The application of an atomic Hartree-Fock-Slater method is exposed in the present work for the simultaneous obtainment of all parameters used in the extended Hueckel method with charge interaction (IEH): The diagonal elements of the Hamiltonian, the constants of the quadratic relation between. (Author). 16 refs., 3 tabs
In preparation for work with aqueous electrolytes at above saturation pressures and at temperatures to 3500C, an equation was developed for the representation of the dielectric constant of water over this range. With this equation and an equation of state for water, the Debye--Hueckel limiting law parameters for osmotic and activity coefficients, enthalpies, heat capacities, volumes, compressibilities, and expansibilities were calculated and are presented. 5 figures, 4 tables
Calculation of complex band structure for low symmetry lattices
Srivastava, Manoj; Zhang, Xiaoguang; Cheng, Hai-Ping
2009-03-01
Complex band structure calculation is an integral part of a first-principles plane-wave based quantum transport method. [1] The direction of decay for the complex wave vectors is also the transport direction. The existing algorithm [1] has the limitation that it only allows the transport direction along a lattice vector perpendicular to the basal plane formed by two other lattice vectors, e.g., the c-axis of a tetragonal lattice. We generalize this algorithm to nonorthogonal lattices with transport direction not aligned with any lattice vector. We show that this generalization leads to changes in the boundary conditions and the Schrodinger's equation projected to the transport direction. We present, as an example, the calculation of the complex band structure of fcc Cu along a direction perpendicular to the (111) basal plane. [1] Hyoung Joon Choi and Jisoon Ihm, Phys. Rev. B 59, 2267 (1999).
Relativistic Band Calculation and the Optical Properties of Gold
Christensen, N Egede; Seraphin, B. O.
1971-01-01
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......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...... 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 ε2 profile calculated in a crude model assuming constant matrix elements matches well the corresponding experimental results. The...
Emission bands of phosphorus and calculation of band structure of rare earth phosphides
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
One approach to adiabatic population transfer by Hueckel molecular orbital theory
To achieve the selective population transfer to the specific excited state of molecules, the delayed-pulse method developed in the three-level system is more attractive and effective than the ordinary π-pulses method. However, two pulses in this adiabatic method are in a counterintuitive order and are significantly overlapped, so that it is very difficult to understand the physical meanings of the dynamical process. Here the authors develop the effective method to understand the adiabatic processes in a pictorial and easy way by using the concept of the Hueckel molecular orbital theory. Then the authors investigate the complete population transfer in the four-level system in detail
Takahashi, M. [Ajinomoto Central Research Lab., Kawasaki (Japan); Bracken, P.; Cizek, J.; Paldus, J. [Univ. of Waterloo, Ontario (Canada)
1995-03-05
The perturbation expansion coefficients for the ground-state energy of the half-filled one-dimensional Hubbard model with N = 4{sub {nu}} + 2, ({nu} = 1,2,...) sites and satisfying cyclic boundary conditions were calculated in the Hueckel limit (U/{beta} {r_arrow} 0), where {beta} designates the one-electron hopping or resonance integral, and U, the two-electron on-site Coulomb integral. This was achieved by solving-order by order-the Lieb-Wu equations, a system of transcendental equations that determines the set of quasi-momenta (k{sub i}) and spin variable {tau}{sub {alpha}} for this model. The exact values for these quantities were found for the N = 6 member ring up to the 20th order in terms of the coupling constant B = U/2{beta}, as well as numerically for 10 {le} N {le} 50, and the N = 6 Lieb-Wu system was reduced to a system of sextic algebraic equations. These results are compared with those of the infinite system derived analytically by Misurkin and Ovchinnikov. It is further shown how the results of this article can be used for the interpolation by the root of a polynomial. It is demonstrated that a polynomial of relatively small degree provides a very good approximation for the energy in the intermediate coupling region. 20 refs., 3 tabs.
Self-consistent Hartree energy band calculation for manganese oxide (MnO)
A self-consistent Hartree energy band calculation was done for the MnO crystal using the linear combination of atomic orbitals (LCAO) method. Gaussian type atomic orbitals were used in the LCAO method. This calculation was done for paramagnetic MnO with the NaCl lattice structure. The results show that the energy bands around the Fermi level of MnO are unusually flat, meaning that the electrons in this region are strongly localized. Therefore short range correlation was added to the results of this band calculation. The short range correlation effects were added by calculating atomic type corrections to the original band structure. The results of this correlation calculation show that a large amount of energy is required to excite an electron from the Mn 3d band. Therefore the lowest excitation (the one that requires the least energy) is an excitation from the top of the O 2p band to the Fermi level. This yields a fundamental band gap of 4.8 eV which is in good agreement with optical absorption experiments. This fundamental band gap of 4.8 eV implies that MnO is an insulator, in agreement with conductivity experiments. The Hartree results for the valence bands of MnO agree very well with the results of photoemission experiments. In comparison to the photoemission data, the results of the self-consistent Hartree calculation are an order of magnitude better than the results of the only other band calculation for MnO. Comparison with band calculations for other transition metal oxides (other than MnO) imply that with a good self-consistent Hartree energy band calculation for MnO can be superior
IBM-2 calculation of band mixing in 132Ba
The band crossing in 132Ba has been investigated by using the interacting boson model. A broken neutron pair has been coupled to a collective boson core. The boson-fermion interaction hamiltonian contains terms which can transform a boson into a pair of quasiparticles and vice versa. The parameters were partly determined by fitting the collective states of 132,134Ba and the yrast states of 131Ba. The energy backbending has been satisfactorily reproduced. Good agreement of the electromagnetic moments has been reached. The structure of the wave functions has been discussed. (author)
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.
Calculation of the Energy Band Diagram of a Photoelectrochemical Water Splitting Cell
Cendula, Peter; Tilley, S. David; Girnenez, Sixto; Bisquert, Juan; Schmid, Matthias; Graetzel, Michael; Schumachert, Juergen O.
2014-01-01
A physical model is presented for the semiconductor electrode of a photoelectrochemical cell. The model accounts for the potential drop in the Helmholtz layer and thus enables description of both band edge pinning and unpinning. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with...
Boorse, R.S.
1993-01-01
Methods of chemical synthesis and theoretical calculation was used to form new materials that have improved adhesion of a thin metal film to a ceramic. Two goals of this investigation were to develop new synthesis of metal-ceramic couples with improved adhesion between the two components and a fundamental understanding of the chemical factors that affect adhesion. Extended Hueckel calculations were performed on a series of Pt- and NiPt-NiO metal-ceramic couples to examine bonding. The calculations showed an 5 fold increase in adhesion energy in NiPt-NiO over Pt-NiO. Bonding across the interface is found to decrease with increased electron donation as interfacially antibonding orbitals are filled. The synthesis of (Al[sub 1[minus]x]Cr[sub x])[sub 2]O[sub 3] mixed metal oxide powders and coatings by sol-gel methodology utilizing three chromium precursors is reported. Thus, Al[Cr(CO)[sub 3]C[sub 5]H[sub 5
Perturbation method for calculation of narrow-band impedance and trapped modes
An iterative method for calculation of the narrow-band impedance is described for a system with a small variation in boundary conditions, so that the variation can be considered as a perturbation. The results are compared with numeric calculations. The method is used to relate the origin of the trapped modes with the degeneracy of the spectrum of an unperturbed system. The method also can be applied to transverse impedance calculations. 6 refs., 6 figs., 1 tab
The band structure of metallic sodium is calculated, using for the first time the self-consistent field variational cellular method. In order to implement the self-consistency in the variational cellular theory, the crystal electronic charge density was calculated within the muffin-tin approximation. The comparison between our results and those derived from other calculations leads to the conclusion that the proposed self-consistent version of the variational cellular method is fast and accurate. (author)
Band Structure Calculation of MnxCoyFe3-x-yO4
Rosenson, A.; Tailhades, Ph.
1997-01-01
Electronic band structure of MnxCoyFe3-x-yO4 has been calculated in high symmetrical points and lines of the first Brillouin zone within the scope one-electron quasirelativistic pseudopotential approach. Atomic potential form-factors have been calculated in accordance with modified LCAO method. Dependence of energy gap Eg=Eg(x,y) against Mn, Co and Fe concentrations is calculated and presented.
Definition of two band parameters for use in photon transport calculations
Cullen, D.E.
1978-04-01
The multigroup photon diffusion equations are derived from the Boltzmann equation. Limitations and assumptions imposed by the diffusion equation are thus apparent. In addition, this approach serves to define all of the required diffusion parameters in terms of cross sections; the relationship to the multi-band parameters used in neutron transport calculations can thus be clearly established. All required two-band parameters are defined in terms of Planckian and Rosseland mean values. (RWR)
Model calculation of oscillatory magnetic breakdown in metals with multiply degenerate bands
Thalmeier, P.; Falicov, L. M.
1981-03-01
We present a model calculation of the oscillatory magnetoresistance in a metal with three degenerate bands. We have in mind the example of body-centered cubic iron where, in the neighborhood of the H point of the Brillouin zone, three bands have multiple intersections and contacts. For magnetic fields along the [011] direction, the Fermi surface in the vicinity of H exhibits a complicated three-band interferometer which leads to complex oscillations in the magnetoresistance. A Fourier analysis of this magnetoresistance reveals that frequencies corresponding to split-beam interference, closed-orbit interference, and mixed type are all present with comparable strength. The connection to the experimental situation is discussed.
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
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 γsub(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)
王学滨
2004-01-01
A method for calculation of temperature distribution in adiabatic shear band is proposed in terms of gradient-dependent plasticity where the characteristic length describes the interactions and interplaying among microstructures. First, the increment of the plastic shear strain distribution in adiabatic shear band is obtained based on gradient-dependent plasticity. Then, the plastic work distribution is derived according to the current flow shear stress and the obtained increment of plastic shear strain distribution. In the light of the well-known assumption that 90% of plastic work is converted into the heat resulting in increase in temperature in adiabatic shear band, the increment of the temperature distribution is presented. Next, the average temperature increment in the shear band is calculated to compute the change in flow shear stress due to the thermal softening effect. After the actual flow shear stress considering the thermal softening effect is obtained according to the Johnson-Cook constitutive relation, the increment of the plastic shear strain distribution, the plastic work and the temperature in the next time step are recalculated until the total time is consumed. Summing the temperature distribution leads to rise in the total temperature distribution. The present calculated maximum temperature in adiabatic shear band in titanium agrees with the experimental observations. Moreover, the temperature profiles for different flow shear stresses are qualitatively consistent with experimental and numerical results. Effects of some related parameters on the temperature distribution are also predicted.
Hybrid functional band gap calculation of SnO6 containing perovskites and their derived structures
We have studied the properties of SnO6 octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO6 containing perovskites. We also have expended the hybrid density functional calculation to the ASnO3/A'SnO3 system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO6 containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO3 for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO6 octahedrons are plotted as polyhedron. (b) Band gap of ASnO3 as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO3/A'SnO3 superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO3, [001] ordered superlattices, and [111] ordered superlattices of ASnO3/A'SnO3 as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO3 and ASnO3/A'SnO3. • The band gap of ASnO3 using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap
Band gap calculation and photo catalytic activity of rare earths doped rutile TiO2
BIAN Liang; SONG Mianxin; ZHOU Tianliang; ZHAO Xiaoyong; DAI Qingqing
2009-01-01
The density of states (DOS) of 17 kinds of rare earths (RE) doped futile TiO2 was by using fast-principles density functional the-ory (DFF) calculation. The band gap widths of RE doped rutile TiO2 were important factors for altering their absorbing wavelengths. The results show that RE ions could obviously reduce the band gap widths and form of energy of rutile TiO2 except Lu, Y, Yb and Sc, and the order of absorbing wavelengths of RE doped rutile TiO2 were the same as that of the results of calculation. The ratio of RE dopant was an-other important factor for the photo catalytic activity of RE doped rutile TiO2, and there was an optimal ratio of dopant. There was a constant for predigesting the calculation difficulty, respectively, which were 0.5mol.% and 100 mol-1 under supposition. The band gap widths of RE doped rutile TiO2 by DFT calculation were much larger than that by experiment. Finally, by transferring the calculation values to experiment values, it could be found and predicted that RE enlarged obviously the absorbing wavelengh of futile TiO2. In addition, the degree of RE ions edging out the Ti atom using the parameters of RE elements was computed.
Calculation of isotopic profile during band displacement on ion exchange resins
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)
Inverse dispersion method for calculation of complex photonic band diagram and PT symmetry
Rybin, Mikhail V.; Limonov, Mikhail F.
2016-04-01
We suggest an inverse dispersion method for calculating a photonic band diagram for materials with arbitrary frequency-dependent dielectric functions. The method is able to calculate the complex wave vector for a given frequency by solving the eigenvalue problem with a non-Hermitian operator. The analogy with PT -symmetric Hamiltonians reveals that the operator corresponds to the momentum as a physical quantity, and the singularities at the band edges are related to the branch points and responses for the features on the band edges. The method is realized using a plane wave expansion technique for a two-dimensional periodic structure in the case of TE and TM polarizations. We illustrate the applicability of the method by the calculation of the photonic band diagrams of an infinite two-dimensional square lattice composed of dielectric cylinders using the measured frequency-dependent dielectric functions of different materials (amorphous hydrogenated carbon, silicon, and chalcogenide glass). We show that the method allows one to distinguish unambiguously between Bragg and Mie gaps in the spectra.
Band gap engineering of early transition-metal-doped anatase TiO₂: first principles calculations.
Li, C; Zhao, Y F; Gong, Y Y; Wang, T; Sun, C Q
2014-10-21
The thermal stability and electronic structures of anatase TiO2 doped with early transition metals (TM) (group III-B = Sc, Y and La; group IV-B = Zr and Hf; group V-B = V, Nb and Ta) have been studied using first principles calculations. It was found that all doped systems are thermodynamically stable, and their band gaps were reduced by 1-1.3 eV compared to pure TiO2. Doping with transition metals affects the strength of the hybrid orbital of TM-O bonding, and the band gap increases approximately linearly with the MP value of TM-O bonding. PMID:25183457
We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results
We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme to obtain corrected band gaps and band offsets. Our calculations include the spin–orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8–1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.
Ribeiro, M. [Centro de Pesquisas Avancadas Wernher von Braun, Av. Alice de Castro P.N. Mattosinho 301, CEP 13098-392 Campinas, SP (Brazil); Ferreira, L.G. [Departamento de Fisica dos Materiais e Mecanica, Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Fonseca, L.R.C. [Center for Semiconductor Components, State University of Campinas, R. Pandia Calogeras 90, 13083-870 Campinas, SP (Brazil); Ramprasad, R. [Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269 (United States)
2012-09-20
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.
k.p Parameters with Accuracy Control from Preexistent First-Principles Band Structure Calculations
Sipahi, Guilherme; Bastos, Carlos M. O.; Sabino, Fernando P.; Faria Junior, Paulo E.; de Campos, Tiago; da Silva, Juarez L. F.
