Slater transition-state band-structure calculations
International Nuclear Information System (INIS)
Slater's transition-state method enables one to calculate excitation energies by means of an artificial state that is halfway between the ground state of an atom or molecule and an excited state. This idea has been adapted to insulators and semiconductors with a band-structure model where a localized hole is created in one cell by removing charge from the top of the valence band and putting it in a delocalized state at the bottom of the conduction band. Significant improvements in calculated band gaps are obtained in most cases over conventional local-density calculations. (c) 2000 The American Physical Society
Comparison of EH with SW-Xsub(alpha) calculations
International Nuclear Information System (INIS)
The electronic structure of octahedral metal atom clusters Me6 of 3d, 4d, and 5d transition metal atoms (V, Cr; Nb, Mo; Ta, W) has been calculated applying two different quantum-chemical approximation methods (Extended Hueckel (EH) method; SW-Xsub(alpha) method). Equilibrium structures, energy level schemes, Fermi energies and band widths as well as densities of states of clusters are discussed in detail
InN{x}As{1-x} band gap energy and band bowing coefficient calculation
Sentosa, D.; Tang, X.; Chua, S. J.
2007-12-01
The band gap energies of zinc-blende InN{x}As{1-x} alloy as a function of its nitrogen composition have been calculated using the density functional theory. The results agree well with those obtained from experimental results. The minimum band gap energy of InN{x}As{1-x} alloy obtained is 70 meV at its N composition of 0.45. The band gap bowing coefficient of InN{x}As{1-x} alloy is obtained from the curve fitting of the simulated band gap energy versus the nitrogen composition, x. The band gap bowing coefficient of zinc-blende InN{x}As{1-x} alloy is found to be 2.072 ± 0.236 eV. The energy band gap for InN is also correctly predicted from this calculation.
One-Component Plasma: Going Beyond Debye-Hueckel
Moreira, Andre G.; Netz, Roland R.
1999-01-01
Using field-theoretic methods, we calculate the internal energy for the One-Component Plasma (OCP). We go beyond the recent calculation by Brilliantov [N. Brilliantov, Contrib. Plasma Phys. 38, pg. 489 (1998) / cond-mat/9805358] by including non-Gaussian terms. We show that, for the whole range of the plasma parameter Gamma, the effect of the higher-order terms is small and that the final result is not improved relative to the Gaussian theory when compared to simulations.
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. It is shown that the photoemission results are extremely well described in terms of a model assuming all transitions to be direct whereas a nondirect model fails. The ?2 profile calculated in a crude model assuming constant matrix elements matches well the corresponding experimental results. The calculated interband edge (??i=2.38 eV) agrees with experimental values, and the absorption tail below the interband edge which is found in experimental traces is also contained in the theoretical curve. By means of a calculation of the Fermi surface and the constant-energy-difference surfaces it has been possible to trace out the regions in k? space where the edge and tail transitions occur. It is demonstrated that structure in the static reflection curves are not related to critical points in the band structure. The arguments are supported by calculations of temperature shifts of the critical-point energies and comparison to the observed temperature shifts of the elements of structure in the experimental ?2 function. Such structure may originate in extended rather than localized regions of k? space. In contrast, critical-point transitions show up clearly in modulated reflectance spectra, and all elements of structure are fully accounted for by our band model. The temperature and strain responses in the band structure are determined by performing the RAPW calculation with two lattice constants and estimating the effects ofthe lattice vibrations by means of an OPW-LCAO (linear combination of atomic orbitals) scheme with pseudopotential Fourier constants reduced by the appropriate Debye-Waller factors. The phonon spectrum has been calculated for the latter purpose.
Reduced Bloch mode expansion for periodic media band structure calculations
Hussein, Mahmoud I
2008-01-01
Reduced Bloch mode expansion is presented for fast periodic media band structure calculations. The expansion employs a natural basis composed of a selected reduced set of Bloch eigenfunctions. The reduced basis is selected within the irreducible Brillouin zone at high symmetry points determined by the medium's crystal structure and group theory (and possibly at additional related points). At each of the reciprocal lattice selection points, a number of Bloch eigenfunctions are selected up to the frequency range of interest for the band structure calculations. Since it is common to initially discretize the periodic unit cell and solution field using some choice of basis, reduced Bloch mode expansion is practically a secondary expansion that uses a selected set of Bloch eigenvectors. Such expansion therefore keeps, and builds on, any favorable attributes a primary expansion approach might exhibit. Being in line with the well known concept of modal analysis, the proposed approach maintains accuracy while reducing...
The calculation of band gap energy in zinc oxide films
Arif, Ali; Belahssen, Okba; Gareh, Salim; Benramache, Said
2015-01-01
We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor; the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 200 and 500 °C. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation (2), so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.
Hueckel model for metal clusters: Ground states and low energy isomers
International Nuclear Information System (INIS)
Hueckel model with one s-electron per atom is used to study the geometries and electronic structures of clusters of 9 to 22 atoms. Two different optimization schemes for obtaining the ground states are used; (i) minimization of an approximate Hueckel ground state energy starting from a random geometry and (ii) simulated annealing. Both methods give similar and new ground state geometries for clusters with 10 to 14 atoms. All clusters with more than 10 atoms will be distorted if the bond distance is allowed to vary ±5.5%. The ground states of clusters with atoms 10, 11, 12, and 14 are found to have the N=9 cluster as the basic building block, whereas the N=13 cluster is a distorted cuboctahedron. As a general trend, the deformation of clusters increases from atom number 8 to 14 and shrinks again from 15 to 20 atoms, in accordance with jellium model results
Band gap calculations with Becke-Johnson exchange potential
International Nuclear Information System (INIS)
Recently, a simple analytical form for the exchange potential was proposed by Becke and Johnson. This potential, which depends on the kinetic-energy density, was shown to reproduce very well the shape of the exact exchange potential (obtained with the optimized effective potential method) for atoms. Calculations on solids show that the Becke-Johnson potential leads to a better description of band gaps of semiconductors and insulators with respect to the standard local density and Perdew-Burke-Ernzerhof approximations for the exchange-correlation potential. Comparison is also made with the values obtained with the Engel-Vosko exchange potential which was also developed using the exact exchange potential
Emission bands of phosphorus and calculation of band structure of rare earth phosphides
International Nuclear Information System (INIS)
The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band
Band-structure calculations of specular reflection in spin valves
International Nuclear Information System (INIS)
Band structure calculations are carried out on three types of spin-valve structures: (1) simple spin valves, (2) dual spin valves, and (3) spin valves with a synthetic antiferromagnet. The effect of specular reflection is studied by comparing the transport properties of spin valves with resistive metallic and insulating layers at the outer boundaries. In the spin valve with a synthetic antiferromagnet, an insulating layer needs to be inserted inside the reference layer to achieve similar enhancement to the giant magnetoresistance as the other two types of spin valves with insulating outer boundaries. Results are analyzed in terms of s - d scattering in the different spin channels with different boundary conditions. [copyright] 2001 American Institute of Physics
Comparison of EH with SW-X/sub alpha/ calculations
International Nuclear Information System (INIS)
The electronic structure of small niobium clusters Nb/sub n/ (n = 2, 4, 6, 9) has been calculated applying two different quantum-chemical approximation methods (Extended Hueckel (EH) method; SW-X/sub alpha/ method). It was found that both the methods led to the same results concerning equilibrium structures, energy level schemes, Fermi energies and band widths as well as the densities of states of the clusters. In solving solid state problems of transition metals with the aid of the cluster model a better adaptation of the EH method should be expected by adjusting the EH parameters to the SW-X/sub alpha/ results. (author)
Calculation of RIXS spectra of cuprates using band structure parameters
Shi, Yifei; Klich, Israel; Benjamin, David; Demler, Eugene
2015-03-01
We explore the quasi particle theory to study the Resonant Inelastic X-ray Scattering(RIXS) by using the band structure parameters. We use both the determinant method(D. Benjamin, I. Klich and E. Demler, Phys. Rev. Lett. 112, 247002(2014)) and the expansion in the core-hole potential. The methods are applied to the (CaxLa1?x)(Ba1 . 75 - xLa0 . 25 + x)Cu3Oy, (x= 0 . 1 and 0 . 4). We find that by using the band structure alone we can obtain quantitative agreement with the experimental data, especially for the position of the peak.
International Nuclear Information System (INIS)
Amorphous indium tin oxide films were grown on a polyethylene terephthalate substrate by RF-magnetron sputtering. The energy band, which contained not only the width of the optical band but also detailed information about the Fermi level (Ef) and mobility edge (Ec'), was calculated according to the theory of amorphous semiconductors with the experimental parameters of transmittance and electrical conductivity. Furthermore, the calculated energy band can be used to effectively explain both the variation of electrical conductivity and the weak absorption at the wavelength range of 750-800 nm in our experiment. An indirect transition was also clearly observed in our samples during the calculation of the optical energy band.
First-principle band calculation of ruthenium for various phases
Watanabe, S; Kai, T; Shiiki, K
2000-01-01
The total energies and the magnetic moments of Ru for HCP, BCC, FCC, BCT structures were calculated by using a first-principle full-potential linearized augmented plane-wave (FLAPW) method based on the generalized gradient approximation (GGA). HCP has the lowest energy among the structures calculated, which agrees with the experimental result that HCP is the equilibrium phase of Ru. The total energy of BCT Ru has the local minimum at c/a=sq root 2 (FCC) with a=5.13 au, c=7.25 au and c/a=0.83 with a=6.15 au, c=5.11 au. It is pointed out that these phases are possibly metastable. The BCC structure, which corresponds to BCT with a=c=5.78 au, is unstable because it is at a saddle point of the total energy. BCT Ru of c/a<1 has a magnetic moment at the stable volume.
Nazrul Rosli, Ahmad; Fatimah Wahab, Izzati; Zabidi, Noriza Ahmad; Abu Kassim, Hasan
2015-06-01
Sodium intercalation in graphite (GIC-Na) was investigated by the first principle calculation. The structure of GIC-Na was calculated using density functional theory (DFT) with the aid of CASTEP module of Material Studio. The exchange correlation functional has been treat by local density approximation (LDA) and generalized gradient approximation (GGA). It was shown that, unlike potassium GIC and lithium GIC, the band gap of GIC-Na was not induced and has same value of band gap with bulk graphite.
Ab Initio calculation of band gap renormalization in highly excited GaAs
Spataru, C D; Louie, S G; Spataru, Catalin D.; Benedict, Lorin X.; Louie, Steven G.
2004-01-01
We present ab initio quasiparticle self-energy calculations in crystalline GaAs for cases of intense electronic excitation (~ 10% of valence electrons excited into conduction band), relevant for high-intensity ultra-short pulsed laser experiments. Calculations are performed using an out-of-equilibrium generalization of the GW approximation based on the Keldysh Green's function approach. Our results indicate that while the band gap is a sensitive function of the amount of excitation, it is not possible to induce complete band gap closure in this system by purely electronic means.
Calculations of N 2 triplet states vibrational populations and band emissions in venusian dayglow
Bhardwaj, Anil; Jain, Sonal Kumar
2012-02-01
A model for N 2 triplet states band emissions in the venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N 2 triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N 2, populations of different levels of N 2 triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N 2 triplet band emissions are calculated, the values for Vegard-Kaplan (A3?u+-X1?g+), First Positive (B3?g-A3?u+), Second Positive ( C3? u - B3? g), and Wu-Benesch ( W3? u - B3? g) bands of N 2, are 1.9 (3.2), 3 (6), 0.4 (0.8), and 0.5 (1.1) kR, respectively, for solar minimum (maximum) conditions. The intensities of the three strong Vegard-Kaplan bands (0, 5), (0, 6), and (0, 7) are 94 (160), 120 (204), and 114 (194) R, respectively, for solar minimum (maximum) conditions. Limb profiles are calculated for VK (0, 4), (0, 5), (0, 6) and (0, 7) bands. The calculated intensities on Venus are about a factor 10 higher than those on Mars. The present study provides a motivation for a search of N 2 triplet band emissions in the dayglow of Venus.
Emergence of rotational bands in ab initio no-core configuration interaction calculations
Caprio, M A; Vary, J P; Smith, R
2015-01-01
Rotational bands have been observed to emerge in ab initio no-core configuration interaction (NCCI) calculations for p-shell nuclei, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. We investigate the ab initio emergence of nuclear rotation in the Be isotopes, focusing on 9Be for illustration, and make use of basis extrapolation methods to obtain ab initio predictions of rotational band parameters for comparison with experiment. We find robust signatures for rotational motion, which reproduce both qualitative and quantitative features of the experimentally observed bands.
Dielectric band structure of crystals: General properties, and calculations for silicon
International Nuclear Information System (INIS)
We shift the dielectric band structure method, orginially proposed by Baldereschi and Tosatti for the description of microscopic electronic screening in crystals. Some general properties are examined first, including the requirements of causality and stability. The specific test case of silicon is then considered. Dielectric bands are calculated, according to several different prescriptions for the construction of the dielectric matrix. It is shown that the results allow a very direct appraisal of the screening properties of the system, as well as of the quality of the dielectric model adopted. The electronic charge displacement induced by ?sub(25') and X3 phonon-like displacements of the atoms is also calculated and compared with the results of existent full self-consistent calculations. Conclusions are drawn on the relative accuracies of the dielectric band structures. (author)
Pryor, Craig
1997-01-01
The electronic structure of pyramidal shaped InAs/GaAs quantum dots is calculated using an eight-band strain dependent $\\bf k\\cdot p$ Hamiltonian. The influence of strain on band energies and the conduction-band effective mass are examined. Single particle bound-state energies and exciton binding energies are computed as functions of island size. The eight-band results are compared with those for one, four and six bands, and with results from a one-band approximation in whic...
DEFF Research Database (Denmark)
Christensen, N. Egede; Feuerbacher, B.
1974-01-01
The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi-surface experiments and to optical-reflectance measurements up to 5-eV photon energy. The temperature and strain responses in the band structure are estimated from band calculations with four different lattice constants. The band structure was determined in the entire Brillouin zone and is applied to a calculation of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.
Andriyevsky, B. V.; Romanyuk, N. A.; Romanyuk, N. N.; Myshchyshyn, O. Ya.; Jaskólski, M.; Stadnyk, V. I.
2012-10-01
The genetic origin of a ferroelectric crystal of guanidinium aluminum sulfate hexahydrate has been established and the spectral dependences of the electron density of states, the electron energy, and the optical functions ?1( ??) and ?2( ??) for this crystal have been calculated in terms of the density functional theory. It has been found that there is a weak dependence of the energy of electrons in the upper valence bands on the wave vector. The calculated values of the band gap ( E g ˜ 5.44 eV) and refractive indices are in agreement with the experimental results. It has been shown that there is a strong anisotropy of the spectral band ?2( ??) in the region of 6 eV, which is predominantly formed by the p states of carbon (˜60%) and nitrogen (˜40%) atoms of the C(NH2)3 group.
Calculations of N2 triplet states vibrational populations and band emissions in Venusian dayglow
Bhardwaj, Anil
2011-01-01
A model for N2 triplet states band emissions in the Venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N2 triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N2, populations of different levels of N2 triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N2 triplet band emissions are calculated, the values for Vegard-Kaplan (A^3Sigma_u^+ - X^1Pi_g^+), First Positive (B^3Pi_g - A^3Sigma_u^+), Second Positive (C^3Pi_u - B^3Pi_g), and Wu-Benesch (W^3Delta_u - B^3Pi_g) bands of N2, are 1.9 (3.2), 3 ...
Calculation of isotopic profile during band displacement on ion exchange resins
International Nuclear Information System (INIS)
A method has been developed to calculate the isotopic profile during band displacement on ion exchange resins using computer simulation. Persoz had utilized this technique earlier for calculating the isotopic profile during band displacement as well as frontal analysis. The present report deals with a simplification of the method used by Persoz by reducing the number of variables and making certain approximations where the separation factor is not far from unity. Calculations were made for the typical case of boron isotope separation. The results obtained by the modified method were found to be in very good agreement with those obtained by using an exact equation, at the same time requiring conside--rably less computer time. (author)
Energy Technology Data Exchange (ETDEWEB)
Ribeiro, M. [Centro de Pesquisas Avancadas Wernher von Braun, Av. Alice de Castro P.N. Mattosinho 301, CEP 13098-392 Campinas, SP (Brazil); Ferreira, L.G. [Departamento de Fisica dos Materiais e Mecanica, Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Fonseca, L.R.C. [Center for Semiconductor Components, State University of Campinas, R. Pandia Calogeras 90, 13083-870 Campinas, SP (Brazil); Ramprasad, R. [Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269 (United States)
2012-09-20
We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme to obtain corrected band gaps and band offsets. Our calculations include the spin-orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8-1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.
Calculating the Energy Band Structure Using Sampling and Greens Function Techniques
Khoshnegar, Milad; Arjmandi, Nima; Khorasani, Sina
2012-01-01
In this paper, a new method based on Greens function theory and Fourier transform analysis has been proposed for calculating band structure with high accuracy and low processing time. This method utilizes sampling of potential energy in some points of crystals unit cell with Dirac delta functions, then through lattice Fourier transform gives us a simple and applicable formula for most of nanostructures. Sampling of potential in a crystal lattice of any kind contains accurate approximation of actual potential energy of atoms in the crystal. The step forward regarding the method concentrated on two novel ideas, Firstly, the potential was sampled and approximated by delta functions spread over the unit cell. Secondly, the principal equation of lattice is translated into reciprocal lattice and resulted in a huge reduction of calculations. By this method, it is possible to extract the band structure of any one, two or three dimensional crystalline structure.
Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow
Jain, Sonal Kumar; Bhardwaj, Anil
2011-07-01
A model for N2 Vegard-Kaplan (VK) band (A3?u+ - X1?g+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet states of N2, the population of any given level of N2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, first positive (B3?g - A3?u+), second positive (C3?u - B3?g), and Wu-Benesch (W3?u - B3?g) bands of N2. A reduction in the N2 density by a factor of 3 in the Mars thermospheric general circulation model is required to obtain agreement between calculated limb profiles of VK (0-6) and SPICAM observation. Calculations are carried out to asses the impact of model parameters, namely, electron impact cross sections, solar EUV flux, and model atmosphere, on the emission intensities. Constraining the N2/CO2 ratio by SPICAM observations, we suggest the N2/CO2 ratios to be in the range 1.1-1.4% at 120 km, 1.8-3.2% at 140 km, and 4-7% at 170 km. During high solar activity the overhead intensity of N2 VK band emissions would be ˜2.5 times higher than that during low solar activity.
DEFF Research Database (Denmark)
Lu, Jing Tao; Christensen, Rasmus Bjerregaard
2014-01-01
We extend the simple and efficient lowest order expansion (LOE) for inelastic electron tunneling spectroscopy (IETS) to include variations in the electronic structure on the scale of the vibration energies. This enables first-principles calculations of IETS line shapes for molecular junctions close to resonances and band edges. We demonstrate how this is relevant for the interpretation of experimental IETS using both a simple model and first-principles simulations.
Calculation of the band structure of 2d conducting polymers using the network model
International Nuclear Information System (INIS)
the network model has been used to calculate the band structure the gap energy and Fermi level of conducting polymers in two dimensions. For this purpose, a geometrical classification of possible polymer chains configurations in two dimensions has been introduced leading to a classification of the unit cells based on the number of bonds in them. The model has been applied to graphite in 2D, represented by a three bonds unit cell, and, as a new case, the anti-parallel Polyacetylene chains (PA) in two dimensions, represented by a unit cell with four bons. The results are in good agreement with the first principles calculations. (author)
Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow
Jain, Sonal Kumar
2011-01-01
A model for N2 Vegard-Kaplan (VK) band (A^3Sigma_u^+ - X^1Sigma_g^+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet states of N2, the population of any given level of N2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, first positive (B^3Pi_g - A^3Sigma_u^+), second positive (C^3Pi_u - B^3Pi_g), and Wu-Benesch (W^3Delta_u - B^3Pi_g) bands of N2. A reduction in the N2 density by a factor of 3 ...
Accurate band gaps of semiconductors and insulators from Quantum Monte Carlo calculations
Nazarov, Roman; Hood, Randolph; Morales, Miguel
2015-03-01
Ab initio calculations are useful tools in developing materials with targeted band gaps for semiconductor industry. Unfortunately, the main workhorse of ab initio calculations - density functional theory (DFT) in local density approximation (LDA) or generalized gradient approximation (GGA) underestimates band gaps. Several approaches have been proposed starting from empirical corrections to more elaborate exchange-correlation functionals to deal with this problem. But none of these work well for the entire range of semiconductors and insulators. Deficiencies of DFT as a mean field method can be overcome using many-body techniques. Quantum Monte Carlo (QMC) methods can obtain a nearly exact numerical solutions of both total energies and spectral properties. Diffusion Monte Carlo (DMC), the most widely used QMC method, has been shown to provide gold standard results for different material properties, including spectroscopic constants of dimers and clusters, equation of state for solids, accurate descriptions of defects in metals and insulators. To test DMC's accuracy in a wider range of semiconductors and insulators we have computed band gaps of several semiconductors and insulators. We show that DMC can provide superior agreement with experiment compared with more traditional DFT approaches including high level exchange-correlation functionals (e.g. HSE).
Ab initio calculations of band structure and thermophysical properties for SnS2 and SnSe2
He, Xiancong; Shen, Honglie
2012-04-01
The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.
Energy Technology Data Exchange (ETDEWEB)
Hong, S.Y.
2000-02-01
In search of very small band-gap polymers, the authors have quantum-chemically investigated the electronic structures of various polypentafulvalenes (PFVs) fused with six-membered rings. Geometrical parameters of the polymers were optimized through semiempirical Hartree-Fock band calculations at the Austin Model 1 (AM1) level. Electronic structures of the polymers were obtained through modified extended Hueckel band calculations by adopting AM1-optimized geometries. It is predicted that poly(di-vinylenedioxy-pentafulvalene) and poly(di-vinylenedithia-pentafulvalene) would possess nearly zero band gaps (corresponding to {lambda}{sub max}) despite their large bond-length alternation of {approximately}0.1 A. However, these polymers are expected to be very susceptible to oxidation. Poly(di-butylene-pentafulvalene) and poly(dipyrazinopentafulvalene) are estimated to possess band gaps comparable with that (1.13 eV) of PFV. The calculated band gap of poly(di-ethylenedioxy-pentafulvalene) is 0.77 eV, smaller than that of PFV by 0.36 eV. The authors explained the evolution of band gaps of the polymers through molecular orbital arguments.
International Nuclear Information System (INIS)
The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa-Kohn-Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented
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.
International Nuclear Information System (INIS)
Ab initio band structure calculations of the orthorhombic Hg3TeCl4 crystals of the symmetry D2h15 were performed and the topology of its valence band was analyzed in the framework of the elementary energy bands concepts. The effective masses of charge carriers were estimated. It was demonstrated that the anisotropy of the effective mass tensor components does not coincide with the mechanical one of the Hg3TeCl4 crystal. A possible reason of this fact was proposed.
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Solubility data of CO2 in aqueous N-methyldiethanolamine (MDEA) solutions of concentration (2.52, 3.36, and 4.28) kmol/m3 were obtained at temperatures (313, 323, and 343) K and partial pressures ranging from about (30 to 5000) kPa. A thermodynamic model based on extended Debye-Hueckel theory was applied to predict and correlate of CO2 solubility in various aqueous amine solutions. The effect of piperazine (PZ) concentration on CO2 loading in MDEA solutions was determined at PZ concentration (0.36, 0.86, and 1.36) kmol/m3. Using experimental data in various temperatures the interaction parameters of activity coefficient model for these systems were determined. The results show the model consistency with experimental and literature data and PZ is beneficial to the CO2 loading. The comparison of results of this study with previous data work shows the wide range of CO2 loading considered in this work and the better agreement of model with experimental data. The average absolute relative deviation percent (?AAD) for all data points were 8.11%.
Srivastava, Ankit
2013-01-01
In this paper we present a Graphical Processing Unit accelerated mixed variational formulation for fast phononic band-structure calculation of arbitrarily complex unit cells and report speed gains of a hundred fold over unoptimized serial cpu computations. To the author's knowledge this is the first application of gpu computing to a non-FE/FDTD bandstructure algorithm. The formulation is presented in a form which is applicable to 1-, 2-, and 3-D cases. However, in this paper we concentrate on optimizing the formulation within the paradigm of gpu computing, presenting results for 2-D unit cells. We describe the application of the formulation with a long term view towards highly efficient and massively distributed band-structure algorithms suitable for tackling optimization and inverse problems. We report that the accurate band-structure evaluation over the boundary of the Irreducible Brillouin Zone (IBZ) for the first 18 phononic branches of a complex 2-D unit cell (with 1132 different phases) can be achieved ...
Quantum Debye-Hueckel theory and the possible plasma phase transition
Energy Technology Data Exchange (ETDEWEB)
Baker, G. Jr.
1998-09-03
In this paper the author first sketches the calculation of the pressure of a neutral, ion-electron gas as an expansion in powers of the electron charge, e, by means of the Matsubara, finite-temperature, many-body, perturbation theory. He then goes on to derive the Debye-H{umlt u} term and other equations to support his contentions. His results support but do not prove the existence of a phase transition.
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Band structures of PbTe can be abnormally bended via dual-doping on both the cationic and anionic sites to form camel-back multivalley energy band structures near the band edge. As a result, additional carrier pockets and strong intervalley scattering of carriers are introduced. Boltzmann transport calculations indicate that their contradictory effects yield remarkably enhanced power factor due to the improved thermopower and almost unchanged electrical conductivity in low temperature and high carrier concentration ranges. These findings prove dual-doping-induced band bending as an effective approach to improve the thermoelectric properties of PbTe and other similar materials
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Fine structure (FS) of the secondary electron emission spectrum (SEMS) os iridium perpendicular to (111) surface and of the total current spectrum (TCS) of Ir polycrystal was interpreted theoretically. The calculations took account of the energy dependence of the energy band level expansion, the electron-electron and the electron-plasmon contributions into distribution function of nonequilibrium electrons current isotopic component from the electrons scattered within the surface. SEMS and TCS FS was shown to result mainly from the electron structure of the terminal state. The elaborated technique enabled to separate the volume effect in SEMS and TCS from the surface ones. Dependence of SEMS and TCS FS on the geometrical structure and the degree of crystal ordering was proved. In that case, moderation of FS intensity served as a measure of defectiveness within a specimen near-the-surface range
A combined representation method for use in band structure calculations. 1: Method
Friedli, C.; Ashcroft, N. W.
1975-01-01
A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.
International Nuclear Information System (INIS)
The first part of the review presents basic facts about computational methods, especially about linearized methods of muffin-tin orbitals (LMTO), augmented plane waves (LAPW), and augmented spherical waves (ASW) for a number of energy characteristics of interatomic coupling. The energy band structure and the energetics of the chemical bonding in stoichiometric binary refractory compounds such as monoxides, monocarbides, and mononitrides of transition metals and in dicarbides of yttrium, strontium, and barium are discussed including a study of the equations of state and internal pressures. The electronic structure, properties, and chemical bonding of ternary refractory compounds (Ti and Nb nitrocarbides, Sc oxicarbides) and of vacancy-containing phases of non-stoichiometric refractory compounds are calculated and discussed. The results demonstrate that the studies are fairly fruitful. 83 refs
Band calculations of the GPA high-pressure effects on the heavy lanthanide metals
Energy Technology Data Exchange (ETDEWEB)
Tokita, M. [Fukuoka Institute of Technology, Fukuoka 811-0295 (Japan)]. E-mail: tokita@fit.ac.jp; Zenmyo, K. [Fukuoka Institute of Technology, Fukuoka 811-0295 (Japan); Mito, M. [Kyushu Institute of Technology, Kitakyushu 804-8550 (Japan); Matsumoto, K. [Kyushu Institute of Technology, Kitakyushu 804-8550 (Japan); Takeda, K. [Kyushu University, Fukuoka 812-8581 (Japan)
2007-03-15
Jackson's group and Mito's group have performed the systematic studies for the GPa high-pressure effects on the magnetic properties of the heavy lanthanide elements. They found that the Curie temperatures decrease linearly with increasing pressure and the magnetic signals disappear at around 9.0 GPa for Gd, 7.5 GPa for Tb, 7.4 GPa for Dy and 11.0 GPa for Ho. With the Anderson's point of view, the results of our band calculation conclude that some part of the decreasing of the bulk magnetization of Gd by pressure is caused by the narrowing of the bandwidth of itinerant s, d hybridized conduction electrons and the broadening of the bandwidth of localized f-orbital electrons.
Polfus, Jonathan M; Bjørheim, Tor S; Norby, Truls; Haugsrud, Reidar
2012-09-01
The nitrogen related defect chemistry and electronic structure of wide band gap oxides are investigated by density functional theory defect calculations of N(O)(q), NH(O)(×), and (NH2)(O)(·) as well as V(O)(··) and OH(O)(·) in MgO, CaO, SrO, Al(2)O(3), In(2)O(3), Sc(2)O(3), Y(2)O(3), La(2)O(3), TiO(2), SnO(2), ZrO(2), BaZrO(3), and SrZrO(3). The N(O)(q) acceptor level is found to be deep and the binding energy of NH(O)(×) with respect to N(O)' and (OH(O)(·) is found to be significantly negative, i.e. binding, in all of the investigated oxides. The defect structure of the oxides was found to be remarkably similar under reducing and nitriding conditions (1 bar N(2), 1 bar H(2) and 1 × 10(-7) bar H(2)O): NH(O)(×) predominates at low temperatures and [N(O)'] = 2[V(O)(··) predominates at higher temperatures (>900 K for most of the oxides). Furthermore, we evaluate how the defect structure is affected by non-equilibrium conditions such as doping and quenching. In terms of electronic structure, N(O)' is found to introduce isolated N-2p states within the band gap, while the N-2p states of NH(O)(×) are shifted towards, or overlap with the VBM. Finally, we assess the effect of nitrogen incorporation on the proton conducting properties of oxides and comment on their corrosion resistance in nitriding atmospheres in light of the calculated defect structures. PMID:22828729
Ab-initio calculations of the Optical band-gap of TiO2 thin films
Wunderlich, W; Tanemura, M; Tanemura, S; Jin, P; Kaneko, K; Terai, A; Nabatova-Gabin, N; Belkada, R; Wunderlich, Wilfried; Miao, Lei; Tanemura, Masaki; Tanemura, Sakae; Jin, Ping; Kaneko, Kenji; Terai, Asuka; Nabatova-Gabin, Nataliya; Belkada, Rachid
2004-01-01
Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band-gap of TiO2 plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO3 substrates was correlated to the lattice constants estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO3. In order to interpret the optical band gap expansion for both phases, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. T...
Zong, YiXin; Xia, JianBai
2015-07-01
The plane-wave expansion (PWE) method is employed to calculate the photonic band structures of metal/dielectric (M/D) periodic systems. We consider a one-dimensional (1D)M/D superlattice with ametal layer characterized by a frequency-dependent dielectric function. To calculate the photonic band of such a system, we propose a new method and thus avoid solving the nonlinear eigenvalue equations. We obtained the frequency dispersions and the energy distributions of eigen-modes of 1D superlattices. This general method is applicable to calculate the photonic band of a broad class of physical systems, e.g. 2D and 3D M/D photonic crystals. For comparison, we present a simple introduction of the finite-difference (FD) method to calculate the same system, and the agreement turns out to be good. But the FD method cannot be applied to the TM modes of the M/D superlattice.
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The objective of the present study is to evaluate variations of the re-ordered wide band model for non-grey radiative transfer calculations in 3D enclosures using the discrete ordinates method. First, the performance of various angular and spatial discretisation schemes of the discrete ordinates method is investigated. Then, several formulations, averaging procedures, and scaling methods of the re-ordered wide band model are tested, and the results are validated against those of a statistical narrow band model. The grey gases formulation using three optimised absorption coefficient is found to be the most efficient method
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
Band gap calculations of the semiconductor BNxP1?x using modified Becke–Johnson approximation
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Highlights: ? The Modified Becke–Johnson scheme gives a very accurate band gap. ? We have shown the invalidity of Vegard’s linear rule for BNxP1?x. ? The band gap changes with alloy concentration are important in band gap engineering. - Abstract: In this work, the electronic properties of BN, BP and BNxP1?x compounds have been investigated by means of first-principles density-functional total-energy calculation using the all-electron full potential linear augmented plane-wave method (FP-LAPW). The (FP-LAPW) method was used within the density functional theory (DFT) along with the Engel–Vosko and Becke–Johnson exchange correlation potential. The energy bands along high symmetry directions, the density of states and bowing distributions are calculated. The results have been discussed in terms of previously existing experimental and theoretical data, and comparisons with similar compounds have been made. Analysis of band structure suggests direct and pseudo-direct band gaps for both compounds.
Robert, Cédric,; Perrin, Mathieu; Cornet, Charles; Even, Jacky; Jancu, Jean-Marc
2012-01-01
Band structure calculations of strained Ga(NAsP) quantum wells are performed within the framework of the extended-basis sp3d5s* tight-binding model. The nitrogen contribution is taken into account by introducing an additional sN orbital into the tight-binding basis. Biaxial strain effects on the band alignment of bulk Ga(NAsP) is studied for the ultra-diluted regime. We demonstrate a good agreement with experimental data both for transition energies and optical gain in Ga(NAsP) quantum wells....
Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.
2015-04-01
High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.
Empirical calculations for ground state band level energies of 76Kr and 74Se nuclei
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The neutron deficient nuclei 76Kr and 74Se (N=40) in the mass region A=80 exhibit interesting properties like shape coexistence, triaxiality, large quadrupole deformation patterns, strong upbends in kinetic moment of inertia of yrast bands and complex band structure. The spectroscopy of these nuclei is of special interest because both the proton and neutron shells are partially filled which results in large deformation in the ground state
Band-gap engineering in chemically conjugated bilayer graphene: Ab initio calculations
Duong, Dinh Loc; Lee, Seung Mi; Chae, Sang Hul; Ta, Quang Huy; Lee, Si Young; Han, Gang Hee; Bae, Jung Jun; Lee, Young Hee
2012-05-01
One-side chemical conjugation of bilayer graphene has limitations not only on opening a band gap of less than 0.2 eV due to a small electric field across bilayer graphene but also on generating highly degenerate semiconducting properties by shifting the Fermi level into either a valence band or a conduction band due to the requirement of heavy doping concentration. Here, we proposed a new strategy of band-gap engineering of bilayer graphene by chemically conjugating double sides of bilayer graphene, one side with an electron-donating group and another side with an electron-withdrawing group. The compensated charges not only created a large band gap of 0.3 eV by invoking an internally strong local dipole field in bilayer graphene but also removed degeneracy by shifting the Fermi level within the band gap. Our approach is easy and straightforward, environmentally stable, and scalable for integration, which is in good contrast with the previous reports of fabricating nanoribbons and high electric field operation.
Ab initio calculation of natural band offsets of all group IV, II-VI and III-V semiconductors
Wei, Su-Huai; Walsh, Aron; Li, Yong-Hua; Gong, Xingao
2010-03-01
The natural band offset between semiconductors is one of the most fundamental properties in materials physics. It is a necessary quantity to assess charge transport and quantum confinement, and is of particular relevance to the design of optoelectronic devices which feature an interface between two or more materials. However, in the past, the natural band offset calculations were based on the assumption that certain reference levels (core levels, average Coulomb potentials, etc.) have zero absolute deformation potential, and thus align between the bulk and heterostructures. In this study [1], using an all-electron band structure approach, we have systematically calculated the natural band offsets between all group IV, III-V and II-VI semiconductor compounds, taking into account the deformation potential of the core states. This revised approach removes assumptions regarding the deformation potential of the reference levels, and offers a more reliable prediction of the `natural' unstrained offsets. Comparison is made to experimental work, where a noticeable improvement is found compared to previous methodologies. [1] Y.-H. Li et al., Appl. Phys. Lett. 94, 212109 (2009).
ZnxCd1?xSe nanomultipods with tunable band gaps: synthesis and first-principles calculations
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In this paper, we demonstrate that ZnxCd1?xSe nanomultipods can be synthesized via a facile and nontoxic solution-based method. Interesting aspects of composition, morphology and optical properties were deeply explored. The value of Zn/(Zn+Cd) could be altered across the entire range from 0.08 to 0.86 by varying the ratio of cation precursor contents. The band gap energy could be linearly tuned from 1.88 to 2.48 eV with respect to the value of Zn/(Zn+Cd). The experiment also showed that oleylamine played a dominant role in the formation of multipod structure. A possible growth mechanism was further suggested. First-principles calculations of band gap energy and density of states in the Vienna ab initio simulation package code were performed to verify the experimental variation tendency of the band gap. Computational results indicated that dissimilarities of electronic band structures and orbital constitutions determined the tunable band gap of the as-synthesized nanomultipod, which might be promising for versatile applications in relevant areas of solar cells, biomedicine, sensors, catalysts and so on. (paper)
Gebele, O; Krey, U; Krompiewski, S
1999-01-01
By an accurate Green's function method we calculate resistances and the corresponding Giant Magneto-Resistance effects (GMR) of two metallic ferromagnetic films separated by different spacers, metallic and non-metallic ones, in a simplified model on a sc lattice, in CPP and CIP geometries (i.e. current perpendicular or parallel to the planes), without impurities, or with interface- or bulk impurities. The electronic structure of the systems is approximated by two hybridized orbitals per atom, to mimic s-bands and d-bands and their hybridization. We show that such calculations usually give rough estimates only, but of the correct order of magnitude; in particular, the predictions on the impurity effects depend strongly on the model parameters. One of our main results is the prediction of huge CPP-GMR effects for {\\it non-metallic} spacers in the ballistic limit.
Variational band theory of vibronic polarons in crystals. III. Numerical calculations
Georgiev, M; Ivanovich, M D
2006-01-01
In the preceding Part II, we derived variational equations for the phonon Fourier amplitudes and for the Fourier amplitudes of the fractional contribution of the electronic bands to the trial variational state. These equations are now solved by means of iterations for each value of the total momentum in order to obtain the energy vs. momentum relation for the ground state. Another result is mapping out the phonon and band Fourier amplitudes in the parameter space of the mixing constant and the electron hopping energy.
Band-gap bowing calculation of Si xSn 1- x alloy
Ferhat, M.; Zaoui, A.
2001-04-01
Using ab initio pseudopotential method within the local density approximation we have investigated the electronic properties of Si xSn 1- x semiconducting alloy. The bowing parameter of the band-gap energy variation with alloy concentration is found to be large. We also analyzed its origin in terms of chemical and structural effects.
Constrained Nudged Elastic Band calculation of the Peierls barrier with atomic relaxations.
Czech Academy of Sciences Publication Activity Database
Gröger, Roman; Vitek, V.
2012-01-01
Ro?. 20, ?. 3 (2012), 035019. ISSN 0965-0393 R&D Projects: GA ?R GAP204/10/0255; GA MŠk(CZ) ED1.1.00/02.0068 Institutional research plan: CEZ:AV0Z20410507 Keywords : dislocation * Peierls barrier * Nudged Elastic Band Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.932, year: 2012
Band-structure parameters by genetic algorithm
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A genetic algorithm has been used to solve a complex multidimensional parameter-fitting problem. We will focus on the parameters of an empirical tight-binding Hamiltonian. The method is used to approximate the electronic energy band structure if energy values are known for a few wave vectors of high symmetry. Compared to the usual manual procedure this method is more accurate and automatic. This approach, based on the extended Hueckel theory (EHT), has provided a list of EHT parameters for IV-IV and III-V semiconductors with zinc-blende structure and helped us to find a symmetry in the EHT. copyright 1996 The American Physical Society
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Theoretical calculation of spectra of two new types of fundamental radioluminescence of dielectrics - intraband electron and band-to-band hole ones - was conducted. These types of radioluminescence were revealed and studied experimentally due to the use of two high-power nano- and picosecond radiation sources for dielectric excitation - high-current electron accelerators and lasers with generators of ultraviolet harmonics. Satisfactory agreement of calculated spectra with ones, measured experimentally, was achieved. Correlation of calculation results with experimental data enabled to determine some important parameters of electron spectrum and specifically the upper boundary of passive region for conduction band ionization for CsI crystals. 27 refs., 8 figs
Band-gap bowing coefficients in large size-mismatched II-VI alloys: first-principles calculations
Moon, Chang-Youn; Wei, Su-Huai; Zhu, Y. Z.; Chen, G. D.
2006-12-01
Band-gap bowing coefficients in large size-mismatched II-VI alloys MIIX1-xVIOx with MII=Zn and Cd, and XVI=S , Se, and Te in the zinc-blende structure are calculated using first-principles methods. We show that in these systems, the bowing coefficients are large and composition dependent. The bowing coefficients increase as the size and chemical mismatch between the constituents increase. The bowing coefficients for the Zn alloys are larger than the corresponding Cd alloys, but smaller than the corresponding III-V alloys. We show that these results can be explained by the size and atomic eigenvalue differences between the constituents and the resulting band offsets and isovalent defect levels in these systems. Our results are compared with recent experimental data.
