Band structure of W and Mo by empirical pseudopotential method
Sridhar, C. G.; Whiting, E. E.
1977-01-01
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.
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Yang, Chao
2009-07-17
We present a practical approach to calculate the complex band structure of an electrode for quantum transport calculations. This method is designed for plane wave based Hamiltonian with nonlocal pseudopotentials and the auxiliary periodic boundary condition transport calculation approach. Currently there is no direct method to calculate all the evanescent states for a given energy for systems with nonlocal pseudopotentials. On the other hand, in the auxiliary periodic boundary condition transport calculation, there is no need for all the evanescent states at a given energy. The current method fills this niche. The method has been used to study copper and gold nanowires and bulk electrodes.
Directory of Open Access Journals (Sweden)
Pablo Rivero
2015-06-01
Full Text Available We present in this article a pseudopotential (PP database for DFT calculations in the context of the SIESTA code [1–3]. Comprehensive optimized PPs in two formats (psf files and input files for ATM program are provided for 20 chemical elements for LDA and GGA exchange-correlation potentials. Our data represents a validated database of PPs for SIESTA DFT calculations. Extensive transferability tests guarantee the usefulness of these PPs.
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Alasia, F. [Dipartimento di Fisica, Universita di Milano, via Celoria 16, I-20133 Milano (Italy); Serra, L. [Departament de Fisica, Universitat de les Illes Balears, E-07071 Palma de Mallorca (Spain); Broglia, R.A. [Dipartimento di Fisica, Universita di Milano, Via Celoria 16, I-20133 Milano (Italy)]|[Istituto Nazionale di Fisica Nucleare, Sezione di Milano, via Celoria 16, I-20133 Milano (Italy)]|[The Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen (Denmark); Van Giai, N. [Division de Physique Theorique, Institut de Physique Nucleaire, F-91406 Orsay Cedex (France); Lipparini, E. [Dipartimento di Fisica, Universita degli Studi di Trento, Trento, I-38050 Povo Trento (Italy)]|[Gruppo Collegato, Istituto Nationale di Fisica Nucleare, Trento I-38050 Povo Trento (Italy); Roman, H.E. [Institut fur Theoretische Physik, Universitaet Giessen, Heinrich-Buff-Ring 16, 35392 Giessen (Germany)
1995-09-15
Using realistic nonlocal pseudopotentials to describe ion-valence electron interaction, we perform self-consistent calculations of ground and excited states of spherical alkali-metal clusters within the local-density approximation. The ion pseudopotential is uniformly averaged in the cluster sphere within the proposed pseudopotential jellium model. It is found that in small clusters, pseudopotentials lead to predictions that strongly improve those of the jellium model and are very close to the results found previously with pseudo-Hamiltonians.
Alasia, F.; Serra, Ll.; Broglia, R. A.; van Giai, Nguyen; Lipparini, E.; Roman, H. E.
1995-09-01
Using realistic nonlocal pseudopotentials to describe ion-valence electron interaction, we perform self-consistent calculations of ground and excited states of spherical alkali-metal clusters within the local-density approximation. The ion pseudopotential is uniformly averaged in the cluster sphere within the proposed pseudopotential jellium model. It is found that in small clusters, pseudopotentials lead to predictions that strongly improve those of the jellium model and are very close to the results found previously with pseudo-Hamiltonians.
First principles pseudopotential calculations on aluminum and aluminum alloys
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Davenport, J.W.; Chetty, N.; Marr, R.B.; Narasimhan, S.; Pasciak, J.E.; Peierls, R.F.; Weinert, M.
1993-12-31
Recent advances in computational techniques have led to the possibility of performing first principles calculations of the energetics of alloy formation on systems involving several hundred atoms. This includes impurity concentrations in the 1% range as well as realistic models of disordered materials (including liquids), vacancies, and grain boundaries. The new techniques involve the use of soft, fully nonlocal pseudopotentials, iterative diagonalization, and parallel computing algorithms. This approach has been pioneered by Car and Parrinello. Here the authors give a review of recent results using parallel and serial algorithms on metallic systems including liquid aluminum and liquid sodium, and also new results on vacancies in aluminum and on aluminum-magnesium alloys.
Smidstrup, Søren; Stradi, Daniele; Wellendorff, Jess; Khomyakov, Petr A.; Vej-Hansen, Ulrik G.; Lee, Maeng-Eun; Ghosh, Tushar; Jónsson, Elvar; Jónsson, Hannes; Stokbro, Kurt
2017-11-01
We present an efficient implementation of a surface Green's-function method for atomistic modeling of surfaces within the framework of density functional theory using a pseudopotential localized basis set approach. In this method, the system is described as a truly semi-infinite solid with a surface region coupled to an electron reservoir, thereby overcoming several fundamental drawbacks of the traditional slab approach. The versatility of the method is demonstrated with several applications to surface physics and chemistry problems that are inherently difficult to address properly with the slab method, including metal work function calculations, band alignment in thin-film semiconductor heterostructures, surface states in metals and topological insulators, and surfaces in external electrical fields. Results obtained with the surface Green's-function method are compared to experimental measurements and slab calculations to demonstrate the accuracy of the approach.
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Burkatzki, Mark Thomas
2008-07-01
The author presents scalar-relativistic energy-consistent Hartree-Fock pseudopotentials for the main-group and 3d-transition-metal elements. The pseudopotentials do not exhibit a singularity at the nucleus and are therefore suitable for quantum Monte Carlo (QMC) calculations. The author demonstrates their transferability through extensive benchmark calculations of atomic excitation spectra as well as molecular properties. In particular, the author computes the vibrational frequencies and binding energies of 26 first- and second-row diatomic molecules using post Hartree-Fock methods, finding excellent agreement with the corresponding all-electron values. The author shows that the presented pseudopotentials give superior accuracy than other existing pseudopotentials constructed specifically for QMC. The localization error and the efficiency in QMC are discussed. The author also presents QMC calculations for selected atomic and diatomic 3d-transitionmetal systems. Finally, valence basis sets of different sizes (VnZ with n=D,T,Q,5 for 1st and 2nd row; with n=D,T for 3rd to 5th row; with n=D,T,Q for the 3d transition metals) optimized for the pseudopotentials are presented. (orig.)
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White, W.T. III
1985-11-04
We have studied two-photon absorption in solids theoretically and experimentally. We have shown that it is possible to use accurate band structure techniques to compute two-photon absorption spectra within 15% of measured values in a wide band-gap material, ZnS. The empirical pseudopotential technique that we used is significantly more accurate than previous models of two-photon absorption in zinc blende materials, including present tunneling theories (which are essentially parabolic-band results in disguise) and the nonparabolic-band formalism of Pidgeon et al. and Weiler. The agreement between our predictions and previous measurements allowed us to use ZnS as a reference material in order to validate a technique for measuring two-photon absorption that was previously untried in solids, pulsed dual-beam thermal lensing. With the validated technique, we examined nonlinear absorption in one other crystal (rutile) and in several glasses, including silicates, borosilicates, and one phosphate glass. Initially, we believed that the absorption edges of all the materials were comparable; however, subsequent evidence suggested that the effective band-gap energies of the glasses were above the energy of two photons in our measurement. Therefore, we attribute the nonlinear absorption that we observed in glasses to impurities or defects. The measured nonlinear absorption coefficients were of the order of a few cm/TW in the glasses and of the order of 10 cm/GW in the crystals, four orders of magnitude higher than in glasses. 292 refs.
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Mo, O.; Riera, A.; Yaez, M.
1985-06-01
We present an extension of the analytical method of Macias and Riera to calculate radial couplings, to include model potentials or (local and nonlocal) pseudopotentials, in the Hamiltonian. As an illustration, energies, couplings, and momentum matrix elements are presented and discussed for the two-effective-electron NaH quasimolecule, as a stringent test case.
Figgen, Detlev; Wedig, Anja; Stoll, Hermann; Dolg, Michael; Eliav, Ephraim; Kaldor, Uzi
2008-01-14
The four-component atomic intermediate-Hamiltonian Fock-space coupled cluster (IHFSCC) code of Landau et al. [J. Chem. Phys. 115, 6862 (2001)] has been adapted to two-component calculations with relativistic pseudopotentials of the energy-consistent variety. Recently adjusted energy-consistent pseudopotentials for group 11 and 12 transition elements as well as group 13 and 14 post-d main group elements, which were fitted to atomic valence spectra from four-component multiconfiguration Dirac-Hartree-Fock calculations, are tested in IHFSCC calculations for ionization potentials, electron affinities, and excitation energies of a variety of atoms and ions. Where comparison is possible, the deviations from experimental data are in good agreement with those found in previously published IHFSCC all-electron calculations: experimental data are usually reproduced within a few hundred wavenumbers.
Yadav, Jayprakash; Rafique, S. M.; Kumari, Shanti
2009-10-01
In the present paper some superconducting (SC) state parameters of metals Ga, Cd and In have been studied through Harrison's First Principle [HFP] pseudopotential technique using McMillan's formalism. The impact of choosing two different sets of core energy eigenvalues viz. Herman-Skillman and Clementi (or Experimental) has been studied.
Nguyen, Phuong Hoa; Hofmann, Karl R.; Paasch, Gernot
2003-07-01
In a previous article [J. Appl. Phys. 92, 5359 (2002)], we presented a combination of a full-band Monte Carlo method using an advanced band structure and a variable Brillouin zone discretization, with phonon scattering rates based on the screened pseudopotential considering the positions of the atoms in the elementary cell. To make the method suitable for sufficiently fast applications, such as device simulations, the simplest wave number dependent approximation was introduced. It contains an average of the cell structure factor, and only two fit parameters: The acoustic and the optical deformation potentials. As the pseudopotential, the Ashcroft model potential is chosen, and screening is taken into account using the Lindhard dielectric function. In the present article, based on the study of the influence of the two deformation potentials on the electron and hole drift velocities in Si and Ge, we show how to select the deformation potentials. Depending on the targeted agreement with experimental results, the pairs of deformation potentials for electrons and holes can be used uniformly for a wide temperature range or separately for different temperatures. For Ge, we achieve remarkable quantitative agreement with the temperature, field, and orientation dependencies of experimental electron and hole drift velocities in the wide temperature range from 77 to 300 K with a single set of the two deformations potentials for each carrier type. A detailed comparative simulation of the transport properties in Ge and Si at different temperatures is presented which is comprised of the steady-state dependence of the drift velocity on the electric field, the low-field mobility, and transient transport. Peculiarities of the drift velocity-field dependencies, such as the anisotropy, and a negative differential mobility are discussed in terms of the different band structures in connection with the field dependence of the simulated distribution functions. For doped materials, ionized
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Kheloufi, Nawal; Bouzid, Abderrazak, E-mail: a_bouzid34@hotmail.com
2016-06-25
We present band gap calculations of zinc-blende ternary CdS{sub x}Te{sub 1-x} semiconductors within the standard DFT and quasiparticle calculations employing pseudopotential method. The DFT, the local density approximation (LDA) and the Generalized Gradient Approximation (GGA) based calculations have given very poor results compared to experimental data. The quasiparticle calculations have been investigated via the one-shot GW approximation. The present paper discuses and confirms the effect of inclusion of the semicore states in the cadmium (Cd) pseudopotential. The obtained GW quasiparticle band gap using Cd{sup +20} pseudopotential has been improved compared to the obtained results from the available pseudopotential without the treatment of semicore states. Our DFT and quasiparticle band gap results are discussed and compared to the available theoretical calculations and experimental data. - Graphical abstract: Band gaps improvement concerning the binary and ternary alloys using the GW approximation and Cd{sup 20+} pseudopotential with others levels of approximations (the LDA and GGA approximation employing the Cd{sup 12+} and the LDA within Cd{sup 20+} pseudopotential). - Highlights: • The direct Γ- Γ and indirect Γ- X and Γ- L bands gaps show a nonlinear behavior when S content is enhanced. • The quasiparticle band gap result for the investigated semiconductors is improved using the GW approximation. • All CdS{sub x}Te{sub 1-x} compounds in all compositions range from 0 to 1 are direct band gap semiconductors.
Vocadlo; Price; Wood
2000-06-01
An investigation of the relative stability of the two known polymorphs of RuSi, having the epsilon-FeSi and CsCl structures, has been made by first-principles pseudopotential calculations. The resulting cell volumes and fractional coordinates at P = 0 are in good agreement with experiment. Application of high pressure to the epsilon-FeSi phase of RuSi is predicted to produce a structure having almost perfect sevenfold coordination. However, it appears that RuSi having the CsCl-type structure will be the thermodynamically most stable phase for pressures greater than 3.6 GPa. Fitting of the calculated internal energy versus volume to a fourth-order logarithmic equation of state led to values (at T = 0 K) for the bulk modulus, K0, of 202 and 244 GPa for the epsilon-FeSi and CsCl phases, respectively, in excellent agreement with experiment. Band-structure calculations for both phases are also presented.
Band calculation of lonsdaleite Ge
Chen, Pin-Shiang; Fan, Sheng-Ting; Lan, Huang-Siang; Liu, Chee Wee
2017-01-01
The band structure of Ge in the lonsdaleite phase is calculated using first principles. Lonsdaleite Ge has a direct band gap at the Γ point. For the conduction band, the Γ valley is anisotropic with the low transverse effective mass on the hexagonal plane and the large longitudinal effective mass along the c axis. For the valence band, both heavy-hole and light-hole effective masses are anisotropic at the Γ point. The in-plane electron effective mass also becomes anisotropic under uniaxial tensile strain. The strain response of the heavy-hole mass is opposite to the light hole.
Levashov, P R; Sin'ko, G V; Smirnov, N A; Minakov, D V; Shemyakin, O P; Khishchenko, K V
2010-12-22
In the present work, we compare the thermal contribution of electrons to thermodynamic functions of metals in different models at high densities and electron temperatures. One of the theoretical approaches, the full-potential linear-muffin-tin-orbital method, treats all electrons in the framework of density functional theory (DFT). The other approach, VASP, uses projector-augmented-wave pseudopotentials for the core electrons and considers the valent electrons also in the context of DFT. We analyze the limitations of the pseudopotential approach and compare the DFT results with a finite-temperature Thomas-Fermi model and two semiempirical equations of state.
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Levashov, P R; Minakov, D V; Shemyakin, O P; Khishchenko, K V [Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya 13 Building 2, Moscow 125412 (Russian Federation); Sin' ko, G V; Smirnov, N A, E-mail: pasha@ihed.ras.r [Russian Federal Nuclear Center-Zababakhin All-Russia Research Institute of Technical Physics, Snezhinsk 456770, Chelyabinsk region (Russian Federation)
2010-12-22
In the present work, we compare the thermal contribution of electrons to thermodynamic functions of metals in different models at high densities and electron temperatures. One of the theoretical approaches, the full-potential linear-muffin-tin-orbital method, treats all electrons in the framework of density functional theory (DFT). The other approach, VASP, uses projector-augmented-wave pseudopotentials for the core electrons and considers the valent electrons also in the context of DFT. We analyze the limitations of the pseudopotential approach and compare the DFT results with a finite-temperature Thomas-Fermi model and two semiempirical equations of state.
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Imai, Y. [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Higashi 1-1 Tsukuba, Ibaraki 305-8565 (Japan); Watanabe, A. [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Higashi 1-1 Tsukuba, Ibaraki 305-8565 (Japan)
2006-06-29
The electronic structures of platinum group elements (Ru, Os, Rh, Ir, Pd, and Pt) silicides have been calculated. Ir{sub 3}Si{sub 5} is a semiconductor with the direct gap of 1.14 eV. Among monosilicides, RuSi and OsSi with the FeSi-type structure are semiconductors with the gap values of 0.21 and 0.41 eV but RhSi, IrSi, PdSi, and PtSi with the MnP-type structure are metals. No semiconducting compounds can be found in other platinum group elements silicides other than known Ru{sub 2}Si{sub 3}, Os{sub 2}Si{sub 3}, and OsSi{sub 2}.
Electronic structure prediction via data-mining the empirical pseudopotential method
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Zenasni, H.; Aourag, H. [LEPM, URMER, Departement of Physics, University Abou Bakr Belkaid, Tlemcen 13000 (Algeria); Broderick, S.R.; Rajan, K. [Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011-2230 (United States)
2010-01-15
We introduce a new approach for accelerating the calculation of the electronic structure of new materials by utilizing the empirical pseudopotential method combined with data mining tools. Combining data mining with the empirical pseudopotential method allows us to convert an empirical approach to a predictive approach. Here we consider tetrahedrally bounded III-V Bi semiconductors, and through the prediction of form factors based on basic elemental properties we can model the band structure and charge density for these semi-conductors, for which limited results exist. This work represents a unique approach to modeling the electronic structure of a material which may be used to identify new promising semi-conductors and is one of the few efforts utilizing data mining at an electronic level. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Hill, J Grant; Peterson, Kirk A
2017-12-28
New correlation consistent basis sets based on pseudopotential (PP) Hamiltonians have been developed from double- to quintuple-zeta quality for the late alkali (K-Fr) and alkaline earth (Ca-Ra) metals. These are accompanied by new all-electron basis sets of double- to quadruple-zeta quality that have been contracted for use with both Douglas-Kroll-Hess (DKH) and eXact 2-Component (X2C) scalar relativistic Hamiltonians. Sets for valence correlation (ms), cc-pVnZ-PP and cc-pVnZ-(DK,DK3/X2C), in addition to outer-core correlation [valence + (m-1)sp], cc-p(w)CVnZ-PP and cc-pwCVnZ-(DK,DK3/X2C), are reported. The -PP sets have been developed for use with small-core PPs [I. S. Lim et al., J. Chem. Phys. 122, 104103 (2005) and I. S. Lim et al., J. Chem. Phys. 124, 034107 (2006)], while the all-electron sets utilized second-order DKH Hamiltonians for 4s and 5s elements and third-order DKH for 6s and 7s. The accuracy of the basis sets is assessed through benchmark calculations at the coupled-cluster level of theory for both atomic and molecular properties. Not surprisingly, it is found that outer-core correlation is vital for accurate calculation of the thermodynamic and spectroscopic properties of diatomic molecules containing these elements.
Electronic band-structure calculations of some magnetic chromium compounds
VANBRUGGEN, CF; HAAS, C; DEGROOT, RA
1989-01-01
In this paper band-structure calculations of CrS, CrSe, Cr3Se4 and CrSb are presented. Together with our accompanying results for the chromium tellurides, these calculations give a coherent picture of the changes in the electronic structure caused by anion substitution and by introduction of cation
Bulk modulus of metals according to structureless pseudopotential ...
African Journals Online (AJOL)
structureless pseudopotential model was fully developed. The developed method was used to calculate the bulk modulus and kinetic energy contribution to the bulk modulus of 46 elemental metals. The results obtained were compared with experimental values and their variation with electron density parameter was studied ...
First-principles electronic-band calculations on organic conductors
Directory of Open Access Journals (Sweden)
Shoji Ishibashi
2009-01-01
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.
Four-band Hamiltonian for fast calculations in intermediate-band solar cells
Luque, Antonio; Panchak, Aleksandr; Vlasov, Alexey; Martí, Antonio; Andreev, Viacheslav
2016-02-01
The 8-dimensional Luttinger-Kohn-Pikus-Bir Hamiltonian matrix may be made up of four 4-dimensional blocks. A 4-band Hamiltonian is presented, obtained from making the non-diagonal blocks zero. The parameters of the new Hamiltonian are adjusted to fit the calculated effective masses and strained QD bandgap with the measured ones. The 4-dimensional Hamiltonian thus obtained agrees well with measured quantum efficiency of a quantum dot intermediate band solar cell and the full absorption spectrum can be calculated in about two hours using Mathematica© and a notebook. This is a hundred times faster than with the commonly-used 8-band Hamiltonian and is considered suitable for helping design engineers in the development of nanostructured solar cells.
Development of Electron-positron Screened Pseudopotential ...
African Journals Online (AJOL)
... a trend in the variation of the screened pseudopotential for metals in the same group in the periodic table and also that the higher the positron annihilation rate in a metal the higher the screened pseudopotential experienced before annihilation. Nigeria Journal of Pure and Applied Physics VOLUME 1, AUGUST 2000, pp.
Relativistic Band Calculation and the Optical Properties of Gold
DEFF Research Database (Denmark)
Christensen, N Egede; Seraphin, B. O.
1971-01-01
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...... and comparison to the observed temperature shifts of the elements of structure in the experimental ε2 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...
Nudged elastic band calculations accelerated with Gaussian process regression
Koistinen, Olli-Pekka; Dagbjartsdóttir, Freyja B.; Ásgeirsson, Vilhjálmur; Vehtari, Aki; Jónsson, Hannes
2017-10-01
Minimum energy paths for transitions such as atomic and/or spin rearrangements in thermalized systems are the transition paths of largest statistical weight. Such paths are frequently calculated using the nudged elastic band method, where an initial path is iteratively shifted to the nearest minimum energy path. The computational effort can be large, especially when ab initio or electron density functional calculations are used to evaluate the energy and atomic forces. Here, we show how the number of such evaluations can be reduced by an order of magnitude using a Gaussian process regression approach where an approximate energy surface is generated and refined in each iteration. When the goal is to evaluate the transition rate within harmonic transition state theory, the evaluation of the Hessian matrix at the initial and final state minima can be carried out beforehand and used as input in the minimum energy path calculation, thereby improving stability and reducing the number of iterations needed for convergence. A Gaussian process model also provides an uncertainty estimate for the approximate energy surface, and this can be used to focus the calculations on the lesser-known part of the path, thereby reducing the number of needed energy and force evaluations to a half in the present calculations. The methodology is illustrated using the two-dimensional Müller-Brown potential surface and performance assessed on an established benchmark involving 13 rearrangement transitions of a heptamer island on a solid surface.
Mixed ultrasoft/norm-conserved pseudopotential scheme
DEFF Research Database (Denmark)
Stokbro, Kurt
1996-01-01
A variant of the Vanderbilt ultrasoft pseudopotential scheme, where the norm conservation is released for only one or a few angular channels, is presented. Within this scheme some difficulties of the truly ultrasoft pseudopotentials are overcome without sacrificing the pseudopotential softness. (i......) Ghost states are easily avoided without including semicore shells. (ii) The ultrasoft pseudo-charge-augmentation functions can be made softer. (iii) The number of nonlocal operators is reduced. The scheme will be most useful for transition metals, and the feasibility and accuracy of the scheme...
Compton profiles and band structure calculations of IV-VI layered compounds GeS and GeSe
Rathor, A.; Sharma, V.; Heda, N. L.; Sharma, Y.; Ahuja, B. L.
2008-04-01
First ever isotropic experimental Compton profiles of GeS and GeSe are presented. Moreover, we present Compton profiles, energy bands and density of states (DOS) using Hartree-Fock, density functional and pseudopotential schemes. It is seen that the Hartree-Fock and density functional theories show a reasonable agreement with the experiment. The equal-valence-electron-density profiles show that GeS is more ionic than GeSe. We have also reported energy bands and DOS using full potential linearized augmented plane-wave method.
ELECTRONIC-STRUCTURE OF THE LEAD MONOXIDES - BAND-STRUCTURE CALCULATIONS AND PHOTOELECTRON-SPECTRA
TERPSTRA, HJ; DEGROOT, RA; HAAS, C
1995-01-01
PbO is a layer compound which exists in two polymorphic forms, a red tetragonal (alpha) and a yellow orthorhombic (beta) modification. Ab initio band-structure calculations are presented for both phases. The calculated energy gaps are in agreement with optical data. The band-structure calculations
Energy Technology Data Exchange (ETDEWEB)
Richard, N
2002-07-01
In the Density Functional Theory Framework, the pseudopotential formalism offers a broader scope of study than other theoretical methods such as global relaxation of the parameters of the cell or ab initio molecular dynamics simulations. This method has been widely used to study light elements or transition metals but never to study f elements. We have generated two non local norm conserving Trouillier-Martins pseudopotentials (one in LDA and one in GGA) for the cerium. To check the validity of the pseudopotentials, we have calculated the equilibrium volume and the incompressibility modulus and compared our results to previous all-electron calculations. If the GGA and non linear core corrections are used, the equation of state is in a good agreement with the experimental equation of state. A static study of the previously proposed high pressure phases give a transitions fcc-a''(I)-bct. Using the pseudopotentials we have generated, an ab initio molecular dynamics simulation at constant pressure, in the region between 5 and 12 GPa where the stable phase of cerium is not well defined, lead us to predict that a centred monoclinic structure, as the a''(I) phase previously observed in some experiments, is the most stable phase. We have also generated pseudopotentials for the light actinides (Th, Pa, U and Np). We have study their phase transitions under pressure at zero temperature. We compared our results with all electron results. The structure parameters have always been relaxed in this study. And for the first time in pseudopotential calculation, the spin-orbit coupling has been taken into account. The curves describing the variation of the volume or the incompressibility modulus depending on the elements and the phase transitions are always in agreement with the one found in the all electron calculations. (author)
Band structure and optical properties of LiKB4O7 single crystal
Smok, P; Seinert, H; Kityk, [No Value; Berdowski, J
2003-01-01
The band structure (BS), electronic charge density distribution and linear optical properties of the LiKB4O7 (LKB4) single crystal are calculated using a self-consistent norm-conserving pseudo-potential method within the framework of the local density approximation theory. Dispersion of the
The Band Structure of Polymers: Its Calculation and Interpretation. Part 2. Calculation.
Duke, B. J.; O'Leary, Brian
1988-01-01
Details ab initio crystal orbital calculations using all-trans-polyethylene as a model. Describes calculations based on various forms of translational symmetry. Compares these calculations with ab initio molecular orbital calculations discussed in a preceding article. Discusses three major approximations made in the crystal case. (CW)
DEFF Research Database (Denmark)
Christensen, N. Egede; Feuerbacher, B.
1974-01-01
The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure...
The Band Structure of Polymers: Its Calculation and Interpretation. Part 3. Interpretation.
Duke, B. J.; O'Leary, Brian
1988-01-01
In this article, the third part of a series, the results of ab initio polymer calculations presented in part 2 are discussed. The electronic structure of polymers, symmetry properties of band structure, and generalizations are presented. (CW)
MODEL PSEUDOPOTENTIAL OF THE ELECTRON - NEGATIVE ION INTERACTION
Directory of Open Access Journals (Sweden)
Yu.Rudavskii
2003-01-01
Full Text Available Generalization of the Anderson model to describe the states of electronegative impurities in liquid-metal alloys is the main aim of the present paper. The effects of the random inner field on the charge impurity states is accounted for selfconsistently. Qualitative and quantitative estimation of hamiltonian parameters has been carried out. The limits of the proposed model applicability to a description of real systems are considered. Especially, the case of the oxygen impurity in liquid sodium is studied. The modelling of the proper electron-ionic interaction potential is the main goal of the paper. The parameters of the proposed pseudopotential are analyzed in detail. The comparison with other model potentials have been carried out. Resistivity of liquid sodium containing the oxygen impurities is calculated with utilizing the form-factor of the proposed model potential. Dependence of the resistivity on impurity concentration and on the charge states is received.
Energy Technology Data Exchange (ETDEWEB)
Fang, Jingtian, E-mail: jingtian.fang@utdallas.edu; Vandenberghe, William G.; Fu, Bo; Fischetti, Massimo V. [Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080 (United States)
2016-01-21
We present a formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials. This formalism offers explicit atomistic wavefunctions and an accurate band structure, enabling a detailed study of the characteristics of devices with a nanometer-scale channel and body. Assuming externally applied potentials that change slowly along the electron-transport direction, we invoke the envelope-wavefunction approximation to apply the open boundary conditions and to develop the transport equations. We construct the full-band open boundary conditions (self-energies of device contacts) from the complex band structure of the contacts. We solve the transport equations and present the expressions required to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gate-all-around (GAA) silicon nanowire field-effect transistor with a body-size of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ∼66 mV/decade and a drain-induced barrier-lowering of ∼2.5 mV/V. Our theoretical calculations predict that low-dimensionality channels in a 3D GAA architecture are able to meet the performance requirements of future devices in terms of SS swing and electrostatic control.
Calculation of semiconductor band gaps with the M06-L density functional.
Zhao, Yan; Truhlar, Donald G
2009-02-21
The performance of the M06-L density functional has been tested for band gaps in seven semiconductors plus diamond and MgO. Comparison with the local spin density approximation (LSDA), Becke-Lee-Yang-Parr (BLYP), Perdew-Burke-Eernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and Heyd-Scuseria-Ernzerhof (HSE) functionals shows that M06-L has improved performance for calculating band gaps as compared to other local functionals, but it is less accurate than the screened hybrid HSE functional for band gaps.
Numerical calculation of acoustic radiation from band-vibrating structures via FEM/FAQP method
Directory of Open Access Journals (Sweden)
GAO Honglin
2017-08-01
Full Text Available The Finite Element Method (FEM combined with the Frequency Averaged Quadratic Pressure method (FAQP are used to calculate the acoustic radiation of structures excited in the frequency band. The surface particle velocity of stiffened cylindrical shells under frequency band excitation is calculated using finite element software, the normal vibration velocity is converted from the surface particle velocity to calculate the average energy source (frequency averaged across intensity, frequency averaged across pressure and frequency averaged across velocity, and the FAQP method is used to calculate the average sound pressure level within the bandwidth. The average sound pressure levels are then compared with the bandwidth using finite element and boundary element software, and the results show that FEM combined with FAQP is more suitable for high frequencies and can be used to calculate the average sound pressure level in the 1/3 octave band with good stability, presenting an alternative to applying frequency-by-frequency calculation and the average frequency process. The FEM/FAQP method can be used as a prediction method for calculating acoustic radiation while taking the randomness of vibration at medium and high frequencies into consideration.
Soriano, L; Abbate, M; Pen, H; Prieto, P; Sanz, JM
We studied the electronic structure of TiN and VN by means of band structure calculations and spectroscopic techniques. The band structure calculations show that the bonding in these compounds is mostly covalent. The Fermi level intersects the transition metal 3d bands giving rise to the metallic
Calculation of line parameters of the ν3 band of monodeuterated methane: Nitrogen broadening
Lavrentieva, N. N.; Dudaryonok, A. S.; Buldyreva, J. V.
2017-09-01
Halfwidths and shifts of CH3D lines are calculated for the case of nitrogen broadening. The calculations are performed for room temperature (296 K) for vibrational-rotational lines in the ν3 parallel band, with the rotational quantum numbers varying in the ranges of 0 ≤ J ≤ 70 and 0 ≤ K ≤ 20. For each line, the temperature-dependence characteristics are calculated in the range of 200-400 K recommended for the HITRAN database. The calculations are carried out using a semiempirical method with a correction factor the parameters of which are adjusted on a number of experimental values.
Tan's distributions and Fermi-Huang pseudopotential in momentum space
DEFF Research Database (Denmark)
Valiente, Manuel
2012-01-01
The long-standing question of finding the momentum representation for the s-wave zero-range interaction in three spatial dimensions is here solved. This is done by expressing a certain distribution, introduced in a formal way in [ S. Tan Ann. Phys. (NY) 323 2952 (2008)], explicitly. The resulting...... form of the Fourier-transformed pseudopotential remains very simple. Operator forms for the so-called Tan's selectors, which, together with Fermi-Huang pseudopotential, largely simplify the derivation of Tan's universal relations for the Fermi gas, are here derived and are also very simple. A momentum...... cutoff version of the pseudopotential is also provided, and with this no apparent contradiction to the notion of integrals in Tan's methods is left. The equivalence, even at the intermediate-step level, between the pseudopotential approach and momentum-space renormalization of the bare Dirac delta...
The use of bulk states to accelerate the band edge statecalculation of a semiconductor quantum dot
Energy Technology Data Exchange (ETDEWEB)
Vomel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques,Osni A.; Dongarra, Jack J.
2006-05-10
We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations.
He, Jiangang; Franchini, Cesare
2017-08-16
In this paper we assess the predictive power of the self-consistent hybrid functional scPBE0 in calculating the band gap of oxide semiconductors. The computational procedure is based on the self-consistent evaluation of the mixing parameter α by means of an iterative calculation of the static dielectric constant using the perturbation expansion after discretization (PEAD) method and making use of the relation α = 1/ε_{∞}. Our materials dataset is formed by 30 compounds covering a wide range of band gaps and dielectric properties, and includes materials with a wide spectrum of application as thermoelectrics, photocatalysis, photovoltaics, transparent conducting oxides, and refractory materials. Our results show that the scPBE0 functional provides better band gaps than the non self-consistent hybrids PBE0 and HSE06, but scPBE0 does not show significant improvement on the description of the static dielectric constants. Overall, the scPBE0 data exhibit a mean absolute percentage error of 14 % (band gaps) and 10 % (α = 1/ε_{∞}). For materials with weak dielectric screening and large excitonic biding energies scPBE0, unlike PBE0 and HSE06, overestimates the band gaps, but the value of the gap become very close to the experimental value when excitonic effects are included (e.g. for SiO_{2}). However, special caution must be given to the compounds with small band gaps due to the tendency of scPBE0 to overestimate the dielectric constant in proximity of the metallic limit. © 2017 IOP Publishing Ltd.
Fast calculation algorithm for discrete resonance-based band-pass filter
Directory of Open Access Journals (Sweden)
Toso Pankovski
2016-09-01
Full Text Available A discrete resonant band-pass filter with a fast calculation algorithm, which can be used to perform discrete frequency transformations, is presented. The algorithm has low memory consumption requirements. It implements a numerical integration method, simulating a harmonic resonator element modeled by the under-damped driven oscillator equations, expressed in a discrete form. The output from the presented filter is a discrete function with an amplitude of the steady-solution that closely matches the theoretical steady-solution amplitude of the continuous band-pass filter output. Multiple discrete resonant band-pass filters can be used to build a filter bank, which in turn can be used to perform a time-to-frequency transformation of discrete signals. The filter achieves a frequency and a time localization without utilizing the time windowing method. The presented stand-alone calculation algorithm related to this filter produces its output with a delay of just one sampling period. The algorithm’s calculation cost is only 3 multiplications and 3 additions per sample, and does not require long memory buffers. The presented transformation does not surpass the precision of the Discrete Fourier and Discrete Wavelet Transformations. However, it may prove essential when the noise-artifacts of the near-real-world simulation are necessary in order to produce some specific auditory-perception phenomena.
Directory of Open Access Journals (Sweden)
Yu Wang
2002-01-01
Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.
Empirical pseudo-potential studies on electronic structure of ...
Indian Academy of Sciences (India)
Wintec
and the lowest unoccupied molecular orbital (LUMO) as a function of shape and size of the quantum dots. Our studies explain the ... Keywords. Quantum dots; empirical pseudo-potential; electronic structure; HOMO–LUMO gap. 1. Introduction ...... both the finite and infinite well EMA breaks down and introduces significant ...
Empirical pseudo-potential studies on electronic structure of ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 31; Issue 3. Empirical pseudo-potential studies on electronic structure of semiconducting quantum dots. Anjali Kshirsagar Neelesh ... Theoretical investigations of electronic structure of quantum dots is of current interest in nanophase materials. Empirical theories such ...
Directory of Open Access Journals (Sweden)
D. P. Samajdar
2014-01-01
Full Text Available The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1-xBix and InSb1-xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E+ levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E− energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.
Thermoelectric Properties and Band Structure Calculations of Novel Boron Network Compounds
Mori, Takao; Nishimura, Toshiyuki; Grin, Yuri; Shishido, Toetsu; Nakajima, Kazuo
2009-03-01
Boron is an interesting element, tending to form atomic networks such as 2D atomic nets and clusters, with some analogy to carbon systems which have been more extensively studied. Boron has one less electron than carbon and thus is electron deficient when forming atomic networks, but this causes it to have a special affinity with the rare earth elements and as a result, many new compounds have recently been discovered [1]. Their potential as viable thermoelectric materials is attracting interest since they are high-temperature materials and possess intrinsic low thermal conductivity, with some compounds exhibiting Seebeck coefficients in excess of 200 μV/K above 1000 K. The thermoelectric properties and band structure calculations of novel borides such as RB44Si2, RB17CN, RB22C2N, RB28.5C4 will be presented. Features in the band structure near the Fermi level indicate large doping effects in these compounds. Various doping experiments were carried out resulting in large increases to the figure of merit. [1] T. Mori, ``Higher Borides,'' in: Handbook on the Physics and Chemistry of Rare Earths, Vol. 38, (North-Holland, Amsterdam, 2008) p. 105-173.
Amanullah, Mohamed Jamal Bin; Adam, Tijjani; Dhahi, Th S.; Mohammed, Mohammed; Hashim, U.; Noriman, N. Z.; Dahham, Omar S.
2017-09-01
Silicon is the most important material in semiconductor industry. As nano-devices shrink in size, the conventional understanding of electronic devices are no longer applicable as quantum effects start to play an important role for the behavior of the device. At the same time, when structures are approaching atomic scale, the precise fabrication by photo-lithographic techniques, for example, are not even applicable. Very often, the fabrication of regular structures rely on self-assembly is susceptible to fluctuations. Therefore, a deeper understanding to exploit the quantum behavior of nano-devices and precise control of building nano-structures are highly desired. Thus, genetic algorithm based on first principle analysis to optimize silicon nanowires electron and elastic properties is proposed. One nanometer (1nm) surface reconstruction by using genetic algorithm combined with ab-initio calculation is proposed. The SiNWs behavior to quasi-direct band gap transition with the decrease size and the band gap properties under different electrical voltage will be determined.
BAND-STRUCTURE AND CLUSTER-MODEL CALCULATIONS OF LACOO(3) IN THE LOW-SPIN PHASE
ABBATE, M; POTZE, R; SAWATZKY, GA; FUJIMORI, A
1994-01-01
We present band-structure and cluster-model calCulatiOns Of LaCoO3 in the low-spin phase. The purpose of these calculations is to contrast and complement the results and conclusions of recent spectroscopic studies. The total density of states (DOS) is compared to the photoemission spectrum; the
Sharma, S; Dewhurst, J K; Ambrosch-Draxl, C
2005-09-23
We present the first all-electron full-potential exact exchange (EXX) Kohn-Sham density functional calculations on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr, and Xe). We remove one of the main computational obstacles of such calculations by the use of a highly efficient basis for inversion of the response function. We find that the band gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. The locations of d bands, determined using the full-potential EXX method, are in excellent agreement with experiment, irrespective of whether these are core, semicore, or valence states. We conclude that the inclusion of the core-valence interaction is necessary for accurate determination of EXX Kohn-Sham band structures and that EXX alone is not a complete answer to the band-gap problem in semiconductors.
First-principles calculations of band offsets and polarization effects at InAs/InP interfaces
Hajlaoui, C.; Pedesseau, L.; Raouafi, F.; Ben Cheikh Larbi, F.; Even, J.; Jancu, J.-M.
2015-09-01
We have performed first-principles calculations of the band alignment of InAs/InP heterojonctions on InP. The strained valence-band offset of 0.43 eV and 0.38 eV is calculated for the cubic and wurtzite phases respectively. No built-in electric fields are evidenced in the simulations. Spontaneous polarization and piezoelectric constants are calculated for both InP and InAs. The flat-band alignment and its dependence on crystalline phases implicate a possible way of patterning InAs/InP quantum wire structures with thickness engineering and electronic properties suited for optical devices.
Directory of Open Access Journals (Sweden)
O. Funk
2003-03-01
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
Directory of Open Access Journals (Sweden)
O. Funk
Full Text Available This paper addresses the statistics underlying cloudy sky radiative transfer (RT by inspection of the distribution of the path lengths of solar photons. Recent studies indicate that this approach is promising, since it might reveal characteristics about the diffusion process underlying atmospheric radiative transfer (Pfeilsticker, 1999. Moreover, it uses an observable that is directly related to the atmospheric absorption and, therefore, of climatic relevance. However, these studies are based largely on the accuracy of the measurement of the photon path length distribution (PPD. This paper presents a refined analysis method based on high resolution spectroscopy of the oxygen A-band. The method is validated by Monte Carlo simulation atmospheric spectra. Additionally, a new method to measure the effective optical thickness of cloud layers, based on fitting the measured differential transmissions with a 1-dimensional (discrete ordinate RT model, is presented. These methods are applied to measurements conducted during the cloud radar inter-comparison campaign CLARE’98, which supplied detailed cloud structure information, required for the further analysis. For some exemplary cases, measured path length distributions and optical thicknesses are presented and backed by detailed RT model calculations. For all cases, reasonable PPDs can be retrieved and the effects of the vertical cloud structure are found. The inferred cloud optical thicknesses are in agreement with liquid water path measurements.
Key words. Meteorology and atmospheric dynamics (radiative processes; instruments and techniques
First-principles energy band calculation for CaBi{sub 2}O{sub 4} with monoclinic structure
Energy Technology Data Exchange (ETDEWEB)
Nakamura, Hiroyuki; Ishii, Shin' ichirou [Integrated Arts and Science, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985 (Japan); Yamada, Kenji [Department of Materials Science and Chemical Engineering, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985 (Japan); Matsushima, Shigenori, E-mail: smatsu@kct.ac.jp [Department of Materials Science and Chemical Engineering, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985 (Japan); Arai, Masao [Computational Materials Science Center (CMSC), National Institute of Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044 (Japan); Kobayashi, Kenkichiro [Department of Materials Science, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011 (Japan)
2010-05-15
The electronic structure of CaBi{sub 2}O{sub 4} is calculated by a GGA approach. The valence band maximum is approximately located at the {Gamma}-point or the Y-point and the conduction band minimum at the V-point. This means that CaBi{sub 2}O{sub 4} is an indirect energy gap material. The conduction band is composed of Bi 6p-O 2p interaction. On the other hand, the valence band can be divided into two energy regions ranging from -9.92 to -7.40 eV (lower valence band) and -4.69 to 0 eV (upper valence band). The former is mainly constructed from Bi 6s states interacting slightly with O 2s and 2p states, and the latter consists of O 2p states hybridizing with Bi 6s and 6p states. The states near the valence band maximum are strongly localized and the mobility of holes generated by band gap excitation is predicted to be fairly low.
Calculating joint confidence bands for impulse response functions using highest density regions
Lütkepohl, Helmut; Staszewska-Bystrova, Anna; Winker, Peter
2016-01-01
This paper proposes a new non-parametric method of constructing joint confidence bands for impulse response functions of vector autoregressive models. The estimation uncertainty is captured by means of bootstrapping and the highest density region (HDR) approach is used to construct the bands. A Monte Carlo comparison of the HDR bands with existing alternatives shows that the former are competitive with the bootstrap-based Bonferroni and Wald confidence regions. The relative tightness of the H...
Calculating Joint Bands for Impulse Response Functions using Highest Density Regions
Winker, Peter; Lütkepohl, Helmut; Staszewska-Bystrova, Anna
2016-01-01
This paper proposes a new non-parametric method of constructing joint confidence bands for impulse response functions of vector autoregressive models. The estimation uncertainty is captured by means of bootstrapping and the highest density region (HDR) approach is used to construct the bands. A Monte Carlo comparison of the HDR bands with existing alternatives shows that the former are competitive with the bootstrap-based Bonferroni and Wald confidence regions. The relative tightness of the H...
Effect of exact Coulomb-exchange calculations on band-head spectra of odd-proton nuclei
Directory of Open Access Journals (Sweden)
Koh Meng-Hock
2017-01-01
Full Text Available Previous calculations of band-head energy spectra of odd-mass heavy nuclei in the Hartree-Fock-plus-Bardeen-Cooper-Schrieffer (HF-BCS framework showed that the agreement with data is better for odd-neutron as compared to odd-proton nuclei. The reason for a poorer agreement with data for the latter have been ascribed to the possible usage of the Slater approximation in calculating the Coulomb-exchange term. In this work, we report the effect of exact Coulomb-exchange calculations on band-head energy spectra of two odd-proton nuclei (namely 237Np and 241Am as compared to the results obtained using the Slater approximation. We performed self-consistent blocking calculations while taking the breaking of time-reversal symmetry at the mean-field level into account due to the unpaired nucleon. The SkM* and SIII parametrizations of the Skyrme interaction have been employed to approximate the effective nucleon-nucleon interaction while a seniority force is used for the pairing channel. Contrary to what was expected, our preliminary results show no improvement on the band-head spectra as compared to data when the Coulomb-exchange term is calculated exactly.
First principles calculations of niobium substitution in strontium titanate
Energy Technology Data Exchange (ETDEWEB)
Astala, R.; Bristowe, P.D. [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge (United Kingdom)
2002-02-18
We have studied the effects of Nb incorporation in strontium titanate using DFT plane-wave pseudopotential calculations. Substitution of the impurity on a Ti site in the bulk crystal causes outward relaxations of the neighbouring Ti ions but does not affect the oxygen ions. A conduction band state localized on the Ti ions becomes occupied confirming the donor behaviour of the defect. The formation energy of the impurity is studied under different oxidation conditions. We have also studied the incorporation of Nb near to a {sigma}=3(111) grain boundary. The results indicate that Nb segregation is unfavourable due to Coulomb repulsion effects. (author). Letter-to-the-editor.
Devashish, D.; Hasan, Shakeeb B.; Van Der Vegt, J. J.W.; Vos, Willem L.
2017-01-01
We study numerically the reflectivity of three-dimensional (3D) photonic crystals with a complete 3D photonic band gap. We employ the finite element method to study crystals with the cubic diamondlike inverse woodpile structure. The high-index backbone has a dielectric function similar to silicon.
Gao, Shiyuan; Yang, Li
2017-10-01
Doped free carriers can substantially renormalize electronic self-energy and quasiparticle band gaps of two-dimensional (2D) materials. However, it is still challenging to quantitatively calculate this many-electron effect, particularly at the low doping density that is most relevant to realistic experiments and devices. Here we develop a first-principles-based effective-mass model within the G W approximation and show a dramatic band-gap renormalization of a few hundred meV for typical 2D semiconductors. Moreover, we reveal the roles of different many-electron interactions: The Coulomb-hole contribution is dominant for low doping densities while the screened-exchange contribution is dominant for high doping densities. Three prototypical 2D materials are studied by this method: h -BN , Mo S2 , and black phosphorus, covering insulators to semiconductors. Especially, anisotropic black phosphorus exhibits a surprisingly large band-gap renormalization because of its smaller density-of-state that enhances the screened-exchange interactions. Our work demonstrates an efficient way to accurately calculate band-gap renormalization and provides quantitative understanding of doping-dependent many-electron physics of general 2D semiconductors.
Calculations of Energy Shift of the Conduction Band-Edge in Doped and Compensated GaP
Endo, Tamio; Itoh, Nobuhiko; Okino, Yasushi; 遠藤, 民生; 伊藤, 伸彦; 沖野, 祥[他
1989-01-01
The energy shifts of the parabolic conduction band-edge at 77 and 300K with doping the Te-donor in GaP were calculated in the nondegenerate system for the two cases ; unintentional and intentional compensations, using the two models proposed by Hwang abd by Mahan. The total parabolic shift △EM（△EH）, and the contributions of the exchangeinteraction △μex（△Ee） and of the Coulomb interaction △μed（△Ec） calculated by the Mahan's model (Hwang's model), increase with increasing donor concentration in...
Ab initio calculation of the Structural, Mechanical and ...
African Journals Online (AJOL)
ADOWIE PERE
ABSTRACT: An ab initio plane-wave Pseudopotential calculations using the density functional theory (DFT) .... wave Pseudopotential PWPP method with the ..... Γ the longitudinal optical LO branch shows a sharp increasing amount of upward dispersion while the TO , a flat/horizontal dispersion it was also observed that the ...
Fang, CM; vanSmaalen, S; Wiegers, GA; Haas, C; deGroot, RA
1996-01-01
In order to understand the electronic structure of the misfit layer compound (LaS)(1.14)NbS2 we carried out an ab initio band-structure calculation in a supercell approximation. The band structure is compared with that of the components NbS2 and LaS. The calculations show that the electronic
Fang, Jingtian
As transistors, the most basic component of central processing units (CPU) in all electronic products, are scaling down to the nanometer scale, quantum mechanical effects must be studied to investigate their performance. A formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials is presented in this dissertation. We develop the transport equations and show the expressions to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gate-all-around (GAA) silicon nanowire field-effect transistor (FET) with a body-size of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ˜66 mV/decade and a drain-induced barrier-lowering of ~2.5 mV/V. This formalism is also applied to assess the ballistic performance of FETs with armchair-edge graphene nanoribbon (aGNRs) and silicon nanowire (SiNWs) channels and with gate lengths ranging from 5 nm to 15 nm. The device characteristics of the transistors with a 5 nm gate length are compared. Source-to-drain tunneling effects are investigated for SiNWFETs and GNRFETs by comparing the I-V characteristics of each respective transistor with different channel lengths. While a uniform dielectric constant is assumed in solving Poisson equation for the devices simulated above, the knowledge of the atomistic (i.e., local) dielectric permittivity that considers the atomistic electron distribution and quantum-confinement effect is necessary to treat the electrostatic properties accurately. The local permittivity can also provide information about the dielectric property at the interfaces. We use the random-phase approximation, first-order perturbation theory, and empirical pseudopotentials to calculate the static polarizability, susceptibility, and dielectric response function in graphene and GNRs. While the
Applicability of the wide-band limit in DFT-based molecular transport calculations.
Verzijl, C.J.; Seldenthuis, J.S.; Thijssen, J.M.
2013-01-01
Transport properties of molecular junctions are notoriously expensive to calculate with ab initio methods, primarily due to the semi-infinite electrodes. This has led to the introduction of different approximation schemes for the electrodes. For the most popular metals used in experiments, such as
Applicability of the wide-band limit in DFT-based molecular transport calculations
Verzijl, C.J.O.; Seldenthuis, J.S.; Thijssen, J.M.