The k.p method is a successful approach to obtain band structure, optical and transport properties of semiconductors. It overtakes the ab initio methods in confined systems due to its low computational cost since it is a continuum method that does not require all the atoms' orbital information. From an effective one-electron Hamiltonian, the k.p matrix representation can be calculated using perturbation theory and the parameters identified by symmetry arguments. The parameters determination, however, needs a complementary approach. In this paper, we developed a general method to extract the k.p parameters from preexistent band structures of bulk materials that is not limited by the crystal symmetry or by the model. To demonstrate our approach, we applied it to zinc blende GaAs band structure calculated by hybrid density functional theory within the Heyd-Scuseria-Ernzerhof functional (DFT-HSE), for the usual 8 ×8 k.p Hamiltonian. Our parameters reproduced the DFT-HSE band structure with great accuracy up to 20% of the first Brillouin zone (FBZ). Furthermore, for fitting regions ranging from 7-20% of FBZ, the parameters lie inside the range of values reported by the most reliable studies in the literature. The authors acknowledge financial support from the Brazilian agencies CNPq (Grant #246549/2012-2) and FAPESP (Grants #2011/19333-4, #2012/05618-0 and #2013/23393-8).
The calculation of the band structure in 3D phononic crystal with hexagonal lattice
Aryadoust, Mahrokh; Salehi, H. [University of Shahid Chamran, Ahvaz (Iran, Islamic Republic of). Dept. of Physics
2015-07-01
In this article, the propagation of acoustic waves in the phononic crystals (PCs) of three dimensions with the hexagonal (HEX) lattice is studied theoretically. The PCs are constituted of nickel (Ni) spheres embedded in epoxy. The calculations of the band structure and the density of states are performed using the plane wave expansion (PWE) method in the irreducible part of the Brillouin zone (BZ). In this study, we analyse the dependence of the band structures inside (the complete band gap width) on c/a and filling fraction in the irreducible part of the first BZ. Also, we have analysed the band structure of the ALHA and MLHKM planes. The results show that the maximum width of absolute elastic band gap (AEBG) (0.045) in the irreducible part of the BZ of HEX lattice is formed for c/a=6 and filling fraction equal to 0.01. In addition, the maximum of the first and second AEBG widths are 0.0884 and 0.0474, respectively, in the MLHKM plane, and the maximum of the first and second AEBG widths are 0.0851 and 0.0431, respectively, in the ALHA plane.
Band-gap shrinkage calculations and analytic model for strained bulk InGaAsP
Connelly, Michael J.
2015-02-01
Band-gap shrinkage is an important effect in semiconductor lasers and optical amplifiers. In the former it leads to an increase in the lasing wavelength and in the latter an increase in the gain peak wavelength as the bias current is increased. The most common model used for carrier-density dependent band-gap shrinkage is a cube root dependency on carrier density, which is strictly only true for high carrier densities and low temperatures. This simple model, involves a material constant which is treated as a fitting parameter. Strained InGaAsP material is commonly used to fabricate polarization insensitive semiconductor optical amplifiers (SOAs). Most mathematical models for SOAs use the cube root bandgap shrinkage model. However, because SOAs are often operated over a wide range of drive currents and input optical powers leading to large variations in carrier density along the amplifier length, for improved model accuracy it is preferable to use band-gap shrinkage calculated from knowledge of the material bandstructure. In this letter the carrier density dependent band-gap shrinkage for strained InGaAsP is calculated by using detailed non-parabolic conduction and valence band models. The shrinkage dependency on temperature and both tensile and compressive strain is investigated and compared to the cube root model, for which it shows significant deviation. A simple power model, showing an almost square-root dependency, is derived for carrier densities in the range usually encountered in InGaAsP laser diodes and SOAs.
Band-gap shrinkage calculations and analytic model for strained bulk InGaAsP
Band-gap shrinkage is an important effect in semiconductor lasers and optical amplifiers. In the former it leads to an increase in the lasing wavelength and in the latter an increase in the gain peak wavelength as the bias current is increased. The most common model used for carrier-density dependent band-gap shrinkage is a cube root dependency on carrier density, which is strictly only true for high carrier densities and low temperatures. This simple model, involves a material constant which is treated as a fitting parameter. Strained InGaAsP material is commonly used to fabricate polarization insensitive semiconductor optical amplifiers (SOAs). Most mathematical models for SOAs use the cube root bandgap shrinkage model. However, because SOAs are often operated over a wide range of drive currents and input optical powers leading to large variations in carrier density along the amplifier length, for improved model accuracy it is preferable to use band-gap shrinkage calculated from knowledge of the material bandstructure. In this letter the carrier density dependent band-gap shrinkage for strained InGaAsP is calculated by using detailed non-parabolic conduction and valence band models. The shrinkage dependency on temperature and both tensile and compressive strain is investigated and compared to the cube root model, for which it shows significant deviation. A simple power model, showing an almost square-root dependency, is derived for carrier densities in the range usually encountered in InGaAsP laser diodes and SOAs. (paper)
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 ...
Band-structure calculations and structure-factor estimates of Cu - their complementarity
Rather than an uncritical comparison of experimental and theoretical values, the various sets of structure-factor values of copper metal derived from experimental diffraction procedures are mutally compared as also are the various sets of theoretical values derived from band-structure calculations. This approach reveals the presence of outlier sets in each group and allows recognition of their condition before any attempt is made to intercompare the groups. Within the experimental group, the γ-ray values do not appear to sustain the absolute status originally claimed from them. Within the theoretical group, an inadequacy in defining the core contribution is indicated. The latter conclusion suggests that it is an inappropriate operation to make direct comparison between diffraction-sourced experimental values of structure factors and theoretical values from band-structure calculations. Instead, the latter should be used on a complementary basis with the full (sin θ)/λ range of experimental values to establish the best core contribution. The minor valence-bond contribution to scattering, which is largely restricted to the low (sin θ)/λ region, is most sensitively defined by reference to band-structure prediction of photoemission spectral distribution. Attention is drawn to the possible significance of the form-factor curve versus (sin θ)/λ being dependent on the unit-cell dimension. (orig.)
Isotopic selectivity calculations are carried out for minor calcium isotopes against the major isotope 40Ca for the single-resonance two-step and double-resonance three-step photoionization schemes with narrow-band lasers by using spectral simulation (SS) and modified spectrum (MS) approaches. The results of these calculations are compared with the density matrix (DM) results reported in the literature. It is noted that the values of isotopic selectivity from the SS approach do not agree with those from the DM approach whereas the MS approach, considering hole burning in the Doppler-broadened atomic spectrum, predicts selectivity values which are in good agreement with the DM results. It is argued that one can adequately use the simple MS approach rather than the complex DM approach for the calculation of isotopic selectivity of multi-step photoionization with single-frequency lasers. (author)
Calculation Method for Flight Limit Load of V-band Clamp Separation Shock
Iwasa, Takashi; Shi, Qinzhong
A simplified calculation method for estimating a flight limit load of the V-band clamp separation shock was established. With this method, the flight limit load is estimated through addition of an appropriate envelope margin to the results acquired with the simplified analysis method proposed in our previous paper. The envelope margin used in the method was calculated based on the reviews on the differences observed between the results of a pyroshock test and the analysis. Using the derived envelope margin, a calculating formula of the flight limit load, which envelopes the actual pyroshock responses with a certain probability, was developed. Based on the formula, flight limit loads for several actual satellites were estimated and compared to the test results. The comparative results showed that the estimated flight limit loads appropriately envelope the test results, which confirmed the effectiveness of the proposed method.
Bloch mode synthesis: Ultrafast methodology for elastic band-structure calculations
Krattiger, Dimitri; Hussein, Mahmoud I.
2014-12-01
We present a methodology for fast band-structure calculations that is generally applicable to problems of elastic wave propagation in periodic media. The methodology, called Bloch mode synthesis, represents an extension of component mode synthesis, a set of substructuring techniques originally developed for structural dynamics analysis. In Bloch mode synthesis, the unit cell is divided into interior and boundary degrees-of-freedom, which are described, respectively, by a set of normal modes and a set of constraint modes. A combination of these mode sets then forms a reduced basis for the band structure eigenvalue problem. The reduction is demonstrated on a phononic-crystal model and a locally resonant elastic-metamaterial model and is shown to accurately predict the frequencies and Bloch mode shapes with a dramatic decrease in computation time in excess of two orders of magnitude.
Smith, Matthew W.; Dallmeyer, Ian; Johnson, Timothy J.; Brauer, Carolyn S.; McEwen, Jean-Sabin; Espinal, Juan F.; Garcia-Perez, Manuel
2016-04-01
Raman spectroscopy is a powerful tool for the characterization of many carbon 27 species. The complex heterogeneous nature of chars and activated carbons has confounded 28 complete analysis due to the additional shoulders observed on the D-band and high intensity 29 valley between the D and G-bands. In this paper the effects of various vacancy and substitution 30 defects have been systematically analyzed via molecular modeling using density functional 31 theory (DFT) and how this is manifested in the calculated gas-phase Raman spectra. The 32 accuracy of these calculations was validated by comparison with (solid-phase) experimental 33 spectra, with a small correction factor being applied to improve the accuracy of frequency 34 predictions. The spectroscopic effects on the char species are best understood in terms of a 35 reduced symmetry as compared to a “parent” coronene molecule. Based upon the simulation 36 results, the shoulder observed in chars near 1200 cm-1 has been assigned to the totally symmetric 37 A1g vibrations of various small polyaromatic hydrocarbons (PAH) as well as those containing 38 rings of seven or more carbons. Intensity between 1400 cm-1 and 1450 cm-1 is assigned to A1g 39 type vibrations present in small PAHs and especially those containing cyclopentane rings. 40 Finally, band intensity between 1500 cm-1 and 1550 cm-1 is ascribed to predominately E2g 41 vibrational modes in strained PAH systems. A total of ten potential bands have been assigned 42 between 1000 cm-1 and 1800 cm-1. These fitting parameters have been used to deconvolute a 43 thermoseries of cellulose chars produced by pyrolysis at 300-700 °C. The results of the 44 deconvolution show consistent growth of PAH clusters with temperature, development of non-45 benzyl rings as temperature increases and loss of oxygenated features between 400 °C and 46 600 °C
Friedrich, C.; Müller, M.C.T.D.; Blügel, S.
2011-01-01
Recently, Shih et al. [Phys. Rev. Lett. 105, 146401 (2010)] published a theoretical band gap for wurtzite ZnO, calculated with the non-self-consistent GW approximation, that agreed surprisingly well with experiment while deviating strongly from previous studies. They showed that a very large number of empty bands is necessary to converge the gap. We reexamine the GW calculation with the full-potential linearized augmented-plane-wave method and find that even with 3000 bands the band gap is no...
Yu Wang
2002-01-01
Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.
D. P. Samajdar
2014-01-01
Full Text Available The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1-xBix and InSb1-xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E+ levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E− energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.
First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2
HOU Xing-Gang; LIU An-Dong; HUANG Mei-Dong; LIAO Bin; WU Xiao-Ling
2009-01-01
The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density funetionai theory with the full-potentiai linearized-augraented-plane-wave method.New occupied bands ore found between the band gaps of both Ag-doped rutile and anatase TiO2.The formation of these new bands Capri be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption.
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
Voltage effect in PTCR ceramics: Calculation by the method of tilted energy band
A numerical model for the calculation of the electrical characteristics of donor-doped BaTiO3 semiconducting ceramics is suggested. This paper established a differential equation about electron level on the base of Poisson equation, and solved the equation with Runge-Kutta method. Under extra electric field, electrical characteristics have been calculated by the method of tilted energy band. We have quantitatively computed the positive temperature coefficient of resistivity (PTCR) behavior of donor-doped BaTiO3 semiconducting ceramics and its voltage effect, and further obtained non-linear current-voltage characteristics with different grain sizes at different temperature. The results pointed out that the resistance jumping is reduced with increasing electric field applied; current and voltage relation follows Ohm's law below Curie temperature, and exhibits strong non-linear above Curie temperature; the non-linear coefficient shows a maximum value at temperature the resistivity reaches maximum and with grain size closed to depletion region width. The results are compared with experimental data.
Hybrid functional calculations on the band gap bowing parameters of In x Ga1‑x N
Mei, Lin; Yixu, Xu; Jianhua, Zhang; Shunqing, Wu; Zizhong, Zhu
2016-04-01
The electronic band structures and band gap bowing parameters of In x Ga1‑x N are studied by the first-principles method based on the density functional theory. Calculations by employing both the Heyd-Scuseria-Ernzerh of hybrid functional (HSE06) and the Perdew-Burke-Ernzerhof (PBE) one are performed. We found that the theoretical band gap bowing parameter is dependent significantly on the calculation method, especially on the exchange-correlation functional employed in the DFT calculations. The band gap of In x Ga1‑x N alloy decreases considerably when the In constituent x increases. It is the interactions of s–s and p–p orbitals between anions and cations that play significant roles in formatting the band gaps bowing. In general, the HSE06 hybrid functional could provide a good alternative to the PBE functional in calculating the band gap bowing parameters. Project supported by the National Natural Science Foundation of China (Nos. 11204257, 21233004) and the China Postdoctoral Science Foundation (No. 2012M511447).
Empiric k·p Hamiltonian calculation of the band-to-band photon absorption in semiconductors
The Empiric k·p Hamiltonian method is usually applied to nanostructured semiconductors. In this paper, it is applied to a homogeneous semiconductor in order to check the adequacy of the method. In this case, the solutions of the diagonalized Hamiltonian, as well as the envelope functions, are plane waves. The procedure is applied to the GaAs and the interband absorption coefficients are calculated. They result in reasonable agreement with the measured values, further supporting the adequacy of the Empiric k·p Hamiltonian method
Yang Ping; Li Pei; Zhang Li-Qiang; Wang Xiao-Liang; Wang Huan; Song Xi-Fu; Xie Fang-Wei
2012-01-01
The lattice,the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by firstprinciples 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.
Zerveas, George; Caruso, Enrico; Baccarani, Giorgio; Czornomaz, Lukas; Daix, Nicolas; Esseni, David; Gnani, Elena; Gnudi, Antonio; Grassi, Roberto; Luisier, Mathieu; Markussen, Troels; Osgnach, Patrik; Palestri, Pierpaolo; Schenk, Andreas; Selmi, Luca; Sousa, Marilyne; Stokbro, Kurt; Visciarelli, Michele
2016-01-01
We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k · p and non-parabolic effective mass models. Parameter sets for the non-parabolic Γ, the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In0.53Ga0.47 As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III-V semiconductor band structure calculation methods and calibrated band parameters for device simulations.