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Sulfur (S)-doped titanium dioxide (TiO2) was synthesized by ion implantation and subsequent thermal annealing. The S ions were implanted into the single crystals of rutile TiO2 at a fluence of 8x1015 ions/cm2. According to the results of Rutherford backscattering spectroscopy and ion channeling analysis, the irradiation damage recovered by annealing at 600 deg. C in air. In the annealed crystal, the S atoms occupied oxygen sites for form Ti-S bonds, as confirmed by x-ray photoelectron spectroscopy. Compared to the pure TiO2, a photocurrent was observed in the lower-energy regions for the S-doped TiO2. Based on the theoretical analyses by the first-principles band calculations using the full potential linearized augmented plane-wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the band gap narrowing in the S-doped TiO2. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm (<2.9 eV)
Petrova, T. M.; Solodov, A. M.; Solodov, A. A.; Starikov, V. I.
2014-11-01
The water vapor line broadening and shifting for 94 lines in the ?1+?2+?3 band induced by argon pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm-1 and in a wide pressure range of Ar. The calculations of the broadening coefficients ? and ? were performed in the framework of the semi-classical method. The intermolecular potential was taken as the sum of pair potentials which, in turn, were modeled by the Lennard-Jones potentials. Optimal sets of potential parameters given the best discrepancy of measured broadening coefficients are found. The influence of the rotational dependence of an intermolecular potential and its repulsive part on the calculated coefficients ? and ? is discussed.
International Nuclear Information System (INIS)
High-pressure 155Gd Moessbauer measurements on Gd metal, GdCo5, GdRu2Si2, and Gd2Co17N3 were performed at 4.2 K. The maximum pressures reached were about 18 GPa. The resulting volume reductions of 20 30% were determined using high-pressure x-ray diffraction. The pressure dependence of the electric-field gradients and hyperfine fields obtained for the first three systems was compared with predictions from first-principles band-structure calculations. Significant changes of the hyperfine parameters are observed, especially for elemental Gd metal. With increasing pressure, an increase of the electron density at the Gd nuclei is found in all compounds. The values of the hyperfine field initially increase with pressure. For Gd metal the induced structural phase transitions result in large changes in the electric-field gradient at the nucleus (Vzz). The intermetallic compounds show no structural phase transitions and relatively small changes in Vzz. The combination of experiment and calculations indicates that the transition-metal magnetic moments decrease at high pressure. Although for zero pressure predictions of the electric-field gradient and the hyperfine fields, based on the calculations, are quite accurate, the calculated pressure dependence of the hyperfine parameters for Gd, GdCo5, and GdRu2Si2 does not in all cases lead to a satisfactory agreement with experiment. The application of pressures therefore may give additional stimulus for the improvement of the theoretical description of band structures and hyperfine parameters. copyright 1997 The American Physical Society
Lv, Shaoning; Zeng, Yijian; Wen, Jun; Su, Zhongbo
2015-04-01
Soil effective temperature Teff is one of the basic parameter in passive microwave remote sensing for soil moisture. Meanwhile, the dedicated current and future satellite soil moisture monitoring missions use L-Band as the operating frequency. However, Teff at L-Band is strongly affected by the soil moisture and temperature profiles. A two-layer scheme and its corresponding multilayer form were developed to accommodate such influence. In this study, the soil moisture/temperature data collected at Maqu Network are used to verify the newly developed schemes. The key findings are:1) the new two-layer scheme is able to assess which site is relatively in higher accuracy for estimating Teff. It is found that on average nearly 20% of the signal cannot be captured by Maqu Network, with the currently-assumed common installation configuration. It is important to know this since the spatial averaged value is used to retrieve soil moisture with the brightness temperature sensed by the satellite sensors; 2) With the developed method, it is able to identify that the observation pair at 5cm and 20cm is the optimal sampling depth for calculating Teff for the core-site in Maqu Network. It is suggested that the newly developed method can provide an objective way in configuring an optimal soil moisture/temperature network and improve the representativeness of the existing networks, in terms of calculating Teff, by identifying the optimal sampling depth.
The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll
Energy Technology Data Exchange (ETDEWEB)
Reimers, Jeffrey R. [School of Physics and Materials Science, The University of Technology, Sydney NSW (Australia); Cai, Zheng-Li [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane QLD4001 (Australia); Kobayashi, Rika [Australian National University Supercomputer Facility, Mills Rd, Canberra, ACT 0200 (Australia); Rätsep, Margus [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Freiberg, Arvi [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia and Institute of Molecular and Cell Biology, University of Tartu, Riia 23, 51010 Tartu (Estonia); Krausz, Elmars [Research School of Chemistry, The Australian National University, Canberra 2601 (Australia)
2014-10-06
We recently established a novel assignment of the visible absorption spectrum of chlorophyll-a that sees the two components Q{sub x} and Q{sub y} of the low-energy Q band as being intrinsically mixed by non-adiabatic coupling. This ended 50 years debate as to the nature of the Q bands, with prior discussion poised only in the language of the Born-Oppenheimer and Condon approximations. The new assignment presents significant ramifications for exciton transport and quantum coherence effects in photosystems. Results from state of the art electronic structure calculations have always been used to justify assignments, but quantitative inaccuracies and systematic failures have historically limited usefulness. We examine the role of CAM-B3LYP time-dependent density-functional theory (TD-DFT) and Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) calculations in first showing that all previous assignments were untenable, in justifying the new assignment, in making some extraordinary predictions that were vindicated by the new assignment, and in then identifying small but significant anomalies in the extensive experimental data record.
The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll
International Nuclear Information System (INIS)
We recently established a novel assignment of the visible absorption spectrum of chlorophyll-a that sees the two components Qx and Qy of the low-energy Q band as being intrinsically mixed by non-adiabatic coupling. This ended 50 years debate as to the nature of the Q bands, with prior discussion poised only in the language of the Born-Oppenheimer and Condon approximations. The new assignment presents significant ramifications for exciton transport and quantum coherence effects in photosystems. Results from state of the art electronic structure calculations have always been used to justify assignments, but quantitative inaccuracies and systematic failures have historically limited usefulness. We examine the role of CAM-B3LYP time-dependent density-functional theory (TD-DFT) and Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) calculations in first showing that all previous assignments were untenable, in justifying the new assignment, in making some extraordinary predictions that were vindicated by the new assignment, and in then identifying small but significant anomalies in the extensive experimental data record
Ab initio calculations of quasiparticle band structure in correlated systems LDA++ approach
Lichtenstein, A I
1997-01-01
We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated d- or f- electrons. The main feature of this approach is the taking into account the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). In the case of strong interactions (U/W>>1 - rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix the band structure problem is formulated as the functional problem on Nmm' for f-electrons and the standard LDA-functional for delocalized electrons. In the case of moderate correlations (U/W=1 metal-insulator regime) we start from the dynamical mean field iterative perturbation scheme (IPS) of G. Kotliar et. al. and also make use of our multiband atomic Green function. Finally for the weak interactions (U/W<1 -transition metals) the self-consistent diagrammatic fluctuation- exchange (FLEX)-approach of N. Bicker...
Shimada, Mitsuhiro; Shimizu, Yoshifumi R
2015-01-01
By employing the angular momentum projection technique we propose a method to reliably calculate the quantum spectrum of nuclear collective rotation. The method utilizes several cranked mean-field states with different rotational frequencies and they are superposed in the sense of the configuration mixing or the generator coordinate method, after performing the projection; the idea was originally suggested by Peierls-Thouless in 1962. It is found that the spectrum as a result of the configuration mixing does not essentially depend on chosen sets of cranking frequencies if the number of mean-field states utilized in the mixing is larger than a certain small value. We apply this method to three examples employing the Gogny D1S effective interaction and show that it is useful to study high-spin rotational bands by means of the angular momentum projection method.
Broderick, Christopher A.; Harnedy, Patrick E.; Ludewig, Peter; Bushell, Zoe L.; Volz, Kerstin; Manning, Robert J.; O’Reilly, Eoin P.
2015-09-01
Using photovoltage (PV) spectroscopy we analyse the electronic structure of a series of GaBixAs{}1-x/(Al)GaAs dilute bismide quantum well (QW) laser structures. The use of polarisation-resolved PV measurements allows us to separately identify transitions involving bound light- and heavy-hole states in the QWs, as well as bound-to-continuum transitions from the QWs to the barriers. Analysis of these transitions enables us to probe the GaBixAs{}1-x/(Al)GaAs conduction and valence band offsets, thereby quantifying the band offsets. Using a 12-band {k}\\cdot {p} Hamiltonian, we extract the band offsets in the QWs explicitly by constraining the Bi-related parameters of the model against the experimentally measured transition energies. The PV measurements and {k}\\cdot {p} calculations we present provide the first explicit confirmation of a type-I band offset at the GaBixAs{}1-x/GaAs heterointerface near x = 2%. This result, combined with the theory we present for calculating the band offsets at GaBixAs{}1-x/(Al)GaAs heterointerfaces, can be used to determine the band offsets at arbitrary Bi composition x.
Electronic band structure and specific features of Sm2NiMnO6 compound: DFT calculation
International Nuclear Information System (INIS)
The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm2NiMnO6 compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm2NiMnO6 compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (EF). The calculated density of states at the EF is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (?) is found to be 3.74, 4.25 and 4.54 mJ/mol K2 for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed. - Highlights: • The compound is metallic with strong hybridization near the Fermi energy. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of two sheets. • The bonding features are analyzed using the electronic charge density
Electronic band structure and specific features of Sm{sub 2}NiMnO{sub 6} compound: DFT calculation
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H. [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic)
2013-09-15
The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm{sub 2}NiMnO{sub 6} compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm{sub 2}NiMnO{sub 6} compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (E{sub F}). The calculated density of states at the E{sub F} is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (?) is found to be 3.74, 4.25 and 4.54 mJ/mol K{sup 2} for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed. - Highlights: • The compound is metallic with strong hybridization near the Fermi energy. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of two sheets. • The bonding features are analyzed using the electronic charge density.
Energy Technology Data Exchange (ETDEWEB)
Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Bekenev, V.L.; Denysyuk, N.M. [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Parasyuk, O.V. [Department of Inorganic and Physical Chemistry, Eastern European National University, 13 Voli Avenue, Lutsk 43025 (Ukraine); Fedorchuk, A.O. [Department of Inorganic and Organic Chemistry, Lviv National University of Veterinary Medicine and Biotechnologies, Pekarska St., 50, 79010 Lviv (Ukraine)
2014-01-05
Highlights: • Electronic structure of TlPb{sub 2}Cl{sub 5} is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p{sup *} states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb{sub 2}Cl{sub 5} is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb{sub 2}Cl{sub 5} are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb{sub 2}Cl{sub 5} using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb{sub 2}Cl{sub 5} is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb{sub 2}Cl{sub 5} is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb{sub 2}Cl{sub 5} compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar{sup +} ion-irradiated surfaces of a TlPb{sub 2}Cl{sub 5} polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb{sub 2}Cl{sub 5} surface.
Calculation of the band structure of GdCo2, GdRh2 e GdIr2 by the APW method
International Nuclear Information System (INIS)
The band structure of GdCo2, GdRh2, GdIr2 has been calculated by the APW method. A histogram of the density of states is presented for each compound. The bands are transition-metal-like, with s-d hybridization near the Fermi level. The 5d character near the Fermi level increases as one goes from Co to Ir
Barnett, Alex H
2010-01-01
In this paper, we consider band-structure calculations governed by the Helmholtz or Maxwell equations in piecewise homogeneous periodic materials. Methods based on boundary integral equations are natural in this context, since they discretize the interface alone and can achieve high order accuracy in complicated geometries. In order to handle the quasi-periodic conditions which are imposed on the unit cell, the free-space Green's function is typically replaced by its quasi-periodic cousin. Unfortunately, the quasi-periodic Green's function diverges for families of parameter values that correspond to resonances of the empty unit cell. Here, we bypass this problem by means of a new integral representation that relies on the free-space Green's function alone, adding auxiliary layer potentials on the boundary of the unit cell itself. An important aspect of our method is that by carefully including a few neighboring images, the densities may be kept smooth and convergence rapid. This framework results in an integr...
Kozyra, Pawe?; Góra-Marek, Kinga; Datka, Jerzy
2015-02-01
The values of extinction coefficients of Ctbnd C and Cdbnd C IR bands of ethyne and ethene interacting with Cu+ and Ag+ in zeolites were determined in quantitative IR experiments and also by quantumchemical DFT calculations with QM/MM method. Both experimental and calculated values were in very good agreement validating the reliability of calculations. The values of extinction coefficients of ethyne and ethene interacting with bare cations and cations embedded in zeolite-like clusters were calculated. The interaction of organic molecules with Cu+ and Ag+ in zeolites ZSM-5 and especially charge transfers between molecule, cation and zeolite framework was also discussed in relation to the values of extinction coefficients.
Kozyra, Pawe?; Góra-Marek, Kinga; Datka, Jerzy
2015-02-01
The values of extinction coefficients of CC and CC IR bands of ethyne and ethene interacting with Cu+ and Ag+ in zeolites were determined in quantitative IR experiments and also by quantumchemical DFT calculations with QM/MM method. Both experimental and calculated values were in very good agreement validating the reliability of calculations. The values of extinction coefficients of ethyne and ethene interacting with bare cations and cations embedded in zeolite-like clusters were calculated. The interaction of organic molecules with Cu+ and Ag+ in zeolites ZSM-5 and especially charge transfers between molecule, cation and zeolite framework was also discussed in relation to the values of extinction coefficients. PMID:25307963
International Nuclear Information System (INIS)
The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by first-principles calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0–13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO. (condensed matter: structural, mechanical, and thermal properties)
International Nuclear Information System (INIS)
Absorption spectra of nitric oxide in the ?(0,0) and ?(1,0) bands have been measured for hard temperature conditions up to 1700 K in order to validate a model for the simulation of these two bands. The good agreement between experiments and calculations (relative errors of 2-5% for the ?(0,0) band and 10-15% for the ?(1,0) band) consolidates the two important assumptions concerning the intermediate Hund's case between (a) and (b) for the X2? state of the ?(0,0) and ?(1,0) absorption bands and the use of collisional broadening parameters of ?(0,0) to simulate the ?(1,0) band. Using this simulation, a study of the Beer-Lambert law behavior at high temperature has been carried out. With the instrument resolution used for these experiments, it was shown that a correction of the Beer-Lambert law is necessary. To apply this technique for the measurements of NO concentrations inside the combustion chamber of an optical SI engine, a new formulation of the Beer-Lambert law has been introduced, since the modified form proposed in the literature is no longer applicable in the total column range of interest
International Nuclear Information System (INIS)
The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP
First-principles calculation of the band gap of AlxGa1¡-xN and InxGa1¡-xN
Directory of Open Access Journals (Sweden)
Roberto N\\u00FA\\u00F1ez-Gonz\\u00E1lez
2008-01-01
Full Text Available Ab-initio calculations of the band gap variation of AlxGa1¡xN and InxGa1¡xN ternary compounds were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW method, within the Density Functional Theory (DFT. These nitrides were modeled in their wurtzite structure using the supercell method, for concentrations x = 0, 0.25, 0.50, 0.75 and 1.0. To optimize the cell parameters of the binary compounds we used the PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996 3865 exchange correlation functional. For the band structure calculations, we used both PBE96 and EV93 (Engel et al., Phys. Rev. B 47 (1993 13164 exchange correlation functionals. We considered experimental and calculated (with PBE96 lattice parameters to work out the electronic properties. We found that the fundamental gap is direct in all compounds. The calculation with EV93 functional gives a better band gap estimation for binary nitrides. The bowing parameter was also estimated obtaining the values b = 0.74 eV for AlxGa1¡xN and b = 2.12 eV for InxGa1¡xN.
Kobayashi, Hajime; Kobayashi, Norihito; Hosoi, Shizuka; Koshitani, Naoki; Murakami, Daisuke; Shirasawa, Raku; Kudo, Yoshihiro; Hobara, Daisuke; Tokita, Yuichi; Itabashi, Masao
2013-07-01
Hopping and band mobilities of holes in organic semiconductors at room temperature were estimated from first principle calculations. Relaxation times of charge carriers were evaluated using the acoustic deformation potential model. It is found that van der Waals interactions play an important role in determining accurate relaxation times. The hopping mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) in bulk single crystalline structures were found to be smaller than 4 cm(2)?Vs, whereas the band mobilities were estimated between 36 and 58 cm(2)?Vs, which are close to the maximum reported experimental values. This strongly suggests that band conductivity is dominant in these materials even at room temperature. PMID:23822320
International Nuclear Information System (INIS)
The band gap of InxGa1-xN alloys does not only depend on the In composition, but also on the strain state and the ordering of In atoms. We performed a theoretical study to disentangle the different effects. According to our results, the band gaps of InxGa1-xN alloys show parabolic behavior in compressive regions and linear dependence in the tensile regions. We further find a universal bowing behavior in InxGa1-xN alloys for the whole In content range under constant relative strain. Inhomogeneous In distributions lead to a narrower band gap, but are energetically unfavorable. Based on the calculated results, an interpolating form for the band gap as a function of ordering, biaxial strain and chemical content for InxGa1-xN alloys is suggested. Our results provide guidance to determine the band gaps of InxGa1-xN alloys under real experiment conditions.
DEFF Research Database (Denmark)
Svane, Axel; Christensen, Niels Egede
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 approximation provides a correct description of the electronic structure around the gap, in contrast to the local-density approximation, which leads to inverted gaps in the lead chalcogenides. The QSGW calculations are in good quantitative agreement with experimental values of the gaps and masses. At moderate hole doping a complex filamental Fermi-surface structure develops with ensuing large density of states. The pressure-induced gap closure leads to linear (Dirac-type) band dispersions around the L point.
International Nuclear Information System (INIS)
This work reports on a theoretical study of superlattices based on Cd1-xZnxS quantum dots embedded in an insulating material. We show, in particular, how this system can be assumed to a series of flattened cylindrical quantum dots with a finite barrier height at the boundary. In this paper, are also reviewed the approximations needed to calculate the band edges of the Cd1-xZnxS superlattices with use of the Kronig-Penney model. The electronic states and the electron effective masses of both ?1- and ?2-minibands have been computed as a function of zinc composition for different inter-quantum dot separations. As is found, the CdS system is appropriate to give rise a superlattice behavior for conduction electrons in a relatively large range of inter-sheet separations. An attempt to explain the electron band parameters calculated will be presented.
Peng, Peng; Mu, Yao-Ming; Pei, S. S.
2005-06-01
By solving the one-dimensional time-independent Schrödinger equation and Poisson equation simultaneously, we have numerically simulated the energy-band diagram and steady-state carrier distribution of the type-II Interband cascade lasers based on InAs/InGaSb/AlSb multi-quantum wells. The energy levels and wavefunctions of electron and hole in the active region of type-II interband cascade lasers were obtained self-consistently. Our results show that the effects of carrier distribution on band structure should be taken into account in the simulation and design of laser device.
Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan
2014-07-01
Generalized Bloch wave functions of bulk structures, which are composed of not only propagating waves but also decaying and growing evanescent waves, are known to be essential for defining the open boundary conditions in the calculations of the electronic surface states and scattering wave functions of surface and junction structures. Electronic complex band structures being derived from the generalized Bloch wave functions are also essential for studying bound states of the surface and junction structures, which do not appear in conventional band structures. We present a novel calculation method to obtain the generalized Bloch wave functions of periodic bulk structures by solving a generalized eigenvalue problem, whose dimension is drastically reduced in comparison with the conventional generalized eigenvalue problem derived by Fujimoto and Hirose [Phys. Rev. B 67, 195315 (2003)], 10.1103/PhysRevB.67.195315. The generalized eigenvalue problem derived in this work is even mathematically equivalent to the conventional one, and, thus, we reduce computational cost for solving the eigenvalue problem considerably without any approximation and losing the strictness of the formulations. To exhibit the performance of the present method, we demonstrate practical calculations of electronic complex band structures and electron transport properties of Al and Cu nanoscale systems. Moreover, employing atom-structured electrodes and jellium-approximated ones for both of the Al and Si monatomic chains, we investigate how much the electron transport properties are unphysically affected by the jellium parts.
Energy Technology Data Exchange (ETDEWEB)
Novokhatski, A,; /SLAC
2012-02-17
The behavior of the longitudinal wake fields excited by a very short bunch in the SLAC S-band constant gradient accelerating structures has been studied. Wake potential calculations were performed for a bunch length of 10 microns using the author's code to obtain a numerical solution of Maxwell's equations in the time domain. We have calculated six accelerating sections in the series (60-ft) to find the stationary solution. While analyzing the computational results we have found a new formula for the Green's function. Wake potentials, which are calculated using this Green's function are in amazingly good agreement with numerical results over a wide range of bunch lengths. The Green's function simplifies the wake potential calculations and can be easily incorporated into the tracking codes. This is very useful for beam dynamics studies of the linear accelerators of LCLS and FACET.
International Nuclear Information System (INIS)
The band structure of InSb thin films with (1?0?0) surface orientation is calculated using the empirical pseudopotential method (EPM) to evaluate the performance of nanoscale devices using a InSb substrate. Contrary to the predictions by simple effective mass approximation methods (EMA), our calculation reveals that the ? valley is still the lowest lying conduction valley. Based on EPM calculations, we obtained the important electronic structure and transport parameters, such as effective mass and valley energy minimum, of InSb thin film as a function of the film thickness. Our calculations reveal that the 'effective mass' of ?-valley electrons increases with the scaling down of the film thickness. We also provide an assessment of nanoscale InSb thin film devices using a non-equilibrium Green's function under the effective mass framework in the ballistic regime
Govardhani.Immadi; Sarat K Kotamraju; Habibulla Khan; M.Venkata Narayana
2014-01-01
With the increased demand for long distance Tele communication day by day, satellite communication system was developed. Satellite communications utilize L, C, Ku and Ka bands of frequency to fulfil all the requirements. Utilization of higher frequencies causes severe attenuation due to rain. Rain attenuation is noticeable for frequencies above 10ghz. Amount of attenuation depends on whether the operating wave length is comparable with rain drop diameter or not. In this paper the main focus i...
International Nuclear Information System (INIS)
Full text: The light alkaline-earths form an interesting series of metal oxides from a chemical and structural perspective. Calcium and magnesium oxides are often considered 'ideal' ionic solids and occur naturally in cubic rocksalt structures, whilst beryllium oxide displays some properties typical of covalent solids and occurs in the hexagonal wurtzite structure. A number of theoretical investigations of the electronic structure of these oxides have been reported in the literature (see, for example, Kotani and Akai), and compared with available optical and photoemission measurements. However, these techniques do not reveal the complete band structure and cannot always be compared directly with the calculations. A thorough test of various theoretical models requires measurement of the full band-dispersions of these oxides. Towards this end, some progress has been made by Tjeng et al. using angle-resolved photoemission on MgO, but to our knowledge, similar experiments have not been performed for the other alkaline-earth oxides. We report direct measurements of the full band dispersions of BeO, MgO and CaO using electron momentum spectroscopy and compare our results with LCAO calculations using CRYSTAL98 software. Such comparisons can be used to critically assess the quantitative accuracy of various approximations used in current density functional theories
International Nuclear Information System (INIS)
Using method of local coherent potential one calculated the local partial and total densities of electronic states of CuGa(SxSe1-x)2 solid solutions (x = 0, 0.17, 0.33, 0.50, 0.67, 0.83, 1.0) and in approximation of a virtual crystal. Parameters of the crystalline lattice of the investigated chalcopyrite solid solutions were calculated using the Jaffe and Zunger theory with application of tetrahedral Poling radii. Evaluation of Eg linear forbidden band width shows Eg linear dependence on sulfur x concentration in anion sublattice. It corresponds to the experimental data, but Eg values in the calculations turned to be by 0.5 eV smaller than the experimental ones
International Nuclear Information System (INIS)
We have performed first-principles band structure calculations in order to investigate vibronic and optical properties of YBa2Cu3O7. A formalism describing temperature dependent Raman spectra from such ab-initio results has been applied to the 500 cm-1 apex oxygen mode and its overtone in good agreement with experimental results. The dynamical matrix of the five A1g modes established by atomic-force calculations is studied in detail showing rather good agreement with experimental eigenfrequencies and normal coordinates. The effect of isotope substitutions on the phonon frequencies is investigated. We demonstrate that the calculated vibronic properties of high Tc materials are improved by applying a generalized gradient correction scheme for the treatment of exchange and correlation effects instead of the local-density approximation. (orig.)
Scientific Electronic Library Online (English)
P. Cabral do, Couto; R. C., Guedes; B. J. Costa, Cabral.
2004-03-01
Full Text Available Electronic properties of liquid water were investigated by sequential Monte Carlo/Quantum mechanics calculations. The density of states (DOS) and HOMO-LUMO gap (E G) of liquid water have been determined by Hartree-Fock and Density Functional Theory (DFT) calculations. The quantum mechanical calculat [...] ions were carried out over uncorrelated supermolecular structures generated by the Monte Carlo simulations. The DFT calculations were performed with a modified B3LYP exchange-correlation functional proposed by Abu-Awwad and Politzer which was parametrized to reproduce valence orbital energies in agreement with experimental ionization potentials of the water molecule. We have analyzed the dependence of the DOS and HOMO-LUMO gap on the number of water molecules and on surface effects. Our prediction for E G is 6:5 ± 0:5 eV in good agreement with a recent experimental prediction of 6.9 eV.
Directory of Open Access Journals (Sweden)
Govardhani.Immadi
2014-05-01
Full Text Available With the increased demand for long distance Tele communication day by day, satellite communication system was developed. Satellite communications utilize L, C, Ku and Ka bands of frequency to fulfil all the requirements. Utilization of higher frequencies causes severe attenuation due to rain. Rain attenuation is noticeable for frequencies above 10ghz. Amount of attenuation depends on whether the operating wave length is comparable with rain drop diameter or not. In this paper the main focus is on drop size distribution using empirical methods, especially Marshall and Palmer distributions. Empirical methods deal with power law relation between the rain rate(mm/h and radar reflectivity(dBz. Finally it is discussed about the rain rate variation, radar reflectivity, drop size distribution, that is made for two rain events at K L University, Vijayawada on 4th September 2013 and on 18 th August 2013.
Stability and band gaps of InGaP, BGaP, and BInGaP alloys: Density-functional supercell calculations
Energy Technology Data Exchange (ETDEWEB)
Jenichen, Arndt [Leibniz-Institute for Surface Modification, Permoserstrasse 15, 04303 Leipzig (Germany); Engler, Cornelia [Wilhelm-Ostwald-Institute of Physical and Theoretical Chemistry, University Leipzig, Linnestrasse 2, 04103 Leipzig (Germany)
2010-01-15
Energies and band gaps of (InGa)P, (BGa)P and (BInGa)P alloys, including the antisite boron substitutions, are calculated using supercells and the density-functional method. The influence of the substituent concentration and arrangement on the stability and band gaps is investigated and compared with experimental findings. Linearly corrected band-gap widths reproduce well experimental and GW data. The most stable structures of the ternary alloys are 200/211 arrangements of the substituents. The T-x phase diagram for (InGa)P provides no miscibility gap for usual growth temperatures. However, for (BGa)P alloys a large miscibility gap is obtained between about 2% and 99% boron, what confirms experimental results. In quaternary (BInGa)P, boron and indium atoms prefer the (220) but also the (110) position to each other. A 2:1 ratio is preferred for the indium to the boron content. Supercell with the most probable B{sub 1}In{sub n}Ga{sub 31-n}P{sub 32} structure (n = 2). (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Electronic band structure calculations for GaxIn1-xASyP1-y alloys lattice matched to InP
Bechiri, A.; Benmakhlouf, F.; Allouache, H.; Bacha, S.; Bouarissa, N.
2012-02-01
A pseudopotential formalism coupled with the virtual crystal approximation are applied to study the effect of compositional disorder upon electronic band structure of cubic GaxIn1-xAsyP1-y quarternary alloys lattice matched to InP. The effects of compositional variations are properly included in the calculations. Very good agreement is obtained between the calculated values and the available experimental data for the lattice-matched alloy to InP. The absorption at the fundamental optical gaps is found to be direct within a whole range of the y composition whatever the lattice-matching to the substrate of interest. The alloy system GaxIn1-xAsyP1-y lattice matched to InP is suggested to be suitable for an efficient light emitting device (ELED) material.
Seo, Dong-Hwa; Urban, Alexander; Ceder, Gerbrand
2015-09-01
Transition-metal (TM) oxides play an increasingly important role in technology today, including applications such as catalysis, solar energy harvesting, and energy storage. In many of these applications, the details of their electronic structure near the Fermi level are critically important for their properties. We propose a first-principles-based computational methodology for the accurate prediction of oxygen charge transfer in TM oxides and lithium TM (Li-TM) oxides. To obtain accurate electronic structures, the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional is adopted, and the amount of exact Hartree-Fock exchange (mixing parameter) is adjusted to reproduce reference band gaps. We show that the HSE06 functional with optimal mixing parameter yields not only improved electronic densities of states, but also better energetics (Li-intercalation voltages) for LiCo O2 and LiNi O2 as compared to the generalized gradient approximation (GGA), Hubbard U corrected GGA (GGA +U ), and standard HSE06. We find that the optimal mixing parameters for TM oxides are system specific and correlate with the covalency (ionicity) of the TM species. The strong covalent (ionic) nature of TM-O bonding leads to lower (higher) optimal mixing parameters. We find that optimized HSE06 functionals predict stronger hybridization of the Co 3 d and O 2 p orbitals as compared to GGA, resulting in a greater contribution from oxygen states to charge compensation upon delithiation in LiCo O2 . We also find that the band gaps of Li-TM oxides increase linearly with the mixing parameter, enabling the straightforward determination of optimal mixing parameters based on GGA (? =0.0 ) and HSE06 (? =0.25 ) calculations. Our results also show that G0W0@GGA +U band gaps of TM oxides (M O ,M =Mn ,Co ,Ni ) and LiCo O2 agree well with experimental references, suggesting that G0W0 calculations can be used as a reference for the calibration of the mixing parameter in cases when no experimental band gap has been reported.
Rinke, P; Neugebauer, J; Freysoldt, C; Scheffler, M; Rinke, Patrick; Qteish, Abdallah; Neugebauer, Joerg; Freysoldt, Christoph; Scheffler, Matthias
2005-01-01
We report quasiparticle-energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group-III-nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridisation compared to t...
International Nuclear Information System (INIS)
Recent measurements have shown that the transitions deexciting the 453 keV 7/2- level in 183W to the K = 1/2- and 3/2- bands are strongly retarded. The data for B(M1) and B(E2) are analyzed in terms of the RPC model (rotation + particle motion + coupling). With the ?K = 1 (Coriolis) coupling, the K-forbidden M1-transitions proceed via admixtures of high-lying 5/2- bands. A reasonable and unambiguous fit to the data is obtained by varying the strength of the coupling. Allowing for various uncertainties and corrections, one finds that the inertial parameter (the inverse of the coupling constant, i. e. 2J(2?)2/(?)2 may have values between roughly 1 and 3 times the rigid rotator value of 2J(2?)2/(?)2, thus being unexpectedly large. Calculations with the ?K=2 coupling were also performed and turn out not to give better agreement with experiment
Datta, Soumendu; Kaphle, Gopi Chandra; Baral, Sayan; Mookerjee, Abhijit
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)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)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. PMID:26328845
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Highlights: •Decrease in the occupancy of Mn 3d orbitals with doping. •Greater splitting of the eg orbitals due to the increased Jahn–Teller distortion with doping. •Decrease in O 2p–Mn 3d charge transfer character with doping. •Increase in charge transfer energy and band gap with doping. •Calculations hint a subtle change from a charge transfer to Mott–Hubbard type insulator with doping. -- Abstract: The electronic structures of Nd1?xYxMnO3 (x = 0–0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L3,2- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L3,2-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn–Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x = 0.5 composition with respect to x = 0 suggest a subtle change from a charge transfer to Mott Hubbard type insulator
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?, ?H?, ?G? and ?S? have been calculated by Coats-Redfern (CR) and Horowitz-Metzger (HM) methods. The optical band gaps of the isolated complexes have been calculated from absorption spectra and the results indicated semi-conducting nature of the investigated complexes. The interactions between the copper (II) complex and calf thymus DNA (CT-DNA) have been studied by UV spectra. The results confirm that the Cu(II) complex binds to CT-DNA.
Ochi, Masayuki; Sodeyama, Keitaro; Tsuneyuki, Shinji
2014-02-01
Based on the random-phase approximation and the transcorrelated (TC) method, we optimize the Jastrow factor together with one-electron orbitals in the Slater determinant in the correlated wave function with a new scheme for periodic systems. The TC method is one of the promising wave function theories for first-principles electronic structure calculation, where the many-body wave function is approximated as a product of a Slater determinant and a Jastrow factor, and the Hamiltonian is similarity-transformed by the Jastrow factor. Using this similarity-transformed Hamiltonian, we can optimize the one-electron orbitals without evaluating 3N-dimensional integrations for the N-electron system. In contrast, optimization of the Jastrow factor within the framework of the TC method is computationally much more expensive and has not been performed for solid-state calculations before. In this study, we also benefit from the similarity-transformation in optimizing the Jastrow factor. Our optimization scheme is tested in applications to some solids from narrow-gap semiconductors to wide-gap insulators, and it is verified that the band gap of a wide-gap insulator and the lattice constants of some solids are improved by this optimization with reasonable computational cost.
International Nuclear Information System (INIS)
Based on the random-phase approximation and the transcorrelated (TC) method, we optimize the Jastrow factor together with one-electron orbitals in the Slater determinant in the correlated wave function with a new scheme for periodic systems. The TC method is one of the promising wave function theories for first-principles electronic structure calculation, where the many-body wave function is approximated as a product of a Slater determinant and a Jastrow factor, and the Hamiltonian is similarity-transformed by the Jastrow factor. Using this similarity-transformed Hamiltonian, we can optimize the one-electron orbitals without evaluating 3N-dimensional integrations for the N-electron system. In contrast, optimization of the Jastrow factor within the framework of the TC method is computationally much more expensive and has not been performed for solid-state calculations before. In this study, we also benefit from the similarity-transformation in optimizing the Jastrow factor. Our optimization scheme is tested in applications to some solids from narrow-gap semiconductors to wide-gap insulators, and it is verified that the band gap of a wide-gap insulator and the lattice constants of some solids are improved by this optimization with reasonable computational cost
First-principles calculation of the band gap of Al xGa1-xN and In xGa1-x N
Scientific Electronic Library Online (English)
Roberto, Núñez-González; Armando, Reyes-Serrato; Alvaro, Posada-Amarillas; Donald H, Galván.
2008-11-01
Full Text Available En este trabajo se realizaron cálculos de primeros principios de la variación del ancho de banda prohibido en los compuestos ternarios Al xGa1-xN e In xGa1-x N, utilizando el Método Linealizado de Ondas Planas Aumentadas con Potencial Completo (FLAPW), dentro del marco de la Teoría del Funcional de [...] la Densidad (DFT). Los nitruros fueron modelados en una estructura tipo wurzita utilizando el método de supercelda, y considerando las concentraciones x = 0, 0.25, 0.50, 0.75 y 1.0. Para la optimización de los parámetros de red se utilizó el potencial de correlación-intercambio PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996) 3865). Para el cálculo de la estructura de bandas de energía se utilizaron los funcionales PBE96 y EV93 (Engel et al., Phys. Rev. B 47 (1993) 13164). Se consideraron parámetros de red experimentales y calculados (con PBE96) para los cálculos de las propiedades electrónicas. Nuestros cálculos indican que la banda prohibida fundamental es directa en estos compuestos. Los cálculos con el funcional EV93 dan como resultado una mejor estimación de los anchos de las bandas prohibidas de los compuestos binarios. Calculamos el parámetro de curvatura, obteniendo los valores b = 0.74 eV para Al xGa1-xN y b = 2.12 eV para In xGa1-x N. Abstract in english Ab-initio calculations of the band gap variation of Al xGa1-xN and In xGa1-x N ternary compounds were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method, within the Density Functional Theory (DFT). These nitrides were modeled in their wurtzite structure using the su [...] percell method, for concentrations x = 0, 0.25, 0.50, 0.75 and 1.0. To optimize the cell parameters of the binary compounds we used the PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996) 3865) exchange-correlation functional. For the band structure calculations, we used both PBE96 and EV93 (Engel et al., Phys. Rev. B 47 (1993) 13164) exchange-correlation functionals. We considered experimental and calculated (with PBE96) lattice parameters to work out the electronic properties. We found that the fundamental gap is direct in all compounds. The calculation with EV93 functional gives a better band gap estimation for binary nitrides. The bowing parameter was also estimated obtaining the values b = 0.74 eV for Al xGa1-xN and b = 2.12 eV for In xGa1-x N.
Sakai, Osamu
2010-11-01
Band calculations for Ce compounds with the AuCu3-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem was solved by a method named NCA f2vc (noncrossing approximation including the f2 state as a vertex correction). The calculations take into account the crystal-field splitting, the spin-orbit interaction, and the correct exchange process of the f1 ? f0, f2 virtual excitation. These are necessary features in the quantitative band theory for Ce compounds and in the calculation of their excitation spectra. The results of applying the calculation to CePd3 and CeRh3 are presented as the first in a series of papers. The experimental results of the photoemission spectrum (PES), the inverse PES, the angle-resolved PES, and the magnetic excitation spectra were reasonably reproduced by the first-principles DMFT band calculation. At low temperatures, the Fermi surface (FS) structure of CePd3 is similar to that of the band obtained by the local density approximation. It gradually changes into a form that is similar to the FS of LaPd3 as the temperature increases, since the 4f band shifts to the high-energy side and the lifetime broadening becomes large.
International Nuclear Information System (INIS)
Band calculations for Ce compounds with the AuCu3-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem was solved by a method named NCA f2vc (noncrossing approximation including the f2 state as a vertex correction). The calculations take into account the crystal-field splitting, the spin-orbit interaction, and the correct exchange process of the f1 ? f0, f2 virtual excitation. These are necessary features in the quantitative band theory for Ce compounds and in the calculation of their excitation spectra. The results of applying the calculation to CePd3 and CeRh3 are presented as the first in a series of papers. The experimental results of the photoemission spectrum (PES), the inverse PES, the angle-resolved PES, and the magnetic excitation spectra were reasonably reproduced by the first-principles DMFT band calculation. At low temperatures, the Fermi surface (FS) structure of CePd3 is similar to that of the band obtained by the local density approximation. It gradually changes into a form that is similar to the FS of LaPd3 as the temperature increases, since the 4f band shifts to the high-energy side and the lifetime broadening becomes large. (author)
International Nuclear Information System (INIS)
Crystal structure of homologous compounds, Zn3In2O6, Zn4In2O7, Zn5In2O8, Zn7In2O10, and In2O3 were refined by X-ray Rietveld analysis. Band structures of the homologous compounds were evaluated by first-principle calculation (Cambridge Serial Total Energy Package, CASTEP), using the structural data obtained from the Rietveld analysis. According to the results of CASTEP calculations, a sharp cut-off at the Fermi level could be observed when In3+ preferentially occupies the tetrahedral site (Zn3In2O6(4)) or the trigonal bipyramid site (Zn3In2O6(5)) in the (InZnk)Ok+1+ layers. The cut-off at the Fermi level could not be observed when In3+ and Zn2+ are totally disordered at these sites. Electronic structure calculation suggested that Zn3In2O6(4) is a good conductor and that Zn3In2O6(5) is a poor conductor. Results of geometry optimization indicate that the formation enthalpy of Zn3In2O6(4) was lower than that of Zn3In2O6(5). Considering the electronic structure and the formation enthalpy, Zn3In2O6(4) in which In3+ in tb>6(4) in which In3+ in the (InZnk)Ok+1+ layer occupies the tetrahedral site preferentially, is likely to be the favored structure
International Nuclear Information System (INIS)
Band structure calculations were performed for tungsten nitride, cobalt tungsten nitrides, and platinum slabs. The major requirements for the development of a superior cathode catalyst are: (1) that the Fermi level of the cathode catalyst is close to the energy level of the lowest unoccupied molecular orbital of O2, the lowest unoccupied atomic orbital of an oxygen atom, and the lowest unoccupied atomic orbital of a hydrogen atom so that they can readily interact with one another; and (2) that the cathode catalysts have smaller ?E value which represent the difference between the Fermi level and the peak position of the density of states of the Op orbital of O2 adsorbed on the catalyst. The active site structures of cobalt tungsten nitrides for activation of the oxygen reduction reaction were found to have the surface structure of Co-O-Co, which lowered the unoccupied orbital of the oxygen atom to approximately that of the Fermi level. However, this structure concomitantly lowered the Fermi level, which resulted in an increase in ?E. Consequently, the optimal cathode catalyst regarding the surface conformation contains a Co-O-Co structure that is dispersed on the surface of the cobalt tungsten nitride. The cobalt tungsten oxynitride exhibited a catalytic activity for the oxygen reduction reaction. A linear dependence is observed between the ?E and the oxygen reduction reaction offset potentials of the tungsten nitride, cobalt tungsteof the tungsten nitride, cobalt tungsten nitride, cobalt tungsten oxynitride, and platinum.