2013-01-01
Transport properties of molecular junctions are notoriously expensive to calculate with ab initio methods, primarily due to the semi-infinite electrodes. This has led to the introduction of different approximation schemes for the electrodes. For the most popular metals used in experiments, such as
Nault, Zachary; Cancio, Antonio
2013-03-01
Much recent development in DFT has focused on improving GGAs. Two schemes are second order GGA (SOGGA) and the APBE which builds the GGA from atomic systems and not the HEG. Both of these have been tested within an all electron (AE) environment, providing the most accurate results. The focus of many simulations, however, is on large systems using pseudopotentials (PsP's). Are these PsP calculations, which rely on functionals tested in an AE environment, accurately reproducing the AE ground state properties? If not, can the deficiencies be identified? To assess this, we use the PsP generator APE, using the functional library libXC which works with the PsP package ABINIT and the AE package Elk. We generate standard Troullier-Martin PsP's based on common and new XC functionals (LDA, PBE, PBEsol, APBE, SOGGA) and test their performance in 13 solids (Na, Li, Al, C, Si, GaAs, NaCl, LiF, LiCl, Cu, Pd, Rh, and Ag). We measure how well three ground state properties (lattice constant, bulk modulus, and cohesive energy) are calculated with PsP's as compared to the corresponding AE calculations.
Umari, P; Petrenko, O; Taioli, S; De Souza, M M
2012-05-14
Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy.
Calculation and analysis for the quasi-optical biconical cavity in submillimeter band
Hu, Xiaochao; Wang, Shijie
1986-06-01
The performance characteristics of a quasi-optical biconical cavity (like that described by Gustinci, 1977) as a submm-wave receiver antenna are investigated theoretically. The distribution of EM fields in the loaded cavity is calculated; the relationship between cavity size and the input impedance and receiving coefficient is determined; and the conditions for impedance and beam-pattern matching are obtained. For a given divergence angle of the Gaussian beam, the maximum receiving coefficient is obtained with an opening 1.5 times the beam-waist diameter. Diagrams and graphs are provided.
A diffusion Monte Carlo study of sign problems from non-local pseudopotentials
Tubman, Norm; Morales-Silva, Miguel; Dubois, Jonathan; Hood, Randolph
2012-02-01
Difficulties can arise in simulating various Hamiltonian operators efficiently in diffusion Monte Carlo (DMC) such as those associated with non-local pseudopotentials which require the introduction of an approximate form. The locality approximation and T-moves are two widely used techniques in fixed-node diffusion Monte Carlo (FN-DMC) that provide a tractable approach for treating non-local pseudopotentials, however their use introduces an uncontrolled approximation. Exact treatment of the non-local pseudopotentials in FN-DMC introduces a sign problem with the associated Green's function matrix elements which take on both positive and negative values. Here we present an analysis of the nature of the sign problem that non-local operators introduce into the Green's function. We then consider the feasibility of running DMC simulations in which the non-local pseudopotentials are treated exactly and demonstrate the algorithm on a few molecular systems.
Ueda, Shigenori; Hamada, Ikutaro
2017-12-01
The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.
Fang, C.M.; Groot, R.A. de; Wiegers, G.A.; Haas, C.
1996-01-01
In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)1.20TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar
Fang, CM; deGroot, RA; Wiegers, GA; Haas, C
1996-01-01
In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)(1.20)TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar
LETTER TO THE EDITOR: First principles calculations of niobium substitution in strontium titanate
Astala, R.; Bristowe, P. D.
2002-02-01
We have studied the effects of Nb incorporation in strontium titanate using DFT plane-wave pseudopotential calculations. Substitution of the impurity on a Ti site in the bulk crystal causes outward relaxations of the neighbouring Ti ions but does not affect the oxygen ions. A conduction band state localized on the Ti ions becomes occupied confirming the donor behaviour of the defect. The formation energy of the impurity is studied under different oxidation conditions. We have also studied the incorporation of Nb near to a Σ = 3(111) grain boundary. The results indicate that Nb segregation is unfavourable due to Coulomb repulsion effects.
Band structure of fcc-C60 solid state crystal study
Directory of Open Access Journals (Sweden)
S Javanbakht
2009-09-01
Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of σ and π bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.
Effective mass calculations for shallow acceptors in nitrides
Emmert-Aronson, Jacob; Lambrecht, W. R. L.
2012-02-01
In the effective mass approximation for shallow acceptors in semiconductors, the defect eigenstates are written as a product of a slowly varying envelope function and the band extrema Bloch functions. The Kohn-Luttinger Hamiltonian describing the valence band manifold in zincblende, or its generalization for other crystals structures, then becomes a set of coupled differential equations for the envelope function. These can be solved by a variational approach with hydrogenic type basis functions. We have implemented this approach for the appropriate Hamiltonians for zincblende, wurtzite and an orthorhombic crystal structure occurring for II-IV-N2 semiconductors. The Hamiltonian parameters used were extracted from first-principles GW calculations. The central cell correction to the Coulomb potential was added based on pseudopotential differences as proposed by Mireles and Ulloa (Phys. Rev. B 58, 3879 (1998)). Results are presented for various acceptors in GaN, AlN, InN, ZnGeN2 and ZnSnS2. The effects of varying the crystal field splitting parameter, and the type of pseudopotentials (including or not semicore d-states) were investigated.
Energy Technology Data Exchange (ETDEWEB)
Su Xiaoxing, E-mail: xxsu@bjtu.edu.c [School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044 (China); Li Jianbao; Wang Yuesheng [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China)
2010-05-15
If the energy bands of a phononic crystal are calculated by the finite difference time domain (FDTD) method combined with the fast Fourier transform (FFT), good estimation of the eigenfrequencies can only be ensured by the postprocessing of sufficiently long time series generated by a large number of FDTD iterations. In this paper, a postprocessing method based on the high-resolution spectral estimation via the Yule-Walker method is proposed to overcome this difficulty. Numerical simulation results for three-dimensional acoustic and two-dimensional elastic systems show that, compared with the classic FFT-based postprocessing method, the proposed method can give much better estimation of the eigenfrequencies when the FDTD is run with relatively few iterations.
Investigations of press-induced band gap changes in PbS
Li, Wei; He, Qin-yu; Wang, Yin-zhen; Wang, Teng
2017-11-01
We applied the hydrostatic and uniaxial pressure respectively to cubic PbS based on the plane-wave pseudo-potential density functional theory. The calculated results indicate that the band gap of PbS closes and reopens under hydrostatic pressure like a topological crystalline insulator, although it isn't a topological crystalline insulator because the pressure induced phase transition will occur when the hydrostatic pressure increases to about 2.2 GPa in fact. In addition, we find that, unlike the case of hydrostatic pressing, when the uniaxial pressure is applied along [0 0 1] direction, PbS is converted from a direct band gap semiconductor to an indirect band gap semiconductors.
Phase transition and electronic properties of SbI3: First-principles calculations
Sun, Xiao-Xiao; Li, Cong; Hou, Qing-Yu; Zhang, Yue
2017-06-01
We have performed the first-principles pseudopotential calculations to investigate the structural phase transition and electronic properties of SbI3 considering several possible phases as a function of pressure from 0 GPa to 100 GPa. Our calculations show that this material undertakes a structural transformation from the R-3 phase to high-pressure P21/c phase at about 6.5 GPa with a relative volume collapse of 4.3%. We also have investigated the elastic properties and energy band structure of SbI3 under hydrostatic pressure. The calculation suggests that the R-3 phase is a semiconductor with an indirect band gap of about 2.16 eV at 0 Gpa. Under the influence of pressure, we have found that high-pressure P21/c phase has transformed to metal at about 55 GPa.
Energy Technology Data Exchange (ETDEWEB)
Takhloukh, A; Grosdidier, B; Hellal, S [Laboratoire de Physique des Milieux Denses, Universite de Metz, Institut de Physique -electronique et de chimie 1 BdArago, 57078 Metz cedex 3 (France); Regnaut, C [Laboratoire de Physique des Liquides et des Milieux Complexes, Universite de Paris 12, Faculte des Sciences et Technologie, 61 Av. du General de Gaulle, 94 010 Creteil cedex (France)], E-mail: regnaut@univ-parisl2.fr
2008-02-15
Using perturbation theory and classical molecular dynamics simulations, we study the static structure and demixing behaviour of the liquid LiNa alloy from the pseudopotential approach and different classes of models. We find that the norm conserving pseudopotential does not lead to demixing while various local models, with few adjustable parameters correctly predict the structure and spinodal unstability in the alloy. Transferability of the pseudopotential to the alloy is improved if the parameters are fitted to some bulk or structural properties of the pure metal. We find that demixion can be predicted when the structure factors of the pure liquid Li and Na are reasonably reproduced from such pseudopotentials.
Many-pole model of inelastic losses applied to calculations of XANES
Energy Technology Data Exchange (ETDEWEB)
Kas, J J; Vinson, J; Rehr, J J [University of Washington, Department of Physics, Box 351560, Seattle, WA 98195-1560 (United States); Trcera, N [Synchrotron Soleil, L' Orme des Merisiers, Saint-Aubin - BP 48, 91192 GIF-SUR-YVETTE Cedex (France); Cabaret, D [Institut de Mineralogie et Physique des Milieux Condenses, UMR 7590 CNRS, Universite Pierre et Marie Curie, Universite Paris Diderot, IPGP, IRD, 140 rue de Lourmel, 75015 Paris (France); Shirley, E L, E-mail: hebhop@u.washington.ed [NIST, Optical Technology Division, 100 Bureau Drive, Mail Stop 8441, Gaithersburg, MD 20899-8441 (United States)
2009-11-15
Conventional Kohn-Sham band-structure methods for calculating deep-core x-ray spectra typically neglect photoelectron self-energy effects, which give rise to an energy-dependent shift and broadening of the spectra. Here an a posteriori procedure is introduced to correct for these effects. The method is based on ab initio calculations of the GW self-energy using a many-pole model and a calculation of the dielectric function in the long wavelength limit using either the FEFF8 real-space Green's function code, or the AI2NBSE interface between the National Institute of Standards and Technology (NIST) Bethe-Salpeter equation solver (NBSE) and the ABINIT pseudopotential code. As an example the method is applied to core level x-ray spectra of LiF and MgAl{sub 2}O{sub 4} calculated using (respectively) OCEAN, an extension of the AI2NBSE code for core level excitations, and the PARATEC pseudopotential code with the core-hole treated using a super-cell. The method satisfactorily explains the discrepancy between experiment and calculations.
Energy Technology Data Exchange (ETDEWEB)
Song, T., E-mail: songting_lzjtu@yeah.net [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Ma, Q. [School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Sun, X.W., E-mail: xsun@carnegiescience.edu [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Liu, Z.J., E-mail: liuzj_lzcu@163.com [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Department of Physics, Lanzhou City University, Lanzhou 730070 (China); Fu, Z.J. [School of Electrical and Electronic Engineering, Chongqing University of Arts and Sciences, Chongqing 402160 (China); Wei, X.P.; Wang, T.; Tian, J.H. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2016-09-07
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.
Oliveira, Micael J. T.; Nogueira, Fernando
2008-04-01
We present a computer package designed to generate and test norm-conserving pseudo-potentials within Density Functional Theory. The generated pseudo-potentials can be either non-relativistic, scalar relativistic or fully relativistic and can explicitly include semi-core states. A wide range of exchange-correlation functionals is included. Program summaryProgram title: Atomic Pseudo-potentials Engine (APE) Catalogue identifier: AEAC_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 88 287 No. of bytes in distributed program, including test data, etc.: 649 959 Distribution format: tar.gz Programming language: Fortran 90, C Computer: any computer architecture, running any flavor of UNIX Operating system: GNU/Linux RAM: APE also has a very sophisticated and user-friendly input system. Running time: The example given in this paper (Si) takes 10 s to run on a Pentium IV machine clocked at 2 GHz.
Relating the defect band gap and the density functional band gap
Schultz, Peter; Edwards, Arthur
2014-03-01
Density functional theory (DFT) is an important tool to probe the physics of materials. The Kohn-Sham (KS) gap in DFT is typically (much) smaller than the observed band gap for materials in nature, the infamous ``band gap problem.'' Accurate prediction of defect energy levels is often claimed to be a casualty--the band gap defines the energy scale for defect levels. By applying rigorous control of boundary conditions in size-converged supercell calculations, however, we compute defect levels in Si and GaAs with accuracies of ~0.1 eV, across the full gap, unhampered by a band gap problem. Using GaAs as a theoretical laboratory, we show that the defect band gap--the span of computed defect levels--is insensitive to variations in the KS gap (with functional and pseudopotential), these KS gaps ranging from 0.1 to 1.1 eV. The defect gap matches the experimental 1.52 eV gap. The computed defect gaps for several other III-V, II-VI, I-VII, and other compounds also agree with the experimental gap, and show no correlation with the KS gap. Where, then, is the band gap problem? This talk presents these results, discusses why the defect gap and the KS gap are distinct, implying that current understanding of what the ``band gap problem'' means--and how to ``fix'' it--need to be rethought. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's NNSA under contract DE-AC04-94AL85000.
Energy Technology Data Exchange (ETDEWEB)
Rakhecha, Shalu, E-mail: shalurakhecha@yahoo.com; Vyas, P. R.; Gohel, V. B. [Department of Physics, School of Sciences, Gujarat University, Ahmedabad - 380009, Gujarat (India); Bhatt, N. K. [Department of Physics, Sardar Patel University, Vallabh Vidyanagar - 388120, Gujarat (India)
2016-05-06
In the present communication, we have computed static and dynamic properties (binding energy-E, bulk modulus-B and second moment- <ω{sup 2}>) as well as first order pressure induced phase transition (FCC-BCC) using local form of pseudopotential for Calcium and Strontium. The form of pseudopotential used for the computation is directly extracted from Generalized Pseudopotential Theory (GPT) which contains three parameters (r{sub c}, r{sub d} and β). We have suggested a simple method using which pseudopotential is determined by single parameter (β). Our computed results for binding energy and bulk modulii are in excellent agreement with experimental findings and are better than other theoretical results. The present study confirms that s-d hybridization is accounted properly in the presently used pseudopotential and can be extended for the study of lattice mechanical properties of these metals.
Band structure and optical parameters of the SnO2(110) surface
Mäki-Jaskari, Matti A.; Rantala, Tapio T.
2001-08-01
With a first-principles-density-functional method, combined with two different pseudopotentials, ideal oxidized and reduced surfaces of tin oxide are studied. The band structures of bulk and the surface systems are calculated and compared. The nature of the surface Sn2+ ions, their outward relaxation, associated ``dangling bonds'' and band gap states are considered. Also ultraviolet optical constants are determined by using the electric dipole approximation with a scissor correction, and noted to agree with experiments. The presence of the surface, and more significantly, its removed bridging oxygen atoms, becomes apparent in a formation of a new absorption feature. This is predicted to cause about 0.7 eV decrease of the absorption edge.
Li, Qing; Luo, K H
2013-11-01
In this paper, we aim to address an important issue about the pseudopotential lattice Boltzmann (LB) model, which has attracted much attention as a mesoscopic model for simulating interfacial dynamics of complex fluids, but suffers from the problem that the surface tension cannot be tuned independently of the density ratio. In the literature, a multirange potential was devised to adjust the surface tension [Sbragaglia et al., Phys. Rev. E 75, 026702 (2007)]. However, it was recently found that the density ratio of the system will be changed when the multirange potential is employed to adjust the surface tension. An alternative approach is therefore proposed in the present work. The basic strategy is to add a source term to the LB equation so as to tune the surface tension of the pseudopotential LB model. The proposed approach can guarantee that the adjustment of the surface tension does not affect the mechanical stability condition of the pseudopotential LB model, and thus provides a separate control of the surface tension and the density ratio. Meanwhile, it still retains the mesoscopic feature and the computational simplicity of the pseudopotential LB model. Numerical simulations are carried out for stationary droplets, capillary waves, and droplet splashing on a thin liquid film. The numerical results demonstrate that the proposed approach is capable of achieving a tunable surface tension over a very wide range and can keep the density ratio unchanged when adjusting the surface tension.
Pseudopotential description of rare earths in oxides: The case of Er2Si2O7
DEFF Research Database (Denmark)
Lægsgaard, Jesper; Stokbro, Kurt
2001-01-01
The applicability of ultrasoft pseudopotentials to the problem of rare-earth incorporation in silicates is investigated using the compound Er2Si2O7 as a test case. It is found that density-functional theory within the generalized gradient approximation provides a good description of the structural...
DEFF Research Database (Denmark)
Svane, Axel; Christensen, Niels Egede; Cardona,, M.
2010-01-01
The electronic band structures of PbS, PbSe, and PbTe in the rocksalt structure are calculated with the quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included. The semiconducting gaps and their deformation potentials as well as the effective masses are obtained. The GW...
Energy Technology Data Exchange (ETDEWEB)
Silva, Cleuton de Souza [Instituto de Química, Universidade Estadual de Campinas, Barão Geraldo, P.O. Box 6154, 13083-970 Campinas, São Paulo (Brazil); Instituto de Ciências Exatas e Tecnologia, Universidade Federal do Amazonas, Campus de Itacoatiara, 69100-021 Itacoatiara, Amazonas (Brazil); Pereira, Douglas Henrique [Departamento de Ciências Exatas e Biotecnológicas, Universidade Federal do Tocantins, Campus de Gurupi, 77410-530 Gurupi, Tocantins (Brazil); Custodio, Rogério, E-mail: roger@iqm.unicamp.br [Instituto de Química, Universidade Estadual de Campinas, Barão Geraldo, P.O. Box 6154, 13083-970 Campinas, São Paulo (Brazil)
2016-05-28
The G4CEP composite method was developed from the respective G4 all-electron version by considering the implementation of compact effective pseudopotential (CEP). The G3/05 test set was used as reference to benchmark the adaptation by treating in this work atoms and compounds from the first and second periods of the periodic table, as well as representative elements of the third period, comprising 440 thermochemical data. G4CEP has not reached a so high level of accuracy as the G4 all-electron theory. G4CEP presented a mean absolute error around 1.09 kcal mol{sup −1}, while the original method presents a deviation corresponding to 0.83 kcal mol{sup −1}. The similarity of the optimized molecular geometries between G4 and G4CEP indicates that the core-electron effects and basis set adjustments may be pointed out as a significant factor responsible for the large discrepancies between the pseudopotential results and the experimental data, or even that the all-electron calculations are more efficient either in its formulation or in the cancellation of errors. When the G4CEP mean absolute error (1.09 kcal mol{sup −1}) is compared to 1.29 kcal mol{sup −1} from G3CEP, it does not seem so efficient. However, while the G3CEP uncertainty is ±4.06 kcal mol{sup −1}, the G4CEP deviation is ±2.72 kcal mol{sup −1}. Therefore, the G4CEP theory is considerably more reliable than any previous combination of composite theory and pseudopotential, particularly for enthalpies of formation and electron affinities.
Lucatto, Bruno; Assali, Lucy V. C.; Pela, Ronaldo Rodrigues; Marques, Marcelo; Teles, Lara K.
2017-08-01
A major challenge in creating a quantum computer is to find a quantum system that can be used to implement the qubits. For this purpose, deep centers are prominent candidates, and ab initio calculations are one of the most important tools to theoretically study their properties. However, these calculations are highly involved, due to the large supercell needed, and the computational cost can be even larger when one goes beyond the Kohn-Sham scheme to correct the band gap problem and achieve good accuracy. In this work, we present a method that overcomes these problems and provides the optical transition energies as a difference of Kohn-Sham eigenvalues; even more, provides a complete and accurate band structure of the defects in a semiconductor. Despite the original motivations, the presented methodology is a general procedure, which can be used to systematically study the optical transitions between localized levels within the band gap of any system. The method is an extension of the low-cost and parameter-free DFT-1/2 approximate quasiparticle correction, and allows it to be applied in the study of complex defects. As a benchmark, we apply the method to the NV- center in diamond. The agreement with experiments is remarkable, with an accuracy of 0.1 eV. The band structure agrees with the expected qualitative features of this system, and thus provides a good intuitive physical picture by itself.
Predoi-Cross, A.; Malathy Devi, V.; Sutradhar, P.; Sinyakova, T.; Buldyreva, J.; Sung, K.; Smith, M. A. H.; Mantz, A. W.
2016-07-01
This paper presents the results of a spectroscopic line shape study of self- and nitrogen-broadened 12CH3D transitions in the ν3 and ν5 bands in the Triad region. We combined five pure gas spectra with eighteen spectra of lean mixtures of 12CH3D and nitrogen, all recorded with a Bruker IFS-125 HR Fourier transform spectrometer. The spectra have been analyzed simultaneously using a multispectrum nonlinear least squares fitting technique. N2-broadened line parameters for 184 transitions in the ν3 band and 205 transitions in the ν5 band were measured. In addition, line positions and line intensities were measured for 168 transitions in the ν3 band and 214 transitions in the ν5 band. We have observed 10 instances of weak line mixing corresponding to K″=3 A1 or A2 transitions. Comparisons were made for the N2-broadening coefficients and associated temperature exponents with corresponding values calculated using a semi-classical Robert Bonamy type formalism that involved an inter-molecular potential with terms corresponding to short- and long-range interactions, and exact classical molecular trajectories. The theoretical N2-broadened coefficients are overestimated for high J values, but are in good agreement with the experimental values for small and middle range J values.
Lycett-Brown, Daniel; Luo, Kai H
2015-02-01
The pseudopotential lattice Boltzmann method has been widely used to simulate many multiphase flow applications. However, there still exist problems with reproducing realistic values of density ratio and surface tension. In this study, a higher-order analysis of a general forcing term is derived. A forcing scheme is then constructed for the pseudopotential method that is able to accurately reproduce the full range of coexistence curves. As a result, multiphase flow of arbitrarily high density ratios independent of the surface tension can be simulated. Furthermore, the interface width can be tuned to allow for grid refinement and systematic error reduction. Numerical results confirm that the proposed scheme enables independent control of density ratio, surface tension, and interface width simultaneously.
Dijkstra, J.; Weitering, H.H.; Haas, C.; Groot, R.A. de
1989-01-01
Electronic band-structure calculations are presented for the ferromagnetic compounds CrTe, Cr3Te4 and Cr2Te3. In these compounds the Cr 3d-Te 5p covalency and the Cr 3dz2-Cr 3dz2 overlap along the c axis are the most important interactions. The magnetic polarisation of Te is parallel to the Cr local
Ab initio band structure calculations of the low-temperature phases of Ag2Se, Ag2Te and Ag3AuSe2
Fang, C.M.; Groot, R.A. de; Wiegers, G.A.
Ab initio band structure calculations were performed for the low-temperature modifications of the silver chalcogenides β-Ag2Se, β-Ag2Te and the ternary compound β-Ag3AuSe2 by the local spherical wave (LSW) method. Coordinates of the atoms of β-Ag2Se and β-Ag3AuSe2 were obtained from refinements
Kozyra, Paweł; Góra-Marek, Kinga; Datka, Jerzy
2015-02-05
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. Copyright © 2014 Elsevier B.V. All rights reserved.
Platnick, Steven; Fontenla, Juan M.
2006-01-01
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.
Fang, Changming; Li, Wun-Fan; Koster, Rik S; Klimeš, Jiří; van Blaaderen, Alfons; van Huis, Marijn A
2015-01-07
Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For simulations of phase transformations and chemical reactions in water or aqueous solutions whereby an accurate description of the electronic structure is required, we suggest to use these advanced GW corrections in combination with the statistical analysis of quantum mechanical MD simulations.
Tsang, Leung; Tan, Shurun
2016-01-25
The broadband Green's function with low wavenumber extraction (BBGFL) is applied to the calculations of band diagrams of two-dimensional (2D) periodic structures with dielectric scatterers. Periodic Green's functions of both the background and the scatterers are used to formulate the dual surface integral equations by approaching the surface of the scatterer from outside and inside the scatterer. The BBGFL are applied to both periodic Green's functions. By subtracting a low wavenumber component of the periodic Green's functions, the broadband part of the Green's functions converge with a small number of Bloch waves. The method of Moment (MoM) is applied to convert the surface integral equations to a matrix eigenvalue problem. Using the BBGFL, a linear eigenvalue problem is obtained with all the eigenmodes computed simultaneously giving the multiband results at a point in the Brillouin zone Numerical results are illustrated for the honeycomb structure. The results of the band diagrams are in good agreement with the planewave method and the Korringa Kohn Rostoker (KKR) method. By using the lowest band around the Γ point, the low frequency dispersion relations are calculated which also give the effective propagation constants and the effective permittivity in the low frequency limit.
Kang, Chang-Jong; Ahn, Kyo-Hoon; Lee, Kwan-Woo; Min, Byung Il
2013-05-01
SrPt3P has recently been reported to exhibit superconductivity with Tc = 8.4 K. To explore its superconducting mechanism, we have performed electron and phonon band calculations based on the density functional theory, and found that the superconductivity in SrPt3P is described well by the strong coupling phonon-mediated mechanism. We have demonstrated that superconducting charge carriers come from pdπ-hybridized bands between Pt and P ions, which couple to low energy (˜5 meV) phonon modes confined on the ab in-plane. These in-plane phonon modes, which do not break antipolar nature of SrPt3P, enhance both the electron--phonon coupling constant λ and the critical temperature Tc. There is no hint of a specific phonon softening feature in the phonon dispersion, and the effect of the spin--orbit coupling on the superconductivity is found to be negligible.
Roark, E. B.; Mohon, M. L.; Prouty, N.; Guillemette, R. N.; Fallon, S.; Ross, S. W.
2015-12-01
Deep-sea black corals (Leiopathes sp.) are long-lived (up to 4,000 yrs old), and grow in a tree-like fashion depositing growth rings in their skeleton. Scanning electron microscopy at 900x magnification was used to image thin sections and identify peaks in iodine intensity using energy dispersive x-ray spectroscopy in three specimens from the Gulf of Mexico. Age determination by counting visual growth bands and iodine peaks were compared to both radiocarbon and U/Th-derived ages. The first specimen (GOM-JSL04-4734-BC1) has an iodine peak count age of 695 ±70, and growth band age of 785 ± 80 which compare quite well to the radiocarbon age of 670 ±40 years and a U/Th age of 780 ±16 years. There was similar agreement between the radiocarbon ages (1399 ±30 and 670 ±35 years) and the iodine peak count ages (1240 ±125 and 715±70 years) for the remaining two specimens with growth rates ranging from 11 ±3 to 16 ±2 µm yr-1 for all 3 specimens. Using the independent (iodine derived) age models in conjunction with the radiocarbon data, a high resolution ocean reservoir age record was developed for the last 600 years. Reservoir ages varied from 120 to 550 14C years on decadal to centennial time scales. The modern reservoir age in the GOM is 235 ±11 14C years. The preferred explanation for the variability found in these reservoir ages is related to changes in the strength of the Yucatan Current. This novel approach combines the identification of growth bands captured in high-resolution SEM in combination with synchronous peaks in skeleton iodine composition and is the first to validate that both can be used as annual chronometers. Using the independent iodine age models in conjunction with the radiocarbon records, ocean reservoir age records can be developed for the last ~500 to 1000 years.
Rio, Beatriz G del; González, Luis E
2014-11-19
We have performed a comprehensive study of the properties of liquid Be, Ca and Ba, through the use of orbital free ab initio simulations. To this end we have developed a force-matching method to construct the necessary local pseudopotentials from standard ab initio calculations. The structural magnitudes are analyzed, including the average and local structures and the dynamic properties are studied. We find several common features, like an asymmetric second peak in the structure factor, a large amount of local structures with five-fold symmetry, a quasi-universal behaviour of the single-particle dynamic properties and a large degree of positive dispersion in the propagation of collective density fluctuations, whose damping is dictated by slow thermal relaxations and fast viscoelastic ones. Some peculiarities in the dynamic properties are however observed, like a very high sound velocity and a large violation of the Stokes-Einstein relation for Be, or an extremely high positive dispersion and a large slope in the dispersion relation of shear waves at the onset of the wavevector region where they are supported for Ba.
Phosphorus {delta}-doped silicon: mixed-atom pseudopotentials and dopant disorder effects
Energy Technology Data Exchange (ETDEWEB)
Carter, Damien J; Marks, Nigel A [Nanochemistry Research Institute, Curtin University, PO Box U1987, Perth WA 6845 (Australia); Warschkow, Oliver; McKenzie, David R, E-mail: d.carter@curtin.edu.au [Centre for Quantum Computer Technology, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia)
2011-02-11
Within a full density functional theory framework we calculate the band structure and doping potential for phosphorus {delta}-doped silicon. We compare two different representations of the dopant plane; pseudo-atoms in which the nuclear charge is fractional between silicon and phosphorus, and explicit arrangements employing distinct silicon and phosphorus atoms. While the pseudo-atom approach offers several computational advantages, the explicit model calculations differ in a number of key points, including the valley splitting, the Fermi level and the width of the doping potential. These findings have implications for parameters used in device modelling.
Alfianto, E.; Rusydi, F.; Aisyah, N. D.; Fadilla, R. N.; Dipojono, H. K.; Martoprawiro, M. A.
2017-05-01
This study implemented DFT method into the C++ programming language with object-oriented programming rules (expressive software). The use of expressive software results in getting a simple programming structure, which is similar to mathematical formula. This will facilitate the scientific community to develop the software. We validate our software by calculating the energy band structure of Silica, Carbon, and Germanium with FCC structure using the Projector Augmented Wave (PAW) method then compare the results to Quantum Espresso calculation’s results. This study shows that the accuracy of the software is 85% compared to Quantum Espresso.
Ona-Ruales, Jorge Oswaldo; Ruiz-Morales, Yosadara
2017-06-01
Annellation Theory and ZINDO/S semiempirical calculations have been used for the calculation of the locations of maximum absorbance (LMA) of the Ultraviolet-Visible (UV-Vis) of 31 C_{34}H_{16} PAHs (molecular mass 424 Da) with unknown protocols of synthesis. The presence of benzo[a]pyrene bay-like regions and dibenzo[a,l]pyrene fjord-like regions in several of the structures that could be linked to an enhancement of the biological behavior and carcinogenic activity stresses the importance of C_{34}H_{16} PAHs in fields like molecular biology and cancer research. In addition, the occurrence of large PAHs in oil asphaltenes exemplifies the importance of these calculations for the characterization of complex systems. The C_{34}H_{16} PAH group is the largest molecular mass group of organic compounds analyzed so far following the Annellation Theory and ZINDO/S methodology. Future analysis using the same approach will provide evidence regarding the LMA of other high molecular mass PAHs.
Iché-Tarrat, Nathalie; Marsden, Colin J
2008-08-21
We have investigated the performance of DFT in U(VI) chemistry. A large, representative selection of functionals has been tested, in combination with two ECPs developed in Stuttgart that have different-sized cores (60 and 78 electrons for U). In addition, several tests were undertaken with another 14 electron pseudopotential, which was developed in Los Alamos. The experimental database contained vibrational wavenumbers, thermochemical data, and (19)F chemical shifts for molecules of the type UF(6-n)Cl(n). For the prediction of vibrational wavenumbers, the large-core RECP (14 electrons) gives results that are at least as good as those obtained with the small-core RECP (32 electrons). GGA functionals are as successful as hybrid GGA for vibrational spectroscopy; typical errors are only a few percent with the Stuttgart pseudopotentials. For thermochemistry, hybrid versions of DFT are more successful than GGA, LDA, or meta-GGA. Marginally better results are obtained with a 32 electron ECP than with 14; since the experimental uncertainties are at least 25 kJ/mol for each reaction, the best functionals give results that are essentially indistinguishable from experiment. However, large-basis CCSD(T) results match experiment better than any DFT that we examined. Our findings for NMR spectroscopy are rather disappointing; no combination of pseudopotential, functional, and basis yields even a qualitatively correct prediction of trends in the (19)F chemical shifts of UF(6-n)Cl(n) species. Results yielded by the large-core RECP are, in general, slightly less bad than those obtained with the small core. We conclude that DFT cannot be recommended for predictions of NMR spectra in this series of compounds, though this conclusion should not be generalized. Our most important result concerns the good performance of the large-core Stuttgart pseudopotential. Given its computational efficiency, we recommend that it be used with DFT methods for the prediction of molecular geometries
Energy Technology Data Exchange (ETDEWEB)
Qian, Denghui, E-mail: qdhsd318@163.com; Shi, Zhiyu, E-mail: zyshi@nuaa.edu.cn
2017-05-03
This paper couples the plane wave expansion (PWE) and finite element (FE) methods to calculate the band structures of the semi-infinite beam-like phononic crystals (PCs) with the infinite periodicity in z-direction and finiteness in x–y plane. Explicit matrix formulations are developed for the calculation of band structures. In order to illustrate the applicability and accuracy of the proposed coupled plane wave expansion and finite element (PWE/FE) method to beam-like PCs, several examples are displayed. At first, PWE/FE method is applied to calculate the band structures of the Pb/rubber beam-like PCs with circular and rectangular cross sections, respectively. Then, it is used to calculate the band structures of steel/epoxy and steel/aluminum beam-like PCs with the same geometric parameters. Last, the band structure of the three-component beam-like PC is also calculated by the proposed method. Moreover, all the results calculated by PWE/FE method are compared with those calculated by finite element (FE) method, and the corresponding results are in good agreement. - Highlights: • The concept of the semi-infinite beam-like phononic crystals (PCs) is proposed. • The PWE/FE method is proposed and formulized to calculate the band structures of the semi-infinite beam-like PCs. • The strong applicability and high accuracy of PWE/FE method are verified.
Mirsakiyeva, Amina; Hugosson, Hâkan W.; Linares, Mathieu; Delin, Anna
2017-10-01
The conducting polymer poly(3,4-ethylenedioxythiophene), or PEDOT, is an attractive material for flexible electronics. We present combined molecular dynamics and quantum chemical calculations, based on density functional theory, of EDOT oligomers and isoelectronic selenium and tellurium derivatives (EDOS and EDOTe) to address the effect of temperature on the geometrical and electronic properties of these systems. With finite size scaling, we also extrapolate our results to the infinite polymers, i.e., PEDOT, PEDOS, and PEDOTe. Our computations indicate that the most favourable oligomer conformations at finite temperature are conformations around the flat trans-conformation and a non-flat conformation around 45° from the cis-conformation. Also, the dihedral stiffness increases with the atomic number of the heteroatom. We find excellent agreement with experimentally measured gaps for PEDOT and PEDOS. For PEDOT, the gap does not increase with temperature, whereas this is the case for its derivatives. The conformational disorder and the choice of the basis set both significantly affect the calculated gaps.
Sugimura, Natsuhiko; Igarashi, Yoko; Aoyama, Reiko; Shibue, Toshimichi
2017-02-01
Analysis of the fragmentation pathways of molecules in mass spectrometry gives a fundamental insight into gas-phase ion chemistry. However, the conventional intrinsic reaction coordinates method requires knowledge of the transition states of ion structures in the fragmentation pathways. Herein, we use the nudged elastic band method, using only the initial and final state ion structures in the fragmentation pathways, and report the advantages and limitations of the method. We found a minimum energy path of p-benzoquinone ion fragmentation with two saddle points and one intermediate structure. The primary energy barrier, which corresponded to the cleavage of the C-C bond adjacent to the CO group, was calculated to be 1.50 eV. An additional energy barrier, which corresponded to the cleavage of the CO group, was calculated to be 0.68 eV. We also found an energy barrier of 3.00 eV, which was the rate determining step of the keto-enol tautomerization in CO elimination from the molecular ion of phenol. The nudged elastic band method allowed the determination of a minimum energy path using only the initial and final state ion structures in the fragmentation pathways, and it provided faster than the conventional intrinsic reaction coordinates method. In addition, this method was found to be effective in the analysis of the charge structures of the molecules during the fragmentation in mass spectrometry.
Crossing points in the electronic band structure of vanadium oxide
Directory of Open Access Journals (Sweden)
Keshav N. Shrivastava
2010-03-01
Full Text Available The electronic band structures of several models of vanadium oxide are calculated. In the models 1-3, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 4 vanadium atoms. In model 1, a=b=c 2.3574 Å; in model 2, a= 4.7148 Å, b= 2.3574 Å and c= 2.3574 Å; and in model 3, a= 4.7148 Å, b= 2.3574 Å and c= 4.7148 Å. In the models 4-6, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 2 vanadium atoms. In model 4, a=b= 4.551 Å and c= 2.851 Å; in model 5, a=b=c= 3.468 Å; and in model 6, a=b=c= 3.171 Å. We have searched for a crossing point in the band structure of all the models. In model 1 there is a point at which five bands appear to meet but the gap is 7.3 meV. In model 2 there is a crossing point between G and F points and there is a point between F and Q with the gap ≈ 3.6608 meV. In model 3, the gap is very small, ~ 10-5 eV. In model 4, the gap is 5.25 meV. In model 5, the gap between Z and G points is 2.035 meV, and in model 6 the gap at Z point is 4.3175 meV. The crossing point in model 2 looks like one line is bent so that the supersymmetry is broken. When pseudopotentials are replaced by a full band calculation, the crossing point changes into a gap of 2.72 x 10-4 eV.
Accuracy and Transferability of Ab Initio Electronic Band Structure Calculations for Doped BiFeO3
Gebhardt, Julian; Rappe, Andrew M.
2017-11-01
BiFeO3 is a multiferroic material and, therefore, highly interesting with respect to future oxide electronics. In order to realize such devices, pn junctions need to be fabricated, which are currently impeded by the lack of successful p-type doping in this material. In order to guide the numerous research efforts in this field, we recently finished a comprehensive computational study, investigating the influence of many dopants onto the electronic structure of BiFeO3. In order to allow for this large scale ab initio study, the computational setup had to be accurate and efficient. Here we discuss the details of this assessment, showing that standard density-functional theory (DFT) yields good structural properties. The obtained electronic structure, however, suffers from well-known shortcomings. By comparing the conventional DFT results for alkali and alkaline-earth metal doping with more accurate hybrid-DFT calculations, we show that, in this case, the problems of standard DFT go beyond a simple systematic error. Conventional DFT shows bad transferability and the more reliable hybrid-DFT has to be chosen for a qualitatively correct prediction of doping induced changes in the electronic structure of BiFeO3.
Energy Technology Data Exchange (ETDEWEB)
Liu Qijun, E-mail: dianerliu@yahoo.com.c [State Key Lab of Solidification Processing, College of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China); Liu Zhengtang; Feng Liping [State Key Lab of Solidification Processing, College of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China)
2010-04-15
Structural parameters, elastic, electronic, bonding and optical properties of delafossite CuAlO{sub 2} have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. We have derived the bulk, shear and Young's modulus, Poisson coefficient for delafossite CuAlO{sub 2}. We estimated the Debye temperature of CuAlO{sub 2} from the acoustic velocity. Electronic and chemical bonding properties have been studied throughout the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for delafossite CuAlO{sub 2}, the dielectric function is calculated, which shows a significant optical anisotropy in the components of polarization directions (1 0 0) and (0 0 1).
Energy Technology Data Exchange (ETDEWEB)
Datta, Soumendu, E-mail: soumendu@bose.res.in; Baral, Sayan; Mookerjee, Abhijit [Department of Condensed Matter Physics and Material Sciences, S.N. Bose National Centre for Basic Sciences, JD Block, Sector-III, Salt Lake City, Kolkata 700 098 (India); Kaphle, Gopi Chandra [Central Department of Physics, Tribhuvan University, Kathmandu (Nepal)
2015-08-28
Using density functional theory (DFT) based electronic structure calculations, the effects of morphology of semiconducting nanostructures on the magnetic interaction between two magnetic dopant atoms as well as a possibility of tuning band gaps have been studied in the case of the bi-doped (ZnO){sub 24} nanostructures with the impurity dopant atoms of the 3d late transition metals—Mn, Fe, Co, Ni, and Cu. To explore the morphology effect, three different structures of the host (ZnO){sub 24} nano-system, having different degrees of spatial confinement, have been considered: a two dimensional nanosheet, a one dimensional nanotube, and a finite cage-shaped nanocluster. The present study employs hybrid density functional theory to accurately describe the electronic structure of all the systems. It is shown here that the magnetic coupling between the two dopant atoms remains mostly anti-ferromagnetic in the course of changing the morphology from the sheet geometry to the cage-shaped geometry of the host systems, except for the case of energetically most stable bi-Mn doping, which shows a transition from ferromagnetic to anti-ferromagnetic coupling with decreasing aspect ratio of the host system. The effect of the shape change, however, has a significant effect on the overall band gap variations of both the pristine as well as all the bi-doped systems, irrespective of the nature of the dopant atoms and provides a means for easy tunability of their optoelectronic properties.
Hay, J.
Consideration is given to problems of pure frequency detection in the magnetic recording of acoustic noise in the presence of zero crossings by sinusoidal reference waves and narrow-band random processes. The principle of the partial detection of a sine wave based on isochronous zero crossings near a given coherent sequence threshold is reviewed, and a track detection criterion is introduced. A model of the signal detection process is then presented based on a probabilistic description of zero crossings which permits the definition of the normalized duration of a coherent sequence of zero crossings, and the model is validated in an experimental study of a narrow band process centered at 3240 Hz. The probability of the simultaneous detection of two channels is also calculated. The application of the model to parasitic detection in a two-frequency code is considered. Attention is then given to the relation between the isochronism of the coherent sequences of zero crossings and spectral sharpness, and a means for the direct estimation of the autocorrelation envelope of the narrowband noise process is derived.
Anisotropic pseudopotential characterization of quantum Hall systems under a tilted magnetic field
Yang, Bo; Lee, Ching Hua; Zhang, Chi; Hu, Zi-Xiang
2017-11-01
We analytically derived the effective two-body interaction for a finite thickness quantum Hall system with a harmonic perpendicular confinement and an in-plane magnetic field. The anisotropic effective interaction in the lowest Landau level (LLL) and first Landau level (1LL) are expanded in the basis of the generalized pseudopotentials (PPs), and we analyze how the coefficients of some prominent isotropic and anisotropic PPs depend on the thickness of the sample and the strength of the in-plane magnetic field. We also investigate the stability of the topological quantum Hall states, especially the Laughlin state and its emergent guiding center metric, which we can now compute analytically. An interesting reorientation of the anisotropy direction of the Laughlin state in the 1LL is revealed, and we also discuss various possible experimental ramifications for this quantum Hall system with broken rotational symmetry.
Scalable real space pseudopotential-density functional codes for materials applications
Chelikowsky, James R.; Lena, Charles; Schofield, Grady; Saad, Yousef; Deslippe, Jack; Yang, Chao
2015-03-01
Real-space pseudopotential density functional theory has proven to be an efficient method for computing the properties of matter in many different states and geometries, including liquids, wires, slabs and clusters with and without spin polarization. Fully self-consistent solutions have been routinely obtained for systems with thousands of atoms. However, there are still systems where quantum mechanical accuracy is desired, but scalability proves to be a hindrance, such as large biological molecules or complex interfaces. We will present an overview of our work on new algorithms, which offer improved scalability by implementing another layer of parallelism, and by optimizing communication and memory management. Support provided by the SciDAC program, Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences. Grant Numbers DE-SC0008877 (Austin) and DE-FG02-12ER4 (Berkeley).
Hu, Anguang; Chan, Nora W. C.; Dunlap, Brett I.
2017-08-01
The computation of s-type Gaussian pseudopotential matrix elements involving low powers of the distance from the pseudopotential center using Gaussian orbitals can be reduced to familiar integrals. They may be directly expressed as either simple three-center overlap integrals for even powers of the radial distance from the pseudopotential center or related to the three-center nuclear integrals of a Gaussian charge distribution for odd powers. Orbital angular momentum about each atom is added to these integrals by solid-harmonic differentiation with respect to its center. The solid-harmonic addition theorem allows all the integrals to be factored into products of invariant one-dimensional integrals involving the Gaussian exponents and angular factors that contain the azimuthal quantum numbers but are independent of all Gaussian exponents. Precomputing the angular factors allow looping over all Gaussian exponents about the three centers. The fact that solid harmonics are eigenstates of angular momentum removes the singularities seen in previous treatments of pseudopotential matrix elements.
Hussien, Mostafa A.; Nawar, Nagwa; Radwan, Fatima M.; Hosny, Nasser Mohammed
2015-01-01
Bi-nuclear metal complexes derived from the reaction of Cu(II), Co(II), Ni(II) and Zn(II) acetates with the Schiff-base ligand (H2L) resulted from the condensation of 2-amino-ethanoic acid (glycine) and acetylacetone have been synthesized and characterized by elemental analyses, Raman spectra, FT-IR, ES-MS, UV-Vis., 1H NMR, ESR, thermal analyses (TG, DTG and DTA) and magnetic measurements. The results showed that, the Schiff base ligand can bind two metal ions in the same time. It coordinates to the first metal ion as mono-negative bi-dentate through azomethine nitrogen and enolic carbonyl after deprotonation. At the same time, it binds to the second metal ion via carboxylate oxygen after deprotonation. The thermodynamic parameters E∗, ΔH∗, ΔG∗ and ΔS∗ have been calculated by Coats-Redfern (CR) and Horowitz-Metzger (HM) methods. The optical band gaps of the isolated complexes have been calculated from absorption spectra and the results indicated semi-conducting nature of the investigated complexes. The interactions between the copper (II) complex and calf thymus DNA (CT-DNA) have been studied by UV spectra. The results confirm that the Cu(II) complex binds to CT-DNA.
Hong, Sung Un; Singh, Satendra Pal; Pyo, Myoungho; Park, Woon Bae; Sohn, Kee-Sun
2017-06-28
A novel oxynitride compound, Pr4-xCaxSi12O3+xN18-x, synthesized using a solid-state route has been characterized as a monoclinic structure in the C2 space group using Rietveld refinement on synchrotron powder X-ray diffraction data. The crystal structure of this compound was disordered due to the random distribution of Ca/Pr and N/O ions at various Wyckoff sites. A pragmatic approach for an ab initio calculation based on density function theory (DFT) for this disordered compound has been implemented to calculate an acceptable value of the band gap and formation energy. In general, for the DFT calculation of a disordered compound, a sufficiently large super cell and infinite variety of ensemble configurations is adopted to simulate the random distribution of ions; however, such an approach is time consuming and cost ineffective. Even a single unit cell model gave rise to 43 008 independent configurations as an input model for the DFT calculations. Since it was nearly impossible to calculate the formation energy and the band gap energy for all 43 008 configurations, an elitist non-dominated sorting genetic algorithm (NSGA-II) was employed to find the plausible configurations. In the NSGA-II, all 43 008 configurations were mathematically treated as genomes and the calculated band gap and the formation energy as the objective (fitness) function. Generalized gradient approximation (GGA) was first employed in the preliminary screening using NSGA-II, and thereafter a hybrid functional calculation (HSE06) was executed only for the most plausible GGA-relaxed configurations with lower formation and higher band gap energies. The final band gap energy (3.62 eV) obtained after averaging over the selected configurations, resembles closely the experimental band gap value (4.11 eV).
Calculation Of Phonon Dispersion Frequencies For Bcc Tantalum ...
African Journals Online (AJOL)
The phonon dispersion frequencies are calculated from first principles for bcc Tantalum using a resonance pseudopotential model. It was also possible, using this scheme, to account for the anomalous feature of the Ta dispersion curve observed experimentally in the (ε,o,o,) direction where the frequencies of the transverse ...
Vaitheeswaran, G; Kanchana, V; Zhang, Xinxin; Ma, Yanming; Svane, A; Christensen, N E
2016-08-10
A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent [Formula: see text] approximation. The [Formula: see text] calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides.
van Harrevelt, Rob; van Hemert, Marc C.
2000-04-01
A complete three-dimensional quantum mechanical description of the photodissociation of water in the B˜ band, starting from its rotational ground state, is presented. In order to include B˜-X˜ vibronic coupling and the B˜-Ã Renner-Teller coupling, diabatic electronic states have been constructed from adiabatic electronic states and matrix elements of the electronic angular momentum operators, following the procedure developed by A. J. Dobbyn and P. J. Knowles [Mol. Phys. 91, 1107 (1997)], using the ab initio results discussed in the preceding paper. The dynamics is studied using wave packet methods, and the evolution of the time-dependent wave function is discussed in detail. Results for the H2O and D2O absorption spectra, OH(A)/OH(X) and OD(A)/OD(X) branching ratios, and rovibrational distributions of the OH and OD fragments are presented and compared with available experimental data. The present theoretical results agree at least qualitatively with the experiments. The calculations show that the absorption spectrum and the product state distributions are strongly influenced by long-lived resonances on the adiabatic B˜ state. It is also shown that molecular rotation plays an important role in the photofragmentation process, due to both the Renner-Teller B˜-X˜ mixing, and the strong effect of out-of-plane molecular rotations (K>0) on the dynamics at near linear HOH and HHO geometries.
Ivády, Viktor; Gali, Adam; Abrikosov, Igor A.
2017-11-01
Hybrid functionals’ non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT + V w method (Ivády et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT + V w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA + U, and therefore allowing for a demonstration of the advantages of the proposed scheme.
Anomalous behavior of the semiconducting gap in WO3 from first-principles calculations
Wijs, G.A. de; Boer, P.K. de; Groot, R.A. de; Kresse, G.
1999-01-01
Several crystal structures of tungsten trioxide have been studied with a first-principles pseudopotential method. The electronic band gap increases significantly with the distortion of the octahedra that are the building blocks of the various crystal structures. Moreover, the tilting of the
First-principles calculations of the electronic and structural properties of GaSb
Energy Technology Data Exchange (ETDEWEB)
Castaño-González, E.-E. [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Seña, N. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mendoza-Estrada, V.; González-Hernández, R., E-mail: rhernandezj@uninorte.edu.co [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Dussan, A. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mesa, F., E-mail: fredy.mesa@urosario.edu.co [Universidad del Rosario, Grupo NanoTech, Facultad de Ciencias Naturales y Matemáticas (Colombia)
2016-10-15
In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B{sub 0}); while for the cohesive energy (E{sub coh}), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.
