and their compounds and the impurity bands in doped semiconductors. It is described the narrow band systems by the Hubbard Hamiltonian. (A.C.A.S.)

410

Broad-band beam buncher  

Science.gov (United States)

A broad-band beam buncher is disclosed, comprising an evacuated housing, an electron gun therein for producing an electron beam, a buncher cavity having entrance and exit openings through which the beam is directed, grids across such openings, a source providing a positive DC voltage between the cavity and the electron gun, a drift tube through which the electron beam travels in passing through such cavity, grids across the ends of such drift tube, gaps being provided between the drift tube grids and the entrance and exit grids, a modulator for supplying an ultrahigh frequency modulating signal to the drift tube for producing velocity modulation of the electrons in the beam, a drift space in the housing through which the velocity modulated electron beam travels and in which the beam is bunched, and a discharge opening from such drift tube and having a grid across such opening through which the bunched electron beam is discharged into an accelerator or the like. The buncher cavity and the drift tube may be arranged to constitute an extension of a coaxial transmission line which is employed to deliver the modulating signal from a signal source. The extended transmission line may be terminated in its characteristic impedance to afford a broad-band response and the device as a whole designed to effect broad-band beam coupling, so as to minimize variations of the output across the response band.

Goldberg, David A. (Walnut Creek, CA); Flood, William S. (Berkeley, CA); Arthur, Allan A. (Martinez, CA); Voelker, Ferdinand (Orinda, CA)

1986-01-01

411

Band structure and nuclear dynamics  

International Nuclear Information System (INIS)

The relation between the Variable Moment of Inertia model and the Interacting Boson Model are discussed from a phenomenological viewpoint. New results on ground state mean-square radii in nuclei far from stability are reported, and a discussion of band structure extending to high angular momentum states and methods of extracting information on the underlying dynamics is given

412

Omnidirectional band gap in Fibonacci photonic crystals with metamaterials using a band-edge formalism  

Science.gov (United States)

Omnidirectional zero- nmacr gaps in one-dimensional photonic crystals with a Fibonacci basis containing frequency dependent metamaterials are examined. In this study, the band structure and band gaps are determined by an explicit band-edge equation rather than by a traditional dispersion equation. We find that the present method has better numerical stability than traditional methods, especially for calculating the zero- nmacr gap in the photonic crystals with metamaterials. We observe that the change in the width and location of the omnidirectional zero- nmacr gap is limited for the Fibonacci photonic crystals with different generation orders. However, the width of the omnidirectional gap in the Fibonacci photonic crystals is significantly affected by the filling factor of the metamaterials. We also find that the width of the gap will be maximum at an optimum filling factor. The gap will vanish if the filling factor is greater than a critical value. Moreover, for a given filling factor and a metamaterial, it is interesting that the gap will be enlarged as the refractive index of the traditional layer increases.

Hsueh, W. J.; Chen, C. T.; Chen, C. H.

2008-07-01

413

Highly Deformed Bands in Hf-175  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two high-spin regularly spaced rotational bands with large dynamical moments of inertia have been identified in Hf-175 with the Gammasphere spectrometer. These new bands are very similar to the previously identified triaxial superdeformed bands in the hafnium nuclei. However, the new bands in Hf-175 have been linked into the known level scheme and thereby provide the first firm spin assignments for these structures in this region. In order to understand the new bands, theoretical calculati...

Scholes, D. T.; Cullen, D. M.; Kondev, F. G.; Janssens, R. V.; Carpenter, M. P.; Hartley, D. J.; Djongolov, M. K.; Sletten, G.; Hagemann, G.; Wheldon, C.; Walker, P. M.; Abu Saleem, K.; Ahmad, I.; Balabanski, D. L.; Chowdhury, P.

2004-01-01

414

Quasiparticle band structures and optical properties of magnesium fluoride.  

Science.gov (United States)

The quasiparticle and optical properties of magnesium fluoride (MgF(2)) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment. PMID:22277330

Yi, Zhijun; Jia, Ran

2012-02-29

415

The absolute energy positions of conduction and valence bands of selected semiconducting minerals  

Energy Technology Data Exchange (ETDEWEB)

The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge energies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H{sub 2}O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H{sub 2}O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sulfides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H{sub 2}O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.

Xu, Y.; Schoonen, M.A.A.

2000-04-01

416

Development of ALMA Band 8 (385-500 GHz) Cartridge  

Science.gov (United States)

We have developed a cartridge-type receiver covering from 385 to 500 GHz for pre-production of ALMA Band 8. It receives two orthogonal polarizations and down-converts the sideband-separated signals to intermediate frequencies (IF) between 4 and 8 GHz. The cartridge-type receiver consists of a cold optics, a feed horn, an OMT, two sideband-separating SIS mixers, cryogenic multipliers of local oscillator (LO). These components were individually tested and then the cartridge was integrated and tested as a complete assembly. We have also developed equipment to test both components and the integrated receiver. The single sideband (SSB) noise temperature of this receiver is 130 K at the band center and 180 K at the band edges. The beam pattern and cross-polarization pattern are consistent with physical optical calculation. These results are promising for receiver production to the Atacama Large Millimeter/submillimeter Array (ALMA).

Sekimoto, Y.; Iizuko, Y.; Satou, N.; Ito, T.; Kumagai, K.; Kamikura, M.; Naruse, M.; Shan, W. L.