International Nuclear Information System (INIS)
The complex Robert-Bonamy (CRB) formalism was used to calculate the half-width, its temperature dependence, and the line shift for CO2 for transitions in the 30012?00001 and 30013?00001 bands with O2 as the perturbing gas. The calculations were done for rotational quantum numbers from J=0 to J=120 with no ad hoc scaling of the line shape equations. The intermolecular potential parameters are adjusted on accurate experimental measurements of the half-widths, its temperature dependence, and the pressure-induced line shifts so that a single intermolecular potential reproduces all three parameters. Using the results of this work and previous results for N2-broadening, air-broadening line shape parameters were also determined. The comparison of the CRB calculations with the experimental data available in the literature for the three line shape coefficients demonstrates the quality of the present calculations for the both bands under study.
Mourad, Daniel; Kruse, Carsten; Klembt, Sebastian; Retzlaff, Reiner; Gartner, Mariuca; Anastasescu, Mihai; Hommel, Detlef; Czycholl, Gerd
2010-01-01
Compound semiconductor alloys of the type ABC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects a...
Sakai, Osamu
2010-01-01
Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem was solved by a method named NCA$f^{2}$vc (noncrossing approximation including the $f^{2}$ state as a vertex correction). The calculations take into account the crystal-field splitting, the spin-orbit interaction, and the correct exchange process of the $f^{1} \\rightarrow f^{0},f^{2}$ virtual excitat...
Polak, M. P.; Scharoch, P.; Kudrawiec, R.
2015-09-01
Bi-induced changes in the band structure of Ga–V–Bi and In–V–Bi alloys are calculated within the density functional theory (DFT) for alloys with Bi ?3.7% and the observed chemical trends are discussed in the context of the virtual crystal approximation (VCA) and the valence band anticrossing (VBAC) model. It is clearly shown that the incorporation of Bi atoms into III–V host modifies both the conduction band (CB) and the valence band (VB). The obtained shifts of bands in GaP1?xBix, GaAs1?xBix, GaSb1?xBix, InP1?xBix, InAs1?xBix, and InSb1?xBix are respectively, 15, ?29, ?16, ?27, ?15, and ?10 meV/%Bi for CB, 82, 62, 16, 79, 45, and 16 meV/%Bi for VB, and ?17, ?3, ?2, ?8, ?6, and 14 meV/%Bi for spin–orbit split off band. The Bi-induced reduction of the band gap is very consistent with the available experimental data. The chemical trends observed in our calculations as well as in experimental data are very clear: in a sequence of alloys from III–P–Bi to III–Sb–Bi the Bi-induced changes in the band structure weaken. For dilute GaSb1?xBix and InSb1?xBix alloys the band structure modification, in the first approximation, can be described within the VCA, while for Ga–V–Bi and In–V–Bi alloys with V = As or P another phenomenological approach is needed to predict the Bi-induced changes in their band structure. We have found that a combination of the VCA with the VBAC model, which is widely applied for highly mismatched alloys, is suitable for this purpose. The chemical trends for III–V–Bi alloys observed in our DFT calculations are also exhibited by the coupling parameter {C}BiM, which describes the magnitude of interaction between Bi-induced levels and VB states in the VBAC model. This coupling parameter monotonously decreases along the sequence of alloys from III–P–Bi to III–Sb–Bi.
Calculation of the g-tensor and 29Si hyperfine tensors of the E'1 centre in silicon dioxide
International Nuclear Information System (INIS)
Both the g-tensor and the tensors of 29Si hyperfine interactions are calculated for the model of an O- vacancy in ?-quartz with asymmetric lattice distortion proposed by Yip and Fowler to explain the E'1 centre in SiO2. The extended Hueckel theory (EHT) is applied to an ?-quartz cluster. The dangling bonds of the outer atoms are saturated by hydrogen. Theoretical and experimental results agree quantitatively well. Similar calculations are performed for the analogous model in ?-cristobalite. Computations with and without consideration of Sisub(3d) functions are compared. (author)
International Nuclear Information System (INIS)
We succeeded in growing a high-quality single crystal of NpRhGa5 by the Ga-flux method and observed the de Haas-van Alphen oscillation in the antiferromagnetic state. Four kinds of nearly cylindrical Fermi surfaces, which correspond to main Fermi surfaces, were clearly detected. These quasi-two-dimensional Fermi surfaces are formed in the flat antiferromagnetic Brillouin zone and are well explained on the basis of spin- and orbital-polarized LAPW energy band calculations. The cyclotron masses are moderately enhanced, ranging from 8.1 to 11.7 m0, which are approximately four times larger than the corresponding band masses. This is the first case where the 5f-itinerant band model is applicable to a neptunium magnetic compound. (letter to the editor)
Energy Technology Data Exchange (ETDEWEB)
Kumar, Suresh [Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India)
2014-08-14
Magnetic Rotation (MR) band crossing is studied systematically in N=78 isotones (La, Pr, Pm and Eu) using Tilted Axis Cranking (TAC) model. The observables such as I(¯h) vs ¯h?, excitation energy E(MeV) vs spin I(¯h), and the B(M1)/B(E2) vs I(¯h) were considered to pinpoint MR crossing in these nuclei. The results of tilted axis cranking were compared with these experimental observables. The B(M1) and B(E2) values were also reported and used to understand the crossing behaviour of these MR bands. The systematic evolution of this phenomenon in N=78 odd-Z istotones leads to understand the role of nucleons in MR band crossing.
Energy Technology Data Exchange (ETDEWEB)
Cui, Ying; Lee, Sangheon; Leyson, Gerard; Freysoldt, Christoph; Neugebauer, Joerg [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str. 1, 40627 Duesseldorf (Germany)
2013-07-01
The band gap of In{sub x}Ga{sub 1-x}N alloys does not only depend on the In composition, but also on the strain state and the ordering of In atoms. We performed a theoretical study to disentangle the different effects. According to our results, the band gaps of In{sub x}Ga{sub 1-x}N alloys show parabolic behavior in compressive regions and linear dependence in the tensile regions. We further find a universal bowing behavior in In{sub x}Ga{sub 1-x}N alloys for the whole In content range under constant relative strain. Inhomogeneous In distributions lead to a narrower band gap, but are energetically unfavorable. Based on the calculated results, an interpolating form for the band gap as a function of ordering, biaxial strain and chemical content for In{sub x}Ga{sub 1-x}N alloys is suggested. Our results provide guidance to determine the band gaps of In{sub x}Ga{sub 1-x}N alloys under real experiment conditions.
Ultrawide Band Electromagnetic Pulses
International Science & Technology Center (ISTC)
Development of New Calculation-Theoretical and Metrologic Approaches in Technology of Ultrawide Band Electromagnetic Pulses, Elaboration and Investigation of Standard Field-Forming Systems of Subnanosecond Pulse Field
Sakai, Osamu; Harima, Hisatomo
2012-01-01
Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The results of applying the calculation to CeIn$_{3}$ and CeSn$_{3}$ are presented as the second in a series of papers. The Kondo temperature and crystal-field splitting are obtained, respectively, as 190 and 390 K (CeSn$_{3}$), 8 and 160 K (CeIn$_{3}$ under ambient pressure), and 30 and 240 K (CeIn$_{3}$ at a pressure of 2.75 GPa...
Sakai, Osamu; Harima, Hisatomo
2012-02-01
Band calculations for Ce compounds with the AuCu3-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The results of applying the calculation to CeIn3 and CeSn3 are presented as the second in a series of papers. The Kondo temperature and crystal-field splitting are obtained, respectively, as 190 and 390 K (CeSn3), 8 and 160 K (CeIn3 under ambient pressure), and 30 and 240 K (CeIn3 at a pressure of 2.75 GPa). Experimental results for the photoemission spectrum are reasonably well reproduced. In CeSn3, a Fermi surface (FS) structure similar to that obtained by a refined calculation based on the local density approximation (LDA) is obtained. In CeIn3, the topology of the FS structure is different from that obtained by the LDA calculation but seems to be consistent with the results of de Haas--van Alphen experiments. Cyclotron mass of the correct magnitude is obtained in both compounds. The experimental result for the angular correlation of the electron-positron annihilation radiation is reasonably well reproduced on the basis of the itinerant 4f picture. A band calculation for CeIn3 in the antiferromagnetic state was carried out, and it was shown that the occupied 4f state should have a very shallow level.
International Nuclear Information System (INIS)
Compound semiconductor alloys of the type AxB1-xC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband sp3 tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present talk, we concentrate on bulk CdxZn1-xSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdxZn1-xSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on CdxZn1-xSe nanowires reported in the literature.
Mourad, Daniel; Czycholl, Gerd; Kruse, Carsten; Klembt, Sebastian; Retzlaff, Reiner; Hommel, Detlef; Gartner, Mariuca; Anastasescu, Mihai
2010-10-01
Compound semiconductor alloys of the type AxB1-xC find widespread applications as their electronic bulk band gap varies continuously with x , and therefore a tailoring of the energy gap is possible by variation in the concentration. We model the electronic properties of such semiconductor alloys by a multiband sp3 tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present paper, we concentrate on bulk CdxZn1-xSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdxZn1-xSe layers prepared by molecular beam epitaxy and photoluminescence measurements on catalytically grown CdxZn1-xSe nanowires reported in the literature.
Energy Technology Data Exchange (ETDEWEB)
Mourad, Daniel; Czycholl, Gerd [Institut fuer Theoretische Physik, Universitaet Bremen (Germany); Kruse, Carsten; Klembt, Sebastian; Retzlaff, Reiner; Hommel, Detlef [Institut fuer Festkoerperphysik, Universitaet Bremen (Germany); Gartner, Mariuca; Anastasescu, Mihai [Institute fuer Physikalische Chemie ' ' Ilie Murgulescu' ' , Rumaenische Akademie (Romania)
2011-07-01
Compound semiconductor alloys of the type A{sub x}B{sub 1-x}C find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband sp{sup 3} tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present talk, we concentrate on bulk Cd{sub x}Zn{sub 1-x}Se as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of Cd{sub x}Zn{sub 1-x}Se layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on Cd{sub x}Zn{sub 1-x}Se nanowires reported in the literature.
Mourad, Daniel; Klembt, Sebastian; Retzlaff, Reiner; Gartner, Mariuca; Anastasescu, Mihai; Hommel, Detlef; Czycholl, Gerd
2010-01-01
Compound semiconductor alloys of the type ABC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present paper, we concentrate on bulk CdZnSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdZnSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on catalytically grown CdZnSe nanowires reported in the ...
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.
Field theoretic calculation of the surface tension for a model electrolyte system
International Nuclear Information System (INIS)
We carry out the calculation of the surface tension for a model electrolyte to first order in a cumulant expansion about a free-field theory equivalent to the Debye-Hueckel approximation. In contrast with previous calculations, the surface tension is calculated directly without recourse to integrating thermodynamic relations. The system considered is a monovalent electrolyte with a region at the interface, of width h, from which the ionic species are excluded. In the case where the external dielectric constant ?0 is smaller than the electrolyte solution's dielectric constant ? we show that the calculation at this order can be fully regularized. In the case where h is taken to be zero the Onsager-Samaras limiting law for the excess surface tension of dilute electrolyte solutions is recovered, with corrections coming from a nonzero value of ?0/?
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…
International Nuclear Information System (INIS)
In the paper the technique and results of the magnetic field calculation in the bending block model of IFVE booster taking into account the magnetoanisotropic steel features, as a working material, are presented. Two versions of steel rolling direction orientation relative to the mean plane of the operating magnet gap are considered. It is shown, that transverse orientation provides better field homogeneity
Czech Academy of Sciences Publication Activity Database
Karakalos, S.; Ladas, S.; Jane?ek, P.; Šutara, F.; Nehasil, V.; Tsud, N.; Prince, K.; Matolín, V.; Cháb, Vladimír; Papanicolaou, N.I.; Dianat, A.; Gross, A.
2008-01-01
Ro?. 516, ?. 10 (2008), s. 2962-2965. ISSN 0040-6090 Institutional research plan: CEZ:AV0Z10100521 Keywords : surface alloys * electronic structure calculations * photoelectron spectroscopy * synchrotron radiation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.884, year: 2008
Wang, Jianwei; Zhang, Yong; Wang, Lin-Wang
2015-07-01
We propose a systematic approach that can empirically correct three major errors typically found in a density functional theory (DFT) calculation within the local density approximation (LDA) simultaneously for a set of common cation binary semiconductors, such as III-V compounds, (Ga or In)X with X =N ,P ,As ,Sb , and II-VI compounds, (Zn or Cd)X , with X =O ,S ,Se ,Te . By correcting (1) the binary band gaps at high-symmetry points ? , L , X , (2) the separation of p -and d -orbital-derived valence bands, and (3) conduction band effective masses to experimental values and doing so simultaneously for common cation binaries, the resulting DFT-LDA-based quasi-first-principles method can be used to predict the electronic structure of complex materials involving multiple binaries with comparable accuracy but much less computational cost than a GW level theory. This approach provides an efficient way to evaluate the electronic structures and other material properties of complex systems, much needed for material discovery and design.
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...
International Nuclear Information System (INIS)
In this work, Complex Robert-Bonamy calculations of half-widths and line shifts were done for N2-broadening of water for 1639 transitions in the rotational band using two models for the trajectories. The first is a model correct to second order in time, the Robert-Bonamy parabolic approximation. The second is the solution of Hamilton's equations. Both models use the isotropic part of the atom-atom potential to determine the trajectories. The present calculations used an intermolecular potential expanded to 20th order to assure the convergence of the half-widths and line shifts. The aim of the study is to assess if the difference in the half-widths and line shifts determined from the two trajectory models is greater than the accuracy requirements of the spectroscopic and remote sensing communities. The results of the calculations are compared with measurements of the half-widths and line shifts. It is shown that the effects of the trajectory model greatly exceed the needs of current remote sensing measurements and that line shape parameters calculated using trajectories determined by solving Hamilton's equations agree better with measurement.
Lamouroux, J.; Gamache, R. R.; Laraia, A. L.; Ma, Q.; Tipping, R. H.
2012-01-01
In this work, Complex Robert-Bonamy calculations of half-widths and line shifts were done for N2-broadening of water for 1639 transitions in the rotational band using two models for the trajectories. The first is a model correct to second order in time, the Robert-Bonamy parabolic approximation. The second is the solution of Hamilton's equations. Both models use the isotropic part of the atom-atom potential to determine the trajectories. The present calculations used an intermolecular potential expanded to 20th order to assure the convergence of the half-widths and line shifts. The aim of the study is to assess if the difference in the half-widths and line shifts determined from the two trajectory models is greater than the accuracy requirements of the spectroscopic and remote sensing communities. The results of the calculations are compared with measurements of the half-widths and line shifts. It is shown that the effects of the trajectory model greatly exceed the needs of current remote sensing measurements and that line shape parameters calculated using trajectories determined by solving Hamilton's equations agree better with measurement.
... gastric banding before deciding to have the procedure. Advertisements for a device or procedure may not include ... feeds Follow FDA on Twitter Follow FDA on Facebook View FDA videos on YouTube View FDA photos ...
International Nuclear Information System (INIS)
Calculations of the half-width, its temperature dependence, and the line shift are made for the rotational states J=0-120 for two of the Fermi-tetrad bands (30012?00001 and 30013?00001) of CO2 perturbed by N2. The calculations employ the semi-classical complex Robert-Bonamy method with no ad hoc scaling, J-dependent or otherwise, and an intermolecular potential (IP) comprised of an electrostatic part, an atom-atom part, and an isotropic London dispersion part. The averaging over the impact parameter b and relative speed v are explicitly carried out. Many interesting features about CO2 as the radiating molecule are elucidated. Effects of the trajectory model, the order of the expansion of the atom-atom component of the potential, and the inclusion of the imaginary terms are studied. It is shown that the results are very sensitive to the intermolecular potential. The final IP parameters give results that demonstrate excellent agreement with measurement for the three line shape parameters studied in this work.
International Nuclear Information System (INIS)
Excited states in the neutron-deficient nucleus 170Os were identified up to spin (24+) in the yrast band and to spin (23-) in the lowest negative-parity band. Deformation systematics implied by the 2+ state energies for the very light osmium isotopes are compared with theory. Band-crossing frequencies, alignments and alignment gains are compared with cranked shell model calculations. Deformation changes are required to obtain detailed agreement. A three-band mixing approach is invoked to explain the low spin yrast anomaly in 172Os and to reproduce the yrast band in 170Os. The excitation energy of the postulated intruder band in 1700s and 172Os is deduced
Chemically induced compaction bands in geomaterials
Stefanou, Ioannis; Sulem, Jean
2013-04-01
Compaction bands play an important role in oil production and may provide useful information on various geological processes. Various mechanisms can be involved at different scales: the micro scale (e.g. the grain scale), the meso scale (e.g. the Representative Element Volume) and the macro scale (e.g. the structure). Moreover, hydro-chemo-mechanical couplings might play an important role in triggering instabilities in the form of compaction bands. Compaction bands can be seen as an instability of the underneath mathematical problem leading to localization of deformation [1,2,3]. Here we explore the conditions of compaction banding in quartz-based geomaterials by considering the effect of chemical dissolution and precipitation [4,5]. In due course of the loading process grain crushing affects the residual strength, the porosity and the permeability of the material. Moreover, at the micro-level, grain crushing results in an increase of the grain specific surface, which accelerates the dissolution [6]. Consequently, the silica is removed more rapidly from the grain skeleton and the overall mechanical properties are degraded due to chemical factors. The proposed model accounts for these phenomena. In particular, the diffusion of the diluted in the water silica is considered through the mass balance equation of the porous medium. The reduction of the mechanical strength of the material is described through a macroscopic failure criterion with chemical softening. The grain size reduction is related to the total energy input [7]. A grain size and porosity dependent permeability law is adopted. These degradation mechanisms are coupled with the dissolution/precipitation reaction kinetics. The obtained hydro-chemo-mechanical model is used to investigate the conditions, the material parameters and the chemical factors inducing compaction bands formation. References [1] J.W. Rudnicki, and J.R. Rice. "Conditions for the Localization of Deformation in Pressure-sensitive Dilatant Materials." Journal of the Mechanics and Physics of Solids 23.6 (1975): 371-394. [2] I. Vardoulakis and J. Sulem: Bifurcation analysis in geomechanics. Blackie. 1995. [3] J.W. Rudnicki, "Conditions for Compaction and Shear Bands in a Transversely Isotropic Material." International Journal of Solids and Structures 39.13-14 (2002): 3741-3756. [4] L.-B. Hu and T. Hueckel. "Coupled Chemo-mechanics of Intergranular Contact: Toward a Three-scale Model." Computers and Geotechnics 34.4 (2007): 306-327. [5] R. Nova, R. Castellanza, and C. Tamagnini. "A Constitutive Model for Bonded Geomaterials Subject to Mechanical And/or Chemical Degradation." International Journal for Numerical and Analytical Methods in Geomechanics 27.9 (2003): 705-732. [6] J.D. Rimstidt and H.L. Barnes. "The Kinetics of Silica-water Reactions." Geochimica et Cosmochimica Acta 44.11 (1980): 1683-1699. [7] P.V. Lade, J.A. Yamamuro and P.A. Bopp "Significance of Particle Crushing in Granular Materials." Journal of Geotechnical Engineering, 122.4 (1996): 309-316.
Energy Technology Data Exchange (ETDEWEB)
Landeros-Ayala, S.; Neri-Vela, R; Cruz-Sanchez, H.; Hernandez-Bautista, H. [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)
2002-03-01
In the last years, the peak in the demand of satellite communication service has caused the saturation in the use of the frequencies corresponding to the band, Cand Ku. Due to this, the engineers have looked for viable alternatives, in order to satisfy the current requisition, as well as the future demand, for which a considerable increment is expected. One of these alternatives is the use of the Ka Band (20Hz/30Hz), that is why the importance of studying the propagation effects that are experienced at these frequencies, especially the attenuation effect by rain, as in this case, where it is significant. The present article has the purpose to describe the use of the Modelo DAH (whose authors are Asoka Dissanayake, Jeremy Allnutt and Fatim Haidara), mixed with the global maps of distribution of rain by Crane, for the calculation of the attenuation by rain in satellite communication systems operated in the Ka Band. Besides, antenna diameters for the systems of communications in Ka Band in different locations of the Mexican Republic, using for it the attenuation margins for rain obtained through the Modelo DAH, and using as references the characteristics of the ANIK F2 satellite and a terrestrial station VSAT, are proposed. [Spanish] En los ultimos anos, el auge en la demanda de servicios de comunicacion por satelite ha provocado la saturacion en los uso de la frecuencia correspondientes a las bandas C y Ku. Debido a esta razon, se han buscado alternativas viables para poder satisfacer la demanda actual, asi como la demanda futura, para la cual se espera un incremento considerable. Una de estas alternativas es el uso de Banda Ka (20Hz/30Hz), de ahi la importancia del estudio sobre los efectos de programacion que se experimentan a esta frecuencia, en especial, el efecto de atencion por lluvias, ya que sen este caso resulta ser significativa. El presente articulo tiene como finalidad describir el uso del Modelo DAH (cuyos autores son Asoka Dissanayake, Jeremy Allnutt y Fatim Haidara), combinado con los mapas globales de distribucion de lluvia de Crane, para el calculo de la atencion por lluvia en sistema de comunicacion por satelite que operen en la Banda Ka. Ademas, se proponen diametros de antena para los sistemas de comunicaciones en Banda Ka en diferentes localidades de la Republica Mexicana, empleando para ello, los margenes de atencion por lluvia obtenidos a trav del Modelo DAH, y usando como referencia las caracteristicas del satelite de comunicaciones ANIK F2 y de una estacion terrena VSAT.Se muestra una fig. de la atenuacion por lluvia a 27.5 gHz y de los diametros de antena para banda Ka en Mexico. Se da una tabla de la atenuacion por lluvia a 29.5 GHz y a 20.2 GHz.
Candidate chiral bands in 198Tl
International Nuclear Information System (INIS)
High-spin states in 198Tl were studied using the 197Au(?, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast ?h9/2 x ?i13/2-1 band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality. (orig.)
Nonzero Quadrupole Moments of Candidate Tetrahedral Bands
International Nuclear Information System (INIS)
Negative-parity bands in the vicinity of 156Gd and 160Yb have been suggested as candidates for the rotation of tetrahedral nuclei. We report the observation of the odd and even-spin members of the lowest energy negative-parity bands in 160Yb and 154Gd. The properties of these bands are similar to the proposed tetrahedral band of 156Gd and its even-spin partner. Band-mixing calculations are performed and absolute and relative quadrupole moments deduced for 160Yb and 154Gd. The values are inconsistent with zero, as required for tetrahedral shape, and the bands are interpreted as octupole vibrational bands. The failure to observe the in-band E2 transitions of the bands at low spins can be understood using the measured B(E1) and B(E2) values.
Investigation of chiral bands in 106Ag
International Nuclear Information System (INIS)
Dipole bands in 106Ag have been studied with the ?-detector array AFRODITE at iThemba LABS, South Africa. A 96Zr(14N,4n)106Ag reaction at a beam energy of 71 MeV has been used. The three previously known negative-parity bands in 106Ag have been extended. Bands 1 and 2 were proposed to be chiral partner bands. However, in view of the present results, bands 2 and 3 seem to be better candidates for chiral partner bands since their staggering parameters, B(M1)/B(E2) ratios, kinematic moments of inertia and quasiparticle alignments agree much better than those of bands 1 and 2. Triaxial relativistic mean field (RMF) and particle-rotor model (PRM) calculations support this interpretation. In the potential energy surface of 106Ag, obtained in RMF calculations, two minima have been found in the ?2-? plane. Based on PRM calculations using the deformation parameters of the two minima and a ?h11/2 x ?g-19/2 particle-hole configuration, bands 2 and 3 may represent partners with chiral vibration at ??12degree. Band 1, located in the other minimum, may be a magnetic dipole band or the partner of a second pair of chiral bands.
More than thirty bands in 177Re
International Nuclear Information System (INIS)
The level scheme of 177Re has been extended extensively, with fragments of more than thirty bands, characterised by a given signature, observed. Alignments at low frequency in one-quasiparticle bands are interpreted as deformation effects and compared with the predictions of cranking calculations. The previously assigned one-quasiparticle ?i13/2 band is shown to be a mixture of three-quasiparticle and vibrational character. The non-observation of the one-quasiparticle ?i13/2 band is explained as being due to crossings of its s-band by competing bands. A number of high-K bands are also reported, including five- and seven-quasiparticle bands. Configuration assignments for these bands are aided by comparing experimental gK values with ''effective'' gK values, calculated with a semi-classical expression taking Coriolis mixing into account. The population of the yrast band was observed to oscillate with every four units of spin. (orig.)
Candidate chiral bands in {sup 198}Tl
Energy Technology Data Exchange (ETDEWEB)
Lawrie, E.A.; Lawrie, J.J.; Bark, R.A.; Mullins, S.M.; Murray, S.H.T. [Themba LABS, Somerset West (South Africa); Vymers, P.A.; Maliage, S.M.; Masiteng, P.L.; Ramashidzha, T.M.; Sharpey-Schafer, J.F.; Shirinda, O. [Themba LABS, Somerset West (South Africa); University of the Western Cape, Bellville (South Africa); Vieu, Ch.; Schueck, C. [CNRS - IN2P3, Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, Orsay (France); Lindsay, R. [University of the Western Cape, Bellville (South Africa); Mabala, G.K. [Themba LABS, Somerset West (South Africa); University of Cape Town, Department of Physics, Rondebosch (South Africa); Ragnarsson, I. [Lund University, Division of Mathematical Physics, LHT, Lund (Sweden)
2010-07-15
High-spin states in {sup 198}Tl were studied using the {sup 197}Au({alpha}, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast {pi}h{sub 9/2} x {nu}i{sub 13/2}{sup -1} band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality. (orig.)
Computational optical band gap bowing of III-V semiconductors alloys
Ferhat, M.
2004-08-01
A phenomenological model is described for the calculations of the optical band bowing of III-V semiconductor alloys. The optical band gap bowing is shown to account successfully for theoretical calculations and the experimental data.
Competition between triaxial bands and highly deformed intruder bands around 180Os
International Nuclear Information System (INIS)
Angular momentum alignment processes in nuclei around 180Os are discussed within the deformed shell model using the Woods-Saxon potential and the monopole pairing interaction. The crossings between bands of different structures are analysed and predictions are made for the possible observation of highly deformed intruder bands. Predictions of Q0 moments are presented for the highly deformed bands and tables of calculated deformations for 178-183Os are given. (orig.)
A simple theoretical approach to calculate the electrical conductivity of nonideal copper plasma
International Nuclear Information System (INIS)
A simple theoretical approach to calculate the electrical conductivity of partially ionized nonideal copper plasma is introduced. The densities of plasma species are calculated, to machine accuracy, including electronic excitation and allowing for high ionization states up to the atomic number of the element. Depression of ionization energies is taken into account using an interpolation formula that is valid over a wide range of densities. The formula yields the results of the Debye-Hueckel and the ion-sphere models at the limiting boundaries of low and high densities, respectively. The nonideal Coulomb logarithm is represented by an analytic wide-range formula supplemented by a specially tailored cutoff parameter. Effects of excluding excited and high ionization states on the calculation of ionization equilibrium and electrical conductivity of copper are investigated and assessed. Computational results of the electrical conductivity are compared with results from other theoretical models and available experimental measurements and showed reasonable agreement. A discussion about the choice of the ion-sphere radius is included and concerns about thermodynamic inconsistency when using the modified nonideal Saha equations are discussed and cleared
International Nuclear Information System (INIS)
An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented
IEEE
2013-08-30
In this activity, learners explore the design of rubber band powered cars. Learners work in teams of "engineers" to design and build their own rubber band cars out of everyday items. They test their rubber band cars, evaluate their results, and present to the group.
Wu, Dong-Lan; Tan, Bin; Qin, Jiu-Ying; Wan, Hui-Jun; Xie, An-Dong; Yan, Bing; Ding, Da-Jun
2015-11-01
Ab initio calculations on potential energy curves (PECs), spectroscopic constants, transition dipole moments, radiative transition probabilities and lifetimes for the ground state (X(2)?(+)) and the first excited state (A(2)?) of MgX (X=F, Cl, Br, I) molecules are determined by high-level internally contracted multi-reference configuration interaction (ic-MRCI) method. In order to improve the calculation, the Davidson modification (+Q) and scalar relativistic correction are included. The present results show that most of spectroscopic constants are in accordance with the measurements, the equilibrium internuclear distance Re increases while the other spectroscopic constants reduce along with the increasing of the atomic number of the halogen from F to I. Diagonal vibrational transitions are found to be dominant for the A(2)??X(2)?(+) system of MgX molecules. The corresponding radiative lifetimes of ?'=0 are computed to be 7.24, 9.98, 18.94 and 22.72ns for MgF, MgCl, MgBr, and MgI, respectively. The calculated result of MgF molecule is in good agreement with the recent theoretical result of 7.16ns, with a small relative error percent of 1.11%. PMID:26072381
Photonic band structure of highly deformable, self-assembling systems
Bermel, Peter A.; Warner, Mark
2001-01-01
We calculate the photonic band structure at normal incidence of highly deformable, self-assembling systems - cholesteric elastomers subjected to external stress. Cholesterics display brilliant reflection and lasing owing to gaps in their photonic band structure. The band structure of cholesteric elastomers varies sensitively with strain, showing new gaps opening up and shifting in frequency. A novel prediction of a total band gap is made, and is expected to occur in the vici...
Yrast Band in 122I and Band Termination
International Nuclear Information System (INIS)
High spin states of the odd-odd nucleus 122I have been investigated via the fusion-evaporation reaction 116Cd(11B, 5n) at a beam energy of 68 MeV. The yrast band is extended up to I? = (29+). The band termination at I? = (22+) reported in previous studies is confirmed and interpreted as arising from a shape change from collective prolate to noncollective oblate according to Total-Routhian-Surface (TRS) calculations. In addition, the I?=(29+) state is assigned to the [?h11/2(?g7/2)2]23/2-[(?h11/2)3(?d5/2)2]35/2- configuration corresponding to the full alignment of all valance nucleons outside the semi-closed shell.
Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.
Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun
2015-01-01
We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369
Photonic band gap structure simulator
Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.
2006-10-03
A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.
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.
Influence of band interaction on superdeformed rotational bands
International Nuclear Information System (INIS)
With the first discovery of high spin superdeformed (SD) band in 152Dy, more than 250 SD bands have been observed in A ? 190, 150, 130, 80 mass regions. Except for a few SD bands, the spins of most of them have not been established experimentally. The influence of band interaction on SD bands is investigated in detail. The results based on an analysis of the band-mixing of two bands for such bands will be presented
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...
Photoemission from CsI - Calculation.
Distefano, T. H.
1973-01-01
Calculations of optical and photoemission spectra for CsI based on first-order allowed transitions between Bloch-wave states are discussed. The calculations, utilizing energy-band data for CsI published by Onodera (1968), were performed by computer sampling of regions in the Brillouin zone. The photoelectric spectra of CsI, calculated on the basis of an interpolated band scheme, display features which are in general agreement with the experimentally determined photoelectric energy distribution curves.
Investigation of chiral bands in {sup 106}Ag
Energy Technology Data Exchange (ETDEWEB)
Lieder, Evgenia [Themba LABS, Somerset West (South Africa); FhG, INT, Euskirchen (Germany); Lieder, Rainer; Bark, Rob; Lawrie, Elena; Lawrie, Kobus; Ntshangase, Sifiso; Mullins, Simon; Papka, Paul; Kheswa, Ntombi [Themba LABS, Somerset West (South Africa); Meng, Jie [PhS, PKU, Beijing (China); PhS, BUAA, Beijing (China); Qi, Bin [SDU, Weihai (China); Zhang, Shuangquan; Li, Zhipan [PhS, PKU, Beijing (China)
2010-07-01
Dipole bands in {sup 106}Ag have been studied with the {gamma}-detector array AFRODITE at iThemba LABS, South Africa. A {sup 96}Zr({sup 14}N,4n){sup 106}Ag reaction at a beam energy of 71 MeV has been used. The three previously known negative-parity bands in {sup 106}Ag have been extended. Bands 1 and 2 were proposed to be chiral partner bands. However, in view of the present results, bands 2 and 3 seem to be better candidates for chiral partner bands since their staggering parameters, B(M1)/B(E2) ratios, kinematic moments of inertia and quasiparticle alignments agree much better than those of bands 1 and 2. Triaxial relativistic mean field (RMF) and particle-rotor model (PRM) calculations support this interpretation. In the potential energy surface of {sup 106}Ag, obtained in RMF calculations, two minima have been found in the {beta}{sub 2}-{gamma} plane. Based on PRM calculations using the deformation parameters of the two minima and a {nu}h{sub 11/2} x {pi}g{sup -1}{sub 9/2} particle-hole configuration, bands 2 and 3 may represent partners with chiral vibration at {gamma}{approx}12degree. Band 1, located in the other minimum, may be a magnetic dipole band or the partner of a second pair of chiral bands.
Electronic band structure of lithium, sodium and potassium fluorides
International Nuclear Information System (INIS)
A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good
Bhardwaj, Anil; Jain, Sonal Kumar
2013-01-01
Present study deals with the model calculations of CO Cameron band and CO2+ ultraviolet doublet emissions in the dayglow of Venus. The overhead and limb intensities of CO Cameron band and CO2+ UV doublet emissions are calculated for low, moderate, and high solar activity conditions. Using updated cross sections, the impact of dierent e-CO cross section for Cameron band production is estimated. The electron impact on CO is the major source mechanism of Cameron band, followed ...
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.
Band gap of a topological insulator nanotube
International Nuclear Information System (INIS)
We study the electronic structure of a topological insulator Bi2Te3 cylindrical nanotube. The energy spectrum was calculated in the framework of the kp theory near the ? point of the surface Brilloiun zone. A band gap size dependence of the topological insulator nanotube was studied. A comparative analysis of the topological insulator direct band gap of Bi2Te3 and Bi2Se3 nanowires as a function of radius was performed. Due to a high surface-to-volume ratio, a variation in the ratio of the nanotube external radius to internal radius provides a 50-fold decrease in the topological insulator band gap compared to the respective bulk value. The size dependence of the topological insulator nanotube band gap is much stronger than that for the topological insulator nanowires. (authors)
Nitric oxide gamma band emission rate factor
Cravens, T. E.
1977-01-01
Molecular fluorescence emission rate factors for the strong bands of the nitric oxide gamma system have been calculated using recent branching ratios and different temperatures. For the 1-0 gamma band the effects of self-absorption by NO have been taken into account, and effective emission rate factors were calculated for a range of NO column densities at several different temperatures. For column densities near 10 to the 16th/sq cm self-absorption corrections to the emission rate factor can be significant. The emission rate factor for the 1-0 gamma band is 7.19 or 7.68 x 10 to the -6th photons/molecule/sec depending upon the use of experimental or theoretical branching ratios.
International Nuclear Information System (INIS)
Numerical estimations of the ligand hyperfine structure parameters of ZnSe:Mn2+ based on three models (Extended Hueckel Theory-Self-Consistent Charge and Configuration, scattered-wave, and LCAO methods) are given
Hornreich, R.; Kugler, M.; Shtrikman, S.; Sommers, C.
1997-01-01
We present structures, based on rods, that exhibit phonon band gaps. Structures based on rods made out of segments of different materials have very large gaps or multiple gaps. For homogeneous cylinders smaller gaps exist. Possible applications are discussed.
International Nuclear Information System (INIS)
One of the major challenges in the study of superdeformation is to directly connect the large number of superdeformed bands now known to the yrast states. In this way, excitation energies, spins and parities can be assigned to the levels in the second well which is essential to establish the collective and single-particle components of these bands. This paper will review some of the progress which has been made to understand the decay of superdeformed bands using the new arrays including the measurement of the total decay spectrum and the establishment of direct one-step decays from the superdeformed band to the yrast line in 194Hg. 42 refs., 5 figs
Martindale Calculators is a Web-based tool collection that contains over 19,000 online calculators created by over "3,450" very "creative" individuals, businesses and â??tax supported entities world wide.â? The collection is organized by the following topics: mathematics; statistics; science A-Z; chemistry; physics, astrophysics and astronomy; engineering A-Z; and electrical engineering, computer engineering, & computer science. Each section includes a wealth of websites to explore, all related to mathematical calculations, mostly course materials and articles. Another section lists online calculators relevant for various industries, such as aviation, cosmetics, insurance, and library science. The list is organized alphabetically and creatively stretches the meaning of â??calculatorâ? to include such things as name translators and databases on animal breeds.
Yin, Wan-Jian; Gong, Xin-Gao; Wei, Su-Huai
2008-10-01
The unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys are investigated using first-principles calculations. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band-edge states and found that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence-band offset between Ge and Sn is larger than the natural conduction-band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band-edge states.
Supersymmetry and Identical Bands
Von Brentano, P.
2003-01-01
Supersymmetry as applied to identical bands is discussed. A review of the work of the Koeln-Dubna group on this topic is given and examples in 171,172Yb, 173,174Hf, and 195,194Pt are discussed. The role of pseudo-spin in the supersymmetry is investigated. A recent precision lifetime measurement for identical bands in 171,172Yb is discussed.
A Holographic Model of Two-Band Superconductor
Wen, Wen-Yu; Wu, Mu-Sheng; Wu, Shang-Yu(Institute of Physics, National Chiao Tung University, Hsinchu 300, Taiwan)
2013-01-01
We construct a holographic two-band superconductor model with interband Josephson coupling. We investigate the effects the Josephson coupling has on the superconducting condensates and the critical temperature for their formation numerically, as well as analytically where possible. We calculate the AC conductivity and find it qualitatively similar to the single band superconductor. We investigate the nodal structure of our holographic two-band superconductor from the low tem...
Highly deformed intruder bands in the A ? 130 mass region
International Nuclear Information System (INIS)
Deformed shell model calculations based on an average Woods-Saxon potential with a monopole pairing force included show for a number of nuclei close to A ? 130 the appearance of rotational bands with a large deformation, ?2 ? 0.4. These bands, which are related to the alignment of i13/2 neutrons, become yrast at high spin (I > or approx. 30 ?) and can be identified with the so-called 'superdeformed' bands observed in e.g. 132Ce. (orig.)
Band moment of inertia in signature partner and identical SD bands in A = 190 mass region
International Nuclear Information System (INIS)
Since the observation of the first high spin superdeformed (SD) band in 152Dy, they have been discovered and intensively studied in several mass regions A ? 190, 150, 130 and 80. However, it is still difficult to observe the links between the SD bands and normal deformed (ND) states with known spins. Therefore, the exact excitations energies, spins, and parities of SD bands remain uncertain. The discrete ?-rays connecting the states of the yrast SD band 194Hg(1) to ND states with known spins were observed and the spins and excitation energies of all members of 194Hg(1) band were established experimentally. Recently, a link between SD and ND bands has also been observed in 190Hg. Therefore, the measured spins of these SD bands provide a significant test of the validity of the approaches to fix the spins of the SD bands. It is noted that all the available approaches profit from the comparison of the calculated transition energies or dynamic moment of inertia with the experimental results and usually are referred to as the best fit method (BFM). This also implies that the kinematic moment of inertia is also not a well established quantity
Band-gap bowing, band offsets, and electron affinity for InGaN alloys: A DFT study.
Moses, Poul; van de Walle, Chris
2009-03-01
InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve InGaN-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band bowing and absolute band positions of InGaN alloys using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. Detailed surface calculations have been performed that, combined with bulk calculations for alloys, yield information about the positions of valence and conduction bands on an absolute energy scale. We will discuss bowing effects, band offsets, and electron affinities in light of the application of InGaN alloys for photochemical hydrogen production. [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)
Variationally-optimized muffin-tin potentials for band calculations
International Nuclear Information System (INIS)
A method is suggested to determine the best local periodic crystal potential V(r) by minimizing the Hartree-Fock expectation value of the energy. The explicit form of the integral equation for the local exchange potential is obtained for the special case of the Muffin-tin aproximation. (author)
Electronic band structure of CdF2
International Nuclear Information System (INIS)
Energy distribution curves (EDC) of electrons photoemitted (h?1 = 21.22 eV and h?2 = 40.8 eV) from the valence band (F-2p) and the Cd 4d band of a CdF2 crystal are measured and the valence and conduction band structures are calculated using the local empirical pseudopotential method (EPM). Comparison of the measured and calculated data show that the three main maxima measured in the valence band correspond well to the maxima in X5, L3, and X5 obtained in the calculated histogram of the valence band density of states. The influence of the final-state structure on the position of peaks in the valence band is not observed on EDCs obtained for both, h?1 and h?2 photoemission exciting energies. For Cd 4d band the wide splitting of 1.46 eV is obtained only for h?1 = 21.22 eV while it is not obtained on EDC for h?2 = 40.8 eV. This Cd 4d band splitting may be caused by the influence of the final density-of-states maximum obtained in conduction band in X1-point. The results obtained are compared with reflectivity data available in the literature. (author)
NORMALIZATION OF WAVE FUNCTION OF THE BAND STATES
Directory of Open Access Journals (Sweden)
Abdurahim A. Okhunov
2015-05-01
Full Text Available Low – lying band states are one of the most fundamental excitation modes in the energy spectra of deformed nuclei. Present paper a theoretically analysis the properties of deformed nucley within the phenomenological model (Usmanov 2010. The normalization of the wave functions of low – lying excited band states are calculated.