Zacharias, Marios; Giustino, Feliciano
2016-08-01
Recently, Zacharias et al. [Phys. Rev. Lett. 115, 177401 (2015), 10.1103/PhysRevLett.115.177401] developed an ab initio theory of temperature-dependent optical absorption spectra and band gaps in semiconductors and insulators. In that work, the zero-point renormalization and the temperature dependence were obtained by sampling the nuclear wave functions using a stochastic approach. In the present work, we show that the stochastic sampling of Zacharias et al. can be replaced by fully deterministic supercell calculations based on a single optimal configuration of the atomic positions. We demonstrate that a single calculation is able to capture the temperature-dependent band-gap renormalization including quantum nuclear effects in direct-gap and indirect-gap semiconductors, as well as phonon-assisted optical absorption in indirect-gap semiconductors. In order to demonstrate this methodology, we calculate from first principles the temperature-dependent optical absorption spectra and the renormalization of direct and indirect band gaps in silicon, diamond, and gallium arsenide, and we obtain good agreement with experiment and with previous calculations. In this work we also establish the formal connection between the Williams-Lax theory of optical transitions and the related theories of indirect absorption by Hall, Bardeen, and Blatt, and of temperature-dependent band structures by Allen and Heine. The present methodology enables systematic ab initio calculations of optical absorption spectra at finite temperature, including both direct and indirect transitions. This feature will be useful for high-throughput calculations of optical properties at finite temperature and for calculating temperature-dependent optical properties using high-level theories such as G W and Bethe-Salpeter approaches.
The band structures of III-V semiconductors (InP, InAs, InSb, GaAs, and GaSb) are calculated using the HSE06 hybrid functional, GW, and local potentials optimized for the description of band gaps. We show that the inclusion of a quarter of the exact HF exchange allows to predict accurate direct band gaps for InP, InAs, and InSb, i.e., 1.48, 0.42, 0.28 eV, in good agreement with recent experiments, i.e., 1.42, 0.42, 0.24 eV, respectively. The calculated effective masses and Luttinger parameters are also in reasonable agreement with experiment, although a tendency towards underestimation is observed with increasing anion mass. In order to find more efficient methods than hybrid functionals, the modified Becke-Johnson exchange potential is also employed to calculate the effective masses. The agreement of the effective masses with experiment is comparable to the one obtained with the HSE06 hybrid functional. Therefore, this opens a way to model band structures of much large systems than possible using hybrid functionals.
The paper presents two ways of improving the Jacobi–Davidson method for calculating the eigenvalues and eigenvectors described by eight-band k · p model for quantum dots and other low dimensional structures. First, the method is extended by the application of time reversal symmetry operator. This extension allows efficient calculations of the twofold degeneracy present in the multiband k · p model and other interior eigenvalues. Second, the preconditioner for the indefinite matrix which comes from the discretization of the eight band k · p Hamiltonian is presented. The construction of this preconditioner is based on physical considerations about energy band structure in the k · p model. On the basis of two real examples, it is shown that the preconditioner can significantly shorten the time needed to calculate the interior eigenvalues, despite the fact that the memory usage of the preconditioner and Hamiltionian is comparable. Finally, some technical details for implementing the eight band k · p Hamiltonian and the eigensolver are provided
Schottky barrier formation and band bending revealed by first- principles calculations
Jiao, Yang; Hellman, Anders; Fang, Yurui; Gao, Shiwu; Käll, Mikael
2015-06-01
The formation of a Schottky barrier at the metal-semiconductor interface is widely utilised in semiconductor devices. With the emerging of novel Schottky barrier based nanoelectronics, a further microscopic understanding of this interface is in high demand. Here we provide an atomistic insight into potential barrier formation and band bending by ab initio simulations and model analysis of a prototype Schottky diode, i.e., niobium doped rutile titania in contact with gold (Au/Nb:TiO2). The local Schottky barrier height is found to vary between 0 and 1.26 eV depending on the position of the dopant. The band bending is caused by a dopant induced dipole field between the interface and the dopant site, whereas the pristine Au/TiO2 interface does not show any band bending. These findings open the possibility for atomic scale optimisation of the Schottky barrier and light harvesting in metal-semiconductor nanostructures.
Mathew, Xavier
2000-07-01
In recent years there has been an increased interest in flexible, lightweight photovoltaic modules based on thin metallic substrates. This paper reports some optoelectronic properties of electrodeposited CdTe thin films grown onto lightweight stainless steel (SS) foils. The optoelectronic properties were investigated with Schottky barriers of Au/CdTe/SS structure. The influence of the built-in potential of the Schottky junction on the bulk and the interface recombination of the photo-generated minority carriers is explained with the existing models. The voltage-dependent collection functions influence the photocurrent of the devices in both short- and long-wavelength regions of the spectrum. It is observed that in the photovoltaic mode the contribution due to the collection functions depends on the open-circuit voltage of the device. Au/CdTe Schottky devices, having higher open-circuit voltage, exhibit a better response in the long wavelength region. This is due to the efficient collection of the carriers generated in the bulk of the film and in such devices the contribution from the bulk collection function is higher. The enhancement in the bulk collection function causes a shift in the response of the device to higher wavelengths giving lower values for the calculated band gap. Due to this dependence of the long wavelength response on the open-circuit voltage of the devices, the band gap calculated from the photocurrent of different Schottky devices gives different values for the band gap of the material. Thus the method of calculating the band gap from the photocurrent of Schottky devices can lead to erroneous conclusions regarding the band gap of the material.
Reflectivity calculated for a 3D silicon photonic band gap crystal with finite support
Devashish, D; van der Vegt, J J W; Vos, Willem L
2016-01-01
We study numerically the reflectivity of three-dimensional (3D) photonic crystals with a complete 3D photonic band gap, with the aim to interpret recent experiments. We employ the finite element method to study crystals with the cubic diamond-like inverse woodpile structure. The high-index backbone has a dielectric function similar to silicon. We study crystals with a range of thicknesses up to ten unit cells ($L \\leq 10 c$). The crystals are surrounded by vacuum, and have a finite support as in experiments. The polarization-resolved reflectivity spectra reveal Fabry-P{\\'e}rot fringes related to standing waves in the finite crystal, as well as broad stop bands with nearly $100~\\%$ reflectivity, even for thin crystals. From the strong reflectivity peaks, it is inferred that the maximum reflectivity observed in experiments is not limited by finite size. The frequency ranges of the stop bands are in excellent agreement with stop gaps in the photonic band structure, that pertain to infinite and perfect crystals. ...
Comparison of CONDOR, FCI and MAFIA Calculations for a 150MW S-Band Klystron with Measurements
Sprehn, Daryl W
2003-06-11
To facilitate the design of high power klystrons an investigation into the reliability and accuracy of three modern particle-in-cell codes was performed. A 150 MW S-band klystron for which measurements were available was used for this comparison. The field calculations of the particle-in-cell codes are based on a finite difference time domain scheme, and use a port approximation to speed up the convergence to steady state. However, they differ in many details (e.g. calculation of E, B or A, {psi}; space charge correction; 2D or 3D modeling of output cavity).
Constrained Nudged Elastic Band calculation of the Peierls barrier with atomic relaxations
Gröger, Roman; Vitek, V.
2012-01-01
Roč. 20, č. 3 (2012), 035019. ISSN 0965-0393 R&D Projects: GA ČR 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
Electron momentum density and band structure calculations of {alpha}- and {beta}-GeTe
Vadkhiya, Laxman [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Arora, Gunjan [Department of Physics, Techno India NJR Institute of Technology, Udaipur 313002, Rajasthan (India); Rathor, Ashish [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Ahuja, B.L., E-mail: blahuja@yahoo.com [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India)
2011-12-15
We have measured isotropic experimental Compton profile of {alpha}-GeTe by employing high energy (662 keV) {gamma}-radiation from a {sup 137}Cs isotope. To compare our experiment, we have also computed energy bands, density of states, electron momentum densities and Compton profiles of {alpha}- and {beta}-phases of GeTe using the linear combination of atomic orbitals method. The electron momentum density is found to play a major role in understanding the topology of bands in the vicinity of the Fermi level. It is seen that the density functional theory (DFT) with generalised gradient approximation is relatively in better agreement with the experiment than the local density approximation and hybrid Hartree-Fock/DFT. - Highlights: > Compton profile of {alpha}-GeTe using a 20 Ci {sup 137}Cs Compton spectrometer. > Compared experimental Compton data with density functional theory. > Reported energy bands and density of states of {alpha}- and {beta}-GeTe. > EVED profiles analysed to check the covalent character.
Momentum-dependent band spin splitting in semiconducting MnO2: a density functional calculation.
Noda, Yusuke; Ohno, Kaoru; Nakamura, Shinichiro
2016-05-11
Recently, manganese-oxide compounds have attracted considerable attention, in particular, as candidate materials for photochemical water-splitting reactions. Here, we investigate electronic states of pristine manganese dioxides (MnO2) in different crystal phases using spin-polarized density functional theory (DFT) with Hubbard U correction. Geometrical structures and band dispersions of α-, β-, δ-, and λ-MnO2 crystals with collinear magnetic [ferromagnetic (FM) and antiferromagnetic (AFM)] orders are discussed in detail. We reveal that penalty energies that arise by violating the Goodenough-Kanamori rule are important and the origin of the magnetic interactions of the MnO2 crystals is governed by the superexchange interactions of Mn-O-Mn groups. In addition, it is found that momentum-dependent band spin splitting occurs in the AFM α-, β-, and δ-MnO2 crystals while no spin splitting occurs in the AFM λ-MnO2 crystal. Our results show that spin-split band dispersions stem from the different orientations of Mn-centred oxygen octahedra. Such interesting electronic states of the MnO2 crystals are unraveled by our discussion on the relationship between the effective (spin-dependent) single-electron potentials and the space-group symmetry operations that map up-spin Mn atoms onto down-spin Mn atoms. This work provides a basis to understand the relationship between the spin-dependent electronic states and the crystallography of manganese oxides. Another relationship to the recent experimental observations of the photochemical oxygen evolution of MnO2 crystals is also discussed. PMID:27119122
Band-gap corrected density functional theory calculations for InAs/GaSb type II superlattices
We performed pseudopotential based density functional theory (DFT) calculations for GaSb/InAs type II superlattices (T2SLs), with bandgap errors from the local density approximation mitigated by applying an empirical method to correct the bulk bandgaps. Specifically, this work (1) compared the calculated bandgaps with experimental data and non-self-consistent atomistic methods; (2) calculated the T2SL band structures with varying structural parameters; (3) investigated the interfacial effects associated with the no-common-atom heterostructure; and (4) studied the strain effect due to lattice mismatch between the two components. This work demonstrates the feasibility of applying the DFT method to more exotic heterostructures and defect problems related to this material system
Cageao, R. P.; Ha, Y. L.; Jiang, Y.; Morgan, M. F.; Yung, Y. L.; Sander, S. P.
1997-01-01
A calculation of the A2 sigma --> X2 pi (0, 0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant fluorescence in the terrestrial atmosphere is presented in this paper. The most accurate available line parameters have been used. Special consideration has been given to the solar input flux because of its highly structured Fraunhofer spectrum. The calculation for the OH atmospheric emission rate factor in the solar resonant fluorescent case is described in detail with examples and intermediate results. Results of this calculation of OH emission rate factors for individual rotational lines are on average 30% lower than the values obtained in an earlier work.
The well-known 'augmented plane waves' method, for the calculation of electronic states in crystals, is first reviewed. A modification of this method in the case of insulators is then described, which treats exchange in the exact Hartree-Fock formulation, without use of the common free-electron approximation. The band structure of several rare gases (Ne, Ar) and ionic compounds (LiF, NaF, KF, LiCl, NaCl, KCl) has been calculated and discussed. The main point is the strong influence of correlation effects which must be taken into account before comparison between calculated and measured optical transitions. Such an improvement is obtained by including a local polarization potential in the one-electron Hamiltonian, leading to a good agreement of the theoretical transitions with the experimental ones. (author)
Christensen, N. Egede; Feuerbacher, B.
1974-01-01
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...
Zhong, Hongxia; Quhe, Ruge; Wang, Yangyang; Ni, Zeyuan; Ye, Meng; Song, Zhigang; Pan, Yuanyuan; Yang, Jinbo; Yang, Li; Lei, Ming; Shi, Junjie; Lu, Jing
2016-03-01
Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency.
Zhong, Hongxia; Quhe, Ruge; Wang, Yangyang; Ni, Zeyuan; Ye, Meng; Song, Zhigang; Pan, Yuanyuan; Yang, Jinbo; Yang, Li; Lei, Ming; Shi, Junjie; Lu, Jing
2016-01-01
Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency. PMID:26928583
Lu, Jing Tao; Christensen, Rasmus Bjerregaard; Foti, Giuseppe;
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 clo...
Density functional calculation of band-parameters for boron nitride at normal and high pressures
The present work employs the total-energy pseudopotential technique within the framework of the density-functional theory with both the local-density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional so as to calculate the structural, electronic, chemical bonding and elastic properties of BN in the zinc-blende structure at normal and high pressures. The results are generally in good agreement with the available experimental data. We found that in many cases (except may be for elastic constants) the GGA improves agreement with experiment. The calculations showed that the transition pressure for BN from the zinc-blende phase to the rocksalt phase is much smaller than previously reported theoretical values
Metal-ceramic interface adhesion: Band structure calculations on Pt-NiO couples
Boorse, R.S.; Burlitch, J.M.; Hoffmann, R.; Alemany, P. (Cornell Univ., Ithaca, NY (United States))
1993-04-01
A problem of critical technological importance and fundamental scientific interest in materials science and materials engineering is that of adhesion between metals and ceramics. metal-ceramic adhesion is important to such industrial areas as microelectronics, catalysts, protective coatings for metals and metal-ceramic composite materials. Under certain annealing conditions Pt-NiO couples form NiPt intermetallic layers at the interface. It has been suggested that an observed 4-fold increase in the ultimate shear strength of the interface upon inclusion of a 1-nm-thick NiPt interlayer is caused by metal-oxygen bonding at the interface. Extended Huckel calculations, within the tight-binding formalism, have been performed on a series of Pt- and NiPt-NiO metal-ceramic couples to elucidate the nature of the bonding at these interfaces. the calculations showed an approximately 5-fold increase in adhesion energy in NiPt-NiO over Pt-NiO. This attributed to the more efficient electron donating capability of nickel compared to that of platinum. Bonding across the interface is found to decrease with increased electron donation as interfacially antibonding orbitals are filled. Theoretical reasons for the eventual mechanical failure in the oxide component are adduced. 25 refs., 7 figs., 3 tabs.
The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll
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.