Chander, Gyanesh; Mishra, N.; Helder, Dennis L.; Aaron, David; Choi, T.; Angal, A.; Xiong, X.
2010-01-01
Different applications and technology developments in Earth observations necessarily require different spectral coverage. Thus, even for the spectral bands designed to look at the same region of the electromagnetic spectrum, the relative spectral responses (RSR) of different sensors may be different. In this study, spectral band adjustment factors (SBAF) are derived using hyperspectral Earth Observing-1 (EO-1) Hyperion measurements to adjust for the spectral band differences between the Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) and the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) top-of-atmosphere (TOA) reflectance measurements from 2000 to 2009 over the pseudo-invariant Libya 4 reference standard test site.
Shih, Ko-Han; Chang, Yin-Jung
2018-01-01
Solar energy conversion via internal photoemission (IPE) across a planar p-type Schottky junction is quantified for aluminum (Al) and copper (Cu) in the framework of direct transitions with non-constant matrix elements. Transition probabilities and k-resolved group velocities are obtained based on pseudo-wavefunction expansions and realistic band structures using the pseudopotential method. The k-resolved number of direct transitions, hole photocurrent density, quantum yield (QY), and the power conversion efficiency (PCE) under AM1.5G solar irradiance are subsequently calculated and analyzed. For Al, the parabolic and "parallel-band" effect along the U-W-K path significantly enhances the transition rate with final energies of holes mainly within 1.41 eV below the Fermi energy. For Cu, d-state hot holes mostly generated near the upper edge of 3d bands dominate the hole photocurrent and are weekly (strongly) dependent on the barrier height (metal film thickness). Hot holes produced in the 4s band behave just oppositely to their d-state counterparts. Non-constant matrix elements are shown to be necessary for calculations of transitions due to time-harmonic perturbation in Cu. Compared with Cu, Al-based IPE in p-type Schottky shows the highest PCE (QY) up to about 0.2673% (5.2410%) at ΦB = 0.95 eV (0.5 eV) and a film thickness of 11 nm (20 nm). It is predicted that metals with relatively dispersionless d bands (such as Cu) in most cases do not outperform metals with photon-accessible parallel bands (such as Al) in photon energy conversion using a planar p-type Schottky junction.
Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl
Isaeva, E.I.; Lichtenstein, A.I.; Vekilov, Y.K.; Smirnova, E.A.; Abrikosov, I.A.; Simak, S.I.; Ahuja, R.; Johansson, B.
2004-01-01
The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available
Shomali, E.; Abdolhosseini Sarsari, I.; Javad Hashemifar, S.; Alaei, M.
2017-08-01
In this paper, dye sensitized solar cell based on nano dye molecule N3 are investigated by using density functional computations. The main focus is on the N3 dye molecule and corresponding complexes formed at the interface between electrolyte and dye, during the regeneration process. The optimizaed geometry and electronic structure of the molecule and complexs are calculated by using the pseudopotential as well as full-potential techniques. The absorption spectra of metalliferous dye molecule, N3, and its complexes are computed in the framework of time dependent density functional theory. We determine the reaction path of dye regeneration by Nudged Elastic Band (NEB) method. IR spectrum of the N3 dye molecule were also calculated. We found that complexes of N3 dye molecule and transition states formed in reactions, are magnetic.
Bimetallic two-dimensional PtAg coverage on h-BN substrate: First-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Ersan, F. [Department of Physics, Adnan Menderes University, Aydın 09100 (Turkey); Gökoğlu, G. [Department of Physics, Karabük University, Karabük 78050 (Turkey); Aktürk, E., E-mail: ethem.akturk@adu.edu.tr [Department of Physics, Adnan Menderes University, Aydın 09100 (Turkey)
2014-06-01
This paper presents a study on the coverage of PtAg layer on h-BN 2D system using plane-wave pseudopotential method within density functional theory. There emerge interesting electronic and magnetic properties by the coverage of PtAg on h-BN. FM (ferromagnetic) and AFM (antiferromagnetic) states are considered for PtAg. As the most stable configuration, Pt atom is bound to the top site of N and Ag is adsorbed to hollow site in the (2 × 2) coverage with a binding energy about −1.013 eV. While bare h-BN is nonmagnetic semiconductor with a band gap of 4.58 eV, the band gap becomes 0.18 eV with an AFM semiconductor ground state upon coverage of PtAg adlayer. The electronic structure calculations reveal that the electronic band gap of the composite system is controlled by d-states of Pt atom. The material can have possible applications in spintronics and in catalysis with decreased and engineered band gap.
Energy Technology Data Exchange (ETDEWEB)
Cherrad, Djellal, E-mail: cherradphisic@yahoo.fr [Laboratory for Developing New Materials and their Characterizations, University of Setif (Algeria); Selmani, L. [University Center of BBA (Algeria); Maouche, D. [Laboratory for Developing New Materials and their Characterizations, University of Setif (Algeria); Maamache, M. [Department of Physics, Faculty of Sciences, University of Setif (Algeria)
2011-03-24
Research highlights: > In this study the B/G values of ANTi{sub 3} show that these materials behave as ductile. > Band structures show that are conductors and exhibit magnetism. > Therefore lead to lower T{sub c} or no superconducting behavior in our compounds. > The chemical bonding in ANTi{sub 3} compounds may be covalent-ionic. > Elastic properties of our compounds show a correlation with the bonding properties. - Abstract: We use an ab initio pseudopotential plane wave (PP-PW) method within the generalized gradient approximation (GGA) and the local density approximation (LDA) to study the structural, elastic and electronic properties of the unexplored antiperovskite ANTi{sub 3} compounds. The elastic constants C{sub 11}, C{sub 12}, C{sub 44} and their pressure dependence are calculated. We derived the bulk, shear and Young's moduli for ideal monocrystalline and for polycrystalline ANTi{sub 3} aggregates which we have classified as ductile in nature. Band structures reveal that these compounds are conductors. The covalent ionic bands nature is due to the strong hybridization between Ti 3d and N 2p states. The Ti 3d states play dominant roles near the Fermi levels for all these compounds. The energy difference between spin polarized calculations and the nonspin polarized calculations indicate that ANTi{sub 3} compounds exhibit magnetism at their equilibrium lattice constants.
Benchmark density functional theory calculations for nanoscale conductance
DEFF Research Database (Denmark)
Strange, Mikkel; Bækgaard, Iben Sig Buur; Thygesen, Kristian Sommer
2008-01-01
We present a set of benchmark calculations for the Kohn-Sham elastic transmission function of five representative single-molecule junctions. The transmission functions are calculated using two different density functional theory methods, namely an ultrasoft pseudopotential plane-wave code...... a systematic downshift of the SIESTA transmission functions relative to the plane-wave results. The effect diminishes as the atomic orbital basis is enlarged; however, the convergence can be rather slow....
Energy Technology Data Exchange (ETDEWEB)
Bouhemadou, A. [Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria)], E-mail: a_bouhemadou@yahoo.fr; Khenata, R. [Department of Physics, University of Mascara, 29000 Mascara (Algeria); Chegaar, M.; Maabed, S. [Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria)
2007-11-19
The density functional theory (DFT) calculations of structural, elastic, electronic and optical properties of the cubic antiperovskite AsNMg{sub 3} has been reported using the pseudo-potential plane wave method (PP-PW) within the generalized gradient approximation (GGA). The equilibrium lattice, bulk modulus and its pressure derivative have been determined. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline AsNMg{sub 3} aggregate. We estimated the Debye temperature of AsNMg{sub 3} from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNMg{sub 3} compound, and it still awaits experimental confirmation. Band structure, density of states and pressure coefficients of energy gaps are also given. The fundamental band gap ({gamma}-{gamma}) initially increases up to 4 GPa and then decreases as a function of pressure. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. The all results are compared with the available theoretical and experimental data.
Manivasagam, Sivabalan; Laury, Marie L; Wilson, Angela K
2015-07-02
The relativistic-pseudopotential correlation consistent composite approach (rp-ccCA) was used to determine the enthalpy of formation (ΔHf) of 24 first row (3d) transition metal compounds. The rp-ccCA-derived ΔHf's were compared to ΔHf's previously obtained with an all-electron composite method for transition metals (ccCA-TM). For the 3d metal systems, rp-ccCA achieves transition metal accuracy, within 3 kcal/mol of reliable experimental data, overall. By utilizing pseudopotentials within the rp-ccCA methodology, we observed a significant computational time savings (53%) in comparison to the all-electron basis sets employed within ccCA-TM. With the proven reliability and accuracy of rp-ccCA, the methodology was employed to construct a calibration set of 210 second-row (4d) transition metal compounds and their ΔHf's. The 4d calibration set is referred to as 4dHf-210. Within the 4dHf-210 set, there were 61 molecules with available experimental data. The average experimental uncertainty was 4.05 kcal/mol and the mean absolute deviation of rp-ccCA was 3.64 kcal/mol, excluding outliers (10 total). This study provides a large set of energetics that can be used to gauge existing and future computational methodologies and to aid experimentalists in reaction design.
Parameter-free calculation of K alpha chemical shifts for Al, Si, and Ge oxides
DEFF Research Database (Denmark)
Lægsgaard, Jesper
2001-01-01
The chemical shifts of the K alpha radiation line from Al, Si, and Ge ions between their elemental and oxide forms are calculated within the framework of density functional theory using ultrasoft pseudopotentials. It is demonstrated that this theoretical approach yields quantitatively accurate...
Kamimura, Sunao; Obukuro, Yuki; Matsushima, Shigenori; Nakamura, Hiroyuki; Arai, Masao; Xu, Chao-Nan
2015-12-01
The electronic structure of Sr3Sn2O7 is evaluated by the scalar-relativistic full potential linearized augmented plane wave (FLAPW+lo) method using the modified Becke-Johnson potential (Tran-Blaha potential) combined with the local density approximation correlation (MBJ-LDA). The fundamental gap between the valence band (VB) and conduction band (CB) is estimated to be 3.96 eV, which is close to the experimental value. Sn 5s states and Sr 4d states are predominant in the lower and upper CB, respectively. On the other hand, the lower VB is mainly composed of Sn 5s, 5p, and O 2p states, while the upper VB mainly consists of O 2p states. These features of the DOS are well reflected by the optical transition between the upper VB and lower CB, as seen in the energy dependence of the dielectric function. Furthermore, the absorption coefficient estimated from the MBJ-LDA is similar to the experimental result.
Energy Technology Data Exchange (ETDEWEB)
Yu, Jaehyung [Department of Mechanical Science and Engineering, 1206 W Green Street, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Wagner, Lucas K. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Ertekin, Elif, E-mail: ertekin@illinois.edu [Department of Mechanical Science and Engineering, 1206 W Green Street, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); International Institute for Carbon Neutral Energy Research - WPI-I" 2CNER, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan)
2015-12-14
The fixed node diffusion Monte Carlo (DMC) method has attracted interest in recent years as a way to calculate properties of solid materials with high accuracy. However, the framework for the calculation of properties such as total energies, atomization energies, and excited state energies is not yet fully established. Several outstanding questions remain as to the effect of pseudopotentials, the magnitude of the fixed node error, and the size of supercell finite size effects. Here, we consider in detail the semiconductors ZnSe and ZnO and carry out systematic studies to assess the magnitude of the energy differences arising from controlled and uncontrolled approximations in DMC. The former include time step errors and supercell finite size effects for ground and optically excited states, and the latter include pseudopotentials, the pseudopotential localization approximation, and the fixed node approximation. We find that for these compounds, the errors can be controlled to good precision using modern computational resources and that quantum Monte Carlo calculations using Dirac-Fock pseudopotentials can offer good estimates of both cohesive energy and the gap of these systems. We do however observe differences in calculated optical gaps that arise when different pseudopotentials are used.
Energy Technology Data Exchange (ETDEWEB)
Schleife, A; Bechstedt, F
2012-02-15
Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical-absorption spectra (including excitonic effects) for several transparent conducting oxides. We discuss HSE+G{sub 0}W{sub 0} results for band structures, fundamental band gaps, and effective electron masses of MgO, ZnO, CdO, SnO{sub 2}, SnO, In{sub 2}O{sub 3}, and SiO{sub 2}. The Bethe-Salpeter equation is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE+G{sub 0}W{sub 0} approach and the solution of the Bethe-Salpeter equation are very well-suited to describe the electronic structure and the optical properties of various transparent conducting oxides in good agreement with experiment.
Azhar, N. S.; Taib, M. F. M.; Hassan, O. H.; Yahya, M. Z. A.; Ali, A. M. M.
2017-03-01
Crystal structures of α-Bi2O3 and β-Bi2O3 were calculated using Cambridge serial total energy package (CASTEP) based on the first-principles plane-wave ultrasoft pseudopotential method within local density approximation (LDA) and generalized gradient approximation (GGA) together with Perdew-Burke-Ernzerhof (GGA-PBE) and Perdew-Burke-Ernzerhof revised for solid (GGA-PBEsol). The structural parameter of α-Bi2O3 and β-Bi2O3 are in good agreement with previous experimental and theoretical data. All of the polymorphs were calculated for the total density of states (TDOS) and the partial density of states (PDOS) of Bi, O atoms. Density of states exhibits hybridization of Bi 6s and O 2p orbitals and the calculated charge density profiles exhibit the ionic character in the chemical bonding of this compound. The narrowed band gap (E g) and red-shift of light absorption edge are responsible for the photocatalytic activity of Bi2O3 for water splitting application. The optical properties such as optical absorption and electron energy loss function were calculated to show the best structure among these polymorphs for the photocatalytic water splitting application.
Foxman, Derek; Beishuizen, Meindert
2002-01-01
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…
Coutinho, S. S.; Tavares, M. S.; Barboza, C. A.; Frazão, N. F.; Moreira, E.; Azevedo, David L.
2017-12-01
We report the results of a theoretical study on the behavior of the structural, optoelectronic, vibrational, including infrared and Raman theoretical spectra, phonon spectrum, and thermodynamic properties of 3R- and 2H- polytypes of molybdenum disulfide (MoS2) using density functional theory (DFT) considering both the local density and generalized gradient approximation, LDA and GGA, respectively. Calculated lattice parameters are close to the experimental measurements, and an indirect band gap E(A →KΓ) = 1.33 eV (0.68 eV) was obtained within the GGA (LDA) level of calculation, considering the 3R-polytype, and for the 2H- polytype an indirect band gap E(Γ → KΓ) = 1.30 eV (0.70 eV) was obtained within the GGA (LDA) approximation. The complex dielectric function and absorption of 3R-MoS2 and 2H-MoS2 polytypes were shown to be sensitive to the plane of polarization of the incident light. The phonon dispersion relation together with density of states (DOS) as well as theoretical peaks of the infrared (IR) and Raman spectra in the frequency range of 0-800 cm-1 was analyzed and assigned, considering the norm-conserved pseudopotentials. The thermodynamic potentials, the specific heat at constant volume and Debye temperature of the 3R-MoS2 and 2H-MoS2 polytypes are also calculated, whose dependence on the temperature are discussed.
DEFF Research Database (Denmark)
Rasmussen, Filip Anselm; Schmidt, Per Simmendefeldt; Winther, Kirsten Trøstrup
2016-01-01
Calculating the quasiparticle (QP) band structure of two-dimensional (2D) materials within the GW self-energy approximation has proven to be a rather demanding computational task. The main reason is the strong q dependence of the 2D dielectric function around q = 0 that calls for a much denser sa...... gap of the three prototypical 2D semiconductors, MoS2, h-BN, and phosphorene, including the effect of self-consistency at the GW0 level. The method is implemented in the open source code GPAW....
Casula, Michele; Moroni, Saverio; Sorella, Sandro; Filippi, Claudia
2010-04-01
We propose improved versions of the standard diffusion Monte Carlo (DMC) and the lattice regularized diffusion Monte Carlo (LRDMC) algorithms. For the DMC method, we refine a scheme recently devised to treat nonlocal pseudopotential in a variational way. We show that such scheme—when applied to large enough systems—maintains its effectiveness only at correspondingly small enough time-steps, and we present two simple upgrades of the method which guarantee the variational property in a size-consistent manner. For the LRDMC method, which is size-consistent and variational by construction, we enhance the computational efficiency by introducing: (i) an improved definition of the effective lattice Hamiltonian which remains size-consistent and entails a small lattice-space error with a known leading term and (ii) a new randomization method for the positions of the lattice knots which requires a single lattice-space.
Broderick, Christopher A.; Usman, Muhammad; O'Reilly, Eoin P.
2013-01-01
Incorporation of bismuth (Bi) in dilute quantities in (In)GaAs has been shown to lead to unique electronic properties that can in principle be exploited for the design of high efficiency telecomm lasers. This motivates the development of simple models of the electronic structure of these dilute bismide alloys, which can be used to evaluate their potential as a candidate material system for optical applications. Here, we begin by using detailed calculations based on an $sp^{3}s^{*}$ tight-bind...
Mohseni, Naimeh; Bahram, Morteza; Olivieri, Alejandro C
2014-03-25
In order to achieve the second-order advantage, second-order data per sample is usually required, e.g., kinetic-spectrophotometric data. In this study, instead of monitoring the time evolution of spectra (and collecting the kinetic-spectrophotometric data) replicate spectra are used to build a virtual second order data. This data matrix (replicate mode×λ) is rank deficient. Augmentation of these data with standard addition data [or standard sample(s)] will break the rank deficiency, making the quantification of the analyte of interest possible. The MCR-ALS algorithm was applied for the resolution and quantitation of the analyte in both simulated and experimental data sets. In order to evaluate the rotational ambiguity in the retrieved solutions, the MCR-BANDS algorithm was employed. It has been shown that the reliability of the quantitative results significantly depends on the amount of spectral overlap in the spectral region of occurrence of the compound of interest and the remaining constituent(s). Copyright © 2013 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Nelson, J.S.; Jones, E.D. [Semiconductor Materials and Device Sciences Department, 1113, MS-0601, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Myers, S.M.; Follstaedt, D.M. [Semiconductor Nanostructure Physics Department, 1112, MS-1414, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Hjalmarson, H.P. [Compound Semiconductor Technology Department, 1322, MS-0603, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Schirber, J.E. [Solid State Sciences Department, 1100, MS-1437, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Schneider, R.P. [Semiconductor Materials Department, 1311, MS-0603, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Fouquet, J.E.; Robbins, V.M.; Carey, K.W. [Hewlett Packard Laboratories, 3500 Deer Creek Road, Palo Alto, California 94303 (United States)
1996-06-01
A number of complementary experimental characterization tools and theoretical band structure methods were used to determine unambiguously the band-edge luminescence as a function of Al concentration, and to place an upper limit on the short-wavelength emission of InAlGaP alloys lattice matched to GaAs. In particular, the direct-to-indirect band-gap crossing has been determined by analyzing a series of metalorganic vapor-phase-epitaxy-grown In{sub 0.49}(Al{sub {ital y}}Ga{sub 1{minus}{ital y}}){sub 0.51}P alloys lattice matched to GaAs with double-crystal x-ray analysis, Rutherford backscattering spectroscopy, pressure- and temperature-dependent photoluminescence, and transmission electron microscopy. The experimental measurements are compared to first-principles plane-wave pseudopotential band structure calculations for the ternary end points, InGaP and InAlP. The maximum room temperature direct band gap is found to be 2.24 eV, corresponding to an Al composition of {ital y}=0.52{plus_minus}0.02, in good agreement with the theoretical prediction of 0.58{plus_minus}0.05. {copyright} {ital 1996 The American Physical Society.}
Lattice Dynamics of Beryllium from a First-Principles Nonlocal Pseudopotential Approach
DEFF Research Database (Denmark)
Walter, F. King; Cutler, P. H.
1970-01-01
dielectric-screening function employing the Kohn-Sham approximation for exchange among the conduction electrons. The energy-wave-number characteristic F(q) is constructed from the Hartree-Fock-Slater (HFS) wave function for Be++; this is used to calculate the phonon dispersion relations in the [0001], [011̅...... 0], and [112̅ 0] directions. Good agreement is obtained with neutron diffraction experiments. The three independent elastic shear constants are also calculated from F(q); good agreement with experiment is obtained for C and C′, but only fair results obtain for c44....
Band structure and phonon properties of lithium fluoride at high pressure
Energy Technology Data Exchange (ETDEWEB)
Panchal, J. M., E-mail: amitjignesh@yahoo.co.in [Government Engineering College, Gandhinagar 382028, Gujarat (India); Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India); Joshi, Mitesh [Government Polytechnic for Girls, Athwagate, Surat395001, Gujarat (India); Gajjar, P. N., E-mail: pngajjar@rediffmail.com [Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India)
2016-05-23
High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.
Ibrahim, Magdy A.; Halim, Shimaa Abdel; Roushdy, N.; Farag, A. A. M.; El-Gohary, Nasser M.
2017-11-01
Reaction of 4-methoxy-5-oxo-5H-furo[3,2-g]chromene-6-carboxaldehyde (1) with hydroxylamine hydrochloride resulted in ring transformation producing the novel 5-hydroxy-4-methoxy-7-oxo-7H-furo[3,2-g]chromene-6-carbonitrile (HMOFCC). The structure was deduced based on its correct elemental analysis and spectral data (IR, 1H NMR, 13C NMR and mass spectra). The geometries of the HMOFCC were completely optimized by means of DFT-B3LYP/6-311++G (d,p) theoretical level. The ground state properties such as; total energy, the energy of HOMO and LUMO and Mulliken atomic charges were also determined. In addition, the two solvents; polar (methanol) and nonpolar (dioxane) were utilized to extract the electronic absorption spectra. The assignment of the detected bands was discussed by TD-DFT calculations. A cauliflower-like, as well as, needle-like leaves morphologies were observed using scanning electron microscope images. Two direct optical band gaps were extracted from the photon energy dependence of absorption coefficient at the band edges and found to be 1.16 and 2.56 eV. A characteristic emission peak of photoluminescence spectrum was observed and shifted depending on the solvent type. A remarkable rectification characteristic of HMOFCC/p-Si heterojunction confirms the diode-like behavior. The main important parameters like series resistance, shunt resistance and reverse saturation current show illumination dependence under influence of the illumination intensity range 20-100 mW/cm2. The heterojunction based HMOFCC showed phototransient properties under various illumination intensities which give the recommendation for the studied heterojunction in the field of optoelectronic device application.
Directory of Open Access Journals (Sweden)
M. P. Polak
2016-01-01
Full Text Available Structural and elastic properties of AlNxP1-x, a novel semiconductor alloy, are studied from the first principles in both zinc-blende and wurtzite structures. Performances of the finite difference (FD method and the density functional perturbation theory (DFPT are tested and compared. Both of these methods are applied to two different approaches of alloy simulation, a supercell of 16 and 32 atoms (for zinc-blende and wurtzite structures, resp. and the alchemical mixing (AM method, where the pseudopotentials are mixed in an appropriate way to form an alloy. All elastic properties, including the elastic tensors, elastic moduli, Poisson’s ratio, B/G, and relaxation coefficient, as well as lattice parameters are calculated using all said methods. Conclusions about the use of the approaches investigated in this paper and about their performance are drawn. In addition, in both crystal structures, the band gap is studied in the whole composition range using the MBJLDA functional. The band gap bowings are unusually high, which confirms earlier reports.
Implementation of highly parallel and large scale GW calculations within the OpenAtom software
Ismail-Beigi, Sohrab
The need to describe electronic excitations with better accuracy than provided by band structures produced by Density Functional Theory (DFT) has been a long-term enterprise for the computational condensed matter and materials theory communities. In some cases, appropriate theoretical frameworks have existed for some time but have been difficult to apply widely due to computational cost. For example, the GW approximation incorporates a great deal of important non-local and dynamical electronic interaction effects but has been too computationally expensive for routine use in large materials simulations. OpenAtom is an open source massively parallel ab initiodensity functional software package based on plane waves and pseudopotentials (http://charm.cs.uiuc.edu/OpenAtom/) that takes advantage of the Charm + + parallel framework. At present, it is developed via a three-way collaboration, funded by an NSF SI2-SSI grant (ACI-1339804), between Yale (Ismail-Beigi), IBM T. J. Watson (Glenn Martyna) and the University of Illinois at Urbana Champaign (Laxmikant Kale). We will describe the project and our current approach towards implementing large scale GW calculations with OpenAtom. Potential applications of large scale parallel GW software for problems involving electronic excitations in semiconductor and/or metal oxide systems will be also be pointed out.
Gonzalez Del Rio, Beatriz; Gonzalez Tesedo, Luis Enrique
We report results of an orbital-free ab initio molecular dynamics (OF-AIMD) study of the free liquid surface of Sn at 1000 K. A key ingredient in the OF-AIMD method is the local ionic pseudopotential describing the ions-valence electrons interaction. We have developed a force-matching method to derive a local ionic pseudopotential suitable to account for a rapidly varying density system, such as in a free liquid surface. We obtain very good results for several structural properties. We have also studied the evolution of some dynamical properties when going from the central region (where the system behaves like the bulk liquid) towards the free liquid surface. We aknowledge the spanish MSI (Project FIS2012-33126) and the University of Valladolid for the provision of a PhD grant.
Nemati, Maedeh; Shateri Najaf Abady, Ali Reza; Toghraie, Davood; Karimipour, Arash
2018-01-01
The incorporation of different equations of state into single-component multiphase lattice Boltzmann model is considered in this paper. The original pseudopotential model is first detailed, and several cubic equations of state, the Redlich-Kwong, Redlich-Kwong-Soave, and Peng-Robinson are then incorporated into the lattice Boltzmann model. A comparison of the numerical simulation achievements on the basis of density ratios and spurious currents is used for presentation of the details of phase separation in these non-ideal single-component systems. The paper demonstrates that the scheme for the inter-particle interaction force term as well as the force term incorporation method matters to achieve more accurate and stable results. The velocity shifting method is demonstrated as the force term incorporation method, among many, with accuracy and stability results. Kupershtokh scheme also makes it possible to achieve large density ratio (up to 104) and to reproduce the coexistence curve with high accuracy. Significant reduction of the spurious currents at vapor-liquid interface is another observation. High-density ratio and spurious current reduction resulted from the Redlich-Kwong-Soave and Peng-Robinson EOSs, in higher accordance with the Maxwell construction results.
Lee, Jin-Woong; Singh, Satendra Pal; Kim, Minseuk; Hong, Sung Un; Park, Woon Bae; Sohn, Kee-Sun
2017-08-21
A metaheuristics-based design would be of great help in relieving the enormous experimental burdens faced during the combinatorial screening of a huge, multidimensional search space, while providing the same effect as total enumeration. In order to tackle the high-throughput powder processing complications and to secure practical phosphors, metaheuristics, an elitism-reinforced nondominated sorting genetic algorithm (NSGA-II), was employed in this study. The NSGA-II iteration targeted two objective functions. The first was to search for a higher emission efficacy. The second was to search for narrow-band green color emissions. The NSGA-II iteration finally converged on BaLi2Al2Si2N6:Eu2+ phosphors in the Eu2+-doped Ca-Sr-Ba-Li-Mg-Al-Si-Ge-N compositional search space. The BaLi2Al2Si2N6:Eu2+ phosphor, which was synthesized with no human intervention via the assistance of NSGA-II, was a clear single phase and gave an acceptable luminescence. The BaLi2Al2Si2N6:Eu2+ phosphor as well as all other phosphors that appeared during the NSGA-II iterations were examined in detail by employing powder X-ray diffraction-based Rietveld refinement, X-ray absorption near edge structure, density functional theory calculation, and time-resolved photoluminescence. The thermodynamic stability and the band structure plausibility were confirmed, and more importantly a novel approach to the energy transfer analysis was also introduced for BaLi2Al2Si2N6:Eu2+ phosphors.
High-energy band structure of gold
DEFF Research Database (Denmark)
Christensen, N. Egede
1976-01-01
The band structure of gold for energies far above the Fermi level has been calculated using the relativistic augmented-plane-wave method. The calculated f-band edge (Γ6-) lies 15.6 eV above the Fermi level is agreement with recent photoemission work. The band model is applied to interpret...
Mal, Indranil; Samajdar, D. P.; Das, T. D.
2017-06-01
GaAsNSb is a promising candidate for use in GaAs-based optoelectronic devices in the 1.33-1.55 μm wavelength region. We have calculated the band structure of dilute nitride-antimonide GaAs1-x-yNxSby alloys, lattice matched to GaAs, using Band anticrossing (BAC) and Valence Band Anticrossing (VBAC) model in conjugation with k·p Hamiltonian method. This mathematical model in the form of a 16 band Hamiltonian matrix is used to examine the shift of different bands as a function of Sb concentration for both bulk and quantum well structures for GaAsNSb/GaAs. The band parameters such as energy gap, spin-orbit splitting energy, carrier effective masses, band offsets, and strain generated due to the growth of GaAsNSb/GaAs heterostructures as a function of Sb and N concentrations are calculated and compared with the recent experimental data. The substitution of As atoms due to the incorporation of N and Sb impurity atoms causes a significant band gap reduction of ∼330 meV for GaAs0.931Sb0.05N0.019 alloys. The enhancement of spin-orbit splitting energy causes a crossover between Eg and Δso for Sb and N concentration of 27 and 10 at % respectively. Suitable tuning of the band offset values with Sb and N concentrations makes GaAsNSb/GaAs alloy system an efficient alternative for band gap engineering and fabricating photonic device structures.
Energy Technology Data Exchange (ETDEWEB)
Landeros-Ayala, S.; Neri-Vela, R; Cruz-Sanchez, H.; Hernandez-Bautista, H. [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)
2002-03-01
In the last years, the peak in the demand of satellite communication service has caused the saturation in the use of the frequencies corresponding to the band, Cand Ku. Due to this, the engineers have looked for viable alternatives, in order to satisfy the current requisition, as well as the future demand, for which a considerable increment is expected. One of these alternatives is the use of the Ka Band (20Hz/30Hz), that is why the importance of studying the propagation effects that are experienced at these frequencies, especially the attenuation effect by rain, as in this case, where it is significant. The present article has the purpose to describe the use of the Modelo DAH (whose authors are Asoka Dissanayake, Jeremy Allnutt and Fatim Haidara), mixed with the global maps of distribution of rain by Crane, for the calculation of the attenuation by rain in satellite communication systems operated in the Ka Band. Besides, antenna diameters for the systems of communications in Ka Band in different locations of the Mexican Republic, using for it the attenuation margins for rain obtained through the Modelo DAH, and using as references the characteristics of the ANIK F2 satellite and a terrestrial station VSAT, are proposed. [Spanish] En los ultimos anos, el auge en la demanda de servicios de comunicacion por satelite ha provocado la saturacion en los uso de la frecuencia correspondientes a las bandas C y Ku. Debido a esta razon, se han buscado alternativas viables para poder satisfacer la demanda actual, asi como la demanda futura, para la cual se espera un incremento considerable. Una de estas alternativas es el uso de Banda Ka (20Hz/30Hz), de ahi la importancia del estudio sobre los efectos de programacion que se experimentan a esta frecuencia, en especial, el efecto de atencion por lluvias, ya que sen este caso resulta ser significativa. El presente articulo tiene como finalidad describir el uso del Modelo DAH (cuyos autores son Asoka Dissanayake, Jeremy Allnutt y
Energy-band structure in strained silicon: A 20-band kṡp and Bir-Pikus Hamiltonian model
Richard, Soline; Aniel, Frédéric; Fishman, Guy; Cavassilas, Nicolas
2003-08-01
A strain Bir-Pikus Hamiltonian Hst, associated with a 20-band sp3s* kṡp Hamiltonian Hkp, is used to describe the valence band and the first two conduction bands all over the Brillouin zone. Because the local (in k space) deformation potentials Ⅺu and Ⅺd used in pseudopotential method are unusable in kṡp theory, we show that taking into account the Bir-Pikus parameters (a, b) of the Brillouin zone center in the Hst Hamiltonian allows one to describe the dispersion relation in the whole Brillouin zone. The method is applied to strained Si on a relaxed Si1-xGex alloy. The values of the energy band gap, and of the Δ2-4 conduction band splitting between the four equivalent in-plane valleys Δ4 and the two valleys along the growth direction Δ2 are in very good agreement with those reported in other publications. The small value of the spin-orbit splitting in silicon is taken explicitly into account. We show that the valence band splitting is consequently not proportional to the stress.
Intensity formulas for triplet bands
Budo, A.
1982-01-01
Previous work in this area is surveyed and the mathematics involved in determining the quantitative intensity measurements in triplet bands is presented. Explicit expressions for the intensity distribution in the branches of the 3 Sigma-3 Pi and 1 Sigma-3Pi bands valid for all values of the coupling constant Y of the 3 Pi terms are given. The intensity distribution calculated according to the formulas given is compared with measurements of PH, 3 Pi-3 Sigma. Good quantitative agreement is obtained.
Directory of Open Access Journals (Sweden)
Sanjeev K. Gupta
2013-03-01
Full Text Available In the frame work of density functional theoretical calculations, the electronic and lattice dynamical properties of graphene (multilayers and supercell have been systematically investigated and analyzed using the plane wave pseudopotentials within the generalized gradient approximation and local density approximation functional. We have also studied the functionalization of graphene by adsorption and absorption of transition metals like Al and Ag. We find that the electronic properties exhibit large sensitivity to the number of layers and doping. The Al and Ag doped graphene exhibits peak at Fermi level in the density of states arising from the flat bands near Fermi level. The bonding of metal atoms and graphene leads to a charge transfer between them and consequently shift Fermi level with respect to the conical point at K-point. The adsorption of Ag/Al atoms suggests an effective interaction between the adatoms and graphene layers without disturbing the original graphene structure of lower graphene layers. Compared to single layer graphene, the optical phonon E2g mode and out of plane ZA mode at Γ-point splits in the bi-, tri- and four- layer graphene. We observe a shift for highest optical branch at Dirac K- point. We find that the different derivatives of graphene have different phonon dispersion relations. We demonstrate that there is removal of degeneracy of ZO/ZA modes at K- point with transition metal doping. The highest optical phonon branch becomes flat at Dirac point with doping of transition metals. Our study points that the substituted graphene sheets can have potential applications in ordered-disordered separated quantum films with two to four layers of atoms and new nano devices using graphene.
Shein, I. R.; Ivanovskii, A. L.
2011-03-01
By means of first-principles calculations, we studied in detail the structural, elastic, and electronic properties of the tetragonal CaBe2Ge2-type 5.2 K superconductor SrPt2As2 in comparison with two hypothetical SrPt2As2 polymorphs with ThCr2Si2-type structures, which differ in the atomic configurations of the [Pt2As2] (or [As2Pt2]) blocks. We found that CaBe2Ge2-type SrPt2As2 is a unique system with near-Fermi bands of a complicated character and an “intermediate”-type Fermi surface, which consists of electronic pockets having a cylinderlike [two-dimensional (2D)] topology (typical of 122 FeAs phases) together with 3D-like electronic and hole pockets, which are characteristic of ThCr2Si2-like iron-free low-Tc superconductors. Our analysis revealed that, as distinct from ThCr2Si2-like 122 phases, other features of CaBe2Ge2-like SrPt2As2 are as follows: (1) There are essential differences in the contributions from [Pt2As2] and [As2Pt2] blocks to the near-Fermi region; conduction is anisotropic and occurs mainly in the [Pt2As2] blocks. (2) A 3D system of strong covalent Pt-As bonds is formed (inside and between [Pt2As2] and [As2Pt2] blocks), which is responsible for enhanced stability of this polymorph. (3) There is essential charge anisotropy between adjacent [Pt2As2] and [As2Pt2] blocks. We also predict that CaBe2Ge2-like SrPt2As2 is a mechanically stable and relatively soft material with high compressibility, which will behave in a ductile manner. In contrast, the ThCr2Si2-type SrPt2As2 polymorphs, which contain only [Pt2As2] or [As2Pt2] blocks, are less stable, have Fermi surfaces of a multisheet three-dimensional type like the ThCr2Si2-like iron-free 122 phases, and therefore will be ductile materials with high elastic anisotropy. Based on our data for the three simplest SrPt2As2 polymorphs we assume that there may exist a family of higher-order polytypes, which can be formed as a result of various stackings of the two main types of building blocks ([Pt2As2
Magnetism in bulk and finite size graphene multilayers and its effect on the band gaps
Sahu, Bhagawan; Min, Hongki; Banerjee, Sanjay; MacDonald, Allan
2011-03-01
In this talk, we will address the edge state magnetism and the resulting modulation of band gaps induced by quantum confinements in multilayer graphene ribbons and flakes. The magnetism arising from random point defects such as vacancies in bulk graphene layers will also be presented. The robustness of magnetism with respect to the edge disorder and the saturating agents in finite size graphene layers and with respect to the defect concentrations in bulk graphene layers will be discussed. A numerical approach based on density functional theory which uses plane-wave basis set and pseudopotentials for ion-electron interactions will be used for elucidating the complex interplay of magnetism, external electric field applied perpendicular to the layers and the resulting band gaps. Financial support from SRC-NRI SWAN center is acknowledged.
Gradient and vorticity banding
Dhont, Jan K.G.; Briels, Willem J.
2008-01-01
"Banded structures" of macroscopic dimensions can be induced by simple shear flow in many different types of soft matter systems. Depending on whether these bands extend along the gradient or vorticity direction, the banding transition is referred to as "gradient banding" or "vorticity banding,"
Gastric banding surgery - your diet; Obesity - diet after banding; Weight loss - diet after banding ... about any problems you are having with your diet, or about other issues related to your surgery ...
Band-limited power flow into enclosures
Pope, L. D.; Wilby, J. F.
1977-01-01
Equations for the band-limited power flow to a cavity in the low-frequency regime are derived. The total power to cavity is obtained by summing separate calculations of the power from structural modes resonant in the band and power from structural modes resonant below the band. High-frequency relations compatible with the usual statistical energy analysis and generalized to include other excitations in addition to diffuse fields are also provided.
Directory of Open Access Journals (Sweden)
Larry W. Burggraf
2013-07-01
Full Text Available To find low energy SinCn structures out of hundreds to thousands of isomers we have developed a general method to search for stable isomeric structures that combines Stochastic Potential Surface Search and Pseudopotential Plane-Wave Density Functional Theory Car-Parinello Molecular Dynamics simulated annealing (PSPW-CPMD-SA. We enhanced the Sunders stochastic search method to generate random cluster structures used as seed structures for PSPW-CPMD-SA simulations. This method ensures that each SA simulation samples a different potential surface region to find the regional minimum structure. By iterations of this automated, parallel process on a high performance computer we located hundreds to more than a thousand stable isomers for each SinCn cluster. Among these, five to 10 of the lowest energy isomers were further optimized using B3LYP/cc-pVTZ method. We applied this method to SinCn (n = 4–12 clusters and found the lowest energy structures, most not previously reported. By analyzing the bonding patterns of low energy structures of each SinCn cluster, we observed that carbon segregations tend to form condensed conjugated rings while Si connects to unsaturated bonds at the periphery of the carbon segregation as single atoms or clusters when n is small and when n is large a silicon network spans over the carbon segregation region.
National Oceanic and Atmospheric Administration, Department of Commerce — Declination is calculated using the current International Geomagnetic Reference Field (IGRF) model. Declination is calculated using the current World Magnetic Model...
A theoretical study of perovskite CsXCl3 (X=Pb, Cd) within first principles calculations
Energy Technology Data Exchange (ETDEWEB)
Ilyas, Bahaa M., E-mail: bahaastring@gmail.com [Department of Physics, University Of Dohuk (Iraq); Elias, Badal H. [Laboratory of Theoretical Physics, Department of Physics, Faculty of Sciences, University of Dohuk (Iraq)
2017-04-01
The structural, elastic, electronic, optical acoustic and thermodynamic properties of the cubic perovskite CsPbCl{sub 3} and CsCdCl{sub 3} unit cell, were studied using an ultra-soft pseudopotential plane wave, the Trouiller-Martins-Functional was utilized to perform these calculations. The study was implemented within both the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA). the Generalized Gradient Approximation (GGA) scheme proposed by van Leeuwen-Baerends which is the same as the Perdew-Wang 92 functional have been carried out to preform our calculations. As for the Local Density Approximation (LDA) the Teter-Pade parametrization (4/93) was implemented which is the same as Perdew-Wang that in its turn reproduces the Ceperley-Alder-Functional. The computed GGA/LDA-lattice parameter for both CsCdCl{sub 3} and CsPbCl{sub 3} is in an exquisite agreement with the experimental and theoretical results. The energy band structure shows that CsCdCl{sub 3} is Γ–R indirect band gap insulator, while CsPbCl{sub 3} is an insulator with a direct band gap Γ–Γ separating the valence bands from the conduction bands, which shows metallic nature after pressure 30 GPa. A hybridization exists between Pb-p states and Cl-p states for CsPbCl{sub 3}, and Cd-p states and Cs-p states for the CsCdCl{sub 3} in the valence bonding region. Optimization of both cell shape (geometry) volume were investigated as pressure of 0–20 GPa and 0–40 GPa for the CsCdCl{sub 3} and CsPbCl{sub 3} respectively. The Pressure dependence of cubic perovskite elastic constants, Young modulus, bulk and shear moduli, Lame’s constants, elastic anisotropy factor, elastic wave velocities, phonon dispersion, Debye temperature and the density of states of CsXCl{sub 3} (X=Pb, Cd) were theoretically calculated and compared with the other available theoretical results. The above elastic constants reveal the fact that both compounds are stable and show nature of ductility. For
Band gaps induced by vacuum photons in closed semiconductor cavities
Kibis, O. V.; Arnardottir, K. B.; Shelykh, I. A.
2014-01-01
We consider theoretically a closed (zero-dimensional) semiconductor microcavity where confined vacuum photonic mode is coupled to electrons in valence band of the semiconductor. It is shown that vacuum-induced virtual electron transitions between valence and conduction bands result in renormalization of electron energy spectrum. As a consequence, vacuum-induced band gaps appear within the valence band. Calculated values of the band gaps are of sub-meV scale, that makes this QED effect to be m...
Vidya, R.; Ravindran, P; Fjellvåg, H.; Svensson, B. G.; Monakhov, E.; Ganchenkova, M.; Nieminen, Risto M.
2011-01-01
Formation energies of various intrinsic defects and defect complexes in ZnO have been calculated using a density-functional-theory-based pseudopotential all-electron method. The various defects considered are oxygen vacancy (VO), zinc vacancy (VZn), oxygen at an interstitial site (Oi), Zn at an interstitial site (Zni), Zn at VO (ZnO), O at VZn(OZn), and an antisite pair (combination of the preceding two defects). In addition, defect complexes like (VO+Zni) and Zn-vacancy clusters are studied....
Triaxial superdeformed bands in {sup 86}Zr
Energy Technology Data Exchange (ETDEWEB)
Sarantites, D.G.; LaFosse, D.R.; Devlin, M.; Lerma, F. [Chemistry Department, Washington University, St. Louis, Missouri 63130 (United States); Wood, V.Q.; Saladin, J.X.; Winchell, D.F. [Physics Department, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Baktash, C.; Yu, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Fallon, P.; Lee, I.Y.; Macchiavelli, A.O.; MacLeod, R.W. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Afanasjev, A.V.; Ragnarsson, I. [Department of Mathematical Physics, Lund Institute of Technology, Box 118, S-22100 Lund (Sweden)
1998-01-01
Four new superdeformed bands have been found in the nucleus {sup 86}Zr. The good agreement between experiment and configuration-dependent shell correction calculations suggests that three of the bands have triaxial superdeformed shapes. Such unique features in mass A{approximately}80 superdeformed bands have been predicted, but not observed experimentally until now. A fourth band in {sup 86}Zr is interesting due to a fairly constant and unusually high dynamic moment of inertia. Possible interpretations of this structure are discussed. {copyright} {ital 1998} {ital The American Physical Society}
Directory of Open Access Journals (Sweden)
Soyoun Son
2016-02-01
Full Text Available In porous media, pore geometry and wettability are determinant factors for capillary flow in drainage or imbibition. Pores are often considered as cylindrical tubes in analytical or computational studies. Such simplification prevents the capture of phenomena occurring in pore corners. Considering the corners of pores is crucial to realistically study capillary flow and to accurately estimate liquid distribution, degree of saturation and dynamic liquid behavior in pores and in porous media. In this study, capillary flow in polygonal tubes is studied with the Shan-Chen pseudopotential multiphase lattice Boltzmann model (LBM. The LB model is first validated through a contact angle test and a capillary intrusion test. Then capillary rise in square and triangular tubes is simulated and the pore meniscus height is investigated as a function of contact angle θ. Also, the occurrence of fluid in the tube corners, referred to as corner arc menisci, is studied in terms of curvature versus degree of saturation. In polygonal capillary tubes, the number of sides leads to a critical contact angle θc which is known as a key parameter for the existence of the two configurations. LBM succeeds in simulating the formation of a pore meniscus at θ > θc or the occurrence of corner arc menisci at θ < θc. The curvature of corner arc menisci is known to decrease with increasing saturation and decreasing contact angle as described by the Mayer and Stoewe-Princen (MS-P theory. We obtain simulation results that are in good qualitative and quantitative agreement with the analytical solutions in terms of height of pore meniscus versus contact angle and curvature of corner arc menisci versus saturation degree. LBM is a suitable and promising tool for a better understanding of the complicated phenomena of multiphase flow in porous media.
Band structure of semiconductors
Tsidilkovski, I M
2013-01-01
Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio
Shi, Guangsha
theoretical upper limit of the figure of merit. I also determined the electronic structures and thermoelectric properties of Mg2Si, Mg2Ge, and Mg2Sn, a family of Earth-abundant thermoelectric compounds. I uncovered the importance of quasiparticle corrections and the proper treatment of pseudopotentials in the determination of the band gaps and the thermoelectric transport properties at high temperatures. The methods and codes I developed in my research form a general predictive toolbox for the design and optimization of the functional properties of materials for energy applications.
LHC Bellows Impedance Calculations
Dyachkov, M
1997-01-01
To compensate for thermal expansion the LHC ring has to accommodate about 2500 bellows which, together with beam position monitors, are the main contributors to the LHC broad-band impedance budget. In order to reduce this impedance to an acceptable value the bellows have to be shielded. In this paper we compare different designs proposed for the bellows and calculate their transverse and longitudinal wakefields and impedances. Owing to the 3D geometry of the bellows, the code MAFIA was used for the wakefield calculations; when possible the MAFIA results were compared to those obtained with ABCI. The results presented in this paper indicate that the latest bellows design, in which shielding is provided by sprung fingers which can slide along the beam screen, has impedances smaller tha those previously estimated according to a rather conservative scaling of SSC calculations and LEP measurements. Several failure modes, such as missing fingers and imperfect RF contact, have also been studied.
Band Structure and Optical Properties of Ordered AuCu3
DEFF Research Database (Denmark)
Skriver, Hans Lomholt; Lengkeek, H. P.
1979-01-01
initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement...
SRD 166 MEMS Calculator (Web, free access) This MEMS Calculator determines the following thin film properties from data taken with an optical interferometer or comparable instrument: a) residual strain from fixed-fixed beams, b) strain gradient from cantilevers, c) step heights or thicknesses from step-height test structures, and d) in-plane lengths or deflections. Then, residual stress and stress gradient calculations can be made after an optical vibrometer or comparable instrument is used to obtain Young's modulus from resonating cantilevers or fixed-fixed beams. In addition, wafer bond strength is determined from micro-chevron test structures using a material test machine.
Band-Structure of Thallium by the LMTO Method
DEFF Research Database (Denmark)
Holtham, P. M.; Jan, J. P.; Skriver, Hans Lomholt
1977-01-01
The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s...
Band parameters of phosphorene
DEFF Research Database (Denmark)
Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.
2015-01-01
Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory...
Hubbard-U band-structure methods
DEFF Research Database (Denmark)
Albers, R.C.; Christensen, Niels Egede; Svane, Axel
2009-01-01
The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many-body techniq......-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....... 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...
Spectral band selection for classification of soil organic matter content
Henderson, Tracey L.; Szilagyi, Andrea; Baumgardner, Marion F.; Chen, Chih-Chien Thomas; Landgrebe, David A.
1989-01-01
This paper describes the spectral-band-selection (SBS) algorithm of Chen and Landgrebe (1987, 1988, and 1989) and uses the algorithm to classify the organic matter content in the earth's surface soil. The effectiveness of the algorithm was evaluated comparing the results of classification of the soil organic matter using SBS bands with those obtained using Landsat MSS bands and TM bands, showing that the algorithm was successful in finding important spectral bands for classification of organic matter content. Using the calculated bands, the probabilities of correct classification for climate-stratified data were found to range from 0.910 to 0.980.
Energy bands and gaps near an impurity
Energy Technology Data Exchange (ETDEWEB)
Mihóková, E., E-mail: mihokova@fzu.cz [Institute of Physics, Acad. of Sciences of the Czech Rep., Cukrovarnická 10, 162 53 Prague 6 (Czech Republic); Schulman, L.S., E-mail: schulman@clarkson.edu [Physics Department, Clarkson University, Potsdam, NY 13699-5820 (United States)
2016-10-07
It has been suggested that in the neighborhood of a certain kind of defect in a crystal there is a bend in the electronic band. We confirm that this is indeed possible using the Kronig–Penney model. Our calculations also have implications for photonic crystals. - Highlights: • Energy bands can bend near an impurity in the host lattice. • We confirm possibility of energy band bending by using Kronig–Penney model. • The impurity can have profound effect on wave function structure.
Electronic band structure of beryllium oxide
Sashin, V A; Kheifets, A S; Ford, M J
2003-01-01
The energy-momentum resolved valence band structure of beryllium oxide has been measured by electron momentum spectroscopy (EMS). Band dispersions, bandwidths and intervalence bandgap, electron momentum density (EMD) and density of occupied states have been extracted from the EMS data. The experimental results are compared with band structure calculations performed within the full potential linear muffin-tin orbital approximation. Our experimental bandwidths of 2.1 +- 0.2 and 4.8 +- 0.3 eV for the oxygen s and p bands, respectively, are in accord with theoretical predictions, as is the s-band EMD after background subtraction. Contrary to the calculations, however, the measured p-band EMD shows large intensity at the GAMMA point. The measured full valence bandwidth of 19.4 +- 0.3 eV is at least 1.4 eV larger than the theory. The experiment also finds a significantly higher value for the p-to-s-band EMD ratio in a broad momentum range compared to the theory.