Multiple levels in intermediate band solar cells
Luque, Antonio; Linares, Pablo G.; Antolín, Elisa; Cánovas, Enrique; Farmer, Corrie D.; Stanley, Colin R.; Martí, Antonio
2010-01-01
The presence of multiple energy levels in the intermediate band solar cell (IBSC) is studied by detailed balance calculations under ideal conditions. Multiple levels are found experimentally in IBSCs made with quantum dots (QDs) which act to reduce the limiting efficiency determined from detailed balance calculations. JL-VOC measurements up to 1000 suns on IBSCs are presented together with their fitting to modified detailed balance calculations. It is found that the introduction of the QDs degrades the performance of the host cell but the sub-bandgap cell operates close to ideality.
Directory of Open Access Journals (Sweden)
Yoshit V. Gidh
2013-02-01
Full Text Available A thorough grounding in mathematics enhances educational and occupational opportunities for all people, whether sighted or visually impaired. In day-to-day routines, a practical understanding of mathematics allows a person to function more successfully and independently.? Access to, and doing mathematics, is one of the biggest obstacles for blind students in school and at the university. Our Braille Calculator will present new approaches to offering blind students better access to math, to provide new tools for doing math. In this report, the basic problems and solutions to the problem are discussed as a means of laying the groundwork for our Braille Calculator. Many aspects and concepts of mathematics are visual and spatial in nature. Students who are blind or visually impaired, and their teachers, now have standards which are closely aligned with those used for sighted students. Braille mathematics standards are essential to ensure that functionally blind students become literate in mathematics. However for complex engineering and statistical calculations even sighted students have to depend on Calculator. So we came up with an idea of Braille Calculator
New materials for intermediate band photovoltaic cells. A theoretical and experimental approach
Wahnón Benarroch, Perla; Palacios Clemente, Pablo; Aguilera Bonet, Irene; Seminóvski Pérez, Yohanna; Conesa, Jose Carlos; Lucena, Raquel
2010-01-01
Density functional theory calculations of certain transition-metal doped semiconductors show a partially occupied relatively narrow band located between valence band and conduction band. These novel systems, containing the metallic band, are called intermediate-band materials. They have enhanced optoelectronic properties which allow an increase in solar energy conversion efficiency of conventional solar cells. We previously proposed III-V, chalcopyrite and sulfide derived compounds show...
Quantitative analysis on electric dipole energy in Rashba band splitting
Hong, Jisook; Rhim, Jun-Won; Kim, Changyoung; Ryong Park, Seung; Hoon Shim, Ji
2015-09-01
We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime.
Characterization of superdeformed bands in Zn62
Gellanki, J.; Ragnarsson, I.; Rudolph, D.; Svensson, C. E.; Andersson, L.-L.; Andreoiu, C.; Baktash, C.; Carpenter, M. P.; Charity, R. J.; Chiara, C. J.; Eberth, J.; Ekman, J.; Fahlander, C.; Haslip, D. S.; Johansson, E. K.; Lafosse, D. R.; Paul, S. D.; Pechenaya, O. L.; Reviol, W.; Rietz, R. Du; Sarantites, D. G.; Seweryniak, D.; Sobotka, L. G.; Thomas, H. G.; Torres, D. A.; Waddington, J. C.; Wilson, J. N.; Yu, C. H.; Zhu, S.
2009-11-01
Combined data from four fusion-evaporation reaction experiments were utilized to investigate deformed and superdeformed structures in 3062Zn32. Combination of the Gammasphere ?-ray spectrometer and ancillary particle detection systems allowed for the connection of rotational bands to well-known, low-lying excited states in Zn62, as well as spectroscopy of discrete high-spin states reaching excitation energies of Ex=42.5 MeV. Four well- or superdeformed bands in Zn62 are characterized and described by means of cranked Nilsson-Strutinsky calculations.
Photon ratchet intermediate band solar cells
Yoshida, M.; Ekins-Daukes, N. J.; Farrell, D. J.; Phillips, C. C.
2012-06-01
In this paper, we propose an innovative concept for solar power conversion—the "photon ratchet" intermediate band solar cell (IBSC)—which may increase the photovoltaic energy conversion efficiency of IBSCs by increasing the lifetime of charge carriers in the intermediate state. The limiting efficiency calculation for this concept shows that the efficiency can be increased by introducing a fast thermal transition of carriers into a non-emissive state. At 1 sun, the introduction of a "ratchet band" results in an increase of efficiency from 46.8% to 48.5%, due to suppression of entropy generation.
Electron currents associated with an auroral band
International Nuclear Information System (INIS)
Measurements of electron pitch angle distributions and energy spectra over a broad auroral band were used to calculate net electric current carried by auroral electrons in the vicinity of the band. The particle energy spectrometers were carried by a Nike-Tomahawk rocket launched from Poker Flat, Alaska, at 0722 UT on February 25, 1972. Data are presented which indicate the existence of upward field-aligned currents of electrons in the energy range 0.5-20 keV. The spatial relationship of these currents to visual structure of the auroral arc and the characteristics of the electrons carrying the currents are discussed
Band Gaps and Single Scattering of Phononic Crystal
Xiaoyi Huang; Jingcui Peng; Huanyou Wang; Gui Jin
2011-01-01
A method is introduced to study the transmission and scattering properties of acoustic waves in two–dimen- sional phononic band gap (PBG) materials. First, it is used to calculate the transmission coefficients of PBG samples. Second, the transmitted power is calculated based on the far field approach. We have also calcu- lated the scattering cross section, the results indicate that phononic band gap appear in frequency regions between two well separated resonance states.
Friedman, S. Morgan.
This simple inflation calculator uses the Consumer Price Index to adjust any given amount of money, from 1800 to 1998. Creator S. Morgan Friedman uses data from the Historical Statistics of the United States for statistics predating 1975 and the annual Statistics Abstracts of the United States for data from 1975 to 1998. Links to other online inflation information are also included.
Distribution Free Prediction Bands
Lei, Jing
2012-01-01
We study distribution free, nonparametric prediction bands with a special focus on their finite sample behavior. First we investigate and develop different notions of finite sample coverage guarantees. Then we give a new prediction band estimator by combining the idea of "conformal prediction" (Vovk et al. 2009) with nonparametric conditional density estimation. The proposed estimator, called COPS (Conformal Optimized Prediction Set), always has finite sample guarantee in a stronger sense than the original conformal prediction estimator. Under regularity conditions the estimator converges to an oracle band at a minimax optimal rate. A fast approximation algorithm and a data driven method for selecting the bandwidth are developed. The method is illustrated first in simulated data. Then, an application shows that the proposed method gives desirable prediction intervals in an automatic way, as compared to the classical linear regression modeling.
Everts, Martin
2006-01-01
In the following article the ideal band-pass filter is derived and explained in order to subsequently analyze the approximations by Baxter and King (1999) and Christiano and Fitzgerald (2003). It can be shown that the filters by Baxter and King and Christiano and Fitzgerald primarily differ in two assumptions, namely in the assumption about the spectral density of the analyzed variables as well as in the assumption about the symmetry of the weights of the band-pass filter. In the article at h...
Synthesizing folded band chaos.
Corron, Ned J; Hayes, Scott T; Pethel, Shawn D; Blakely, Jonathan N
2007-04-01
A randomly driven linear filter that synthesizes Lorenz-like, reverse-time chaos is shown also to produce Rössler-like folded band wave forms when driven using a different encoding of the random source. The relationship between the topological entropy of the random source, dissipation in the linear filter, and the positive Lyapunov exponent for the reverse-time wave form is exposed. The two drive encodings are viewed as grammar restrictions on a more general encoding that produces a chaotic superset encompassing both the Lorenz butterfly and Rössler folded band paradigms of nonlinear dynamics. PMID:17500950
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
Nonadditivity in moments ofinertia of high-K multiquasiparticle bands
Zhang, Zhen-Hua; Wu, Xi; Lei, Yi-An; Zeng, Jin-Yan
2008-09-01
The experimental high-K 2- and 3-quasiparticle bands of well deformed rare-earth nuclei are analyzed. It is found that there exists significant nonadditivity in moments of inertia (MOIs) for these bands. The microscopic mechanism of the rotational bands is investigated by the particle number conserving (PNC) method in the frame of cranked shell model with pairing, in which the blocking effects are taken care of exactly. The experimental rotational frequency dependence of these bands is well reproduced in PNC calculations. The nonadditivity in MOIs originates from the destructive interference between Pauli blocking effects. Supported by National Natural Science Foundation of China (10675006, 10675007, 10435010)
Fano resonances and band structure of two dimensional photonic structures
Markos, Peter
2015-01-01
We show that the frequency spectrum of two dimensional photonic crystals is strongly influenced by Fano resonances which can be excited already in the linear array of dielectric cylinders. To support this claim, we calculate the transmission of electromagnetic wave through linear array of dielectric cylinders and show that frequencies of observed Fano resonances coincides with position of narrow frequency bands found in the spectra of corresponding two-dimensional photonic crystals. Split of frequency band or overlap of two bands, observed in the band structure of photonic structures are also associated with Fano resonances.
Gutzwiller theory of band magnetism in LaOFeAs
International Nuclear Information System (INIS)
For the iron pnictide LaOFeAs we investigate multi-band Hubbard models which are assumed to capture the relevant physics. In our calculations, we employ the Gutzwiller variational theory which is a genuine many particle approach. We will present results both on the paramagnetic and antiferromagnetic phases of our model systems. These results show that a five band-model is not adequate to capture the relevant physics in LaOFeAs. However, our results for the eight band-model which includes the arsenic 4p bands reproduce the experimental data, especially the small magnetic moment, for a broad parameter regime.
Tunable and sizable band gap in silicene by surface adsorption
Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, YangYang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing
2012-01-01
Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50?eV. The ab i...
DUAL BAND MONOPOLE ANTENNA DESIGN
Directory of Open Access Journals (Sweden)
P. Jithu
2013-06-01
Full Text Available The WLAN and Bluetooth applications become popular in mobile devices, integrating GSM and ISM bands operation in one compact antenna, can reduce the size of mobile devices. Recently, lot many investigations are carried out in designing a dual band antennas with operating frequencies in GSM band and in ISM band for mobile devices. Printed monopoles are under this investigation. In this paper, dual-band printed monopoles are presented to operate at GSM band i.e. 900 MHz and ISM band i.e. 2.4 GHz. We intend to observe the antenna characteristics on the network analyzer and verify the theoretical results with the practical ones.
Small Quadrupole Deformation for the Dipole Bands in 112In
Trivedi, T; Sethi, J; Saha, S; Kumar, S; Naik, Z; Parkar, V V; Naidu, B S; Deo, A Y; Raghav, A; Joshi, P K; Jain, H C; Sihotra, S; Mehta, D; Jain, A K; Choudhury, D; Negi, D; Roy, S; Chattopadhyay, S; Singh, A K; Singh, P; Biswas, D C; Bhowmik, R K; Muralithar, S; Singh, R P; Kumar, R; Rani, K
2012-01-01
High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\\sim$ 20$\\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations.
Venkatesh Kumaran, P.
2006-01-01
The whole circuit is obtained from the sun through a molecule called "Rhodopsin and bacteriorhodopsin". These molecules have the capability of trapping and storing energy from the sun light. These molecules are placed on the outer surface of the calculator to trap the energy and store it themselves for latter usage. The thickness of the whole circuit measures less than 300nm.The top layer is made up of layer which will show the different keys and a display unit. "Molecules a...
Beguería, Santiago; Vicente Serrano, Sergio M.
2009-01-01
[EN] *Objectives: The program calculates time series of the Standardised Precipitation-Evapotransporation Index (SPEI). *Technical Characteristics: The program is executed from the Windows console. From an input data file containing monthly time series of precipitation and mean temperature, plus the geographic coordinates of the observatory, the program computes the SPEI accumulated at the time interval specified by the user, and generates a new data file with the SPEI time serie...
Yoshit V. Gidh; Mahesh S. Latey; Arpita roy, Kunal Shah; Savita Ingle
2013-01-01
A thorough grounding in mathematics enhances educational and occupational opportunities for all people, whether sighted or visually impaired. In day-to-day routines, a practical understanding of mathematics allows a person to function more successfully and independently.? Access to, and doing mathematics, is one of the biggest obstacles for blind students in school and at the university. Our Braille Calculator will present new approaches to offering blind students better access to math, to pr...
De Michielis, L.; Da?tekin, N.; Biswas, A.; Lattanzio, L.; Selmi, L.; Luisier, M.; Riel, H.; Ionescu, A. M.
2013-09-01
In this paper, an analytical band-to-band tunneling model is proposed, validated by means of drift-diffusion simulation and comparison with experimental data, implemented in Verilog-A, and finally proven with SPICE simulator through simulation of circuits featuring tunneling diodes. The p-n junction current calculation starts from a non-local Band-to-Band tunneling theory including the electron-phonon interaction and therefore it is particularly suited for indirect semiconductor materials such as silicon- or germanium-based interband tunneling devices.
Bollinger Bands Thirty Years Later
Leeds, Mark
2012-01-01
The goal of this study is to explain and examine the statistical underpinnings of the Bollinger Band methodology. We start off by elucidating the rolling regression time series model and deriving its explicit relationship to Bollinger Bands. Next we illustrate the use of Bollinger Bands in pairs trading and prove the existence of a specific return duration relationship in Bollinger Band pairs trading.Then by viewing the Bollinger Band moving average as an approximation to th...
DEFF Research Database (Denmark)
Andersen, O. Krogh
1975-01-01
Two approximate methods for solving the band-structure problem in an efficient and physically transparent way are presented and discussed in detail. The variational principle for the one-electron Hamiltonian is used in both schemes, and the trial functions are linear combinations of energy-independent augmented plane waves (APW) and muffin-tin orbitals (MTO), respectively. The secular equations are therefore eigenvalue equations, linear in energy. The trial functions are defined with respect to a muffin-tin (MT) potential and the energy bands depend on the potential in the spheres through potential parameters which describe the energy dependence of the logarithmic derivatives. Inside the spheres, the energy-independent APW is that linear combination of an exact solution, at the arbitrary but fixed energy E?, and its energy derivative which matches continuously and differentiably onto the plane-wave part in the interstitial region. The energies obtained with the linear-APW method for the MT potential have errors of order (E-Ev)4. Similarly, the energy-independent MTO is that linear combination which matches onto that solution of the Laplace equation in the interstitial region which is regular at infinity. The energies obtained with the linear-MTO method have additional errors of order (E-Vmtz)2, arising from the interstitial region where the potential is Vmtz. The linear-APW (LAPW) method combines desirable features of the APW and OPW methods; it can treat d bands, the energy dependence of its pseudopotential is linear and, owing to the smoothness of the energy-independent APW at the spheres, non-MT contributions to the potential are included principally through their Fourier components. The linear-MTO (LMTO) method is particularly suited for closely packed structures and it combines desirable features of Korringa-Kohn-Rostoker, linear-combination-of-atomic-orbitals, and cellular methods; the secular matrix is linear in energy, the overlap integrals factorize as potential parameters and structure constants, the latter are canonical in the sense that they neither depend on the energy nor the cell volume and they specify the boundary conditions on a single MT or atomic sphere in the most convenient way. This method is very well suited for self-consistent calculations. The empty-lattice test is applied to the linear-MTO method and the free-electron energy bands are accurately reproduced. Finally, it is shown how relativistic effects may be included in both the LAPW and LMTO methods.
WGBH
2010-01-01
In this design challenge activity, learners build a car that can travel at least four feet using rubber band power and use the design process to debug problems. Learners can follow up this activity with the "Motorized Car" and "Customized Car" activities in the Leader Notes guide.
A simple experimental apparatus made of rubber band and books is used by student teams challenged with demonstrating the concepts of friction, force, and inertia. This resource is from PUMAS - Practical Uses of Math and Science - a collection of brief examples created by scientists and engineers showing how math and science topics taught in K-12 classes have real world applications.
2012-04-09
In this demonstration, learners explore the thermal properties of rubber. Learners investigate whether a rubber band contracts or expands when heated. Learners discover that when rubber is heated it behaves differently than most familiar materials. Most materials expand when they are heated, but rubber contracts.
Watsonville Environmental Science Workshop
2011-01-01
In this activity, learners build styrofoam boats powered by twisted rubber bands. Use this activity to introduce learners to potential energy, kinetic energy, Newton's Laws of Motion, rotational motion, and density. Note: a drill is required for this activity, and is not included in the cost of materials.
Watsonville Environmental Science Workshop
2011-01-01
In this activity, learners construct speedy vehicles made out of paper plates and powered by twisted rubber bands. This toy is an excellent demonstration of potential and kinetic energy and how things move. This project can also be used to help learners understand Newton's Laws of Motion and friction. Activity guide has detailed step-by-step instructions, illustrations, and focus questions.
Don Rathjen
2009-01-01
In this activity, learners make a simple spring-like scale using a rubber band instead of a spring, and calibrate the scale in newtons (N). Learners will gain an understanding of and familiarity with the newton as a unit of force, and use the scale to weigh common objects.
Energy Technology Data Exchange (ETDEWEB)
Cser, L. [Research Inst. for Solid State Physics, Budapest (Hungary)
1995-11-01
Several methods helping to utilize the neutron spectra emitted by pulsed neutron sources with better efficiency are considered (e.g. supermirror neutron guides, multidetectors, wide band polarizers and the method of pseudostatistical modulation). The present status of proposed approaches are reviewed. (author) 7 figs., 6 refs.
Symmetrical band-pass loudspeaker systems
Matusiak, Grzegorz Piotr
2001-12-01
Loudspeaker systems are analyzed in a doctoral dissertation. The dissertation concerns loudspeaker systems, which are known as subwoofers or band-pass loudspeaker systems. Their advantages include: high- quality sound reproduction in the low-frequency range, small dimensions, small nonlinear distortions and the fact that they can be placed anywhere in a room or car. Band-pass loudspeaker systems are used widely in the so- called Home Theatre as well as to provide sound in cinema, theatre, concert, discotheque, opera, operetta, philharmonic and amphitheater halls, at open-air concerts, and so on. Various designs are mass-produced by a large number of manufacturers. The study covers an analysis of band-pass loudspeaker systems to which the frequency transformation, i.e. the reactance transformation, has been applied. Since this is a symmetrical transformation, amplitude frequency responses of the studied band-pass systems are also symmetrical (logarithmic scale of a frequency). As a result, the high-pass loudspeaker system design method, known as the Thiele-Small, Benson analysis, can be employed. The investigations include the formulation of band-pass system equations (fourth, sixth and eighth-order polynomials) and the subsequent derivation of relations for the calculation of system parameters. The obtained results enable the calculation of optimum designs for prescribed alignments, e.g. (Chebyshev) equal-ripple, (Butterworth) maximally flat, or quasi-maximally flat (QB). The analysis covers fourth, sixth and eighth-order symmetrical systems. Eighth-order systems have been divided into three kinds according to three ways of physical realization. The doctoral dissertation includes band-pass loudspeaker systems, which can be designed with active or passive filters or without the filter. Designed systems consist of a loudspeaker whose front of a diaphragm is loaded with a Helmholtz resonator, i.e. an enclosure with a vent, which radiates sound outwards. The back is loaded with a closed-box or the Helmholtz resonator.
Shambayati, Shervin
2006-01-01
This viewgraph presentation reviews the Mars Reconnaissance Orbiter use of the Ka-band. Due to lack of spectrum at X-band (8.41 GHz) NASA is switching to Ka-band (32 GHz) for its Deep Space Missions. This is 50 MHz bandwidth at X-band vs. 500 MHz at Ka-band. Weather events cause a greater degradation for the Ka-band link. Therefore, the Ka-band needs to be operated in a different manner than the X-band. The Ka-band achieves a maximum average capacity at a lower weather reliability than X-band (80 to 90% for Ka-band vs. 95% for X-band). Studies have been done to suggest different methods of operation for Ka-band. The Mars Reconnaissance Orbiter (MRO) will allow us to evaluate the proposed methods of operations for the Ka-band The MRO is the first spacecraft to have a fully functioning independent Ka-band downlink stream.
Elucidating the stop bands of structurally colored systems through recursion
Amir, Ariel
2012-01-01
Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...
Graphene Nanoribbon Conductance Model in Parabolic Band Structure
Directory of Open Access Journals (Sweden)
Mohammad Taghi Ahmadi
2010-01-01
Full Text Available Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel.
Edge configurational effect on band gaps in graphene nanoribbons
Deepika, Kumar, T. J. Dhilip; Shukla, Alok; Kumar, Rakesh
2015-03-01
In this article, we put forward a resolution to the prolonged ambiguity in energy band gaps between theory and experiments of fabricated graphene nanoribbons (GNRs). Band structure calculations using density functional theory are performed on oxygen-passivated GNR supercells of customized edge configurations without disturbing the inherent s p2 hybridization of carbon atoms. Direct band gaps are observed for both zigzag and armchair GNRs, consistent with the experimental reports. In addition, we provide an explanation of the experimentally observed scattered band gap values of GNRs as a function of width in a crystallographic orientation on the basis of edge configurations. We conclude that edge configurations of GNRs significantly contribute to band gap formation in addition to its width for a given crystallographic orientation and will play a crucial role in band gap engineering of GNRs for future research on fabrication of nanoelectronic devices.
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...
New Kronig-Penney equation emphasizing the band edge conditions
International Nuclear Information System (INIS)
The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However, the standard Kronig-Penney equation does not explicitly state the band edge conditions. This paper derives a new solution for the Kronig-Penney problem that explicitly displays the band edge conditions as well as contains all other essential physics of band formation. Therefore, the present exposition should show the student that the band edge conditions are not simply special cases of the familiar Kronig-Penney equation but, instead, are an integral part of the band theory. For the computationally minded student, the new equation is particularly convenient for calculating the positions of closely spaced band edges. The present results can be taught alongside the Kronig-Penney equation in advanced undergraduate or beginning graduate quantum mechanics, solid state theory and photonics courses dealing with wave propagation through periodic layered media
Yin, Wan-Jian; Gong, Xin-Gao; Wei, Su-Huai
2009-03-01
Most semiconductor alloy AxB1-x has a non-linear dependence of its band gap Eg(x) as a function of the alloy composition x, and the variation is usually described by a parabolic function Eg(x) = xEg^A + (1-x)Eg^B - bgx(1-x), where Eg^A and Eg^B are the band gaps of A and B at their respective equilibrium lattice constants and bg is the so-called bowing parameter. The conventional band-edge distribution of bg is usually described by the equation bVBM(CBM) = ?EVBM(CBM)/?Egbg , where ?EVBM(CBM) and ?EVBM(CBM) are VBM and CBM natural band offsets. Using first-principles calculations, we investigate the unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band edge states and find that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence band offset between Ge and Sn is larger than the natural conduction band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band edge states.
Poeuf, B; Samson, P; Magalon, G
2008-12-01
Amniotic band syndrome is a well-described clinical entity, which includes several congenital deformities. Hand malformations and limb defects represent the most frequent clinical characteristics, gathering, with variable localization, constriction rings, acrosyndactylies and amniotic amputations. Other anomalies of skull, face, body wall and internal organs, sometimes complex and lethal, are significantly associated with this syndrome. The syndrome is then included in the larger entity of limb body wall complex (LBWC). Congenital ring constriction, amniotic band disruption complex, or congenital transverse defect are some of the numerous synonyms defining this malformative syndrome, showing either its clinical variability, or the uncertainties surrounding its etiology. Indeed, several pathogenic theories have been successively opposed, bringing about a certain degree of confusion. Recent experimental genetic studies could unify the different fetal malformations. The surgical treatment actually applies only to the aftereffects of the intrauterine phenomenon, until antenatal diagnosis followed by in utero surgery will be perfected. PMID:18948051
Population of rotational bands in superheavy nuclei
Antonenko N.V.; Adamian G.G.; Sargsyan V.V.; Zubov A.S.
2012-01-01
Using the statistical approach, we study the population of ground-state rotational bands of superheavy nuclei produced in the fusion-evaporation reactions 208Pb(48Ca, 2n)254No, 206Pb(48Ca, 2n)252No, and 204Hg(48Ca, 2n)250Fm. We calculate relative intensities of E2-transitions between the rotational states and entry spin distributions of the residual nuclei, evaporation residue cross sections, and excitation functions for these reactions. Fermi-gas model is used for the calculation of level de...
International Nuclear Information System (INIS)
Partial level scheme of the neutron deficient 111Sn isotope is established upto an excitation energy of about 9 MeV and I? = 43/2- from ?-rays following 103Rh(12C,p3n) reaction. Clear evidence for the existence of a negative parity rotational band above I? = 23/2-, most probably based on 3p-2h configuration, is obtained. (orig.)
Ab Initio Calculations of Oxosulfatovanadates
DEFF Research Database (Denmark)
FrØberg, Torben; Johansen, Helge
1996-01-01
Restricted Hartree-Fock and multi-configurational self-consistent-field calculations together with secondorder perturbation theory have been used to study the geometry, the electron density, and the electronicspectrum of (VO2SO4)-. A bidentate sulphate attachment to vanadium was found to be stable with anO-V-O angle of 72.5 degrees . The calculated spectrum shows bands in reasonable agreement with anexperimental spectrum which has been attributed to (VO2SO4)-. The geometry and the electron density fortwo binuclear vanadium complexes proposed as intermediates in the vanadium catalyzed SO2 oxidationhave further been studied.
Bandcrossing of magnetic rotation bands in 137Pr
International Nuclear Information System (INIS)
The odd mass nucleus 137Pr has been studied to high spins in order to investigate the magnetic rotation phenomenon in mass 130 region using the 122Sn(19F,4n)137Pr reaction at a beam energy of 80 MeV. A known ?I=1 band has been extended to J?=47/2- with the addition of three new transitions. Directional Correlation of Oriented Nuclei (DCO) ratios and linear polarization measurements have been performed to assign the multipolarities of gamma transitions and the spins and parities of the energy levels in this band, now established as the M1 band. The combination of M1 transitions along with cross over E2 transitions have been observed in this band for the first time. The experimentally deduced B(M1)/B(E2) ratios show a decrease with increasing spin after band-crossing suggesting magnetic rotation. TAC calculations for the 3qp: ?h11/2 x ?(h11/2)-2 configuration reproduce the experimental observations in the lower spin part of the ?I=1 band and the 5qp: ?h11/2(g7/2)2 x ?(h11/2)-2 configuration reproduces the ?I=1 band at higher spins; the crossing of the bands based on the two configuration leads to a back-bending also. Theoretical calculations also support a magnetic rotation nature for both the configurations
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 by Pd 5p, Te 6s and Te 5d states. Density of states and joint density of states have been calculated from the bands determined over the appropriate irreducible zone. The Fermi surface consists of two closed sheets in band 11 and band 13, and sheets in band 12 connected to one another by tubes. The results allow an explanation of most of the de Haas-van Alphen frequencies observed previously.
Computational optical band gap bowing of III-V semiconductors alloys
Energy Technology Data Exchange (ETDEWEB)
Ferhat, M. [Departement de Physique, Universite des Sciences et de la Technologie d' Oran (USTO), Oran (Algeria)
2004-08-01
A phenomenological model is described for the calculations of the optical band bowing of III-V semiconductor alloys. The optical band gap bowing is shown to account successfully for theoretical calculations and the experimental data. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Sant, Saurabh; Lodha, Saurabh; Ganguly, Udayan; Mahapatra, Souvik; Heinz, Frederik O.; Smith, Lee; Moroz, Victor; Ganguly, Swaroop
2013-01-01
We present nonlocal empirical pseudopotential calculations for SiGe alloys employing a novel nonlinear interpolation scheme. Our interpolation scheme is able to correctly model for the first time the band gap bowing observed in relaxed SiGe alloys. The valence-band-edge and conduction-band-edge energies in relaxed Si1-xGex for arbitrary x, which are difficult to obtain by experimental techniques, have been evaluated using pseudopotential calculations. We have also calculated the band energies of pseudomorphic [100]-strained Si1-xGex alloys grown over unstrained Si1-yGey substrates. The energy gaps, valence and conduction band offsets, effective masses, and strain induced splittings in pseudomorphic SiGe layers are calculated for the whole range of alloy compositions x and y.
Electron band theory 1952-1962
International Nuclear Information System (INIS)
Work undertaken by the Theoretical Physics Division between 1952 and 1965 to obtain an understanding of electrons in metals, with uranium and the actinides and the structurally-important transition metals as the main targets is examined. A main result of that period was a conviction that the majority of the physical properties of all metals, except the 4f rare-earth series and the actinides beyond uranium, were dominated by band effects which could be described well enough for most purposes by simple one-electron calculations with simple self-consistent fields. The period from 1960 on showed increasingly clearly the necessity of incorporating relativistic spin-orbit coupling terms in the heavy metals, and some 'local exchange field' correction to the fields close to nuclei. The problems of the non-local interaction of spins - highly important for alloy theory and for antiferromagnetic instability -required the evolution of computers large enough to produce wave-functions at all wave-vectors for all bands so that the susceptibility at arbitrary wave-vector could be computed. This work has not proved to be very illuminating so far, and much interest again focusses today on heuristic arguments that give qualitative descriptions of band structures, such as canonical d-bands to account for crystal structure. (UK)
Nuclear rotational spectral theories and its application to superdeformed bands
International Nuclear Information System (INIS)
The recent developments of rotational spectral theories and its application to superdeformed bands were briefly reviewed. The superdeformed bands in A?190 region were analyzed and the spins of energy level were determined by the least-square fitting experimental transition energy with the formula of Bohr-Mottelson's I(I + 1) expansions. The superdeformed bands in A?150 region were analyzed by using the kinematic moments of inertia formula J(1) = 2? + (4/3)??2 + (6/5)??4 in order to extract level spin. The results show that the calculated J(1) of 20 superdeformed bands in Tb and Dy isotopes are agreement excellently with that of extracted from expression ?2(2 I-1)/E?(I). In particular, the spin of the lowest level of the first discovered high-spin SD band 152Dy(1) predicted to be I0 26 is more proper
Highly deformed high-spin band in 125I
International Nuclear Information System (INIS)
High-spin states in 125I have been investigated using the reaction 82Se(48Ca, p4n) at a beam energy of 200 MeV and ?-ray coincidence events were detected using the Gammasphere spectrometer. A deformed rotational band, extending up to I?=95/2-, was observed for the first time in a heavier odd-A iodine nucleus. The characteristics of the band are very similar to those of the highly deformed bands observed recently in neighboring nuclei and it is essentially identical to one of the previously known bands in 126Xe. The experimental results are compared to cranked Nilsson-Strutinsky calculations and possible configurations for the band are discussed.
Band alignment of SnS/Zn(O,S) heterojunctions in SnS thin film solar cells
Sun, Leizhi; Haight, Richard; Sinsermsuksakul, Prasert; Bok Kim, Sang; Park, Helen Hejin; Gordon, Roy Gerald
2013-01-01
Band alignment is critical to the performance of heterojunction thin film solar cells. In this letter, we report band alignment studies of SnS/Zn(O,S) heterojunctions with various compositions of Zn(O,S). Valence band offsets (VBOs) are measured by femtosecond laser pump/probe ultraviolet photoelectron spectroscopy (fs-UPS) from which conduction band offsets (CBOs) are calculated by combining with band gaps obtained by optical transmission/reflection measurements. The SnS/Zn(O,S) heterojuncti...
Flat-band ferromagnetism in quantum dot superlattices
Tamura, Hiroyuki; SHIRAISHI, KENJI; Kimura, Takashi; Takayanagi, Hideaki
2001-01-01
Possibility of flat-band ferromagnetism in quantum dot arrays is theoretically discussed. By using a quantum dot as a building block, quantum dot superlattices are possible. We consider dot arrays on Lieb and kagome lattices known to exhibit flat band ferromagnetism. By performing an exact diagonalization of the Hubbard Hamiltonian, we calculate the energy difference between the ferromagnetic ground state and the paramagnetic excited state, and discuss the stability of the f...
Signatures of band-like tunnelling in granular nanowires
Fransson, J.; Lin, J. -F.; Rotkina, L.; Bird, J P; Bennett, P. A.
2005-01-01
We explore the problem of tunneling through disorderd nanowires, comprised of a random distribution of metallic grains, by means of a many-body model that captures the essential physics of the system. The random configuration of grains gives rise to a smooth band-like set of states, which mediates current flow through the nanowire. Analytical and numerical calculations show the characteristic signature of this unusual band-like transport to be a quadratic variation of the cu...
Nuclear field theory treatment of K not= 0 rotational bands
International Nuclear Information System (INIS)
The properties of the lowest members of K not= 0 rotational bands are described as anharmonic vibrational bands. The anharmonicity is calculated by the method called Nuclear Field Theory (particle-vibration coupling). It is shown to be important not to truncate the diagrammatic expansion at a fixed number of vertices. Instead, the way in which the diagrams depend on the number of degrees of freedom participating is used to guide the truncation. (orig.)
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.
Temperature Dependence of the Band Gap of Semiconducting Carbon Nanotubes
Rodrigo B. Capaz; Spataru, Catalin D.; Tangney, Paul; Cohen, Marvin. L.; Louie, Steven G.
2004-01-01
The temperature dependence of the band gap of semiconducting single-wall carbon nanotubes (SWNTs) is calculated by direct evaluation of electron-phonon couplings within a ``frozen-phonon'' scheme. An interesting diameter and chirality dependence of $E_g(T)$ is obtained, including non-monotonic behavior for certain tubes and distinct ``family'' behavior. These results are traced to a strong and complex coupling between band-edge states and the lowest-energy optical phonon mod...
Band-gap narrowing in ordered and disordered semiconductor alloys
International Nuclear Information System (INIS)
Either spontaneous or artificial ordering of semiconductor alloys into CuAu-like, chalcopyrite, or CuPt-like structures is predicted to be accompanied by a reduction in the direct band gaps relative to the average over the binaries. In this letter calculated results are presented for seven III-V and II-VI alloys. We identify the mechanism for this band-gap narrowing as band folding followed by repulsion between the folded states. The latter is coupled by the non-zinc-blende component of the superlattice potential. The same physical mechanism (but to a different extent) is responsible for gap bowing in disordered alloys
Electronic band structure of pseudodirect chalcopyrite semiconductors. 1
International Nuclear Information System (INIS)
The band structure of the chalcopyrite semiconductor CdSiP2 is calculated using the empirical pseudopotential method applied successfully already in the case of ZnSiP2. The band structure is in good agreement with recent experimental data, especially with the inverse crystal field splitting found by Shileika et al. The influence of the three contributions to the deviation of the chalcopyrite structure from a cubic one (antisymmetric cation potential, tetragonal compression and distortion of the anion sublattice) on the band structure and the optical transition energies is investigated in detail for both ZnSiP2 and CdSiP2. (author)
Pressure effects on the band structure of gadolinium
International Nuclear Information System (INIS)
APW calculations of the band structure of gadolinium were made to investigate the effects of decrease in lattice parameters coupled with an increase in c/a ratio. It is found that compared with normal pressure results, decreasing the lattice constants lowers the bottom of the band, and increasing c/a modifies the detailed band structure, particularly near GAMMA. Changes in the density of states were computed and it is found that the Fermi energy is now much closer to the levels near K. It is estimated that the density of states at the Fermi energy, and magnetic properties depending on it, are reduced by 15 percent from normal. (auth)
Morphologies of three-dimensional shear bands in granular media
Fazekas, S; Kertész, J; Wolf, D E
2005-01-01
Using three-dimensional Distinct Element Method with spherical particles we simulated shear band formation of granular materials in axisymmetric triaxial shear test. The calculated three-dimensinoal shear band morphologies are in good agreement with those found experimentally. We observed spontaneous symmetry braking strain localization provided it was allowed by the boundaries. If the symmetry was enforced, we found strain hardening. We discuss the formation mechanism of shear bands in the light of our observations and compare our results with high resolution NMR experiments.
Unfolding the band structure of non-crystalline photonic band gap materials.
Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining
2015-01-01
Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434
Unfolding the band structure of non-crystalline photonic band gap materials
Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining
2015-01-01
Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434
International Nuclear Information System (INIS)
The paper presents a review of the observational investigations of the diffuse interstellar bands (DIBs) which, despite being the object of considerable research, remain unidentified since 1921. The review is focused on the most recent investigations done with the aid of solid-state detectors which make it possible to obtain high S/N spectra. It is shown that DIBs may be divided into three (or more) families probably caused by different agents. The observed profiles are usually altered by Doppler splitting when reddened stars are observed through several clouds. Also, single clouds may differ considerably in their optical properties. The paper presents intrinsic (i.e., originating in single clouds) high-resolution profiles of several DIBs. These profiles are not dependent on the structure of the interstellar medium toward the observed objects. 39 references
Himmelsmechanik. Band III: Gravitationstheorie.
Schneider, M.
This book is the third in a now four volume set (for the first volume see 55.003.023, the second see 58.003.013). Der dritte Band des Lehrbuchs über Himmelsmechanik behandelt deren Formulierung auf der Grundlage der Einsteinschen Gravitationstheorie. Dargestellt werden zunächst die Strukturen der Minkowskischen Raumzeit und ihre Folgen für die Orts- und Zeitmessung. Anschließend werden die Einsteinsche Raumzeit durch eine konstruktive Axiomatik begründet und die Einsteinschen Feldgleichungen aufgestellt. Ausführlich werden das Schwarzschild-Problem, lineare und nach-Newtonsche Näherungen der Feld- und Bewegungsgleichungen behandelt. Daran schließt sich an die Behandlung der Ausbreitung elektromagnetischer Wellen und eine Theorie der Bezugssysteme in der Einsteinschen Raumzeit. Breiten Raum nimmt die Darstellung des relativistischen Zwei- und N-Körper-Problems, die Spin-Bahn-Kopplung, die relativistische Theorie von Rotation und Figur von Körpern ein.
Intermediate band solar cell with many bands: Ideal performance
Brown, Andrew S.; Green, Martin A.
2003-11-01
When the intermediate band solar cell (IBSC) absorbs sunlight, electrons are excited not only between the valence and conduction bands of the semiconductor material constituting the cell, but also between these bands and one or more additional bands that lie within the normally forbidden band gap of the material. Therefore, this device has the potential to reach high conversion efficiencies by increasing the photogenerated current (due to these multiple step excitations) without reducing the open-circuit voltage. In this article, a general method of describing the operation of the IBSC with N bands is presented for the cases where both the valence and conduction bands are unrestricted and restricted in their width. It is found that for the restricted IBSC, all of the intermediate bandwidths must be zero to satisfy the applied constraints. The efficiency for the unrestricted IBSC device under maximally concentrated black-body radiation with an infinite number of bands is estimated to be 85.0%. Under an air mass (AM) of 1.5 global radiation, an efficiency of 53.5% for the five-band IBSC is found to be the upper limit. Finally, the IBSC is found to be robust to changes in the AM.
The yrast rotational bands of selenium-74 and krypton-77
International Nuclear Information System (INIS)
New states in the positive parity yrast bands of 74Se and 77Kr have been observed with the reactions 52Cr(28Si,?2p)74Se and 52Cr (28Si,2pn)77Kr at 98 MeV. The target consisted of approximately 1 mg/cm2 natural chromium (84% 52Cr abundance) evaporated on a thick lead backing. The new states extend the known level scheme of 74Se up to I? = (22+) and most of the transitions in the other previously reported bands have been seen. For the states I? ? 6+ the spectrum shows a relatively constant moment of inertia parameter (h2/2?) = 27.8 ± 0.5 keV. Excited positive parity states up to spin (41/2) have been observed in 77Kr. ?I = 1 transitions have been identified throughout the positive parity band. The energies, mixing ratios and B(M1) transition rates for these transitions alternate in size as the spin increases. A cranked shell model analysis was performed along with Strutinsky-Bogolyubov cranking calculations. The observed decrease in the signature splitting of the ?g9/2 band has been attributed to a band crossing due to an aligning pair of g9/2 protons. Prolate quadrupole deformations of ?2 = 0.34 for the ground band and ?2 = 0.26 for the first excited band are predicted. This band crossing is associated with a shape change caused by the polarization effect of aligned quasiparticles
Band-Structure of Thallium by the LMTO Method
DEFF Research Database (Denmark)
Holtham, P. M.; Jan, J. P.
1977-01-01
The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s and p bands for the HCP structure. Energy bands have been evaluated both with and without spin-orbit coupling which is particularly large in thallium. Energy bands close to the Fermi level were found to be mainly 6p like in character. The 6s states lay below the 6p bands and were separated from them by an energy gap. The 6d and 7s bands were found to be far above the Fermi level and the 5d states were found to be far below it. Fermi surface properties and the electronic specific heat are computed and compared with experiment. The joint density of states has also been computed and is in reasonable agreement with experimental optical properties.