Inelastic scattering of electrons in a crystalline environment may be represented by a complex non-hermitian potential. Completed generalised expressions for this inelastic electron scattering potential matrix, including virtual inelastic scattering, are derived for outer-shell electron and plasmon excitations. The relationship between these expressions and the general anisotropic dielectric response matrix of the solid is discussed. These generalised expressions necessarily include the off-diagonal terms representing effects due to departure from translational invariance in the interaction. Results are presented for the diagonal back structure dependent inelastic and virtual inelastic scattering potentials for Si, from a calculation of the inverse dielectric matrix in the random phase approximation. Good agreement is found with experiment as a function of incident energies from 10 eV to 100 keV. Anisotropy effects and hence the interaction de localisation represented by the off-diagonal scattering potential terms, are found to be significant below 1 keV. 38 refs., 2 figs
Coehoorn, R.; Haas, C.; Dijkstra, J.; Flipse, C.J.F.; de Groot, R. A.; Wold, A.
1987-01-01
The band structures of the semiconducting layered compounds MoSe2, MoS2, and WSe2 have been calculated self-consistently with the augmented-spherical-wave method. Angle-resolved photoelectron spectroscopy of MoSe2 using He I, He II, and Ne I radiation, and photon-energy-dependent normal-emission photoelectron spectroscopy using synchrotron radiation, show that the calculational results give a good description of the valence-band structure. At about 1 eV below the top of the valence band a dis...
Deguchi, Daiki; Sato, Kazunori; Kino, Hiori; Kotani, Takao
2016-05-01
We have recently implemented a new version of the quasiparticle self-consistent GW (QSGW) method in the ecalj package released at http://github.com/tkotani/ecalj. Since the new version of the ecalj package is numerically stable and more accurate than the previous versions, we can perform calculations easily without being bothered with tuning input parameters. Here we examine its ability to describe energy band properties, e.g., band-gap energy, eigenvalues at special points, and effective mass, for a variety of semiconductors and insulators. We treat C, Si, Ge, Sn, SiC (in 2H, 3C, and 4H structures), (Al, Ga, In) × (N, P, As, Sb), (Zn, Cd, Mg) × (O, S, Se, Te), SiO2, HfO2, ZrO2, SrTiO3, PbS, PbTe, MnO, NiO, and HgO. We propose that a hybrid QSGW method, where we mix 80% of QSGW and 20% of LDA, gives universally good agreement with experiments for these materials.
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.
Sánchez, K.; Aguilera, I.; Palacios, P.; Wahnón, P.
2009-04-01
Quantum calculations based on density-functional theory are carried out with the aim of discovering the origin of the electronic properties of Ti-implanted Si. This compound is a potential kind of intermediate-band photovoltaic material. Experimental results show a donor level at a few tenths of an eV below the conduction band for this compound. This could correspond to the electronic transition from an intermediate band to the conduction band of the host silicon. The structural, energetic, and electronic properties of several possible configurations appearing from the implantation of Ti on Si are calculated at different dilution levels in order to agree with the experimental conditions. Among the implantation processes, all of which are energetically unfavorable, interstitial Ti setting implies the energetic balance closest to the equilibrium, which agrees with the experimental measurements. Our conclusions predict that interstitial Ti atoms are responsible for the electronic transition found from the measurements, forecasting that a band fulfilling all the requirements of an intermediate-band material is formed in the compound. The optical absorption coefficient of an interstitially Ti-implanted Si compound is shown to illustrate the photoabsorption enhancement achieved in the main part of the solar spectrum with regard to bulk Si.
Karakalos, S.; Ladas, S. [Department of Chemical Engineering, University of Patras and FORTH/ICE-HT, POB 1414, 26504 Rion (Patras) (Greece); Janecek, P.; Sutara, F.; Nehasil, V. [Department of Electronic and Vacuum Physics, Charles University, V.Holesovickach 2, 18000 Prague 8 (Czech Republic); Tsud, N. [Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste (Italy); Prince, K. [Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste (Italy); INFM, Laboratorio TASC, in Area Science Park, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste (Italy); Matolin, V. [Department of Electronic and Vacuum Physics, Charles University, V.Holesovickach 2, 18000 Prague 8 (Czech Republic); Chab, V. [Institute of Physics, Czech Academy of Sciences, Cucrovarnicka 10, 16200 Prague (Czech Republic); Papanicolaou, N.I. [Department of Physics, University of Ioannina, P.O. Box 1186, 45110 Ioannina (Greece)], E-mail: nikpap@uoi.gr; Dianat, A.; Gross, A. [Institute of Theoretical Chemistry, University of Ulm, D-89069 Ulm (Germany)
2008-03-31
Photoelectron spectroscopy using synchrotron radiation and ab-initio electronic structure calculations were used in order to describe the fine structure of the valence band in the Sn/Ni(111) system. The characteristic contributions of each metal in the valence band photoemission spectra obtained with a photon energy of 80 eV and their changes upon the formation of the ({radical}3 x {radical}3)R30{sup o} Sn/Ni(111) surface alloy were also born out in the calculated density-of-states curves in fair agreement with the experiments. The Sn-Ni interaction leads to a considerable broadening of the valence band width at the bimetallic surfaces.
Svane, Axel; Christensen, Niels Egede; Cardona,, M.;
2010-01-01
The electronic band structures of PbS, PbSe, and PbTe in the rocksalt structure are calculated with the quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included. The semiconducting gaps and their deformation potentials as well as the effective masses are obtained. The GW...
Cageao, R. P.; Ha, Y. L.; Jiang, Y.; Morgan, M. F.; Yung, Y. L.; Sander, S. P.
1996-01-01
A calculation of the A(sup 2)(Sigma) leads to...X(sup 2)II (0,0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant flourenscence in the terrestrial atmosphere is presented in this paper.
1978-01-01
Various methods for calculating the transmission functions of the 15 micron CO2 band are described. The results of these methods are compared with laboratory measurements. It is found that program P4 provides the best agreement with experimental results on the average.
Aizawa, H.; Kuroki, K.; Yasuzuka, S.; Yamada, J.
2012-11-01
We perform a first-principles band calculation for a group of quasi-two-dimensional organic conductors β-(BDA-TTP)2MF6 (M = P, As, Sb and Ta). The ab-initio calculation shows that the density of states is correlated with the bandwidth of the singly occupied (highest) molecular orbital, while it is not necessarily correlated with the unit-cell volume. The direction of the major axis of the cross section of the Fermi surface lies in the Γ-B-direction, which differs from that obtained by the extended Hückel calculation. Then, we construct a tight-binding model which accurately reproduces the ab-initio band structure. The obtained transfer energies give a smaller dimerization than in the extended Hückel band. As to the difference in the anisotropy of the Fermi surface, the transfer energies along the inter-stacking direction are smaller than those obtained in the extended Hückel calculation. Assuming spin-fluctuation-mediated superconductivity, we apply random phase approximation to a two-band Hubbard model. This two-band Hubbard model is composed of the tight-binding model derived from the first-principles band structure and an on-site (intra-molecule) repulsive interaction taken as a variable parameter. The obtained superconducting gap changes sign four times along the Fermi surface like in a d-wave gap, and the nodal direction is different from that obtained in the extended Hückel model. Anion dependence of Tc is qualitatively consistent with the experimental observation.
Lee, Joohwi; Seko, Atsuto; Shitara, Kazuki; Nakayama, Keita; Tanaka, Isao
2016-03-01
Machine learning techniques are applied to make prediction models of the G0W0 band gaps for 270 inorganic compounds using Kohn-Sham (KS) band gaps, cohesive energy, crystalline volume per atom, and other fundamental information of constituent elements as predictors. Ordinary least squares regression (OLSR), least absolute shrinkage and selection operator, and nonlinear support vector regression (SVR) methods are applied with two levels of predictor sets. When the KS band gap by generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) or modified Becke-Johnson (mBJ) is used as a single predictor, the OLSR model predicts the G0W0 band gap of randomly selected test data with the root-mean-square error (RMSE) of 0.59 eV. When KS band gap by PBE and mBJ methods are used together with a set of predictors representing constituent elements and compounds, the RMSE decreases significantly. The best model by SVR yields the RMSE of 0.24 eV. Band gaps estimated in this way should be useful as predictors for virtual screening of a large set of materials.
Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer
2014-01-01
So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB$_2$(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle...
Gumhalter, Branko; Kovač, Vjekoslav; Caruso, Fabio; Lambert, Henry; Giustino, Feliciano
2016-07-01
Since the earliest implementations of the various GW approximations and cumulant expansion in the calculations of quasiparticle propagators and spectra, several attempts have been made to combine the advantageous properties and results of these two theoretical approaches. While the GW-plus-cumulant approach has proven successful in interpreting photoemission spectroscopy data in solids, the formal connection between the two methods has not been investigated in detail. By introducing a general bijective integral representation of the cumulants, we can rigorously identify at which point these two approximations can be connected for the paradigmatic model of quasiparticle interaction with the dielectric response of the system that has been extensively exploited in recent interpretations of the satellite structures in photoelectron spectra. We establish a protocol for consistent practical implementation of the thus established GW +cumulant scheme and illustrate it by comprehensive state-of-the-art first-principles calculations of intrinsic angle-resolved photoemission spectra from Si valence bands.
To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn2FeSi, Fe2MnSi, Fe2FeSi, Fe2CoSi, and Co2FeSi) with an L21 structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co2FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed. - Highlights: ► Electronic band structure calculations of L21 full Heusler alloy thin films. ► Spintronic materials. ► Electronic properties dependency on layer thickness.
Datta, Soumendu, E-mail: soumendu@bose.res.in; Baral, Sayan; Mookerjee, Abhijit [Department of Condensed Matter Physics and Material Sciences, S.N. Bose National Centre for Basic Sciences, JD Block, Sector-III, Salt Lake City, Kolkata 700 098 (India); Kaphle, Gopi Chandra [Central Department of Physics, Tribhuvan University, Kathmandu (Nepal)
2015-08-28
Using density functional theory (DFT) based electronic structure calculations, the effects of morphology of semiconducting nanostructures on the magnetic interaction between two magnetic dopant atoms as well as a possibility of tuning band gaps have been studied in the case of the bi-doped (ZnO){sub 24} nanostructures with the impurity dopant atoms of the 3d late transition metals—Mn, Fe, Co, Ni, and Cu. To explore the morphology effect, three different structures of the host (ZnO){sub 24} nano-system, having different degrees of spatial confinement, have been considered: a two dimensional nanosheet, a one dimensional nanotube, and a finite cage-shaped nanocluster. The present study employs hybrid density functional theory to accurately describe the electronic structure of all the systems. It is shown here that the magnetic coupling between the two dopant atoms remains mostly anti-ferromagnetic in the course of changing the morphology from the sheet geometry to the cage-shaped geometry of the host systems, except for the case of energetically most stable bi-Mn doping, which shows a transition from ferromagnetic to anti-ferromagnetic coupling with decreasing aspect ratio of the host system. The effect of the shape change, however, has a significant effect on the overall band gap variations of both the pristine as well as all the bi-doped systems, irrespective of the nature of the dopant atoms and provides a means for easy tunability of their optoelectronic properties.
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
Electron densities and chemical bonding in TiC, TiN and TiO derived from energy band calculations
It was the aim of this paper to describe the chemical bonding of TiC, TiN and TiO by means of energy bands and electron densities. Using the respective potentials we have calculated the bandstructure of a finer k-grid with the linearized APW method to obtain accurate densities of states (DOS). These DOS wer partitioned into local partial contributions and the metal d DOS were further decomposed into tsub(2g) and esub(g) symmetry components in order to additionally characterize bonding. The electron densities corresponding to the occupied valence states are obtained from the LAPW calculations. They provide further insight into characteristic trends in the series from TiC to TiO: around the nonmetal site the density shows increasing localisation; around the metal site the deviation from spherical symmetry changes from esub(g) to tsub(2g). Electron density plots of characteristic band states allow to describe different types of bonding occurring in these systems. For TiC and TiN recent measurements of the electron densities exist for samples of TiCsub(0.94) and TiNsub(0.99), where defects cause static displacements of the Ti atoms. If this effect can be compensated by an atomic model one hopefully can extrapolate to stoichiometric composition. This procedure allows a comparison with structure factors derived from theoretical electron densities. The agreement for TiN is very good. For TiC the extrapolated data agree in terms of the deviations from spherical symmetry near the Ti site with the LAPW data, but the densities around both atoms are more localized than in theory. An explanation could be: a) the defects affect the electronic structure in TiCsub(0.94) with respect to TiCsub(1.0): b) the applied atomic model does not properly extrapolate to stoichiometry, because parameters of this model correlate or become unphysical. (Author)
Sonal Singhal; A K Saxena; S Dasgupta
2007-10-01
The electron drift mobility in conduction band of GaAs has been calculated before, but for the first time, we have made attempts to estimate the electron mobilities in higher energy L and X minima. We have also calculated the value of mobility of two-dimensional electron gas needed to predict hetero-structure device characteristics using GaAs. Best scattering parameters have been derived by close comparison between experimental and theoretical mobilities. Room temperature electron mobilities in , L and X valleys are found to be nearly 9094, 945 and 247 cm2 /V-s respectively. For the above valleys, the electron masses, deformation potentials and polar phonon temperatures have been determined to be (0.067, 0.22, 0.39m 0 ), (8.5, 9.5, 6.5 eV), and (416, 382, 542 K) as best values, respectively. The 2-DEG electron mobility in minimum increases to 1.54 × 106 from 1.59 × 105 cm2 /V-s (for impurity concentration of 1014 cm-3) at 10 K. Similarly, the 2-DEG electron mobility values in L and X minima are estimated to be 2.28 × 105 and 1.44 × 105 cm2 /V-s at 10 K, which are about ∼ 4.5 and ∼ 3.9 times higher than normal value with impurity scattering present.
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
Petrenko, Taras; Neese, Frank
2012-12-21
In this work, an improved method for the efficient automatic simulation of optical band shapes and resonance Raman (rR) intensities within the "independent mode displaced harmonic oscillator" is described. Despite the relative simplicity of this model, it is able to account for the intensity distribution in absorption (ABS), fluorescence, and rR spectra corresponding to strongly dipole allowed electronic transitions with high accuracy. In order to include temperature-induced effects, we propose a simple extension of the time dependent wavepacket formalism developed by Heller which enables one to derive analytical expressions for the intensities of hot bands in ABS and rR spectra from the dependence of the wavepacket evolution on its initial coordinate. We have also greatly optimized the computational procedures for numerical integration of complicated oscillating integrals. This is important for efficient simulations of higher-order rR spectra and excitation profiles, as well as for the fitting of experimental spectra of large molecules. In particular, the multimode damping mechanism is taken into account for efficient reduction of the upper time limit in the numerical integration. Excited state energy gradient as well as excited state geometry optimization calculations are employed in order to determine excited state dimensionless normal coordinate displacements. The gradient techniques are highly cost-effective provided that analytical excited state derivatives with respect to nuclear displacements are available. Through comparison with experimental spectra of some representative molecules, we illustrate that the gradient techniques can even outperform the geometry optimization method if the harmonic approximation becomes inadequate. PMID:23267471
Vaitheeswaran, G.; Kanchana, V.; Zhang, Xinxin; Ma, Yanming; Svane, A.; Christensen, N. E.