1994-01-01
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.
Density-functional calculation of van der Waals forces for free-electron-like surfaces
DEFF Research Database (Denmark)
Hult, E.; Hyldgaard, P.; Rossmeisl, Jan
2001-01-01
A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well...... as for the interaction between the surfaces themselves. The densities and static image-plane positions that are needed as input in the van der Waals functional are calculated self-consistently within density-functional theory using the generalized-gradient approximation, pseudopotentials, and plane waves. This study...... shows that the van der Waals density functional is applicable to realistic surfaces. The need for physically correct surface models, especially for open surfaces, is also illustrated. Finally the parameters for the anisotropic interaction of O-2 with Al are calculated....
McCarty, George
1982-01-01
How THIS BOOK DIFFERS This book is about the calculus. What distinguishes it, however, from other books is that it uses the pocket calculator to illustrate the theory. A computation that requires hours of labor when done by hand with tables is quite inappropriate as an example or exercise in a beginning calculus course. But that same computation can become a delicate illustration of the theory when the student does it in seconds on his calculator. t Furthermore, the student's own personal involvement and easy accomplishment give hi~ reassurance and en couragement. The machine is like a microscope, and its magnification is a hundred millionfold. We shall be interested in limits, and no stage of numerical approximation proves anything about the limit. However, the derivative of fex) = 67.SgX, for instance, acquires real meaning when a student first appreciates its values as numbers, as limits of 10 100 1000 t A quick example is 1.1 , 1.01 , 1.001 , •••• Another example is t = 0.1, 0.01, in the functio...
Altman, Timothy Meyer; Wright, Gary K.
2012-01-01
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…
PIJNACKER, LP; FERWERDA, MA
1995-01-01
Banding techniques were carried out on metaphase chromosomes of zebrafish (Danio rerio) embryos. The karyotypes with the longest chromosomes consist of 12 metacentrics, 26 submetacentrics, and 12 subtelocentrics (2n = 50). All centromeres are C-band positive. Eight chromosomes have a pericentric
DEFF Research Database (Denmark)
Petersen, Kurt Erling
1986-01-01
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...
Relativistic Band Structure and Fermi Surface of PdTe2 by the LMTO Method
DEFF Research Database (Denmark)
Jan, J. P.; Skriver, Hans Lomholt
1977-01-01
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...
Superdeformed bands in [sup 191]Tl
Energy Technology Data Exchange (ETDEWEB)
Pilotte, S.; Yu, C.; Jin, H.Q.; Lewis, J.M.; Riedinger, L.L. (Department of Physics, University of Tennessee, Knoxville, Tennessee 37996 (United States)); Liang, Y.; Janssens, R.V.F.; Carpenter, M.P.; Khoo, T.L.; Lauritsen, T.; Soramel, F. (Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Bearden, I.G. (Purdue University, West Lafayette, Indiana 47907 (United States)); Baktash, C.; Garrett, J.D.; Johnson, N.R.; Lee, I.Y.; McGowan, F.K. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States))
1994-02-01
High spin states in the [sup 191]Tl nucleus have been populated via the [sup 159]Tb ([sup 36]S,4[ital n]) reaction at 165 MeV. Two weakly populated rotational bands have been observed with properties (energy spacings and dynamic moments of inertia) very similar to those of other superdeformed bands in the [ital A][similar to]190 region. The two bands can be interpreted as signature partners which exhibit some signature splitting for rotational frequencies [h bar][omega][ge]0.2 MeV. They are interpreted within the framework of cranked Woods-Saxon calculations as being based on the proton [ital i][sub 13/2]([Omega]=5/2) intruder orbital, in agreement with pairs of superdeformed bands seen in neighboring odd Tl nuclei.
Infrared diffuse interstellar bands
Galazutdinov, G. A.; Lee, Jae-Joon; Han, Inwoo; Lee, Byeong-Cheol; Valyavin, G.; Krełowski, J.
2017-05-01
We present high-resolution (R ˜ 45 000) profiles of 14 diffuse interstellar bands in the ˜1.45 to ˜2.45 μm range based on spectra obtained with the Immersion Grating INfrared Spectrograph at the McDonald Observatory. The revised list of diffuse bands with accurately estimated rest wavelengths includes six new features. The diffuse band at 15 268.2 Å demonstrates a very symmetric profile shape and thus can serve as a reference for finding the 'interstellar correction' to the rest wavelength frame in the H range, which suffers from a lack of known atomic/molecular lines.
Energy Technology Data Exchange (ETDEWEB)
Bouneau, S.; Azaiez, F.; Duprat, J. [IPN, Orsay (France)] [and others
1996-12-31
The study of the superdeformed (SD) {sup 196}Pb nucleus has been revisited using the EUROGAM phase 2 spectrometer. In addition to the known yrast and two lowest excited SD bands, a third excited SD band has been seen. All of the three excited bands were found to decay to the yrast SD band through, presumably, E1 transitions, allowing relative spin and excitation energy assignments. Comparisons with calculations using the random-phase approximation suggest that all three excited bands can be interpreted as octupole vibrational structures.
Conjugate-gradient optimization method for orbital-free density functional calculations.
Jiang, Hong; Yang, Weitao
2004-08-01
Orbital-free density functional theory as an extension of traditional Thomas-Fermi theory has attracted a lot of interest in the past decade because of developments in both more accurate kinetic energy functionals and highly efficient numerical methodology. In this paper, we developed a conjugate-gradient method for the numerical solution of spin-dependent extended Thomas-Fermi equation by incorporating techniques previously used in Kohn-Sham calculations. The key ingredient of the method is an approximate line-search scheme and a collective treatment of two spin densities in the case of spin-dependent extended Thomas-Fermi problem. Test calculations for a quartic two-dimensional quantum dot system and a three-dimensional sodium cluster Na216 with a local pseudopotential demonstrate that the method is accurate and efficient. (c) 2004 American Institute of Physics.
Laparoscopic gastric banding - discharge
... heart disease Gastric bypass surgery Laparoscopic gastric banding Obesity Obstructive sleep apnea - adults Type 2 diabetes Patient Instructions Weight-loss surgery - after - what to ask your doctor Weight- ...
Band alignments of graphene-like III-nitride semiconductors
Ota, Yuichi
2018-02-01
Band alignment in graphene-like III-nitride semiconductors was investigated using first principles calculations and an empirical formula. We estimated the band edge positions using two simple approaches based on the energy of the band gap center (BGC) and electron affinity rules. The energy positions relative to the vacuum level were determined from the BGC and Mulliken electronegativities. These methods provided similar trends in the band lineup. The valence band and conduction band offsets determined by the first principles calculations agreed with the empirical results to within 0.5 eV. The findings suggest that the first principles and empirical methods provide a useful guide for high-throughput device design.
Investigation of lifetimes in dipole bands of {sup 141}Eu
Energy Technology Data Exchange (ETDEWEB)
Podsvirova, E.O.; Pasternak, A.A. [Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425, Juelich (Germany); A.F. Ioffe Physical Technical Institute RAS, RU-194021, St. Petersburg (Russian Federation); Lieder, R.M.; Gast, W.; Jaeger, H.M.; Mihailescu, L. [Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425, Juelich (Germany); Chmel, S. [Institut fuer Strahlen- und Kernphysik, University of Bonn, D-53115, Bonn (Germany); Venkova, T. [Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425, Juelich (Germany); Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, BG-1784, Sofia (Bulgaria); Angelis, G. de; Napoli, D.R.; Gadea, A. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, I-35020, Legnaro (Italy); Bazzacco, D.; Menegazzo, R.; Lunardi, S. [Dipartimento di Fisica dell' Universita and Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131, Padova (Italy); Urban, W.; Droste, C.; Morek, T.; Rzaca-Urban, T. [Institute of Experimental Physics, University of Warsaw, PL-00-681, Warszawa (Poland); Duchene, G. [Institut de Recherches Subatomique IReS, F-67037, Strasbourg (France)
2004-07-01
Lifetimes have been measured for dipole bands in {sup 141}Eu using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole bands can be interpreted as magnetic rotational bands. (orig.)
Investigation of lifetimes in dipole bands of {sup 142}Gd
Energy Technology Data Exchange (ETDEWEB)
Pasternak, A.A.; Podsvirova, E.O. [Forschungszentrum Juelich, Institut fuer Kernphysik, Juelich (Germany); A.F. Ioffe Physical Technical Institute, RAS, St. Petersburg (Russian Federation); Lieder, R.M.; Gast, W.; Jaeger, H.M.; Mihailescu, G. [Forschungszentrum Juelich, Institut fuer Kernphysik, Juelich (Germany); Chmel, S. [University of Bonn, Institut fuer Strahlen- und Kernphysik, Bonn (Germany); Venkova, T. [Forschungszentrum Juelich, Institut fuer Kernphysik, Juelich (Germany); Bulgarian Academy of Sciences, Institute of Nuclear Research and Nuclear Energy, Sofia (Bulgaria); De Angelis, G.; Napoli, D.R.; Gadea, A. [Laboratori Nazionali di Legnaro, Istituto Nazionale di Fisica Nucleare, Legnaro (Italy); Bazzacco, D.; Menegazzo, G.; Lunardi, R. [Universita di Padova, Dipartimento di Fisica, Padova (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova (Italy); Urban, W.; Droste, C.; Morek, T.; Rzaca-Urban, T. [University of Warsaw, Institute of Experimental Physics, Warszawa (Poland); Duchene, G. [Institut de Recherches Subatomique, IReS, Strasbourg (France); Dewald, A. [Universitaet zu Koeln, Institut fuer Kernphysik, Koeln (Germany)
2005-02-01
Lifetimes have been measured for dipole bands in {sup 142}Gd using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (shears mechanism with Principal Axis Cranking) models. The dipole bands DB1 to DB4 can be interpreted as magnetic rotational bands. (orig.)
Restrictive techniques: gastric banding
Directory of Open Access Journals (Sweden)
Katia Cristina da Cunha
2006-03-01
Full Text Available Surgery for the treatment of severe obesity has a definite role onthe therapeutic armamentarium all over the world. Initiated 40years ago, bariatric surgery has already a long way thanks tohundred of surgeons, who had constantly searched for the besttechnique for the adequate control of severe obesity. Among theimportant breakthroughs in obesity surgery there is theadjustable gastric band. It is a sylastic band, inflatable andadjustable, which is placed on the top of the stomach in order tocreate a 15-20 cc pouch, with an outlet of 1.3cm. The adjustablegastric band has also a subcutaneous reservoir through whichadjustments can be made, according to the patient evolution.The main feature of the adjustable gastric band is the fact thatis minimal invasive, reversible, adjustable and placedlaparoscopically. Then greatly diminishing the surgical traumato the severe obese patient. Belachew and Favretti’s techniqueof laparoscopic application of the adjustable gastric band isdescribed and the evolution of the technique during this years,as we has been practiced since 1998. The perioperative care ofthe patient is also described, as well as the follow-up and shortand long term controls.
Photonic band-gap optimisation in inverted FCC photonic crystals
Doosje, M; Hoenders, BJ; Knoester, J; Lenstra, D; Visser, TD; Leeuwen, KAH
2000-01-01
We present results of band-structure calculations for inverted photonic crystal structures. We consider a structure of air spheres in a dielectric background, arranged in an FCC lattice, with cylindrical tunnels connecting each pair of neighbouring spheres. The width of the band gap is optimised by
Electronic band structure of PuCoGa sub 5
Szajek, A
2003-01-01
The electronic band structure is presented for PuCoGa sub 5 , the recently discovered superconductor with T sub C approx 18 K. The band structure is calculated by the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. (letter to the editor)
Determination of conduction and valence band electronic structure ...
Indian Academy of Sciences (India)
Electronic structures of rutile and anatase polymorph of TiO2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti -band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses ...
Limitations to band gap tuning in nitride semiconductor alloys
DEFF Research Database (Denmark)
Gorczyca, I.; Suski, T.; Christensen, Niels Egede
2010-01-01
Relations between the band gaps of nitride alloys and their lattice parameters are presented and limits to tuning of the fundamental gap in nitride semiconductors are set by combining a large number of experimental data with ab initio theoretical calculations. Large band gap bowings obtained...
Rotational band structure in sup 75 Se
Energy Technology Data Exchange (ETDEWEB)
Johnson, T.D.; Glasmacher, T.; Holcomb, J.W.; Womble, P.C.; Tabor, S.L. (Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)); Nazarewicz, W. (Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States) Joint Institute for Heavy Ion Research, Holifield Heavy Ion Research Facility, Oak Ridge, Tennessee 37831 (United States))
1992-08-01
The high-spin states of {sup 75}Se have been investigated using the {sup 59}Co ({sup 19}F, 2{ital pn}) reaction at 55 MeV. The positive-parity band has been extended to {ital I}{sup {pi}}=29/2{sup +} and the unfavored signature has been identified. The negative-parity band has been extended to {ital I}{sup {pi}}=19/2{sup {minus}} and band crossings were observed for the first time in both bands. Eleven new lifetimes were measured using the Doppler-shift attenuation method which allowed for extraction of transition strengths and transition quadrupole moments. The {ital B}({ital M}1) strengths exhibit a staggering dependent on the signature splitting. Calculations based on the Woods-Saxon-Bogolyubov cranking model explain the signature-dependent alignment process in the {ital g}{sub 9/2} bands and predict signature inversion in all bands at high rotational frequencies. It is argued that the data are consistent with the transition from triaxial shapes with {gamma}{similar to}{minus}30{degree}, characteristic of one-quasiparticle configurations, to triaxial shapes with {gamma}{similar to}30{degree}, characteristic of a three-quasiparticle configuration containing one aligned pair of {ital g}{sub 9/2} protons.
DeHaas-vanAlphen Effect and LMTO Band-structure of LaSn3
DEFF Research Database (Denmark)
Boulet, R. M.; Jan, J. -P.; Skriver, Hans Lomholt
1982-01-01
Results of de Haas-van Alphen experiments in the intermetallic compound LaSn3 can be explained by a linear muffin-tin orbital band structure calculation without involving the f bands of lanthanum.......Results of de Haas-van Alphen experiments in the intermetallic compound LaSn3 can be explained by a linear muffin-tin orbital band structure calculation without involving the f bands of lanthanum....
Begaud, Xavier
2013-01-01
Ultra Wide Band Technology (UWB) has reached a level of maturity that allows us to offer wireless links with either high or low data rates. These wireless links are frequently associated with a location capability for which ultimate accuracy varies with the inverse of the frequency bandwidth. Using time or frequency domain waveforms, they are currently the subject of international standards facilitating their commercial implementation. Drawing up a complete state of the art, Ultra Wide Band Antennas is aimed at students, engineers and researchers and presents a summary of internationally recog
Calculation of the vibrational properties of LiMgAs.
Mellouki, A; Bennecer, B; Kalarasse, F
2009-07-29
We have studied the vibrational properties of the filled tetrahedral semiconductor LiMgAs and its binary analog AlAs by using the plane-wave pseudopotential method within density functional theory. The calculated lattice constants for the studied compounds are in good agreement with previous theoretical and experimental results. The phonon dispersion curves and phonon density of states are calculated by using density functional perturbation theory. The sound speeds in different directions are quantitatively similar in LiMgAs and AlAs. The assignment of the zone center modes to the relative motion of the atoms shows that the lower optic modes are due to the Mg-As pair vibrations, while for the upper ones the Li-Mg pair dominates, which is attributed to the smaller Mg atom mass. The longitudinal interatomic force constant of Mg-As is about 66% higher than that of Li-As, showing the relatively high covalency of the former bond.
Calculation of the vibrational properties of LiMgAs
Energy Technology Data Exchange (ETDEWEB)
Mellouki, A; Bennecer, B; Kalarasse, F, E-mail: b_bennacer@hotmail.co [Physics Laboratory at Guelma, Faculty of Science and Engineering, University of Guelma, PO Box 401, Guelma 24000 (Algeria)
2009-07-29
We have studied the vibrational properties of the filled tetrahedral semiconductor LiMgAs and its binary analog AlAs by using the plane-wave pseudopotential method within density functional theory. The calculated lattice constants for the studied compounds are in good agreement with previous theoretical and experimental results. The phonon dispersion curves and phonon density of states are calculated by using density functional perturbation theory. The sound speeds in different directions are quantitatively similar in LiMgAs and AlAs. The assignment of the zone center modes to the relative motion of the atoms shows that the lower optic modes are due to the Mg-As pair vibrations, while for the upper ones the Li-Mg pair dominates, which is attributed to the smaller Mg atom mass. The longitudinal interatomic force constant of Mg-As is about 66% higher than that of Li-As, showing the relatively high covalency of the former bond.
Shetty, Prathvi; Menezes, Leo Theobald; Tauro, Leo Francis; Diddigi, Kumar Arun
2013-10-01
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.
Shetty, Prathvi; Menezes, Leo Theobald; Tauro, Leo Francis; Diddigi, Kumar Arun
2012-01-01
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.
Colloquium: Topological band theory
Bansil, A.; Lin, Hsin; Das, Tanmoy
2016-04-01
The first-principles band theory paradigm has been a key player not only in the process of discovering new classes of topologically interesting materials, but also for identifying salient characteristics of topological states, enabling direct and sharpened confrontation between theory and experiment. This review begins by discussing underpinnings of the topological band theory, which involve a layer of analysis and interpretation for assessing topological properties of band structures beyond the standard band theory construct. Methods for evaluating topological invariants are delineated, including crystals without inversion symmetry and interacting systems. The extent to which theoretically predicted properties and protections of topological states have been verified experimentally is discussed, including work on topological crystalline insulators, disorder and interaction driven topological insulators (TIs), topological superconductors, Weyl semimetal phases, and topological phase transitions. Successful strategies for new materials discovery process are outlined. A comprehensive survey of currently predicted 2D and 3D topological materials is provided. This includes binary, ternary, and quaternary compounds, transition metal and f -electron materials, Weyl and 3D Dirac semimetals, complex oxides, organometallics, skutterudites, and antiperovskites. Also included is the emerging area of 2D atomically thin films beyond graphene of various elements and their alloys, functional thin films, multilayer systems, and ultrathin films of 3D TIs, all of which hold exciting promise of wide-ranging applications. This Colloquium concludes by giving a perspective on research directions where further work will broadly benefit the topological materials field.
Leggett modes and multi-band superconductivity in Sr2RuO4
Huang, Wen; Scaffidi, Thomas; Sigrist, Manfred; Kallin, Catherine
2016-01-01
Sr$_2$RuO$_4$ is a prototypical multi-band superconductor with three bands crossing the Fermi level. These bands exhibit distinct dimensional characteristics, with one quasi-2D $\\gamma$-band and two quasi-1D $\\alpha$- and $\\beta$-bands. This leads to the expectation that the superconductivity on the $\\gamma$-band may be only weakly Josephson-coupled to that on the other two bands. Based on an explicit microscopic weak coupling calculation appropriate for Sr$_2$RuO$_4$, we study the collective...
Calculated Electronic Behavior and Spectrum of Mg+@C60 Using a Simple Jellium-shell Model
Directory of Open Access Journals (Sweden)
H. A. Schuessler
2004-11-01
Full Text Available Abstract: We present a method for calculating the energy levels and wave functions of any atom or ion with a single valence electron encapsulated in a Fullerene cage using a jelluim-shell model. The valence electron-core interaction is represented by a one-body pseudo-potential obtained through density functional theory with strikingly accurate parameters for Mg+ and which reduces to a purely Coulombic interaction in the case of H. We find that most energy states are affected little by encapsulation. However, when either the electron in the non-encapsulated species has a high probability of being near the jellium cage, or when the cage induces a maximum electron probability density within it, the energy levels shift considerably. Mg+ shows behavior similar to that of H, but since its wave functions are broader, the changes in its energy levels from encapsulation are slightly more pronounced. Agreement with other computational work as well as experiment is excellent and the method presented here is generalizable to any encapsulated species where a one-body electronic pseudo-potential for the free atom (or ion is available. Results are also presented for off-center hydrogen, where a ground state energy minimum of -14.01 eV is found at a nuclear displacement of around 0.1 ÃƒÂ….
Lehrer, H; Weise, A; Michel, S; Starke, H; Mrasek, K; Heller, A; Kuechler, A; Claussen, U; Liehr, T
2004-01-01
To clarify the nature of chromosome sub-bands in more detail, the multicolor banding (MCB) probe-set for chromosome 5 was hybridized to normal metaphase spreads of GTG band levels at approximately 850, approximately 550, approximately 400 and approximately 300. It could be observed that as the chromosomes became shorter, more of the initial 39 MCB pseudo-colors disappeared, ending with 18 MCB pseudo-colored bands at the approximately 300-band level. The hierarchically organized splitting of bands into sub-bands was analyzed by comparing the disappearance or appearance of pseudo-color bands of the four different band levels. The regions to split first are telomere-near, centromere-near and in 5q23-->q31, followed by 5p15, 5p14, and all GTG dark bands in 5q apart from 5q12 and 5q32 and finalized by sub-band building in 5p15.2, 5q21.2-->q21.3, 5q23.1 and 5q34. The direction of band splitting towards the centromere or the telomere could be assigned to each band separately. Pseudo-colors assigned to GTG-light bands were resistant to band splitting. These observations are in concordance with the recently proposed concept of chromosome region-specific protein swelling. Copyright 2003 S. Karger AG, Basel
Directory of Open Access Journals (Sweden)
Jovana Đorđević
2009-04-01
Full Text Available Amniotic band syndrome (ABS is a set of congenital malformations attributed to amniotic bands that entangle fetal parts during intrauterine life, which results in a broad spectrum of anatomic disturbances - ranging from minor constriction rings and lymphedema of the digits to complex, bizarre multiple congenital anomalies incompatible with life. ABS is not very often, but should be considered in every newborn with congenital anomalies, especially defects of extremities and/or body walls. ABS can be diagnosed prenatally by ultrasound; otherwise, the defects are seen after birth. Child's karyotyping is of great importance, in order to avoid misdiagnosis and incorrect information of recurrence risk. A team of specialists should be included in the treatment and follow-up of children with ABS, according to individual needs of every single patient.The aim of this paper is to point out diagnostic and therapeutic approaches in newborns with ABS trough the report of two cases.
Subcutaneous fascial bands--a qualitative and morphometric analysis.
Li, Weihui; Ahn, Andrew C
2011-01-01
Although fascial bands within the subcutaneous (SQ) layer are commonly seen in ultrasound images, little is known about their functional role, much less their structural characteristics. This study's objective is to describe the morphological features of SQ fascial bands and to systematically evaluate the bands using image analyses tools and morphometric measures. In 28 healthy volunteers, ultrasound images were obtained at three body locations: the lateral aspect of the upper arm, medial aspect of the thigh and posterior aspect of lower leg. Using image analytical techniques, the total SQ band area, fascial band number, fascial band thickness, and SQ zone (layer) thickness were determined. In addition, the SQ spatial coherence was calculated based on the eigenvalues associated with the largest and smallest eigenvectors of the images. Fascial bands at these sites were contiguous with the dermis and the epimysium forming an interconnected network within the subcutaneous tissue. Subcutaneous blood vessels were also frequently encased by these fascial bands. The total SQ fascial band area was greater at the thigh and calf compared to the arm and was unrelated to SQ layer (zone) thickness. The thigh was associated with highest average number of fascial bands while calf was associated with the greatest average fascial band thickness. Across body regions, greater SQ zone thickness was associated with thinner fascial bands. SQ coherence was significantly associated with SQ zone thickness and body location (calf with statistically greater coherence compared to arm). Fascial bands are structural bridges that mechanically link the skin, subcutaneous layer, and deeper muscle layers. This cohesive network also encases subcutaneous vessels and may indirectly mediate blood flow. The quantity and morphological characteristics of the SQ fascial band may reflect the composite mechanical forces experienced by the body part.
Subcutaneous fascial bands--a qualitative and morphometric analysis.
Directory of Open Access Journals (Sweden)
Weihui Li
Full Text Available BACKGROUND: Although fascial bands within the subcutaneous (SQ layer are commonly seen in ultrasound images, little is known about their functional role, much less their structural characteristics. This study's objective is to describe the morphological features of SQ fascial bands and to systematically evaluate the bands using image analyses tools and morphometric measures. METHODS: In 28 healthy volunteers, ultrasound images were obtained at three body locations: the lateral aspect of the upper arm, medial aspect of the thigh and posterior aspect of lower leg. Using image analytical techniques, the total SQ band area, fascial band number, fascial band thickness, and SQ zone (layer thickness were determined. In addition, the SQ spatial coherence was calculated based on the eigenvalues associated with the largest and smallest eigenvectors of the images. RESULTS: Fascial bands at these sites were contiguous with the dermis and the epimysium forming an interconnected network within the subcutaneous tissue. Subcutaneous blood vessels were also frequently encased by these fascial bands. The total SQ fascial band area was greater at the thigh and calf compared to the arm and was unrelated to SQ layer (zone thickness. The thigh was associated with highest average number of fascial bands while calf was associated with the greatest average fascial band thickness. Across body regions, greater SQ zone thickness was associated with thinner fascial bands. SQ coherence was significantly associated with SQ zone thickness and body location (calf with statistically greater coherence compared to arm. CONCLUSION: Fascial bands are structural bridges that mechanically link the skin, subcutaneous layer, and deeper muscle layers. This cohesive network also encases subcutaneous vessels and may indirectly mediate blood flow. The quantity and morphological characteristics of the SQ fascial band may reflect the composite mechanical forces experienced by the body part.
Phonon spectra of elpasolites Cs2NaRF6 (R=Y,Yb): Ab initio calculations
Chernyshev, Vladimir; Petrov, Vladislav; Nikiforov, Anatoliy; Zakiryanov, Dmitriy
2015-12-01
The influence of hydrostatic pressure on structure and dynamics of a crystal lattice of elpasolites Cs2NaYbF6 and Cs2NaYF6 (S.G. 225) within ab initio approach is investigated. Frequencies and irreducible representations (irreps) of phonon modes are determined. Elastic constants are calculated. The calculations are carried out within MO LCAO approach using DFT method with hybrid functionalities of B3LYP and PBE0 in CRYSTAL09 periodic code. For the description of rare earth ion the pseudopotential replacing internal orbitals including 4f orbitals was used. External 5s and 5p orbitals defining chemical bond were described by valence basis sets.
Noise exposure in marching bands
Keefe, Joseph
2005-09-01
Previous studies involving orchestras have shown that music ensembles can produce hazardous noise levels. There are no similar data for marching bands and pep bands. In order to evaluate the noise levels produced by marching and pep bands, 1/3-octave-band sound-pressure levels were measured while these groups rehearsed and performed. Data were collected while marching with the bands to ensure a realistic environment. Comparing these data to OSHA and NIOSH criteria, marching and pep band exposures often exceed safe values. For typical exposures, OSHA doses range from 11% to 295%, while NIOSH doses range from 35% to 3055%. Exposures that would be considered hazardous in the workplace are common in marching and pep bands; students and band directors should take steps to recognize the risk posed by various instruments and various locations, and should implement hearing conservation efforts.
Quantum Monte Carlo Calculations of Excitations in Hydrogenated Germanium Clusters
Vincent, Jordan; Kim, Jeongnim; Martin, Richard
2006-03-01
Quantum Monte Carlo (QMC) calculations are presented for energies of ground and excited states of Ge atom and hydrogen passivated closed-shell molecules and clusters: GeH4, Ge2H6, Ge5H12, Ge10H16 and Ge29H36. We compare the results for excitations with previous QMC and time-dependant Density Functional Theory (TD- DFT) done for the corresponding Silicon clusters [1,2]; in particular; we find that preliminary results for lowest excitation enregy of Ge29H36 5.08[29]eV is lower than the gap 5.4eV reported for Si[2]. Core-valence partitioning for Ge is implemented by replacing the core-states with a Hartree-Fock pseudopotential plus a Core Polarization Potential (CPP)[3]. Core-valence correlation treated by the CPP is shown to be essential for accurate atomic energies and significant for the molecules, but smaller in the clusters. [1] Porter et. al., PRB 64, 035320 (2001). [2] Williamson et. al., PRL 89, 196803 (2002). [3] Shirley and Martin, PRB 47, 15413 (1993)
Microscopic study of low-lying collective bands in 77Kr
Indian Academy of Sciences (India)
The structure of the collective bands in 77Kr is investigated within our deformed shell model (DSM) based on Hartree-Fock states. The different levels are classified into collective bands on the basis of their (2) values. The calculated = 5/2+ ground band agrees reasonably well with the experiment. An attempt has been ...
A model for the direct-to-indirect band-gap transition in monolayer ...
Indian Academy of Sciences (India)
Abstract. A monolayer of MoSe2 is found to be a direct band-gap semiconductor. We show, within ab-initio electronic structure calculations, that a modest biaxial tensile strain of 3% can drive it into an indirect band-gap semiconductor with the valence band maximum (VBM) shifting from K point to point. An analysis of the ...
DEFF Research Database (Denmark)
Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco
2014-01-01
The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all......-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...
Microstrip microwave band gap structures
Indian Academy of Sciences (India)
Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are ...
Semiconductors bonds and bands
Ferry, David K
2013-01-01
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.
Morphologies of omega band auroras
Sato, Natsuo; Yukimatu, Akira Sessai; Tanaka, Yoshimasa; Hori, Tomoaki
2017-08-01
We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east-west-aligned auroras, rather than via the rotation or shear motion of preexisting east-west-aligned auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.
Band Structure and Fermi-Surface Properties of Ordered beta-Brass
DEFF Research Database (Denmark)
Skriver, Hans Lomholt; Christensen, N. E.
1973-01-01
The band structure of ordered β-brass (β′-CuZn) has been calculated throughout the Brillouin zone by the augmented-plane-wave method. The present band model differs from previous calculations with respect to the position and width of the Cu 3d band. The derived dielectric function ε2(ω) and the p......The band structure of ordered β-brass (β′-CuZn) has been calculated throughout the Brillouin zone by the augmented-plane-wave method. The present band model differs from previous calculations with respect to the position and width of the Cu 3d band. The derived dielectric function ε2(ω...
Atmospheric Solar Heating in Minor Absorption Bands
Chou, Ming-Dah
1998-01-01
Solar radiation is the primary source of energy driving atmospheric and oceanic circulations. Concerned with the huge computing time required for computing radiative transfer in weather and climate models, solar heating in minor absorption bands has often been neglected. The individual contributions of these minor bands to the atmospheric heating is small, but collectively they are not negligible. The solar heating in minor bands includes the absorption due to water vapor in the photosynthetically active radiation (PAR) spectral region from 14284/cm to 25000/cm, the ozone absorption and Rayleigh scattering in the near infrared, as well as the O2 and CO2 absorption in a number of weak bands. Detailed high spectral- and angular-resolution calculations show that the total effect of these minor absorption is to enhance the atmospheric solar heating by approximately 10%. Depending upon the strength of the absorption and the overlapping among gaseous absorption, different approaches are applied to parameterize these minor absorption. The parameterizations are accurate and require little extra time for computing radiative fluxes. They have been efficiently implemented in the various atmospheric models at NASA/Goddard Space Flight Center, including cloud ensemble, mesoscale, and climate models.
S-Band Doppler Wave Radar System
Directory of Open Access Journals (Sweden)
Zezong Chen
2017-12-01
Full Text Available In this paper, a novel shore-based S-band microwave Doppler coherent wave radar (Microwave Ocean Remote SEnsor (MORSE is designed to improve wave measurements. Marine radars, which operate in the X band, have been widely used for ocean monitoring because of their low cost, small size and flexibility. However, because of the non-coherent measurements and strong absorption of X-band radio waves by rain, these radar systems suffer considerable performance loss in moist weather. Furthermore, frequent calibrations to modify the modulation transfer function are required. To overcome these shortcomings, MORSE, which operates in the S band, was developed by Wuhan University. Because of the coherent measurements of this sensor, it is able to measure the radial velocity of water particles via the Doppler effect. Then the relation between the velocity spectrum and wave height spectrum can be used to obtain the wave height spectra. Finally, wave parameters are estimated from the wave height spectra by the spectrum moment method. Comparisons between MORSE and Waverider MKIII are conducted in this study, and the results, including the non-directional wave height spectra, significant wave height and average wave period, are calculated and displayed. The correlation coefficient of the significant wave height is larger than 0.9, whereas that of the average wave period is approximately 0.4, demonstrating the effectiveness of MORSE for the continuous monitoring of ocean areas with high accuracy.
Chappell, Helen; Duer, Melinda; Groom, Nicholas; Pickard, Chris; Bristowe, Paul
2008-01-28
The surface characteristics of hydroxyapatite (HA) are probed using a combination of NMR spectroscopy and first principles calculations. The NMR spectrum is taken from a bone sample and the first principles calculations are performed using a plane-wave density functional approach within the pseudopotential approximation. The computational work focuses on the (100) and (200) surfaces, which exhibit a representative range of phosphate, hydroxyl and cation bonding geometries. The shielding tensors for the 31P, 1H and 17O nuclei are calculated from the relaxed surface structures using an extension of the projector augmented-wave method. The calculated 31P chemical shifts for the surface slab are found to be significantly different from the bulk crystal and are consistent with the NMR data from bone and also synthetically prepared nanocrystalline samples of HA. Rotational relaxations of the surface phosphate ions and the sub-surface displacement of other nearby ions are identified as causing the main differences. The investigation points to further calculations of other crystallographic surfaces and highlights the potential of using NMR with ab initio modelling to fully describe the surface structure and chemistry of HA, which is essential for understanding its reactivity with the surrounding organic matrix.
Unoccupied band structure of wurtzite GaN(0001)
Energy Technology Data Exchange (ETDEWEB)
Valla, T.; Johnson, P.D. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States); Dhesi, S.S.; Smith, K.E. [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States); Doppalapudi, D.; Moustakas, T.D. [Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Shirley, E.L. [NIST, PHY B208, Gaithersburg, Maryland 20899 (United States)
1999-02-01
We report an inverse photoemission study of the unoccupied states of thin-film {ital n}-type wurtzite GaN. For incident electron energies below 30 eV, free-electron bands do not provide a good description of the initial state. However, using a calculated quasiparticle band structure for the initial state, we can obtain good agreement between our measurements and the calculated low-lying conduction bands. No evidence of unoccupied surface states is observed in the probed part of the Brillouin zone, confirming earlier angle resolved photoemission studies, which identified the surface states on GaN(0001) as occupied dangling bond states, resonant with the valence band. {copyright} {ital 1999} {ital The American Physical Society}
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band ...
Microscopic study of positive-parity yrast bands of 224− 234 Th ...
Indian Academy of Sciences (India)
The positive-parity bands in 224−234Th are studied using the projected shell model (PSM) approach. The energy levels, deformation systematics, (2) transition probabilities and nuclear -factors are calculated and compared with the experimental data. The calculation reproduces the observed positive-parity yrast bands ...
Structure of negative parity yrast bands in odd mass 125− 131Ce ...
Indian Academy of Sciences (India)
The negative parity yrast bands of neutron-deficient 125-131Ce nuclei are studied by using the projected shell model approach. Energy levels, transition energies and (1)/(2) ratios are calculated and compared with the available experimental data. The calculations reproduce the band-head spins of negative parity ...
Structure of negative parity yrast bands in odd mass 125−131Ce ...
Indian Academy of Sciences (India)
Abstract. The negative parity yrast bands of neutron-deficient 125−131Ce nuclei are studied by using the projected shell model approach. Energy levels, transition energies and B(M1)/B(E2) ratios are calculated and compared with the available experimental data. The calculations reproduce the band-head spins of negative ...
Valence band energy spectrum of HgTe quantum wells with an inverted band structure
Minkov, G. M.; Aleshkin, V. Ya.; Rut, O. E.; Sherstobitov, A. A.; Germanenko, A. V.; Dvoretski, S. A.; Mikhailov, N. N.
2017-07-01
The energy spectrum of the valence band in HgTe /CdxHg1 -xTe quantum wells of a width (8 -20 ) nm has been studied experimentally by magnetotransport effects and theoretically in the framework of a four-band k P method. Comparison of the Hall density with the density found from a period of the Shubnikov-de Haas (SdH) oscillations clearly shows that the degeneracy of states of the top of the valence band is equal to 2 at the hole density p SdH oscillations shows that mh is equal to (0.25 ±0.02 ) m0 and weakly increases with the hole density. Such a value of mh and its dependence on the hole density are in a good agreement with the calculated effective mass.
Parsons, Zackary
2017-01-01
The Wide Band Artificial Pulsar (WBAP) is an instrument verification device designed and built by the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virgina. The site currently operates the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) and the Versatile Green Bank Astronomical Spectrometer (VEGAS) digital backends for their radio telescopes. The commissioning and continued support for these sophisticated backends has demonstrated a need for a device capable of producing an accurate artificial pulsar signal. The WBAP is designed to provide a very close approximation to an actual pulsar signal. This presentation is intended to provide an overview of the current hardware and software implementations and to also share the current results from testing using the WBAP.
Chiral topological excitons in a Chern band insulator
Chen, Ke; Shindou, Ryuichi
2017-10-01
A family of semiconductors called Chern band insulators are shown to host exciton bands with nonzero topological Chern integers and chiral exciton edge modes. Using a prototypical two-band Chern insulator model, we calculate a cross-correlation function to obtain the exciton bands and their Chern integers. The lowest exciton band acquires Chern integers such as ±1 and ±2 in the electronic Chern insulator phase. The nontrivial topology can be experimentally observed both by a nonlocal optoelectronic response of exciton edge modes and by a phase shift in the cross-correlation response due to the bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum wells, and (Bi,Sb)2Te3 thin films are promising candidates for a platform of topological excitonics.
Tunable band structures in digital oxides with layered crystal habits
Shin, Yongjin; Rondinelli, James M.
2017-11-01
We use density functional calculations to show that heterovalent cation-order sequences enable control over band-gap variations up to several eV and band-gap closure in the bulk band insulator LaSrAlO4. The band-gap control originates from the internal electric fields induced by the digital chemical order, which induces picoscale band bending; the electric-field magnitude is mainly governed by the inequivalent charged monoxide layers afforded by the layered crystal habit. Charge transfer and ionic relaxations across these layers play secondary roles. This understanding is used to construct and validate a descriptor that captures the layer-charge variation and to predict changes in the electronic gap in layered oxides exhibiting antisite defects and in other chemistries.
1996-01-01
Dark crisscrossing bands on Jupiter's moon Europa represent widespread disruption from fracturing and the possible eruption of gases and rocky material from the moon's interior in this four-frame mosaic of images from NASA's Galileo spacecraft. These and other features suggest that soft ice or liquid water was present below the ice crust at the time of disruption. The data do not rule out the possibility that such conditions exist on Europa today. The pictures were taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996. Many of the dark bands are more than 1,600 kilometers (1,000 miles) long, exceeding the length of the San Andreas fault of California. Some of the features seen on the mosaic resulted from meteoritic impact, including a 30- kilometer (18.5 mile) diameter crater visible as a bright scar in the lower third of the picture. In addition, dozens of shallow craters seen in some terrains along the sunset terminator zone (upper right shadowed area of the image) are probably impact craters. Other areas along the terminator lack craters, indicating relatively youthful surfaces, suggestive of recent eruptions of icy slush from the interior. The lower quarter of the mosaic includes highly fractured terrain where the icy crust has been broken into slabs as large as 30 kilometers (18.5 miles) across. The mosaic covers a large part of the northern hemisphere and includes the north pole at the top of the image. The sun illuminates the surface from the left. The area shown is centered on 20 degrees north latitude and 220 degrees west longitude and is about as wide as the United States west of the Mississippi River. The Galileo mission is managed by NASA's Jet Propulsion Laboratory.
Model development for MODIS thermal band electronic cross-talk
Chang, Tiejun; Wu, Aisheng; Geng, Xu; Li, Yonghong; Brinkmann, Jake; Keller, Graziela; Xiong, Xiaoxiong (Jack)
2016-10-01
MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands. Among them, 16 thermal emissive bands covering a wavelength range from 3.8 to 14.4 μm. After 16 years on-orbit operation, the electronic crosstalk of a few Terra MODIS thermal emissive bands develop substantial issues which cause biases in the EV brightness temperature measurements and surface feature contamination. The crosstalk effects on band 27 with center wavelength at 6.7 μm and band 29 at 8.5 μm increased significantly in recent years, affecting downstream products such as water vapor and cloud mask. The crosstalk issue can be observed from nearly monthly scheduled lunar measurements, from which the crosstalk coefficients can be derived. Most of MODIS thermal bands are saturated at moon surface temperatures and the development of an alternative approach is very helpful for verification. In this work, a physical model was developed to assess the crosstalk impact on calibration as well as in Earth view brightness temperature retrieval. This model was applied to Terra MODIS band 29 empirically for correction of Earth brightness temperature measurements. In the model development, the detector nonlinear response is considered. The impacts of the electronic crosstalk are assessed in two steps. The first step consists of determining the impact on calibration using the on-board blackbody (BB). Due to the detector nonlinear response and large background signal, both linear and nonlinear coefficients are affected by the crosstalk from sending bands. The crosstalk impact on calibration coefficients was calculated. The second step is to calculate the effects on the Earth view brightness temperature retrieval. The effects include those from affected calibration coefficients and the contamination of Earth view measurements. This model links the measurement bias with crosstalk coefficients, detector nonlinearity, and the ratio of Earth measurements between the sending and receiving bands. The correction
Gate-induced band ferromagnetism in an organic polymer
Arita, Ryotaro; Suwa, Yuji; Kuroki, Kazuhiko; Aoki, Hideo
2001-01-01
We propose that a chain of five-membered rings (polyaminotriazole) should be ferromagnetic with an appropriate doping that is envisaged to be feasible with an FET structure. The ferromagnetism is confirmed by a spin density functional calculation, which also shows that ferromagnetism survives the Peierls instability. We explain the magnetism in terms of Mielke and Tasaki's flat-band ferromagnetism with the Hubbard model. This opens a new possibility of band ferromagnetism in purely organic po...
Systematic description of superdeformed bands in the mass-190 region
Energy Technology Data Exchange (ETDEWEB)
Sun, Yang; Guidry, M. [Oak Ridge National Lab., TN (United States)]|[Univ. of Tennessee, Knoxville, TN (United States); Zhang, Jing-ye [Univ. of Tennessee, Knoxville, TN (United States)
1996-12-31
Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. The authors calculation of electromagnetic properties and pairing correlations provides an understanding of the observed gradual increase of dynamical moments of inertia with angular momentum observed in many bands in this mass region.
Simulation of radar backscattering from snowpack at X-band and Ku-band
Gay, Michel; Phan, Xuan-Vu; Ferro-Famil, Laurent
2016-04-01
This paper presents a multilayer snowpack electromagnetic backscattering model, based on Dense Media Radiative Transfer (DMRT). This model is capable of simulating the interaction of electromagnetic wave (EMW) at X-band and Ku-band frequencies with multilayer snowpack. The air-snow interface and snow-ground backscattering components are calculated using the Integral Equation Model (IEM) by [1], whereas the volume backscattering component is calculated based on the solution of Vector Radiative Transfer (VRT) equation at order 1. Case study has been carried out using measurement data from NoSREx project [2], which include SnowScat data in X-band and Ku-band, TerraSAR-X acquisitions and snowpack stratigraphic in-situ measurements. The results of model simulations show good agreement with the radar observations, and therefore allow the DMRT model to be used in various applications, such as data assimilation [3]. [1] A.K. Fung and K.S. Chen, "An update on the iem surface backscattering model," Geoscience and Remote Sensing Letters, IEEE, vol. 1, no. 2, pp. 75 - 77, april 2004. [2] J. Lemmetyinen, A. Kontu, J. Pulliainen, A. Wiesmann, C. Werner, T. Nagler, H. Rott, and M. Heidinger, "Technical assistance for the deployment of an x- to ku-band scatterometer during the nosrex ii experiment," Final Report, ESA ESTEC Contract No. 22671/09/NL/JA., 2011. [3] X. V. Phan, L. Ferro-Famil, M. Gay, Y. Durand, M. Dumont, S. Morin, S. Allain, G. D'Urso, and A. Girard, "3d-var multilayer assimilation of x-band sar data into a detailed snowpack model," The Cryosphere Discussions, vol. 7, no. 5, pp. 4881-4912, 2013.
Observation of high-spin oblate band structures in Pm141
Gu, L.; Zhu, S. J.; Wang, J. G.; Yeoh, E. Y.; Xiao, Z. G.; Zhang, S. Q.; Meng, J.; Zhang, M.; Liu, Y.; Ding, H. B.; Xu, Q.; Zhu, L. H.; Wu, X. G.; He, C. Y.; Li, G. S.; Wang, L. L.; Zheng, Y.; Zhang, B.
2011-06-01
The high-spin states of Pm141 have been investigated through the reaction Te126(F19,4n) at a beam energy of 90 MeV. A previous level scheme has been updated with spins up to 49/2ℏ. Six collective bands at high spins are newly observed. Based on the systematic comparison, one band is proposed as a decoupled band; two bands with strong ΔI=1 M1 transitions inside the bands are suggested as the oblate bands with γ ~-60°; three other bands with large signature splitting have been proposed with the oblate-triaxial deformation with γ~ -90°. The triaxial n-particle-n-hole particle rotor model calculations for one of the oblate bands in Pm141 are in good agreement with the experimental data. The other characteristics for these bands have been discussed.
Goings, Joshua J; Li, Xiaosong
2016-06-21
One of the challenges of interpreting electronic circular dichroism (ECD) band spectra is that different states may have different rotatory strength signs, determined by their absolute configuration. If the states are closely spaced and opposite in sign, observed transitions may be washed out by nearby states, unlike absorption spectra where transitions are always positive additive. To accurately compute ECD bands, it is necessary to compute a large number of excited states, which may be prohibitively costly if one uses the linear-response time-dependent density functional theory (TDDFT) framework. Here we implement a real-time, atomic-orbital based TDDFT method for computing the entire ECD spectrum simultaneously. The method is advantageous for large systems with a high density of states. In contrast to previous implementations based on real-space grids, the method is variational, independent of nuclear orientation, and does not rely on pseudopotential approximations, making it suitable for computation of chiroptical properties well into the X-ray regime.
Electronic properties and charge density of BexZn1− xTe alloys
Indian Academy of Sciences (India)
Electronic band structure calculations are performed for the BeZn1−Te (0 ≤ ≤ 1 in steps of 0.2) alloys following the empirical pseudopotential method. The alloying effects are modelled through the modified virtual crystal approximation. Throughout the composition, valence band maximum resides at the point.
Directory of Open Access Journals (Sweden)
Zhipeng Wang
2015-12-01
Full Text Available Spectral bands of the Visible Infrared Imaging Radiometer Suite (VIIRS instrument aboard the Suomi National Polar-orbiting Partnership (S-NPP satellite are spatially co-registered. The accuracy of the band-to-band registration (BBR is one of the key spatial parameters that must be characterized. Unlike its predecessor, the Moderate Resolution Imaging Spectroradiometer (MODIS, VIIRS has no on-board calibrator specifically designed to perform on-orbit BBR characterization. To circumvent this problem, a BBR characterization method for VIIRS reflective solar bands (RSB based on regularly-acquired lunar images has been developed. While its results can satisfactorily demonstrate that the long-term stability of the BBR is well within ±0.1 moderate resolution band pixels, undesired seasonal oscillations have been observed in the trending. The oscillations are most obvious between the visible/near-infrared bands and short-/middle wave infrared bands. This paper investigates the oscillations and identifies their cause as the band/spectral dependence of the centroid position and the seasonal rotation of the lunar images over calibration events. Accordingly, an improved algorithm is proposed to quantify the rotation and compensate for its impact. After the correction, the seasonal oscillation in the resulting BBR is reduced from up to 0.05 moderate resolution band pixels to around 0.01 moderate resolution band pixels. After removing this spurious seasonal oscillation, the BBR, as well as its long-term drift are well determined.
National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Calculator will calculate the total magnetic field, including components (declination, inclination, horizontal intensity, northerly intensity,...
... NIAAA College Materials Supporting Research Special Features CollegeAIM College Administrators Parents & Students Home > Special Features > Calculators > Alcohol Calorie Calculator Weekly Total 0 Calories Alcohol Calorie ...
Guo, Yuzheng; Robertson, John
2017-09-01
We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.
Energy Technology Data Exchange (ETDEWEB)
Yablonovitch, E. [Univ. of California, Los Angeles, CA (United States)
1993-05-01
We learned how to create 3-dimensionally periodic dielectric structures which are to photon waves, as semiconductor crystals are to electron waves. That is, these photonic crystals have a photonic bandgap, a band of frequencies in which electromagnetic waves are forbidden, irrespective of propagation direction in space. Photonic bandgaps provide for spontaneous emission inhibition and allow for a new class of electromagnetic micro-cavities. If the perfect 3-dimensional periodicity is broken by a local defect, then local electromagnetic modes can occur within the forbidden bandgap. The addition of extra dielectric material locally, inside the photonic crystal, produces {open_quotes}donor{close_quotes} modes. Conversely, the local removal of dielectric material from the photonic crystal produces {open_quotes}acceptor{close_quotes} modes. Therefore, it will now be possible to make high-Q electromagnetic cavities of volume {approx_lt}1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric micro-resonators can cover the range all the way from millimeter waves, down to ultraviolet wavelengths.
Electric field tuning of the band gap in graphene multilayers
Avetisyan, A. A.; Partoens, B.; Peeters, F. M.