International Nuclear Information System (INIS)
Preliminary results from our charge self-consistent LCAO band structure (CSCBS) calculations with Bloch sums as the basis reveal that a noncorrosive reduced band gap electrode for photoelectrochemical solar cells may be produced from a (1:1) mixture of ?-PbO2 and TiO2 (both rutile). The band gaps for the constituents (?-PbO2 and TiO2) and the 1:1 mixture are calculated and a detailed characterization of the valence and the conduction bands is undertaken to offer a possible mechanism for the reduction of the band gap of the mixture. The band gap for the perovskite PbTiO3 is also calculated to offer a guideline for selecting from the competing pathways to the fabrication of noncorrosive photoelectrochemical electrodes
Comparison of RESRAD with hand calculations
International Nuclear Information System (INIS)
This report is a continuation of an earlier comparison done with two other computer programs, GENII and PATHRAE. The dose calculations by the two programs were compared with each other and with hand calculations. These band calculations have now been compared with RESRAD Version 5.41 to examine the use of standard models and parameters in this computer program. The hand calculations disclosed a significant computational error in RESRAD. The Pu-241 ingestion doses are five orders of magnitude too small. In addition, the external doses from some nuclides differ greatly from expected values. Both of these deficiencies have been corrected in later versions of RESRAD
Spectra of {gamma} rays feeding superdeformed bands
Energy Technology Data Exchange (ETDEWEB)
Lauritsen, T.; Khoo, T.L.; Henry, R.G. [and others
1995-08-01
The spectrum of {gamma}rays coincident with SD transitions contains the transitions which populate the SD band. This spectrum can provide information on the feeding mechanism and on the properties (moment of inertia, collectivity) of excited SD states. We used a model we developed to explain the feeding of SD bands, to calculate the spectrum of feeding {gamma}rays. The Monte Carlo simulations take into account the trigger conditions present in our Eurogam experiment. Both experimental and theoretical spectra contain a statistical component and a broad E2 peak (from transitions occurring between excited states in the SD well). There is good resemblance between the measured and calculated spectra although the calculated multiplicity of an E2 bump is low by {approximately}30%. Work is continuing to improve the quality of the fits, which will result in a better understanding of excited SD states. In addition, a model for the last steps, which cool the {gamma} cascade into the SD yrast line, needs to be developed. A strong M1/E2 low-energy component, which we believe is responsible for this cooling, was observed.
Peculiarities of band structure in bivalent rare earth monosulfides
International Nuclear Information System (INIS)
Total and local partial densities of states in rare-earth (SmS, EuS, YbS) monosulfides were calculated by the Green function method. Calculational results are compared with the x-ray and x-ray electron spectroscopy data. It is established that in YbS and EuS in comparison with SmS a band of metal f-states moves away from the conductivity band bottom thus increasing the energy-gap width. It is concluded with provision for value of charge transfer between sulfur and REE atoms that chemical bond in REE monosulfides is not purely ionic
Dr. P. Mallikarjuna Rao; Prof. Ch.Srinivasa Kumar
2011-01-01
This paper deals with the concept of filter banks. Filter banks are a group of band-pass filters connected in parallel. Each parallel connection forms a channel for different frequency-bands present in the input signal. The output of the filter bank is formed by merging these channels. The main theme behind the use of filter banksis to boost or attenuate different individual bands of frequencies present in a signal, without affecting other bands. There are several ways of realizing an filter ...
Sequential chromosome banding in fishes.
Czech Academy of Sciences Publication Activity Database
Rábová, Marie; Völker, M.; Pelikánová, Šárka; Ráb, Petr
Enfield : CRC Press, 2015, s. 92-102. ISBN 9781482211986 Institutional support: RVO:67985904 Keywords : fish cytogentics * genetic analyses * chromosome banding Subject RIV: EB - Genetics ; Molecular Biology
International Nuclear Information System (INIS)
We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.
Single Band Helical Antenna in Axial Mode
Directory of Open Access Journals (Sweden)
Parminder Singh
2012-11-01
Full Text Available Helical antennas have been widely used in a various useful applications, due to their low weight and low profile conformability, easy and cheap realization.Radiation properties of this antenna are examined both theoretically and experimentally. In this paper, an attempt has been made to investigate new helical antenna structure for Applications. CST MWS Software is used for the simulation and design calculations of the helical antennas. The axial ratio, return loss, VSWR, Directivity, gain, radiation pattern is evaluated. Using CST MWS simulation software proposed antenna is designed/simulated and optimized. The antenna exhibits a single band from 0 GHz to 3 GHz for GPS and several satellite applications
International Nuclear Information System (INIS)
Polycrystalline ZnO thin films both undoped and doped with various types of impurities, which covered the wide carrier concentration range of 1016–1021 cm?3, were prepared by magnetron sputtering, and their optical-band gaps were investigated. The experimentally measured optical band-gap shifts were analyzed by taking into account the carrier density dependent effective mass determined by the first-order nonparabolicity approximation. It was shown that the measured shifts in optical band-gaps in ZnO films doped with cationic dopants, which mainly perturb the conduction band, could be well represented by theoretical estimation in which the band-gap widening due to the band-filling effect and the band-gap renormalization due to the many-body effect derived for a weakly interacting electron-gas model were combined and the carrier density dependent effective mass was incorporated. - Highlights: ? Optical band-gaps of polycrystalline ZnO thin films were analyzed. ? Experimental carrier concentration range covered from 1016 to 1021 cm?3. ? Nonparabolic conduction band parameters were used in theoretical analysis. ? The band-filling and the band-gap renormalization effects were considered. ? The measured optical band-gap shifts corresponded well with the calculated ones
Study of multiphonon ??-band in neutron-rich 112Ru nucleus and molybdenum isotopes
Kumari, Parveen; Mittal, H. M.
2015-08-01
The structure of multiphonon K = 4 ??-band of {}112{Ru}, {}104{Mo}, {}106{Mo} , and {}108{Mo} nuclei are investigated using the recently proposed modified soft rotor formula (MSRF). The positive values of the moment of inertia and small values of softness parameter are obtained. The calculated values of moment of inertia of ??-band are almost equal to the moment of inertia of ?-band, which indeed should be equal to the moment of inertia of ground band. The constant energy parameter EK in the MSRF is also illustrated for K = 4 ??-band. The staggering pattern in the multiphonon ??-band is also discussed in detail. The study of one-phonon K = 2 ?-band and two-phonon K = 4 ??-band using MSRF yields good energy values.
Photonic band structure of two-dimensional metal/dielectric photonic crystals
Zong, Yi-Xin; Xia, Jian-Bai
2015-09-01
An improved plane wave expansion method for the numerical calculation of photonic bands of metal/dielectric photonic crystal (PC) are presented. This method is applied to two-dimensional PCs with frequency-dependent dielectric constants. We obtained the photonic band structure of three kinds of structures: sawtooth, cylinder and hole PCs. The results show that the lowest band-1 is relatively flat, and does not approach zero. Also, there is no complete band-gap that extends throughout the first Brillouin zone for these three structures. However, there are partial band-gaps in different directions in the first Brillouin zone. For the complementary cylinder and hole PCs, their photonic bands are similar except for the lowest three bands; the hole PC’s lowest frequency of band-1 is larger than that of cylinder PC for the configuration R/d??=??0.2.
The study of energy bands in neutron-deficient 123,125Ce nuclei
International Nuclear Information System (INIS)
Theoretical investigation of energy bands of 123,125Ce is performed by applying the projected shell model approach. The present calculation is viewed to reproduce the known experimental data of these nuclei, qualitatively. Not only this, the configurations of diverse bands are also obtained by an analysis of the band diagrams. The low-lying states of the bands are seen to arise from one quasiparticle configuration whereas the high-spin states arise from multi-quasiparticle configurations. The signature partner band of negative parity band is predicted in 123Ce. The ground state bands and relative energies of some bands with respect to them are predicted in 123,125Ce that can be helpful for future experiments
Transition strengths and shapes of 2-qp bands in 74Se and 76Kr
Mukherjee, G.; Joshi, P.; Roy, S. N.; Datta, S.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.
1999-09-01
The lifetimes of the states of -ve parity 2-qp bands of N = 40 nuclei 74Se and 76Kr were measured. The transition strengths and quadrupole moments, obtained from the lifetimes, show a large collectivity of such bands in both the nuclei. The alignment frequencies were calculated from Woods-Saxon cranking model. Previously suggested quasi proton nature of band 5 and 6 of 74Se were argued to be based on quasi neutron excitations. The total Routhian surface calculations suggest triaxial shapes with large +ve and -ve values of triaxiality parameter after proton and neutron alignments in these bands respectively.
Obtaining an intermediate band photovoltaic material through the Bi insertion in CdTe
Seminóvski Pérez, Yohanna; Palacios Clemente, Pablo; Wahnón Benarroch, Perla
2013-01-01
Defect interaction can take place in CdTe under Te and Bi rich conditions. We demonstrate in this work through first principles calculations, that this phenomenon allows a Jahn Teller distortion to form an isolated half-filled intermediate band in the host semiconductor band-gap. This delocalized energy band supports the experimental deep level reported in the host band-gap of CdTe at a low bismuth concentration. Furthermore, the calculated optical absorption of CdTe:Bi in this work shows a s...
Interplay between proton and neutron S-bands in the Xe-Ba-Ce-region
International Nuclear Information System (INIS)
Two-quasiparticle bands of positive parity (S-bands) in even-even nuclei in the Xe-Ba-Ce region are systematically examined. The equilibrium deformations for the ground-state band as well as for proton and neutron (h11/2)2 configurations are obtained from total routhian surface (TR-surfaces) calculations. By comparing systematic trends of calculated and experimental crossing frequencies, attempts are made to assign the various bands as having an (h11/2)2 neutron or proton character, respectively. (orig.)
Quasiparticle band structures and thermoelectric transport properties of p-type SnSe
Shi, Guangsha; Kioupakis, Emmanouil
2014-01-01
We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calcul...
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...
International Nuclear Information System (INIS)
High-spin states of 159Dy have been studied by using reaction 150Nd(13C, 4n). Two rotational bands based on the configurations ?[521]3/2 and ?[642]5/2 have been extended to 57/2- and 61/2+ states, respectively. A neutron AB crossing has been observed around ??=0.26 MeV in the ?[521]3/2 band. It has been observed that the signature splitting is inverted after the band crossing in the ?[521]3/2 band. The first band crossing has been observed around ??=0.38 MeV in the ?[642]5/2 band. Seven E1 transitions from the ?[521]3/2 band to the ?[642]5/2 band have been observed and discussed on the base of Generalized Intensity Relation. It is found that the B(E1)/B(E2) ratios for 47/2- and 43/2- states become enhanced relatively to those for the lower-spin states
Definitive experimental evidence for two-band superconductivity in MgB2
Tsuda, S; Yokoya, T.; Takano, Y; Kito, H.; Matsushita, A.; Yin, F.; Harima, H.; Shin, S
2003-01-01
The superconducting gap of MgB2 has been studied by high-resolution angle-resolved photoemission spectroscopy (ARPES). The momentum(k)-resolving capability of ARPES enables us to identify the s- and p-orbital derived bands predicted from band structure calculations and to successfully measure the superconducting gap on each band. The results show that superconducting gaps with values of 5.5 meV and 2.2 meV open on the s-band and the p-band, respectively, but both the gaps cl...
Identification of the unfavored N=7 superdeformed band in 191Hg
International Nuclear Information System (INIS)
A new superdeformed band has been identified in 191Hg bringing the total number of bands observed in this nucleus to four. The new band has properties similar to those of a superdeformed band reported recently in 193Hg. Both bands are believed to be built on the unfavored signature of the j15/2 intruder configuration. Comparisons between the data and cranked Woods-Saxon calculations highlight the strengths and weaknesses of theory in describing high-N orbitals at large deformation
Comparison between ab initio energy band structures of various chlorinated polyethylene derivatives
Assad Abdel-Raouf, Mohamed
1989-09-01
The band structures of various chlorinated polyethylene derivatives are calculated using an ab initio self-consisten field (SCF) linear combination of atomic orbitals (LCAO) technique. The results illustrate that the conduction band is shifted steadily towards lower energies as the number of chlorine atoms in the unit cell increases, and the gap between valence and conduction bands is decreased monotonically. The possibility of n-doping is explored. The comparison between the band structures of the chlorinated polymers and that of polytrifluorochloroethylene shows that the latter possesses a lower-lying conduction band and is, therefore, more adequate for doping.
International Nuclear Information System (INIS)
High spin states in 76Rb were investigated via the reaction 40Ca(40Ca,3pn)76Rb at 128 MeV. The level scheme was established from ??, ??? and recoil-? coincidences measured in the EUROGAM I array in combination with the Daresbury recoil separator. The known rotational bands were extended up to the excitation energy Ex?9.2 MeV and spins I?=(21+) and (19-). The band head energies could be fixed by many interband transitions. Two new bands were identified. The level scheme is discussed in terms of the cranked shell model. In the negative parity bands 76Rb behaves like a rigid rotor until the first band crossings
Information retrieval from wide-band meteorological data - An example
Adelfang, S. I.; Smith, O. E.
1983-01-01
The methods proposed by Smith and Adelfang (1981) and Smith et al. (1982) are used to calculate probabilities over rectangles and sectors of the gust magnitude-gust length plane; probabilities over the same regions are also calculated from the observed distributions and a comparison is also presented to demonstrate the accuracy of the statistical model. These and other statistical results are calculated from samples of Jimsphere wind profiles at Cape Canaveral. The results are presented for a variety of wavelength bands, altitudes, and seasons. It is shown that wind perturbations observed in Jimsphere wind profiles in various wavelength bands can be analyzed by using digital filters. The relationship between gust magnitude and gust length is modeled with the bivariate gamma distribution. It is pointed out that application of the model to calculate probabilities over specific areas of the gust magnitude-gust length plane can be useful in aerospace design.
Compact Dual Band Microstrip Antenna for Ku-Band Application
M.T. Islam; Misran, N; A.T. Mobashsher
2010-01-01
A new design of dual band compact microstrip antenna is proposed for Ku-band applications. Dual band is achieved using three pairs of thin slits from the sides of a rectangular patch and feeding with a microstrip feedline. The antenna has a compact structure and the total size is 9.50 by 10 by 0.254 mm. The result shows that the return loss of -23.83 dB is achieved at the first resonant frequency of 12.54 GHz and -14.04 dB is obtained at the second resonant frequency of 14.15 GHz. The antenna...
Electronic structure calculations on nitride semiconductors and their alloys
International Nuclear Information System (INIS)
Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)
Calculated thermoelectric properties of La-filled skutterudites
D. J. Singh; Mazin, I.I.
1997-01-01
The thermoelectric properties of La-filled skutterudites are discussed from the point of view of their electronic structures. These are calculated from first principles within the local density approximation. The electronic structure is in turn used to determine transport related quantities. Virtual crystal calculations for La(Fe,Co)_4Sb_{12} show that the system obeys near rigid band behavior with varying Co concentration, and has a substantial band gap at a position corres...
Band gap engineering strategy via polarization rotation in perovskite ferroelectrics
International Nuclear Information System (INIS)
We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2?eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics
Band offsets in c-Si/Si-XII heterojunctions
Mustafa, Jamal I.; Malone, Brad D.; Cohen, Marvin L.; Louie, Steven G.
2014-08-01
Silicon has a rich phase diagram with a multitude of phases existing over a wide range of pressures and temperatures, in addition to the common cubic silicon (c-Si) phase. One such phase, Si-XII, was first observed less than 2 decades ago in diamond anvil experiments, and more recently as a product of nanoindentation. In some of these latter experiments, I-V measurements were performed to characterize the c-Si/Si-XII interface that results when Si-XII is formed in cubic silicon substrates. In this paper we describe calculations of the band offsets in c-Si/Si-XII heterojunctions. We find that the heterojunction is of Type I and that the band offsets are estimated to be ?Ev=0.3 eV and ?Ec=0.5 eV for the valence bands and conduction bands, respectively.
Band-gap engineering in fluorographene nanoribbons under uniaxial strain
International Nuclear Information System (INIS)
Based on extensive first-principles calculations, we report the structural and electronic properties of fluorinated graphene, i.e., fluorographene nanoribbons (FGNRs) under uniaxial strain. Our results indicate that the FGNRs are semiconductors with wide direct band gaps regardless of their edge structures. Moreover, the band gap of FGNR can be effectively modulated nonlinearly with the applied uniaxial elastic strain, where the band gap value increases first and then reduces when the applied strain changes from ?10.0% to 10.0%. This abnormal behavior mainly originates from the electronic structures of valence and conduction band edges, which is quite different from previously reported linear behavior on graphene nanoribbon. Our results imply the great potential applications of FGNRs in the optical electronics
Lasing at the band edges of plasmonic lattices
Schokker, A Hinke
2014-01-01
We report room temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback lasers, a central question is how the underlying band structure from which lasing emerges is modified by both the much stronger scattering and the disadvantageous loss of metal. We use spectrally resolved back-focal plane imaging to measure the wavelength- and angle dependence of emission below and above threshold, thereby mapping the band structure. We find that for silver particles, the band structure is strongly modified compared to dielectric reference DFB lasers, since the strong scattering gives large stop gaps. In contrast, gold particles scatter weakly and absorb strongly, so that thresholds are higher, but the band structure is not strongly modified. The experimental findings are supported by finite element and fourier modal method calculations of the...
Multiple triaxial bands and abnormal signature inversion in 7433As
International Nuclear Information System (INIS)
Excited states of the odd–odd nucleus 74As have been investigated via heavy ion fusion evaporation reaction 70Zn(7Li,3n)74As at beam energy of 30 MeV. The properties of the positive- and the negative- parity bands can be interpreted in terms of the Cranked Nilsson–Strutinsky (CNS) model calculations which show that the observed bands are built on the triaxial deformed shape. The inversion of the favored and unfavored signature branches observed in the positive-parity bands presents at high spins rather than normal signature inversion occurs at low spins. This phenomenon may be explained as the origin of unpaired band crossing in a highly rotating triaxial nucleus.
Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices
DEFF Research Database (Denmark)
Gorczyca, I.; Suski, T.
2012-01-01
InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5 the band gap closes and the systems become “metallic”. These effects are related to the existence of the built-in electric fields that strongly influence valence- and conduction-band profiles and thus determine effective band gap and emission energies of the superlattices. Varying the widths of the quantum wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.
Quantitative analysis on electric dipole energy in Rashba band splitting.
Hong, Jisook; Rhim, Jun-Won; Kim, Changyoung; Ryong Park, Seung; Hoon Shim, Ji
2015-01-01
We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime. PMID:26323493
Population and properties of superdeformed bands in A ? 150 region
International Nuclear Information System (INIS)
The production of superdeformed nuclei, treated as cluster configurations in the A ? 150 region is described in the framework of statistical approach and the dinuclear system concept. The competition of particle emission from the dinuclear system and quasifission is taken into account. The calculated nuclear characteristics of the superdeformed band in 152Dy are close to the experimental values.
Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems
International Nuclear Information System (INIS)
Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH2 and YH2 were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH2 cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 2 lattice. These experimental results also suggest that, in contrast to recent calculations, LaH3 is a small-band-gap semiconductor
First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications
International Nuclear Information System (INIS)
First-principles calculations of the band offsets between Cu2ZnSnS4 (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.
Calculated thermoelectric properties of La-filled skutterudites
Singh, D J
1997-01-01
The thermoelectric properties of La-filled skutterudites are discussed from the point of view of their electronic structures. These are calculated from first principles within the local density approximation. The electronic structure is in turn used to determine transport related quantities. Virtual crystal calculations for La(Fe,Co)_4Sb_{12} show that the system obeys near rigid band behavior with varying Co concentration, and has a substantial band gap at a position corresponding to the composition LaFe_3% CoSb_{12}. The valence band maximum occurs at the $\\Gamma$ point and is due to a singly degenerate dispersive band, which by itself would not be favorable for high thermopower. However, very flat transition metal derived bands occur in close proximity and become active as the doping level is increased, giving a non-trivial dependence of the properties on carrier concentration and explaining the favorable thermoelectric properties.
Jena Band of Louisiana Choctaw
Gregory, Hiram F.
1977-01-01
Documenting the development and struggles of the Jena Band of American Indian Choctaws in Louisiana, this article describes the remarkable autonomy of these people in the face of governmental/racial discrimination. (JC)
Fitting the observed PAH bands
Cami, Jan; Bauschlicher, C.; Peeters, E.; Mattioda, A.; Allamandola, L.
2009-01-01
The interstellar infrared emission spectrum with strong bands near 3.3, 6.2, 7.7, and 11.2 micron is common throughout the Universe. These bands -- often called the Unidentified InfraRed (UIR) bands or Aromatic InfraRed Bands (AIB) -- dominate the mid-IR spectra of most galactic objects and they have been detected in a large number of extragalactic objects. Not only are these features observed in many different objects, there is also significant variability in the spectroscopic details from one object to another and from one region to another within extended sources. Clearly, these spectra contain a wealth of information which reflects the physical conditions in the emission zones and composition of the emitting materials. Many studies have therefore attempted to use these easily observed features as diagnostic tools for various purposes. It is now widely accepted that this spectrum is produced by fluorescent emission from highly vibrationally excited polycyclic aromatic hydrocarbon molecules (PAHs) and closely related species and the features are now often referred to as the PAH emission bands. In this presentation, we use the NASA Ames PAH IR Spectroscopic Database and a simplified model for PAH physics to present a detailed comparison with observations of the UIR bands representing the different characteristic classes of UIR spectra. We find that we can closely reproduce the observed UIR spectra for all classes in the ranges 6--9 micron and 10--14 micron, offering credibility for the hypothesis that the UIR bands are indeed due to the various vibrational modes of PAHs and related species. We will also show how the spectral variations of the PAH bands in different environments can be explained by differences in the size distribution, the charge state and the precise chemical composition of the contributing molecules.
Band structure from random interactions
Bijker, R
2000-01-01
The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P)=0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally thought.
Ultraviolet bands of potassium dimer
International Nuclear Information System (INIS)
The ultraviolet band spectra of potassium dimer have been investigated. The studies were performed in absorption in the second order of a 3.4 m Ebert spectrograph with a reciprocal dispersion of 2.6 A/mm. A number of new bands in the electronic states G and H not previously reported have been observed. The vibrational analysis is performed and molecular constants are evaluated. (author)
International Nuclear Information System (INIS)
High spin states in 196Hg have been populated in the 198Pt(?,6n) reaction at 65 MeV and the level scheme has been extended. A new dipole band has been observed and a previously observed dipole has been confirmed. Excitation energies, spins and parities of these bands were determined from DCO ratio and linear polarization measurements. Possible quasiparticle excitations responsible for these structures are discussed.
Optimization of Photonic Band Structures
Richter, Markus
2010-01-01
In this work we study mathematical optimization problems that arise in the design of photonic crystals, whose band structures should exhibit specific properties. To this end we develop a mathematical model for time-harmonic wave propagation in three-dimensional, periodic media. We investigate the dependency of band structures on the medium structure and develop two types of optimization algorithms. The performance of these algorithms is demonstrated through several of numerical experiments.
Band Gaps and Localization in Acoustic Propagation in Water with Air-cylinders
ye, Zhen; Hoskinson, Emile
2000-01-01
Multiple scattering of waves leads to many peculiar phenomena such as complete band gaps in periodic structures and wave localization in disordered media. Within a band gap excitations are evanescent; when localized they remain confined in space until dissipated. Here we report acoustic band gap and localization in a 2D system of air-cylinders in water. Exact numerical calculations reveal the unexpected result that localization is relatively independent of the precise locati...
Formation of dispersive hybrid bands at an organic-metal interface
González-Lakunza, N.; Fernández-Torrente, I.; Franke, K. J.; Lorente, N.; Arnau, Andrés; Pascual, J. I.
2008-01-01
An electronic band with quasi-one dimensional dispersion is found at the interface between a monolayer of a charge-transfer complex (TTF-TCNQ) and a Au(111) surface. Combined local spectroscopy and numerical calculations show that the band results from a complex mixing of metal and molecular states. The molecular layer folds the underlying metal states and mixes with them selectively, through the TTF component, giving rise to anisotropic hybrid bands. Our results suggest tha...
Identification of a possible proton two-quasiparticle band in 158Sm
Wang, E. H.; Hamilton, J. H.; Ramayya, A. V.; Hwang, J. K.; Liu, S. H.; Brewer, N. T.; Luo, Y. X.; Rasmussen, J. O.; Zhu, S. J.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.
2014-12-01
High-spin states in neutron-rich 158Sm have been reinvestigated by measuring the prompt ? rays emitted in the spontaneous fission of 252Cf . A new negative-parity band has been established up to spin 12. By comparison with the theoretical calculations, a two-quasiparticle state with ? 5 /2 [532 ] ? ? 5 /2 [413 ] configuration has been proposed for the band head. The systematics of the two-quasiparticle states and bands in this region are discussed.
Kolek, Andrzej
2015-05-01
The formulas are derived that enable calculations of intersubband absorption coefficient within nonequilibrium Green's function method applied to a single-band effective-mass Hamiltonian with the energy dependent effective mass. The derivation provides also the formulas for the virtual valence band components of the two-band Green's functions which can be used for more exact estimation of the density of states and electrons and more reliable treatment of electronic transport in unipolar n-type heterostructure semiconductor devices.
Electronic Structure and Valence Band Spectra of $Bi_{4}Ti_{3}O_{12}$
Postnikov, A V; Mersch, F; Neumann, M; Kurmaev, E Z; Cherkashenko, V M; Nemnonov, S N; Galakhov, V R; Bartkowski, St.
1995-01-01
The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
Postnikov, A. V.; Bartkowski, St.; Mersch, F.; Neumann, M.; Kurmaev, E. Z.; Cherkashenko, V. M.; Nemnonov, S. N.; Galakhov, V. R.
1995-01-01
The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.
Isogeometric analysis of shear bands
Berger-Vergiat, Luc; McAuliffe, Colin; Waisman, Haim
2014-08-01
Numerical modeling of shear bands present several challenges, primarily due to strain softening, strong nonlinear multiphysics coupling, and steep solution gradients with fine solution features. In general it is not known a priori where a shear band will form or propagate, thus adaptive refinement is sometimes necessary to increase the resolution near the band. In this work we explore the use of isogeometric analysis for shear band problems by constructing and testing several combinations of NURBS elements for a mixed finite element shear band formulation. Owing to the higher order continuity of the NURBS basis, fine solution features such as shear bands can be resolved accurately and efficiently without adaptive refinement. The results are compared to a mixed element formulation with linear functions for displacement and temperature and Pian-Sumihara shape functions for stress. We find that an element based on high order NURBS functions for displacement, temperature and stress, combined with gauss point sampling of the plastic strain leads to attractive results in terms of rate of convergence, accuracy and cpu time. This element is implemented with a -bar strain projection method and is shown to be nearly locking free.
Dosimetry of narrow band UVB treatments
International Nuclear Information System (INIS)
Full text: For many years psoriasis has been treated with broad band UVB lamps. These lamps have a bell shaped spectrum which peaks at 305 nm and extends from 280 nm to 350 nm. However research with monochromatic UV radiation has shown that wavelengths between 300 nm and 320 nm are the most efficacious for clearing psoriasis while wavelengths below 305 nm are most effective for producing the undesirable side effect of erythema (sunburn). In response to these findings Philips developed a narrow band UVB tube in which a large fraction of the output was confined to a narrow peak (bandwidth 2.5 nm) situated at 311 nm. Christchurch Hospital replaced broad band UVB with narrow band treatments in August 1995 and as this required UV exposures to be substantially increased new protocols had to be developed. Three aspects needed to be addressed. These were translating the dose from broad band to narrow band for current patients, determining the initial dose for new patients and developing a formula for increasing subsequent exposures to both types of patient. To translate doses the spectral irradiance (?W/cm2/nm) that would fall on the patient was measured in both the old broad band and the new narrow band treatment units and from this UV doses were calculated. All doses were expressed in mJ/cm2 of unweighted UV over the range 250 nm to 400 nm. The erythemal effectiveness of the two units were compared by using the CIE 1987 curve to express doses in terms CIE 1987 curve to express doses in terms of the equivalent exposure of monochromatic 297 nm radiation. It was found that an exposure of 3.96 mJ/cm2 from the broad band FS40 tubes and 12.79 mJ/cm2 from the narrow band TL/01 tubes were both equivalent to 1.00 mJ/cm2 of monochromatic 297 nm radiation so when transferring patients all broad band doses needed to be increased by a factor of 3.2. Before transferring any patients this factor was confirmed by conducting two minimal erythema dose (MED) tests on a normal subject, one in each unit. For new patients a narrow band treatment schedule has been developed which is based on the patient' s MED. Before commencing treatments the patient is given an MED test using untanned skin on the inner surface of the forearm. The initial dose is 70% of the MED and each subsequent exposure is increased by a constant increment, namely 21.4% of the initial dose. This progression continues until the dose reaches three times the MED at which time it is held constant. Treatments are given twice per week up to a maximum of 30 treatments or until the psoriasis clears. If mild erythema occurs the next treatment is held at the previous dose while for more severe erythema it is missed entirely. This schedule is similar to the one in use at The Royal Victoria Infirmary, Newcastle upon Tyne, but with two minor exceptions. In Newcastle the increments are larger (on average 45% of the initial dose) but they only occur once a week. The transfer from broad band to narrow band was accomplished successfully without any incidence of erythema. After four months experience the 31 patients who were currently following the MED based protocol were reviewed. The lowest MED measured was 500 mJ/cm2 while the highest (three in number) exceeded 1110 mJ/cm2. Eleven of the patients exhibited erythema at some point in their treatment but it was only necessary to reduce the dose increment in one case. Of the remaining 20 patients, 13 who showed poor clearing of their psoriasis were placed on a dose schedules in which the dose increments were increased by between 20 % to 33%. In view of the fact almost equal numbers of patients received too large or too small a dose the schedule can be considered to be a good compromise
N2 triplet band emissions in the dayglow of Venus, Mars, and Titan
Jain, Sonal Kumar; Bhardwaj, Anil
2012-07-01
Vegard-Kaplan (VK) and Second Positive emissions of N_2 are common features in the terrestrial dayglow and aurora and have been studied extensively. Recent discoveries of N_2 triplet band emissions on Mars by SPICAM/Mars-Express and on Titan by Cassini UVIS have led planetary scientists to look for the processes governing the N_2 triplet band emissions in different planetary atmospheres. Present work deals with the modeling of N_2 triplet band emission on Mars, Venus, and Titan. A model for N_2 triplet band emissions has been developed and used to explain the recent observations of N_2 Vegard-Kaplan (VK) (A^3?_u^+ - X^1?^+_g ) band on Mars and Titan. Steady state photoelectron fluxes and volume excitation rates have been calculated using the Analytical Yield Spectra technique. Since interstate cascading is important for triplet states of N_2, the population of any given level of N_2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, First Positive ( B^3?_g - A^3?^+_u ), Second Positive ( C^3?_u - B^3?_g ), Wu-Benesch (W^3?_u - B^3?_g), Reverse First Positive, Herman--Kaplan (E ? A), E ? B, and E ? C bands of N_2. The N_2 VK band span wavelength range from far ultraviolet to visible, and some transitions even originate at wavelength more than 1000 nm . Our calculations show that the overhead intensity of VK bands in the wavelength range 400--800, 300--190, 200--300, and 150--200 nm are 22%, 39%, 35%, and 4% of the total VK band emission. Emissions between 600 and 800 nm wavelength consist of about 50% of the total First Positive band system. Major portion of Second Positive band emissions lie in wavelengths between 300 and 400 nm, which is more than 90% of the total Second Positive band overhead intensity. On Mars, a reduction in the N_2 density by a factor of 3 in the Mars thermospheric general circulation model is required to obtain agreement between calculated limb profiles of VK (0-6) and the SPICAM/MEX observation. On Titan, the calculated intensity of N_2 VK band in 150--190 nm wavelength range is in good agreement with the Cassini-UVIS observation. Calculations are also carried out on Venus using this model. Calculated intensities on Venus are about factor of 10 higher than that on Mars. The results will be presented and discussed.
X-ray aided permeability computations inside compaction bands in sandstones
Andrade, J.; Lenoir, N.; Sun, W.; Rudnicki, J. W.
2009-12-01
This work presents preliminary data on permeability calculations using 3D X-ray tomography images taken inside and outside compaction bands. Aztec sandstone samples are taken from the Valley of Fire in Nevada and are scanned using the synchrotron APS facility at Argonne National Laboratory. The 3D microstructures inside and outside the compaction bands, formed in situ, are then used to perform lattice Boltzmann computations to estimate the components of permeability in different principal directions. We show that i) the permeability component in the direction perpendicular to the compaction band is reduced by orders of magnitude in the presence of a compaction band, ii) inside the compaction band, there is a strong anisotropy manifested by the permeability tensor, and iii) the Kozeny-Carman relation does a pretty good job at estimating the permeability outside of the compaction band, but fails to estimate the reduction in permeability in the presence of compaction bands.
Band structures and alignment properties in 74Se
Döring, J.; Johns, G. D.; Riley, M. A.; Tabor, S. L.; Sun, Y.; Sheikh, J. A.
1998-06-01
High-spin states in the even-even nucleus 74Se were investigated via the 65Cu(12C, p2n)74Se reaction at a beam energy of 50 MeV. On the basis of coincidence data three of the known bands were extended to higher spins and two new bands were found. Experimental crossing frequencies were deduced for various band structures and compared with cranked-shell-model results. Previous assignments of g9/2 quasiproton and g9/2 quasineutron alignments along the yrast line were confirmed when a near-prolate shape is assumed. Hartree-Fock-Bogoliubov calculations predict a deformed shape for excited states in 74Se which shows, however, a considerable softness in triaxiality. For the first time in the mass 70 region, band structures and quasiparticle alignments in 74Se were also investigated using the projected shell model. The calculations support the previous conclusions for the positive-parity states and predict that the lowest negative-parity bands are signature partners based on g9/2 quasiproton excitations, with a g9/2 quasineutron crossing at higher frequencies leading to a four-quasiparticle configuration at high spins.
Sharma, S; Ambrosch-Draxl, C
2005-01-01
Exact exchange (EXX) Kohn-Sham calculations within an all-electron full-potential method are performed on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. Full-potential band-gaps are also not significantly better for $sp$ semiconductors than for insulators, as had been found for pseudopotentials. The locations of $d$-band states, determined using the full-potential EXX method, are in excellent agreement with experiment, irrespective of whether these states are core, semi-core or valence. We conclude that the inclusion of the core-valence interaction is necessary for accurate determination of EXX Kohn-Sham band structures, indicating a possible deficiency in pseudopotential calculations.
Description of staggering phenomenon of the superdeformed bands in SUq(2) symmetry
International Nuclear Information System (INIS)
The staggering phenomenon of the superdeformed bands 149Gd(1), 148Gd(6) and 148Eu (1) is analyzed with a SUq(2) rotational spectroscopy expression. When the spin of the head of band is chosen properly, the calculating bifurcation of ?I = 4 is agreement with that extracted from experiment
Model for minority-carrier band-gap states in semiconductors
International Nuclear Information System (INIS)
A variational calculation is presented for the energies of electrons and holes which interact with a random distribution of donor impurities in a semiconductor. At high density, smaller band-gap narrowing is predicted for a random distribution than for an ordered one. A new model is presented for the minority-carrier states in the band gap
EFFECT OF MAGNETIC DISORDER ON THE SPECTRAL DENSITY OF THE d BAND IN FERROMAGNETIC METALS
Kanamori, J.; S. Imada
1988-01-01
It is shown that previous calculations of the spectral density of an extra hole or electron in Fe and Ni can be parametrized with a simple CPA in terms of an exchange splitting parameter and level position in the band both measured in the unit of an effective band width even in the presence of the short range order.
Band structure of absorptive two-dimensional photonic crystals
van der Lem, Han; Tip, Adriaan; Moroz, Alexander
2003-06-01
The band structure for an absorptive two-dimensional photonic crystal made from cylinders consisting of a Drude material is calculated. Absorption causes the spectrum to become complex and form islands in the negative complex half-plane. The boundaries of these islands are not always formed by the eigenvalues calculated for Bloch vectors on the characteristic path, and we find a hole in the spectrum. For realistic parameter values, the real part of the spectrum is hardly influenced by absorption, typically less than 0.25%. The employed method uses a Korringa-Kohn-Rostoker procedure together with analytical continuation. This results in an efficient approach that allows these band-structure calculations to be done on a Pentium III personal computer.
Tunneling conductance spectra of a metal/ferromagnet junction within a two-band model
Energy Technology Data Exchange (ETDEWEB)
Pasanai, K., E-mail: krisakronmsu@gmail.com [Department of Physics, Faculty of Science, Mahasarakham University, Khamriang Sub-District, Kantarawichai District, Maha Sarakham 44150 (Thailand); Pairor, P. [School of Physics, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000 (Thailand)
2013-02-15
We present a theory based on a scattering matrix approach to explain the tunneling spectroscopy of a metal/ferromagnet junction. The isotropic one-band free electron model was used to describe the energy dispersion relation of the electrons in a metal layer, while two-band approximation was used to examine the electronic dispersion relation within the ferromagnetic material. s-band and d-band coupling were considered using the two-band approximation. In this work, interfacial spin-flip scattering was neglected. The energy dispersion and tunneling conductance spectra were calculated to study the effect of the coupling strength between the two bands. With no coupling, the energy band will have the crossing point between the bands. In contrast, a gap is opened up at the crossing points. It was found that the size of the gap depends on the coupling strength. Some kinks occurred in the energy band corresponding to the crossing points. The rich features of conductance spectra occurring in the metallic regime have the effects more significant than those occurring in the tunneling regime. In both regimes the conductance spectrum becomes largest if the effective mass of free electrons in the majority of the bands in the ferromagnetic material is approximately in the same order as that of the free electrons in metals. - Highlights: Black-Right-Pointing-Pointer Tunneling conductance spectra of two-band ferromagnet/superconductor are calculated. Black-Right-Pointing-Pointer s-band and d-band of ferromagnet are mixed. Black-Right-Pointing-Pointer The conductance spectra consist of several kinks, depending on the coupling strength. Black-Right-Pointing-Pointer Two-band ferromagnet model is very essential.
Band gap modulation of functionalized metal-organic frameworks.
Musho, Terence; Li, Jiangtan; Wu, Nianqiang
2014-11-21
Metal-organic frameworks (MOFs) have been envisioned as alternatives to planar metallic catalysts for solar-to-fuel conversion. This is a direct result of their porous structure and the ability to tailor their optical absorption properties. This study investigates the band gap modulation of Zr-UiO-66 MOFs from both the computational and experimental points of view for three linker designs that include benzenedicarboxylate (BDC), BDC-NO2, and BDC-NH2. Emphasis in this study was aimed at understanding the influence of the bonding between the aromatic ring and the functional group. A ground state density functional theory (DFT) calculation was carried out to investigate the projected density of states and the origins of the modulation. A time-dependent density functional theory (TDDFT) calculation of the hydrogen terminated linkers confirmed the modulation and accounted for the electron charge transfer providing comparable optical band gap predictions to experimental results. Computational results confirmed the hybridization of the carbon-nitrogen bond in conjunction with the donor state resulting from the NH2 functionalization. The NO2 functionalization resulted in an acceptor configuration with marginal modification to the valence band maximum. The largest modulation was BDC-NH2 with a band gap of 2.75 eV, followed by BDC-NO2 with a band gap of 2.93 eV and BDC with a band gap of 3.76 eV. The electron effective mass was predicted from the band structure to be 8.9 me for all MOF designs. PMID:25269595
Search for superdeformed bands in {sup 154}Dy
Energy Technology Data Exchange (ETDEWEB)
Nisius, D.; Janssens, R.V.F.; Khoo, T.L. [and others
1995-08-01
The island of superdeformation in the vicinity of the doubly magic {sup 152}Dy yrast superdeformed (SD) band is thought to be well understood in the framework of cranked mean field calculations. In particular, the calculations suggested that in {sup 154}Dy there should be no yrast or near yrast SD minimum in the 40-60 h spin range, where SD bands in this mass region are thought to be {sup 153}Dy nucleus, it is populated. However, with the presence of five SD bands in the neighboring necessary to ascertain if the addition of one single neutron diminishes the importance of shell effects to the extent that superdeformation can no longer be sustained. In an experiment utilizing the increased resolving power of the early implementation phase of Gammasphere, the reaction {sup 122}Sn({sup 36}S,4n) at 165 MeV was employed to populate high spin states in {sup 154}Dy. In a four-day run with 36 detectors, over one billion triple and higher fold coincidence events were recorded. One new SD band was identified and was assigned to {sup 154}Dy. From comparisons with the Im{sup (2)} moments of inertia of the SD bands in {sup 152}Dy and {sup 153}Dy, a configuration based on (514)9/2{sup 2} neutrons coupled to the {sup 152}Dy SD core was proposed. One unexpected and as yet unexplained feature of this new SD band is that the transition energies are almost identical to those of an excited SD band in {sup 153}Dy. It is also worth noting that the feeding of the yrast states is similar to that achieved by the deexcitation from the ensemble of all entry states in the reaction. This observation emphasizes the statistical nature of the decay-out process. A paper reporting these results was accepted for publication.