2016-08-01
A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent GW approximation. The GW calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides.
SO2 spectra have been recorded with a quantum cascade laser spectrometer at 9μm. Line positions, line strengths and self-broadening coefficients of 42 lines have been precisely determined. All these parameters have shown some discrepancies with those of the HITRAN database. Moreover several lines found in this study were not present in this database. In order to have a complete line list of transitions of SO2 appearing into the recorded spectra, we have performed a new calculation of the ν1 band of 32SO2, the ν1+ν2-ν2 band of 32SO2 and the ν1 band of 34SO2. This new calculation demonstrates a considerable improvement of the calculations of synthetic spectra of SO2. These new calculations improve the positions (up to 0.03cm-1), the intensities (up to 30%) and the self-broadening coefficients (up to 100%) of the ν1 band of 32SO2 with respect to HITRAN database and permit to obtain a complete set of data for the ν1+ν2-ν2 band of 32SO2 and the ν1 band of 34SO2 where the positions and strengths are in very good agreement with experimental data
Baldacchini, G; Grassano, U M; Scacco, A; Petrova, P; Mladenova, M; Ivanovich, M; Georgiev, M
2007-01-01
We carried out numerical calculations by an extended-Hueckel program in order to check the analytical results reported in the preceding Part I and Part II. We typically consider alkali halide clusters composed of some tens of constituent atoms to calculate electronic energies under static conditions or versus the displacements of particular atoms. Among other things, the off-center displacement of substitutional Li+ impurity in most alkali halides is evidenced. The trigonometric profile of the rotational barriers is also confirmed for KCl.
Calculation of equilibria at elevated temperatures using the MINTEQ geochemical code
Smith, R.W.
1988-12-01
Coefficients and equations for calculating mineral hydrolysis constants, solubility products and formation constants for 60 minerals and 57 aqueous species in the 13 component thermodynamic system K/sub 2/O-Na/sub 2/O-CaO-MgO-FeO-Al/sub 2/O/sub 3/-SiO/sub 2/-CO/sub 2/-H/sub 2/O-HF-HCl-H/sub 2/S-H/sub 2/SO/sub 4/ are presented in a format suitable for inclusion in the MINTEQ computer code. The temperature functions presented for minerals are based on the MINTEQ data base at 25/degree/C and the integration of analytical heat capacity power functions. This approach ensures that the temperature functions join smoothly with the low-temperature data base. A new subroutine, DEBYE, was added to MINTEQ that is used to calculate the theoretical Debye-Hueckel parameters A and B as a function of temperature. In addition, this subroutine also calculates a universal value of the extended Debye-Hueckel parameter, b/sub i/, as a function of temperature. The coefficients and equations provide the capability to use MINTEQ to more accurately calculate water/rock equilibrium for temperatures of up to 250/degree/C, and in dilute, low-sulfate, near neutral groundwaters to 300/degree/C. 52 refs., 1 fig., 6 tabs.
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.
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2011-01-01
First-principles FLAPW-GGA band structure calculations were employed to examine the structural, electronic properties and the chemical bonding picture for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be viewed as "intermediate" systems between two main isostructural groups of superconducting and semiconducting 1111 phases. The Th 5f states participate actively in the formation of valence bands ...
Otsura, Takanori; Nakatsuka, Emi; Nagase, Takashi; Kobayashi, Takashi; Naito, Hiroyoshi
2016-04-01
The power conversion efficiencies (PCEs) as a function of band gap energies and the lowest unoccupied molecular orbital (LUMO) levels of donor materials are studied in bulk-heterojunction organic solar cells (OSCs) fabricated from donor materials and fullerene acceptors. The PCEs of [6,6]-pheynl-C61-butyric acid methyl ester (PC61BM) and [6,6]-pheynl-C71-butyric acid methyl ester (PC71 BM) based OSCs blended with donor materials under the Air Mass 1.5 (AM1.5) spectrum are calculated. In the calculation, the short circuit current densities are determined by band gap energies of donor materials and the open circuit voltages are derived from the difference between the highest occupied molecular orbital (HOMO) levels of donor materials and LUMO levels of PC61BM and PC71 BM. The calculation is in good agreement with the experiments. The PCEs under a fluorescent lamp are also calculated. The calculated PCEs of PC71 BM based OSCs under a fluorescent lamp are higher than those under the AM1.5 spectrum by a factor of 2. The PCEs of thieno [3,4-b] thiophene and benzodithiophene (PTB7):PC71BM based OSCs are studied under the AM1.5 spectrum and a fluorescent lamp spectrum and are consistent with the calculation. PMID:27451630
Comparing LDA-1/2, HSE03, HSE06 and G0W0 approaches for band gap calculations of alloys
It has long been known that the local density approximation and the generalized gradient approximation do not furnish reliable band gaps, and one needs to go beyond these approximations to reliably describe these properties. Among alternatives are the use of hybrid functionals (HSE03 and HSE06 being popular), the GW approximation or the recently proposed LDA-1/2 method. In this work, we compare rigorously the performance of these four methods in describing the band gaps of alloys, employing the generalized quasi-chemical approach to treat the disorder of the alloy and to obtain judiciously the band gap for the entire compositional range. Zincblende InGaAs and InGaN were chosen as prototypes due to their importance in optoelectronic applications. The comparison between these four approaches was guided both by the agreement between the predicted band gap and the experimental one, and by the demanded computational effort (time and memory). We observed that the HSE06 method provided the most accurate results (in comparison with experiments), whereas, surprisingly, the LDA-1/2 method gave the best compromise between accuracy and computational resources. Due to its low computational cost and good accuracy, we decided to double the supercell used to describe the alloys, and employing LDA-1/2 we observed that the bowing parameter changed remarkably, only agreeing with the measured one for the larger supercell, where LDA-1/2 plays an important role. (paper)
Inakura, T; Yamagami, M; Matsuyanagi, K
2002-01-01
With the use of the symmetry-unrestricted cranked Skyrme-Hartree-Fock method in the three-dimensional coordinate-mesh representation, we have carried out a systematic theoretical search for the superdeformed and hyperdeformed rotational bands in the mass A=30-50 region. Along the N=Z line, we have found superdeformed solutions in 32S, 36Ar, 40Ca, 44Ti, and hyperdeformed solutions in 36Ar, 40Ca, 44Ti, 48Cr. The superdeformed band in 40Ca is found to be extremely soft against both the axially symmteric (Y30) and asymmetric (Y31) octupole deformations. An interesting role of symmetry breaking in the mean field is pointed out.
The authors report on the results of electronic band structure calculations of bulk ZnSe, bulk ZnS and the (ZnSe)1(ZnS)1, strained-layer superlattice (SLS) using the ab initio factorized linear combination of atomic orbitals method. The bulk calculations were done using the standard primitive nonrectangular 2-atom zinc blende unit cell, while the SLS calculation was done using a primitive tetragonal 4-atom unit cell modeled from the CuAu I structure. The analytic fit to the SLS crystalline potential was determined by using the nonlinear coefficients from the bulk fits. The CPU time saved by factorizing the energy matrix integrals and using a rectangular unit cell is discussed
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.
Hiremath, C. S.; Kalkoti, G. B.; Aralakkanavar, M. K.
2009-09-01
In the present study, a systematic vibrational spectroscopic investigation for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile (TFB), aided by electronic structure calculations has been carried out. The electronic structure calculations - ab initio (RHF) and hybrid density functional methods (B3LYP) - have been performed with 6-31G* basis set. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. The results of the calculations have been used to simulate IR and Raman spectra for TFB that showed excellent agreement with the observed spectra. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed. A complete assignment of the observed spectra has been proposed.
Harish, R. Sugan; Jayalakshmi, D. S.; Viswanathan, E.; Sundareswari, M.
2016-05-01
The mechanical, electronic, thermodynamic properties and structural stability of tetragonal structured CaNi2P2 and CaNi2Sb2 intermetallic compounds has been studied using the FP-LAPW method based on density functional theory. The PBE-GGA exchange correlation has been applied. Using the computed elastic constants, various elastic moduli such as bulk, shear, Young’s modulus, Poisson’s ratio and anisotropy constant are calculated and discussed. Stability of the compounds is confirmed by using their elastic constants. Pugh’s ratio is calculated to analyze the mechanical nature of the compound.
D'Yachkov, P. N.; Makaev, D. V.
2007-11-01
Every carbon single-walled nanotube (SWNT) can be generated by first mapping only two nearest-neighbor C atoms onto a surface of a cylinder and then using the rotational and helical symmetry operators to determine the remainder of the tubule [C. T. White , Phys. Rev. B 47, 5485 (1993)]. With account of these symmetries, we developed a symmetry-adapted version of a linear augmented cylindrical wave method. In this case, the cells contain only two carbon atoms, and the ab initio theory becomes applicable to any SWNT independent of the number of atoms in a translational unit cell. The approximations are made in the sense of muffin-tin (MT) potentials and local-density-functional theory only. An electronic potential is suggested to be spherically symmetrical in the regions of atoms and constant in an interspherical region up to the two essentially impenetrable cylinder-shaped potential barriers. To construct the basis wave functions, the solutions of the Schrödinger equation for the interspherical and MT regions of the tubule were sewn together using a theorem of addition for cylindrical functions, the resulting basis functions being continuous and differentiable anywhere in the system. With account of analytical equations for these functions, the overlap and Hamiltonian integrals are calculated, which permits determination of electronic structure of nanotube. We have calculated the total band structures and densities of states of the chiral and achiral, semiconducting, semimetallic, and metallic carbon SWNTs (13, 0), (12, 2), (11, 3), (10, 5), (9, 6), (8, 7), (7, 7), (12, 4), and (100, 99) containing up to the 118 804 atoms per translational unit cell. Even for the (100, 99) system with huge unit cell, the band structure can be easily calculated and the results can be presented in the standard form of four curves for the valence band plus one curve for the low-energy states of conduction band. About 150 functions produce convergence of the band structures better then
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…
Karakalos, S.; Ladas, S.; Janeček, P.; Šutara, F.; Nehasil, V.; Tsud, N.; Prince, K.; Matolín, V.; Cháb, Vladimír; Papanicolaou, N.I.; Dianat, A.; Gross, A.
2008-01-01
Roč. 516, č. 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
The optical band positions of W5+ octahedral clusters (WO6)7− in tungsten oxide (WO3)-based glasses are reassigned and suggested. Based on this, the spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) of these W5+ clusters are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, besides the contributions due to crystal-field (CF) mechanism in the extensively-used CF theory, the contributions owing to charge-transfer (CT) mechanism (which are often omitted) are also included. The calculated results are in reasonable agreement with the experimental values and the signs of hyperfine structure constants Ai are suggested. The results are discussed
Peng, Ren-Ming [School of Physics & Electronic Engineering, Mianyang Normal University, Mianyang 621000 (China); Mei, Yang [School of Physics & Electronic Engineering, Mianyang Normal University, Mianyang 621000 (China); Research Center of Computational Physics, Mianyang Normal University, Mianyang 621000 (China); Zheng, Wen-Chen, E-mail: zhengwc1@163.com [Department of Material Science, Sichuan University, Chengdu 610064 (China); Wei, Cheng-Fu [School of Physics & Electronic Engineering, Mianyang Normal University, Mianyang 621000 (China)
2015-03-15
The optical band positions of W{sup 5+} octahedral clusters (WO{sub 6}){sup 7−} in tungsten oxide (WO{sub 3})-based glasses are reassigned and suggested. Based on this, the spin-Hamiltonian parameters (g factors g{sub //}, g{sub ⊥} and hyperfine structure constants A{sub //}, A{sub ⊥}) of these W{sup 5+} clusters are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, besides the contributions due to crystal-field (CF) mechanism in the extensively-used CF theory, the contributions owing to charge-transfer (CT) mechanism (which are often omitted) are also included. The calculated results are in reasonable agreement with the experimental values and the signs of hyperfine structure constants A{sub i} are suggested. The results are discussed.
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.
A calculation of the excitation energy of the 0+ states and of the 2+ states is performed using Monte Carlo methods for the nucleus 154Dy. The Hamiltonian is assumed to be a monopole+quadrupole pairing+quadrupole with the parameters fixed by the spectroscopic Monte Carlo method so as to reproduce the experimental excitation energies of the yrast states up to J 8 within the 50-82 and 82-126 proton and neutron major shells. The resulting Hamiltonian has been diagonalized in the J = 0 and J = 2 subspaces using the quantum Monte Carlo method. The size of the basis is fixed by comparing the yrast energies obtained with the basis-independent spectroscopic Monte Carlo method, and those obtained with the quantum Monte Carlo method. The excitation energy of the 0+2 is much higher than the experimental value. The structure of the 0+2,3 and of the 2+2,3 eigenstates is discussed in terms of fluctuating intrinsic states and resolved in terms of the deformation variables. (brief report)
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Fujisawa, Jun-ichi; Hanaya, Minoru
2016-06-01
Interfacial charge-transfer (ICT) transitions between inorganic semiconductors and π-conjugated molecules allow direct charge separation without loss of energy. This feature is potentially useful for efficient photovoltaic conversions. Charge-transferred complexes of TiO2 nanoparticles with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its analogues (TCNX) show strong ICT absorption in the visible region. The ICT band was reported to be significantly red-shifted with extension of the π-conjugated system of TCNX. In order to clarify the mechanism of the red-shift, in this work, we systematically study electronic structures of the TiO2-TCNX surface complexes (TCNX; TCNE, TCNQ, 2,6-TCNAQ) by ionization potential measurements and density functional theory (DFT) calculations.
High-energy band structure of gold
Christensen, N. Egede
1976-01-01
The band structure of gold for energies far above the Fermi level has been calculated using the relativistic augmented-plane-wave method. The calculated f-band edge (Γ6-) lies 15.6 eV above the Fermi level is agreement with recent photoemission work. The band model is applied to interpret...
Chemically induced compaction bands in geomaterials
Stefanou, Ioannis; Sulem, Jean
2013-04-01
-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.
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
Pashkevich, Yu.; Gnezdilov, V.; Lemmens, P.; Shevtsova, T.; Gusev, A.; Lamonova, K.; Wulferding, D.; Gnatchenko, S.; Pomjakushina, E.; Conder, K.