2009-01-01
A perpendicular electric field applied to multilayers of graphene modifies the electronic structure near the K point and may induce an energy gap in the electronic spectrum. This gap is tunable by the gate voltage and its size depends on the number of layers. We use a tight-binding approach to calculate the band structure and include a self-consistent calculation in order to obtain the density of charge carriers. Results are presented for systems consisting of three and four layers of graphene. The effect of the circular asymmetry of the band structure on the gap is critically examined.
Energy Technology Data Exchange (ETDEWEB)
Alcantara-Nunez, J.A.; Oliveira, J.R.B.; Cybulska, E.W.; Medina, N.H.; Rao, M.N.; Ribas, R.V.; Rizzutto, M.A.; Seale, W.A.; Falla-Sotelo, F.; Wiedemann, K.T. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica; Dimitrov, V.I.; Frauendorf, S. [University of Notre Dame, Notre Dame, IN (United States). Dept. of Physics; Research Center Rossendorf, Dresden (Germany). Institute for Nuclear and Hadronic Physics
2004-09-15
The {sup 105}Rh nucleus has been studied by in-beam {gamma} spectroscopy with the heavy-ion fusion-evaporation reaction {sup 100}Mo({sup 11}B, {alpha}2n{gamma}) at 43 MeV. A rich variety of structures was observed at high and low spin, using {gamma}-{gamma}-t and {gamma}-{gamma}-particle coincidences and 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. (author)
Tautin, J.
1995-01-01
Mr. Tautin reported on the seemingly everchanging structure of biological science units within the Interior Department. Current Congressional proposals would either change the name of the Bird Banding Lab's parent agency or make it part of the Geological Survey. The current Congress has not looked favorably on science budgets within the Interior Department, and the Banding Lab's budget is being squeezed ever tighter.
Long Lake banding project, 1965
US Fish and Wildlife Service, Department of the Interior — This report summarizes the results of a banding project on Long Lake in 1965. The dates at the banding site were July 27th through August 8th. As in the past, the...
Allsup, Randall Everett
2012-01-01
This article provides a theoretical framework through which to reimagine and revitalize contemporary music education practices, using the large ensemble paradigm called "band" as the primary unit of analysis. Literature suggests that band places too much emphasis on teacher control and external measures of validation. Critics propose replacing…
Thermal neutron scattering law calculations using ab initio molecular dynamics
Wormald, Jonathan; Hawari, Ayman I.
2017-09-01
In recent years, methods for the calculation of the thermal scattering law (i.e. S(α,β), where α and β are dimensionless momentum and energy transfer variables, respectively) were developed based on ab initio lattice dynamics (AILD) and/or classical molecular dynamics (CMD). While these methods are now mature and efficient, further advancement in the application of such atomistic techniques is possible using ab initio molecular dynamics (AIMD) methods. In this case, temperature effects are inherently included in the calculation, e.g. phonon density of states (DOS), while using ab initio force fields that eliminate the need for parameterized semi-empirical force fields. In this work, AIMD simulations were performed to predict the phonon spectra as a function of temperature for beryllium and graphite, which are representative nuclear reactor moderator and reflector materials. Subsequently, the calculated phonon spectra were utilized to predict S(α,β) using the LEAPR module of the NJOY code. The AIMD models of beryllium and graphite were 5 × 5 × 5 crystal unit cells (250 atoms and 500 atoms respectively). Electronic structure calculations for the prediction of Hellman-Feynman forces were performed using density functional theory with a GGA exchange correlation functional and corresponding core electron pseudopotentials. AIMD simulations of 1000-10,000 time-steps were performed with the canonical ensemble (NVT thermostat) for several temperatures between 300 K and 900 K. The phonon DOS were calculated as the power spectrum of the AIMD predicted velocity autocorrelation functions. The resulting AIMD phonon DOS and corresponding inelastic thermal neutron scattering cross sections at 300 K, where anharmonic effects are expected to be small, were found to be in reasonable agreement with the results generated using traditional AILD. This illustrated the validity of the AIMD approach. However, since the impact of the temperature on the phonon DOS (e.g. broadening of
Effect of hydrogenation on the band gap of graphene nano-flakes
Energy Technology Data Exchange (ETDEWEB)
Tachikawa, Hiroto, E-mail: hiroto@eng.hokudai.ac.jp; Iyama, Tetsuji; Kawabata, Hiroshi
2014-03-03
The effects of hydrogenation on the band gap of graphene have been investigated by means of density functional theory method. It is generally considered that the band gap increases with increasing coverage of hydrogen atom on the graphene. However, the present study shows that the band gap decreases first with increasing hydrogen coverage and reaches the lowest value at finite coverage (γ = 0.3). Next, the band gap increases to that of insulator with coverage from 0.3 to 1.0. This specific feature of the band gap is reasonably explained by broken symmetry model and the decrease of pi-conjugation. The electronic states of hydrogenated graphene are discussed. - Highlights: • Density functional theory calculations were carried out for hydrogen on graphene • Effects of hydrogenation on the band gap of graphene were examined. • The band gap showed a minimum at a finite coverage. • Mechanism of specific band gap feature was discussed.
Cluster rotational bands in 11B
Directory of Open Access Journals (Sweden)
Danilov A.N.
2016-01-01
Full Text Available Differential cross-sections of 11B+α inelastic scattering at E(α =65 MeV leading to most of the known 11B states at excitation energies up to 14 MeV were measured [1]. The data analysis was done using Modified diffraction model (MDM [2] allowing determining radii of excited states. Radii of the states with excitation energies less than ∼ 7 MeV coincide with the radius of the ground state with an accuracy not less than 0.1 - 0.15 fm. This result is consistent with traditional view on shell structure of low-lying states in 11B. Most of the observed high-energy excited states are distributed among four rotational bands. Moments of inertia of band states are close to the moment of inertia of the Hoyle state of 12C. The calculated radii, related to these bands, are 0.7 - 1.0 fm larger than the radius of the ground state, and are close to the Hoyle state radius. These results are in agreement with existing predictions about various cluster structure of 11B at high excitation energies.
Band gap anomaly and topological properties in lead chalcogenides
Simin, Nie; Xiao, Yan Xu; Gang, Xu; Zhong, Fang
2016-03-01
Band gap anomaly is a well-known issue in lead chalcogenides PbX (X = S, Se, Te, Po). Combining ab initio calculations and tight-binding (TB) method, we have studied the band evolution in PbX, and found that the band gap anomaly in PbTe is mainly related to the high on-site energy of Te 5s orbital and the large s-p hopping originated from the irregular extended distribution of Te 5s electrons. Furthermore, our calculations show that PbPo is an indirect band gap (6.5 meV) semiconductor with band inversion at L point, which clearly indicates that PbPo is a topological crystalline insulator (TCI). The calculated mirror Chern number and surface states double confirm this conclusion. Project supported by the National Natural Science Foundation of China (Grant No. 11204359), the National Basic Research Program of China (Grant No. 2013CB921700), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020100).
Spin susceptibility of Anderson impurities in arbitrary conduction bands
Fang, Tie-Feng; Tong, Ning-Hua; Cao, Zhan; Sun, Qing-Feng; Luo, Hong-Gang
2015-10-01
Spin susceptibility of Anderson impurities is a key quantity in understanding the physics of Kondo screening. Traditional numerical renormalization group (NRG) calculation of the impurity contribution χimp to susceptibility, defined originally by Wilson in a flat wide band, has been generalized before to structured conduction bands. The results brought about non-Fermi-liquid and diamagnetic Kondo behaviors in χimp, even when the bands are not gapped at the Fermi energy. Here, we use the full density-matrix (FDM) NRG to present high-quality data for the local susceptibility χloc and to compare them with χimp obtained by the traditional NRG. Our results indicate that those exotic behaviors observed in χimp are unphysical. Instead, the low-energy excitations of the impurity in arbitrary bands only without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We also demonstrate that unlike the traditional NRG yielding χloc less accurate than χimp, the FDM method allows a high-precision dynamical calculation of χloc at much reduced computational cost, with an accuracy at least one order higher than χimp. Moreover, artifacts in the FDM algorithm to χimp and origins of the spurious non-Fermi-liquid and diamagnetic features are clarified. Our work provides an efficient high-precision algorithm to calculate the spin susceptibility of impurity for arbitrary structured bands, while negating the applicability of Wilson's definition to such cases.
Wang, Mingliang; Wong, Chung F
2006-04-13
We have combined ultrasoft pseudopotential density functional theory utilizing plane wave basis with a Poisson-Boltzmann/solvent-accessible surface area (PB/SA) model to calculate the solvation free energy of small neutral organic compounds in water. The solute charge density obtained from density functional theory was directly used in solving the Poisson-Boltzmann equation to obtain the reaction field. The polarized electronic wave function of the solute in the solvent was solved by including the reaction field in the density functional Hamiltonian. The quantum mechanical and Poisson-Boltzmann equations were solved self-consistently until the charge density and reaction field converged. Using the solute charge density directly instead of a point-charge representation permitted asymmetric distortion and spreading out of the electron cloud. Because the electron density could leave the van der Waals surface to penetrate into the high-dielectric solvent, the reaction field generated by this density was generally smaller than that obtained by using the point-charge representation. In applying this model to calculate the solvation free energy of 31 small neutral organic molecules spanning a range of 25 kcal/mol, we obtained a root-mean-square error of only 1.3 kcal/mol if we allowed one adjustable parameter to shift the calculated solvation free energy.
First principles calculation of thermodynamic properties of NaAlSi ternary
Qin, Jining; Lu, Weijie; Zhang, Di; Fan, Tongxiang
2012-01-01
PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.
Calculation of optical constants and related quantities from optical to x-ray frequencies
Energy Technology Data Exchange (ETDEWEB)
Rehr, J J; Kas, J J [Department of Physics, University of Washington, Seattle, WA 98195 (United States); Prange, M P, E-mail: jjr@phys.washington.ed [Materials Science and Technology Division, ORNL, Oak Ridge, TN 37831 (United States)
2009-11-15
We discuss an efficient approach for calculations of optical to x-ray response based on a spectral function formalism which is implemented in an extension to the real-space Green's function code FEFF. This formalism avoids the need to compute wave-functions explicitly, and is applicable to arbitrary, aperiodic systems. Starting from the complex dielectric constant, the approach gives a number of linear optical constants, including the complex index of refraction the photoabsorption coefficient and energy-loss spectra over a very broad spectral range. These results provide a theoretical complement to standard tables and are useful in a variety of applications including ab initio calculations self-energy shifts, inelastic losses, mean-free paths, and stopping powers. For example, a many-pole self-energy model based on these results makes possible improved, parameter free calculations of various photon- and electron-spectra. The method is compared with experiment and with a pseudopotential-planewave Bethe-Salpeter Equation method.
Band-notched ultrawide band antenna loaded with ferrite slab
Wang, Hao; Zong, Weihua; Sun, Nian X.; Lin, Hwaider; Li, Shandong
2017-05-01
In this paper, a novel technique to design a band-notched UWB antenna by using Yttrium Iron Garnet (YIG) ferrite is proposed. A printed slot UWB antenna with size of 21mm×26 mm×0.8 mm is adopted as a basic antenna. A piece of ferrite slab with size of 5 mm×10 mm×2 mm is attached on the feeding layer of the antenna to achieve band-notched characteristics. The measured -10 dB bandwidth of the antenna without ferrite slab is 2.91-10.98 GHz. With loading of ferrite slab, the bandwidth turns to 2.73-5.12 and 5.87-10.78 GHz. A band notch of 5.12- 5.87 GHz is achieved to filter WLAN 5 GHz (5.15-5.825 GHz) band. The proposed technique has virtue of easy fabrication and keeping antenna miniaturization.
Model Development for MODIS Thermal Band Electronic Crosstalk
Chang, Tiejun; Wu, Aisheng; Geng, Xu; Li, Yonghonh; Brinkman, Jake; Keller, Graziela; Xiong, Xiaoxiong
2016-01-01
MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands. Among them, 16 thermal emissive bands covering a wavelength range from 3.8 to 14.4 m. After 16 years on-orbit operation, the electronic crosstalk of a few Terra MODIS thermal emissive bands developed substantial issues that cause biases in the EV brightness temperature measurements and surface feature contamination. The crosstalk effects on band 27 with center wavelength at 6.7 m and band 29 at 8.5 m increased significantly in recent years, affecting downstream products such as water vapor and cloud mask. The crosstalk effect is evident in the near-monthly scheduled lunar measurements, from which the crosstalk coefficients can be derived. The development of an alternative approach is very helpful for independent verification.In this work, a physical model was developed to assess the crosstalk impact on calibration as well as in Earth view brightness temperature retrieval. This model was applied to Terra MODIS band 29 empirically to correct the Earth brightness temperature measurements. In the model development, the detectors nonlinear response is considered. The impact of the electronic crosstalk is assessed in two steps. The first step consists of determining the impact on calibration using the on-board blackbody (BB). Due to the detectors nonlinear response and large background signal, both linear and nonlinear coefficients are affected by the crosstalk from sending bands. The second step is to calculate the effects on the Earth view brightness temperature retrieval. The effects include those from affected calibration coefficients and the contamination of Earth view measurements. This model links the measurement bias with crosstalk coefficients, detector non-linearity, and the ratio of Earth measurements between the sending and receiving bands. The correction of the electronic cross talk can be implemented empirically from the processed bias at different brightness temperature. The implementation
Comparison of electron bands of hexagonal and cubic diamond
Salehpour, M. R.; Satpathy, S.
1990-02-01
Using the local-density-theory and the linear-muffin-tin-orbitals method, we calculate the electron band structures of hexagonal (lonsdaleite) and cubic diamond. Even though the arrangement of atoms is very similar between the two crystal structures, we find significant differences in the electron bands, especially in the conduction bands. In particular, including estimated corrections on top of the local-density results, we find the lowest theoretical gap of hexagonal diamond to be 4.5 eV, i.e., a remarkable 1.1-eV drop as compared to that of cubic diamond. The lowest gap in the hexagonal structure is still indirect as in the cubic structure, but the gap is now from Γ to K. The reduction of the band gap should be observable in optical-absorption or reflectivity experiments.
Formal Verification of Air Traffic Conflict Prevention Bands Algorithms
Narkawicz, Anthony J.; Munoz, Cesar A.; Dowek, Gilles
2010-01-01
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.
The effect of the band edges on the Seebeck coefficient.
Sonntag, Joachim
2010-06-16
The classical thermopower formulae generally applied for the calculation of the Seebeck coefficient S are argued to be incomplete. S can be separated into two different contributions, a scattering term, S(0), and a thermodynamic term, ΔS, representing the additional change of the electrochemical potential μ with temperature T caused by 'non-scattering' effects, for instance, the band edge shift with T. On the basis of this separation into S(0) and ΔS, it is shown that shifts of the band edges with T lead to an additional contribution to the classical thermopower formulae. This separation provides the basis for an interpretation of positive thermopowers measured for many metals. Positive thermopower is expected if the energy of the conduction band edge increases with T and if this effect overcompensates for the influence of the energy dependent conductivity, σ(E). Using experimental thermopower data, the band edge shifts are determined for a series of liquid normal metals.
Strain sensitivity of band gaps of Sn-containing semiconductors
DEFF Research Database (Denmark)
Li, Hong; Castelli, Ivano Eligio; Thygesen, Kristian Sommer
2015-01-01
Tuning of band gaps of semiconductors is a way to optimize materials for applications within photovoltaics or as photocatalysts. One way to achieve this is through applying strain to the materials. We investigate the effect of strain on a range of Sn-containing semiconductors using density...... functional theory and many-body perturbation theory calculations. We find that the band gaps of bulk Sn oxides with SnO6 octahedra are highly sensitive to volumetric strain. By applying a small isotropic strain of 2% (-2%), a decrease (increase) of band gaps as large as 0.8 to 1.0 eV are obtained. We...... attribute the ultrahigh strain sensitivity to the pure Sn s-state character of the conduction-band edges. Other Sn-containing compounds may show both increasing and decreasing gaps under tensile strain and we show that the behavior can be understood by analyzing the role of the Sn s states in both...
Williams, David E.
1981-01-01
This short quiz for teachers is intended to help them to brush up on their calculator operating skills and to prepare for the types of questions their students will ask about calculator idiosyncracies. (SJL)
Quantum confinement induced shift in energy band edges and band gap of a spherical quantum dot
Borah, P.; Siboh, D.; Kalita, P. K.; Sarma, J. K.; Nath, N. M.
2018-02-01
We have proposed and validated an ansatz as effective potential for confining electron/hole within a spherical quantum dot in order to understand quantum confinement and its consequences associated with energy states and band gap of Spherical Quantum Dots. Within effective mass approximation formalism, we have considered an ansatz incorporating a conjoined harmonic oscillator and Coulomb interaction as the effective potential for confining an electron or a hole within a spherical quantum dot and by employing appropriate boundary conditions, we have calculated the shifts in energy of minimum of conduction band (CBM) and maximum of valence band (VBM) with respect to size of spherical quantum dots. We have also determined the quantum confinement induced shift in band gap energy of spherical quantum dots. In order to verify our theoretical predictions as well as to validate our ansatz, we have performed phenomenological analysis in comparison with available experimental results for quantum dots made of CdSe and observe a very good agreement in this regard. Our experimentally consistent theoretical results also help in mapping the probability density of electron and hole inside a spherical quantum dot. The consistency of our results with available experimental data signifies the capability as well as applicability of the ansatz for the effective confining potential to have reasonable information in the study of real nano-structured spherical systems.
Bahr, Patrick; Hutton, Graham
2015-01-01
In this article we present a new approach to the problem of calculating compilers. In particular, we develop a simple but general technique that allows us to derive correct compilers from high- level semantics by systematic calculation, with all details of the implementation of the compilers falling naturally out of the calculation process. Our approach is based upon the use of standard equational reasoning techniques, and has been applied to calculate compilers for a wide range of language f...
Atmospheric solar heating rate in the water vapor bands
Chou, Ming-Dah
1986-01-01
The total absorption of solar radiation by water vapor in clear atmospheres is parameterized as a simple function of the scaled water vapor amount. For applications to cloudy and hazy atmospheres, the flux-weighted k-distribution functions are computed for individual absorption bands and for the total near-infrared region. The parameterization is based upon monochromatic calculations and follows essentially the scaling approximation of Chou and Arking, but the effect of temperature variation with height is taken into account in order to enhance the accuracy. Furthermore, the spectral range is extended to cover the two weak bands centered at 0.72 and 0.82 micron. Comparisons with monochromatic calculations show that the atmospheric heating rate and the surface radiation can be accurately computed from the parameterization. Comparisons are also made with other parameterizations. It is found that the absorption of solar radiation can be computed reasonably well using the Goody band model and the Curtis-Godson approximation.
Harmonic generation in the generalized Sagdeev pseudopotential
Akbari-Moghanjoughi, M.
2017-09-01
In this paper, we study the nonlinear harmonic generation effect in different oscillator models. For weakly nonlinear systems, we use the generalized forced Korteweg de Vries Burgers (KdVB) and modified KdVB (mKdVB) models in order to classify three fundamentally different harmonic structures in a nonlinear dynamical system. The first is called the internal harmonic structure which exists due to the self oscillation of the system in the absence of dissipation effect and is shown to follow either relations of nf or (2n - 1)f depending on the symmetry of oscillator potential in which n is an integer number and f is the fundamental frequency which is exactly obtained for the Helmholtz oscillator. The second structure is the resonant harmonics which appears in the presence of damping and follows the harmonic structure nf0 in which f0 is the linear resonance frequency. Finally, the last harmonic structure appears in the presence of dissipation and external periodic forcing effects which we call the external harmonic pattern. It is shown that the external harmonic pattern, in which f1 is the driving frequency, always follows the nf1 rule regardless of the potential symmetry. We then extend our analysis to study the harmonic generation in the fully nonlinear generalized Sagdeev potential for real plasmas with isothermal and adiabatic ion fluids and investigate the effects of different plasma parameters such as the fractional ion temperature and normalized ion acoustic speed on all three kinds of harmonic generation.
Autistic Savant Calendar Calculators.
Patti, Paul J.
This study identified 10 savants with developmental disabilities and an exceptional ability to calculate calendar dates. These "calendar calculators" were asked to demonstrate their abilities, and their strategies were analyzed. The study found that the ability to calculate dates into the past or future varied widely among these…
Threlfall, John
2002-01-01
Suggests that strategy choice is a misleading characterization of efficient mental calculation and that teaching mental calculation methods as a whole is not conducive to flexibility. Proposes an alternative in which calculation is thought of as an interaction between noticing and knowledge. Presents an associated teaching approach to promote…
Effect of conduction band nonparabolicity on the optical properties in ...
Indian Academy of Sciences (India)
S Panda and B K Panda coefficients have been calculated in the QWs under a DC electric field which is per- pendicular to the growth direction of the QW. The electric field not only influences the intersub-band transition energies but also shifts the wave functions in the direction of the field. As a result of this, the strength of ...
Band gap bowing in quaternary nitride semiconducting alloys
DEFF Research Database (Denmark)
Gorczyka, Isabela; Suski, T.; Christensen, Niels Egede
2011-01-01
Structural properties of InxGayAl1−x−yN alloys are derived from total-energy minimization within the local-density approximation (LDA). The electronic properties are studied by band structure calculations including a semiempirical correction for the “LDA gap error.” The effects of varying...
Conductive Bands Diminish Electrostatic Discharges
Leung, Philip L.; Whittlesey, Albert
1992-01-01
Electrostatic discharges on surfaces covered with electrically insulating paints reduced by connecting edges of painted surfaces to electrical grounds with band of conductive material. Prevents charge build up on paint which eventually arcs to conductive surface, damaging structures and equipment.
The effective air absorption coefficient for predicting reverberation time in full octave bands.
Wenmaekers, R H C; Hak, C C J M; Hornikx, M C J
2014-12-01
A substantial amount of research has been devoted to producing a calculation model for air absorption for pure tones. However, most statistical and geometrical room acoustic prediction models calculate the reverberation time in full octave bands in accordance with ISO 3382-1 (International Organization for Standardization, 2009). So far, the available methods that allow calculation of air absorption in octave bands have not been investigated for room acoustic applications. In this paper, the effect of air absorption on octave band reverberation time calculations is investigated based on calculations. It is found that the approximation method, as described in the standard ANSI S1.26 (American National Standards Institute, 1995), fails to estimate accurate decay curves for full octave bands. In this paper, a method is used to calculate the energy decay curve in rooms based on a summation of pure tones within the band. From this decay curve, which is found to be slightly concave upwards, T20 and T30 can be determined. For different conditions, an effective intensity attenuation coefficient mB ;eff for the full octave bands has been calculated. This mB ;eff can be used for reverberation time calculations, if results are to be compared with T20 or T30 measurements. Also, guidelines are given for the air absorption correction of decay curves, measured in a scale model.
Energy Technology Data Exchange (ETDEWEB)
Freitas, F. L., E-mail: felipelopesfreitas@gmail.com; Marques, M.; Teles, L. K. [Grupo de Materiais Semicondutores e Nanotecnologia, Instituto Tecnológico de Aeronáutica, 12228-900 São José dos Campos, SP (Brazil)
2016-08-15
We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal Al{sub x}Ga{sub y}In{sub 1–x–y}N semiconductor alloys, employing a cluster expansion method to account for the inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
Directory of Open Access Journals (Sweden)
F. L. Freitas
2016-08-01
Full Text Available We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal AlxGayIn1–x–yN semiconductor alloys, employing a cluster expansion method to account for the inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
Unfolding the band structure of electronic and photonic materials
Maspero, Ross
In this thesis, we develop a generalised unfolding formalism to investigate the electronic and photonic properties of aperiodically-structured materials. We initially focus on GaAsBi alloys for electronic systems and Penrose-structured materials for photonic systems, aperiodic materials that cannot be easily studied using conventional band structure methods. We then extend our study to the supercell approach which facilitates an accurate modelling of the aperiodic structures at the price of obscuring essential physical information, due to a band folding effect. Then introducing a generalised unfolding algorithm, we return the supercell band structure to a traditional form that can again be used to analyse the electronic and photonic properties of the system. GaAsBi, which is a material with the potential to suppress the dominant loss mechanisms in telecommunications devices, was studied using the unfolded supercell band structure approach. We investigated the effect of bismuth on the properties of a host GaAs structure, including band movement, band broadening and effective mass. We validated our approach through a detailed comparison of both band movement and effective masses to the currently available experimental data. Then, we introduced a formalism for calculating the CHSH Auger recombination rates from our unfolded band structure, which will assist in determining the efficiency of the material. Quasicrystalline photonic materials built on the skeleton of Penrose lattices have proven to display photonic properties comparable to the ones found in photonic crystals, but with the added promise of increased isotropy. The photonic band structure of these materials is a prime target for the unfolding formalism because it allows a full exploration of the influence of the increased geometrical symmetry on their photonic characteristics. Furthermore, the network structure investigated demonstrated the existence of a sub-fundamental photonic band gap, a characteristic
Energy Technology Data Exchange (ETDEWEB)
Nagao, Yoshiharu [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment
1998-03-01
In material testing reactors like the JMTR (Japan Material Testing Reactor) of 50 MW in Japan Atomic Energy Research Institute, the neutron flux and neutron energy spectra of irradiated samples show complex distributions. It is necessary to assess the neutron flux and neutron energy spectra of an irradiation field by carrying out the nuclear calculation of the core for every operation cycle. In order to advance core calculation, in the JMTR, the application of MCNP to the assessment of core reactivity and neutron flux and spectra has been investigated. In this study, in order to reduce the time for calculation and variance, the comparison of the results of the calculations by the use of K code and fixed source and the use of Weight Window were investigated. As to the calculation method, the modeling of the total JMTR core, the conditions for calculation and the adopted variance reduction technique are explained. The results of calculation are shown. Significant difference was not observed in the results of neutron flux calculations according to the difference of the modeling of fuel region in the calculations by K code and fixed source. The method of assessing the results of neutron flux calculation is described. (K.I.)
Tuning the band gap in hybrid tin iodide perovskite semiconductors using structural templating.
Knutson, Jeremy L; Martin, James D; Mitzi, David B
2005-06-27
Structural distortions within the extensive family of organic/inorganic hybrid tin iodide perovskite semiconductors are correlated with their experimental exciton energies and calculated band gaps. The extent of the in- and out-of-plane angular distortion of the SnI4(2-) perovskite sheets is largely determined by the relative charge density and steric requirements of the organic cations. Variation of the in-plane Sn-I-Sn bond angle was demonstrated to have the greatest impact on the tuning of the band gap, and the equatorial Sn-I bond distances have a significant secondary influence. Extended Hückel tight-binding band calculations are employed to decipher the crystal orbital origins of the structural effects that fine-tune the band structure. The calculations suggest that it may be possible to tune the band gap by as much as 1 eV using the templating influence of the organic cation.
Electronic energy band parameters of CsCl evaluated on core Bloch states and plane waves
Energy Technology Data Exchange (ETDEWEB)
Syrotyuk, S.V. [Semiconductor Electronics Department, National University ' Lviv Polytechnic' , S. Bandera str. 12, Lviv 79013 (Ukraine); Chornodolskyy, Ya.M. [Physics Department, Ivan Franko National University of Lviv, Kyryla i Mefodiya str. 8, Lviv 79005 (Ukraine)], E-mail: chornodolsky@ukr.net; Stryganyuk, G.B. [HASYLAB at DESY, Notkestr. 85, Hamburg 22607 (Germany); Voloshinovskii, A.S. [Physics Department, Ivan Franko National University of Lviv, Kyryla i Mefodiya str. 8, Lviv 79005 (Ukraine); Rodnyi, P.A. [St. Petersburg State Polytechnical University, Polytekhnicheskaya 29, St. Petersburg 195251 (Russian Federation)
2007-04-15
Electronic energy bands of CsCl crystal have been calculated within the mixed basis approach with using the core Bloch states and plane waves. The calculated energy parameters of the crystal are in the satisfactory agreement with the experimental data obtained from the analysis of the core-valence luminescence spectra. The obtained results form a base for calculation of CVL spectra parameters.
Analysis of compressive failure of layered materials by kink band broadening
DEFF Research Database (Denmark)
Jensen, Henrik Myhre
1999-01-01
Failure by steady state kink band broadening in uni-directional fibre composites or layered materials is analysed. An incremental scheme for calculation of kink band broadening stresses and lock-up conditions in the band for arbitrary material behaviour is presented. The method is illustrated by ...... by material data which are representative for polymer matrix composites for which experimental work exists. (C) 1999 Elsevier Science Ltd. All rights reserved....
Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices
DEFF Research Database (Denmark)
Gorczyca, I.; Suski, T.; Christensen, Niels Egede
2012-01-01
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....
Multicolor emission from intermediate band semiconductor ZnO1-xSex
Welna, M.; Baranowski, M.; Linhart, W. M.; Kudrawiec, R.; Yu, K. M.; Mayer, M.; Walukiewicz, W.
2017-03-01
Photoluminescence and photomodulated reflectivity measurements of ZnOSe alloys are used to demonstrate a splitting of the valence band due to the band anticrossing interaction between localized Se states and the extended valence band states of the host ZnO matrix. A strong multiband emission associated with optical transitions from the conduction band to lower E- and upper E+ valence subbands has been observed at room temperature. The composition dependence of the optical transition energies is well explained by the electronic band structure calculated using the kp method combined with the band anticrossing model. The observation of the multiband emission is possible because of relatively long recombination lifetimes. Longer than 1 ns lifetimes for holes photoexcited to the lower valence subband offer a potential of using the alloy as an intermediate band semiconductor for solar power conversion applications.
Multiphase flow calculation software
Fincke, James R.
2003-04-15
Multiphase flow calculation software and computer-readable media carrying computer executable instructions for calculating liquid and gas phase mass flow rates of high void fraction multiphase flows. The multiphase flow calculation software employs various given, or experimentally determined, parameters in conjunction with a plurality of pressure differentials of a multiphase flow, preferably supplied by a differential pressure flowmeter or the like, to determine liquid and gas phase mass flow rates of the high void fraction multiphase flows. Embodiments of the multiphase flow calculation software are suitable for use in a variety of applications, including real-time management and control of an object system.
Radar Signature Calculation Facility
Federal Laboratory Consortium — FUNCTION: The calculation, analysis, and visualization of the spatially extended radar signatures of complex objects such as ships in a sea multipath environment and...
Waste Package Lifting Calculation
Energy Technology Data Exchange (ETDEWEB)
H. Marr
2000-05-11
The objective of this calculation is to evaluate the structural response of the waste package during the horizontal and vertical lifting operations in order to support the waste package lifting feature design. The scope of this calculation includes the evaluation of the 21 PWR UCF (pressurized water reactor uncanistered fuel) waste package, naval waste package, 5 DHLW/DOE SNF (defense high-level waste/Department of Energy spent nuclear fuel)--short waste package, and 44 BWR (boiling water reactor) UCF waste package. Procedure AP-3.12Q, Revision 0, ICN 0, calculations, is used to develop and document this calculation.
Electrical installation calculations advanced
Kitcher, Christopher
2013-01-01
All the essential calculations required for advanced electrical installation workThe Electrical Installation Calculations series has proved an invaluable reference for over forty years, for both apprentices and professional electrical installation engineers alike. The book provides a step-by-step guide to the successful application of electrical installation calculations required in day-to-day electrical engineering practiceA step-by-step guide to everyday calculations used on the job An essential aid to the City & Guilds certificates at Levels 2 and 3For apprentices and electrical installatio
Evapotranspiration Calculator Desktop Tool
The Evapotranspiration Calculator estimates evapotranspiration time series data for hydrological and water quality models for the Hydrologic Simulation Program - Fortran (HSPF) and the Stormwater Management Model (SWMM).
Electronics Environmental Benefits Calculator
U.S. Environmental Protection Agency — The Electronics Environmental Benefits Calculator (EEBC) was developed to assist organizations in estimating the environmental benefits of greening their purchase,...
Electrical installation calculations basic
Kitcher, Christopher
2013-01-01
All the essential calculations required for basic electrical installation workThe Electrical Installation Calculations series has proved an invaluable reference for over forty years, for both apprentices and professional electrical installation engineers alike. The book provides a step-by-step guide to the successful application of electrical installation calculations required in day-to-day electrical engineering practice. A step-by-step guide to everyday calculations used on the job An essential aid to the City & Guilds certificates at Levels 2 and 3Fo
Single-Band and Dual-Band Infrared Detectors
Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor); Soibel, Alexander (Inventor); Nguyen, Jean (Inventor); Khoshakhlagh, Arezou (Inventor)
2017-01-01
Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed.
Adhesives for fixed orthodontic bands.
Millett, Declan T; Glenny, Anne-Marie; Mattick, Rye Cr; Hickman, Joy; Mandall, Nicky A
2016-10-25
Orthodontic treatment involves using fixed or removable appliances (dental braces) to correct the positions of teeth. It has been shown that the quality of treatment result obtained with fixed appliances is much better than with removable appliances. Fixed appliances are, therefore, favoured by most orthodontists for treatment. The success of a fixed orthodontic appliance depends on the metal attachments (brackets and bands) being attached securely to the teeth so that they do not become loose during treatment. Brackets are usually attached to the front and side teeth, whereas bands (metal rings that go round the teeth) are more commonly used on the back teeth (molars). A number of adhesives are available to attach bands to teeth and it is important to understand which group of adhesives bond most reliably, as well as reducing or preventing dental decay during the treatment period. To evaluate the effectiveness of the adhesives used to attach bands to teeth during fixed appliance treatment, in terms of:(1) how often the bands come off during treatment; and(2) whether they protect the banded teeth against decay during fixed appliance treatment. The following electronic databases were searched: Cochrane Oral Health's Trials Register (searched 2 June 2016), Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 5) in the Cochrane Library (searched 2 June 2016), MEDLINE Ovid (1946 to 2 June 2016) and EMBASE Ovid (1980 to 2 June 2016). We searched ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases. Randomised and controlled clinical trials (RCTs and CCTs) (including split-mouth studies) of adhesives used to attach orthodontic bands to molar teeth were selected. Patients with full arch fixed orthodontic appliance(s) who had bands attached to molars were included. All review authors
The conduction bands of MgO, MgS and HfO2
Boer, P.K. de; Groot, R.A. de
1998-01-01
Electronic structure calculations for MgO, MgS and HfO2 are reported. It is shown that the conduction bands of MgO and MgS have predominantly anion character, contrary to the common picture of the conduction band being derived from cation states. In transition metal oxides, unoccupied anion states
Energy Technology Data Exchange (ETDEWEB)
Wyss, R. [Joint Inst. for Heavy-Ion Research, Oak Ridge, TN (United States). Holifield Heavy Ion Research Facility
1993-12-31
Rotational bands built on intruder configurations are discussed within the Cranked Shell Model. The experimental observed alignment pattern occurring in these bands cannot be accounted for by standard mean field calculations. The discrepancy between theory and experiment is traced back to the fact that the neutron-proton interaction is only partly and indirectly included in the standard mean field approach.
Broad-Band Spectral Indices Variability of BL Lacertae by Wavelet ...
Indian Academy of Sciences (India)
Abstract. BL Lacertae is one of the famous AGN that shows convincing evidence to support periodic variability. We compile R-band data and radio 22 GHz database from the available literature to build the light curves and to calculate broad-band spectral indices. This paper employs the wavelet periodic estimation method.
Chemical calculations and chemicals that might calculate
Barnett, Michael P.
I summarize some applications of symbolic calculation to the evaluation of molecular integrals over Slater orbitals, and discuss some spin-offs of this work that have wider potential. These include the exploration of the mechanized use of analogy. I explain the methods that I use to do this, in relation to mathematical proofs and to modeling step by step processes such as organic syntheses and NMR pulse sequences. Another spin-off relates to biological information processing. Some challenges and opportunities in the information infrastructure of interdisciplinary research are discussed.
Configuration-dependent bands in {sup 169}Re
Energy Technology Data Exchange (ETDEWEB)
Zhou, X.H.; Zhang, Y.H.; Zheng, Y.; Xu, Y.B. [Institute of Modern Physics, Chinese Academy of Sciences, 730000, Lanzhou (China); Oshima, M.; Toh, Y.; Koizumi, M.; Osa, A.; Hayakawa, T.; Hatsukawa, Y.; Shizuma, T. [Japan Atomic Energy Research Institute, 319-1195, Ibaraki, Tokai (Japan); Xu, F.R. [Department of Technical Physics and MOE Key Laboratory, Peking University, 100871, Beijing (China); Sugawara, M. [Chiba Institute of Technology, 275-0023, Chiba, Narashino (Japan)
2004-01-01
High-spin states in {sup 169}Re were studied and resulted in the identification of a strongly coupled band based on the 9/2{sup -}[514] Nilsson state and a decoupled band built on the h{sub 9/2} 1/2{sup -}[541] intruder proton orbit. The cranked-shell-model calculations present configuration-dependent deformations that can explain the different band crossing frequencies. The 9/2{sup -}[514] band in {sup 169}Re shows the largest signature splitting at low spin among the known odd-mass Re isotopes. After the alignment of a pair of i{sub 13/2} neutrons, the phase of the splitting is inverted with a significantly reduced amplitude. For the 9/2{sup -}[514] bands in light odd-A Re isotopes, the signature splitting of the Routhians and its relation with the signature dependence of M1 transition matrix elements are investigated in connection with the deviation of nuclear shape from axial symmetry, suggesting an appreciable negative {gamma} deformation for the very neutron-deficient odd-A Re isotopes. Additionally, a three-quasiparticle band was observed and assigned to be built likely on the {pi}9/2{sup -}[514] x AE configuration. (orig.)
Directory of Open Access Journals (Sweden)
P. Kutin
2006-04-01
Full Text Available This paper deals with design and realization of a PLL synthesizer for the microwave XÃ¢ÂˆÂ’band. The synthesizer is intended for use as a local oscillator in a KÃ¢ÂˆÂ’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.
[Understanding dosage calculations].
Benlahouès, Daniel
2016-01-01
The calculation of dosages in paediatrics is the concern of the whole medical and paramedical team. This activity must generate a minimum of risks in order to prevent care-related adverse events. In this context, the calculation of dosages is a practice which must be understood by everyone. Copyright © 2016 Elsevier Masson SAS. All rights reserved.
High-spin rotational bands in 123I
Singh, Purnima; Singh, A. K.; Wilson, A. N.; Ragnarsson, I.; Hübel, H.; Bürger, A.; Carpenter, M. P.; Chmel, S.; Fallon, P.; Hagemann, G. B.; Herskind, B.; Ha, Hoa; Janssens, R. V. F.; Juhász, K.; Kardan, A.; Khoo, T. L.; Kondev, G.; Korichi, A.; Lauritsen, T.; Nyakó, B. M.; Rogers, J.; Sletten, G.; Timár, J.; Zhu, S.
2012-12-01
High-spin states in 123I were populated in the reaction 80Se(48Ca,p4n)123I at a beam energy of 207 MeV and γ-ray coincidence events were measured using the Gammasphere spectrometer. Three weakly populated, high-spin rotational bands have been discovered with characteristics similar to those of the long collective bands recently observed in other nuclei of this mass region. Configuration assignments are proposed based on calculations within the framework of the cranked Nilsson-Strutinsky approach.
X-Band CubeSat Communication System Demonstration
Altunc, Serhat; Kegege, Obadiah; Bundick, Steve; Shaw, Harry; Schaire, Scott; Bussey, George; Crum, Gary; Burke, Jacob C.; Palo, Scott; O'Conor, Darren
2015-01-01
Today's CubeSats mostly operate their communications at UHF- and S-band frequencies. UHF band is presently crowded, thus downlink communications are at lower data rates due to bandwidth limitations and are unreliable due to interference. This research presents an end-to-end robust, innovative, compact, efficient and low cost S-band uplink and X-band downlink CubeSat communication system demonstration between a balloon and a Near Earth Network (NEN) ground system. Since communication systems serve as umbilical cords for space missions, demonstration of this X-band communication system is critical for successfully supporting current and future CubeSat communication needs. This research has three main objectives. The first objective is to design, simulate, and test a CubeSat S- and X-band communication system. Satellite Tool Kit (STK) dynamic link budget calculations and HFSS Simulations and modeling results have been used to trade the merit of various designs for small satellite applications. S- and X-band antennas have been tested in the compact antenna test range at Goddard Space Flight Center (GSFC) to gather radiation pattern data. The second objective is simulate and test a CubeSat compatible X-band communication system at 12.5Mbps including S-band antennas, X-band antennas, Laboratory for Atmospheric and Space Physics (LASP) /GSFC transmitter and an S-band receiver from TRL-5 to TRL-8 by the end of this effort. Different X-band communication system components (antennas, diplexers, etc.) from GSFC, other NASA centers, universities, and private companies have been investigated and traded, and a complete component list for the communication system baseline has been developed by performing analytical and numerical analysis. This objective also includes running simulations and performing trades between different X-band antenna systems to optimize communication system performance. The final objective is to perform an end-to-end X-band CubeSat communication system
Understanding the difference in cohesive energies between alpha and beta tin in DFT calculations
Directory of Open Access Journals (Sweden)
Fleur Legrain
2016-04-01
Full Text Available The transition temperature between the low-temperature alpha phase of tin to beta tin is close to the room temperature (Tαβ = 130C, and the difference in cohesive energy of the two phases at 0 K of about ΔEcoh =0.02 eV/atom is at the limit of the accuracy of DFT (density functional theory with available exchange-correlation functionals. It is however critically important to model the relative phase energies correctly for any reasonable description of phenomena and technologies involving these phases, for example, the performance of tin electrodes in electrochemical batteries. Here, we show that several commonly used and converged DFT setups using the most practical and widely used PBE functional result in ΔEcoh ≈0.04 eV/atom, with different types of basis sets and with different models of core electrons (all-electron or pseudopotentials of different types, which leads to a significant overestimation of Tαβ. We show that this is due to the errors in relative positions of s and p –like bands, which, combined with different populations of these bands in α and β Sn, leads to overstabilization of alpha tin. We show that this error can be effectively corrected by applying a Hubbard +U correction to s –like states, whereby correct cohesive energies of both α and β Sn can be obtained with the same computational scheme. We quantify for the first time the effects of anharmonicity on ΔEcoh and find that it is negligible.
Zhu, Zhen; Xiao, Jiamin; Sun, Haibin; Hu, Yue; Cao, Ronggen; Wang, Yin; Zhao, Li; Zhuang, Jun
2015-09-07
We used the coherent potential approximation to investigate the band structures of group-IV semiconductor alloys, including Si(x)Ge(1-x), Ge(1-y)Sn(y) and Si(x)Ge(1-x-y)Sn(y). The calculations for Si(x)Ge(1-x) prove the reliability and accuracy of the method we used. For Ge(1-y)Sn(y), the direct band gap optical bowing parameter we obtained is 2.37 eV and the indirect-direct band gap transition point is at y = 0.067, both consistent with the existing experimental data. For Si(x)Ge(1-x-y)Sn(y), with the increase of the Si concentration, the compositional dependency of the band gap becomes complex. An indirect-direct band gap transition is found in Si(x)Ge(1-x-y)Sn(y) in the range of 0 band gaps larger than 0.8 eV at room temperature.
Band gap opening in graphene: a short theoretical study
Sahu, Sivabrata; Rout, G. C.
2017-03-01
Graphene, being a gapless semiconductor, cannot be used in pristine form for nano-electronic applications. Therefore, it is essential to generate a finite gap in the energy dispersion at Dirac point. We present here the tight-binding model Hamiltonian taking into account of various interactions for tuning band gap in graphene. The model Hamiltonian describes the hopping of the π-electrons up to third nearest-neighbours, substrate effects, Coulomb interaction at two sub-lattices, electron-phonon interaction in graphene-on-substrates and high phonon frequency vibrations, besides the bi-layer graphene. We have solved the Hamiltonian using Zubarev's double time single particle Green's function technique. The quasi-particle energies, electron band dispersions, the expression for effective band gap and the density of states (DOS) are calculated numerically. The results are discussed by varying different model parameters of the system. It is observed that the electron DOS and band dispersion exhibit linear energy dependence near Dirac point for nearest-neighbour hopping integral. However, the second and third nearest-neighbour hoppings provide asymmetry in DOS. The band dispersions exhibit wider band gaps with stronger substrate effect. The modified gap in graphene-on-substrate attains its maximum value for Coulomb interaction energy U_{{C}} = 1.7 t1. The critical Coulomb interaction is enhanced to U_{{C}} = 2.5 t1 to produce maximum band gap in the presence of electron-phonon interaction and phonon vibration. The bi-layer graphene exhibits Mexican hat type band gap near Dirac point for transverse gating potential. The other conclusions for the present work are described in the text.
DEFF Research Database (Denmark)
Andersen, O. Krogh
1975-01-01
-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...
Microstrip microwave band gap structures
Indian Academy of Sciences (India)
band characteristics. The controlling of the electromagnetic radiation was possible by employing two frequency selective switches. Use of such MBG structures for the non-destructive evaluation of material properties was demonstrated by replacing the substrate with silicon. Pramana – J. Phys., Vol. 70, No. 4, April 2008. 745 ...
Metaphyseal bands in osteogenesis imperfecta
Directory of Open Access Journals (Sweden)
Suresh S
2010-01-01
Full Text Available An increasing number of patients with osteogenesis imperfecta are undergoing pamidronate therapy to prevent the incidence of fragility fractures. The authors herein report a child aged 3 years who received five cycles of pamidronate, resulting in metaphyseal bands, known as "zebra lines."
Symptomatic mesodiverticular bands in children
African Journals Online (AJOL)
Pediatr Surg 14:21–23 c 2018 Annals of Pediatric. Surgery. Annals of Pediatric Surgery 2018, 14:21–23. Keywords: internal hernia, laparoscopy, Meckel's diverticulum, mesodiverticular band, small bowel obstruction. aS.C. di Clinica Chirurgica Pediatrica, University of Perugia, S. Maria della. Misericordia Hospital, Perugia ...
CHRISTIAN PRACTICAL PRAYING BAND (ACPPB)
African Journals Online (AJOL)
answers or solutions, religious people need charismatic persons to interpret the divine mind. Hence, contemporary ..... if the person is found worthy, the person is sent back to his/her branch as a recognized member of the band of ... Prophetic work in the ACPPB makes it a prayer house with a difference. Apart from Madam.
Analysis and enhancement of flexural wave stop bands in 2D periodic plates
Energy Technology Data Exchange (ETDEWEB)
Song, Yubao [Laboratory of Science and Technology on Integrated Logistics Support, National University of Defense Technology, 410073 Changsha (China); The Marcus Wallenberg Laboratory for Sound and Vibration Research, KTH – The Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Feng, Leping [The Marcus Wallenberg Laboratory for Sound and Vibration Research, KTH – The Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Wen, Jihong, E-mail: wenjihong_nudt1@vip.sina.com [Laboratory of Science and Technology on Integrated Logistics Support, National University of Defense Technology, 410073 Changsha (China); Yu, Dianlong; Wen, Xisen [Laboratory of Science and Technology on Integrated Logistics Support, National University of Defense Technology, 410073 Changsha (China)
2015-07-17
The band structure and enhancement of flexural wave stop bands in a 2D periodic plate are investigated. A unified method for analysing and designing the stop band of the plates with various attached structures is proposed. The effect of attached structures is considered based on their equivalent parameters (added equivalent mass and equivalent moment of inertia). The influences of the equivalent parameters on the band structures are studied. Three cases are considered: adding pure equivalent mass, pure equivalent moment of inertia and the combination of these two. The stop bands are enhanced via the multi interaction between the host plate and the attached structure. The enhancement pattern is determined, and several ways to obtain a wider combined stop band are presented. The frequency response functions of corresponding finite periodic plates are calculated to verify the stop bands and their enhancement in a number of typical cases. - Highlights: • A unified method for studying the stop band of the plates with various simplified attached structures is proposed. • The enhancement of flexural wave stop bands in a 2D phononic plate is investigated. • The stop bands are widened via multi interaction between the host plate and the attached structure. • The enhancement pattern is determined and several ways to get a wider stop band are presented.
DEFF Research Database (Denmark)
Frederiksen, Morten
2014-01-01
Williamson’s characterisation of calculativeness as inimical to trust contradicts most sociological trust research. However, a similar argument is found within trust phenomenology. This paper re-investigates Williamson’s argument from the perspective of Løgstrup’s phenomenological theory of trust....... Contrary to Williamson, however, Løgstrup’s contention is that trust, not calculativeness, is the default attitude and only when suspicion is awoken does trust falter. The paper argues that while Williamson’s distinction between calculativeness and trust is supported by phenomenology, the analysis needs...... to take actual subjective experience into consideration. It points out that, first, Løgstrup places trust alongside calculativeness as a different mode of engaging in social interaction, rather conceiving of trust as a state or the outcome of a decision-making process. Secondly, the analysis must take...
Unit Cost Compendium Calculations
U.S. Environmental Protection Agency — The Unit Cost Compendium (UCC) Calculations raw data set was designed to provide for greater accuracy and consistency in the use of unit costs across the USEPA...
Magnetic Field Grid Calculator
National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Properties Calculator will computes the estimated values of Earth's magnetic field(declination, inclination, vertical component, northerly...
National Stormwater Calculator
EPA’s National Stormwater Calculator (SWC) is a desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States (including Puerto Rico).
Non-Hermiticity Induced Flat Band
Ramezani, Hamidreza
2017-01-01
We demonstrate the emergence of an entire flat band embedded in dispersive bands at the exceptional point of a PT symmetric photonic lattice. For this to occur, the gain and loss parameter effectively alters the size of the partial flat band windows and band gap of the photonic lattice simultaneously. The mode associated with the entire flat band is robust against changes in the system size and survives even at the edge of the lattice. Our proposal offers a route for controllable localization...
Detailed characterization of complex banding in air-cooled bainitic steels
Directory of Open Access Journals (Sweden)
Morales-Rivas L.