Band alignment of semiconductors from density-functional theory and many-body perturbation theory
Hinuma, Yoyo; Grüneis, Andreas; Kresse, Georg; Oba, Fumiyasu
2014-10-01
The band lineup, or alignment, of semiconductors is investigated via first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT). Twenty-one semiconductors including C, Si, and Ge in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, and GaN and ZnO in the wurtzite structure are considered in view of their fundamental and technological importance. Band alignments are determined using the valence and conduction band offsets from heterointerface calculations, the ionization potential (IP) and electron affinity (EA) from surface calculations, and the valence band maximum and conduction band minimum relative to the branch point energy, or charge neutrality level, from bulk calculations. The performance of various approximations to DFT and MBPT, namely the Perdew-Burke-Ernzerhof (PBE) semilocal functional, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, and the GW approximation with and without vertex corrections in the screened Coulomb interaction, is assessed using the GW?1 approximation as a reference, where first-order vertex corrections are included in the self-energy. The experimental IPs, EAs, and band offsets are well reproduced by GW?1 for most of the semiconductor surfaces and heterointerfaces considered in this study. The PBE and HSE functionals show sizable errors in the IPs and EAs, in particular for group II-VI semiconductors with wide band gaps, but are much better in the prediction of relative band positions or band offsets due to error cancellation. The performance of the GW approximation is almost on par with GW?1 as far as relative band positions are concerned. The band alignments based on average interfacial band offsets for all pairs of 17 semiconductors and branch point energies agree with explicitly calculated interfacial band offsets with small mean absolute errors of both ˜0.1eV, indicating a good overall transitivity of the band offsets. The alignment based on IPs from selected nonpolar surfaces performs comparably well in the prediction of band offsets at most of the considered interfaces. The maximum errors are, however, as large as 0.3, 0.4, and 0.7 eV for the alignments based on the average band offsets, branch point energies, and IPs, respectively. This margin of error should be taken into account when performing materials screening using these alignments.
Thermal emissivity for finite three-dimensional photonic band gap crystals
Stimpson, Andrew J.; Dowling, Jonathan P
2002-01-01
We discuss the results of computer model for the thermal emissivity of a three-dimensional photonic band gap (PBG) crystal, specifically an inverted opal structure. The thermal emittance for a range of frequencies and angles is calculated.
Probing Time-Odd and Tensor Terms of The Skyrme Functional in Superdeformed Bands
International Nuclear Information System (INIS)
We briefly discuss Hartree Fock Bogoliubov (HFB) plus self consistent cranking calculations for the superdeformed band in 194Hg, using the full Skyrme energy density functional including tensor terms in the p-h channel.
Spins of superdeformed band in {sup 192}Hg
Energy Technology Data Exchange (ETDEWEB)
Lauritsen, T.; Khoo, T.L.; Henry, R.G. [and others
1995-08-01
Determination of the spins of SD states is the most important challenge in the study of superdeformation. Knowledge of the spin will provide crucial information on SD bands, in particular on the fascinating phenomenon of bands with identical energies and moments of inertia. Angular distribution coefficients of the {gamma}rays decaying out of the {sup 192}Hg SD band were determined using Eurogam data. These coefficients, as well as the spectral shape and multiplicity of the spectrum, are compared with the results of calculations, thereby providing a check on these calculations. From the measured decay multiplicity and the calculated average spin removed per photon (0.3 h), we deduce the average spin {bar I}{sub decay} removed by the {gamma} rays connecting SD and normal states. The spin I{sub SD} of the SD band from which the decay occurs is given by I{sub SD} = {bar I} decay + {bar I} ND, where {bar I} ND is the average spin removed by the normal yrast states. The state from which the major decay out of the SD band occurs is found to have spin 9.5 {plus_minus} 0.8 h. Since angular momentum is (quantized), this leads to a spin assignment of 9 or 10 h. The latter value is favored since the yrast band in the SD well must have only even spin values. This constitutes the first deduction of spin from data in the mass 150 and 190 regions. The spin of 10 h agrees with the spin which is inferred from a model, using the observed moment of inertia (Im){sup (2)}{omega}.
A novel design UWB antenna having band notch characteristics
Gour, Ajay S.; Mathur, Dhirendra
2013-01-01
A Novel Design using two feed structure for Ultra Wide Band Antenna with band notch characteristics is being presented in this paper. The simulated antenna so designed have a compact small physical size of 16 mm (L) × 20 mm (W) × 1.6 mm (h) of the overall design with the patch size as 11.86 mm (L) × 8.96 mm (W). The antenna is designed to simulate at 10 GHz. The substrate used is Duroid™ with a relative permittivity of (?r=2.2) and the return loss so measured is calculated below -10 dB for the range 3.1-19.53 GHz with band notching in the frequency band 5.1-5.8 GHz (i.e. WLAN). To achieve such UWB antenna with band notch, the three concepts used are introduced, the first one is using two feeding structure, the second one is using steps at the bottom of the patch, introducing steps at the bottom centre of the patch for band notching. The final impedance bandwidth so measured is 145 % which is a very high bandwidth so obtained. The optimized antenna designed can be used in any of the wireless device for UWB applications.
Cold versus hot shear banding in bulk metallic glass
Cheng, Y. Q.; Han, Z.; Li, Y.; Ma, E.
2009-10-01
We present an analysis of the shear-banding dynamics in a bulk metallic glass (BMG), including the temperature rise in the band, the sliding speed of the band, and the time elapsed as well as the step size of the shear offset growth in a stop-and-go cycle. This model analysis quantitatively demonstrates that the major shear band can remain cold and slide in a stick-slip manner. We predict that the shear step (distance covered by a stop-and-go cycle) scales with the sample size and machine stiffness. We also illustrate the conditions when such serrated shear is unsustainable and a hot shear band directly develops in a runaway instability (catastrophe). These findings provide physical insight into the shear-instability processes and offer useful information for improving the plasticity of BMGs. The calculation results are used to explain several intriguing recent experimental observations, including the stick slip of the dominant shear-band and the sample-size effects on the plastic-flow behavior of BMGs.
Modelling of Quantum Dots for Intermediate Band Solar Cells
Tomi?, Stanko
We present a theoretical model for design and analysis of semiconductor quantum dot (QD) array-based intermediate band solar cell (IBSC). The plane wave method with periodic boundary conditions is used in expansion of the k?p Hamiltonian for calculation of the electronic and optical structure of InAs/GaAs QD array. Taking into account realistic QD shape, QD periodicity in the array, as well as effects like band mixing between states in the conduction and valence band, strain and piezoelectric field, the model reveals the origin of the intermediate band formation inside forbidden energy gap of the barrier material. Having established the interrelation between QD periodicity and the electronic structure across the QD array Brillouin zone, conditions are identified for the appearance of pure zero density of states regions that separate intermediate band from the rest of the conduction band. For one realistic QD array, we have estimated all important absorption spectra in IBSC, and most important, radiative and nonradiative scattering times. Under radiative limit approximation, we have estimated efficiency of such IBSC to be 39%.
Relaxation and cross section effects in valence band photoemission spectroscopy
International Nuclear Information System (INIS)
Various problems relating to the interpretation of valence band x-ray photoemission (XPS) spectra of solids are discussed. The experiments and calculations reported herein deal with the following questions: (1) To what extent do many-body effects manifest themselves in an XPS valence band spectrum, and thus invalidate a direct comparison between the photoemission energy distribution, I(E), and the density of states, N(E), calculated on the basis of ground-state one-electron theory. (2) The effect of the binding-energy-dependent photoemission cross section on I(E) at XPS energies. (3) In favorable cases indicated by (1) and (2) we examine the effect of the interaction of the crystal field with the apparent spin-orbit splittings of core levels observed in XPS spectra. (4) The use of tight binding band structure calculations to parameterize the electronic band structure from XPS and other data is described. (5) The use of high energy angle-resolved photoemission on oriented single crystals to gain orbital symmetry information is discussed. (6) The evolution of the shape of the photoemission energy distribution (of polycrystalline Cu) as a function of photon energy from 50 less than or equal h ? less than or equal 175 is discussed
Dynamic deformation theory and mutiphonon vibrational bands in 154 Gd
International Nuclear Information System (INIS)
Dynamic deformation theory based on a pairing plus quadrupole model (DPPQ model) is extended to 25 levels belonging to various multiphonon vibrational bands in 154Gd. Although the calculated excited band energies are too high by factors of 1.4-1.7, there is generally reasonable agreement with the experimental energies, B(E2) values, magnetic moments, E2-M1 mixing ratios and E0 moments. Many new values are predicted. A brief comparison with some results derived from a new version of dynamic deformation theory, the so-called DNSB model, is also given
An algebraic approach to scattering and band structure problems
International Nuclear Information System (INIS)
It is shown that both bound and scattering states of a class of potentials are related to the unitary representations of certain groups. For such systems the scattering matrix can be calculated in a completely algebraic way through the use of the Euclidean group to describe asymptotic behaviour. The band structures associated with a family of periodic potentials can also be obtained from the group theory. These results suggest that an algebraic approach to scattering and band structure problems similar to that applied to bound states is possible
Multiple chiral doublet bands of identical configuration in 103Rh
Kuti, I; Timar, J; Sohler, D; Zhang, S Q; Zhang, Z H; Zhao, P W; Meng, J; Starosta, K; Koike, T; Paul, E S; Fossan, D B; Vaman, C
2014-01-01
Three sets of chiral doublet band structures have been identified in the 103Rh nucleus. The properties of the observed chiral doublet bands are in good agreement with theoretical results obtained using constrained covariant density functional theory and particle rotor model calculations. Two of them belong to an identical configuration, and provide the first experimental evidence for a novel type of multiple chiral doublets, where an "excited" chiral doublet of a configuration is seen together with the "yrast" one. This observation shows that the chiral geometry in nuclei can be robust against the increase of the intrinsic excitation energy.
Superdeformed band in the $N = Z+4$ nucleus $^{40}$Ar: A projected shell model analysis
Yang, Ying-Chun; Liu, Yan-Xin; Sun, Yang; Guidry, Mike
2015-01-01
It has been debated whether the experimentally-identified superdeformed rotational band in $^{40}$Ar [E. Ideguchi, et al., Phys. Lett. B 686 (2010) 18] has an axially or triaxially deformed shape. Projected shell model calculations with angular-momentum-projection using an axially-deformed basis are performed up to high spins. Our calculated energy levels indicate a perfect collective-rotor behavior for the superdeformed yrast band. However, detailed analysis of the wave fun...
International Nuclear Information System (INIS)
Properties of high-spin states in the neutron deficient even-even Se isotopes were studied extensively in the past and shape coexistence was found to be responsible for the irregularities in the yrast band of 74Se. Recently, the yrast band was observed up to a tentative 24+ level, where the two highest levels contribute to an unusually strong upbend in the kinematical moment of inertia. In order to investigate this behavior in more detail, a new study of high-spin states in 74Se was initiated. The nucleus was produced via the 64Cu(12C,p2n)74Se reaction at a beam energy of 50 MeV, and the emitted ? rays were detected with the Pittsburgh-Florida State Universities detector array. On the basis of coincidence data new states above the 20+ member of the yrast sequence and a new sideband of positive parity feeding into the yrast band have been found. Moreover, a new band of negative parity on top of a level at 3840.9 keV has been introduced. Three other sequences of positive and negative parity could be extended to higher spin states. The observed change of structure in the bands is interpreted as due to g9/2 quasiparticle alignments
Charge state of the O$_{2}$ molecule during silicon oxidation through hybrid functional calculations
Alkauskas, Audrius; Broqvist, Peter; Pasquarello, Alfredo
2008-01-01
We study the charge state of the diffusing O$_2$ molecule during silicon oxidation through hybrid functional calculations. We calculate charge transition levels of O$_2$ in bulk SiO$_2$ and use theoretical band offsets to align these levels with respect to the Si band edges. To overcome the band-gap problem of semilocal density fuctionals, we employ hybrid functionals with both predefined and empirically adjusted mixing coefficients. We find that the charge transition level ...
Self-consistent calculation of density of states in impure semiconductors
Energy Technology Data Exchange (ETDEWEB)
Grill, R. (Inst. of Physics, Charles Univ., Prague (Czechoslovakia))
1990-12-01
Using the Kadanoff-Baym Green's function formalism the density of states function is calculated. The calculation is performed for the heavy hole band and screened charged impurity scattering in the Born approximation. The results are shown for p-HgCdTe semiconductor. It is argued that a qualitative change of the band near the edge is essential for a band occupation. (orig.).
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,...
Zhu, Zhen; Xiao, Jiamin; Sun, Haibin; Hu, Yue; Cao, Ronggen; Wang, Yin; Zhao, Li; Zhuang, Jun
2015-09-01
We used the coherent potential approximation to investigate the band structures of group-IV semiconductor alloys, including SixGe1-x, Ge1-ySny and SixGe1-x-ySny. The calculations for SixGe1-x prove the reliability and accuracy of the method we used. For Ge1-ySny, 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 SixGe1-x-ySny, 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 SixGe1-x-ySny in the range of 0 < x? 0.20, and the indirect-direct crossover line in the compositional space has the quadratic form of y = 3.4x(2) + 1.11x + 0.07, not the linear form as suggested before. Furthermore, for the Ge lattice-matched alloy Ge1-x(Si0.79Sn0.21)X, our results show that those with 0.18 < X < 0.253 have band gaps larger than 0.8 eV at room temperature. PMID:26222374
The yrast rotational bands of selenium-74 and krypton-77
Energy Technology Data Exchange (ETDEWEB)
Gross, C.J.
1987-01-01
New states in the positive parity yrast bands of {sup 74}Se and {sup 77}Kr have been observed with the reactions {sup 52}Cr({sup 28}Si,{alpha}2p){sup 74}Se and {sup 52}Cr ({sup 28}Si,2pn){sup 77}Kr at 98 MeV. The target consisted of approximately 1 mg/cm{sup 2} natural chromium (84% {sup 52}Cr abundance) evaporated on a thick lead backing. The new states extend the known level scheme of {sup 74}Se up to I{sup {pi}} = (22{sup +}) and most of the transitions in the other previously reported bands have been seen. For the states I{sup {pi}} {ge} 6{sup +} the spectrum shows a relatively constant moment of inertia parameter (h{sup 2}/2{Theta}) = 27.8 {plus minus} 0.5 keV. Excited positive parity states up to spin (41/2) have been observed in {sup 77}Kr. {Delta}I = 1 transitions have been identified throughout the positive parity band. The energies, mixing ratios and B(M1) transition rates for these transitions alternate in size as the spin increases. A cranked shell model analysis was performed along with Strutinsky-Bogolyubov cranking calculations. The observed decrease in the signature splitting of the {nu}g{sub 9/2} band has been attributed to a band crossing due to an aligning pair of g{sub 9/2} protons. Prolate quadrupole deformations of {beta}{sub 2} = 0.34 for the ground band and {beta}{sub 2} = 0.26 for the first excited band are predicted. This band crossing is associated with a shape change caused by the polarization effect of aligned quasiparticles.
The Yrast Rotational Bands of SELENIUM-74 and KRYPTON-77
Gross, Carl J.
1987-09-01
New states in the positive parity yrast bands of ^{74}Se and ^{77}Kr have been observed with the reactions ^{52}Cr( ^{28}Si,alpha 2p)^{74}Se and ^{52}Cr(^ {28}Si,2pn)^{77} Kr at 98 MeV. The target consisted of approximately 1 mg/cm^2 natural chromium (84% ^{52}Cr abundance) evaporated on a thick lead backing. The new states extend the known level scheme of ^{74}Se up to I ^{pi} = (22^+ ) and most of the transitions in the other previously reported bands have been seen. For the states I ^{pi} >=q 6^+ the spectrum shows a relatively constant moment of inertia parameter (hbar ^2/2Theta) = 27.8 +/- 0.5 keV. Excited positive parity states up to spin (41/2) have been observed in ^{77}Kr. DeltaI = 1 transitions have been identified throughout the positive parity band. The energies, mixing ratios and B(M1) transition rates for these transitions alternate in size as the spin increases. A cranked shell model analysis was performed along with Strutinsky-Bogolyubov cranking calculations. The observed decrease in the signature splitting of the nug_ {9/2} band has been attributed to a band crossing due to an aligning pair of g_{9/2 } protons. Prolate quadrupole deformations of beta_2 = 0.34 for the ground band and beta_2 = 0.26 for the first excited band are predicted. This band crossing is associated with a shape change caused by the polarization effect of aligned quasiparticles.
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.
Distillation Calculations with a Programmable Calculator.
Walker, Charles A.; Halpern, Bret L.
1983-01-01
Describes a three-step approach for teaching multicomponent distillation to undergraduates, emphasizing patterns of distribution as an aid to understanding the separation processes. Indicates that the second step can be carried out by programmable calculators. (A more complete set of programs for additional calculations is available from the…
Holographic Multi-Band Superconductor
Huang, Ching-Yu; Lin, Feng-Li; Maity, Debaprasad
2011-01-01
We propose a gravity dual for the holographic superconductor with multi-band carriers. Moreover, the currents of these carriers are unified under a global flavored SO(3) symmetry, which is dual to the bulk SO(3) gauge symmetry. We study the phase diagram of our model, and find it qualitatively agrees with the one for the realistic 2-band superconductor, such as $MgB_2$. We also identify the bulk field dual to the electromagnetic $U(1)_{EM}$ current, which should be invariant...
Kajikawa, Y.
2014-05-01
Experimental data on the thermoelectric properties of p-type CoSb3 reported by Caillat et al. [J. Appl. Phys. 80, 4442 (1996)] have been analyzed, assuming not only a pair of the first valence (v1) and the first conduction (c1) bands but also the second valence (v2) and the second conduction (c2) bands. By taking into account the excitation of carriers into the v2 and the c2 bands, the behavior of the Hall coefficient as well as that of the Seebeck coefficient at high temperatures is well explained. By taking into account the nonparabolicity of the v1 band, the temperature dependence of mobility is well explained with assuming scattering due to acoustic phonons, nonpolar and polar optical phonons, and ionized impurities. Furthermore, various material parameters of CoSb3, such as the band-gap energy, effective masses, and deformation potentials, have been deduced from fitting the calculation to the experimental data on the temperature dependences of the Hall coefficient, the mobility, and the Seebeck coefficient. Among them, the band-gap energy and the effective mass of the v1 band have been corrected from the original values estimated by Caillat et al. In addition, it is shown that the experimental data on the hole-concentration dependences of both the room-temperature Seebeck coefficient and the cyclotron mass are well reproduced by the theoretical calculation using the deduced values for the nonparabolic v1 band.
Band gaps and radii of metallic zigzag single wall carbon nanotubes
International Nuclear Information System (INIS)
The band gaps of metallic zigzag single wall carbon nanotubes are difficult to determine both experimentally and theoretically: Experimentally, it is hard to synthesize pure single carbon nanotubes individually, and theoretically, the main approach, density functional theory is not good at the prediction of a band gap. Here we show a density hybrid functional theory calculation using 6–31 G† basis set to yield accurate band gaps. Consequently, an analytical expression was obtained, indicating that the band gap is related to the nearest-neighbor distance and the radius. These findings should shed light on the electron structure of the single wall carbon nanotubes
Photonic band gaps of two-dimensional ZnO nanorod photonic crystals
International Nuclear Information System (INIS)
We have calculated the photonic band structures of two-dimensional periodic arrays of well aligned ZnO nanorods with a frequency dependent dielectric constant. The ZnO nanorod photonic crystal can exhibit a photonic band gap in the visible range. The dependence of the band gap on the period and radii of the nanorods was shown. From the finite difference time domain simulations, we also showed that the luminescence of a ZnO nanorod could be altered by the photonic band gap effect. Controlling the luminescence of ZnO nanorods can be useful in the implementation of efficient light emitting devices
Band structures in odd-even bromine isotopes A=77-81
International Nuclear Information System (INIS)
The collective bands in odd-even bromine isotopes A=77, 79 and 81 are studied within our deformed configuration-mixing shell model based on self-consistently derived single-particle states. The calculated K=3/2- negative-parity ground band and the K=9/2+ positive-parity band agree reasonably well with experiment. An attempt is made to study the structure of the three quasi-particle band of high-spin states built on the J=13/2- level in these nuclei. (orig.)
Discrete Linking Transitions For A Superdeformed Band In The A ? 80 Region
International Nuclear Information System (INIS)
The yrast superdeformed (SD) band in 84Zr has been linked to states of normal deformation (ND) by three single-step ? decays. The spins and parity of the SD band were determined through angular distributions of two of these links. The properties of this band and its decay to ND states are compared with linked SD bands in other mass regions. SD intensity profiles, calculated SD-ND potential barriers, and results of a statistical-decay analysis suggest there is significant SD-ND mixing involved
Crossing of shears bands in 196Pb
International Nuclear Information System (INIS)
High-spin states in 196Pb have been populated using the reaction 170Er(30Si, 4n). The previously observed shear bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin. (orig.)
Dual-Band Tunable Recursive Active Filter
Segovia Vargas, Daniel; García Pérez, Oscar Alberto; González Posadas, Vicente; Aznar Ballesta, Francisco
2011-01-01
This letter presents a novel recursive active filter topology that provides dual-band performance, with independent tuning capability in both bands. The dual-band operation is achieved by using two independent feedback lines. Additionally, linear phase shifters based on left-handed cells are included in these two branches in order to tune the center frequency of both pass bands.
Programmable calculator stress analysis
International Nuclear Information System (INIS)
Advanced programmable alphanumeric calculators are well suited for closed-form calculation of pressure-vessel stresses. They offer adequate computing power, portability, special programming features, and simple interactive execution procedures. Representative programs that demonstrate calculator capabilities are presented. Problems treated are stress and strength calculations in thick-walled pressure vessels and the computation of stresses near head/pressure-vessel junctures
Large band gap bowing of InxGa1-xN alloys
McCluskey, M. D.; Van de Walle, C. G.; Master, C. P.; Romano, L. T.; Johnson, N. M.
1998-05-01
Band gap measurements have been performed on strained InxGa1-xN epilayers with x?0.12. The experimental data indicate that the bowing of the band gap is much larger than commonly assumed. We have performed first-principles calculations for the band gap as a function of alloy composition and find that the bowing is strongly composition dependent. At x=0.125 the calculated bowing parameter is b=3.5 eV, in good agreement with the experimental values.
Modification of Casimir Forces Due to Band Gaps in Periodic Structures
Villarreal, C.; Esquivel-Sirvent, R.; Cocoletzi, G. H.
The Casimir force between inhomogeneous slabs that exhibit a band-like structure is calculated. The slabs are made of basic unit cells each made of two layers of different materials. As the number of unit cells increases the Casimir force between the slabs changes, since the reflectivity develops a band-like structure characterized by frequency regions of high reflectivity. This is also evident in the difference of the local density of states between free and boundary distorted vacuum, that becomes maximum at frequencies corresponding to the band gaps. The calculations are restricted to vacuum modes with wave vectors perpendicular to the slabs.
Corrugated flat band as an origin of large thermopower in hole doped PtSb2
Directory of Open Access Journals (Sweden)
Kouta Mori
2012-12-01
Full Text Available The origin of the recently discovered large thermopower in hole-doped PtSb2 is theoretically analyzed based on a model constructed from first principles band calculation. It is found that the valence band dispersion has an overall flatness combined with some local ups and downs, which gives small Fermi surfaces scattered over the entire Brillouin zone. The Seebeck coefficient is calculated using this model, which gives good agreement with the experiment. We conclude that the good thermoelectric property originates from this “corrugated flat band”, where the coexistence of large Seebeck coefficient and large electric conductivity is generally expected.
Band-engineered SrTiO{sub 3} nanowires for visible light photocatalysis
Energy Technology Data Exchange (ETDEWEB)
Fu, Q.; He, T.; Li, J. L.; Yang, G. W. [State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Optoelectronic and Functional Composite Materials, Nanotechnology Research Center, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong (China)
2012-11-15
We have theoretically investigated the structural, electronic, and optical properties of perovskite SrTiO{sub 3} nanowires for use in visible light photocatalytic applications using pseudopotential density-functional theory calculations. The electronic structure calculations show that the band gap is modified in the SrTiO{sub 3} nanowires compared with that of the bulk. For TiO{sub 2}-terminated nanowires, the mid-band states induced by the combination of oxygen and strontium atoms on the surface lead to a shift in the valence band toward the conduction band without interference from the edge of the conduction band, which reduces the band gap. On the contrary, the electronic states induced by the combination of oxygen and strontium atoms on the surface of SrO-terminated nanowires lead to a shift in the conduction band toward the valence band. The calculated optical results indicate that the absorption edge of the nanowires shift towards the red-light region. These theoretical results suggest that perovskite SrTiO{sub 3} nanowires are promising candidates for use in visible light photocatalytic processes such as solar-assisted water splitting reactions.
Band-engineered SrTiO3 nanowires for visible light photocatalysis
International Nuclear Information System (INIS)
We have theoretically investigated the structural, electronic, and optical properties of perovskite SrTiO3 nanowires for use in visible light photocatalytic applications using pseudopotential density-functional theory calculations. The electronic structure calculations show that the band gap is modified in the SrTiO3 nanowires compared with that of the bulk. For TiO2-terminated nanowires, the mid-band states induced by the combination of oxygen and strontium atoms on the surface lead to a shift in the valence band toward the conduction band without interference from the edge of the conduction band, which reduces the band gap. On the contrary, the electronic states induced by the combination of oxygen and strontium atoms on the surface of SrO-terminated nanowires lead to a shift in the conduction band toward the valence band. The calculated optical results indicate that the absorption edge of the nanowires shift towards the red-light region. These theoretical results suggest that perovskite SrTiO3 nanowires are promising candidates for use in visible light photocatalytic processes such as solar-assisted water splitting reactions.
Collective band properties in actinide nuclei well deformed
International Nuclear Information System (INIS)
In actinides, proton i13/2 orbitals and neutron j15/2 orbitals are both near Fermi surface. At a great rotation speed, driving and Coriolis forces change the surface forces, in particular, they lower pairing forces inside the nucleus. The use of Coulomb excitation with the help of heavy and very heavy projectiles such as 32S, 84Kr, 142Nd, 208Pb at 232Th together with the most recent techniques of spectroscopy allowed to populate yrast bands of 230Th, 232Th, 235U and 237Np nuclei up to high spin states and together the even-even nuclei states in different collective bands. Experimental results have been analyzed in the frame of the different current models. The low spin states of rotational bands have been reproduced in a previous calculation using the nucleon-nucleon effective interaction of Skyrme III
Extensive ?-ray spectroscopy of band structures in 3062Zn32
Gellanki, J.; Rudolph, D.; Ragnarsson, I.; Andersson, L.-L.; Andreoiu, C.; Carpenter, M. P.; Ekman, J.; Fahlander, C.; Johansson, E. K.; Kardan, A.; Reviol, W.; Sarantites, D. G.; Seweryniak, D.; Svensson, C. E.; Waddington, J. C.
2012-09-01
An experimental study of the 62Zn nucleus has been performed by combining the data sets from four fusion-evaporation reaction experiments. Apart from the previously published data, the present results include ten new rotational band structures and two more superdeformed bands. The Gammasphere Ge-detector array in conjunction with the 4? charged-particle detector array Microball allowed for the detection of ? rays in coincidence with evaporated light particles. The deduced level scheme includes some 260 excited states, which are connected with more than 450 ?-ray transitions. Spins and parities of the excited states have been determined via directional correlations of ? rays emitted from oriented states. The experimental characteristics of the rotational bands are analyzed and compared with results from cranked Nilsson-Strutinsky calculations. The present analysis, combined with available experimental results in the A˜60 mass region, can be used to improve the current set of Nilsson parameters in the N=3 and N=4 oscillator shells.
The electronic band structure of CoS{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Wu Ning [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Losovyj, Ya B [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Wisbey, David [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Belashchenko, K [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Manno, M [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States); Wang, L [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States); Leighton, C [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States); Dowben, P A [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States)
2007-04-16
Angle-resolved and energy-dependent photoemission was used to study the band structure of paramagnetic CoS{sub 2} from high-quality single-crystal samples. A strongly dispersing hybridized Co-S band is identified along the {gamma}-X line. Fermi level crossings are also analysed along this line, and the results are interpreted using band structure calculations. The Fermi level crossings are very sensitive to the separation in the S-S dimer, and it is suggested that the half-metallic gap in CoS{sub 2} may be controlled by the bonding-antibonding splitting in this dimer, rather than by exchange splitting on the Co atoms.
Band structure analysis in SiGe nanowires
Energy Technology Data Exchange (ETDEWEB)
Amato, Michele [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy); Palummo, Maurizia [European Theoretical Spectroscopy Facility (ETSF) (Italy); CNR-INFM-SMC, Dipartimento di Fisica, Universita di Roma, ' Tor Vergata' , via della Ricerca Scientifica 1, 00133 Roma (Italy); Ossicini, Stefano, E-mail: stefano.ossicini@unimore.it [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy) and Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy) and European Theoretical Spectroscopy Facility - ETSF (Italy) and Centro Interdipartimentale ' En and Tech' , Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy)
2012-06-05
One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.
Search for excited superdeformed bands in {sup 151}Dy
Energy Technology Data Exchange (ETDEWEB)
Nisius, D.; Janssens, R.V.F.; Crowell, B. [and others
1995-08-01
Following the first report of superdeformed (SD) bands with identical transition energies in the pairs ({sup 151}Tb*,{sup 152}Dy), ({sup 150}Gd*, {sup 151}Tb) and ({sup 153}Dy*, {sup 152}Dy) (where * denotes an excited SD band), it was proposed by Nazarewicz et al. that the observations could be understood in a strong-coupling approach if pseudo SU(3) symmetry were invoked. In this model there are three limiting values of the decoupling parameter; i.e. a = 0, {plus_minus}1. In the first two cases mentioned above the pairs of bands have nearly identical transition energies and are interpreted as proton excitations involving the [200]1/2 pseudospin orbital coupled to the {sup 152}Dy core, for which the value of the decoupling parameter is calculated to be a =+1.
Radiofrequency signal affects alpha band in resting electroencephalogram.
Ghosn, Rania; Yahia-Cherif, Lydia; Hugueville, Laurent; Ducorps, Antoine; Lemaréchal, Jean-Didier; Thuróczy, György; de Seze, René; Selmaoui, Brahim
2015-04-01
The aim of the present work was to investigate the effects of the radiofrequency (RF) electromagnetic fields (EMFs) on human resting EEG with a control of some parameters that are known to affect alpha band, such as electrode impedance, salivary cortisol, and caffeine. Eyes-open and eyes-closed resting EEG data were recorded in 26 healthy young subjects under two conditions: sham exposure and real exposure in double-blind, counterbalanced, crossover design. Spectral power of EEG rhythms was calculated for the alpha band (8-12 Hz). Saliva samples were collected before and after the study. Salivary cortisol and caffeine were assessed by ELISA and HPLC, respectively. The electrode impedance was recorded at the beginning of each run. Compared with the sham session, the exposure session showed a statistically significant (P GSM-EMFs of a mobile phone affect the alpha band within spectral power of resting human EEG. PMID:25695646
International Nuclear Information System (INIS)
The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyrite-type semiconductor (CuGaS2) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical reflectivity and absorption coefficient of the materials of interest. Calculations for the host semiconductor are in good agreement with experimental results within the limitations of the approach. We find, as desired, that because of the intermediate band, the new Ti-substituted material would be able to absorb photons of energy lower than the band-gap of the host chalcopyrite. We also analyze the partial contributions to the main peaks of its spectrum
Intermediate-Frequency-to-Video-Band Converter
Ham, N. C.; Chavez, V. M.; Chen, V. S.; Sato, T.
1986-01-01
Analog and digital circuits combined to frequency-convert from intermediate frequencies directly to video-band frequencies to meet stringent requirements. IF-to-video-band converter operates on principle of signal-band cancellation in phase-quadrature circuits. Downconverts intermediate frequencies directly to video-band frequencies to near-zero frequency with good image-band rejection and low phase variation within passband.
Residual stress dependant anisotropic band gap of various (hkl) oriented BaI2 films
International Nuclear Information System (INIS)
The thermally evaporated layer structured BaI2 grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48–3.43?eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (?0.071?eV/GPa) found to be significantly higher than that calculated (?0.047?eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass me*=0.66m0 and the hole effective mass mh*=0.53m0 have been determined from the calculated band structure
Residual stress dependant anisotropic band gap of various (hkl) oriented BaI2 films
Kumar, Pradeep; Gulia, Vikash; Vedeshwar, Agnikumar G.
2013-11-01
The thermally evaporated layer structured BaI2 grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48-3.43 eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (-0.071 eV/GPa) found to be significantly higher than that calculated (-0.047 eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass me*=0.66m0 and the hole effective mass mh*=0.53m0 have been determined from the calculated band structure.
Resistive band for turbomachine blade
Energy Technology Data Exchange (ETDEWEB)
Roberts, Herbert Chidsey; Taxacher, Glenn Curtis
2015-08-25
A turbomachine system includes a rotor that defines a longitudinal axis of the turbomachine system. A first blade is coupled to the rotor, and the first blade has first and second laminated plies. A first band is coupled to the first blade and is configured to resist separation of the first and second laminated plies.
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."
DFT calculations with the exact functional
Burke, Kieron
2014-03-01
I will discuss several works in which we calculate the exact exchange-correlation functional of density functional theory, mostly using the density-matrix renormalization group method invented by Steve White, our collaborator. We demonstrate that a Mott-Hubard insulator is a band metal. We also perform Kohn-Sham DFT calculations with the exact functional and prove that a simple algoritm always converges. But we find convergence becomes harder as correlations get stronger. An example from transport through molecular wires may also be discussed. Work supported by DOE grant DE-SC008696.
Band structure of fcc-C60 solid state crystal study
Directory of Open Access Journals (Sweden)
S Javanbakht
2009-09-01
Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of ? and ? bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.
Scientific Electronic Library Online (English)
Juan Carlos, Salcedo-Reyes.
2008-07-01
Full Text Available Aunque la descripción de las aleaciones ternarias semiconductoras se hace tradicionalmente asumiendo la aproximación de compuesto pseudo-binario. Para el caso de aleaciones artificiales de compuestos II-VI y III-V, en las cuales se ha reportado un ordenamiento inducido por el crecimiento, una aproxi [...] mación de este tipo no es aplicable, de modo que, con el fin de hacer una descripción adecuada de las propiedades ópticas y electrónicas de dichas aleaciones artificiales, se debe asumir una descripción atomística que tenga en cuenta la estructura local. En particular, para la aleación ordenada de Zn0.5Cd0.5Se, el cambio de simetría implica que se debe usar una estructura tetragonal simple, dando lugar, principalmente, a dos efectos: i) disminución de la brecha prohibida del material y ii) un desdoblamiento en el máximo de la banda de valencia. En este trabajo se calcula la estructura de bandas de la aleación ordenada de Zn0.5Cd0.5Se usando la aproximación semi-empírica de enlace fuerte teniendo en cuenta interacción a segundos vecinos y se compara con la estructura de bandas obtenida por el método FP-LAPW (full-potential linearized augmentedplane wave). Se obtiene una buena concordancia de las principales características entre las estructuras de bandas calculadas por el método semi-empírico y el método ab initio. Abstract in english Usually, semiconductor ternary alloys are studied via a pseudo-binary approach in which the semiconductor is described like a crystalline array were the cation/anion sub-lattice consist of a random distribution of the cationic/anionic atoms. However, in the case of reported III-V and II-VI artificia [...] l structures, in which an ordering of either the cations or the anions of the respective fcc sub-lattice is involved, a pseudo-binary approach can no longer be employed, an atomistic point of view, which takes into account the local structure, must be used to study the electronic and optical properties of these artificial semiconductor alloys. In particular, the ordered Zn0.5Cd0.5Se alloy has to be described as a crystal with the simple-tetragonal Bravais lattice with a composition equal to the zincblende random ternary alloy. The change of symmetry properties of the tetragonal alloy, in relation to the cubic alloy, results mainly in two effects: i) reduction of the banned gap, and ii) crystal field cleavage of the valence band maximum. In this work, the electronic band structure of the ordered Zn0.5Cd0.5Se alloy is calculated using a second nearest neighbor semi-empirical tight binding method. Also, it is compared with the electronic band structure obtained by FP-LAPW (fullpotential linearized augmented-plane wave) method.
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 in four bands. The first and second bands contain closed sheets, degenerate along a plane in the absence of spin-orbit splitting. The third band contains a multiply-connected sheet. The fourth band consists of undulating columns, degenerate along a plane with the third band in the absence of spin-orbit splitting, and of another closed sheet. Earlier de Haas-van Alphen results are explained semiquantitatively by the model, which also accounts for open orbits seen in high-field magnetoresistance experiments.
Epitaxial strain tuning of polarization and band gap in perovksite SnTiO3
Parker, William; Nakhmanson, Serge; Rondinelli, James
2012-02-01
Lead toxicity has motivated theoretical studies of a tin-based perovskite ferroelectric material. Density-functional calculations predict a polar perovksite ground state for SnTiO3. Simulated epitaxial strain up to ±2% tunes both the magnitude of the polar distortion, its direction, and the electronic band gap --- compressive bi-axial strain creates the largest polar distortions, which occur entirely in the growth direction, while tensile strain reorients the polar displacements, enlarging the band gap. Projected densities of states indicate that the broken four-fold symmetry of the non-growth-oriented distortion allows Ti dxy bands to mix with O px bands, further separating the valence band maximum and conduction band minimum. Comparing Sn and Pb in the perovskite titanate phases shows similar trends and suggests that SnTiO3 ferroelectrics may be viable thin-film alternatives to Pb-based oxides.
Predicted photonic band gaps in diamond-lattice crystals built from silicon truncated tetrahedrons
Woldering, Léon A; Elwenspoek, Miko C
2011-01-01
Recently, a silicon micromachining method to produce tetrahedral silicon particles was discovered. In this report, we determine the optical properties of diamond-lattice photonic crystals when assembled from such particles. The optical properties are found using band structure calculations. We show that crystal structures built from such silicon tetrahedra are expected to display small stop gaps. Wide photonic band gaps appear when truncated tetrahedral particles are used to build the photonic crystals. With such truncated tetrahedral particles, a band gap with a width of 23.6% can be achieved, which is more than twice as wide compared to band gaps in self-assembled diamond-lattices of hard-spheres. The width of the band gap is insensitive to small deviations from the optimal amount of truncation. This works paves the way to a new class of silicon diamond-lattice band gap crystals that can be obtained through self-assembly.
Theory of Band Warping and its Effects on Thermoelectronic Transport Properties
Mecholsky, Nicholas A; Pegg, Ian L; Fornari, Marco
2014-01-01
Optical and transport properties of materials depend heavily upon features of electronic band structures in proximity to energy extrema in the Brillouin zone (BZ). Such features are generally described in terms of multi-dimensional quadratic expansions and corresponding definitions of effective masses. Multi-dimensional expansions, however, are permissible only under strict conditions that are typically violated by degenerate bands and even some non-degenerate bands. Suggestive terms such as "band warping" or "corrugated energy surfaces" have been used to refer to such situations and ad hoc methods have been developed to treat them. While numerical calculations may reflect such features, a complete theory of band warping has not been developed. We develop a generally applicable theory, based on radial expansions, and a corresponding definition of angular effective mass. Our theory also accounts for effects of band non-parabolicity and anisotropy, which hitherto have not been precisely distinguished from, if n...
EHT calculation of the electronic states for the ionic crystals
International Nuclear Information System (INIS)
The cluster model calculations of the electronic structure for the ionic crystals (LiF, NaCl and KCl) are carried out by means of the charge self-consistent Extended Huckel Theory (EHT) including the Madelung Potential. The results show that the 6 x 6 x 6 cluster can be used to simulate the real crystal. The calculated band gaps and the widths of the valence bands are in good agreement with the experimental data. The total and local density of states display the presence of the surface states in the band gap. The contribution to the surface states are almost all from the alkali atoms at the surface. The surface states near the bottom of the conduction band are essentially from the s state and a part of p state of the alkali atoms at the surface
Superdeformed band in the $N = Z+4$ nucleus $^{40}$Ar: A projected shell model analysis
Yang, Ying-Chun; Sun, Yang; Guidry, Mike
2015-01-01
It has been debated whether the experimentally-identified superdeformed rotational band in $^{40}$Ar [E. Ideguchi, et al., Phys. Lett. B 686 (2010) 18] has an axially or triaxially deformed shape. Projected shell model calculations with angular-momentum-projection using an axially-deformed basis are performed up to high spins. Our calculated energy levels indicate a perfect collective-rotor behavior for the superdeformed yrast band. However, detailed analysis of the wave functions reveals that the high-spin structure is dominated by mixed 0-, 2-, and 4-quasiparticle configurations. The calculated electric quadrupole transition probabilities reproduce well the known experimental data and suggest a reduced, but still significant, collectivity in the high spin region. The deduced triaxial deformation parameters are small throughout the entire band, suggesting that triaxiality is not very important for this superdeformed band.