2016-06-01
We report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K over a wide temperature region 3-500 K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed RbδFe2Se2 (122) conductive phase. The superconducting gap with d x 2 - y 2 symmetry has been detected in our spectra. In the range 0-600 cm-1 we observe a weak but highly polarized B1g-type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M0.8+xFe1.6+ySe2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic RbδFe2Se2 phase and the insulating Rb2Fe4Se5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb0.8+xFe1.6+ySe2. Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb2Fe4Se5 phases.
High-spin states of 79Br have been studied in the reaction 76Ge(7Li, 4nγ) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g(9(2)) proton band, and the negative-parity ground state band have been extended to spins of (33(2+)) and (25(2-)), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of β2 ∼ 0.2. The positive-parity α = -(1(2)) band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the νg(9(2)) and πg(9(2)) alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of ℎω ∼ 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g(9(2)) band can be well reproduced by a particle-rotor model calculation with an axially symmetric core
Inakura, T; Yamagami, M; Matsuyanagi, K
2002-01-01
With the use of the symmetry-unrestricted cranked Skyrme-Hartree-Fock method in the three-dimensional coordinate-mesh representation, we have carried out a systematic theoretical search for the superdeformed and hyperdeformed rotational bands in the mass A=30-50 region. Along the N=Z line, we have found superdeformed solutions in sup 3 sup 2 S, sup 3 sup 6 Ar, sup 4 sup 0 Ca, sup 4 sup 4 Ti, and hyperdeformed solutions in sup 3 sup 6 Ar, sup 4 sup 0 Ca, sup 4 sup 4 Ti, sup 4 sup 8 Cr. The superdeformed band in sup 4 sup 0 Ca is found to be extremely soft against both the axially symmetric (Y sub 3 sub 0) and asymmetric (Y sub 3 sub 1) octupole deformations. An interesting role of symmetry breaking in the mean field is pointed out.
Direct band gap silicon allotropes.
Wang, Qianqian; Xu, Bo; Sun, Jian; Liu, Hanyu; Zhao, Zhisheng; Yu, Dongli; Fan, Changzeng; He, Julong
2014-07-16
Elemental silicon has a large impact on the economy of the modern world and is of fundamental importance in the technological field, particularly in solar cell industry. The great demand of society for new clean energy and the shortcomings of the current silicon solar cells are calling for new materials that can make full use of the solar power. In this paper, six metastable allotropes of silicon with direct or quasidirect band gaps of 0.39-1.25 eV are predicted by ab initio calculations at ambient pressure. Five of them possess band gaps within the optimal range for high converting efficiency from solar energy to electric power and also have better optical properties than the Si-I phase. These Si structures with different band gaps could be applied to multiple p-n junction photovoltaic modules. PMID:24971657
Band structure of semiconductors
Tsidilkovski, I M
2013-01-01
Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio
The thermodynamic and electronic parameters : concentration, chemical potential, heat-capacity and thermal electromotive force of hot two-dimensional electron gas in a heterocontact were calculated using a specific distribution function. The obtained expressions describe the dependence of heat-capacity and thermal electromotive force on a film thickness and an electron temperature in a good manner. It was determined that the acquired results calculated for the model under consideration, strongly differed from the results calculated on the base of a Maxwell distribution function
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
Competition between triaxial bands and highly deformed intruder bands around 180Os
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.)
Band parameters of phosphorene
Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.;
2015-01-01
Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory are co...
Flat Band Quastiperiodic Lattices
Bodyfelt, Joshua; Flach, Sergej; Danieli, Carlo
2014-03-01
Translationally invariant lattices with flat bands (FB) in their band structure possess irreducible compact localized flat band states, which can be understood through local rotation to a Fano structure. We present extension of these quasi-1D FB structures under incommensurate lattices, reporting on the FB effects to the Metal-Insulator Transition.
Structure of negative parity yrast bands in odd mass 125-131Ce nuclei
Arun Bharti; Suram Singh; S K Khosa
2010-04-01
The negative parity yrast bands of neutron-deficient 125-131Ce nuclei are studied by using the projected shell model approach. Energy levels, transition energies and (1)/(2) ratios are calculated and compared with the available experimental data. The calculations reproduce the band-head spins of negative parity yrast bands and indicate the multi-quasiparticle structure for these bands.
Band Structure and Optical Properties of Ordered AuCu3
Skriver, Hans Lomholt; Lengkeek, H. P.
1979-01-01
initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement...
Band-Structure of Thallium by the LMTO Method
Holtham, P. M.; Jan, J. P.; Skriver, Hans Lomholt
1977-01-01
The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s and...
Band-selective radiofrequency pulses
Geen, Helen; Freeman, Ray
A theoretical treatment is given of the general problem of designing amplitude-modulated radiofrequency pulses that will excite a specified band of frequencies within a high-resolution NMR spectrum with uniform intensity and phase but with negligible excitation elsewhere. First a trial pulse envelope is defined in terms of a finite Fourier series and its frequency-domain profile calculated through the Bloch equations. The result is compared with the desired target profile to give a multidimensional error surface. The method of simulated annealing is then used to find the global minimum on this surface and the result refined by standard gradient-descent optimization. In this manner, a family of new shaped radio-frequency pulses, known as BURP ( band-selective, uniform response, pure-phase) pulses, has been created. These are of two classes—pulses that excite or invert z magnetization and those that act as general-rotation πr/2 or π pulses irrespective of the initial condition of the nuclear magnetization. It was found convenient to design the latter class as amplitude-modulated time-symmetric pulses. Tables of Fourier coefficients and pulse-shape ordinates are given for practical implementation of BURP pulses, together with the calculated frequency-domain responses and experimental verifications. Examples of the application of band-selective pulses in conventional and multidimensional spectroscopy are given. Pure-phase pulses of this type should also find applications in magnetic resonance imaging where refocusing schemes are undesirable.
Spectral band selection for classification of soil organic matter content
Henderson, Tracey L.; Szilagyi, Andrea; Baumgardner, Marion F.; Chen, Chih-Chien Thomas; Landgrebe, David A.
1989-01-01
This paper describes the spectral-band-selection (SBS) algorithm of Chen and Landgrebe (1987, 1988, and 1989) and uses the algorithm to classify the organic matter content in the earth's surface soil. The effectiveness of the algorithm was evaluated comparing the results of classification of the soil organic matter using SBS bands with those obtained using Landsat MSS bands and TM bands, showing that the algorithm was successful in finding important spectral bands for classification of organic matter content. Using the calculated bands, the probabilities of correct classification for climate-stratified data were found to range from 0.910 to 0.980.
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.
Bulk band gaps in divalent hexaborides
Denlinger, Jonathan; Clack, Jules A.; Allen, James W.; Gweon, Gey-Hong; Poirier, Derek M.; Olson, Cliff G.; Sarrao, John L.; Bianchi, Andrea D.; Fisk, Zachary
2002-08-01
Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for proper inclusion of many-body effects in quasi-particle band calculations.
Stillman, R.
2013-01-01
This website presents practice-based research related to solo simultaneous instrumental performance ('one-man band'). The site was conceived as a creative and widely accessible platform for music and ideas resulting from one-man band activates carried out between 2008 and 2013. Central to this project is an interest in how one-man band technique informs compositional process, including studio production. Through presentation and analysis of the author’s own creative practice, the site exp...
Quantitative analysis on electric dipole energy in Rashba band splitting
Jisook Hong; Jun-Won Rhim; Changyoung Kim; Seung Ryong Park; Ji Hoon Shim
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 calc...
Calculation of Spectra of Solids:
Lindgård, Per-Anker
1975-01-01
The Gilat-Raubenheimer method simplified to tetrahedron division is used to calculate the real and imaginary part of the dynamical response function for electrons. A frequency expansion for the real part is discussed. The Lindhard function is calculated as a test for numerical accuracy....... The conduction electron susceptibility is calculated for Gd, Tb and Dy using the RAPW energy bands by Keeton and Louks....
One-Dimensional Anisotropic Band Gap Structure
无
2000-01-01
The band gap structure of one-dimensional anisotropic photonic crystal has been studied by means of the transfer matrix formalism. From the analytic expressions and numeric calculations we see some general characteristics of the band gap structure of anisotropic photonic crystals, each band separates into two branches and the two branches react to polarization sensitively. In the practical case of oblique incidence, gaps move towards high frequency when the angle of incidence increases. Under some special conditions, the two branches become degenerate again.
Configurations of superdeformed bands in 193Pb
The six superdeformed bands in 193Pb have been studied with the EUROGAM 2 γ-ray spectrometer using the 168Er(30Si,5n)193Pb reaction. The results are discussed in terms of Cranked-Hartree-Fock-Bogoliubov-Lipkin-Nogami calculations. The bands are interpreted as three pairs of signature partners based on quasineutron excitations. Dipole transitions linking two signature partner superdeformed bands have been observed and, for the first time in lead isotopes, the branching ratio has been extracted. (author)
Collective bands in neutron-rich 104Mo nucleus
Levels in the neutron-rich 104Mo nucleus have been investigated by observing prompt γ-rays from the spontaneous fission of 252Cf with the Gamma sphere detector array. The ground-state band, the one-phonon and the two-phonon γ-vibrational bands as well as a quasiparticle band have been confirmed and expanded with spin up to 14ℎ. Other two side bands probably built on new quasiparticle states are identified. The possible configurations for the quasiparticle bands are discussed. Two of the quasiparticle bands show larger moments of inertia and may have pair-free characteristics. The levels of the ground-state band, the one-phonon γ-band and the two-phonon γ-band calculated from a general collective model are in close agreement with the experimental data
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.
Pressure effects on band structures in dense lithium
We studied the change of the band structures in some structures of Li predicted at high pressures, using GGA and GW calculations. The width of the 1s band coming from the 1s electron of Li shows broadening by the pressurization, which is the normal behavior of bands at high pressure. The width of the band just below the Fermi level decreases by the pressurization, which is an opposite behavior to the normal bands. The character of this narrowing band is mostly p-like with a little s-like portion. The band gaps in some structures are really observed even by the GGA calculations. The gaps by the GW calculations increase to about 1.5 times the GGA values. Generally the one-shot GW calculation (diagonal only calculations) gives more reliable values than the GGA, but it may fail to predict band gaps for the case where band dispersion shows complex crossing near the Fermi level. There remains some structures for which GW calculations with off-diagonal elements taken into account are needed to identify the phase to be metallic or semiconducting.
SRD 166 MEMS Calculator (Web, free access) This MEMS Calculator determines the following thin film properties from data taken with an optical interferometer or comparable instrument: a) residual strain from fixed-fixed beams, b) strain gradient from cantilevers, c) step heights or thicknesses from step-height test structures, and d) in-plane lengths or deflections. Then, residual stress and stress gradient calculations can be made after an optical vibrometer or comparable instrument is used to obtain Young's modulus from resonating cantilevers or fixed-fixed beams. In addition, wafer bond strength is determined from micro-chevron test structures using a material test machine.
... make the band tighter or looser any time after you have this surgery. It may be tightened or ... Having problems eating Not losing enough weight Vomiting after you eat Outlook (Prognosis) The final weight loss with ...
CSF oligoclonal banding - slideshow
... presentations/100145.htm CSF oligoclonal banding - series—Normal anatomy ... Overview The cerebrospinal fluid (CSF) serves to supply nutrients to the central nervous system (CNS) and collect waste products, as well as ...
Christiano, Lawrence J.; Terry J. Fitzgerald
1999-01-01
The `ideal' band pass filter can be used to isolate the component of a time series that lies within a particular band of frequencies. However, applying this filter requires a dataset of infinite length. In practice, some sort of approximation is needed. Using projections, we derive approximations that are optimal when the time series representations underlying the raw data have a unit root, or are stationary about a trend. We identify one approximation which, though it is only optimal for one...
Iliotibial band friction syndrome
Lavine, Ronald
2010-01-01
Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for ili...
Frustration phenomena in Josephson point contacts between single-band and three-band superconductors
Within the formalism of Usadel equations the Josephson effect in dirty point contacts between single-band and three-band superconductors is investigated. The general expression for the Josephson current, which is valid for arbitrary temperatures, is obtained. We calculate current-phase relations for very low temperature and in the vicinity of the critical temperature. For three-band superconductors with broken time-reversal symmetry (BTRS) point contacts undergo frustration phenomena with different current-phase relations, corresponding to ?-contacts. For three-band superconductors without BTRS we have close to sinusoidal current-phase relations and absence of the frustration, excepting the case of very low temperature, where under certain conditions two ground states of the point contact are realized. Our results can be used as the potential probe for the detection of the possible BTRS state in three-band superconducting systems.
Accurate band-to-band registration of AOTF imaging spectrometer using motion detection technology
Zhou, Pengwei; Zhao, Huijie; Jin, Shangzhong; Li, Ningchuan
2016-05-01
This paper concerns the problem of platform vibration induced band-to-band misregistration with acousto-optic imaging spectrometer in spaceborne application. Registrating images of different bands formed at different time or different position is difficult, especially for hyperspectral images form acousto-optic tunable filter (AOTF) imaging spectrometer. In this study, a motion detection method is presented using the polychromatic undiffracted beam of AOTF. The factors affecting motion detect accuracy are analyzed theoretically, and calculations show that optical distortion is an easily overlooked factor to achieve accurate band-to-band registration. Hence, a reflective dual-path optical system has been proposed for the first time, with reduction of distortion and chromatic aberration, indicating the potential of higher registration accuracy. Consequently, a spectra restoration experiment using additional motion detect channel is presented for the first time, which shows the accurate spectral image registration capability of this technique.
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.
The complex band structure for armchair graphene nanoribbons
Zhang Liu-Jun; Xia Tong-Sheng
2010-01-01
Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N= 3M-1. The band gap is almost unchanged for N = 3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nmaoribbons, and is also classified into three classes.
Relativistic Band Structure and Fermi Surface of PdTe2 by the LMTO Method
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...
Particle-rotor-model calculations in 125I
Hariprakash Sharma; B Sethi; P Banerjee; Ranjana Goswami; R K Bhandari; Jahan Singh
2001-07-01
Recent experimental data on 125I has revealed several interesting structural features. These include the observation of a three quasiparticle band, prolate and oblate deformed bands, signature inversion in the yrast positive-parity band and identiﬁcation of the unfavoured ℎ11/2 band showing very large signature splitting. In the present work, particle-rotor-model calculations have been performed for the ℎ11/2 band, using an axially symmetric deformed Nilsson potential. The calculations reproduce the experimental results well and predict a moderate prolate quadrupole deformation of about 0.2 for the band.
Shape Coexistence and Band Termination in the Doubly Magic Nucleus 40Ca
DONGBao-guo; GUOHong-chao
2003-01-01
Shape coexistence and band structure near yrast line of the Z=N doubly magic nucleus 40Ca have been investigated by the configuration-dependent cranked Nilsson-Strutinsky approach and the calculated bands show good agreement with experimental observations at high spin. The observed normal deformed and superdeformed bands are explained theoretically and the terminating states are confirmed by the calculations.