2015-01-01
Full Text Available The presence of banding in a hot-rolled air-cooled bainitic steel has been thoroughly characterized. The banded microstructure was observed due to distinctive sensitivities to the etching agent. Microstructural and crystallographic studies by means of Scanning Electron Microscopy and Electron Backscatter Diffraction did not reveal any substantial differences between bands and matrix. However, solute segregation of some alloying elements was detected by Wavelength- Dispersive Spectroscopy, being found that bands are enriched in Cr, Mo and Si and depleted in Mn. Finally, a set of theoretical calculations suggested that the solidification mode is responsible for such unusual partitioning behavior, which is beneficial in terms of the bainitic transformation.
Chiral geometry of higher excited bands in triaxial nuclei with particle-hole configuration
Chen, Q. B.; Yao, J. M.; Zhang, S. Q.; Qi, B.
2010-12-01
The lowest six rotational bands have been studied in the particle-rotor model with the particle-hole configuration πh11/21⊗νh11/2-1 and different values of the triaxiality parameter γ. Both constant and spin-dependent variable moments of inertia (CMI and VMI, respectively) are introduced. The energy spectra, electromagnetic transition probabilities, angular momentum components, and K distribution are examined. It is shown that, besides bands 1 and 2, the predicted bands 3 and 4 in the calculations with both CMI and VMI for atomic nuclei with γ=30° could be interpreted as chiral doublet bands.
Wang, Yaqin; Tang, Wu
2017-12-01
Amorphous indium tin oxide (ITO) thin films were deposited on polymethylmethacrylate and polyethyleneterephthalate substrates by radio frequency magnetron sputtering at room temperature. An interesting substrate morphology effect of ITO films on the conductivity, optical transition type and energy band structure was observed. A simplified film system model with a square potential for surface morphology was employed to explain the difference of conductivity. The energy band structures were also calculated based on the theory of amorphous semiconductor. The conclusion demonstrated the width of optical band gap, as well as the relative position of the Fermi level and mobility edge, which can easily be extended to the band structure determination of other transparent conductive films.
Energy Technology Data Exchange (ETDEWEB)
Lebens-Higgins, Z.; Scanlon, D. O.; Paik, H.; Sallis, S.; Nie, Y.; Uchida, M.; Quackenbush, N. F.; Wahila, M. J.; Sterbinsky, G. E.; Arena, Dario A.; Woicik, J. C.; Schlom, D. G.; Piper, L. F. J.
2016-01-01
We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO _{3} , using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La - BaSnO _{3} is driven purely by electrostatic interactions.
Calculation Tool for Engineering
Lampinen, Samuli
2016-01-01
The Study was conducted as qualitative research for K-S Konesuunnittelu Oy. The company provides mechanical engineering for technology suppliers in the Finnish export industries. The main objective was to study if the competitiveness of the case company could be improved using a self-made Calculation Tool (Excel Tool). The mission was to clarify processes in the case company to see the possibilities of Excel Tool and to compare it with other potential calculation applications. In addition,...
Current interruption transients calculation
Peelo, David F
2014-01-01
Provides an original, detailed and practical description of current interruption transients, origins, and the circuits involved, and how they can be calculated Current Interruption Transients Calculationis a comprehensive resource for the understanding, calculation and analysis of the transient recovery voltages (TRVs) and related re-ignition or re-striking transients associated with fault current interruption and the switching of inductive and capacitive load currents in circuits. This book provides an original, detailed and practical description of current interruption transients, origins,
Numerical method for shear bands in ductile metal with inclusions
Energy Technology Data Exchange (ETDEWEB)
Plohr, Jee Yeon N [Los Alamos National Laboratory; Plohr, Bradley J [Los Alamos National Laboratory
2010-01-01
A numerical method for mesoscale simulation of high strain-rate loading of ductile metal containing inclusions is described. Because of small-scale inhomogeneities, such a composite material is prone to localized shear deformation (adiabatic shear bands). The modeling framework is the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. /27-139, 1992], which ensures that the micromechanical response of the material is reflected in the behavior of the composite at the mesoscale. To calculate the effective plastic strain rate when shear bands are present, the analytic and numerical analysis of shear bands by Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31-41, 1996] is adapted and extended.
Miniaturization for ultrathin metamaterial perfect absorber in the VHF band
Khuyen, Bui Xuan; Tung, Bui Son; Yoo, Young Joon; Kim, Young Ju; Kim, Ki Won; Chen, Liang-Yao; Lam, Vu Dinh; Lee, Youngpak
2017-03-01
An efficient resolution for ultrathin metamaterial perfect absorber (MPA) is proposed and demonstrated in the VHF radio band (30-300 MHz). By adjusting the lumped capacitors and the through vertical interconnects, the absorber is miniaturized to be only λ/816 and λ/84 for its thickness and periodicity with respect to the operating wavelength (at 102 MHz), respectively. The detailed simulation and calculation show that the MPA can maintain an absorption rate over 90% in a certain range of incident angle and with a wide variation of capacitance. Additionally, we utilized the advantages of the initial single-band structure to realize a nearly perfect dual-band absorber in the same range. The results were confirmed by both simulation and experiment at oblique incidence angles up to 50°. Our work is expected to contribute to the actualization of future metamaterial-based devices working at radio frequency.
Band structure parameters of wurtzite and zinc-blende GaAs under strain in the GW approximation
Cheiwchanchamnangij, Tawinan; Lambrecht, Walter R. L.
2011-07-01
Quasiparticle self-consistent GW calculations are used to study the band structure in wurtzite and zinc-blende GaAs. The band-gap change between wurtzite and zinc blende is found to be sensitive to lattice constant and k-point convergence of the GW self-energy. Furthermore, the conduction-band minimum can switch between Γ1 and Γ3 character as a function of strain and the valence-band maximum can cross over from Γ5 to Γ1 under compressive uniaxial strain. The Kohn-Luttinger and Rashba-Sheka-Pikus effective Hamiltonian band structure parameters of zinc-blende and wurtzite GaAs, respectively, are determined from these first-principles band structure calculations. The uniaxial and homogeneous strain dependence of the band structure are studied and summarized in the appropriate strain deformation potential parameters.
Compact Dual Band Antenna Design for Ku / Ka Band Applications
Directory of Open Access Journals (Sweden)
A. Kandwal
2017-10-01
Full Text Available This communication proposes a compact 16 GHz / 30 GHz dual band antenna design for Ku / Ka band applications. The antenna consists of two layers with lower layer having the fed patch and the upper layer having non-periodic element array. The antenna has been designed to operate at two different frequencies with compact dimensions of (8mm x 8mm using Rogers RT 5880. The compact size of this proposed antenna also makes it suitable for integration with the microwave and millimeter wave circuits. The proposed antenna provides high radiation efficiency and a peak gain of about 8 dB at the resonant frequencies with reduced side lobe levels.
Kim, Hyun-Tak
A Mott insulator VO2 (3d1) has a direct gap (Δdirect ~Vdirect) of 0.6 eV and an indirect gap of Δact ~Vdirect ~ 0.15 eV coming from impurity indirect band. At Tc, Δdirect =Δact = O is satisfied and the insulator-to-metal transition (IMT) occurs. The metallic carriers near core region can be trapped when a critical onsite Coulomb Uc exists. Then, a potential energy is defined as Vg =Vdirect +Uc +Vindirect = - (2 2 3) EF (1 + e (NtotNtotntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc ntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc 3) EF (1 + e (NtotNtotntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc ntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc , where Vdirect = - (2 2 3 3) EF is the screened Coulomb pseudopotential at K = 0. Δρ =NtotNtotntot ~ 0 . 018 % ntot ~ 0 . 018 % [1] is defined as the critical doping quantity, where ntot is the carrier density in the direct band and Ntot is the carrier density in the impurity band. In Uc 2 3 3) EF case, it sustains the insulator state. However, when both Uc > (2 2 3 3) EF and Δact = 0 by excitation are satisfied, the IMT occurs in Vg >= 0. This indicates that the excitation (Δact = 0) breaks the Coulomb equilibrium (Vgsustaining Uc) in Eq. (1) ; the Coulomb energy changes from Uc to a Uswitched by the doping (excitation; Δact = 0) and the de-doping (de-excitation; Δact = 0.15 eV) of Δρ =NtotNtotntot ntot to the conduction band, by applying external parameters such as heat, pressure, doping etc. The direct band gap (semiconductor gap) in the Mott insulator smaller than that of dielectric insulators can be explained by Uc.[1] NewJ.Phys.6(2004)52.
Band structure and thermal emission of two dimentional silicon photonic crystal
Directory of Open Access Journals (Sweden)
meysam daneshvar
2017-11-01
Full Text Available In this research, we have studied the photonic band structure, optical properties and thermal emission spectrum of 2D Silicon photonic crystal with hexagonal structure. The band structure, band gap map and the gap size versus radius have been calculated by plane wave expansion method. The maximum band gap size of TE (TM polarization and the complete gap size are 51% (20% and 17% at air hole radius r=0.43a (0.50a and r=0.48a, respectively. The optical properies have been calculated by FDTD methd in the range of 1 to 10 . The thermal emission spectrum has been obtained from absorption by Kirchhoff’s law. The obtaine results show that by engineering the band structure, the thermal emission spectrum of 2D Silicon photonic crystal can be controlled in a manner that can be used in thermophotovoltaic systems.
Band gap engineering in silicene: A theoretical study of density functional tight-binding theory
Zaminpayma, Esmaeil; Nayebi, Payman
2016-10-01
In this work, we performed first principles calculations based on self-consistent charge density functional tight-binding to investigate different mechanisms of band gap tuning of silicene. We optimized structures of silicene sheet, functionalized silicene with H, CH3 and F groups and nanoribbons with the edge of zigzag and armchair. Then we calculated electronic properties of silicene, functionalized silicene under uniaxial elastic strain, silicene nanoribbons and silicene under external electrical fields. It is found that the bond length and buckling value for relaxed silicene is agreeable with experimental and other theoretical values. Our results show that the band gap opens by functionalization of silicene. Also, we found that the direct band gap at K point for silicene changed to the direct band gap at the gamma point. Also, the functionalized silicene band gap decrease with increasing of the strain. For all sizes of the zigzag silicene nanoribbons, the band gap is near zero, while an oscillating decay occurs for the band gap of the armchair nanoribbons with increasing the nanoribbons width. At finally, it can be seen that the external electric field can open the band gap of silicene. We found that by increasing the electric field magnitude the band gap increases.
Energy Technology Data Exchange (ETDEWEB)
Gaudry, Emilie [Laboratoire de Mineralogie-Cristallographie, UMR CNRS 7590, Universite Pierre et Marie Curie, case 115, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Cabaret, Delphine [Laboratoire de Mineralogie-Cristallographie, UMR CNRS 7590, Universite Pierre et Marie Curie, case 115, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Sainctavit, Philippe [Laboratoire de Mineralogie-Cristallographie, UMR CNRS 7590, Universite Pierre et Marie Curie, case 115, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Brouder, Christian [Laboratoire de Mineralogie-Cristallographie, UMR CNRS 7590, Universite Pierre et Marie Curie, case 115, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Mauri, Francesco [Laboratoire de Mineralogie-Cristallographie, UMR CNRS 7590, Universite Pierre et Marie Curie, case 115, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Goulon, Jose [European Synchrotron Radiation Facility BP 220, F-38043 Grenoble Cedex (France); Rogalev, Andrei [European Synchrotron Radiation Facility BP 220, F-38043 Grenoble Cedex (France)
2005-09-14
We determine the structural relaxations around paramagnetic impurities (Ti, Cr, Fe) in corundum ({alpha}-Al{sub 2}O{sub 3}), by combining x-ray absorption near-edge structure (XANES) experiments and ab initio calculations. The structural relaxations are found to be very local. We then show that XANES is sensitive to small variations in interatomic distances within the coordination shell of the absorbing atom. The experiments were carried out on single crystals of ruby and sapphires. Linear dichroic signals are essential to characterize the geometry of the impurity site. The calculations were performed within a self-consistent 'non-muffin-tin' framework, that uses pseudopotentials, a plane-wave basis set, and the continued fraction for the absorption cross section.
Wisniewski, H.; Gourdain, P.-A.
2017-10-01
APOLLO is an online, Linux based plasma calculator. Users can input variables that correspond to their specific plasma, such as ion and electron densities, temperatures, and external magnetic fields. The system is based on a webserver where a FastCGI protocol computes key plasma parameters including frequencies, lengths, velocities, and dimensionless numbers. FastCGI was chosen to overcome security problems caused by JAVA-based plugins. The FastCGI also speeds up calculations over PHP based systems. APOLLO is built upon the WT library, which turns any web browser into a versatile, fast graphic user interface. All values with units are expressed in SI units except temperature, which is in electron-volts. SI units were chosen over cgs units because of the gradual shift to using SI units within the plasma community. APOLLO is intended to be a fast calculator that also provides the user with the proper equations used to calculate the plasma parameters. This system is intended to be used by undergraduates taking plasma courses as well as graduate students and researchers who need a quick reference calculation.
Table of superdeformed nuclear bands and fission isomers
Energy Technology Data Exchange (ETDEWEB)
Firestone, R.B. [Lawrence Berkeley Lab., CA (United States); Singh, B. [McMaster Univ., Hamilton, ON (Canada)
1994-06-01
A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in {sup 152}Dy was predicted for {beta}{sub 2}-0.65. Subsequently, a discrete set of {gamma}-ray transitions in {sup 152}DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of {gamma}-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra.
Rotational bands and shape changes in {sup 105}Rh
Energy Technology Data Exchange (ETDEWEB)
Espinoza-Quinones, F.R.; Cybulska, E.W.; Oliveira, J.R.; Ribas, R.V.; Rao, M.N.; Rizzutto, M.A.; Medina, N.H.; Emediato, L.G.; Seale, W.A.; Botelho, S. [Laboratorio Pelletron, Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo (Brazil)
1997-06-01
The {sup 105}Rh nucleus has been studied by in-beam {gamma} spectroscopy with the heavy-ion fusion-evaporation reaction {sup 100}Mo({sup 11}B, {alpha}2n{gamma}) at 39 MeV. Gamma-gamma-t coincidences and directional correlation ratios were measured. Four rotational bands have been identified with similar characteristics to those in other A{approx}100 odd-proton nuclei. The positive-parity yrast band based on the {pi}g{sub 9/2} configuration and the negative-parity {pi}p{sub 1/2} band, showing large signature splittings, exhibit band crossings at the frequencies of 0.38 MeV and 0.48 MeV, respectively. Experimental Routhians and alignments as well as B(M1)/B(E2) ratios were extracted. The structure of the bands was interpreted within the framework of the cranked shell model and total Routhian surface calculations. {copyright} {ital 1997} {ital The American Physical Society}
The Diffuse Interstellar Bands: Solving a Century Old Problem
Salama, Farid
2017-01-01
The Diffuse Interstellar Bands (DIBs) are a set of apporoximately 500 absorption bands that are seen in the spectra of reddened stars (i.e., stars obscured by the presence of interstellar clouds in their line of sight). The first DIBs were detected in the visible over a century ago. Diffuse Interstellar Bands are now detected from the near ultraviolet to the near infrared in the spectra of reddened stars spanning a variety of interstellar environments in our local, and in other galaxies. Although DIB carriers are a significant part of the interstellar chemical inventory as they account for a noticeable fraction of the interstellar extinction, the nature of their carriers is still unknown over a century after the detection of the first bands. DIB carriers are stable and ubiquitous in a broad variety of interstellar environments and play a unique role in interstellar physics and chemistry. It has long been realized that the solving of the DIB problem requires a strong synergy between astronomical observations, laboratory astrophysics and astrochemistry, quantum chemistry calculations and astrophysical modeling of line-of-sights. In this review, we'll present and discuss the current state of this perplexing problem. We'll review the progress and the failures that have been encountered in the long quest for the identification of the carriers of these ubiquitous interstellar bands.
Shear bands as growing instabilities in viscoanelastic media with memory
Directory of Open Access Journals (Sweden)
Marina Dolfin
2013-09-01
Full Text Available In this paper we investigate the critical conditions under which a small perturbation in an homogeneous continuum can possibly grows into a shear band instability. In particular, we analyze from a thermodynamical viewpoint the phenomenon of shear bands in viscoanelastic media with memory. It is emphasized, in the scientific literature, that the specific adopted rheology strongly affects the results so that a special attention has to be paid, also for engineering purposes, to the accuracy of the rheological model. Several well-known rheological model (for instance the so called Maxwell or Jeffreys media are particular cases of the general model we adopt in the paper to analyze shear bands. Instability conditions, giving rise to shear bands formation, are obtained by introducing small perturbations around an homogeneous deformation into the system of differential equations governing the problem of homogeneous deformations in the considered continuous medium; as a result a non-homogeneous linear dynamical system is obtained whose stability is analyzed. A research perspective in view of a possible comparison with experimental results is proposed; in particular the simple methodology proposed in the paper should be applied in view of using the phenomenon of the initiation of shear bands to calculate the thermomechanical coefficients of real materials.
Zn-VI quasiparticle gaps and optical spectra from many-body calculations
Riefer, A.; Weber, N.; Mund, J.; Yakovlev, D. R.; Bayer, M.; Schindlmayr, Arno; Meier, C.; Schmidt, W. G.
2017-06-01
The electronic band structures of hexagonal ZnO and cubic ZnS, ZnSe, and ZnTe compounds are determined within hybrid-density-functional theory and quasiparticle calculations. It is found that the band-edge energies calculated on the {{G}0}{{W}0} (Zn chalcogenides) or GW (ZnO) level of theory agree well with experiment, while fully self-consistent QSGW calculations are required for the correct description of the Zn 3d bands. The quasiparticle band structures are used to calculate the linear response and second-harmonic-generation (SHG) spectra of the Zn-VI compounds. Excitonic effects in the optical absorption are accounted for within the Bethe-Salpeter approach. The calculated spectra are discussed in the context of previous experimental data and present SHG measurements for ZnO.
The electronic structure of LaO: Ligand field versus ab initio calculations
Schamps, Joël; Bencheikh, Mohammed; Barthelat, Jean-Claude; Field, Robert W.
1995-11-01
The potentially pathological example of LaO has been chosen to test the application of ligand field theory (LFT) to metal monoxides. The test consists of a comparison of closed-shell ligand LFT (CSLLFT) results (in which a 2+/2- ionic M2+O2- model is a priori postulated with a point-charge ligand) against ab initio multiconfiguration self-consistent-field-multireference configuration interaction (MCSCF-MRCI) results (in which no ionicity is assumed a priori and an internal structure is allowed for the ligand). Special care has been devoted to the determination of a La3+ pseudopotential and its associated atomic basis set in order to keep the ab initio model close to the LFT one, yet at the same time capable of clearly exhibiting the consequences and the importance of the restrictions imposed in the CSLLFT model. The ab initio calculations reveal that the effective (Mulliken) ionicity in LaO is not La2+O2- but quite close to La+O-. Despite this, the (2+/2-) ionic CSLLFT model leads to the correct orbital occupations in the ground state but this model cannot account for the significant covalency contribution via the nominal 2pσ and 2pπ oxygen orbitals. The CSLLFT calculations correctly reproduce the excitation energies of the four lowest-lying observed states of LaO: these states are calculated to within 2000 cm-1 and globally better than via ab initio calculations. However, the (2+/2-) ionic CSLLFT model is shown to ignore the existence of a manifold of low-lying quartet (and doublet) states of (1+/1-) ionicity that might be relevant for interpreting features of the spectrum. This result exemplifies the need for developing, beyond the first attempts made in this direction, a computationally manageable open-shell ligand theory for the frequently encountered case of predominantly ionic structures with an open-shell ligand.
Yedukondalu, N.; Vaitheeswaran, G.
2014-06-01
Silver fulminate (AgCNO) is a primary explosive, which exists in two polymorphic phases, namely, orthorhombic (Cmcm) and trigonal (Rbar{3}) forms at ambient conditions. In the present study, we have investigated the effect of pressure and temperature on relative phase stability of the polymorphs using planewave pseudopotential approaches based on Density Functional Theory (DFT). van der Waals interactions play a significant role in predicting the phase stability and they can be effectively captured by semi-empirical dispersion correction methods in contrast to standard DFT functionals. Based on our total energy calculations using DFT-D2 method, the Cmcm structure is found to be the preferred thermodynamic equilibrium phase under studied pressure and temperature range. Hitherto Cmcm and Rbar{3} phases denoted as α- and β-forms of AgCNO, respectively. Also a pressure induced polymorphic phase transition is seen using DFT functionals and the same was not observed with DFT-D2 method. The equation of state and compressibility of both polymorphic phases were investigated. Electronic structure and optical properties were calculated using full potential linearized augmented plane wave method within the Tran-Blaha modified Becke-Johnson potential. The calculated electronic structure shows that α, β phases are indirect bandgap insulators with a bandgap values of 3.51 and 4.43 eV, respectively. The nature of chemical bonding is analyzed through the charge density plots and partial density of states. Optical anisotropy, electric-dipole transitions, and photo sensitivity to light of the polymorphs are analyzed from the calculated optical spectra. Overall, the present study provides an early indication to experimentalists to avoid the formation of unstable β-form of AgCNO.
Yedukondalu, N; Vaitheeswaran, G
2014-06-14
Silver fulminate (AgCNO) is a primary explosive, which exists in two polymorphic phases, namely, orthorhombic (Cmcm) and trigonal (R3) forms at ambient conditions. In the present study, we have investigated the effect of pressure and temperature on relative phase stability of the polymorphs using planewave pseudopotential approaches based on Density Functional Theory (DFT). van der Waals interactions play a significant role in predicting the phase stability and they can be effectively captured by semi-empirical dispersion correction methods in contrast to standard DFT functionals. Based on our total energy calculations using DFT-D2 method, the Cmcm structure is found to be the preferred thermodynamic equilibrium phase under studied pressure and temperature range. Hitherto Cmcm and R3 phases denoted as α- and β-forms of AgCNO, respectively. Also a pressure induced polymorphic phase transition is seen using DFT functionals and the same was not observed with DFT-D2 method. The equation of state and compressibility of both polymorphic phases were investigated. Electronic structure and optical properties were calculated using full potential linearized augmented plane wave method within the Tran-Blaha modified Becke-Johnson potential. The calculated electronic structure shows that α, β phases are indirect bandgap insulators with a bandgap values of 3.51 and 4.43 eV, respectively. The nature of chemical bonding is analyzed through the charge density plots and partial density of states. Optical anisotropy, electric-dipole transitions, and photo sensitivity to light of the polymorphs are analyzed from the calculated optical spectra. Overall, the present study provides an early indication to experimentalists to avoid the formation of unstable β-form of AgCNO.
INVAP's Nuclear Calculation System
Directory of Open Access Journals (Sweden)
Ignacio Mochi
2011-01-01
Full Text Available Since its origins in 1976, INVAP has been on continuous development of the calculation system used for design and optimization of nuclear reactors. The calculation codes have been polished and enhanced with new capabilities as they were needed or useful for the new challenges that the market imposed. The actual state of the code packages enables INVAP to design nuclear installations with complex geometries using a set of easy-to-use input files that minimize user errors due to confusion or misinterpretation. A set of intuitive graphic postprocessors have also been developed providing a fast and complete visualization tool for the parameters obtained in the calculations. The capabilities and general characteristics of this deterministic software package are presented throughout the paper including several examples of its recent application.
Salgado, C A; Salgado, Carlos A.; Wiedemann, Urs Achim
2003-01-01
We calculate the probability (``quenching weight'') that a hard parton radiates an additional energy fraction due to scattering in spatially extended QCD matter. This study is based on an exact treatment of finite in-medium path length, it includes the case of a dynamically expanding medium, and it extends to the angular dependence of the medium-induced gluon radiation pattern. All calculations are done in the multiple soft scattering approximation (Baier-Dokshitzer-Mueller-Peign\\'e-Schiff--Zakharov ``BDMPS-Z''-formalism) and in the single hard scattering approximation (N=1 opacity approximation). By comparison, we establish a simple relation between transport coefficient, Debye screening mass and opacity, for which both approximations lead to comparable results. Together with this paper, a CPU-inexpensive numerical subroutine for calculating quenching weights is provided electronically. To illustrate its applications, we discuss the suppression of hadronic transverse momentum spectra in nucleus-nucleus colli...
First-Principles Electronic Structure Calculations of N2H4 Adsorbed on Single-Wall Carbon Nanotubes
Yu, M.; Tian, W. Q.; Jayanthi, C. S.; Wu, S. Y.
2008-03-01
Recent experiments conducted by Desai et al. [1] reveal that single-wall carbon nanotube (SWCNT) networks exposed to N2H4 vapor at various pressures exhibit considerable drop in resistance with respect to the pristine sample. Experimental findings reveal: (i) n-type behavior for the adsorption of N2H4/SWCNT, and (ii) the binding of N2H4 on SWCNT as chemisorption. In the present work, we have performed first-principles electronic structure calculations [2] for the N2H4 adsorbed on the (14, 0) SWCNT, where several orientations for the N2H4 molecule were considered. Calculations for the combined system were performed using 3 unit cells with the DFT/GGA and ultra soft pseudo-potentials. Our calculations reveal: (i) the binding of N2H4 on SWCNT as physisorption, and (ii) the electronic structure of SWCNT to be practically unaltered by the adsorption of N2H4, suggesting that there will not be a dramatic drop in resistance for N2H4/SWCNT. This is in disagreement with the experimental findings. To further understand the experimental observations, we will discuss mechanisms that may alter the binding nature of N2H4 on SWCNT. [1] S. Desai, G. Sumanasekera, et al. (APS, March 2008). [2] G. Kresse and J. Furthmuller, Phys. Rev. B 54, 11169 (1996).
Yost, Dillon C.; Yao, Yi; Kanai, Yosuke
2017-09-01
In ion irradiation processes, electronic stopping power describes the energy transfer rate from the irradiating ion to the target material's electrons. Due to the scarcity and significant uncertainties in experimental electronic stopping power data for materials beyond simple solids, there has been growing interest in the use of first-principles theory for calculating electronic stopping power. In recent years, advances in high-performance computing have opened the door to fully first-principles nonequilibrium simulations based on real-time time-dependent density functional theory (RT-TDDFT). While it has been demonstrated that the RT-TDDFT approach is capable of predicting electronic stopping power for a wide range of condensed matter systems, there has yet to be an exhaustive examination of the physical and numerical approximations involved and their effects on the calculated stopping power. We discuss the results of such a study for crystalline silicon with protons as irradiating ions. We examine the influences of key approximations in RT-TDDFT nonequilibrium simulations on the calculated electronic stopping power, including approximations related to basis sets, finite size effects, exchange-correlation approximation, pseudopotentials, and more. Finally, we propose a simple and efficient correction scheme to account for the contribution from core-electron excitations to the stopping power, as it was found to be significant for large proton velocities.
MIRA: Dual wavelength band instrument
Directory of Open Access Journals (Sweden)
Robert Georgii
2015-08-01
Full Text Available MIRA is a dual wavelength band instrument operated by Technische Universität München TUM, which provides neutrons over a wide range of wavelengths 3.5 Å < λ < 20 Å combining the two beam ports of MIRA-1 and MIRA-2. The instrument´s setup is modular and allows for various different cold neutron experiments such as diffraction, spectroscopy or reflectometry.
Natural Intermediate Band in I 2 -II-IV-VI4 Quaternary Chalcogenide Semiconductors.
Liu, Qiheng; Cai, Zenghua; Han, Dan; Chen, Shiyou
2018-01-25
An intermediate band in the band gap of semiconductors is fundamental to the development of the intermediate band solar cells, but it is usually produced artificially, which imposes technical challenges on the experimental realization. Here we found that there are natural intermediate bands in the band gaps of the I2-II-IV-VI4 quaternary chalcogenide semiconductors such as Cu2ZnSnS4 and Ag2ZnSnSe4, which had been proposed as promising light-absorber semiconductors in thin film solar cells. By first-principles calculations, we found the lowest conduction band of these I2-II-IV-VI4 semiconductors in the kesterite structure is isolated (a lone band, resulting from the energy separation between Sn 5s and 5p states), which can be viewed as a natural intermediate band. The gap between the intermediate band and higher-energy conduction band can be increased through changing the crystal structure from the zincblende-derived kesterite structure to the wurtzite-derived wurtzite-kesterite structure. In contrast, the intermediate-conduction band gap shrinks when the component element Sn is replaced by Ge (Cu2ZnGeS4), and the gap even disappears (intermediate band disappear) when Sn is replaced by Si (Cu2ZnSiS4). Through tuning the intermediate-conduction and intermediate-valence band gaps, we show that the wurtzite-kesterite structured Ag2ZnSnSe4 may be a potential light-absorber semiconductor in intermediate band solar cells.
Graphing Calculator Mini Course
Karnawat, Sunil R.
1996-01-01
The "Graphing Calculator Mini Course" project provided a mathematically-intensive technologically-based summer enrichment workshop for teachers of American Indian students on the Turtle Mountain Indian Reservation. Eleven such teachers participated in the six-day workshop in summer of 1996 and three Sunday workshops in the academic year. The project aimed to improve science and mathematics education on the reservation by showing teachers effective ways to use high-end graphing calculators as teaching and learning tools in science and mathematics courses at all levels. In particular, the workshop concentrated on applying TI-82's user-friendly features to understand the various mathematical and scientific concepts.
[Gastric band erosion: Alternative management].
Echaverry-Navarrete, Denis José; Maldonado-Vázquez, Angélica; Cortes-Romano, Pablo; Cabrera-Jardines, Ricardo; Mondragón-Pinzón, Erwin Eduardo; Castillo-González, Federico Armando
2015-01-01
Obesity is a public health problem, for which the prevalence has increased worldwide at an alarming rate, affecting 1.7 billion people in the world. To describe the technique employed in incomplete penetration of gastric band where endoscopic management and/or primary closure is not feasible. Laparoscopic removal of gastric band was performed in five patients with incomplete penetrance using Foley catheterization in the perforation site that could lead to the development of a gastro-cutaneous fistula. The cases presented include a leak that required surgical lavage with satisfactory outcome, and one patient developed stenosis 3 years after surgical management, which was resolved endoscopically. In all cases, the penetration site closed spontaneously. Gastric band erosion has been reported in 3.4% of cases. The reason for inserting a catheter is to create a controlled gastro-cutaneous fistula, allowing spontaneous closure. Various techniques have been described: the totally endoscopic, hybrid techniques (endoscopic/laparoscopic) and completely laparoscopic. A technique is described here that is useful and successful in cases where the above-described treatments are not viable. Copyright © 2015. Published by Masson Doyma México S.A.
Relation between Debye temperature and energy band gap of semiconductors
Ullrich, Bruno; Bhowmick, Mithun; Xi, Haowen
2017-04-01
The work addresses an unresolved topic in solid-state physics, i.e., the dependence of the Debye temperature (TD) on the energy band gap (Eg) of semiconducting materials. The systematic calculation of TD by using the ratio of sound velocity and lattice constant from the literature resulted in the relation TD∝exp(Eg). The exponential relationship is confirmed by a theoretical model based on the microscopic analysis of the electrical conductivity in metals and semiconductors.
The movement and decay of ice edge bands in the winter Bering Sea
Martin, S.; Kauffman, P.; Parkinson, C.
1983-01-01
A study of the movement and decay of ice bands in the Bering Sea carried out in March 1981 is described. A pair of radio transponders mounted on ice floes within a band was tracked and the band motion was compared with that of a satellite-tracked buoy deployed in the ice interior. The results show that the bands moved away from the interior pack ice at a speed 30 percent greater than that of the interior ice, that the cause of this band acceleration was very likely the wind-wave radiation stress on the upwind side of the band, and that as the bands moved into warmer water, they decayed both by wind-wave erosion of the upwind edge and by bottom melting. The working of the buoys and the method of deployment are described, as are the band shape, trajectory, and decay. By a calculation of the steady state stress balance on the band, it is shown that the radiation stress can account for the velocity increase of the band relative to the ice interior.
Gravitational constant calculation methodologies
Shakhparonov, V. M.; Karagioz, O. V.; Izmailov, V. P.
2011-01-01
We consider the gravitational constant calculation methodologies for a rectangular block of the torsion balance body presented in the papers Phys. Rev. Lett. 102, 240801 (2009) and Phys.Rev. D. 82, 022001 (2010). We have established the influence of non-equilibrium gas flows on the obtained values of G.
Bogoboyashchiy, V. V.
1997-08-01
Faraday rotation, absorption spectra, and the intrinsic carrier concentration temperature dependencies were investigated in order to determine the interconsistent system of values of the narrow-gap Hg1-xCdxTe band parameters. The undoped and doped with indium or copper crystals with x constant of valence band deformation potential E1 equals 12.5 eV have been determined. It has been found that doping of the material with indium, causes the appearance of donor states in the conduction band about 0.1 eV above the bottom of the band. The band structure of Hg1-xCdxTe (MCT) is studied for a long time, and its peculiarities are well known. The light carriers spectrum is believed to be described in framework of the 3-band Kane's model, and the parabolic approximation for heavy hole subband is thought to be sufficient as a rule. The influence of far bands is taken into account rather seldom. But at the same time, the values of band parameters obtained by different authors are not in a good agreement often. In result, it was impossible to agree with an acceptable accuracy the measured and the calculated values of some physical characteristics of MCT by using the known values of band parameters. In order to achieve perfect conformity between the theory and the experiment, another approach must be used. It is necessary that the complex experiment be carried out with a high accuracy of not only the measuring, but of the mathematical models of studied effects and the calculations too. All the main sources of systematic error should be revealed and removed, and the values of band parameters should be determined over again. Such a study was carried out, and its results are reported in this paper.
Deformation bands in porous sandstones their microstructure and petrophysical properties
Energy Technology Data Exchange (ETDEWEB)
Torabi, Anita
2007-12-15
deformation bands are characterized by strain hardening, these new bands feature a central slip surface, which indicates late strain softening. They lack the characteristic compaction envelop, and are typified by higher porosity and lower permeability than previously-described cataclastic deformation bands. Intense background fracturing of the host rock and significant initial porosity are considered to be important in creating these newly-discovered deformation bands. In a related study, we investigate, for millimeter- wide deformation bands, the scale limitation inherent in laboratory measurements of porosity and permeability. The scale limitations imposed by the deformation band relative to the physical sample size motivated us to develop a new method for determining porosity and permeability based on image processing. While plug measurements measure the effective permeability across a 25.4 mm (1 inch) long sample, which includes both host rock and deformation band, the method presented here provides a means to estimate porosity and permeability of deformation band on microscale. This method utilizes low-order (one- and two orders) spatial correlation functions to analyze high-resolution, high-magnification backscatter images, to estimate the porosity and specific surface area of the pore-grain interface in the deformed sandstones. Further, this work demonstrates the use of a modified version of the Kozeny-Carmen relation to calculate permeability by using porosity and specific surface area obtained through the image processing. The result shows that permeability difference between the band and the host rock is up to four orders of magnitude. Moreover, the porosities and permeabilities estimated from image processing are lower than those obtained from their plug measurements; hence the traditional laboratory measurements have been overestimating permeability because of the previously-unrecognized scale problem. In addition, the image processing results clearly show that
Electron self-energy calculation using a general multi-pole approximation
Soininen, J A; Shirley, E L
2003-01-01
We present a method for calculating the inverse of the dielectric matrix in a solid using a band Lanczos algorithm. The method produces a multi-pole approximation for the inverse dielectric matrix with an arbitrary number of poles. We discuss how this approximation can be used to calculate the screened Coulomb interaction needed for electron self-energy calculations in solids.
Directory of Open Access Journals (Sweden)
E. Kalesaki
2014-01-01
Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
The predicted band gaps using the modified Becke–Johnson(mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic parameters namely, ...
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... The predicted band gaps using the modified Becke–Johnson. (mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic ...
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko. (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, ...
Calculations of quasi-particle spectra of semiconductors under pressure
DEFF Research Database (Denmark)
Christensen, Niels Egede; Svane, Axel; Cardona, M.
2011-01-01
Different approximations in calculations of electronic quasiparticle states in semiconductors are compared and evaluated with respect to their validity in predictions of optical properties. The quasi-particle self-consistent GW (QSGW) approach yields values of the band gaps which are close...
Signature Splitting in 7/2 [633]v band of 175Hf
Directory of Open Access Journals (Sweden)
Singh Jagjit
2014-03-01
Full Text Available In this paper, we present an explanation of signature splitting observed in the one quasiparticle rotational band (7/2[633]ν of 175Hf in terms of one particle plus rotor model (PRM calculations. The role of angular momentum dependence of the inertia parameter and rotational correction term appearing in Coriolis mixing calculations to explain signature effects is discussed.
Calculation of collisional mixing
Koponen, I.; Hautala, M.
1990-06-01
Collisional mixing of markers is calculated by splitting the calculation into two parts. Relocation cross sections have been calculated using a realistic potential in a Monte Carlo simulation. The cross sections are used in the computation of marker relocation. The cumulative effect of successive relocations is assumed to be an uncorrelated transport process and it is treated as a weighted random walk. Matrix relocation was not included in the calculations. The results from this two-step simulation model are compared with analytical models. A fit to the simulated differential relocation cross sections has been found which makes the numerical integration of the Bothe formula feasible. The influence of primaries has been treated in this way. When all the recoils are included the relocation profiles are nearly Gaussian and the Pearson IV distributions yield acceptable profiles in the studied cases. The approximations and cut-off procedures which cause the major uncertainties in calculations are pointed out. The choice of the cut-off energy is shown to be the source of the largest uncertainty whereas the mathematical approximations can be used with good accuracy. The methods are used to study the broadening of a Pt marker in Si mixed by 300 keV Xe ions, broadening of a Ti marker in Al mixed by 300 keV Xe ions and broadening of a Ti marker in Hf mixed by 750 keV Kr ions. The fluence in each case is 2 × 10 16{ions}/{cm 2}. The calculated averages of half widths at half maximum vary between 11-18, 9-12 and 10-15 nm, respectively, depending on the cut-off energy and the mixing efficiencies vary between 11-29, 6-11 and 6-14 {Å5}/{eV}, respectively. The broadenings of Pt in Si and Ti in Al are about two times smaller than the measured values and the broadening of Ti in Hf is in agreement with the measured values.
One- and two-phonon γ -vibrational bands in neutron-rich 107Mo
Marcellino, J.; Wang, E. H.; Zachary, C. J.; Hamilton, J. H.; Ramayya, A. V.; Bhat, G. H.; Sheikh, J. A.; Dai, A. C.; Liang, W. Y.; Xu, F. R.; Hwang, J. K.; Brewer, N. T.; Luo, Y. X.; Rasmussen, J. O.; Zhu, S. J.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.
2017-09-01
Neutron-rich 107Mo has been reinvestigated by analyzing the large statistics γ -γ -γ and γ -γ -γ -γ coincidence data from the spontaneous fission of 252Cf at the Gammasphere detector array. Two new bands have been identified. The potential-energy surface calculations of this nucleus have been performed. The calculations show evidence for the 5 /2+[413 ] configuration of the ground-state band and 7 /2-[523 ] configuration for the 348-keV excited band, as assigned in previous work. The two bands newly established are proposed to be one- and two-phonon γ -vibrational bands built on the 7 /2-[523 ] Nilsson orbital, respectively, in the current paper. Triaxial projected shell-model (TPSM) calculations have been performed to explain the level structure and are found in fair agreement with experimental data. In particular, the TPSM study confirms the γ - and γ γ -vibrational structure for the two observed excited band structures. Systematics of the one- and two-phonon γ -vibrational bands in the A ˜100 Mo series is also discussed.
Microcomputer calculations in physics
Killingbeck, J. P.
1985-01-01
The use of microcomputers to carry out computations in an interactive manner allows the judgement of the operator to be allied with the calculating power of the machine in a synthesis which speeds up the creation and testing of mathematical techniques for physical problems. This advantage is accompanied by a disadvantage, in that microcomputers are limited in capacity and power, and special analysis is needed to compensate for this. These two features together mean that there is a fairly recognisable body of methods which are particularly appropriate for interactive microcomputing. This article surveys a wide range of mathematical methods used in physics, indicating how they can be applied using microcomputers and giving several original calculations which illustrate the value of the microcomputer in stimulating the exploration of new methods. Particular emphasis is given to methods which use iteration, recurrence relation or extrapolation procedures which are well adapted to the capabilities of modern microcomputers.
Prenatal diagnosis of amniotic band syndrome
Directory of Open Access Journals (Sweden)
Laxmi Devi Padmanabhan
2016-01-01
Full Text Available Amniotic band can cause a broad spectrum of anomalies ranging from simple band constrictions to major craniofacial and visceral defects. It can cause significant neonatal morbidity. Accurate diagnosis will help in the management of the present pregnancy and in counseling with regard to future pregnancies. Here we report three cases of amniotic band syndrome detected in the prenatal period.
CONVEYOR FOUNDATIONS CALCULATION
Energy Technology Data Exchange (ETDEWEB)
S. Romanos
1995-03-10
The purpose of these calculations is to design foundations for all conveyor supports for the surface conveyors that transport the muck resulting from the TBM operation, from the belt storage to the muck stockpile. These conveyors consist of: (1) Conveyor W-TO3, from the belt storage, at the starter tunnel, to the transfer tower. (2) Conveyor W-SO1, from the transfer tower to the material stacker, at the muck stockpile.
DEFF Research Database (Denmark)
1999-01-01
An optical fibre having a periodicidal cladding structure provididing a photonic band gap structure with superior qualities. The periodical structure being one wherein high index areas are defined and wherein these are separated using a number of methods. One such method is the introduction...... of additional low index elements, another method is providing elongated elements deformed in relation to a circular cross section. Also described is a cladding structure comprising elongated elements of a material having an index of refraction higher than that of the material adjacent thereto. Using...
Ur Rehman, Shafiq; Li, Z. Y.; Li, H. M.; Ding, Z. J.
2017-11-01
An investigation on the electronic structure and band gap nature of hydrogen passivated wurtzite ZnS/Si and Si/ZnS core/shell nanowires (CSNWs) in the [0001] direction has been performed by means of the density functional theory calculations. We have studied the effects of size and core-to-shell chemical composition ratio on lattice parameter and band gap. Almost all of these CSNWs have the indirect band gap nature for different sizes and different chemical composition ratios; however, in the case of ZnS/Si CSNWs for x = 0.4 with size of 2.7 nm and 3 nm, they show a direct band behavior. This indirect to direct band gap transition is attributed to the direct band gap nature of the core region in their bulk counterpart and strain effect on the core/shell interface. The band gap also demonstrates an increase when the size of both CSNWs is reduced from 3 nm to 2.5 nm, as a consequence of quantum confinement. The band gap modulation is in perfect agreement with the experimental results. The cohesive energy indicates that CSNWs with larger diameters are energetically more stable, and Si/ZnS CSNWs are more stable than ZnS/Si CSNWs.
Studies of the defect structure from the calculations of optical and ...
Indian Academy of Sciences (India)
By calculating the optical spectrum band positions and EPR parameters (g factors, g , g⊥ and zero-field ... along C3-axis from a plane half-way between those formed by the O2− ion [16]. So the VLi above and ... Diagonalizing the energy matrix, the energy levels (and hence the optical spectrum band positions) and the ...
Calculating polaron mobility in halide perovskites
Frost, Jarvist Moore
2017-11-01
Lead halide perovskite semiconductors are soft, polar materials. The strong driving force for polaron formation (the dielectric electron-phonon coupling) is balanced by the light band effective masses, leading to a strongly-interacting large polaron. A first-principles prediction of mobility would help understand the fundamental mobility limits. Theories of mobility need to consider the polaron (rather than free-carrier) state due to the strong interactions. In this material we expect that at room temperature polar-optical phonon mode scattering will dominate and so limit mobility. We calculate the temperature-dependent polaron mobility of hybrid halide perovskites by variationally solving the Feynman polaron model with the finite-temperature free energies of Ōsaka. This model considers a simplified effective-mass band structure interacting with a continuum dielectric of characteristic response frequency. We parametrize the model fully from electronic-structure calculations. In methylammonium lead iodide at 300 K we predict electron and hole mobilities of 133 and 94 cm2V-1s-1 , respectively. These are in acceptable agreement with single-crystal measurements, suggesting that the intrinsic limit of the polaron charge carrier state has been reached. Repercussions for hot-electron photoexcited states are discussed. As well as mobility, the model also exposes the dynamic structure of the polaron. This can be used to interpret impedance measurements of the charge-carrier state. We provide the phonon-drag mass renormalization and scattering time constants. These could be used as parameters for larger-scale device models and band-structure dependent mobility simulations.
The AFLOW Standard for High-throughput Materials Science Calculations
2015-01-01
Engineering, Physics and Chemistry, Duke University, Durham, NC 27708, USA a r t i c l e i n f o Article history: Received 31 May 2015 Received in revised...with the potentials provided with the DFT software package. In VASP, these include Ultra-Soft Pseudopotentials (USPP) [22,23] and Projector -Augmented...intensive reciprocal space. This approach is prone to aliasing errors, and requires the optimization of real-space projectors if these are to be
The geometric structure of the Landau bands
Brüning, J; Geyler, V
2002-01-01
We have proposed a semiclassical explanation of the geometric structure of the spectrum for the two-dimensional Landau Hamiltonian with a two-periodic electric field without any additional assumptions on the potential. Applying an iterative averaging procedure we approximately, with any degree of accuracy, separate variables and describe a given Landau band as the spectrum of a Harper-like operator. The quantized Reeb graph for such an operator is used to obtain the following structure of the Landau band: localized states on the band wings and extended states near the middle of the band. Our approach also shows that different Landau bands have different geometric structure.
Calculations in furnace technology
Davies, Clive; Hopkins, DW; Owen, WS
2013-01-01
Calculations in Furnace Technology presents the theoretical and practical aspects of furnace technology. This book provides information pertinent to the development, application, and efficiency of furnace technology. Organized into eight chapters, this book begins with an overview of the exothermic reactions that occur when carbon, hydrogen, and sulfur are burned to release the energy available in the fuel. This text then evaluates the efficiencies to measure the quantity of fuel used, of flue gases leaving the plant, of air entering, and the heat lost to the surroundings. Other chapters consi
Wintucky, Edwin G.; Simons, Rainee N.
2015-01-01
This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler, fabricated from two dissimilar frequency band waveguides, is capable of isolating power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT) amplifier. Test results from proof-of-concept demonstrations are presented for a Ku-band/Ka-band MDC and a Ka-band/E-band MDC. In addition to power measurements at harmonic frequencies, a potential application of the MDC is in the design of a satellite borne beacon source for atmospheric propagation studies at millimeter-wave (mm-wave) frequencies (Ka-band and E-band).
Chiral flat bands: Existence, engineering, and stability
Ramachandran, Ajith; Andreanov, Alexei; Flach, Sergej
2017-10-01
We study flat bands in bipartite tight-binding networks with discrete translational invariance. Chiral flat bands with chiral symmetry eigenenergy E =0 and host compact localized eigenstates for finite range hopping. For a bipartite network with a majority sublattice chiral flat bands emerge. We present a simple generating principle of chiral flat-band networks and as a showcase add to the previously observed cases a number of new potentially realizable chiral flat bands in various lattice dimensions. Chiral symmetry respecting network perturbations—including disorder and synthetic magnetic fields—preserve both the flat band and the modified compact localized states. Chiral flat bands are spectrally protected by gaps and pseudogaps in the presence of disorder due to Griffiths effects.
Calibration of VIIRS F1 Sensor Fire Detection Band Using lunar Observations
McIntire, Jeff; Efremova, Boryana; Xiong, Xiaoxiong
2012-01-01
Visible Infrared Imager Radiometer Suite (VIIRS) Fight 1 (Fl) sensor includes a fire detection band at roughly 4 microns. This spectral band has two gain states; fire detection occurs in the low gain state above approximately 345 K. The thermal bands normally utilize an on-board blackbody to provide on-orbit calibration. However, as the maximum temperature of this blackbody is 315 K, the low gain state of the 4 micron band cannot be calibrated in the same manner as the rest of the thermal bands. Regular observations of the moon provide an alternative calibration source. The lunar surface temperature has been recently mapped by the DIVINER sensor on the LRO platform. The periodic on-board high gain calibration along with the DIVINER surface temperatures was used to determine the emissivity and solar reflectance of the lunar surface at 4 microns; these factors and the lunar data are then used to fit the low gain calibration coefficients of the 4 micron band. Furthermore, the emissivity of the lunar surface is well known near 8.5 microns due to the Christiansen feature (an emissivity maximum associated with Si-O stretching vibrations) and the solar reflectance is negligible. Thus, the 8.5 micron band is used for relative calibration with the 4 micron band to de-trend any temporal variations. In addition, the remaining thermal bands are analyzed in a similar fashion, with both calculated emissivities and solar reflectances produced.
Exercise-induced changes in EEG alpha power depend on frequency band definition mode.
Gutmann, Boris; Hülsdünker, Thorben; Mierau, Julia; Strüder, Heiko K; Mierau, Andreas
2017-10-18
In the majority of studies investigating cortical alpha oscillations the alpha frequency is defined as a fixed band thus, neglecting recommendations in the EEG literature to adjust the alpha band according to the individual alpha peak frequency (iAPF). Based on our previous findings indicating exhaustive exercise induces an increase of the post-exercise iAPF, we scrutinized the influence of exercise on post-exercise alpha power by comparing fixed and iAPF-adjusted alpha frequency bands. Resting EEG was recorded from 13 scalp locations in nine subjects before, immediately after as well as ten minutes following an exhaustive exercise protocol on a cycle ergometer. Lower and upper band alpha power was calculated for fixed and iAPF-adjusted frequency bands. Post-exercise lower alpha power increased in both fixed and individually defined bands while a higher upper alpha power was only observed in the fixed frequency band condition. Further, the increase in iAPF was positively related to the changes in fixed-band upper alpha power. It is concluded that lower alpha power is significantly increased following exhaustive exercise whereas the results for upper alpha power are substantially influenced by the method of frequency band definition. Therefore, caution is indicated when analyzing and interpreting exercise-induced changes in alpha power. Copyright © 2017 Elsevier B.V. All rights reserved.