2008-04-01

417

Atomic Mirror for Wide-Band Scattering of Single Photon  

CERN Document Server

A resonant two level atom doped in one dimensional waveguide behaves as a mirror, but this single-atom "mirror" can only reflect single photon perfectly at a specific frequency. For a one dimensional coupled-resonator waveguide, we propose to extend the perfect reflection region from a specific frequency to a wide band by placing many atoms individually in the resonators in a finite coordinate region of the waveguide. Such a doped resonator array promises us to control the propagation of a practical photon wave packet with certain momentum distribution instead of a single photon, which is ideally represented by a plane wave with specific momentum. The studies based on the discrete-coordinate scattering theory display that such hybrid structure indeed provides a near-perfect reflection for single photon in a wide band. We also calculated photon group velocity distribution, which shows that the perfect reflection with wide band exactly corresponds to the stopping light region.

Chang, Yue; Sun, C P

2010-01-01

418

Simple description of double bands with mass of approximately 100  

International Nuclear Information System (INIS)

A simple collective model is applied to understand the structure of the ?I=1 doublet bands with the ?h11/2 x ?g9/2 configuration in the doubly-odd nuclei, 98-104Tc and 100-106Rh. In the model, a doubly-odd nucleus is realized when there is one neutron in the 0h11/2 orbital and one proton in the 0g9/2 orbital, and the collective core represents the even-even part of the nucleus. The calculation reproduces the energy spectra and the ratios B(M1; I ? I-1) / B(E2; I ? I-2) for the doublet bands quite well. The analysis of the wave functions reveals new band structure, showing various angular momentum configurations of the neutron and the proton, weakly coupled with the quadrupole collective excitations of the core. (author)

419

Search for excited superdeformed bands in {sup 151}Dy  

Energy Technology Data Exchange (ETDEWEB)

Following the first report of superdeformed (SD) bands with identical transition energies in the pairs ({sup 151}Tb*,{sup 152}Dy), ({sup 150}Gd*, {sup 151}Tb) and ({sup 153}Dy*, {sup 152}Dy) (where * denotes an excited SD band), it was proposed by Nazarewicz et al. that the observations could be understood in a strong-coupling approach if pseudo SU(3) symmetry were invoked. In this model there are three limiting values of the decoupling parameter; i.e. a = 0, {plus_minus}1. In the first two cases mentioned above the pairs of bands have nearly identical transition energies and are interpreted as proton excitations involving the [200]1/2 pseudospin orbital coupled to the {sup 152}Dy core, for which the value of the decoupling parameter is calculated to be a =+1.

Nisius, D.; Janssens, R.V.F.; Crowell, B. [and others

1995-08-01

420

Collective band properties in actinide nuclei well deformed  

International Nuclear Information System (INIS)

In actinides, proton i13/2 orbitals and neutron j15/2 orbitals are both near Fermi surface. At a great rotation speed, driving and Coriolis forces change the surface forces, in particular, they lower pairing forces inside the nucleus. The use of Coulomb excitation with the help of heavy and very heavy projectiles such as 32S, 84Kr, 142Nd, 208Pb at 232Th together with the most recent techniques of spectroscopy allowed to populate yrast bands of 230Th, 232Th, 235U and 237Np nuclei up to high spin states and together the even-even nuclei states in different collective bands. Experimental results have been analyzed in the frame of the different current models. The low spin states of rotational bands have been reproduced in a previous calculation using the nucleon-nucleon effective interaction of Skyrme III

 
 
 
 
421

High-spin E 2 bands in Kr isotopes  

Science.gov (United States)

Bands of E 2 transitions are assigned to 79Kr and 81Kr on the basis of ?-ray singles, ?-? coincidence, angular distribution, and excitation function measurements. These bands can be interpreted as arising from the decoupling of g92 neutrons from the 78Kr and 80Kr cores, respectively, and a comparison is made with the previously reported 77Kr decoupled band. Relative reaction cross sections are in fair agreement with evaporation model calculations. NUCLEAR REACTIONS 72Ge(10B,x?) and 73Ge(11B, x?), E=31, 34, 37, 40 MeV; measured ?(E?,E), ?(E?,?). 73Ge(11B, x?) E=37 MeV, measured Si(Li)-Ge(Li) ?-? coin. 74, 72Ge(10B,x?) E=40 MeV; measured Ge(Li)-Ge(Li) ?-? coin. 79,81Kr deduced levels, J?. Enriched targets.

Clements, J. S.; Medsker, L. R.; Fry, L. H., Jr.; Theisen, L. V.

1980-04-01

422

Electrical conductivity for the strongly correlated and hybridized Hubbard band  

International Nuclear Information System (INIS)

The magnetic and electrical transport properties of strongly correlated Hubbard model (f-band) hybridizing with non-correlated conduction band (c-band) was studied. The many-body model Hamiltonian was treated within the modified alloy analogy scheme and the resulting one-body problem was solved with the use of coherent potential approximation. Within Kubo-Greenwood formalism the dc electrical conductivity for bcc magnetic system was calculated and its variation with temperature and number of electrons was examined for different values of the Coulomb and hybridization (V) coupling constants. We found that the effect of strong correlations and hybridization on the conductivity is similar to that produced by the scattering due to the s-f interaction (spin disorder resistivity). (author)

423

Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides  

International Nuclear Information System (INIS)

The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spec