Band Structure and Fermi-Surface Properties of Ordered beta-Brass
Skriver, Hans Lomholt; Christensen, N. E.
1973-01-01
The band structure of ordered β-brass (β′-CuZn) has been calculated throughout the Brillouin zone by the augmented-plane-wave method. The present band model differs from previous calculations with respect to the position and width of the Cu 3d band. The derived dielectric function ε2(ω) and the...
Relativistic multiple scattering Xα calculations
A one component relativistic theory has recently been developed and tested on isolated atoms and on molecules through the molecular scattered-wave formalism of Johnson, while its application to energy-band calculations (through a relativistic augmented-plane-wave program) has also been considered
Petersen, Kurt Erling
1986-01-01
probabilistic approaches have been introduced in some cases for the calculation of the reliability of structures or components. A new computer program has been developed based upon numerical integration in several variables. In systems reliability Monte Carlo simulation programs are used especially in analysis...... of very complex systems. In order to increase the applicability of the programs variance reduction techniques can be applied to speed up the calculation process. Variance reduction techniques have been studied and procedures for implementation of importance sampling are suggested....
Coriolis mixing of the octupole vibrational bands in 156Gd
Coriolis mixing of negative parity states in 156Gd nucleus is considered within the framework of a phenomenological model. Energy spectrum and ratios of effective probabilities of E1-transitions from the levels of octupole bands are described. Possibilities of E1-transitions from Kπ=2--band states are discussed; intraband E2-transitions in Kπ=0--, 1-- and 2--bands are calculated. 16 refs., 2 figs., 4 tabs
Mclyman, C. W. T. (Inventor)
1974-01-01
A banded transformer core formed by positioning a pair of mated, similar core halves on a supporting pedestal. The core halves are encircled with a strap, selectively applying tension whereby a compressive force is applied to the core edge for reducing the innate air gap. A dc magnetic field is employed in supporting the core halves during initial phases of the banding operation, while an ac magnetic field subsequently is employed for detecting dimension changes occurring in the air gaps as tension is applied to the strap.
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
Optimum band gap of a thermoelectric material
Transport properties of direct-gap semiconductors are calculated in order to find the best thermoelectrics. Previous calculations on semiconductors with indirect band gaps found that the best thermoelectrics had gaps equal to nkBT, where n=6-10 and T is the operating temperature of the thermoelectric device. Here we report similar calculations on direct-gap materials. We find that the optimum gap is always greater than 6kBT, but can be much larger depending on the specific mechanism of electron scattering
Search for superdeformed bands in 154Dy
The island of superdeformation in the vicinity of the doubly magic 152Dy 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 154Dy 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 153Dy 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 122Sn(36S,4n) at 165 MeV was employed to populate high spin states in 154Dy. 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 154Dy. From comparisons with the Im(2) moments of inertia of the SD bands in 152Dy and 153Dy, a configuration based on (514)9/22 neutrons coupled to the 152Dy 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 153Dy. 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
Limitations to band gap tuning in nitride semiconductor alloys
Gorczyca, I.; Suski, T.; Christensen, Niels Egede;
2010-01-01
Relations between the band gaps of nitride alloys and their lattice parameters are presented and limits to tuning of the fundamental gap in nitride semiconductors are set by combining a large number of experimental data with ab initio theoretical calculations. Large band gap bowings obtained...
Exploring the origin of degenerate doublet bands in $^{106}$Ag
Rather, N; Chattopadhyay, S; Roy, S; Rajbanshi, S; Gowsami, A; Bhat, G H; Sheikh, J A; Palit, R; Pal, S; Saha, S; Sethi, J; Biswas, S; Singh, P; Jain, H C
2013-01-01
The electromagnetic transition probabilities of the excited levels for the two nearly degenerate bands of $^{106}$Ag have been measured using the Doppler Shift Attenuation Method. A comparison with the calculated values using triaxial projected shell model approach indicates that these bands originate from two different quasi-particle configurations but constructed from the same mean-field deformation.
Strain sensitivity of band gaps of Sn-containing semiconductors
Li, Hong; Castelli, Ivano Eligio; Thygesen, Kristian Sommer;
2015-01-01
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...
Split Hubbard bands at low densities
Hansen, Daniel; Perepelitsky, Edward; Shastry, B. Sriram
2011-05-01
We present a numerical scheme for the Hubbard model that throws light on the rather esoteric nature of the upper and lower Hubbard bands, which have been invoked often in literature. We present a self-consistent solution of the ladder-diagram equations for the Hubbard model, and show that these provide, at least in the limit of low densities of particles, a vivid picture of the Hubbard split bands. We also address the currently topical problem of decay of the doublon states that are measured in optical trap studies, using both the ladder scheme and also an exact two-particle calculation of a relevant Green’s function.
The band structures of 121,123I nuclei have been studied using a version of the particle-rotor-model in which the experimental excitation energies of the neighbouring (A-1) cores can be fed directly as input parameters. The calculations have been carried out with axially symmetric Nilsson potential with both prolate and oblate deformations. The parameters of the model have been chosen from earlier theoretical work and experimental odd-even mass differences. Only the Coriolis attenuation factor has been treated as adjustable parameter. The theoretical band structures are in very good agreement with the available experimental data. (orig.)
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...
Reviewed is the effect of heat flux of different system parameters on critical density in order to give an initial view on the value of several parameters. A thorough analysis of different equations is carried out to calculate burnout is steam-water flows in uniformly heated tubes, annular, and rectangular channels and rod bundles. Effect of heat flux density distribution and flux twisting on burnout and storage determination according to burnout are commended
Shetty, Prathvi; Menezes, Leo Theobald; Tauro, Leo Francis; Diddigi, Kumar Arun
2012-01-01
Amniotic band syndrome is an uncommon congenital disorder without any genetic or hereditary disposition. It involves fetal entrapment in strands of amniotic tissue and causes an array of deletions and deformations. Primary treatment is plastic and reconstructive surgery after birth with in utero fetal surgery also coming in vogue.
Study of positive parity bands in 137Pr
In this paper the analysis and interpretation of the positive parity states in 137Pr have been reported. The detailed interpretation with configuration assignments and the calculations for the bands will be reported
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.
DUAL BAND MONOPOLE ANTENNA DESIGN
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.
DeHaas-vanAlphen Effect and LMTO Band-structure of LaSn3
Boulet, R. M.; Jan, J. -P.; Skriver, Hans Lomholt
1982-01-01
Results of de Haas-van Alphen experiments in the intermetallic compound LaSn3 can be explained by a linear muffin-tin orbital band structure calculation without involving the f bands of lanthanum.......Results of de Haas-van Alphen experiments in the intermetallic compound LaSn3 can be explained by a linear muffin-tin orbital band structure calculation without involving the f bands of lanthanum....
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...
Geometry of magnetic rotational (MR) band-crossing in MR phenomenon
In this work, a schematic model base on semiclassical (SC) approach of Macchiavelli et.al was proposed to explain MR band-crossing. The MR band-crossing occurs due to the alignment of a pair of valence nucleon and the shear blades re-open to build up a new shear band. Due to the above interpretation of MR band-crossing, the B(M1) value can be calculated when the band changes its structure during crossing. In the present paper, we report semiclassical model to calculate the B(M1) value in the MR band-crossing region
High spin band structure in 139Nd
XU Qiang; ZHU Sheng-Jiang; CHE Xing-Lai; DING Huai-Bo; GU Long; ZHU Li-Hua; WU Xiao-Guang; LIU Ying; HE Chuang-Ye; LI Li-Hua; PAN Bo; HAO Xin; LI Guang-Sheng
2009-01-01
High-spin states in 139Nd nucleus have been reinvestigated with the reaction 128Te (16O, 5n) at a beam energy of 90 MeV. The level scheme has been expanded with spin up to 47/2 h. At the low spin states,the yrast collective structure built on the vh(-1)(11/2) multiplet shows a transitional shape with γ≈32° according to calculations of the triaxial rotor-plus-particle model. Three collective oblate bands with γ～-60° at the high spin states were identified for the first time. A band crossing is observed around hw ～0.4 MeV in one oblate band based on the 25/2- level.
Morrow, S. I.; Haring-Kaye, R. A.; Elder, R. M.; Tabor, S. L.; Tripathi, V.; Bender, P. C.; Medina, N. H.; Allegro, P.; Döring, J.
2013-10-01
Excited states in 70Ge were populated by the 55Mn(18O, p 2 n) fusion-evaporation reaction at 50 MeV performed at Florida State University. Prompt γ- γ coincidences were measured with a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. Examination of the resulting coincidence relations and relative intensity measurements led to an enhanced 70Ge level scheme, including an extension of the proposed γ vibrational band by four new states. Interpretation of the γ band within the context of the staggering parameter S (I) suggests a γ-soft structure, similar to other light Ge isotopes. Total Routhian Surface calculations for the ground-state band are consistent with a picture of γ softness at low spin. This work was supported by the National Science Foundation.
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...
Risk and reliability analysis is increasingly being used in evaluations of plant safety and plant reliability. The analysis can be performed either during the design process or during the operation time, with the purpose to improve the safety or the reliability. Due to plant complexity and safety and availability requirements, sophisticated tools, which are flexible and efficient, are needed. Such tools have been developed in the last 20 years and they have to be continuously refined to meet the growing requirements. Two different areas of application were analysed. In structural reliability probabilistic approaches have been introduced in some cases for the calculation of the reliability of structures or components. A new computer program has been developed based upon numerical integration in several variables. In systems reliability Monte Carlo simulation programs are used especially in analysis of very complex systems. In order to increase the applicability of the programs variance reduction techniques can be applied to speed up the calculation process. Variance reduction techniques have been studied and procedures for implementation of importance sampling are suggested. (author)
S-NPP VIIRS on-orbit Band to Band Registration Estimation using the Moon
Choi, T.
2015-12-01
The Soumi National Polar-orbit Partnership (S-NPP) was successfully launched and has been operational since October 28, 2011, which carries the Visible Infrared Radiometer Suite (VIIRS) with among other instruments. Since VIIRS does not include on-board spatial calibrator such as Spectroradiometric Calibration Assembly (SRCA) on the predecessor sensor called MODerate resolution Imaging Spectroradiometer (MODIS), the on-orbit estimation of the spatial parameters needs to be measured independently. As a well-known radiometric target, the moon is utilized to estimate Band-to-Band (BBR) results as a part of spatial quality factors using the lifetime scheduled lunar collections. The reference band of the BBR is chosen to be the VIIRS band of Imaging band 1 (I1), because of its high signal-to-noise ratio, and high spatial sampling frequency compared to other moderate (M) bands. In this study, the conventional BBR calculation applied MODIS called weighted sum method is applied providing along-track and along-scan direction results. The BBR differences based on the reference band I1 results are very stable over the 3 years of VIIRS operation. The along-scan direction BBR results are mostly within ± 0.5 nominal Ground Sampling Distance (GSD) and the along-track direction BBR values are mostly between + 0.1 and -0.4 GSD. The final BBR results are available publically at the National Oceanic Atmospheric Agency (NOAA) Integrated Calibration Validation System (ICVS) webpage.
Gutzwiller theory of band magnetism in LaOFeAs
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.
Diffuse interstellar absorption bands
XIANG FuYuan; LIANG ShunLin; LI AiGen
2009-01-01
The diffuse interstellar bands (DIBs) are a large number of absorption bands that are superposed on the interstellar extinction curve and are of interstellar origin. Since the discovery of the first two DIBs in the 1920s, the exact nature of DIBs still remains unclear. This article reviews the history of the detec-tions of DIBs in the Milky Way and external galaxies, the major observational characteristics of DIBs, the correlations or anti-correlations among DIBs or between DIBs and other interstellar features (e.g. the prominent 2175 Angstrom extinction bump and the far-ultraviolet extinction rise), and the proposed candidate carriers. Whether they are also present in circumstellar environments is also discussed.
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.
Accurate valence band width of diamond
An accurate width is determined for the valence band of diamond by imaging photoelectron momentum distributions for a variety of initial- and final-state energies. The experimental result of 23.0±0.2 eV2 agrees well with first-principles quasiparticle calculations (23.0 and 22.88 eV) and significantly exceeds the local-density-functional width, 21.5±0.2 eV2. This difference quantifies effects of creating an excited hole state (with associated many-body effects) in a band measurement vs studying ground-state properties treated by local-density-functional calculations. copyright 1997 The American Physical Society
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...
Band Structure Characteristics of Nacreous Composite Materials with Various Defects
Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.
2016-06-01
Nacreous composite materials have excellent mechanical properties, such as high strength, high toughness, and wide phononic band gap. In order to research band structure characteristics of nacreous composite materials with various defects, supercell models with the Brick-and-Mortar microstructure are considered. An efficient multi-level substructure algorithm is employed to discuss the band structure. Furthermore, two common systems with point and line defects and varied material parameters are discussed. In addition, band structures concerning straight and deflected crack defects are calculated by changing the shear modulus of the mortar. Finally, the sensitivity of band structures to the random material distribution is presented by considering different volume ratios of the brick. The results reveal that the first band gap of a nacreous composite material is insensitive to defects under certain conditions. It will be of great value to the design and synthesis of new nacreous composite materials for better dynamic properties.
Semiconductors bonds and bands
Ferry, David K
2013-01-01
As we settle into this second decade of the twenty-first century, it is evident that the advances in micro-electronics have truly revolutionized our day-to-day lifestyle. The technology is built upon semiconductors, materials in which the band gap has been engineered for special values suitable to the particular application. This book, written specifically for a one semester course for graduate students, provides a thorough understanding of the key solid state physics of semiconductors. It describes how quantum mechanics gives semiconductors unique properties that enabled the micro-electronics revolution, and sustain the ever-growing importance of this revolution.
Ab Initio Calculations of Oxosulfatovanadates
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...
Hyperspectral bands prediction based on inter-band spectral correlation structure
Ahmed, Ayman M.; Sharkawy, Mohamed El.; Elramly, Salwa H.
2013-02-01
Hyperspectral imaging has been widely studied in many applications; notably in climate changes, vegetation, and desert studies. However, such kind of imaging brings a huge amount of data, which requires transmission, processing, and storage resources for both airborne and spaceborne imaging. Compression of hyperspectral data cubes is an effective solution for these problems. Lossless compression of the hyperspectral data usually results in low compression ratio, which may not meet the available resources; on the other hand, lossy compression may give the desired ratio, but with a significant degradation effect on object identification performance of the hyperspectral data. Moreover, most hyperspectral data compression techniques exploits the similarities in spectral dimensions; which requires bands reordering or regrouping, to make use of the spectral redundancy. In this paper, we analyze the spectral cross correlation between bands for AVIRIS and Hyperion hyperspectral data; spectral cross correlation matrix is calculated, assessing the strength of the spectral matrix, we propose new technique to find highly correlated groups of bands in the hyperspectral data cube based on "inter band correlation square", and finally, we propose a new technique of band regrouping based on correlation values weights for different group of bands as network of correlation.