Theoretical study on the two-band degenerate-gaps superconductors: Application to SrPt3P
Huang, Hai; Hou, Li-Chao; Zhao, Bin-Peng
2016-09-01
We study the magnetic properties of two-band degenerate-gaps superconductors with two-band isotropic Ginzburg-Landau theory. The exact solutions of upper critical field and London penetration depth are obtained, and the calculations reproduce the experimental data of the recently observed superconducting crystal SrPt3P in a broad temperature range. It directly underlies that SrPt3P is a multi-band superconductor with equal gaps in two Fermi surface sheets.
Self-consistent Green's function method for dilute nitride conduction band structure.
Seifikar, Masoud; O'Reilly, Eoin P; Fahy, Stephen
2014-09-10
We present a self-consistent Green's function (SCGF) approach for the Anderson many-impurity model to calculate the band dispersion and density of states near the conduction band edge in GaN(x)As(1-x) dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the two-band model, which assumes all N states have the same energy, EN; (2) a model which includes a full distribution of N states obtained by allowing for direct interaction between N sites. The density of states, projected onto extended and localised states, calculated by the SCGF two-band model, are in excellent agreement with those previously obtained in supercell calculations and reveal a gap in the density of states just above E(N), in contrast with the results of previous non-self-consistent Green's function calculations. However, including the full distribution of N states in a SCGF calculation removes this gap, in agreement with experiment.
Bhatnagar, Shalabh
2017-01-01
Sound is an emerging source of renewable energy but it has some limitations. The main limitation is, the amount of energy that can be extracted from sound is very less and that is because of the velocity of the sound. The velocity of sound changes as per medium. If we could increase the velocity of the sound in a medium we would be probably able to extract more amount of energy from sound and will be able to transfer it at a higher rate. To increase the velocity of sound we should know the speed of sound. If we go by the theory of classic mechanics speed is the distance travelled by a particle divided by time whereas velocity is the displacement of particle divided by time. The speed of sound in dry air at 20 °C (68 °F) is considered to be 343.2 meters per second and it won't be wrong in saying that 342.2 meters is the velocity of sound not the speed as it's the displacement of the sound not the total distance sound wave covered. Sound travels in the form of mechanical wave, so while calculating the speed of sound the whole path of wave should be considered not just the distance traveled by sound. In this paper I would like to focus on calculating the actual speed of sound wave which can help us to extract more energy and make sound travel with faster velocity.
Multilayer optical calculations
Byrnes, Steven J
2016-01-01
When light hits a multilayer planar stack, it is reflected, refracted, and absorbed in a way that can be derived from the Fresnel equations. The analysis is treated in many textbooks, and implemented in many software programs, but certain aspects of it are difficult to find explicitly and consistently worked out in the literature. Here, we derive the formulas underlying the transfer-matrix method of calculating the optical properties of these stacks, including oblique-angle incidence, absorption-vs-position profiles, and ellipsometry parameters. We discuss and explain some strange consequences of the formulas in the situation where the incident and/or final (semi-infinite) medium are absorptive, such as calculating $T>1$ in the absence of gain. We also discuss some implementation details like complex-plane branch cuts. Finally, we derive modified formulas for including one or more "incoherent" layers, i.e. very thick layers in which interference can be neglected. This document was written in conjunction with ...
Giemsa C-banding of Barley Chromosomes. I: Banding Pattern Polymorphism
DEFF Research Database (Denmark)
Linde-Laursen, Ib
1978-01-01
Twenty barley (Hordeum vulgare) lines studied had a common basic chromosome banding pattern. Most bands ranged from medium to very small in size. The most conspicuous banding occurred at or near the centromeres, in the proximal, intercalary parts of most chromosome arms and beside the secondary c...... 7. Seventeen differently banded karyotypes were found. Some banding pattern polymorphisms can be used in cytological and cytogenetic studies....
Raman bands in Ag nanoparticles obtained in extract of Opuntia ficus-indica plant
Bocarando-Chacon, J.-G.; Cortez-Valadez, M.; Vargas-Vazquez, D.; Rodríguez Melgarejo, F.; Flores-Acosta, M.; Mani-Gonzalez, P. G.; Leon-Sarabia, E.; Navarro-Badilla, A.; Ramírez-Bon, R.
2014-05-01
Silver nanoparticles have been obtained in an extract of Opuntia ficus-indica plant. The size and distribution of nanoparticles were quantified by atomic force microscopy (AFM). The diameter was estimated to be about 15 nm. In addition, energy dispersive X-ray spectroscopy (EDX) peaks of silver were observed in these samples. Three Raman bands have been experimentally detected at 83, 110 and 160 cm-1. The bands at 83 and 110 cm-1 are assigned to the silver-silver Raman modes (skeletal modes) and the Raman mode located at 160 cm-1 has been assigned to breathing modes. Vibrational assignments of Raman modes have been carried out based on the Density Functional Theory (DFT) quantum mechanical calculation. Structural and vibrational properties for small Agn clusters with 2≤n≤9 were determined. Calculated Raman modes for small metal clusters have an approximation trend of Raman bands. These Raman bands were obtained experimentally for silver nanoparticles (AgNP).
Comparison of GTD propagation model wide-band path loss simulation with measurements
Luebbers, Raymond J.; Foose, William A.; Reyner, Gregory
1989-04-01
The geometrical theory of diffraction (GTD) wedge diffraction has been used successfully to predict narrow-band CW radio-wave propagation characteristics. The GTD propagation model uses a two-dimensional terrain profile approximated as piecewise-linear and computes reflection and diffraction effects with model output representing a complex approximation to the narrow-band channel transfer function. Using the narrow-band GTD model as a starting point, a wideband terrain-sensitive model has been developed. The complex wideband channel transfer function calculated by the GTD model is transformed to the time domain via an FFT method. The results are then used to predict time-domain radio transmission loss in the form of a band-limited approximation to the channel impulse response. Important channel parameters such as delay spread and wideband received signal level can then be calculated. The GTD predicted results are compared with measurements.
Optimization of spectral band utilization in gridless WDM optical network
Martins, Indayara B.; Aldaya, Ivan; Perez-Sanchez, G.; Gallion, Philippe
2014-02-01
In this paper, the effects of gridless spectrum allocation in Wavelength Division Multiplexed (WDM) optical networks are examined. The advanced modulation formats and multi-rate transmissions of the signals, which are key parameters in the optical system project, are taken into account. The consumed spectrum, as well as the impact of linear and nonlinear impairments on the signal transmission, are compared to WDM network adopting standard grid and gridless ITU. To analyze the influence of these physical effects, some key network design parameters are monitored and evaluated, such as the guard band size, the signal occupied bandwidth, the laser power and the quality of channels. The applied signal modulation formats were On/Off Keying (OOK), Quadrature Phase Shift keying (QPSK), and Dual Polarization State Phase Modulation (DP-QPSK), whereas the transmission rate per wavelength was varied from 10 Gb/s to 100Ghz. The guard band, signal band, and laser power were swept and the resulted Bit Error Rate (BER) was estimated from the eye-diagram. Analytical calculations and simulations are conducted in order to evaluate the impact of the gridless spectrum allocation on both the spectral consumption and the signal quality of transmission (QoT). Results reveal that a gridless transmission system reduces the spectral consumption while offering an acceptable QoT. This work was carried out with both analytical modeling and numerical calculation using the Optisystem as well as Matlab.
Electron correlations in narrow energy bands: modified polar model approach
Directory of Open Access Journals (Sweden)
L. Didukh
2008-09-01
Full Text Available The electron correlations in narrow energy bands are examined within the framework of the modified form of polar model. This model permits to analyze the effect of strong Coulomb correlation, inter-atomic exchange and correlated hopping of electrons and explain some peculiarities of the properties of narrow-band materials, namely the metal-insulator transition with an increase of temperature, nonlinear concentration dependence of Curie temperature and peculiarities of transport properties of electronic subsystem. Using a variant of generalized Hartree-Fock approximation, the single-electron Green's function and quasi-particle energy spectrum of the model are calculated. Metal-insulator transition with the change of temperature is investigated in a system with correlated hopping. Processes of ferromagnetic ordering stabilization in the system with various forms of electronic DOS are studied. The static conductivity and effective spin-dependent masses of current carriers are calculated as a function of electron concentration at various DOS forms. The correlated hopping is shown to cause the electron-hole asymmetry of transport and ferromagnetic properties of narrow band materials.
Multi-band terahertz metasurface absorber
Wang, Xuying; Wang, Qingmin; Dong, Guoyan; Hao, Yanan; Lei, Ming; Bi, Ke
2017-12-01
A terahertz metasurface perfect absorber with multi-band performance is demonstrated. The absorber is composed of a ground plane and four split-ring resonators (SRRs) with different dimensions, separated by a dielectric spacer. The numerical simulation results illustrate that the proposed absorber has four distinct absorption peaks at resonance frequencies of 4.24, 5.66, 7.22, and 8.97 THz, with absorption rates of 96.8%, 99.3%, 97.3%, and 99.9%, respectively. Moreover, the corresponding full width at half-maximum (FWHM) values are about 0.27, 0.35, 0.32, and 0.42 THz, respectively, which are much broader than those of previously reported absorbers. Besides, the calculated magnetic field distributions allow us to understand the absorption mechanism in detail. The effects of incident angle and azimuthal angle on the absorber are also investigated. The results show that the proposed absorber is partially sensitive to the incident angle, which makes this design promising for practical applications in terahertz imagers and detectors.
Franck-Condon factors and r-centroids for the B-X bands of 10B18O and 11B18O molecules
Directory of Open Access Journals (Sweden)
VOJISLAV BOJOVIC
2005-05-01
Full Text Available Frank–Condon factors and r-centroids have been calculated for the B2S+ –X2S+ bands of the 10B18O and 11B18O isotopic molecules assuming that both the B and X states follow a Morse potential curve. The calculated q n'n" values are compared with observed band intensities and the relationship between the r-centroids and the band positions has been determined and is discussed.
C3H2 : A wide-band-gap semiconductor with strong optical absorption
Lu, Hong-Yan; Cuamba, Armindo S.; Geng, Lei; Hao, Lei; Qi, Yu-Min; Ting, C. S.
2017-10-01
Using first-principles calculations, we predict a new type of partially hydrogenated graphene system, C3H2 , which turns out to be a semiconductor with a band gap of 3.56 eV. The bands are rather flat at the band edges and thus lead to a large density of states, which further results in strong optical absorption between the valence band and the conduction band. Particularly, it shows strong optical absorption at about 4.5 eV for the light polarized along the lines connecting the nearest unhydrogenated carbon atoms. Thus, the predicted C3H2 system may have potential applications for a polarizer as well as other high-efficiency optical devices in the near ultraviolet region.
Out-of-band effects of satellite ocean color sensors.
Wang, Menghua; Naik, Puneeta; Son, SeungHyun
2016-03-20
We analyze the sensor out-of-band (OOB) effects for satellite ocean color sensors of the sea-viewing wild field-of-view sensor (SeaWiFS), the moderate resolution imaging spectroradiometer (MODIS), and the visible infrared imaging radiometer suite (VIIRS) for phytoplankton-dominated open oceans and turbid coastal and inland waters, following the approach of Wang et al. [Appl. Opt.40, 343 (2001)APOPAI0003-693510.1364/AO.40.000343]. The applicability of the open ocean water reflectance model of Morel and Maritorena [J. Geophys. Res.106, 7163 (2001)JGREA20148-022710.1029/2000JC000319] (MM01) for the sensor OOB effects is analyzed for oligotrophic waters in Hawaii. The MM01 model predicted OOB contributions for oligotrophic waters are consistent with the result from in situ measurements. The OOB effects cause an apparent shift in sensor band center wavelengths in radiometric response, which depends on the sensor spectral response function and the target radiance being measured. Effective band center wavelength is introduced and calculated for three satellite sensors and for various water types. Using the effective band center wavelengths, satellite and in situ measured water optical property data can be more meaningfully and accurately compared. It is found that, for oligotrophic waters, the OOB effect is significant for the SeaWiFS 555 nm band (and somewhat 510 nm band), MODIS 412 nm band, and VIIRS 551 nm band. VIIRS and SeaWiFS have similar sensor OOB performance. For coastal and inland waters, however, the OOB effect is generally not significant for all three sensors, even though some small OOB effects do exist. This study highlights the importance of understanding the sensor OOB effect and the necessity of a complete prelaunch sensor characterization on the quality of ocean color products. Furthermore, it shows that hyperspectral in situ optics measurements are preferred for the purpose of accurately validating satellite-measured normalized water
Band-Gap Engineering in two-dimensional periodic photonic crystals
Kushwaha, Manvir S.
1999-01-01
A theoretical investigation is made of the dispersion characteristics of plasmons in a two-dimensional periodic system of semiconductor (dielectric) cylinders embedded in a dielectric (semiconductor) background. We consider both square and hexagonal arrangements and calculate extensive band structures for plasmons using a plane-wave method within the framework of a local theory. It is found that such a system of semiconductor-dielectric composite can give rise to huge full band gaps (with a g...
Amir Reza Sadrolhosseini; Suraya Abdul Rashid; A. S. M. Noor; Alireza Kharazmi; H N Lim; Mohd Adzir Mahdi
2016-01-01
A polypyrrole-nanoparticles reduced graphene oxide nanocomposite layer was prepared using electrochemical method. The prepared samples were characterized using Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and UV-visible spectroscopy. The band gap of nanocomposite layers was calculated from UV-visible spectra and the thermal diffusivity of layers was measured using a photoacoustic technique. As experimental results, the optical band gap was in the range...
Rat gastric banding model for bariatric surgery.
Kanno, Hitoshi; Kiyama, Teruo; Fujita, Itsuo; Kato, Shunji; Yoshiyuki, Toshiro; Tajiri, Takashi
2008-08-01
Adjustable gastric banding is a surgical approach to weight reduction. In this study we created a gastric banding model in rats to better understand the mechanism of body weight loss. Male Sprague-Dawley rats weighing 260 to 280 g were subjected to gastric banding (band group) (n=8) or to a sham operation (control group) (n=8). Body weights were monitored for 14 days, and daily food and water intake and nitrogen balance were monitored for 7 days. Two rats in the band group died of malnutrition due to gastric stomal stenosis and obstruction caused by the gastric banding. Body weight gain during the 14 days after the operation was less in the band group than in the control group (pwater intake during the 7 days after the operation was significantly less in the band group than in the control group (pbalance was significantly less in the band group than in the control group (p<0.01). Gastric banding decreased the body weight gain of rats by decreasing the amount of food intake because of the creation of a small gastric pouch.
Reflectivity calculated for a 3D silicon photonic band gap crystal with finite support
Devashish, D.; Hasan, Shakeeb Bin; van der Vegt, Jacobus J.W.; Vos, Willem L.
2016-01-01
OpenCL is an open standard for parallel programming of heterogeneous compute devices, such as GPUs, CPUs, DSPs or FPGAs. However, the verbosity of its C host API can hinder application development. In this paper we present cf4ocl, a software library for rapid development of OpenCL programs in pure
MODIS/Terra 8-Day Clear Sky Radiance Bias Daily L3 Global 1Deg Zonal Bands V006
National Aeronautics and Space Administration — MODCSR_B files contain 1-degree zonal mean clear-sky biases (observed minus calculated radiance differences) and associated statistics for bands 31 and 33-36 for...
Directory of Open Access Journals (Sweden)
Jose Ángel Silva-Guillén
2016-10-01
Full Text Available Semiconducting transition metal dichalcogenides present a complex electronic band structure with a rich orbital contribution to their valence and conduction bands. The possibility to consider the electronic states from a tight-binding model is highly useful for the calculation of many physical properties, for which first principle calculations are more demanding in computational terms when having a large number of atoms. Here, we present a set of Slater–Koster parameters for a tight-binding model that accurately reproduce the structure and the orbital character of the valence and conduction bands of single layer MX 2 , where M = Mo, W and X = S, Se. The fit of the analytical tight-binding Hamiltonian is done based on band structure from ab initio calculations. The model is used to calculate the optical conductivity of the different compounds from the Kubo formula.
Ross, Vincent; Dion, Denis
2011-05-01
A new C++ library for radiative transfer calculations in the visible and infrared bands which uses MODTRAN as a primary source for atmospheric optical parameters has been developed at Defense R&D Canada, Valcartier (DRDC Valcartier). The main benefit of the library is its capability to perform fast wide spectral band calculations with an appreciably high accuracy. Coherent calculations on wide bands are made possible by using a modified version of the correlated-k theory. The main features of the library are discussed, and comparisons with conventional spectral MODTRAN 4 calculations are presented. It is shown that the library is capable of producing band results that are usually within 5% of MODTRAN 4 with computation times that are thousands of times faster.
First triaxial superdeformed band in sup 1 sup 7 sup 0 Hf
Neusser, A; Bringel, P; Domscheit, J; Mergel, E; Nenoff, N; Singh, A K; Hagemann, G B; Jensen, D R; Bhattacharya, S; Curien, D; Dorvaux, O; Hannachi, F; López-Martens, A
2002-01-01
First evidence is presented for triaxial superdeformation in sup 1 sup 7 sup 0 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.)
Band inversion mechanism in topological insulators: A guideline for materials design
Zhu, Zhiyong
2012-06-01
Alteration of the topological order by band inversion is a key ingredient of a topologically nontrivial material. Using first-principles calculations for HgTe, PtScBi, and Bi2Se3, we argue that it is not accurate to ascribe the band inversion to the spin-orbit coupling. Instead, scalar relativistic effects and/or lattice distortions are found to be essential. Therefore, the search for topologically nontrivial materials should focus on band shifts due to these mechanisms rather than spin-orbit coupling. We propose an effective scheme to search for new topological insulators.
Band gap of two-dimensional fiber-air photonic crystals
Energy Technology Data Exchange (ETDEWEB)
Yang, Shu, E-mail: yangshu5678@163.com; Li, Masha
2016-04-15
A two-dimensional photonic crystal (PC) composed of textile fiber and air is initially discussed in this paper. Textile materials are so called soft materials, which are different from the previous PCs composed of rigid materials. The plain wave expansion method is used to calculate band structure of different PCs by altering component properties or structural parameters. Results show that the dielectric constant of textile fibers, fiber filling ratio and lattice arrangement are effective factors which influence PCs' band gap. Yet lattice constant and fiber diameter make inconspicuous influence on the band gap feature.
Band structure engineering in topological insulator based heterostructures.
Menshchikova, T V; Otrokov, M M; Tsirkin, S S; Samorokov, D A; Bebneva, V V; Ernst, A; Kuznetsov, V M; Chulkov, E V
2013-01-01
The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state.
Ultrafast Electronic Band Gap Control in an Excitonic Insulator.
Mor, Selene; Herzog, Marc; Golež, Denis; Werner, Philipp; Eckstein, Martin; Katayama, Naoyuki; Nohara, Minoru; Takagi, Hide; Mizokawa, Takashi; Monney, Claude; Stähler, Julia
2017-08-25
We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta_{2}NiSe_{5} investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of F_{C}=0.2 mJ cm^{-2}, the band gap narrows transiently, while it is enhanced above F_{C}. Hartree-Fock calculations reveal that this effect can be explained by the presence of the low-temperature excitonic insulator phase of Ta_{2}NiSe_{5}, whose order parameter is connected to the gap size. This work demonstrates the ability to manipulate the band gap of Ta_{2}NiSe_{5} with light on the femtosecond time scale.
Projected Shell Model Description of Positive Parity Band of 130Pr Nucleus
Singh, Suram; Kumar, Amit; Singh, Dhanvir; Sharma, Chetan; Bharti, Arun; Bhat, G. H.; Sheikh, J. A.
2018-02-01
Theoretical investigation of positive parity yrast band of odd-odd 130Pr nucleus is performed by applying the projected shell model. The present study is undertaken to investigate and verify the very recently observed side band in 130Pr theoretically in terms of quasi-particle (qp) configuration. From the analysis of band diagram, the yrast as well as side band are found to arise from two-qp configuration πh 11/2 ⊗ νh 11/2. The present calculations are viewed to have qualitatively reproduced the known experimental data for yrast states, transition energies, and B( M1) / B( E2) ratios of this nucleus. The recently observed positive parity side band is also reproduced by the present calculations. The energy states of the side band are predicted up to spin 25+, which is far above the known experimental spin of 18+ and this could serve as a motivational factor for future experiments. In addition, the reduced transition probability B( E2) for interband transitions has also been calculated for the first time in projected shell model, which would serve as an encouragement for other research groups in the future.
Characterization of chromosomal rearrangements using multicolor-banding (MCB/m-band).
Liehr, Thomas; Weise, Anja; Hinreiner, Sophie; Mkrtchyan, Hasmik; Mrasek, Kristin; Kosyakova, Nadezda
2010-01-01
Molecular cytogenetics and especially fluorescence in situ hybridization (FISH) banding approaches are nowadays standard for the exact characterization of simple, complex, and cryptic chromosomal aberrations within the human genome. FISH-banding techniques are any kind of FISH techniques, which provide the possibility to characterize simultaneously several chromosomal subregions smaller than a chromosome arm. FISH banding methods fitting that definition may have quite different characteristics, but share the ability to produce a DNA-specific chromosomal banding. While the standard techniques such as G-bands by Trypsin using Giemsa banding lead to a protein-related black and white banding pattern, FISH-banding techniques are DNA-specific, more colorful, and thus, more informative. At present, the most frequently applied FISH banding technique is the multicolor banding (MCB/m-band) approach. MCB/m-band is based on region-specific microdissection libraries, producing changing fluorescence intensity ratios along the chromosomes. Here we describe the FISH-banding technique MCB/m-band and illustrate how to apply it for characterization of chromosomal breakpoints with a minimal number of FISH experiments.
Multi-band slow light metamaterial.
Zhu, Lei; Meng, Fan-Yi; Fu, Jia-Hui; Wu, Qun; Hua, Jun
2012-02-13
In this paper, a multi-band slow light metamaterial is presented and investigated. The metamaterial unit cell is composed of three cut wires of different sizes and parallel to each other. Two transparency windows induced by two-two overlaps of absorption bands of three cut wires are observed. The multi-band transmission characteristics and the slow light properties of metamaterial are verified by numerical simulation, which is in a good agreement with theoretical predictions. The impacts of structure parameters on transparency windows are also investigated. Simulation results show the spectral properties can be tuned by adjusting structure parameters of metamaterial. The equivalent circuit model and the synthesis method of the multi-band slow light metamaterial are presented. It is seen from simulation results that the synthesis method accurately predicts the center frequency of the multi-band metamaterial, which opens a door to a quick and accurate construction for multi-band slow light metamaterial.
A new generalized Kohn-Sham method for fundamental band-gaps in solids.
Eisenberg, Helen R; Baer, Roi
2009-06-14
We developed a method for calculating the ground-state properties and fundamental band-gaps of solids, using a generalized Kohn-Sham approach combining a local density approximation (LDA) functional with a long-range explicit exchange orbital functional. We found that when the range parameter is selected according to the formula gamma=A/(epsiloninfinity-epsilon) where epsiloninfinity is the optical dielectric constant of the solid and epsilon=0.84 and A=0.216 a0(-1), predictions of the fundamental band-gap close to the experimental values are obtained for a variety of solids of different types. For most solids the range parameter gamma is small (i.e. explicit exchange is needed only at long distances) so the predicted values for lattice constants and bulk moduli are similar to those based on conventional LDA calculations. Preliminary calculations on silicon give a general band structure in good agreement with experiment.
Topology of two-band superconductors
Energy Technology Data Exchange (ETDEWEB)
Tanaka, Y., E-mail: y.tanaka@aist.go.j [National Institute of Advanced Industrial Science and Technology (AIST), AIST-Tsukuba Central-2-32918, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Iyo, A. [National Institute of Advanced Industrial Science and Technology (AIST), AIST-Tsukuba Central-2-32918, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Tokiwa, K.; Watanabe, T. [Department of Applied Electronics, Faculty of Industrial Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 (Japan); Crisan, A. [National Institute for Materials Physics, P.O. Box MG-7, Bucharest 077125 (Romania); Department of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Sundaresan, A. [Chemistry and Physics of Materials Unit (CPMU), Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560 064 (India); Terada, N. [Department of Electrical and Electronics Engineering, Faculty of of Engineering, Kagoshima University, 1-21-40 Koromoto, Kagoshima, Kagoshima 890-0065 (Japan)
2010-12-15
Two-band superconductivity has a topology different from that in single-band superconductivity. The topology is not always stabilized in an infinitely homogeneous sample. The morphology, grain shape, and pattern of the device (topology of the superconducting materials) is effective in stabilizing the topology. In this report, we discuss a vortex having a small magnetic flux but a large winding number as one plausible topology in a two-band superconductor.
Fluctuation Diamagnetism in Two-Band Superconductors
Adachi, Kyosuke; Ikeda, Ryusuke
2016-01-01
Anomalously large fluctuation diamagnetism around the superconducting critical temperature has been recently observed on iron selenide (FeSe) [S. Kasahara et al., unpublished]. This indicates that superconducting fluctuations (SCFs) play a more significant role in FeSe, which supposedly has two-band structure, than in the familiar single-band superconductors. Motivated by the data in FeSe, SCF-induced diamagnetism is examined in a two-band system, on the basis of a phenomenological approach w...
Multi-band Modelling of Appearance
DEFF Research Database (Denmark)
Stegmann, Mikkel Bille; Larsen, Rasmus
2002-01-01
the appearance of both derived feature bands and an intensity band. As a special case of feature-band augmented appearance modelling we propose a dedicated representation with applications to face segmentation. The representation addresses a major problem within face recognition by lowering the sensitivity...... to lighting conditions. Results show that localisation accuracy of facial features is considerably increased using this appearance representation under normal and abnormal lighting and at multiple scales....
Multi-band Modelling of Appearance
DEFF Research Database (Denmark)
Stegmann, Mikkel Bille; Larsen, Rasmus
2003-01-01
the appearance of both derived feature bands and an intensity band. As a special case of feature-band augmented appearance modelling we propose a dedicated representation with applications to face segmentation. The representation addresses a major problem within face recognition by lowering the sensitivity...... to lighting conditions. Results show that the localisation accuracy of facial features is considerably increased using this appearance representation under diffuse and directional lighting and at multiple scales....
On Rabi oscillations between Bloch bands
Plötz, Patrick
2010-01-01
We study Rabi oscillations between the bands of an arbitrary biased superlattice in a tight-binding model. We reduce the problem to an equation of Whittaker--Hill type and, in absence of any known solutions in closed form, discuss different approximations to describe the oscillations between the Bloch bands. We identify regimes of weak and strong inter-band coupling and compare predictions for these Rabi oscillations to numerical results.
A dual band terahertz metamaterial absorber
Energy Technology Data Exchange (ETDEWEB)
Tao Hu; Fan Kebin; Zhang Xin [Department of Mechanical Engineering, Boston University, Boston, MA 02215 (United States); Bingham, C M; Shrekenhamer, D; Padilla, W J [Department of Physics, Boston College, Chestnut Hill, MA 02467 (United States); Pilon, D; Strikwerda, A C; Averitt, R D, E-mail: xinz@bu.ed, E-mail: raveritt@physics.bu.ed [Department of Physics, Boston University, Boston, MA 02215 (United States)
2010-06-09
We present the design, fabrication and characterization of a dual band metamaterial absorber which experimentally shows two distinct absorption peaks of 0.85 at 1.4 THz and 0.94 at 3.0 THz. The dual band absorber consists of a dual band electric-field-coupled (ELC) resonator and a metallic ground plane, separated by an 8 {mu}m dielectric spacer. Fine tuning of the two absorption resonances is achieved by individually adjusting each ELC resonator geometry.
X-BAND KLYSTRON DEVELOPMENT AT SLAC
Energy Technology Data Exchange (ETDEWEB)
Vlieks, Arnold E.; /SLAC
2009-08-03
The development of X-band klystrons at SLAC originated with the idea of building an X-band Linear Collider in the late 1980's. Since then much effort has been expended in developing a reliable X-band Power source capable of delivering >50 MW RF power in pulse widths >1.5 {micro}s. I will report on some of the technical issues and design strategies which have led to the current SLAC klystron designs.
Electronic structure of crystalline uranium nitride: LCAO DFT calculations
Energy Technology Data Exchange (ETDEWEB)
Evarestov, R.A.; Losev, M.V.; Panin, A.I. [Department of Quantum Chemistry, St. Petersburg State University, 26 University Prospekt, Stary Peterghof, 198504 (Russian Federation); Mosyagin, N.S. [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg District, 188300 (Russian Federation); Titov, A.V. [Department of Quantum Chemistry, St. Petersburg State University, 26 University Prospekt, Stary Peterghof, 198504 (Russian Federation); Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg District, 188300 (Russian Federation)
2008-01-15
The results of the first LCAO DFT calculations of cohesive energy, band structure and charge distribution in uranium nitride (UN) crystal are presented and discussed. The calculations are made with the uranium atom relativistic effective core potentials, including 60, 78 and 81 electrons in the core. It is demonstrated that the chemical bonding in UN crystal has a metallic-covalent nature. Three 5f-electrons are localized on the U atom and occupy the states near the Fermi level. The metallic nature of the crystal is due to the f-character of both the valence-band top and the conduction-band bottom. The covalent bonds are formed by the interaction of 7s- and 6d-states of the uranium atom with the 2p-states of the nitrogen atom. It is shown that the inclusion of 5f-electrons in the atomic core introduces small changes in the calculated cohesive energy of UN crystal and electron charge distribution. However, the inclusion of 5s-, 5p-, 5d-electrons in the valence shell allows the better agreement with the calculated and experimental cohesive-energy value. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Infinitesimal base transformations method for calculating the k.p Hamiltonian of monolayer MoS2
Beiranvand, Khadijeh; Ghalambor Dezfuli, Abdolmohammad; Sabaeian, Mohammad
2017-10-01
In this work, we present the study of monolayer MoS2 band structure using k.p method based on infinitesimal basis transformations perturbation theory. We also study the effect of spin-orbit coupling on the band structure. We have calculated the low energy k.p Hamiltonian and derived the dispersion relations for the last valance band and the first conduction band at K and -K points of the first Brillouin zone. The results clearly show the electron-hole asymmetry and trigonal warping effects. The results also indicate the spin-splitting of the first conduction band.
Valence band electronic structure of Pd based ternary chalcogenide superconductors
Energy Technology Data Exchange (ETDEWEB)
Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)
2016-12-15
Highlights: • VB Photoemission study and DFT calculations on Pd based ternary superconductors are presented. • Nb{sub 2}Pd{sub 0.95}S{sub 5} shows a temperature dependent pseudogap. • VB spectral features of ternary superconductors are correlated to their structural geometry. - Abstract: We present a comparative study of the valence band electronic structure of Pd based ternary chalcogenide superconductors Nb{sub 2}Pd{sub 0.95}S{sub 5}, Ta{sub 2}Pd{sub 0.97}S{sub 6} and Ta{sub 2}Pd{sub 0.97}Te{sub 6} using experimental photoemission spectroscopy and density functional based theoretical calculations. We observe a qualitatively similarity between valence band (VB) spectra of Nb{sub 2}Pd{sub 0.95}S{sub 5} and Ta{sub 2}Pd{sub 0.97}S{sub 6}. Further, we find a pseudogap feature in Nb{sub 2}Pd{sub 0.95}S{sub 5} at low temperature, unlike other two compounds. We have correlated the structural geometry with the differences in VB spectra of these compounds. The different atomic packing in these compounds could vary the strength of inter-orbital hybridization among various atoms which leads to difference in their electronic structure as clearly observed in our DOS calculations.
Maximizing phononic band gaps in piezocomposite materials by means of topology optimization.
Vatanabe, Sandro L; Paulino, Glaucio H; Silva, Emílio C N
2014-08-01
Phononic crystals (PCs) can exhibit phononic band gaps within which sound and vibrations at certain frequencies do not propagate. In fact, PCs with large band gaps are of great interest for many applications, such as transducers, elastic/acoustic filters, noise control, and vibration shields. Previous work in the field concentrated on PCs made of elastic isotropic materials; however, band gaps can be enlarged by using non-isotropic materials, such as piezoelectric materials. Because the main property of PCs is the presence of band gaps, one possible way to design microstructures that have a desired band gap is through topology optimization. Thus in this work, the main objective is to maximize the width of absolute elastic wave band gaps in piezocomposite materials designed by means of topology optimization. For band gap calculation, the finite element analysis is implemented with Bloch-Floquet theory to solve the dynamic behavior of two-dimensional piezocomposite unit cells. Higher order frequency branches are investigated. The results demonstrate that tunable phononic band gaps in piezocomposite materials can be designed by means of the present methodology.
Mode decomposition based on crystallographic symmetry in the band-unfolding method
Ikeda, Yuji; Carreras, Abel; Seko, Atsuto; Togo, Atsushi; Tanaka, Isao
2017-01-01
The band-unfolding method is widely used to calculate the effective band structures of a disordered system from its supercell model. The unfolded band structures show the crystallographic symmetry of the underlying structure, where the difference of chemical components and the local atomic relaxation are ignored. However, it has still been difficult to decompose the unfolded band structures into the modes based on the crystallographic symmetry of the underlying structure, and therefore detailed analyses of the unfolded band structures have been restricted. In this study, a procedure to decompose the unfolded band structures according to the small representations (SRs) of the little groups is developed. The decomposition is performed using the projection operators for SRs derived from the group representation theory. The current method is employed to investigate the phonon band structure of disordered face-centered-cubic Cu0.75Au0.25 , which has large variations of atomic masses and force constants among the atomic sites due to the chemical disorder. In the unfolded phonon band structure, several peculiar behaviors such as discontinuous and split branches are found in the decomposed modes corresponding to specific SRs. They are found to occur because different combinations of the chemical elements contribute to different regions of frequency.
Band engineering of thermoelectric materials.
Pei, Yanzhong; Wang, Heng; Snyder, G J
2012-12-04
Lead chalcogenides have long been used for space-based and thermoelectric remote power generation applications, but recent discoveries have revealed a much greater potential for these materials. This renaissance of interest combined with the need for increased energy efficiency has led to active consideration of thermoelectrics for practical waste heat recovery systems-such as the conversion of car exhaust heat into electricity. The simple high symmetry NaCl-type cubic structure, leads to several properties desirable for thermoelectricity, such as high valley degeneracy for high electrical conductivity and phonon anharmonicity for low thermal conductivity. The rich capabilities for both band structure and microstructure engineering enable a variety of approaches for achieving high thermoelectric performance in lead chalcogenides. This Review focuses on manipulation of the electronic and atomic structural features which makes up the thermoelectric quality factor. While these strategies are well demonstrated in lead chalcogenides, the principles used are equally applicable to most good thermoelectric materials that could enable improvement of thermoelectric devices from niche applications into the mainstream of energy technologies. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Microwave emulations and tight-binding calculations of transport in polyacetylene
Energy Technology Data Exchange (ETDEWEB)
Stegmann, Thomas, E-mail: stegmann@icf.unam.mx [Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Avenida Universidad s/n, 62210 Cuernavaca (Mexico); Franco-Villafañe, John A., E-mail: jofravil@fis.unam.mx [Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apartado Postal J-48, 72570 Puebla (Mexico); Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Avenida Universidad s/n, 62210 Cuernavaca (Mexico); Ortiz, Yenni P. [Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Avenida Universidad s/n, 62210 Cuernavaca (Mexico); Kuhl, Ulrich [Université de Nice – Sophia Antipolis, Laboratoire de la Physique de la Matière Condensée, CNRS, Parc Valrose, 06108 Nice (France); Mortessagne, Fabrice, E-mail: fabrice.mortessagne@unice.fr [Université de Nice – Sophia Antipolis, Laboratoire de la Physique de la Matière Condensée, CNRS, Parc Valrose, 06108 Nice (France); Seligman, Thomas H. [Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Avenida Universidad s/n, 62210 Cuernavaca (Mexico); Centro Internacional de Ciencias, 62210 Cuernavaca (Mexico)
2017-01-05
A novel approach to investigate the electron transport of cis- and trans-polyacetylene chains in the single-electron approximation is presented by using microwave emulation measurements and tight-binding calculations. In the emulation we take into account the different electronic couplings due to the double bonds leading to coupled dimer chains. The relative coupling constants are adjusted by DFT calculations. For sufficiently long chains a transport band gap is observed if the double bonds are present, whereas for identical couplings no band gap opens. The band gap can be observed also in relatively short chains, if additional edge atoms are absent, which cause strong resonance peaks within the band gap. The experimental results are in agreement with our tight-binding calculations using the nonequilibrium Green's function method. The tight-binding calculations show that it is crucial to include third nearest neighbor couplings to obtain the gap in the cis-polyacetylene. - Highlights: • Electronic transport in individual polyacetylene chains is studied. • Microwave emulation experiments and tight-binding calculations agree well. • In long chains a band-gap opens due the dimerization of the chain. • In short chains edge atoms cause strong resonance peaks in the center of the band-gap.
IPC - Isoelectric Point Calculator.
Kozlowski, Lukasz P
2016-10-21
Accurate estimation of the isoelectric point (pI) based on the amino acid sequence is useful for many analytical biochemistry and proteomics techniques such as 2-D polyacrylamide gel electrophoresis, or capillary isoelectric focusing used in combination with high-throughput mass spectrometry. Additionally, pI estimation can be helpful during protein crystallization trials. Here, I present the Isoelectric Point Calculator (IPC), a web service and a standalone program for the accurate estimation of protein and peptide pI using different sets of dissociation constant (pKa) values, including two new computationally optimized pKa sets. According to the presented benchmarks, the newly developed IPC pKa sets outperform previous algorithms by at least 14.9 % for proteins and 0.9 % for peptides (on average, 22.1 % and 59.6 %, respectively), which corresponds to an average error of the pI estimation equal to 0.87 and 0.25 pH units for proteins and peptides, respectively. Moreover, the prediction of pI using the IPC pKa's leads to fewer outliers, i.e., predictions affected by errors greater than a given threshold. The IPC service is freely available at http://isoelectric.ovh.org Peptide and protein datasets used in the study and the precalculated pI for the PDB and some of the most frequently used proteomes are available for large-scale analysis and future development. This article was reviewed by Frank Eisenhaber and Zoltán Gáspári.
The rating reliability calculator
Directory of Open Access Journals (Sweden)
Solomon David J
2004-04-01
Full Text Available Abstract Background Rating scales form an important means of gathering evaluation data. Since important decisions are often based on these evaluations, determining the reliability of rating data can be critical. Most commonly used methods of estimating reliability require a complete set of ratings i.e. every subject being rated must be rated by each judge. Over fifty years ago Ebel described an algorithm for estimating the reliability of ratings based on incomplete data. While his article has been widely cited over the years, software based on the algorithm is not readily available. This paper describes an easy-to-use Web-based utility for estimating the reliability of ratings based on incomplete data using Ebel's algorithm. Methods The program is available public use on our server and the source code is freely available under GNU General Public License. The utility is written in PHP, a common open source imbedded scripting language. The rating data can be entered in a convenient format on the user's personal computer that the program will upload to the server for calculating the reliability and other statistics describing the ratings. Results When the program is run it displays the reliability, number of subject rated, harmonic mean number of judges rating each subject, the mean and standard deviation of the averaged ratings per subject. The program also displays the mean, standard deviation and number of ratings for each subject rated. Additionally the program will estimate the reliability of an average of a number of ratings for each subject via the Spearman-Brown prophecy formula. Conclusion This simple web-based program provides a convenient means of estimating the reliability of rating data without the need to conduct special studies in order to provide complete rating data. I would welcome other researchers revising and enhancing the program.
Band Structure and Contact Resistance of Carbon Nanotubes Deformed by a Metal Contact
Hafizi, Roohollah; Tersoff, Jerry; Perebeinos, Vasili
2017-11-01
Capillary and van der Waals forces cause nanotubes to deform or even collapse under metal contacts. Using ab initio band structure calculations, we find that these deformations reduce the band gap by as much as 30%, while fully collapsed nanotubes become metallic. Moreover, degeneracy lifting due to the broken axial symmetry, and wave functions mismatch between the fully collapsed and the round portions of a CNT, lead to a 3 times higher contact resistance. The latter we demonstrate by contact resistance calculations within the tight-binding approach.
Calculations of superconducting parametric amplifiers performances
Goto, T.; Takeda, M.; Saito, S.; Shimakage, H.
2017-07-01
A superconducting parametric amplifier is an electromagnetic wave amplifier with high-quality characteristics such as a wide bandwidth, an extremely low noise, and a high dynamic range. In this paper, we report on the estimations of a YBCO superconducting parametric amplifier characteristic. The YBCO thin films were deposited on an MgO substrate by a pulsed laser deposition method. Based on the measured YBCO thin film parameters, theoretical calculations were implemented for evaluations of kinetic inductance nonlinearities and parametric gains. The nonlinearity of the YBCO thin film was estimated to be stronger than a single crystal NbTiN thin film. It is indicated that the YBCO parametric amplifier has a potential to be realized the amplifier with the high parametric gain. It is also expected that it could be operated in the range of the high frequency band, at the high temperature, and low applied current.
Fluctuation conductivity in two-band superconductor SmFeAsO0.8F0.2
Directory of Open Access Journals (Sweden)
Askerzade I.N.
2015-09-01
Full Text Available In this study we have calculated the fluctuation conductivity near critical temperature of SmFeAsO0.8F0.2 superconductor using two-band Ginzburg-Landau theory. It was illustrated that in the absence of external magnetic field, the two-band model reduced to a single effective band theory with modified temperature dependences. The calculations revealed three-dimensional character of fluctuations of conductivity in the new Fe-based superconductor SmFeAsO0.8F0.2. It has been shown that such a model is in good agreement with experimental data for this compound.
The limiting efficiency of band gap graded solar cells
Energy Technology Data Exchange (ETDEWEB)
Rafat, Nadia H. [Faculty of Engineering, Cairo University, Giza (Egypt); Habib, S.E.D. [Faculty of electronics and communication, Cairo University, Giza (Egypt)
1998-09-04
Two fundamental mechanisms limit the maximum attainable efficiency of solar cells, namely the radiative recombination and Auger recombination. We show in this paper that proper band gap grading of the solar cell localizes the Auger recombination around the metallurgical junction. Two beneficial effects result from this Auger recombination localization; first the cell is less sensitive to the surface conditions, and second, the previous estimates for the limiting efficiency of solar cells by Shockley, Tiedje, and Green are revised upwardly. We calculate the optimum bandgap grading profile for several real material systems, including GaInAsP lattice matched to InP, and a-SiGe on a-Si substrate
Rotational and vibrational bands in {sup 108}Pd
Energy Technology Data Exchange (ETDEWEB)
Alcantara-Nunez, J.A.; Oliveira, J.R.B.; Cybulska, E.W.; Medina, N.H.; Rao, M.N.; Ribas, R.V.; Rizzutto, M.A.; Seale, W.A.; Falla-Sotelo, F. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica
2004-09-15
The {sup 108}Pd nucleus has been studied with the {sup 100}Mo({sup 11}B, p2n{gamma}) 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 4{pi} charged-particle ancillary detector system. The structure of the bands was interpreted within the framework of the cranked shell model and total Routhian calculations. (author)
Self broadening in the nu-1 band of NH3
Markov, V. N.; Pine, A. S.; Buffa, G.; Tarrini, O.
1993-01-01
Self-broadening coefficients, pressure shifts, and integrated intensities have been measured for Q- and R-branch transitions in the nu-1 fundamental band of ammonia using a difference-frequency laser spectrometer. A strong, systematic J and K dependence of the broadening coefficients, reminiscent of the ground-state inversion transitions, is observed and compared with semiclassical line broadening calculations. Dicke narrowing is evident at intermediate pressures for the sharpest lines, primarily the R(J, 0) transitions. Incipient line mixing is apparent in the Q branch at pressures above about 0.1 bar.
Observation of full plasmonic stop bands in fractal structures
Yasrebi, Navid; Khorasani, Sina; Hazeghi, Aryan; Rashidian, Bizhan
2011-03-01
In the last year's meeting we reported a novel approach for stabilization of numerical calculation of plasmonic propagation band structure. This method enables us to precisely obtain the propagation modes of periodically patterned two-dimensional conducting sheets, with arbitrarily high order of spatial harmonic content. Following the above contribution, we here present successful construction of a periodic fractal structure based on the combination of square array of wires and the space-filling Hilbert curves, leading to very large plasmonic gaps in the propagation spectrum. Different parameters affecting that gap, and the way to control each of them will be presented. Possible applications will be discussed.
Subwavelength-Sized Narrow-Band Anechoic Waveguide Terminations
DEFF Research Database (Denmark)
Santillan, Arturo Orozco; Ærenlund, Emil; Bozhevolnyi, Sergey I.
2016-01-01
We propose and demonstrate the use of a pair of detuned acoustic resonators to efficiently absorb narrowband sound waves in a terminated waveguide. The suggested configuration is relatively simple and advantageous for usage at low frequencies, since the dimensions of the resonators are very small...... compared to the wavelength.We present a theoretical description based on lumped parameters to calculate the absorption coefficient, which agrees very well with experimental data. The experimental results verify that the anechoic (reflection approximately −38 dB) narrow-band (Δf=f ∼ 0.1) termination...
Solid State KA-Band, Solid State W-Band and TWT Amplifiers Project
National Aeronautics and Space Administration — Phase I of the proposal describes plans to develop a state of the art transmitter for the W-Band and KA -Band Cloud Radar system. Our focus will be concentrated in...
An Understanding of the Band Gap Shrinkage in Sn-Doped ZnO for Dye-Sensitized Solar Cells
Yildiz, Abdullah; Ozturk, Elif; Atilgan, Abdullah; Sbeta, Mohamed; Atli, Aycan; Serin, Tulay
2017-12-01
Sn-doped ZnO (TZO) films were deposited onto glass substrates by a spray pyrolysis technique. The temperature-dependent conductivity measurements and room-temperature Hall effect measurements were carried out, which indicated that the films exhibited a degenerate semiconductor behavior. Band gap energy of the films was studied by transmission measurements. With increasing Sn content, band gap shrinkage was observed. It was determined that this shrinkage was associated with the competition between many body interactions and the Burstein-Moss effect. We concluded that there is a good agreement between experimental results and theoretical calculations in terms of the shift in band gap. Furthermore, the effective mass value based on parabolic band considerations needed to be replaced by one based on nonparabolic band structure of ZnO for higher content of Sn (>3% at.) to correlate the calculations with the results.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Gaigong [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Lin, Lin, E-mail: linlin@math.berkeley.edu [Department of Mathematics, University of California, Berkeley, Berkeley, CA 94720 (United States); Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Hu, Wei, E-mail: whu@lbl.gov [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Yang, Chao, E-mail: cyang@lbl.gov [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Pask, John E., E-mail: pask1@llnl.gov [Physics Division, Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)
2017-04-15
Recently, we have proposed the adaptive local basis set for electronic structure calculations based on Kohn–Sham density functional theory in a pseudopotential framework. The adaptive local basis set is efficient and systematically improvable for total energy calculations. In this paper, we present the calculation of atomic forces, which can be used for a range of applications such as geometry optimization and molecular dynamics simulation. We demonstrate that, under mild assumptions, the computation of atomic forces can scale nearly linearly with the number of atoms in the system using the adaptive local basis set. We quantify the accuracy of the Hellmann–Feynman forces for a range of physical systems, benchmarked against converged planewave calculations, and find that the adaptive local basis set is efficient for both force and energy calculations, requiring at most a few tens of basis functions per atom to attain accuracies required in practice. Since the adaptive local basis set has implicit dependence on atomic positions, Pulay forces are in general nonzero. However, we find that the Pulay force is numerically small and systematically decreasing with increasing basis completeness, so that the Hellmann–Feynman force is sufficient for basis sizes of a few tens of basis functions per atom. We verify the accuracy of the computed forces in static calculations of quasi-1D and 3D disordered Si systems, vibration calculation of a quasi-1D Si system, and molecular dynamics calculations of H{sub 2} and liquid Al–Si alloy systems, where we show systematic convergence to benchmark planewave results and results from the literature.
Zhang, Gaigong; Lin, Lin; Hu, Wei; Yang, Chao; Pask, John E.
2017-04-01
Recently, we have proposed the adaptive local basis set for electronic structure calculations based on Kohn-Sham density functional theory in a pseudopotential framework. The adaptive local basis set is efficient and systematically improvable for total energy calculations. In this paper, we present the calculation of atomic forces, which can be used for a range of applications such as geometry optimization and molecular dynamics simulation. We demonstrate that, under mild assumptions, the computation of atomic forces can scale nearly linearly with the number of atoms in the system using the adaptive local basis set. We quantify the accuracy of the Hellmann-Feynman forces for a range of physical systems, benchmarked against converged planewave calculations, and find that the adaptive local basis set is efficient for both force and energy calculations, requiring at most a few tens of basis functions per atom to attain accuracies required in practice. Since the adaptive local basis set has implicit dependence on atomic positions, Pulay forces are in general nonzero. However, we find that the Pulay force is numerically small and systematically decreasing with increasing basis completeness, so that the Hellmann-Feynman force is sufficient for basis sizes of a few tens of basis functions per atom. We verify the accuracy of the computed forces in static calculations of quasi-1D and 3D disordered Si systems, vibration calculation of a quasi-1D Si system, and molecular dynamics calculations of H2 and liquid Al-Si alloy systems, where we show systematic convergence to benchmark planewave results and results from the literature.
Shell model results for T = 1 and T = 0 bands in 66As
Srivastava, Praveen C.; Sahu, R.; Kota, V. K. B.