Photovoltaic properties of low band gap ferroelectric perovskite oxides
Huang, Xin; Paudel, Tula; Dong, Shuai; Tsymbal, Evgeny
2015-03-01
Low band gap ferroelectric perovskite oxides are promising for photovoltaic applications due to their high absorption in the visible optical spectrum and a possibility of having large open circuit voltage. Additionally, an intrinsic electric field present in these materials provides a bias for electron-hole separation without requiring p-n junctions as in conventional solar cells. High quality thin films of these compounds can be grown with atomic layer precision allowing control over surface and defect properties. Initial screening based on the electronic band gap and the energy dependent absorption coefficient calculated within density functional theory shows that hexagonal rare-earth manganites and ferrites are promising as photovoltaic absorbers. As a model, we consider hexagonal TbMnO3. This compound has almost ideal band gap of about 1.4 eV, very high ferroelectric Curie temperature, and can be grown epitaxially. Additionally hexagonal TbMnO3 offers possibility of coherent structure with transparent conductor ZnO. We find that the absorption is sufficiently high and dominated by interband transitions between the Mn d-bands. We will present the theoretically calculated photovoltaic efficiency of hexagonal TbMnO3 and explore other ferroelectric perovskite oxides.
Band structure of CdTe under high pressure
International Nuclear Information System (INIS)
The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (PM = 1.935 Mbar) and the corresponding reduced volume ((V/V0)M = 0.458) are estimated. Metallization occurs via direct closing of band gap at ? point. (author)
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.
Table of superdeformed nuclear bands and fission isomers
International Nuclear Information System (INIS)
A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in 152Dy was predicted for ?2-0.65. Subsequently, a discrete set of ?-ray transitions in 152DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of ?-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra
Strain sensitivity of band gaps of Sn-containing semiconductors
DEFF Research Database (Denmark)
Li, Hong; Castelli, Ivano Eligio
2015-01-01
Tuning of band gaps of semiconductors is a way to optimize materials for applications within photovoltaics or as photocatalysts. One way to achieve this is through applying strain to the materials. We investigate the effect of strain on a range of Sn-containing semiconductors using density functional theory and many-body perturbation theory calculations. We find that the band gaps of bulk Sn oxides with SnO6 octahedra are highly sensitive to volumetric strain. By applying a small isotropic strain of 2% (-2%), a decrease (increase) of band gaps as large as 0.8 to 1.0 eV are obtained. We attribute the ultrahigh strain sensitivity to the pure Sn s-state character of the conduction-band edges. Other Sn-containing compounds may show both increasing and decreasing gaps under tensile strain and we show that the behavior can be understood by analyzing the role of the Sn s states in both the valence and the conduction bands.
Tunable band gaps in bilayer graphene-BN heterostructures
Ramasubramaniam, Ashwin; Naveh, Doron; Towe, ELias
2010-01-01
We investigate band-gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV, and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. The calculations suggest that the graphene-boron nitride heterostructures could ...
Generalized pseudopotential theory of d-band metals
International Nuclear Information System (INIS)
The generalized pseudopotential theory (GPT) of metals is reviewed with emphasis on recent developments. This theory, which attempts to rigorously extend to d-band metals the spirit of conventional simple-metal pseudopotential perturbation theory, has now been optimized and fully integrated with the Kohn-Sham local-density-functional formalism, allowing for systematic first-principles calculations. Recent work on the problems of cohesion, lattice dynamics, structural phase stability, pressure- and temperature-induced phase transitions, and melting is discussed
Pressure-induced s-band ferromagnetism in alkali metals
Pickard, Chris J.; Needs, R. J.
2011-01-01
First-principles density-functional-theory calculations show that compression of alkali metals stabilizes open structures with localized interstitial electrons which may exhibit a Stoner-type instability towards ferromagnetism. We find ferromagnetic phases of the lithium-IV-type, simple cubic, and simple hexagonal structures in the heavier alkali metals, which may be described as s-band ferromagnets. We predict that the most stable phases of potassium at low temperatures and...
Band-theoretical prediction of magnetic anisotropy in uranium monochalcogenides
Shishidou, Tatsuya; Oguchi, Tamio
2000-01-01
Magnetic anisotropy of uranium monochalcogenides, US, USe and UTe, is studied by means of fully-relativistic spin-polarized band structure calculations within the local spin-density approximation. It is found that the size of the magnetic anisotropy is fairly large (about 10 meV/unit formula), which is comparable with experiment. This strong anisotropy is discussed in view of a pseudo-gap formation, of which crucial ingredients are the exchange splitting of U 5f states and t...
Population of rotational bands in superheavy nuclei
International Nuclear Information System (INIS)
The spectroscopy of superheavy elements (SHE) is very important for the modern nuclear physics. Comparing the structure predictions of different theoretical models with the experimental data, one can find out their applicability in the region of SHE. This can be very useful for the determination of the next proton magic number beyond Z = 82. Using the statistical approach, we study the population of rotational bands in super-heavy nuclei produced in fusion-evaporation reactions. The reactions 208Pb(48Ca, 2n)254No, 206Pb(48Ca, 2n)252No, and 204Hg(48Ca, 2n)250Fm are considered. The population cross section of state L+ depends on survival of the compound nucleus against fission. The calculated relative intensities of E2-transitions at different spins, which can be compared with the experimental values, are defined by these partial population cross sections. Fermi-gas model is used for the calculation of level densities, and damping of shell effects with excitation energy and angular momentum is taking into account. For more accurate description of the capture process near the Coulomb barrier we use the quantum diffusion approach based on the formalism of reduced density matrix. Taking the same set of parameters, we also describe the excitation functions for these reactions. The results are in a good agreement with the experiment data. Using the parameter of damping of shell effects with angular momentum, we can estimate the moment of inertia of the nucleus at the saddle point
Deformation bands in porous sandstones their microstructure and petrophysical properties
Energy Technology Data Exchange (ETDEWEB)
Torabi, Anita
2007-12-15
Deformation bands are commonly thin tabular zones of crushed or reorganized grains that form in highly porous rocks and sediments. Unlike a fault, typically the slip is negligible in deformation bands. In this dissertation the microstructure and petrophysical properties of deformation bands have been investigated through microscopy and numerical analysis of experimental and natural examples. The experimental work consists of a series of ring-shear experiments performed on porous sand at 5 and 20 MPa normal stresses and followed by microscopic examination of thin sections from the sheared samples. The results of the ring-shear experiments and comparison of them to natural deformation bands reveals that burial depth (level of normal stress in the experiments) and the amount of shear displacement during deformation are the two significant factors influencing the mode in which grains break and the type of shear zone that forms. Two end-member types of experimental shear zones were identified: (a) Shear zones with diffuse boundaries, which formed at low levels of normal stress and/or shear displacement; and (b) Shear zones with sharp boundaries, which formed at higher levels of normal stress and/or shear displacement. Our interpretation is that with increasing burial depth (approximately more than one kilometer, simulated in the experiments by higher levels of normal stress), the predominant mode of grain fracturing changes from flaking to splitting; which facilitates the formation of sharp-boundary shear zones. This change to grain splitting increases the power law dimension of the grain size distribution (D is about 1.5 in sharp boundary shear zones). Based on our observations, initial grain size has no influence in the deformation behavior of the sand at 5 MPa normal stresses. A new type of cataclastic deformation band is described through outcrop and microscopic studies; here termed a 'slipped deformation band'. Whereas previously reported cataclastic 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, as a result of microstructural variation, both porosity and permeability vary along the leng
EO-1 Hyperion and ALI bands simulation to Landat 7 ETM+ bands for mineral mapping in Milos Island
Nikolakopoulos, Konstantinos G.; Tsombos, Panagiotis I.; Skianis, George Aim.; Vaiopoulos, Dimitrios A.
2008-10-01
During the last two decades, airborne hyperspectral sensors such as the AVIRIS or DAIS have been proved very useful but quite expensive tool for the detection and mapping of earth surface minerals. On November 2000 the launch of the Earth Observing 1 (EO-1) satellite, which included Hyperion, the first spaceborne imaging spectrometer, provided a new low cost tool in remote sensing research. This study evaluates hyperspectral data from Hyperion, as well as multispectral data from the EO-1 Advanced Land Imager (ALI) and the Landsat 7 ETM+ for mineral mapping in Milos Island. The three sensors examined in this study have similar spatial resolution, totally different spectral resolution and radiometric quality characteristics. All the data were collected the same day within one-minute time. As a result the atmospheric conditions were exactly the same and that make the data ideal for comparison. The performance of the EO-1 Hyperion imaging spectrometer with the Advanced Land Imager (ALI) and the Landsat 7 ETM+ sensor was compared using a method that aggregated portions of the Hyperion 10 nm bands to simulate the broader multispectral bands of ALI and ETM+. The general process was to calculate a weighted sum of the Hyperion bands that covered each Landsat band. The weights used in the sum were derived, by comparing the spectral response of the hyperspectral bands with the respective multispectral band. Different band ratios like the TM3/TM1 sensitive on the iron oxide detection, or different combinations sensitive on mineral (TM5/7, TM5/4, TM3/1) or hydrothermal anomalies (TM5/7, TM3/1, TM4/3) detection were used for the comparison of the three data sets and the results are presented in this study.
Consolidated fuel shielding calculations
International Nuclear Information System (INIS)
Irradiated fuel radiation dose rate and radiation shielding requirements are calculated using a validated ISOSHLD-II model. Comparisons are made to experimental measurements. ISOSHLD-11 calculations are documented
Heterogeneous Calculation of ?
International Nuclear Information System (INIS)
A heterogeneous method of calculating the fast fission factor given by Naudet has been applied to the Carlvik - Pershagen definition of ?. An exact calculation of the collision probabilities is included in the programme developed for the Ferranti - Mercury computer
Electronic structure of superconducting gallium-doped germanium from ab-initio calculations
Lebegue, S.
2009-01-01
Using ab-initio calculations, we study the electronic structure of gallium-doped germanium, which was found recently to be a superconductor, with a critical temperature of 0.5 Kelvins, and a particularly low density of Cooper pairs. The calculations of the electronic properties reveal that no sign of an impurity band is observed, and that the Fermi level lies in the valence band of Germanium. Moreover, the calculation of the phonon frequencies shows that a new mode associate...
Research on identical bands of superdeformed nuclei
International Nuclear Information System (INIS)
The recent development of superdeformed identical bands are briefly reviewed. Some typical superdeformed bands are analyzed by the formula of Bohr-Mottelson's I(I + 1) expansion. The results show that the dynamic moments of inertia J(2) of so-called two identical bands are very similar, but kinetic moments of inertia J(1) and band head moments of inertia J0 are not equal. Signature partner bands are almost identical. Their J0, J(1), J(2) are almost identical respectively. Bohr-Mottelson Model is still one model which successfully explains the formation of identical bands
Mechanism of photonic band gap, optical properties, tuning and applications
International Nuclear Information System (INIS)
Mechanism of occurrence of Photonic Band Gap (PBG) is presented for 3-D structure using close packed face centered cubic lattice. Concepts and our work, specifically optical properties of 3-D photonic crystal, relative width, filling fraction, effective refractive index, alternative mechanism of photonic band gap scattering strength and dielectric contrast, effect of fluctuations and minimum refractive index contrast, are reported. The temperature tuning and anisotropy of nematic and ferroelectric liquid crystal infiltrated opal for different phase transitions are given. Effective dielectric constant with filling fraction using Maxwell Garnet theory (MG), multiple modified Maxwell Garnet (MMMG) and Effective Medium theory (EM) and results are compared with experiment to understand the occurrence of PBG. Our calculations of Lamb shifts including fluctuations are given and compared with those of literature values. We have also done band structure calculations including anisotropy and compared isotropic characteristic of liquid crystal. A possibility of lowest refractive index contrast useful for the fabrication of PBG is given. Our calculations for relative width as a function of refractive index contrast are reported and comparisons with existing theoretical and experimental optimal values are briefed. Applications of photonic crystals are summarized. The investigations conducted on PBG materials and reported here may pave the way for understanding the challenges in the field of PBG. (author)
International Nuclear Information System (INIS)
Excited states of 123I were populated via the 116Cd(14N, ?3n) reaction at 65 MeV. The resultant ?-rays were detected using standard ?-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity ?I = 2 sequences have been extended up to 31/2+ and 41/2+. In addition, a number of ?I = 1 transitions linking the two ?I = 2 sequences have been observed. It is suggested that both ?I = 2 sequences are based on a common configuration. This ?I = 1 band is proposed to be built predominantly on the g7/2[404]7/2+ oblate configuration, based on the energy-level spectra, B(M1)/B(E2) ratios and the theoretical predictions from the particle-rotor model. The previously identified ?I = 1 rotational band built on the prolate g9/2[404]9/2+ orbital has also been extended to higher spins. Another previously identified but weakly populated ?I = 1 band is confirmed and is proposed to be built on the d5/2[413]5/2+ configuration with the ground state of 123I as the bandhead
Triaxial deformation and chiral bands in nuclei around mass 130
International Nuclear Information System (INIS)
We report on pair-truncated shell-model calculations of low-lying yrast and quasi-? bands of nuclei around mass 130 using phenomenological effective interactions of pairing plus quadrupole type, where the strengths of interactions are gradually changed as functions of numbers of valence nucleons. The calculations start with even-even nuclei of low-lying states, which exhibit typical features of ?-instability. The model reproduces well experimental energy levels and E2 transition rates. We calculate energy levels of odd-A nuclei, where the effective interactions identical to those obtained from the calculations of the even-even nuclei are employed. The agreement between the theoretical values and the experimental observations is rather well. (author)
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]? 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.
Bosonic condensation in a flat energy band
Baboux, F; Jacqmin, T; Biondi, M; Lemaître, A; Gratiet, L Le; Sagnes, I; Schmidt, S; Türeci, H E; Amo, A; Bloch, J
2015-01-01
Flat bands are non-dispersive energy bands made of fully degenerate quantum states. Such bands are expected to support emergent phenomena with extraordinary spatial and temporal structures, as they strongly enhance the effect of any perturbation induced by disorder, dissipation or interactions. However, flat bands usually appear at energies above the ground state, preventing their study in systems in thermodynamic equilibrium. Here we use cavity polaritons to circumvent this issue. We engineer a flat band in a frustrated lattice of micro-pillar optical cavities. By taking advantage of the non-hermiticity of our system, we achieve for the first time bosonic condensation in a flat band. This allows revealing the peculiar effect of disorder in such band: The condensate fragments into highly localized modes, reflecting the elementary eigenstates produced by geometric frustration. This non-hermitian engineering of a bosonic flat band condensate offers a novel approach to studying coherent phases of light and matte...
Relationship between band populations and band structure in the three-band Hubbard model
International Nuclear Information System (INIS)
We study the two-dimensional three-band Hubbard model by means of a four-pole approximation within the Composite Operator Method framework. The model has been solved by considering as basic composite field a four-component spinor field, which includes the p field, the two Hubbard operators for the d field, and a composite operator describing the p field dressed by the spin excitations of the d field. This solution correctly reproduces many results of numerical simulations. In this manuscript, we investigate the relationship between p-and d- populations and the band structure of the model, by varying the on-site potential, the charge-transfer gap, the doping and the hopping integral between the p orbitals.
Triaxial superdeformed bands in odd-odd 160?168Lu isotopes
International Nuclear Information System (INIS)
The triaxial superdeformed rotational bands in the odd-odd 160?168Lu isotopes are investigated by performing the configuration dependent three-dimensional total routhian surface calculations. About fifty low lying triaxial superdeformed bands have been found for these odd-odd nuclei within the excitation energy of 3 MeV above the normal deformed yrast bands. The calculated equilibrium elongation, triaxial and hexadecapole deformations for these triaxial superdeformed bands are close to the values of ?2?0.4, ??20o and ?4?0.03, respectively. The configurations of calculated triaxial superdeformed bands have been assigned based on the total routhian surface calculations and the analysis of quasiparticle routhians in the rotating frame. The observed yrast triaxial superdeformed band of 164Lu, where the linking transitions between superdeformed and normal deformed states are measured, have been reproduced by the present calculation in the relative energy to the normal deformed band. We show that the stability of superdeformed triaxial shapes in the odd-odd Lu isotopes is similar to that presented in odd-even Lu nuclei, and thus the wobbling excitations could be expected to occur in odd-odd Lu isotopes. The deformation driving effect of the proton high-j low-K orbit play an important role in the formation of the triaxial superdeformed states in both odd-odd and odd-even Lu isotopes, while the shell effect is a fundamental factor for the triaxial superdeformed shapes. The shell gaps and the positions of the deformation driving intruder orbits which are responsible for the triaxial superdeformed minima have been localized, particularly, the neutron N=94 gap and the position of the proton [660]1/2 orbit in the deformed single particle diagram provide the basis for a microscopic understanding of the observed triaxial superdeformed bands in the mass region.
Triaxial superdeformed bands in odd-odd Lu160˜168 isotopes
Ya, Tu; Chen, Y. S.; Yu, S. Y.; Shen, C. W.; Gao, Z. C.; Chen, Y. J.; Liu, L.
2010-12-01
The triaxial superdeformed rotational bands in the odd-odd Lu160˜168 isotopes are investigated by performing the configuration dependent three-dimensional total routhian surface calculations. About fifty low lying triaxial superdeformed bands have been found for these odd-odd nuclei within the excitation energy of 3 MeV above the normal deformed yrast bands. The calculated equilibrium elongation, triaxial and hexadecapole deformations for these triaxial superdeformed bands are close to the values of ?˜0.4, ?˜20° and ?˜0.03, respectively. The configurations of calculated triaxial superdeformed bands have been assigned based on the total routhian surface calculations and the analysis of quasiparticle routhians in the rotating frame. The observed yrast triaxial superdeformed band of 164Lu, where the linking transitions between superdeformed and normal deformed states are measured, have been reproduced by the present calculation in the relative energy to the normal deformed band. We show that the stability of superdeformed triaxial shapes in the odd-odd Lu isotopes is similar to that presented in odd-even Lu nuclei, and thus the wobbling excitations could be expected to occur in odd-odd Lu isotopes. The deformation driving effect of the proton high-j low-K orbit play an important role in the formation of the triaxial superdeformed states in both odd-odd and odd-even Lu isotopes, while the shell effect is a fundamental factor for the triaxial superdeformed shapes. The shell gaps and the positions of the deformation driving intruder orbits which are responsible for the triaxial superdeformed minima have been localized, particularly, the neutron N=94 gap and the position of the proton [660]1/2 orbit in the deformed single particle diagram provide the basis for a microscopic understanding of the observed triaxial superdeformed bands in the mass region.
The laparoscopic banded gastric bypass – operation technique
Directory of Open Access Journals (Sweden)
Simon Küsters
2010-03-01
Full Text Available The banded Roux-en-Y gastric bypass can be used as a primary or revisionary bariatric procedure. This article describesthe operation technique including materials, size and placement of the banding and gives an overview con cerningevolution and indications of the operation. A video of a primary banded Roux-en-Y gastric bypass is presented.
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.)
International Nuclear Information System (INIS)
After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Calculating strain in 3D DEM simulations
O'Sullivan, C.; Butlanska, J.; Cheung, G.
2010-06-01
Particulate DEM allows us to simulate and evaluate in detail the evolution of localizations in particulate material, whether bonded/cemented or unbonded. DEM simulations generate a wealth of particle scale data including particle displacements, velocities and contact forces. Traditionally in geomechanics we understand material response based upon a continuum mechanics framework that considers stress and strain. There is little debate as to how to calculate stress from DEM simulation results, however there is no consensus on how to calculate strain. Most of the methods proposed in the literature to calculate strain have considered the overall response of an assembly of grains, rather than the local in homogeneities that are associated with shear band evolution. This paper outlines the challenges associated with quantifying strain based upon DEM simulation results and demonstrates that a local wavelet based homogenization approach as proposed by may have advantages over triangulation based linear interpolation.
International Nuclear Information System (INIS)
High spin states in 85Sr were populated using the reaction 76Ge(13C, 4n) at a beam energy of 52 MeV. Gamma-gamma coincidence measurements along with investigation of directional correlation ratios were utilized to establish the extended level scheme upto I? = (35/2-). One of the positive parity states observed at 3383.3 keV ((I? = 19/2(+)) may be considered as a magnetic rotational (?I = 1) band, the negative parity states built on 3028.0 level show an irregular behaviour and does not exhibit magnetic rotation.
Identification of the UIR Bands
Johnson, Fred
2015-08-01
Starlight undergoing multiple scattering processes within fluffy grains results in extinction, UV 2175A bump, DIBs and the UIR bands. Spectroscopic lab and DIB data has identified the highly fluorescent molecule Dipyridyl Madnesium Tetrabenzoporphyrin (mgTBP). Reflection and Raman scattering experimental data will be presented which designates this molecule as the primary source for UIR signals. MgTBP sublimes at about 500°C. It is produced via high temperature plasma synthesis within and subsequently ejected from comets which in turn are by-products of solar system-planetary development. Interstellar dust is the left-over refuse which implies prodigious solar system evolution in each galaxy.
International Nuclear Information System (INIS)
Photonic band structures are investigated for both diamond and hexagonal diamond crystals composed of dielectric spheres, and absolute photonic band gaps (PBGs) are found in both cases. In agreement with both Karathanos and Moroz's calculations, a large PBG occurs between the eighth and ninth bands in diamond crystal, but a PBG in hexagonal diamond crystal is found to occur between the sixteenth and seventeenth bands because of the doubling of dielectric spheres in the primitive cell. To explore the physical mechanism of how the photonic band gap might be broadened, we have compared the electric field distributions (|E|2) of the 'valence' and 'conduction' band edges. Results show that the field intensity for the 'conduction' band locates in the inner core of the sphere while that of the 'valence' band concentrates in the outer shell. With this motivation, double-layer spheres are designed to enhance the corresponding photonic band gaps; the PBG is increased by 35% for the diamond structure, and 14% for the hexagonal diamond structure
Band offset measurements in Zn1?x Sb x O/ZnO hetero-junctions
Devi, Vanita; Kumar, Manish; Kumar, Ravindra; Singh, Amanpal; Joshi, B. C.
2015-08-01
Accurate knowledge of the alignment of conduction and valence bands of layers at the heterojunction and warrant knowledge of the band offsets at the interface is essential for Zn1?x Sb x O/ZnO based quantum well device designing and modeling. Under this scenario, valence band offsets of Zn1?x Sb x O/ZnO heterostructures grown by the pulsed laser deposition technique was measured by photoelectron spectroscopy and consequently, the conduction band offset was calculated by UV-visible spectroscopy. The change in band alignment has been observed with the dopant (Sb) concentration. Ratios of conduction band offset to valence band offset were estimated to be 1.67 and 0.04 for x = 0.03 and 0.06, respectively, for Sb doped films. A Type-II band alignment was observed at the Zn0.97Sb0.03O/ZnO interface, whereas the Type-I band alignment took place at the Zn0.94Sb0.06O/ZnO interface.
Three-dimensional dual-band stacked microbolometer design using resistive dipoles and slots
Kim, Hoo; Neikirk, Dean P.
2013-06-01
A dual-band microbolometer with separate absorption of each wavelength band would be desirable for multispectral applications. In addition, a three dimensional (3D) stacked structure would be advantageous for size and integration in focal plane arrays. We present designs for a 3D stacked dual-band microbolometer based on the in-band and out-of-band reflection and transmission characteristics of resistive dipoles and slots. The mechanism of individual absorption in each layer of a dual-band microbolometer is analyzed and simulated to allow the resistive slot layer to efficiently absorb the LWIR band while a superposed resistive dipole layer absorbs the MWIR band. The top dipole layer is designed to have peak absorption at 5 ?m, with a second underlying slot layer and mirror layer designed to have peak absorption at 10 ?m. The stacked combination of two different types of layers provides highly efficient wavelength selective absorption, yielding calculated power absorption efficiency of nearly 100 % for both LWIR and MWIR bands.
This calculator allows users to calculate their ecological footprint in terms of trees required to sequester the carbon from carbon dioxide emissions produced by household use and transportation. Exact emissions figures or national averages can entered into the calculator, and the amount of carbon dioxide generated by burning of fossil fuels is calclulated, as well as the number of trees it will take to remove that amount of carbon dioxide.
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. PMID:25132558
Self-consistent Green's function method for dilute nitride conduction band structure
International Nuclear Information System (INIS)
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 GaNxAs1?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 EN, 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. (paper)
Anomalous band-gap bowing of AlN(1-x)Px alloy
M. J. Winiarski; Polak, M.; Scharoch, P.
2014-01-01
Electronic structure of zinc blende AlN(1-x)$Px alloy has been calculated from first principles. Structural optimisation has been performed within the framework of LDA and the band-gaps calculated with the modified Becke-Jonson (MBJLDA) method. Two approaches have been examined: the virtual crystal approximation (VCA) and the supercell-based calculations (SC). The composition dependence of the lattice parameter obtained from the SC obeys Vegard's law whereas the volume optim...
Waste Package Lifting Calculation
International Nuclear Information System (INIS)
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 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
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,...
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...
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.
Franck-Condon factors and r-centroids for the B-X bands of 10B18O and 11B18O molecules
VOJISLAV BOJOVIC; DIMITRIJE PESIC; ANKICA ANTIC-JOVANOVIC; MIROSLAV KUZMANOVIC
2005-01-01
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.
Accurate screened exchange band structures for transition metal monoxides MnO, FeO, CoO and NiO
Gillen, Roland; Robertson, John
2012-01-01
We report calculations of the band structures and density of states of the four transition metal monoxides MnO, FeO, CoO and NiO using the hybrid density functional sX-LDA. Late transition metal oxides are prototypical examples of strongly correlated materials, which pose challenges for electronic structure methods. We compare our results with available experimental data and show that our calculations yield accurate predictions for the fundamental band gaps and valence bands...
Davison, P. Dru
2007-01-01
This study examined the relationship between band director leadership styles and the strength of student leadership within the bands. This study also examined the differences between leadership styles, student leadership strength, and band festival ratings (marching and concert). Subjects (N = 42) were band directors from Texas and Arkansas who…
Signature and parity splitting in rotational bands and chiral bands. Double minimum potential model
International Nuclear Information System (INIS)
The effects of the signature and parity splitting in nuclear spectra and the properties of the chiral bands are analyzed basing on a one-dimensional Schrödinger equation with a double-minimum potential. Rotational bands in odd axial nuclei, alternating parity bands in even-even nuclei and the chiral bands in odd-odd nuclei are considered. The results obtained are discussed.
International Nuclear Information System (INIS)
Large scale shell model calculations, with dimensions reaching 109, are carried out to describe the recently observed deformed (ND) and superdeformed (SD) bands based on the first and second excited 0+ states of 40Ca at 3.35 MeV and 5.21 MeV respectively. A valence space comprising two major oscillator shells, sd and pf, can accommodate most of the relevant degrees of freedom of this problem. The ND band is dominated by configurations with four particles promoted to the pf-shell (4p-4h in short). The SD band by 8p-8h configurations. The ground state of 40Ca is strongly correlated, but the closed shell still amounts to 65%. The energies of the bands are very well reproduced by the calculations. The out-band transitions connecting the SD band with other states are very small and depend on the details of the mixing among the different np-nh configurations, in spite of that, the calculation describes them reasonably. For the in-band transition probabilities along the SD band, we predict a fairly constant transition quadrupole moment Q0(t) ? 70 e fm2 up to J=10, that decreases toward the higher spins. We submit also that the J=8 states of the deformed and superdeformed band are maximally mixed. (authors)
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).
Band gap bowing and electron localization of GaxIn1-xN
Lee, Byounghak; Wang, Lin Wang
2006-11-01
The band gap bowing and the electron localization of GaxIn1-xN are calculated using both the local density approximation (LDA) and screened-exchange local density functional (sX-LDA) methods. The calculated sX-LDA band gaps are in good agreement with the experimentally observed values, with errors of -0.26 and 0.09eV for bulk GaN and InN, respectively. The LDA band gap errors are 1.33 and 0.81eV for GaN and InN, in order. In contrast to the gap itself, the band gap bowing parameter is found to be very similar in sX-LDA and LDA. We identify the localization of hole states in GaxIn1-xN alloys along In-N-In chains. The predicted localization is stronger in sX-LDA.
First-principles study of direct and narrow band gap semiconducting ?-CuGaO2
Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming
2015-04-01
Semiconducting oxides have attracted much attention due to their great stability in air or water and the abundance of oxygen. Recent success in synthesizing a metastable phase of CuGaO2 with direct narrow band gap opens up new applications of semiconducting oxides as absorber layer for photovoltaics. Using first-principles density functional theory calculations, we investigate the thermodynamic and mechanical stabilities as well as the structural and electronic properties of the ?-CuGaO2 phase. Our calculations show that the ?-CuGaO2 structure is dynamically and mechanically stable. The energy band gap is confirmed to be direct at the ? point of Brillouin zone. The optical absorption occurs right at the band gap edge and the density of states near the valance band maximum is large, inducing an intense absorption of light as observed in experiment.
The minority spin surface bands of CoS{sub 2}(001)
Energy Technology Data Exchange (ETDEWEB)
Wu Ning; Losovyj, Ya B; Dowben, P A [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588-0111 (United States); Sabirianov, R F; Mei, W N [Department of Physics, University of Nebraska at Omaha, Omaha, NE 68182-0266 (United States); Lozova, N [Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, LA 70806 (United States); Manno, M; Leighton, C [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455 (United States)
2009-07-22
Angle-resolved photoemission was used to study the surface electronic band structure of high quality single crystals of ferromagnetic CoS{sub 2} (below 120 K). Strongly dispersing Co t{sub 2g} bands are identified along the (100) k{sub ||} direction, the GAMMA-bar-X-bar line of the surface Brillouin zone, in agreement with model calculations. The calculated surface band structure includes corrections for the previously determined surface structure of CoS{sub 2}(001) and is in general agreement with the experimental photoemission spectra in the region of the Fermi level. There is evidence of the existence of several minority spin surface states, falling into a gap of the projected minority spin bulk CoS{sub 2}(001) band structure.
Dipole bands in high spin states of {sub 57}{sup 135}La{sub 78}
Energy Technology Data Exchange (ETDEWEB)
Garg, Ritika; Kumar, S.; Saxena, Mansi; Goyal, Savi; Siwal, Davinder; Verma, S.; Mandal, S. [Department of Physics and Astrophysics, University of Delhi, Delhi - 110007 (India); Palit, R.; Saha, Sudipta; Sethi, J.; Sharma, Sushil K.; Trivedi, T.; Jadav, S. K.; Donthi, R.; Naidu, B. S. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai - 400005 (India)
2014-08-14
High spin states of {sup 135}La have been investigated using the reaction {sup 128}Te({sup 11}B,4n){sup 135}La at a beam energy of 50.5 MeV. Two negative parity dipole bands (?I = 1) have been established. Crossover E2 transitions have been observed for the first time in one of the dipole bands. For the Tilted Axis Cranking (TAC) calculations, a three-quasiparticle (3qp) configuration ?(h{sub 11/2}){sup 1}??(h{sub 11/2}){sup ?2} and a five-quasiparticle (5qp) configuration ?(h{sub 11/2}){sup 1}(g{sub 7/2}/d{sub 5/2}){sup 2}??(h{sub 11/2}){sup ?2} have been taken for the two negative parity dipole bands. The comparison of experimental observables with TAC calculations supports the configuration assignments for both the dipole bands.
Gladysiewicz, M.; Kudrawiec, R.; Wartak, M. S.
2015-08-01
The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ? 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 ?m. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 ?m and 1.55 ?m) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga0.47In0.53As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 ?m, i.e., at the wavelengths that are not available in current InP-based lasers.
On the order-chaos transition as an explanation of the decay-out of superdeformed bands
International Nuclear Information System (INIS)
We calculate the maximum effect which an order-chaos transition in the normally deformed states can have on the total relative intra-band decay intensity of a superdeformed band. Our results show that the sharp attenuation of the decay intensity cannot be explained solely by an order-chaos transition. (author)
Recent developments in high-spin calculations in atomic nuclei
International Nuclear Information System (INIS)
A brief introduction to the recent achievements in the high-spin domain in nuclear physics is given. Results of the calculations in highly developed rotational bands in deformed nuclei, as well as the calculations in the structure of the yrast isomers are presented. The calculations fail in two aspects: local minima in the yrast line are not confirmed experimentally, the overall slope of the yrast line in 152Dy is considerably overestimated. The calculations of the yrast line with new Woods-Saxon parameters are now in progress. The parameters are chosen to reproduce the large gap in the levels at proton number Z=64. (M.H.)
Multiple Band-Notched UWB Antenna with Band-Rejected Elements Integrated in the Feed Line
Zhu, F.; Gao, S; Ho, ATS; Raed, AA-A; See, CH; Brown, TWC; li, J; Wei, G; Xu, J.
2013-01-01
To mitigate potential interferences with coexisting wireless systems operating over 3.3–3.6 GHz, 5.15–5.35 GHz, or 5.725–5.825 GHz bands, four novel band-notched antennas suitable for ultra-wideband (UWB) applications are proposed. These include UWB antennas with a single wide notched band, a single narrow notched band, dual notched bands, and triple notched bands. Each antenna comprises a half-circle shaped patch with an open rectangular slot and a half-circle shaped ground plane. Good band-...
Novel band structures in silicene on monolayer zinc sulfide substrate
Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping
2014-10-01
Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on ?rst-principles calculations, we find that the interaction energies are in the range of -0.09?0.3?eV?per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05?eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.
Infrared band strengths: Laboratory techniques and applications to astronomical observations
Gerakines, P. A.
2002-09-01
Whenever an abundance measurement is derived by way of infrared spectroscopy, it will typically make use of a laboratory-obtained conversion factor between the size of an IR absorption feature and the (column) density of the molecule under study. This factor is usually called the "absolute absorption intensity" by a chemist or the "band strength" by a typical IR astronomer. Band strengths have been studied in chemistry since the 1950s, and the commonly quoted "accuracy to with a factor of ten" historically required of astronomical calculations has not required much new input into this area. Today, however, astronomical measurements require much higher precision, and it is time for IR astronomers to ask more of laboratory measurements and to understand when and why to use IR band strengths in a more appropriate manner. The history, interpretation, measurement, and common astrophysical applications of infrared band strengths will be discussed. The "secrets" of the laboratory techniques involved in their measurement are described, and a compilation of results from the literature is given along with some new results. Typical astrophysical applications and appropriate uses will also be discussed. Common misconceptions are confronted and two challenges are presented: (i) to the laboratory astrophysics community to produce and advertise accurate values with caveats when necessary, and (ii) to the observational community to use the most appropriate results for the environment under study.
Lasing at the band edges of plasmonic lattices
Schokker, A. Hinke; Koenderink, A. Femius
2014-10-01
We report room-temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback (DFB) lasers, a central question is how the underlying band structure from which lasing emerges is modified by both the much stronger scattering and the disadvantageous loss of metal. We use spectrally resolved back-focal plane imaging to measure the wavelength and angle dependence of emission below and above threshold, thereby mapping the band structure. We find that, for silver particles, the band structure is strongly modified compared to dielectric reference DFB lasers since the strong scattering gives large stop gaps. In contrast, gold particles scatter weakly and absorb strongly, so that thresholds are higher, but the band structure is not strongly modified. The experimental findings are supported by finite element and Fourier modal method calculations of the single-particle scattering strength and lattice extinction.
Endoscopic Treatment of an extruded gastric band
International Nuclear Information System (INIS)
We present the case of a patient in whom a gastric band was placed for the treatment of morbid obesity with good results of loss of weight. One year after the procedure the gastric band started to be extruded into the stomach and this was almost total at 26 months. At this time the band was held only by a small tissue bridge. We did two endoscopic procedures to extract the band. In the first one the tissue bridge was cut using the duodenoscope for a better vision and handling and a needle knife papilotome. The band could not be extracted at the time because it continued to be fixed by the connector to the subcutaneous reservoir. The reservoir had been previously removed. One week later in a second procedure the band was cut using a monofilament biliary wire guide and lithotriptor. Then the band could be extracted easily. We describe the procedures, the difficulties we had and how we resolved them
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).
Photonic band gaps of a two-dimensional square lattice composed by superconducting hollow rods
Diaz-Valencia, B. F.; Calero, J. M.
2014-10-01
In this paper by means of the plane wave expansion method, we have calculated the photonic band structure of 2D photonic crystals consisting of high temperature superconducting hollow cylinders arranged in a square lattice. Band structures were obtained at low frequencies and assuming TM polarization of the incident wave, for different inner radii of the cylinders and for two different temperatures (5 K and 15 K), showing the tunability of photonic band gaps with respect to these parameters. Interesting features, such as the decreasing of cutoff frequency and separation of photonic modes were observed by increasing both the temperature and inner radius. Permittivity contrast and the difference between the inner and outer radius lead to the appearance of new band gaps when compared with the case of solid cylinders. These band gaps can be modulated by the width of the shell and temperature, which may be used for the development of novel optical devices.
Band Alignment for Ambipolar-Doping of SnxZn1-xTe Alloys
International Nuclear Information System (INIS)
Using the first-principles band-structure method and a special quasirandom structure (SQS) approach, we have systematically calculated the alloy bowing coefficients and the nature band offsets of SnxZn1-xTe alloys. We show that the bowing coefficients and band gaps of these alloys are sensitively composition dependent. Due to wave functions full overlapping and delocalization of the Sn outermost p orbits and Zn s orbits, the coupling between these states is very strong, resulting in a significant downshift of conduction band edge with the increase of the Sn concentration x, While the valence band edge keeps almost unchanged compared with that of the binary ZnTe, thus improving the possibility for ambipolar-doping. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
International Nuclear Information System (INIS)
By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.
International Nuclear Information System (INIS)
We calculated numerically the localization length of one-dimensional Anderson model with diagonal disorder. For weak disorder, we showed that the localization length changes continuously as the energy changes from the band center to the boundary of the anomalous region near the band edge. We found that all the localization lengths for different disorder strengths and different energies collapse onto a single curve, which can be fitted by a simple equation. Thus the description of the perturbation theory and the band center anomaly were unified into this equation. -- Highlights: ? We study the band center anomaly of one-dimensional Anderson localization. ? We study numerically the Lyapunov exponent through a parametrization method of the transfer matrix. ? We give a unified equation to describe the band center anomaly and perturbation theory.
Energy Technology Data Exchange (ETDEWEB)
Lucovsky, Gerald; Rayner, Gilbert B.; Zhang Yu; Fulton, Charles C.; Nemanich, Robert J.; Appel, Guenther; Ade, Harald; Whitten, Jerry L
2003-05-15
Transition metal silicates, (ZrO{sub 2}){sub x}(SiO{sub 2}){sub 1-x}, have dielectric constants k>10 that make them attractive for advanced Si devices. Band offset energies relative to Si are an important factor in determining tunneling leakage current, and internal photoemission. Studies by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and X-ray absorption spectroscopy (XAS) are combined with ab initio calculations to identify the compositional variation of the band-gap, and valence and conduction band offset energies of Zr silicate alloys with respect to Si. The minimum conduction band offset, due to Zr 4d* states, is shown to be independent of alloy composition, while valence band offsets decrease monotonically with increasing ZrO{sub 2} content. The implications of these results for direct tunneling are discussed.
Study of the satellite bands of RbCs molecule in the near UV
International Nuclear Information System (INIS)
By comparing high-resolution absorption spectra of Rb and Cs vapor with Rb–Cs vapor mixture spectrum we were able to identify several satellite bands of RbCs molecule at 362.2 nm, 372.5 nm and 390.7 nm. These bands represent lower Rydberg states of the RbCs molecule which may be further studied at ultracold conditions. - Highlights: • Comparison of high-resolution absorption spectra of Rb, Cs and RbCs vapor mixture. • Satellite bands of RbCs molecule at 362.2 nm, 372.5 nm and 390.7 nm. • Avoided crossings of potential curves at long-range inter-atomic region. • The observed satellite bands may be observed in the mixed Rb–Cs MOT. • The satellite bands can be used for comparison with ab initio RbCs calculations
Limaye, Mukta V.; Chen, S. C.; Lee, C. Y.; Chen, L. Y.; Singh, Shashi B.; Shao, Y. C.; Wang, Y. F.; Hsieh, S. H.; Hsueh, H. C.; Chiou, J. W.; Chen, C. H.; Jang, L. Y.; Cheng, C. L.; Pong, W. F.; Hu, Y. F.
2015-06-01
The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S2? (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S2? species, but significantly increases the concentration of larger S clusters [polysulfides (Sn2?, n?>?2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples.
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.