2017-12-01
The results of comprehensive shell model (SM) analyses, within the full {f}5/2{{pg}}9/2 model space, of the recently available experimental data (Ruotsalainen et al (2013) Phys. Rec. C 88 024320) with four T = 0 bands and one T = 1 band in the odd–odd N = Z nucleus 66As are presented. The calculations are performed by using the jj44b effective interaction developed recently by Brown and Lisetskiy for this model space. For the lowest two T = 0 bands and the T = 1 band, the results are in reasonable agreement with experimental data and the deformed shell model is used to identify their intrinsic structure. For the T = 1 band, a structural change at {8}+ is predicted. For the third {9}+ band with T = 0, the shell model B(E2) values and quadrupole moments (in addition to energies) are consistent with the interpretation in terms of an aligned isoscalar np pair in a {g}9/2 orbit coupled to the 64Ge ground band. Similarly, the {9}+ level of band 4 and a close-lying {5}+ level are found to be isomeric states in the analysis. Finally, the energies of the band 5 members, calculated using the shell model with both positive and negative parity, show that the observed levels are most likely negative parity levels. The shell model results with jj44b are compared with results obtained using the JUN45 interaction.
Atomic-Monolayer MoS2 Band-to-Band Tunneling Field-Effect Transistor
Lan, Yann Wen
2016-09-05
The experimental observation of band-to-band tunneling in novel tunneling field-effect transistors utilizing a monolayer of MoS2 as the conducting channel is demonstrated. Our results indicate that the strong gate-coupling efficiency enabled by two-dimensional materials, such as monolayer MoS2, results in the direct manifestation of a band-to-band tunneling current and an ambipolar transport.
Energy Technology Data Exchange (ETDEWEB)
Benedek, R.; Thackeray, M.M. [Argonne National Lab., IL (United States). Chemical Technology Div.; Yang, L.H. [Lawrence Livermore National Lab., CA (United States)
1999-09-01
Interest in the {gamma}-bronze, Li{sub 1+x}V{sub 3}O{sub 8}, as a possible electrode material in rechargeable Li batteries has stimulated several experimental studies on this system. Detailed interpretation of the electrochemical and physical-property measurements is complicated by uncertainties regarding the structural arrangement of Li atoms as a function of x and by a phase transition between two monoclinic structures ({gamma}{sub a}, {gamma}{sub b}) during intercalation. To elucidate the atomic structures and the phase transition, first-principles calculations re performed with the local-density-functional-theory (LDFT) planewave pseudopotential method for both {gamma}{sub a} and {gamma}{sub b} as a function of lithiation. Calculations for the compositions 1+x=1.5 and 1+x=4 confirm that the Li configuration determined in the existing X-ray diffraction structure refinements (at 1+x=1.2 and 1+x=4, respectively), coincide with the predicted low-energy configurations. Structure predictions were made at intermediate compositions, for which no experimental structure measurement is available. The order in which the tetrahedrally coordinated Li sites are filled at equilibrium as a function of x in {gamma}{sub a} was predicted. Calculated electrochemical potentials as a function of composition agree well with experimental data. (orig.)
Error Analysis of Band Matrix Method
Taniguchi, Takeo; Soga, Akira
1984-01-01
Numerical error in the solution of the band matrix method based on the elimination method in single precision is investigated theoretically and experimentally, and the behaviour of the truncation error and the roundoff error is clarified. Some important suggestions for the useful application of the band solver are proposed by using the results of above error analysis.
Kleinberg, L.
1982-01-01
Circuit uses standard components to overcome common limitation of JFET amplifiers. Low-noise band-pass amplifier employs JFET and operational amplifier. High gain and band-pass characteristics are achieved with suitable choice of resistances and capacitances. Circuit should find use as low-noise amplifier, for example as first stage instrumentation systems.
Low band gap polymers for organic photovoltaics
DEFF Research Database (Denmark)
Bundgaard, Eva; Krebs, Frederik C
2007-01-01
Low band gap polymer materials and their application in organic photovoltaics (OPV) are reviewed. We detail the synthetic approaches to low band gap polymer materials starting from the early methodologies employing quinoid homopolymer structures to the current state of the art that relies...
Getting Elementary Students Involved in Band
Moore, Patience
2009-01-01
The author discusses getting elementary students involved in a band. The goals of an elementary band instructor should include introduction of good practice habits, working within an ensemble, and rehearsal procedures, along with the focusing on the essentials of music. Instructors should let students use the basic instruments: flute, clarinet,…
Deformed configurations, band structures and spectroscopic ...
Indian Academy of Sciences (India)
2014-03-20
Mar 20, 2014 ... the deformed solution C (band D2). The intrinsic configurations of various excited bands are determined by the orbits near the Fermi surfaces. In figure 2, we show the orbits near the Fermi surfaces for the uncon- strained and constrained HF solutions of 82Ge. For the 'almost' spherical solution, the.
Bandura, A. V.; Kubicki, J.
2002-12-01
Periodic DFT energy minimizations were performed with Sr(II) and Zn(II) adsorbed onto the (110) face of rutile using the program CASTEP (Accelrys, Inc.). Ultra-soft pseudopotentials, an energy cut-off of 340 eV, the Generalized Gradient Approximation, and Perdew-Wang functionals were employed to calculate energies. A 3-layer thick slab of rutile (alpha-titanium dioxide) was relaxed in P2 symmetry with the central layer of atoms constrained to mimic the bulk experimental crystal coordinates. Both the Sr(II) and Zn(II) were surrounded by a solvation sphere of water molecules on the side opposite the rutile crystal face in order to approximate the water-mineral interface. Sr(II) was found to be stable in a quadradentate configuration bonded to two terminal Ti-OH oxygen atoms and two bridging (Ti-O-Ti) oxygen atoms with a distance of 2.5 Angstroms to the rutile surface. This configuration is essentially the same as that derived by Fenter and coworkers using X-ray standing wave (XSW) spectroscopy. Zn(II) was predicted to be stable in two configurations suggested by XSW spectroscopy: a monodentate complex to a bridging oxygen atom and a bidentate configuration bonded to two terminal Ti-OH oxygen atoms.
First-principle calculation on mechanical and thermal properties of B2-NiSc with point defects
Yuan, Zhipeng; Cui, Hongbao; Guo, Xuefeng
2017-01-01
Using the first-principles plane-wave pseudo-potential method based on density functional theory, the effect of vacancy and anti-position defect on the mechanical and thermal properties of B2-NiSc intermetallics were discussed in detail. Several parameters, such as the shear modulus, bulk modulus, modulus of elasticity, C 11-C 11, the Debye temperature and Poisson's ratio, have been calculated to evaluate the effect of vacancy and anti-position defect on the hardness, ductility and thermal properties of B2-NiSc intermetallics. The results show that VNi, ScNi, VSc and NiSc the four point defects all make the crystal hardness decrease and improve plasticity of B2-NiSc intermetallics. The entropy, enthalpy and free energy of VNi, ScNi, VSc and NiSc are monotonously changed as temperature changes. From the perspective of free energy, NiSc is the most stable, while ScNi is the most unstable. Debye temperature of NiSc intermetallics with four different point defects shows VNi, ScNi, VSc and NiSc the four point defects all reduce the stability of B2-NiSc intermetallics. Project supported by the National Natural Science Foundation of China (Nos. 51301063, 51571086) and the Talent Introduction Foundation of Henan Polytechnic University (No. Y-2009).
Fluctuation diamagnetism in two-band superconductors
Adachi, Kyosuke; Ikeda, Ryusuke
2016-04-01
Anomalously large fluctuation diamagnetism around the superconducting critical temperature has been recently observed in iron selenide (FeSe) [Kasahara et al. (unpublished)]. This indicates that superconducting fluctuations (SCFs) play a more significant role in FeSe, which supposedly has a two-band structure, than in the familiar single-band superconductors. Motivated by the data on FeSe, SCF-induced diamagnetism is examined in a two-band system, on the basis of a phenomenological approach with a Ginzburg-Landau functional. The obtained results indicate that the SCF-induced diamagnetism may be more enhanced than that in a single-band system due to the existence of two distinct fluctuation modes. Such enhancement of diamagnetism unique to a two-band system seems consistent with the large diamagnetism observed in FeSe, though still far from a quantitative agreement.
Band width and multiple-angle valence-state mapping of diamond
Energy Technology Data Exchange (ETDEWEB)
Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J. [Lawrence Berkeley National Lab., CA (United States)] [and others
1997-04-01
The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid`s many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of {+-}1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84{degrees} cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space.
Recommended radiative property data for Venusian entry calculations
Jones, J. J.; Boughner, R. E.; Haggard, K. V.; Nealy, J. E.; Schryer, D. R.; Zoby, E. V.
1974-01-01
A compilation of experimental and calculated data on the radiative properties species important in Venusian entry is presented. Molecular band systems, atomic lines, free-bound, and free-free continua are considered for the principal radiating species of shock heated carbon dioxide. A limited amount of data pertinent to the species in the ablation layer is also included. The assumption is made that the Venus atmosphere so closely approximates pure CO2 that the inviscid layer radiation is due almost entirely to thermally excited CO2. The only exception is the inclusion of data on the Violet band system of CN. Recommendations are made as to best property values for radiative heating calculations. A review of the basic equations and the relationships of the various emission-absorption gas porperties is also included.
Point Defect Calculations in Tungsten
National Research Council Canada - National Science Library
Danilowicz, Ronald
1968-01-01
.... The vacancy migration energy for tungsten was calculated. The calculated value of 1.73 electron volts, together with experimental data, suggests that vacancies migrate in stage III recovery in tungsten...
Perturbation Calculation of two-electron interaction in the ground of ...
African Journals Online (AJOL)
The single-band Hubbard model was studied in one dimensional lattice system which consist only of two sites. The perturbation calculation accounts for the ground state energy and its wave functions .The exact and perturbation calculation are in agreement when the value of the on-site coulomb interaction U is equal to ...
Band-type microelectrodes for amperometric immunoassays
Energy Technology Data Exchange (ETDEWEB)
Lee, Ga-Yeon; Chang, Young Wook; Ko, Hyuk [Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749 (Korea, Republic of); Kang, Min-Jung [Korea Institute of Science and Technology (KIST), Seoul (Korea, Republic of); Pyun, Jae-Chul, E-mail: jcpyun@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749 (Korea, Republic of)
2016-07-20
A band-type microelectrode was made using a parylene-N film as a passivation layer. A circular-type, mm-scale electrode with the same diameter as the band-type microelectrode was also made with an electrode area that was 5000 times larger than the band-type microelectrode. By comparing the amperometric signals of 3,5,3′,5′-tetramethylbenzidine (TMB) samples at different optical density (OD) values, the band-type microelectrode was determined to be 9 times more sensitive than the circular-type electrode. The properties of the circular-type and the band-type electrodes (e.g., the shape of their cyclic voltammograms, the type of diffusion layer used, and the diffusion layer thickness per unit electrode area) were characterized according to their electrode area using the COMSOL Multiphysics software. From these simulations, the band-type electrode was estimated to have the conventional microelectrode properties, even when the electrode area was 100 times larger than a conventional circular-type electrode. These results show that both the geometry and the area of an electrode can influence the properties of the electrode. Finally, amperometric analysis based on a band-type electrode was applied to commercial ELISA kits to analyze human hepatitis B surface antigen (hHBsAg) and human immunodeficiency virus (HIV) antibodies. - Highlights: • A band-type microelectrode was made using a parylene-N film as a passivation layer. • The band-type microelectrode was 14-times more sensitive than circular-type electrode. • The influence of geometry on microelectrode properties was simulated using COMSOL. • The band-type electrode was applied to ELISA kits for hHBsAg and hHIV-antibodies.
Wannier-like functions and tight-binding parametrization for the manganese bands in CaMnO sub 3
Saha-Dasgupta, T
2003-01-01
We study the electronic band structure of CaMnO sub 3 , in order to understand the origin of the dispersion of the Mn(e sub g) bands, which is in contrast with the predicted dispersionless bands within the Anderson-Hasegawa double-exchange model with infinite Hund's-rule coupling. A downfolding technique within the newly developed muffin-tin orbital-based method is used to analyse the density-functional band structure obtained in the local spin density approximation. The finite Hund's coupling parameter in realistic situations allows the same-spin bands on the two manganese sublattices to mix producing a large dispersion. The calculated Wannier functions for the Mn(e sub g) bands also show large oxygen character at sites further away from nearest oxygen sites causing long-ranged Mn-Mn hopping processes.
High-spin states and a new band based on the isomeric state in {sup 152}Nd
Energy Technology Data Exchange (ETDEWEB)
Yeoh, E.Y.; Wang, J.G.; Ding, H.B.; Gu, L.; Xu, Q.; Xiao, Z.G. [Tsinghua University, Department of Physics, Beijing (China); Zhu, S.J. [Tsinghua University, Department of Physics, Beijing (China); Vanderbilt University, Department of Physics, Nashville, TN (United States); Hamilton, J.H.; Ramayya, A.V.; Hwang, J.K.; Liu, S.H.; Li, K. [Vanderbilt University, Department of Physics, Nashville, TN (United States); Yang, Y.C.; Sun, Y. [Shanghai Jiao Tong University, Department of Physcis, Shanghai (China); Luo, Y.X. [Vanderbilt University, Department of Physics, Nashville, TN (United States); Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Rasmussen, J.O.; Lee, I.Y. [Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Ma, W.C. [Mississippi State University, Department of Physics, Mississippi State, MS (United States)
2010-08-15
High-spin states of the neutron-rich {sup 152}Nd nucleus have been reinvestigated by measuring the prompt {gamma} -rays in the spontaneous fission of {sup 252}Cf. The ground-state band and a side negative-parity band have been updated. A new band based on the 2243.7keV isomeric state has been identified. The half-life for the isomeric state has been measured to be 63(7)ns. The projected shell model is employed to study the band structure of this nucleus. The results show that the calculated levels of the bands are in good agreement with the experimental ones, and the isomeric state and the negative-parity band are based on the proton {pi} 5/2{sup -}[532] x {pi}9/2{sup +}[404] and neutron {nu} 3/2{sup -}[521] x {nu}5/2{sup +}[642] two-quasiparticles configurations, respectively. (orig.)
Composite fermions in bands with N -fold rotational symmetry
Ippoliti, Matteo; Geraedts, Scott D.; Bhatt, R. N.
2017-09-01
We study the effect of band anisotropy with discrete rotational symmetry CN (where N ≥2 ) in the quantum Hall regime of two-dimensional electron systems. We focus on the composite Fermi liquid (CFL) at half-filling of the lowest Landau level. We find that the magnitude of anisotropy transferred to the composite fermions decreases very rapidly with N . We demonstrate this by performing density matrix normalization group calculations on the CFL, and comparing the anisotropy of the composite fermion Fermi contour with that of the (noninteracting) electron Fermi contour at zero magnetic field. We also show that the effective interaction between the electrons after projecting into a single Landau level is much less anisotropic than the band, a fact which does not depend on filling and thus has implications for other quantum Hall states as well. Our results confirm experimental observations on anisotropic bands with warped Fermi contours, where the only detectable effect on the composite Fermi contour is an elliptical distortion (N =2 ).
Omnidirectional elastic band gap in finite lamellar structures
Bria, D.; Djafari-Rouhani, B.
2002-11-01
This paper presents a comprehensive theoretical analysis of the occurrence of omnidirectional reflection in one-dimensional phononic crystal structures. We discuss the conditions for a one-dimensional layered structure, made of elastic materials, to exhibit total reflection of acoustic incident waves in a given frequency range, for all incident angles and all polarizations. The property of omnidirectional reflection can be fulfilled with a simple finite superlattice if the substrate from which the incident waves are launched is made of a material with high acoustic velocities (this is very similar to the case of omnidirectional optical mirror where the incident light is generated in vacuum). However, if the substrate is made of a material with low acoustic velocities, we propose two solutions to obtain an omnidirectional band gap, namely, the cladding of a superlattice with a layer of high acoustic velocities, which acts like a barrier for the propagation of phonons, or the association in tandem of two different superlattices in such a way that the superposition of their band structures exhibits an absolute acoustic band gap. We discuss the appropriate choices of the material and geometrical properties to realize such structures. The behavior of the transmission coefficients are discussed in relation with the dispersion curves of the finite structure embedded between two substrates. Both transmission coefficients and densities of states (from which we derive the dispersion curves) are calculated in the framework of a Green's function method.
Endoscopic Management of Eroded Bands Following Banded-Gastric Bypass (with Video).
Shehab, Hany; Gawdat, Khaled
2017-07-01
Banded-gastric bypass is a highly effective bariatric procedure, yet the possibility of band erosion remains a significant drawback. Surgical removal of eroded bands may be associated with significant morbidity. In this study, we assess the efficacy and safety of a solely peroral endoscopic approach for the management of eroded bands in patients with a banded-gastric bypass. Starting January 2012, all patients with banded-gastric bypass and an eroded band were subjected to an attempt at peroral endoscopic removal using endoscopic scissors and/or argon plasma coagulation (APC), regardless of the circumference of band eroding inside the lumen. Sixteen patients presented with eroded bands, 2 were deemed not amenable to endoscopic removal as only part of the thickness was eroded. Of the 14 patients where endoscopic attempts were performed, 12 (86%) were completely removed successfully, while 2 (14%) were cut but could not be extracted and only the intraluminal portion was trimmed. Complete resolution of symptoms occurred in 13 (93%) while in 1 patient (7%) there was partial improvement. Only one endoscopic session was performed per patient with a median time of 37.5 min per session (22-55 min). No complications were encountered. Endoscopic removal of eroded gastric bands in patients with banded-gastric bypass is effective and safe in the majority of patients. When bands are adherent to the gastric wall, removal of the intraluminal portion of the band may lead to full or partial improvement of symptoms. Endoscopic band removal can be attempted even when a small part of band circumference has eroded.
Numerically optimized band boundaries of Planck mean absorption coefficients in air plasma
Kloc, P.; Aubrecht, V.; Bartlova, M.
2017-08-01
Radiation heat transfer plays an important role in the energy balance of plasma in an electric arc and its accurate prediction is essential for the development of new electrical devices. Unfortunately, a very complex spectrum of the absorption coefficient makes accurate radiation heat transfer calculations a very challenging task, especially with complex geometries. Numerical approximation of the absorption coefficient is therefore commonly used to reduce computing demands. This paper presents our contribution to the topic of computing requirements reduction, namely the problem of frequency band selection for mean absorption coefficients (MACs). We show that, with the proper band distribution and averaging method, even a very low number of bands can be sufficient for an accurate approximation of the real radiation heat transfer. The band selection process is based upon numerical optimization with a mean value of each band being calculated as a line limited Planck MAC. Both the line limiting factor and associated characteristic plasma absorption length are investigated in detail and an optimal value equal to the three plasma radii is proposed. Tables for three bands mean absorption coefficients in air at the pressure of 1 bar and temperature range spanning from 300 K to 30 kK are included in this paper. These tables serve as input parameters for a fast evaluation of radiation transfer using either the P1 or discrete ordinates method (DOM) approximation with satisfactory accuracy.
Rain Attenuation Correction of Reflectivity for X-Band Dual-Polarization Radar
Directory of Open Access Journals (Sweden)
Liang Feng
2016-12-01
Full Text Available In order to improve the performance of X-band dual-polarization radars, it is necessary to conduct attenuation correction before using the X-band radar data. This study analyzes a variety of attenuation correction methods for the X-band radar reflectivity, and proposes a high-resolution slide self-consistency correction (SSCC method, which is an improvement of Kim et al.’s method based on Bringi et al.’s original method. The new method is comprehensively evaluated with the observational data of convective cloud, stratiform cloud, and the stratiform cloud with embedded convection. Comparing with the intrinsic reflectivity at X-band calculated from the reflectivity at S-band, it is found that the new method can effectively reduce the correction errors when calculating differential propagation shift increments using the conventional self-consistency attenuation correction method. This method can efficiently correct the X-band dual-polarization radar reflectivity, in particular, for the echoes with reflectivity greater than 35 dBZ.
EFFECTS OF A BAND LOOP ON LOWER EXTREMITY MUSCLE ACTIVITY AND KINEMATICS DURING THE BARBELL SQUAT.
Foley, Ryan C A; Bulbrook, Brittany D; Button, Duane C; Holmes, Michael W R
2017-08-01
Medial knee collapse can signal an underlying movement issue that, if uncorrected, can lead to a variety of knee injuries. Placing a band around the distal thigh may act as a proprioceptive aid to minimize medial collapse of the knee during squats; however, little is known about EMG and biomechanics in trained and untrained individuals during the squat with an elastic band added. To investigate the effects of the TheraBand® Band Loop on kinematics and muscle activity of the lower extremity during a standard barbell back squat at different intensities in both trained and untrained individuals. Cross-sectional, repeated measures. Sixteen healthy, male, university aged-participants were split into two groups of eight, consisting of a trained and untrained group. Participants performed both a 3-repetition maximum (3-RM) and a bodyweight load squat for repetitions to failure. Lower extremity kinematics and surface electromyography of four muscles were measured bilaterally over two sessions, an unaided squat and a band session (band loop placed around distal thighs). Medial knee collapse, measured as a knee width index, and maximum muscle activity were calculated. During the 3-RM, squat weight was unaffected by band loop intervention (p = 0.486) and the trained group lifted more weight than the untrained group (plower for 3-RM squats, regardless of group. Despite minimal changes in kinematics for the untrained group, increased muscle activity with the band loop may suggest that a training aid may, over time, lead to an increase in barbell squat strength by increasing activation of agonist muscles more than traditional, un-banded squats. Greater maximal muscle activity in most muscles during band loop sessions may provide enhanced knee stability via increased activation of stabilizing muscles. 3.
Microscopic mechanism of the tunable band gap in potassium-doped few-layer black phosphorus
Kim, Sun-Woo; Jung, Hyun; Kim, Hyun-Jung; Choi, Jin-Ho; Wei, Su-Huai; Cho, Jun-Hyung
2017-08-01
Tuning band gaps in two-dimensional (2D) materials is of great interest for the fundamental and practical aspects of contemporary material sciences. Recently, black phosphorus (BP) consisting of stacked layers of phosphorene was experimentally observed to show a widely tunable band gap by means of the deposition of potassium (K) atoms on the surface, thereby allowing great flexibility in the design and optimization of electronic and optoelectronic devices. Here, based on density-functional theory calculations, we demonstrates that the donated electrons from K dopants are mostly localized in the topmost BP layer and this surface charging efficiently screens the K ion potential. It is found that, as the K doping increases, the extreme surface charging and its screening of K atoms shift the conduction bands down in energy, i.e., towards a higher binding energy, because they have more charge near the surface, while it has little influence on the valence bands having more charge in the deeper layers. This result provides a different explanation for the observed tunable band gap compared to the previously proposed giant Stark effect where a vertical electric field from the positively ionized K overlayer to the negatively charged BP layers shifts the conduction band minimum Γ1 c (valence band minimum Γ8 v) downwards (upwards). The present prediction of Γ1 c and Γ8 v as a function of the K doping reproduces well the widely tunable band gap, anisotropic Dirac semimetal state, and band-inverted semimetal state, as observed in an angle-resolved photoemission spectroscopy experiment. Our findings shed new light on a route for tunable band gap engineering of 2D materials through the surface doping of alkali metals.
Light-induced gaps in semiconductor band-to-band transitions.
Vu, Q T; Haug, H; Mücke, O D; Tritschler, T; Wegener, M; Khitrova, G; Gibbs, H M
2004-05-28
We observe a triplet around the third harmonic of the semiconductor band gap when exciting 50-100 nm thin GaAs films with 5 fs pulses at 3 x 10(12) W/cm(2). The comparison with solutions of the semiconductor Bloch equations allows us to interpret the observed peak structure as being due to a two-band Mollow triplet. This triplet in the optical spectrum is a result of light-induced gaps in the band structure, which arise from coherent band mixing. The theory is formulated for full tight-binding bands and uses no rotating-wave approximation.
Chaudhuri, B. K.; Mondal, B. N.; Chakraborty, P. K.
2018-02-01
We provide the energy spectrum of an electron in a degenerately doped semiconductor of parabolic band. Knowing the energy spectrum, the density-of-states (DOS) functions are obtained, considering the Gaussian distribution of the potential energy of the impurity states, showing a band tail in them e.g., energy spectrum and density-of-states. Therefore, Fermi integrals (FIs) of DOS functions, having band tail, are developed by the exact theoretical calculations of the same. It is noticed that with heavy dopings in semiconductors, the total FI demonstrates complex functions, containing both real and imaginary terms of different FI functions. Their moduli possess an oscillatory function of η (reduced Fermi energy = Ef/kBT, kB is the Boltzmann constant and T is the absolute temperature) and η e (impurity screening potential), having a series solutions of confluent hypergeometric functions, Φ (a, b; z), superimposed with natural cosine functions of angle θ . The variation of θ with respect to η indicated a resonance at η =1.5. The oscillatory behaviour of FIs show the existence of `band-gaps', both in the real as well as in the forbidden bands as new band gaps in the semiconductor.
Cho, Gookbin; Kim, Jungho
2017-09-01
We theoretically investigate the effect of conduction band non-parabolicity (NPB) on the optical gain spectrum of quantum cascade lasers (QCLs) using the effective two-band finite difference method. Based on the effective two-band model to consider the NPB effect in the multiple quantum wells (QWs), the wave functions and confined energies of electron states are calculated in two different active-region structures, which correspond to three-QW single-phonon and four-QW double-phonon resonance designs. In addition, intersubband optical dipole moments and polar-optical-phonon scattering times are calculated and compared without and with the conduction band NPB effect. Finally, the calculation results of optical gain spectra are compared in the two QCL structures having the same peak gain wavelength of 8.55 μm. The gain peaks are greatly shifted to longer wavelengths and the overall gain magnitudes are slightly reduced when the NPB effect is considered. Compared with the three-QW active-region design, the redshift of the peak gain is more prominent in the four-QW active-region design, which makes use of higher electronic states for the lasing transition.
Directory of Open Access Journals (Sweden)
Xiao-Peng Wang
2015-10-01
Full Text Available In this paper, the tuning characteristics of band gaps and waveguides in a locally resonant phononic crystal structure, consisting of multiple square stubs deposited on a thin homogeneous plate, are investigated. Using the finite element method and supercell technique, the dispersion relationships and power transmission spectra of those structures are calculated. In contrast to a system of one square stub, systems of multiple square stubs show wide band gaps at lower frequencies and an increased quantity of band gaps at higher frequencies. The vibration modes of the band gap edges are analyzed to clarify the mechanism of the generation of the lowest band gap. Additionally, the influence of the stubs arrangement on the band gaps in multi-stub systems is investigated. The arrangements of the stubs were found to influence the band gaps; this is critical to understand for practical applications. Based on this finding, a novel method to form defect scatterers by changing the arrangement of square stubs in a multi-stub perfect phononic crystal plate was developed. Defect bands can be induced by creating defects inside the original complete band gaps. The frequency can then be tuned by changing the defect scatterers’ stub arrangement. These results will help in fabricating devices such as acoustic filters and waveguides whose band frequency can be modulated.
Interface dynamics and banding in rapid solidification
Energy Technology Data Exchange (ETDEWEB)
Karma, A.; Sarkissian, A. (Physics Department, Northeastern University, Boston, Massachusetts 02115 (United States))
1993-01-01
Rapid-solidification experiments on metallic alloys in the last decade have provided widespread observations of a novel banded structure.'' We report the results of numerical and analytical studies of the interface dynamics underlying the formation of this structure in a model of directional solidification which includes both solute and heat diffusion and nonequilibrium effects. The thrust of these studies is on the unsteady dynamics of the planar interface and thermal effects. The main conclusion is that the origin of banding can be related to relaxation oscillations of the solidification front, characterized by large variations of the interface velocity, which are dramatically affected by latent-heat diffusion. Without the latter, the oscillations are found to be reasonably well approximated by the phenomenological model of Carrard [ital et] [ital al]. [Acta Metall. 40, 983 (1992)], and the band spacing is inversely proportional to the temperature gradient. In contrast, with latent-heat diffusion the band spacing is insensitive to the temperature gradient, but is controlled instead by the interplay of solute and heat diffusion. The smallness of the solutal diffusivity to thermal diffusivity ratio is exploited to explain analytically this effect and to derive considerably simpler equations of interface motion that provide an efficient numerical means to study the nonplanar interface dynamics expected to cause dark bands. A reasonable agreement with experiment is found for the spacing of banded structures dominated by light-band microsegregation-free regions in Al-Fe alloys.
Energy Technology Data Exchange (ETDEWEB)
Ochi, Masayuki, E-mail: ochi@phys.sci.osaka-u.ac.jp; Arita, Ryotaro [RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198 (Japan); JST ERATO Isobe Degenerate pi-Integration Project, Advanced Institute for Materials Research (AIMR), Tohoku University, Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Yamamoto, Yoshiyuki [Department of Physics, The University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033 (Japan); Tsuneyuki, Shinji [Department of Physics, The University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033 (Japan); Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581 (Japan)
2016-03-14
We develop an iterative diagonalization scheme in solving a one-body self-consistent-field equation in the transcorrelated (TC) method using a plane-wave basis set. Non-Hermiticity in the TC method is well handled with a block-Davidson algorithm. We verify that the required computational cost is efficiently reduced by our algorithm. In addition, we apply our plane-wave-basis TC calculation to some simple sp-electron systems with deep core states to elucidate an impact of the pseudopotential approximation to the calculated band structures. We find that a position of the deep valence bands is improved by an explicit inclusion of core states, but an overall band structure is consistent with a regular setup that includes core states into the pseudopotentials. This study offers an important understanding for the future application of the TC method to strongly correlated solids.
Determination of band alignment in the single-layer MoS2/WSe2 heterojunction
Chiu, Ming-Hui
2015-07-16
The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.
Modulating the band gap of a boron nitride bilayer with an external electric field for photocatalyst
Energy Technology Data Exchange (ETDEWEB)
Tang, Y. R.; Cao, J. X., E-mail: jxcao@xtu.edu.cn [Department of Physics, Xiangtan University, Xiangtan, Hunan 411105 (China); Zhang, Y. [Department of Physics and Information Technology, Baoji University of Arts and Sciences, Baoji 721016 (China)
2016-05-21
By virtue of first principle calculations, we propose an approach to reduce the band gap of layered semiconductors through the application of external electric fields for photocatalysis. As a typical example, the band gap of a boron nitride (BN) bilayer was reduced in the range from 4.45 eV to 0.3 eV by varying the external electric field strength. More interestingly, it is found that the uppermost valence band and the lowest conduction band are dominated by the N-p{sub z} and B-p{sub z} from different layers of the BN sheet, which suggests a wonderful photoexcited electron and hole separation system for photocatalysis. Our results imply that the strong external electric field can present an abrupt polarized surface.
Simulation of A 90o Differential Phase Shifter for Korean VLBI Network 129 GHz Band Polarizer
Directory of Open Access Journals (Sweden)
Moon-Hee Chung
2010-09-01
Full Text Available A simulation for the design of a 90o differential phase shifter aimed toward Korean VLBI Network (KVN 129 GHz band polarizer is described in this paper. A dual-circular polarizer for KVN 129 GHz band consists of a 90o differential phase shifter and an orthomode transducer. The differential phase shifter is made up of a square waveguide with two opposite walls loaded with corrugations. Three-dimensional electromagnetic simulation has been performed to predict the 90o differential phase shifter’s characteristics. The simulation for the differential phase shifter shows that the phase shift is 90o ± 3.3o across 108-160 GHz and the return losses of two orthogonal modes are better than -30 dB within the design frequency band. According to the simulation results the calculated performance is quite encouraging for KVN 129 GHz band application.
Multiple triaxial bands and abnormal signature inversion in {sup 74}{sub 33}As
Energy Technology Data Exchange (ETDEWEB)
Hu, Shi-Peng [China Institute of Atomic Energy, Beijing 102413 (China); College of Physics Science and Technology, Shenzhen University, Shenzhen 518060 (China); Ma, Hai-Liang [China Institute of Atomic Energy, Beijing 102413 (China); Cao, Xue-Peng [China Institute of Atomic Energy, Beijing 102413 (China); Department of Physics, Dongbei Normal University, Changchun 130024 (China); Wu, Xiao-Guang, E-mail: wxg@ciae.ac.cn [China Institute of Atomic Energy, Beijing 102413 (China); Zhang, Huan-Qiao [China Institute of Atomic Energy, Beijing 102413 (China); Hua, Hui; Sun, Jun-Jie [School of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Sun, Hui-Bin [College of Physics Science and Technology, Shenzhen University, Shenzhen 518060 (China); He, Chuang-Ye; Zheng, Yun; Li, Guang-Sheng [China Institute of Atomic Energy, Beijing 102413 (China); Li, Cong-Bo [China Institute of Atomic Energy, Beijing 102413 (China); College of Physics, Jilin University, Changchun 130012 (China); Yao, Shun-He; Yu, Bei-Bei; Wang, Jin-Long [China Institute of Atomic Energy, Beijing 102413 (China); Li, Hong-We; Wu, Yi-Heng [China Institute of Atomic Energy, Beijing 102413 (China); College of Physics, Jilin University, Changchun 130012 (China); Liu, Jia-Jian; Luo, Peng-Wei [China Institute of Atomic Energy, Beijing 102413 (China); College of Physics Science and Technology, Shenzhen University, Shenzhen 518060 (China); Xu, Chuan [School of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); and others
2014-05-01
Excited states of the odd–odd nucleus {sup 74}As have been investigated via heavy ion fusion evaporation reaction {sup 70}Zn({sup 7}Li,3n){sup 74}As at beam energy of 30 MeV. The properties of the positive- and the negative- parity bands can be interpreted in terms of the Cranked Nilsson–Strutinsky (CNS) model calculations which show that the observed bands are built on the triaxial deformed shape. The inversion of the favored and unfavored signature branches observed in the positive-parity bands presents at high spins rather than normal signature inversion occurs at low spins. This phenomenon may be explained as the origin of unpaired band crossing in a highly rotating triaxial nucleus.
Conduction band edge effective mass of La-doped BaSnO{sub 3}
Energy Technology Data Exchange (ETDEWEB)
James Allen, S., E-mail: allen@itst.ucsb.edu; Law, Ka-Ming [Physics Department, University of California, Santa Barbara, California 93106-5100 (United States); Raghavan, Santosh; Schumann, Timo; Stemmer, Susanne [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States)
2016-06-20
BaSnO{sub 3} has attracted attention as a promising material for applications requiring wide band gap, high electron mobility semiconductors, and moreover possesses the same perovskite crystal structure as many functional oxides. A key parameter for these applications and for the interpretation of its properties is the conduction band effective mass. We measure the plasma frequency of La-doped BaSnO{sub 3} thin films by glancing incidence, parallel-polarized resonant reflectivity. Using the known optical dielectric constant and measured electron density, the resonant frequency determines the band edge electron mass to be 0.19 ± 0.01. The results allow for testing band structure calculations and transport models.
TiO2 Band Restructuring by B and P Dopants.
Directory of Open Access Journals (Sweden)
Lei Li
Full Text Available An examination of the effect of B- and P-doping and codoping on the electronic structure of anatase TiO2 by performing density functional theory calculations revealed the following: (i B- or P-doping effects are similar to atomic undercoordination effects on local bond relaxation and core electron entrapment; (ii the locally entrapped charge adds impurity levels within the band gap that could enhance the utilization of TiO2 to absorb visible light and prolong the carrier lifetime; (iii the core electron entrapment polarizes nonbonding electrons in the upper edges of the valence and conduction bands, which reduces not only the work function but also the band gap; and (iv work function reduction enhances the reactivity of the carriers and band gap reduction promotes visible-light absorption. These observations may shed light on effective catalyst design and synthesis.
Jahidin, A H; Megat Ali, M S A; Taib, M N; Tahir, N Md; Yassin, I M; Lias, S
2014-04-01
This paper elaborates on the novel intelligence assessment method using the brainwave sub-band power ratio features. The study focuses only on the left hemisphere brainwave in its relaxed state. Distinct intelligence quotient groups have been established earlier from the score of the Raven Progressive Matrices. Sub-band power ratios are calculated from energy spectral density of theta, alpha and beta frequency bands. Synthetic data have been generated to increase dataset from 50 to 120. The features are used as input to the artificial neural network. Subsequently, the brain behaviour model has been developed using an artificial neural network that is trained with optimized learning rate, momentum constant and hidden nodes. Findings indicate that the distinct intelligence quotient groups can be classified from the brainwave sub-band power ratios with 100% training and 88.89% testing accuracies. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.
A Dynamical Theory for Hurricane Spiral Bands
1992-05-01
dynamical fields from Hurricane Josephine (1984) ........... 4 1.2 Cross-band dynamical fields from Tropical Depression Irma (1987) .......... 5 1.3...FUNDING NUMBERS A Dynamical Theory for Hurricane Spii’al Bands 6. AUTHOR(S) Thomas A. Guinn, Captain 7. PERFORMING ORGANIZATION NAME(S) AND ADuRESS...S*nrdard Form 298 (R&v 2-89) 1 " I 0n, T ! ’’r." Author: Captain Thomas A. Guinn, USAF Title: A dynamical theory for hurricane spiral bands. Date
NLTE ANALYSIS OF HIGH-RESOLUTION H -BAND SPECTRA. I. NEUTRAL SILICON
Energy Technology Data Exchange (ETDEWEB)
Zhang, Junbo; Shi, Jianrong; Liu, Chao [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100012 (China); Pan, Kaike [Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059 (United States); Prieto, Carlos Allende, E-mail: sjr@bao.ac.cn [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)
2016-12-20
We investigated the reliability of our silicon atomic model and the influence of non-local thermodynamical equilibrium (NLTE) on the formation of neutral silicon (Si i) lines in the near-infrared (near-IR) H -band. We derived the differential Si abundances for 13 sample stars with high-resolution H -band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as well as from optical spectra, both under local thermodynamical equilibrium (LTE) and NLTE conditions. We found that the differences between the Si abundances derived from the H -band and from optical lines for the same stars are less than 0.1 dex when the NLTE effects are included, and that NLTE reduces the line-to-line scatter in the H -band spectra for most sample stars. These results suggest that our Si atomic model is appropriate for studying the formation of H -band Si lines. Our calculations show that the NLTE corrections of the Si i H -band lines are negative, i.e., the final Si abundances will be overestimated in LTE. The corrections for strong lines depend on surface gravity, and tend to be larger for giants, reaching ∼−0.2 dex in our sample, and up to ∼−0.4 dex in extreme cases of APOGEE targets. Thus, the NLTE effects should be included in deriving silicon abundances from H -band Si i lines, especially for the cases where only strong lines are available.
Madelung and Hubbard interactions in polaron band model of doped organic semiconductors.
Png, Rui-Qi; Ang, Mervin C Y; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K H
2016-09-01
The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π-π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine-fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime.
Visual nesting system for irregular cutting-stock problem based on rubber band packing algorithm
Directory of Open Access Journals (Sweden)
Xiaoping Liao
2016-05-01
Full Text Available This article deals with the packing problem of irregular items allocated into a rectangular sheet to minimize the waste. Conventional solution is not visual during the packing process. It obtains a reasonable and relatively satisfactory solution between the nesting time and nesting solution. This article adopts a physical method that uses rubber band packing algorithm to simulate a rubber band wrapping those packing irregular items. The simulation shows a visual and fast packing process. The resultant rubber band force is applied in the packing items to translate, rotate, and slide them to make the area decrease and obtain a high packing density. An improved analogy QuickHull algorithm is presented to obtain extreme points of rubber band convex hull. An adaptive module could set a variable rubber band force and a variable time step to make a proper convergence and no intersection. A quick convex decomposition method is used to solve the problem of concave polygon. A plural vector expression approach is adopted to calculate the resultant vector of the rubber band force. Several cases are compared with the benchmark problems to prove rubber band packing algorithm performance.
Compact Bioimplantable MICS and ISM Band Antenna Design for Wireless Biotelemetry Applications
Directory of Open Access Journals (Sweden)
M. Palandoken
2017-12-01
Full Text Available A compact dual-band bioimplantable antenna with novel resonator geometry is designed for dual-band wireless biotelemetry applications in MICS and ISM bands. The radiating element geometry is based on an L-shaped transmission line fed anti-spiral resonator structure, which is loaded with the spiral resonator at the end to increase the effective electrical length. The effect of resonator geometric parameters on the return loss is discussed with the inclusion of three layered lossy human model in the numerical calculations. The footprint size of the optimized bioimplantable antenna is 15 x 15 x 1.92 mm^3, having the total surface area of λ0/20 x λ0/20, where λ0 is the free space wavelength at 403 MHz in MICS band. The compact dual-band antenna has the impedance bandwidth of 24.81% at 403 MHz and 14.7% at 2.45 GHz with the gain values -12.25dBi and -12.4 dBi in MICS and ISM bands, respectively. The average SAR values at the resonance frequencies are numerically computed to find out the input power delivered to the antenna for the reliable operation. The radiation parameters and 3D radiation patterns indicate the potential use of the proposed implantable antenna with the permissible gain in dual-band wireless biotelemetry applications.
A novel theoretical model for the temperature dependence of band gap energy in semiconductors
Geng, Peiji; Li, Weiguo; Zhang, Xianhe; Zhang, Xuyao; Deng, Yong; Kou, Haibo
2017-10-01
We report a novel theoretical model without any fitting parameters for the temperature dependence of band gap energy in semiconductors. This model relates the band gap energy at the elevated temperature to that at the arbitrary reference temperature. As examples, the band gap energies of Si, Ge, AlN, GaN, InP, InAs, ZnO, ZnS, ZnSe and GaAs at temperatures below 400 K are calculated and are in good agreement with the experimental results. Meanwhile, the band gap energies at high temperatures (T > 400 K) are predicted, which are greater than the experimental results, and the reasonable analysis is carried out as well. Under low temperatures, the effect of lattice expansion on the band gap energy is very small, but it has much influence on the band gap energy at high temperatures. Therefore, it is necessary to consider the effect of lattice expansion at high temperatures, and the method considering the effect of lattice expansion has also been given. The model has distinct advantages compared with the widely quoted Varshni’s semi-empirical equation from the aspect of modeling, physical meaning and application. The study provides a convenient method to determine the band gap energy under different temperatures.
First-principles study on the electronic structure and optical properties of CrSi2
Zhou, Shiyun; Xie, Quan; Yan, Wanjun; Chen, Qian
2009-01-01
Using the first principle methods based on the plane-wave pseudo-potential theory, band structure, density of states and optical properties of CrSi2 were studied. The calculation of band structure shows that CrSi2 is an indirect semiconductor whose band gap is 0.353 eV. Density of states is mainly composed of 3d electron of Cr and 3p electron of Si. Dielectric function, refractive index, reflectivity, and absorption coefficient of CrSi2 are also calculated. The calculation results of optical properties are in agreement with the experiments.
[Hyperspectral Band Selection Based on Spectral Clustering and Inter-Class Separability Factor].
Qin, Fang-pu; Zhang, Ai-wu; Wang, Shu-min; Meng, Xian-gang; Hu, Shao-xing; Sun, Wei-dong
2015-05-01
With the development of remote sensing technology and imaging spectrometer, the resolution of hyperspectral remote sensing image has been continually improved, its vast amount of data not only improves the ability of the remote sensing detection but also brings great difficulties for analyzing and processing at the same time. Band selection of hyperspectral imagery can effectively reduce data redundancy and improve classification accuracy and efficiency. So how to select the optimum band combination from hundreds of bands of hyperspectral images is a key issue. In order to solve these problems, we use spectral clustering algorithm based on graph theory. Firstly, taking of the original hyperspectral image bands as data points to be clustered , mutual information between every two bands is calculated to generate the similarity matrix. Then according to the graph partition theory, spectral decomposition of the non-normalized Laplacian matrix generated by the similarity matrix is used to get the clusters, which the similarity between is small and the similarity within is large. In order to achieve the purpose of dimensionality reduction, the inter-class separability factor of feature types on each band is calculated, which is as the reference index to choose the representative bands in the clusters furthermore. Finally, the support vector machine and minimum distance classification methods are employed to classify the hyperspectral image after band selection. The method in this paper is different from the traditional unsupervised clustering method, we employ spectral clustering algorithm based on graph theory and compute the interclass separability factor based on a priori knowledge to select bands. Comparing with traditional adaptive band selection algorithm and band index based on automatically subspace divided algorithm, the two sets of experiments results show that the overall accuracy of SVM is about 94. 08% and 94. 24% and the overall accuracy of MDC is about 87
Bouldi, N.; Vollmers, N. J.; Delpy-Laplanche, C. G.; Joly, Y.; Juhin, A.; Sainctavit, Ph.; Brouder, Ch.; Calandra, M.; Paulatto, L.; Mauri, F.; Gerstmann, U.
2017-08-01
An efficient first-principles approach to calculate x-ray magnetic circular dichroism (XMCD) and x-ray natural circular dichroism (XNCD) is developed and applied in the near-edge region at the K and L1 edges in solids. Computation of circular dichroism requires precise calculations of x-ray absorption spectra (XAS) for circularly polarized light. For the derivation of the XAS cross section, we used a relativistic description of the photon-electron interaction that results in an additional term in the cross section that couples the electric dipole operator with an operator σ .(ɛ ×r ) that we call the spin position operator. The numerical method relies on pseudopotentials, on the gauge including projected augmented-wave method, and on a collinear spin relativistic description of the electronic structure. We apply the method to calculations of K -edge XMCD spectra of ferromagnetic iron, cobalt, and nickel and of I L1-edge XNCD spectra of α -LiIO3 , a compound with broken inversion symmetry. For XMCD spectra we find that, even if the electric dipole term is the dominant one, the electric quadrupole term is not negligible (8% in amplitude in the case of iron). The term coupling the electric dipole operator with the spin-position operator is significant (28% in amplitude in the case of iron). We obtain a sum rule relating this term to the spin magnetic moment of the p states. In α -LiIO3 we recover the expected angular dependence of the XNCD spectra.
Electronic Structure and Optical Properties of the Lonsdaleite Phase of Si, Ge and diamond
De, Amrit; Pryor, Craig E.
2012-01-01
Crystalline semiconductors may exist in different polytypic phases with significantly different electronic and optical properties. In this paper, we calculate the electronic structure and optical properties of diamond, Si and Ge in the lonsdaleite (hexagonal-diamond) phase. We use an empirical pseudopotentials method based on transferable model potentials, including spin-orbit interactions. We obtain band structures, densities of states and complex dielectric functions calculated in the dipol...
Photonic band gaps in materials with triply periodic surfaces and related tubular structures
Michielsen, K; Kole, JS
2003-01-01
We calculate the photonic band gap of triply periodic bicontinuous cubic structures and of tubular structures constructed from the skeletal graphs of triply periodic minimal surfaces. The effect of the symmetry and topology of the periodic dielectric structures on the existence and the
The Electronic Band Structure of Platinum Oxide (PtO) | Omehe ...
African Journals Online (AJOL)
We have performed the electronic band structure of the bulk and monolayer of PtO using the full potential linear muffin-tin orbital and the projector augmented wave method with the density functional theory. We applied the LDA and LDA+U scheme to both methods. It was found out that the LDA calculation of bulk PtO ...
Electron-Phonon Renormalization of Electronic Band Structures of C Allotropes and BN Polymorphs
Tutchton, Roxanne M.; Marchbanks, Christopher; Wu, Zhigang
The effect of lattice vibration on electronic band structures has been mostly neglected in first-principles calculations because the electron-phonon (e-ph) renormalization of quasi-particle energies is often small (Career Award (Grant No. DE-SC0006433). Computations were carried out at the Golden Energy Computing Organization at CSM and the National Energy Research Scientific Computing Center (NERSC).
Band Structure and Fermi Surface of Cu2Sb by the LMTO Method
DEFF Research Database (Denmark)
Jan, J. P.; Skriver, Hans Lomholt
1977-01-01
The linear muffin-tin orbital (LMTO) method of bandstructure calculation has been applied to the simple tetragonal compound Cu2Sb. The d bands of Cu lie substantially below the Fermi level, and the Fermi surface is a recognizable distortion of the free-electron model. The Fermi surface has sheets...
Phase Transitions in the Hubbard Model for a Half Filled Band
Jonkman, Harry Th.; Kommandeur, Jan
1982-01-01
The phase-transitions for a half-filled band can be numerically calculated from the Hubbard Hamiltonian with an exponential inter-site dependence of the transfer integral. Even for four sites with four electrons the results compare very well with experiments on spin susceptibilities and the
Study of energy bands and magnetic properties of Co 2 CrSi ...
Indian Academy of Sciences (India)
LSDA+U) with the inclusion of Hubbard potential U is used. Our calculation shows indirect bandgap of 0.91 eV in the minority channel of DOS. This is supported by band structures and hence favoured the half metallic ferromagnetic (HMF) nature of ...
Grain size dependent optical band gap of CdI2 films
Indian Academy of Sciences (India)
The thermally evaporated stoichiometric CdI2 films show good -axis alignment normal to substrate plane for film thickness up to 200 nm. The optical absorption data indicate an allowed direct interband transition across a gap of 3.6 eV in confirmation with earlier band structure calculations. However, part of the absorption ...
Atomically Thin Ordered Alloys of Transition Metal Dichalcogenides: Stability and Band Structures
DEFF Research Database (Denmark)
Pandey, Mohnish; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer
2016-01-01
We explore the possibility of modulating the electronic band edges of the transition metal dichalcogenides (TMD) via alloying of different semiconductors within the same group (intra-group alloying). The stability of the ordered alloys is assessed from the calculated mixing enthalpy which is found...
DEFF Research Database (Denmark)
Wacker, Andreas; Jauho, Antti-Pekka; Zeuner, S.
1997-01-01
We report a combined theoretical and experimental study of electrical transport in weakly coupled doped superlattices. Our calculations exhibit negative differential conductivity at sufficiently high electric fields for all dopings. In low-doped samples the presence of impurity bands modifies the...