Band-pass microstrip filters on high-temperature superconductor films
International Nuclear Information System (INIS)
Results of simulation and experimental study of band-pass filters on coupled microstrip resonators made on HTSC films are presented. It is shown that the application of trustworthy models of HTSC filter elements allows to solve the synthesis problem of HTSC filters in the form of an integral circuit without using of additional tuning elements. Two filter configurations at the frequency 1.75 GHz with the pass band 4% are investigated. Good agreement between experimental and calculated results is observed
Electroexcitation of the ground-state rotational band in 181Ta
International Nuclear Information System (INIS)
Elastic and inelastic form factors for electron scattering from the ground-state rotational band of 181Ta have been studied for momentum transfers 0.4 fm-1 -1. The data are shown to provide an independent check of the rotational assumption, thus adding confidence that the experimental form factors are characteristic of a stable intrinsic state associated with the rotational band. The data are also compared to a Hartree-Fock calculation using density-dependent interactions
Theory of valence-band and core-level photoemission from plutonium dioxide
Kolorenc, Jindrich; Kozub, Agnieszka L.; Shick, Alexander B.
2014-01-01
The correlated-band theory implemented as a combination of the local-density approximation with the dynamical mean-field theory is applied to PuO2. An insulating electronic structure, consistent with the experimental valence-band photoemission spectra, is obtained. The calculations yield a nonmagnetic ground state that is characterized by a noninteger filling of the plutonium 5f shell. The noninteger filling as well as the satellites appearing in the 4f core-level photoemiss...
Study of the Multiphonon Bands in 156Gd by the DPPQ Model
Gupta, J. B.
1983-07-01
The recent extension of the energy spectrum of 156Gd to include up to five K? = 0+, two K? = 2+ and two K? = 4+ rotational bands from an (n, ?) reaction study allows further tests of the validity of the dynamic pairing-plus-quadrupole model of nuclei. Eight of these rotational bands are obtained in the model, though the calculated energy scale is much expanded. Their decay characteristics are compared with experiment.
International Nuclear Information System (INIS)
Functional description of the programme package Cord-2 for PWR core design calculations is presented. Programme package is briefly described. Use of the package and calculational procedures for typical core design problems are treated. Comparison of main results with experimental values is presented as part of the verification process. (author)
Band-gap bowing, band offsets, and electron affinities for AlN, GaN, InN and InGaN: A DFT study
Moses, Poul Georg; van de Walle, Chris G.; Miao, Maosheng
2009-11-01
AlN, GaN, and InN and their alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve nitride-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band gap and absolute band positions of AlN, GaN, InN and InGaN using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. Detailed surface calculations have been performed that, combined with bulk calculations for alloys, yield information about the positions of valence and conduction bands on an absolute energy scale. We will discuss bowing effects, band offsets, and electron affinities in light of the application for photochemical hydrogen production. [4pt] [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)
Multiple band structure in 74 Kr
International Nuclear Information System (INIS)
In order to obtain a consistent picture for the structure of the of A ? 70 mass region dominated by shape coexistence phenomena we determine the relevant degrees of freedom dynamically by the effective many body Hamiltonian using the complex version of the EXCITED VAMPIR approach. General symmetry projected Hartree-Fock-Bogolyubov quasi-particle determinants are used as trial configurations and the underlying mean fields as well as the configuration mixing are determined by chains of variational calculations with symmetry projection before variation. We used essentially complex HFB transformation imposing time-reversal and axial symmetry on the quasi particle transformation and include neutron-proton as well as parity mixing in the mean field. In this way we account for time-odd unnatural parity correlation as well as T = 0 and T = 1 neutron-proton pairing in the mean fields. We investigated the lowest even spin positive parity states up to spin 20+ in 74 Kr. For all investigated states from spin 0+ to 10+ the main projected determinant for the yrast solution is prolate deformed and for the first excited state is oblate deformed in the intrinsic system. For higher spins the oblate minimum is going higher in energy. The presence of many prolate minima close in energy with the first one is revealed by the structure of the wave functions and the strong mixing of states found for the intermediate spins result in a very complicate decay pattern. The predicted multiple band structure was confirmed by recent experimental data
Band description of materials with localizing orbitals
International Nuclear Information System (INIS)
Density functional theory is a form of many-body theory which maps the problem onto an equivalent single particle-like system by limiting to the ground state (or some limited ensemble). So it should be surprising that this ground state theory could have any relevance whatsoever to the excitation properties of a material - and yet it does when used carefully. However, the most interesting materials involve active orbitals which are at least partially localized in space and this has profound effects both on the ground state and the excitation spectrum. My long term interest is in Ce and actinide compounds such that the popular concerns are mixed valence, heavy fermions, and the various forms of magnetic transitions. Band structure calculations can give a great deal of information concerning the mechanisms and degree of the localization as shown by examples using the Ce and U Ll2 structured materials and the Ce cubic Laves phase materials. There are some difficulties due to an incomplete knowledge of the functionals involved which causes an underestimate of the local character. This is illustrated and discussed
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.
Flexible single pump hybrid fiber amplifier for the S+C bands
Rocha, A. M.; Nogueira, R. N.
2014-06-01
This work proposes optical amplification in the S+C bands using a hybrid optical fiber amplifier (HFA) that uses a single wavelength pump. Its configuration is based on an erbium doped amplifier (EDFA) to provide gain over the C band and a distributed Raman fiber amplifier (RFA) to attain gain over the S band. Moreover, the proposed amplifier uses standard commercially available fibers. The HFA was numerically characterized and its optimal configuration was calculated using optimization procedures based on genetic algorithms. A flexible HFA configuration was achieved allowing a span length up to 100 km.
A 100 MHz 4 channels Narrow-band Chebyshev Filter for LTE Application
Directory of Open Access Journals (Sweden)
Othman A.R.
2014-12-01
Full Text Available This paper presents the design of a 100 MHz bandwidth with suitable for 4 channels narrow-band using Chebyshev filter at 5.75 GHz frequency. The design development includes calculation, simulation, measurement and testing. The simulation has been simulated using Ansoft Designer software to determine the bandwidth and the insertion loss, |S21|. The band-pass filter design used Duriod 5880 TLY-5A-0200-CH/CH microstrip substrate parameters and lumped components with Chebyshev passive filter topology. The design is useful for applications in multi-channel narrow-band of wireless communication systems for front-end receiver architecture design.
Aguilera Bonet, Irene; Palacios Clemente, Pablo; Wahnón Benarroch, Perla
2008-01-01
The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyrite-type semiconductor (CuGaS2) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical re...
Radiation-Induced Effects on the Optical Band Gap of TGSP Single Crystals
International Nuclear Information System (INIS)
The effect of X- or gamma -radiation on the optical band gap of TGSP crystals doped with 40% or 50% of phosphoric acid has been investigated. The transmittance near the absorption edge of un-irradiated and irradiated TGSP crystals with different X- or -gamma radiation doses has been measured. The absorption coefficient (alpha) of un-irradiated and irradiated crystals was calculates, and shows an increase under the influence of irradiated . Monotonic decrease in the value of the optical band gap (Eg)with the increase of irradiation doses was observed. Crystal irradiated with high doses shows a board absorption band centered at about 4.75 eV
Thermal genesis of the bottom of main electron's energy band in a flat nanofilm
International Nuclear Information System (INIS)
By the example of a plane nanoheterosystem ?-HgS/?-CdS, the shift of the electron's band bottom as a function of both the film thickness and the temperature is numerically calculated. It is shown that, as the temperature grows, the electron-phonon interaction in the processes of absorption and emission leads to a shift of the band bottom to the region of lower energies. The mechanisms of the increase in the shift with the temperature in films with various thickness, as well as the reasons for different shift rates of the electron's band bottom with increase in the temperature, are established
Direct experimental visualization of waves and band structure in 2D photonic crystal slabs
International Nuclear Information System (INIS)
We demonstrate for the first time the ability to perform time resolved imaging of terahertz (THz) waves propagating within a photonic crystal (PhC) slab. For photonic lattices with different orientations and symmetries, we used the electro-optic effect to record the full spatiotemporal evolution of THz fields across a broad spectral range spanning the photonic band gap. In addition to revealing real-space behavior, the data let us directly map the band diagrams of the PhCs. The data, which are in good agreement with theoretical calculations, display a rich set of effects including photonic band gaps, eigenmodes and leaky modes
Conduction band intersubband transitions in Ge/SiGe quantum wells
De Seta, M.; Capellini, G.; Busby, Y.; Evangelisti, F.; Ortolani, M.; Virgilio, M.; Grosso, G.; Pizzi, G.; Nucara, A.; Lupi, S.
2009-08-01
In this letter we present the experimental evidence of intersubband absorption in the conduction band of compressively strained germanium quantum wells bounded by Ge-rich SiGe barriers. The measured absorption energies are in the terahertz range and are interpreted by means of tight binding calculations which include self-consistent band-bending and depolarization effects. From the comparison of experimental and numerical results a conduction band offset along the L line of about 120 meV has been estimated for the studied heterostructures.
Prediction of Band Structure of $Bi_2Te_3$-related Binary and Ternary Thermoelectric Materials
Ryu, Byungki; Oh, Min-Wook; Kim, Bong-Seo; Lee, Ji Eun; Joo, Sung-Jae; Min, Bok-Ki; Lee, HeeWoong; Park, Sudong
2015-01-01
Density functional calculations have performed to study the band structures of $Bi_2Te_3$-related binary ($Bi_2Te_3$, $Sb_2Te_3$, $Bi_2Se_3$, and $Sb_2Se_3$) and $Sb$/$Se$ doped ternary compounds [$(Bi_{1-x}Sb_x)_2Te_3$ and $Bi_2(Te_{1-y}Se_y)_3$]. It is found that the band gap can be increased by $Sb$ doping and it is monotonically increased by $Se$ doping. In ternary compounds, the change of the conduction band structure is more significant, as compared to the change of va...
Anomalous electrical resistivity and Hall constant of Anderson lattice with finite f-band width
Panwar, S S
2002-01-01
We study here an extension of the periodic Anderson model by considering finite f-band width. A variational method is used to study the temperature dependence of electronic transport properties of Anderson lattice for different values of the f-band width. The electrical resistivity rho(T) and Hall constant R sub H (T) calculated show qualitatively the features experimentally observed in heavy fermion materials. We find that as f-band width increases, the low temperature peak in rho(T) disappears, while the low-temperature peak in R sub H (T) becomes sharper. (author)
Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions
International Nuclear Information System (INIS)
CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass.
Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures
Directory of Open Access Journals (Sweden)
Yijie Zeng
2014-10-01
Full Text Available The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM is confined in Si, while the valence band maximum (VBM is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively.
Band-gap engineering in TiO2-based ternary oxides
McLeod, J. A.; Green, R. J.; Kurmaev, E. Z.; Kumada, N.; Belik, A. A.; Moewes, A.
2012-05-01
The electronic structure of several ternary oxides (Sn2TiO4, PbTiO3, Bi2Ti4O11, and Bi4Ti3O12) based on binary lone-pair oxides (SnO, PbO, and Bi2O3) and a d0 oxide (TiO2) is investigated using soft x-ray spectroscopy and electronic-structure calculations. We find that the valence band of these ternary oxides is bounded by bonding (at the bottom of the valence band) and antibonding (at the top of the valence band) O 2p lone-pair ns (Sn 5s, Pb 6s, Bi 6s) hybridized states, while the conduction band is dominated by unoccupied Ti 3d states. The existence of these two features is found to be independent of crystal structure or stoichiometry. The calculated hybridization in the bonding O 2p lone-pair ns states is in reasonable agreement with the relative intensity of this feature in the measured x-ray emission spectra. The dominant influence on the conduction and the valence bands in the ternary oxides is due to different aspects of the electronic structure in the parent binary oxides, and we consequently find that the band gap of the ternary oxide is found to be a stoichiometric-weighed addition of the band gaps of the parent oxides.
Band offsets and optical bowings of chalcopyrites and Zn-based II-VI alloys
International Nuclear Information System (INIS)
Using first-principles band-structure theory we have systematically calculated the (i) alloy bowing coefficients, (ii) alloy mixing enthalpies, and (iii) interfacial valence- and conduction-band offsets for three mixed-anion (CuInX2, X=S, Se, Te) and three mixed-cation (CuMSe2, M=Al, Ga, In) chalcopyrite systems. The random chalcopyrite alloys are represented by special quasirandom structures (SQS). The calculated bowing coefficients are in good agreement with the most recent experimental data for stoichiometric alloys. Results for the mixing enthalpies and the band offsets are provided as predictions to be tested experimentally. Comparing our calculated bowing and band offsets for the mixed-anion chalcopyrite alloys with those of the corresponding Zn chalcogenide alloys (ZnX, X=S, Se, Te), we find that the larger p-d coupling in chalcopyrite alloys reduces their band offsets and optical bowing. Bowing parameters for ordered, Zn-based II-VI alloys in the CuAu, CuPt, and chalcopyrite structures are presented: we find that ordered Zn2SeTe has bowing coefficients of 1.44 and 3.15 eV in the CuAu and CuPt structures, while the random ZnSexTe1-x alloy has a bowing of 1.14 eV. The band alignment between CuInSe2 and CuInSe2-derived ordered vacancy compounds are also presented
Anomalous band-gap bowing of AlN1?xPx alloy
International Nuclear Information System (INIS)
Highlights: •Structural and electronic properties of AlN1?xPx from first principles. •The supercell and the virtual crystall approximation methods applied and compared. •Anomalously high band-gap bowing found. •Similarities of band-gap behavior to that in BN1?xPx noticed. •Performance of MBJLDA with the pseudopotential approach discussed. -- Abstract: Electronic structure of zinc blende AlN1?xPx alloy has been calculated from first principles. Structural optimization has been performed within the framework of LDA and the band-gaps calculated with the modified Becke–Jonson (MBJLDA) method. Two approaches have been examined: the virtual crystal approximation (VCA) and the supercell-based calculations (SC). The composition dependence of the lattice parameter obtained from the SC obeys Vegard’s law whereas the volume optimization in the VCA leads to an anomalous bowing of the lattice constant. A strong correlation between the band-gaps and the structural parameter in the VCA method has been observed. On the other hand, in the SC method the supercell size and atoms arrangement (clustered vs. uniform) appear to have a great influence on the computed band-gaps. In particular, an anomalously big band-gap bowing has been found in the case of a clustered configuration with relaxed geometry. Based on the performed tests and obtained results some general features of MBJLDA are discussed and its performance for similar systems predicted
Gutierrez-Arenas, R. A.; MENDOZA, D
2011-01-01
In this paper we describe an application of the finite difference method to obtain the transverse magnetic photonic band gap diagram of a photonic crystal. The strategy of this method is to formulate the Maxwell equations in finite differences in order to write a computational code. We present experiments that confirm the validity of the calculations of the photonic band diagram as well as the refraction indix of such structure. All calculations were made for two dimensional...
Valence and conduction band edges charge densities in ZnS compound with zinc-blende structure
Energy Technology Data Exchange (ETDEWEB)
Bechiri, A; Benmakhlouf, F; Bacha, S; Allouache, H; Bouarissa, N, E-mail: bechiri@yahoo.fr
2010-11-15
The electronic valence and conduction charge densities at the {gamma}-dot and X k-points are calculated as a function of position in the unit cell for ZnS in the zinc-blende structure using wave functions derived from empirical pseudopotential band-structure calculations. Detailed plots of the charge density along the [111] direction and in the (110) plane are presented and discussed for the total valence bands and the first and second conduction ones.
Valence and conduction band edges charge densities in ZnS compound with zinc-blende structure
Bechiri, A.; Benmakhlouf, F.; Bacha, S.; Allouache, H.; Bouarissa, N.
2010-11-01
The electronic valence and conduction charge densities at the dot gamma and X k-points are calculated as a function of position in the unit cell for ZnS in the zinc-blende structure using wave functions derived from empirical pseudopotential band-structure calculations. Detailed plots of the charge density along the [111] direction and in the (110) plane are presented and discussed for the total valence bands and the first and second conduction ones.
Pressure variation of the valence band width in Ge: A self-consistent GW study
DEFF Research Database (Denmark)
Modak, Paritosh; Svane, Axel
2009-01-01
Analyzing x-ray emission spectra XES of germanium under pressure Struzhkin et al. [Phys. Rev. Lett. 96, 137402 (2006)] found that the valence band width of diamond Ge does not vary with pressure. This contradicts the usual experience and also what is predicted by density-functional calculations. In the present work we report results of quasiparticle self-consistent GW (QSGW) band calculations for diamond- as well as ?-tin-type Ge under pressure. For both phases we find that the band width increases with pressure. For ?-tin Ge this agrees with experiment and density-functional theory, but for diamond Ge neither the local density approximation nor the QSGW calculations agree with the conclusions drawn from the XES data.
Band gap bowing in quaternary nitride semiconducting alloys
DEFF Research Database (Denmark)
Gorczyka, Isabela; Suski, T.
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 the composition and atomic arrangements are examined using a supercell geometry. An analytical expression for the band gap is derived for the entire range of compositions. The range of (x, y) values for which InxGayAl1?x?yN is lattice matched to GaN, and the ensuing energy gaps, are given. This range of available gaps becomes smaller when In atoms form clusters. Comparison to experimental data is made.
Band gap bowing in quaternary nitride semiconducting alloys
Gorczyca, I.; Suski, T.; Christensen, N. E.; Svane, A.
2011-06-01
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 the composition and atomic arrangements are examined using a supercell geometry. An analytical expression for the band gap is derived for the entire range of compositions. The range of (x, y) values for which InxGayAl1-x-yN is lattice matched to GaN, and the ensuing energy gaps, are given. This range of available gaps becomes smaller when In atoms form clusters. Comparison to experimental data is made.
Coherent current states in a two-band superconductor
Yerin, Y S
2006-01-01
Homogeneous current states in thin films and Josephson current in superconducting microbridges are studied within the frame of a two-band Ginzburg-Landau theory. By solving the coupled system of equations for two order parameters the depairing current curves and Josephson current-phase relation are calculated for different values of phenomenological parameters gamma and eta. Coefficients gamma and eta describe the coupling of order parameters (proximity effect) and their gradients (drag effect) respectively. For definite values of parameters the dependence of current j on superfluid momentum contains local minimum and corresponding bi-stable states. It is shown that the Josephson microbridge from two-band superconductor can demonstrate pi-junction behaviour.
The APOGEE Spectral Line List for H band Spectroscopy
Shetrone, Matthew; Lawler, James; Prieto, Carlos Allende; Johnson, Jennifer A; Smith, Verne; Cunha, Katia; Holtzman, Jon; Perez, Ana Garcia; Meszaros, Szabolcs; Sobeck, Jennifer; Zamora, Olga; Garcia-Hernandez, Anibal; Souto, Diogo; Chojnowski, Drew; Koesterke, Lars; Majewski, Steven
2015-01-01
We present the $H$ band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP), and present three different versions that have been used at various stages of the project. The methodology for the newly calculated astrophysical line lists is reviewed. The largest of these three line lists contains 134457 molecular and atomic transitions. In addition to the format adopted to store the data, the line lists are available in MOOG, Synspec and Turbospectrum formats. We also present a list of $H$ band spectral features that are either poorly represented or completely missing in our line list. This list is based on the average...
Quasiparticle calculations for solids and molecules
Kioupakis, Emmanouil Stylianos
Advances in modern materials research have a direct impact in technological innovation. Devices such as transistors, light emitting diodes, photovoltaic cells and thermoelectric modules are only possible due to the nature of the underlying materials. One challenge for theorists is the understanding and prediction of the properties of these materials. With the advent of density functional theory, highly accurate ab initio electronic structure calculations for the electronic ground state became a routine and valuable research tool[1, 2, 3, 4]. Fundamental properties such as the atomic structure, chemical bonding, total energy and vibrational frequencies can be determined, and issues like the surface reconstruction, interface geometry, atomic diffusion and the energetics of reactions can be addressed. However, not all relevant material properties are determined by the ground state. For those that involve excited states, such as the band structure and electronic band gap, the optical absorption spectrum and optical gap, the electron transport properties, the effective mass tensor and the alignment of the bands at the interface of two materials, we need an understanding of the excited quasiparticles of the system. While density functional theory gives accurate values for the ground state properties, the Kohn-Sham eigenvalues do not have a direct physical meaning and cannot be identified with quasiparticle energies. For these, we need to use methods that correctly provide excited state properties. One method that can provide accurate quasiparticle energies and wave functions is the GW method, where G is the one-particle Green's function and W the screened Coulomb interaction. Today, GW quasiparticle calculations can routinely be performed for a wide array of solids, molecules and nanosystems with a quasiparticle energy accuracy of ˜0.1 eV. Moreover, one can employ the Bethe-Salpeter equation formalism to take into account the electron-hole interaction and determine the optical absorption spectrum and the exciton binding energies in good agreement with experiment. In this work, we present some results of quasiparticle calculations for solid and molecular systems. We studied bismuth telluride, an important thermoelectric material, and determined its quasiparticle band structure and effective mass tensor. We also performed GW calculations starting from the LDA+ U mean-field solution for solid hydrogen in the bcc crystal structure, a model system that exhibits strong electronic correlations in the low density limit and a metal-insulator transition driven by correlation effects. Finally, we use GW quasiparticle methods to determine the electronic properties and understand the scanning tunneling microscope experiment results of tetramantane molecules deposited on a gold surface and the optical absorption properties of a spiropyran/merocyanine photoisomer pair.
nuclear reactor design calculations
International Nuclear Information System (INIS)
In this work , the sensitivity of different reactor calculation methods, and the effect of different assumptions and/or approximation are evaluated . A new concept named error map is developed to determine the relative importance of different factors affecting the accuracy of calculations. To achieve this goal a generalized, multigroup, multi dimension code UAR-DEPLETION is developed to calculate the spatial distribution of neutron flux, effective multiplication factor and the spatial composition of a reactor core for a period of time and for specified reactor operating conditions. The code also investigates the fuel management strategies and policies for the entire fuel cycle to meet the constraints of material and operating limitations
Radioactive cloud dose calculations
International Nuclear Information System (INIS)
Radiological dosage principles, as well as methods for calculating external and internal dose rates, following dispersion and deposition of radioactive materials in the atmosphere are described. Emphasis has been placed on analytical solutions that are appropriate for hand calculations. In addition, the methods for calculating dose rates from ingestion are discussed. A brief description of several computer programs are included for information on radionuclides. There has been no attempt to be comprehensive, and only a sampling of programs has been selected to illustrate the variety available
Design of Folded Multilayer Microstrip Tri-Band Hairpin Band Pass Filter
Directory of Open Access Journals (Sweden)
K. Vidhya
2013-07-01
Full Text Available This study presents a novel approach for realizing miniaturized multi layer folded tri band micro-strip band pass filter for Wireless Local Area Network (WLAN and Worldwide interoperatability for Microwave Access (WiMAX applications. The proposed filter consists of a pair of folded hairpin stepped impedance resonators and pair of open loop resonators to achieve tri-band performance. The size of the folded micro-strip tri-band filter is reduced by nearly 60% due to the structural folding arrangement of SIR compared with conventional multilayer triband filter. The folded hairpin resonator helps to reduce the size of the filter. The stepped impedance resonators are designed to operate at the first and third pass bands and the open loop resonators at the second pass band. The design methodology of the tri-band band pass filter was presented. The simulated results of proposed tri-band filter were compared with the conventional one and tabulated.
Shuttle Ku-band and S-band communications implementations study
Huth, G. K.; Nessibou, T.; Nilsen, P. W.; Simon, M. K.; Weber, C. L.
1979-01-01
The interfaces between the Ku-band system and the TDRSS, between the S-band system and the TDRSS, GSTDN and SGLS networks, and between the S-band payload communication equipment and the other Orbiter avionic equipment were investigated. The principal activities reported are: (1) performance analysis of the payload narrowband bent-pipe through the Ku-band communication system; (2) performance evaluation of the TDRSS user constraints placed on the S-band and Ku-band communication systems; (3) assessment of the shuttle-unique S-band TDRSS ground station false lock susceptibility; (4) development of procedure to make S-band antenna measurements during orbital flight; (5) development of procedure to make RFI measurements during orbital flight to assess the performance degradation to the TDRSS S-band communication link; and (6) analysis of the payload interface integration problem areas.
47 CFR 15.713 - TV bands database.
2010-10-01
...2010-10-01 2010-10-01 false TV bands database. 15.713 Section 15.713 Telecommunication...Television Band Devices § 15.713 TV bands database. (a) Purpose. The TV bands database serves the following functions:...
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 ?-brass (??-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 ?2(?) and the photoemission spectra agree well with experiments. We find that the main absorption edge as observed in the ?2 trace has contributions from conduction-band transitions as well as transitions from the Cu d states. The comparison to photoemission results indicates that the calculated Cu d bands are too narrow, but that their position relative to the Fermi level is correct. The derived Fermi-surface model allows a detailed interpretation of the de Hass-van Alphen (dHvA) data. The present model has no open orbit along for B?? ?110?. This agrees with dHvA as well as magnetoresistance measurements. Four new extremal cross sections have been found and related to previously unexplained dHvA frequencies. In general, the Fermi-surface dimensions agree extremely well with dHvA measurements, and the ratios between the experimental and the calculated cyclotron masses vary between 1.18 and 1.43.
Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice
Energy Technology Data Exchange (ETDEWEB)
Liu, Wan-guo; Pan, Feng-ming, E-mail: fmpan@nuaa.edu.cn; Cai, Li-wei
2014-05-15
Highlights: • Plane wave expansion is generalized to superconductor-medium periodic structure. • A wider band gap appears than that in conventional photonic crystals. • Part of original energy levels are rearranged upon consideration of the superconductivity. • Band gap width decreases monotonically with penetration length, but not with the filling factor. • Band gaps can be partially shut down or opened by adjusting filling factor. - Abstract: Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor.
Theory of Band Warping and its Effects on Thermoelectronic Transport Properties
Mecholsky, Nicholas; Resca, Lorenzo; Pegg, Ian; Fornari, Marco
2015-03-01
Transport properties of materials depend upon features of band structures near extrema in the BZ. Such features are generally described in terms of quadratic expansions and effective masses. Such expansions, however, are permissible only under strict conditions that are sometimes violated by materials. Suggestive terms such as ``band warping'' have been used to refer to such situations and ad hoc methods have been developed to treat them. We develop a generally applicable theory, based on radial expansions, and a corresponding definition of angular effective mass which also accounts for effects of band non-parabolicity and anisotropy. Further, we develop precise procedures to evaluate band warping quantitatively and as an example we analyze the warping features of valence bands in silicon using first-principles calculations and we compare those with semi-empirical models. We use our theory to generalize derivations of transport coefficients for cases of either single or multiple electronic bands, with either quadratically expansible or warped energy surfaces. We introduce the transport-equivalent ellipsoid and illustrate the drastic effects that band warping can induce on thermoelectric properties using multi-band models. Vitreous State Laboratory and Samsung's GRO program.
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Kanaya, Kazuyuki
The results of main QCD calculations performed on the dedicated parallel computer QCDPAX are reviewed. A project to construct a new parallel computer aiming at the peak performance of 300 GFLOPS is reported.
International Nuclear Information System (INIS)
A Monte Carlo algorithm to efficiently calculate static alpha eigenvalues, N = ne/sup ?t/, for supercritical systems has been developed and tested. A direct Monte Carlo approach to calculating a static alpha is to simply follow the buildup in time of neutrons in a supercritical system and evaluate the logarithmic derivative of the neutron population with respect to time. This procedure is expensive, and the solution is very noisy and almost useless for a system near critical. The modified approach is to convert the time-dependent problem to a static ?-eigenvalue problem and regress ? on solutions of a- k-eigenvalue problem. In practice, this procedure is much more efficient than the direct calculation, and produces much more accurate results. Because the Monte Carlo codes are intrinsically three-dimensional and use elaborate continuous-energy cross sections, this technique is now used as a standard for evaluating other calculational techniques in odd geometries or with group cross sections
In-clustering induced anomalousbehavior of band gap in InAlN and InGaN
DEFF Research Database (Denmark)
Gorczyca, I.; Suski, T.
2010-01-01
Electronic band structure calculations of In containing ternary nitride alloys are presented showing a strong modification of the band gap, EG and its pressure coefficient, dEG/dp, as a function of In-content. Two different arrangements of In atoms are considered: uniform and clustered. It is shown that Indium clustering is the additional, large factor leading to the unusual bowings of the band gaps and their pressure coefficients. The theoretical results are compared with experimental data on variations of EG with In content. In the analysis of observed phenomena we point out the particular role of the uppermost valence band.
Effect of Dopant Concentrations on Conversion Efficiency of SiC-Based Intermediate Band Solar Cells
Heidarzadeh, H.; Rostami, A.; Dolatyari, M.; Rostami, G.
It was recognized that the introducing of a narrow metallic band states in the crystal structure of semiconductors make materials that they can be used as intermediate band materials for improving the power conversion efficiency of high band gap single junction solar cells. In these structures intermediate bands would serve as a "stepping stone" for photons with different energies to excite electrons from the valence to the conduction bands. Low-energy photons can be captured by this method that would pass through a conventional solar cell. An optimal IBSC (intermediate band solar cells) has a total band gap of about 1.95 eV and 3C-SiC has the closest band gap to this value (band gap of 2.2 eV). Excellent electronic properties of 3C-SiC such as high electron mobility and saturated electron drift velocity and its suitable band gap makes it an important alternative material for light harvesting technologies instead of conventional semiconductors like silicon. In this condition detailed balance analysis predicts a limiting efficiency of more than 55 % for an optimized, single junction intermediate band solar cell that it is higher than efficiency of an optimized two junction tandem solar cell. In this study we have analyzed Fe doped 3C-SiC by ab initio calculations for Fe concentration of 1.05, 1.85, 3.22, and 5.55 %. The results show conversion efficiency for designed solar cell change with altering in Fe contents. The maximum efficiency has been obtained for crystals with 3 % Fe3+ as dopant in 3C-SiC structure.
Polarization propagator calculations
International Nuclear Information System (INIS)
The latest theoretical developments of the polarization propagator method are discussed. This propagator is the double-time Green's function which describes the propagation of a density disturbance through an interacting system. The application of the method in calculations of excitation properties of atomic, molecular and metallic systems are outlined with examples of calculations of electronic spectra, radiative lifetimes of excited states, second order optical and magnetic properties and ground state correlation energies. (C.F.)
Big Bang Nucleosynthesis Calculation
Kurki-Suonio, Hannu
2001-01-01
I review standard big bang nucleosynthesis and some versions of nonstandard BBN. The abundances of the primordial isotopes D, He-3, and Li-7 produced in standard BBN can be calculated as a function of the baryon density with an accuracy of about 10%. For He-4 the accuracy is better than 1%. The calculated abundances agree fairly well with observations, but the baryon density of the universe cannot be determined with high precision. Possibilities for nonstandard BBN include i...
Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)
1997-01-01
The current methods of quantum chemical calculations will be reviewed. The accent will be on the accuracy that can be achieved with these methods. The basis set requirements and computer resources for the various methods will be discussed. The utility of the methods will be illustrated with some examples, which include the calculation of accurate bond energies for SiF$_n$ and SiF$_n^+$ and the modeling of chemical data storage.
Johansson, Stig
This pair of pH calculation programs serves as an excellent tool for anyone wishing to calculate the pH of a solution containing multiple acids and bases. These programs allow practitioners to predict the pH of simple and complex acid/base solutions and buffers. They may be downloaded free of charge via the website. Users are encouraged to carefully read the guides provided by the author.
Fusion cross section calculations
International Nuclear Information System (INIS)
We have calculated fusion cross sections for a large body of data using the critical distance, the static extrapush and the static fast fission models. A dynamical calculation, including friction forces, has also been performed. A comparison between the different approaches is done. We show that we are still far from accurately predicting fusion cross sections although the general trend is in some cases satisfactory for models using new concepts about fusion
Calculating a Biodiversity Index
In this Biodiversity Counts activity, students learn how scientists calculate a biodiversity index using a page from the phone book as their data source. The printable five-page PDF handout includes a series of inquiry-based questions to get students thinking about what they already know about biodiversity and how living and non-living things are connected, step-by-step directions for calculating a biodiversity index, and a worksheet that includes brainstorming questions and areas for recording answers.
Coherent band pathways between knots and links
Buck, Dorothy
2014-01-01
We categorise coherent band (aka nullification) pathways between knots and 2-component links. Additionally, we characterise the minimal coherent band pathways (with intermediates) between any two knots or 2-component links with small crossing number. We demonstrate these band surgeries for knots and links with small crossing number. We apply these results to place lower bounds on the minimum number of recombinant events separating DNA configurations, restrict the recombination pathways and determine chirality and/or orientation of the resulting recombinant DNA molecules.
Efficiency of Medium-Band Surveys
Wolf, Christian; Meisenheimer, Klaus; Röser, Hermann-Josef
2000-01-01
We simulate multi-color surveys, which use the same telescope time on different filter sets of broad-band and medium-band filters. We use a photometric classification method for identifying stars, galaxies and quasars and for estimating multi-color redshifts of extragalactic objects. A library of >65000 color templates is used for comparison with observed objects. Spectroscopy from the CADIS survey has proven the performance of the method. We learned, that medium-band survey...
Two-band Ginzburg-Landau theory for the lower critical field Hc1 in MgB2
International Nuclear Information System (INIS)
The temperature dependence of the lower critical field Hc1(T) for the superconducting magnesium diboride, MgB2, is studied in the vicinity of Tc using a two-band Ginzburg-Landau (G-L) theory. The theoretically calculated Hc1(T) near Tc exhibits a negative curvature. The results are shown to be in good agreement with the experimental data. In addition, two-band G-L theory calculations give a temperature dependence of the Ginzburg-Landau parameter ?(T)=?(T)/?(T), which varies little with the temperature in a manner similar to the microscopic single-band BSC theory. (author)
Influence of distortion on the electronic band structure of CuInSe2
Tototzintle-Huitle, H; Rodríguez, José Alberto; Baquero, R
2005-01-01
We present a tight-binding calculation of the influence of distorsion on the bulk electronic structure of the chalcopyrite CuInSe2. We calculate the ideal case and then the effect of the inclusion of the distortions. We analyze our results in detail and conclude from a comparison with other work that the distortions must be included in the Hamiltonian to get a proper account of the electronic band structure. We use our new Hamiltonian to study the effect that both the tetragonal and the anionic distortion have on the (112) surface electronic band structure. We find this effect non-negligible.
Extended mode in blocked impurity band detectors for terahertz radiation detection
International Nuclear Information System (INIS)
We demonstrate the existence of an interfacial barrier in blocked impurity band (BIB) detectors using temperature-dependent dark current and corresponding theoretical calculations. Considering the effects of the interfacial barrier, the calculated photoresponse is in good agreement with the experimental results. A dual-excitation model, including the direct excitation over the full barrier and excitation to the band minimum with subsequent tunneling into the blocking layer, is proposed to quantitatively explain the observed photoresponse extension. A concept of extended-mode detection is developed to suggest the option for some selective photoresponse in the terahertz region and open the possibility of extending BIB photoresponse to lower frequency.
Band Structure of Carbon Nanotubes in a Perpendicular Electric Field 2.0
Ravaioli, Umberto
The NanoEd Resource Portal, a â??dynamic repository for information dissemination, research and collaborations among the community of nanoscale science and engineering education (NSEE) learners, teachers and researchers,â? provides this interactive simulator. Contributed by Professor Umberto Ravaioli from the University of Illinois at Urbana-Champaign, this simulator performs "band structure calculations for zigzag and armchair type carbon nanotubes (CNT)." This band structure calculator could prove useful for both students and instructors in the field, and could prove valuable in the classroom as well.
Band crossing and triaxiality in 129Ce
International Nuclear Information System (INIS)
Gamma-ray decays from states in 129Ce have been studied using 16O-induced reactions on 116Sn and 117Sn targets. Previously known positive- and negative-parity bands have been extended to spins of 31/2 and 39/2, respectively. Band crossings are seen for the first time in 129Ce and occur near the same rotational frequency as the hsub(11/2) proton band crossing in 130Ce. The signature splittings in the bands are discussed in terms of the cranked shell model with a prolate deformation. (author)
Possible chiral bands in 194Tl
International Nuclear Information System (INIS)
High spin states in 194Tl, excited through the 181Ta(18O,5n) fusion evaporation reaction, were studied using the AFRODITE array at iThemba LABS. Candidate chiral bands built on the ?h9/2 x ?i13/21 configuration were found. Furthermore these bands were observed through a band crossing caused by the excitation of a ?i13/2 pair. Above the band crossing the excitation energies remain close, suggesting that chirality may persist for the four quasiparticle configuration too.
Fundamentals of Intermediate Band Solar Cells
Martí, Antonio; Luque, Antonio
Intermediate band solar cells aim to exploit the energy of below bandgap energy photons. They are based on materials that are characterised by the existence of an additional electronic band (intermediate band) located in between the conduction and valence band. An optimised IBSC has near the same limiting efficiency potential (63.2%) than a triple junction solar cells but without requiring tunnel junctions to connect the single gap solar cells. This chapter reviews its fundamental theory and introduces the different approaches that are being followed towards its implementation: quantum dots, the insertion of suitable impurities into a semiconductor host at sufficiently high densities (bulk approach) and the molecular approaches.
Band edge singularities and density of states in YTaO4 and YNbO4
International Nuclear Information System (INIS)
We study the structural and electronic properties of YTaO4 and YNbO4 by means of accurate first-principle total energy calculations. The calculations are based on density functional theory (DFT). The total energy, electronic band structure, and density of states are calculated via the full potential linear-augmented plane wave approach, as implemented in the WIEN2K code, within the framework of DFT. The results show that the valence bands of tantalate and niobate systems are from O 2p states. Conduction bands are divided into two parts. The lower conduction band is mainly composed of Ta 5d or Nb 4d states and the upper conduction bands involve contribution mainly from Y 4d states of YTaO4 or YNbO4. The efficient band gaps in yttrium tantalate and niobate are determined about 4.8 and 4.1 eV, respectively. The agreement between the calculations and the experimental data is excellent. The efficient band gap and a simple model illustrating excitation and emission process in considered host lattices are discussed. (authors)
Isolated flat bands and spin-1 conical bands in two-dimensional lattices
Green, Dmitry; Santos, Luiz; Chamon, Claudio
2010-08-01
Dispersionless bands, such as Landau levels, serve as a good starting point for obtaining interesting correlated states when interactions are added. With this motivation in mind, we study a variety of dispersionless (“flat”) band structures that arise in tight-binding Hamiltonians defined on hexagonal and kagome lattices with staggered fluxes. The flat bands and their neighboring dispersing bands have several notable features: (a) flat bands can be isolated from other bands by breaking time-reversal symmetry, allowing for an extensive degeneracy when these bands are partially filled; (b) an isolated flat band corresponds to a critical point between regimes where the band is electron-like or hole-like, with an anomalous Hall conductance that changes sign across the transition; (c) when the gap between a flat band and two neighboring bands closes, the system is described by a single spin-1 conical-like spectrum, extending to higher angular momentum the spin-1/2 Dirac-like spectra in topological insulators and graphene; (d) some configurations of parameters admit two isolated parallel flat bands, raising the possibility of exotic “heavy excitons”; and (e) we find that the Chern number of the flat bands, in all instances that we study here, is zero.
Calculational methods for PWRs
International Nuclear Information System (INIS)
The design procedure for PWR reactors has two main stages: the assembly transport calculations (computed by the APOLLO code) and the core calculation, achieved by the diffusion code CRONOS. For rodded or poisoned assemblies, the transport calculation uses the DP00 option (no cell cylinderization and face differentiation) at the very time when the non rodded ones are accurately treated by the ROTH option (cell cylinderization and no face differentiation). The core calculation in diffusion theory necessitates condensations for cross sections: on space (pin-by-pin or per assembly) and energy (2 groups). Different numerical methods have been studied (finite elements and finite differences). The 3D power transient calculations need more accurate flux precision criteria than fuel depletion studies. This comes from the evolution of the axial Xenon distribution. In case of large meshes (homogeneous description of the core), the linear approximations are not precise enough to render the radial flux shape. Sufficient results are given by the parabolic finite element with 4 meshes per assembly, with a reduced cost compared to the cubic approximation with 4 meshes, chosen as reference. When taking into account the feedback effects for 2D core calculations, the power shape is more sensible to the heat transfer coefficient than to the thermalhydraulic mesh and to the channel exchange hypothesis. This design procedure has been compared to measures that have been obtained at the beginning of life of the CP1 PWR 900 reactors. The homogeneous one overestimates the rod efficiency (about 6%). The pin-by-pin calculation is in very good agreement with the measurements. (author). 10 refs, 7 figs, 5 tabs
Residual stress dependant anisotropic band gap of various (hkl) oriented BaI{sub 2} films
Energy Technology Data Exchange (ETDEWEB)
Kumar, Pradeep; Gulia, Vikash; Vedeshwar, Agnikumar G., E-mail: agni@physics.du.ac.in, E-mail: agvedeshwar@gmail.com [Thin Film Laboratory, Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India)
2013-11-21
The thermally evaporated layer structured BaI{sub 2} grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48–3.43?eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (?0.071?eV/GPa) found to be significantly higher than that calculated (?0.047?eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass m{sub e}{sup *}=0.66m{sub 0} and the hole effective mass m{sub h}{sup *}=0.53m{sub 0} have been determined from the calculated band structure.