Comparison of broad-band and narrow-band red and near-infrared vegetation indices
An experiment has been conducted in which narrow-band field reflectance spectra were acquired of a rooted pinyon pine canopy with five different gravel backgrounds. Leaf area was successively removed as the measurements were repeated. From these reflectance spectra, narrow-band and broad-band (AVHRR, TM, MSS) red and near-infrared (NIR) vegetation index values were calculated. The performance of the vegetation indices was evaluated based on their capability to accurately estimate leaf area index (LAI) and percent green cover. Background effects were found for each of the tested vegetation indices. However, the background effects are most pronounced in the normalized difference vegetation index (NDVI) and ratio vegetation index (RVI). Background effects can be reduced using either the perpendicular vegetation index (PVI) or soil adjusted vegetation index (SAVI) formulations. The narrow-band versions of these vegetation indices had only slightly better accuracy than their broad-band counterparts. The background effects were minimized using derivative based vegetation indices, which measure the amplitude of the chlorophyll red-edge using continuous narrow-band spectra from 626 nm to 795 nm. (author)
Bandcrossing of magnetic rotation bands in 137Pr
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 ΔI=1 band has been extended to Jπ=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: πh11/2 x ν(h11/2)-2 configuration reproduce the experimental observations in the lower spin part of the ΔI=1 band and the 5qp: πh11/2(g7/2)2 x ν(h11/2)-2 configuration reproduces the ΔI=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
Electron band theory 1952-1962
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)
Shape evolution of yrast-band in 78Kr
Joshi, P. K.; Jain, H. C.; Palit, R.; Mukherjee, G.; Nagaraj, S.
2002-03-01
Lifetimes have been measured up to the I=22 + level in the yrast positive-parity band for 78Kr using the recoil distance and lineshape analysis methods. The B(E2) and Qt values obtained from these measurements show a significant drop with increasing spin. The band crossings and the observed variation in Qt are understood through cranked shell-model, TRS and configuration-dependent shell-correction calculations assuming an oblate deformation for 78Kr at low spins.
Electronic Band Engineering of Epitaxial Graphene by Atomic Intercalation
Jayasekera, Thushari; Sandin, Andreas; Xu, Shu; Wheeler, Virginia; Gaskill, D. K.; Rowe, J. E.; Kim, K. W.; Dougherty, Daniel B.; Buongiorno Nardelli, M.
2012-02-01
Using calculations from first principles, we have investigated possible ways of engineering the electronic band structure of epitaxial graphene on SiC. In particular, intercalation of different atomic species, such as Hydrogen, Fluorine, Sodium, Germanium, Carbon and Silicon is shown to modify and tune the interface electronic properties and band alignments. Our results suggest that intercalation in graphene is quite different from that in graphite, and could provide a fundamentally new way to achieve electronic control in graphene electronics.
Phase solitons and subgap excitations in two-band superconductors
Samokhin, K. V.
2012-01-01
A phase soliton is a topological defect peculiar to two-band superconductors, which is associated with a $2\\pi$ winding of the relative phase of the two superconducting condensates. We study the quasiparticle spectrum in the presence of a single planar phase soliton. We show that the order parameter phase variation in each of the bands leads to the existence of subgap states bound to the soliton. Calculation of the soliton energy valid at all temperatures is presented, with the exact analytic...
Systematic description of superdeformed bands in the mass-190 region
Sun, Yang; Guidry, M. [Oak Ridge National Lab., TN (United States)]|[Univ. of Tennessee, Knoxville, TN (United States); Zhang, Jing-ye [Univ. of Tennessee, Knoxville, TN (United States)
1996-12-31
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.
Flat Bands Under Correlated Perturbations
Bodyfelt, Joshua D.; Leykam, Daniel; Danieli, Carlo; Yu, Xiaoquan; Flach, Sergej
2014-01-01
Flat band networks are characterized by coexistence of dispersive and flat bands. Flat bands (FB) are generated by compact localized eigenstates (CLS) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLS without additional renormalization, yet with surprising consequencies: (i) states are expelled from the FB energy $E_{FB}$, (ii) the localization length of eigenstates vanishes as $\\xi \\sim 1 / \\ln (E- E_{FB})$, (iii)...
Cluster banding heat source model
Zhang Liguo; Ji Shude; Yang Jianguo; Fang Hongyuan; Li Yafan
2006-01-01
Concept of cluster banding heat source model is put forward for the problem of overmany increment steps in the process of numerical simulation of large welding structures, and expression of cluster banding heat source model is deduced based on energy conservation law.Because the expression of cluster banding heat source model deduced is suitable for random weld width, quantitative analysis of welding stress field for large welding structures which have regular welds can be made quickly.
Development of Wide Band Feeds
Ujihara, H.; Ichikawa, R.
2012-12-01
Wide Band feeds are being developed at NICT, NAOJ, and some universities in Japan for VLBI2010, SKA, and MARBLE. SKA, the Square Kilometre Array, will comprise thousands of radio telescopes with square kilometer aperture size for radio astronomy. MARBLE consists of small portable VLBI stations developed at NICT and GSI in Japan. They all need wide band feeds with a greater than 1:10 frequency ratio. Thus we have been studying wide band feeds with dual linear polarization for these applications.
Electronic band structure and photoemission: A review and projection
A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs
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 by electron and ph...
In-band and inter-band B(E2) values within the Triaxial Projected Shell Model
The Triaxial Projected Shell Model (TPSM) has been successful in providing a microscopic description of the energies of multi-phonon vibrational bands in deformed nuclei. We report here on an extension of the TPSM to allow, for the first time, calculations of B(E2) values connecting γ- and γγ-vibrational bands and the ground-state band. The method is applied to 166,168Er. It is shown that most of the existing B(E2) data can be reproduced rather well, thus strongly supporting the classification of these states as γ-vibrational states. However, significant differences between the data and the calculation are seen in those B(E2) values which involve odd-spin states of the γ-band. Understanding these discrepancies requires accurate experimental measurements and perhaps further improvements of the TPSM. (orig.)
Nuclear rotational-band interaction-mechanism revisited
The technique of band-interaction calculations has been widely used for many years in the context of nuclear structure studies and a number of approximations have generally been made in this context. In this article we examine the impact of certain of these simplifications, basing our study on the interaction of some model bands. We show that large uncertainties can result when the interacting-band model is used under the assumptions that quite often are not even explicitly mentioned - neither verified. (author)
Band alignment of two-dimensional lateral heterostructures
Zhang, Junfeng; Xie, Weiyu; Zhang, S B
2016-01-01
Band alignment in two-dimensional (2D) lateral heterostructures is fundamentally different from three-dimensional (3D), as Schottky barrier height is at the Schottky-Mott limit and band offset is at the Anderson limit, regardless interfacial conditions. This robustness arises because, in the asymptotic limit, effect of interfacial dipole vanishes. First-principles calculations of graphene/h-BN and MoS2/WS2 show that 2D junction width W is typically an order of magnitude longer than 3D. Therefore, heterostructures with dimension less than W can also be made, leading to tunable band alignment.
Normal and superdeformed cluster bands in heavy nuclei
Buck, B; Horner, M J; Pérez, S M
2000-01-01
We apply a principle of maximum stability to determine the most favoured core-cluster decompositions of sup 1 sup 9 sup 4 Hg, sup 2 sup 3 sup 6 U and sup 2 sup 4 sup 0 Pu. The results suggest two distinct modes of clusterization for each nucleus, one of which can be associated with the ground state band, and the other with an excited superdeformed band. We compare the calculated properties of these bands with the corresponding data available in all three nuclei.
In this paper, a new type of narrow-band function is proposed for the artificial history simulation method based on narrow-band superposition, which aims to meet the needs of both fitting of the target response spectrum and envelop of the power spectral density. The new narrow-band function is based on the normal distribution function and trigonometric functions. Its band width can be controlled and it decays rapidly on both sides. While the target response spectrum is fitted by superimposing the new narrow-band time history, the power spectral density is enveloped by modifying the Fourier amplitude spectrum locally. The numerical example demonstrates that not only the artificial time history generated by this algorithm reaches high matching precision to the target response spectrum, but also the corresponding calculated power spectrum envelopes the target power spectrum. (authors)
Garage Band or GarageBand[R]? Remixing Musical Futures
Vakeva, Lauri
2010-01-01
In this paper, I suggest that it is perhaps time to consider the pedagogy of popular music in more extensive terms than conventional rock band practices have to offer. One direction in which this might lead is the expansion of the informal pedagogy based on a "garage band" model to encompass various modes of digital artistry wherever this artistry…
Simultaneous confidence bands in linear regression analysis
Ah-Kine, Pascal Soon Shien
2010-01-01
A simultaneous confidence band provides useful information on the plausible range of an unknown regression model. For a simple linear regression model, the most frequently quoted bands in the statistical literature include the two-segment band, the three-segment band and the hyperbolic band, and for a multiple linear regression model, the most com- mon bands in the statistical literature include the hyperbolic band and the constant width band. The optimality criteria for confid...
Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco;
2014-01-01
The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all......-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...... distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators....
Spectra of {gamma} rays feeding superdeformed bands
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.
Hubbard-U band-structure methods
Albers, R.C.; Christensen, Niels Egede; Svane, Axel
2009-01-01
The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many...... inconsistent with what the calculations actually do. Although many of these calculations are often treated as essentially first-principles calculations, in fact, we argue that they should be viewed from an entirely different point of view, namely, as based on phenomenological many-body corrections to band-structure......-body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations are...
Geometry-independent energy band simulator for radially symmetric diodes
Kirkpatrick, T.; Buonassisi, T.
2016-07-01
In this work, a geometrically independent method to calculate the energy band diagram of radially symmetric diodes is reported. For radially symmetric diodes, the calculation of electron (or hole) energies across the junction can be reduced to a singular spatially dependent variable. Because geometry is not incorporated into the calculation a priori, by reducing the physics to a single spatial variable, energy band calculations can be performed in multiple geometries, simultaneously, for direct comparison to each other. The calculation outlined herein is pseudo-analytical and does not utilize finite element and/or control volume methods. It is, therefore, capable of generating spatially analytic equations for analyzing limiting scenarios of the junction, beneficial for yielding insight into the physics and design criteria of depletion for non-planar semiconducting devices.
Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities
Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent
Allsup, Randall Everett
2012-01-01
This article provides a theoretical framework through which to reimagine and revitalize contemporary music education practices, using the large ensemble paradigm called "band" as the primary unit of analysis. Literature suggests that band places too much emphasis on teacher control and external measures of validation. Critics propose replacing…
Simple band model of doped fullerene crystal
We used quantum billiard with many scattering centers to describe conducting electrons properties in AC60 crystals, where A denotes alkali metal. We focus our attention on the A3C60 crystal, for which we calculate the band structure, density of states, and conductivity for normal electrons. Conductivity shows linear dependence on temperature in this model, which agrees well with experimental data. We also discuss consequences of our results for superconductivity mechanism in A3C60 and possibilities of analogous approach to describe electron properties in fused fullerenes and multiply connected carbon clusters. (author)
Sculpting the band gap: a computational approach.
Prasai, Kiran; Biswas, Parthapratim; Drabold, D A
2015-01-01
Materials with optimized band gap are needed in many specialized applications. In this work, we demonstrate that Hellmann-Feynman forces associated with the gap states can be used to find atomic coordinates that yield desired electronic density of states. Using tight-binding models, we show that this approach may be used to arrive at electronically designed models of amorphous silicon and carbon. We provide a simple recipe to include a priori electronic information in the formation of computer models of materials, and prove that this information may have profound structural consequences. The models are validated with plane-wave density functional calculations. PMID:26490203
Single Band Helical Antenna in Axial Mode
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
Band engineering in transition metal dichalcogenides: Stacked versus lateral heterostructures
Guo, Yuzheng; Robertson, John
2016-06-01
We calculate a large difference in the band alignments for transition metal dichalcogenide (TMD) heterojunctions when arranged in the stacked layer or lateral (in-plane) geometries, using direct supercell calculations. The stacked case follows the unpinned limit of the electron affinity rule, whereas the lateral geometry follows the strongly pinned limit of alignment of charge neutrality levels. TMDs therefore provide one of the few clear tests of band alignment models, whereas three-dimensional semiconductors give less stringent tests because of accidental chemical trends in their properties.
Photonic band gaps with layer-by-layer double-etched structures
Periodic layer-by-layer dielectric structures with full three-dimensional photonic band gaps have been designed and fabricated. In contrast to previous layer-by-layer structures the rods in each successive layer are at an angle of 70.5 degree to each other, achieved by etching both sides of a silicon wafer. Photonic band-structure calculations are utilized to optimize the photonic band gap by varying the structural geometry. The structure has been fabricated by double etching Si wafers producing millimeter wave photonic band gaps between 300 and 500 GHz, in excellent agreement with band calculations. Overetching this structure produces a multiply connected geometry and increases both the size and frequency of the photonic band gap, in very good agreement with experimental measurements. This new robust double-etched structure doubles the frequency possible from a single Si wafer, and can be scaled to produced band gaps at higher frequencies. copyright 1996 American Institute of Physics
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 β-PbO2 and TiO2 (both rutile). The band gaps for the constituents (β-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
W-Band Sheet Beam Klystron Simulation
Colby, E.R.; Caryotakis, G.; Fowkes, W.R.; /SLAC; Smithe, D.N.; /Mission Res., Newington
2005-09-12
With the development of ever higher energy particle accelerators comes the need for compactness and high gradient, which in turn require very high frequency high power rf sources. Recent development work in W-band accelerating techniques has spurred the development of a high-power W-band source. Axisymmetric sources suffer from fundamental power output limitations (P{sub sat} {approx} {lambda}{sup 2}) brought on by the conflicting requirements of small beam sizes and high beam current. The sheet beam klystron allows for an increase in beam current without substantial increase in the beam current density, allowing for reduced cathode current densities and focusing field strengths. Initial simulations of a 20:1 aspect ratio sheet beam/cavity interaction using the 3 dimensional particle-in-cell code Magic3D have demonstrated a 35% beam-power to RF power extraction efficiency. Calculational work and numerical simulations leading to a prototype W-band sheet beam klystron will be presented, together with preliminary cold test structure studies of a proposed RF cavity geometry.
Microstrip microwave band gap structures
V Subramanian
2008-04-01
Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.
Collective bands in superdeformed nuclei
The collective properties of excited superdeformed bands have been investigated in the framework of self-consistent cranked Nilsson plus quasiparticle random-phase approximation. The expected octupole nature of some bands observed recently in some nuclei has been confirmed by a comparative analysis of their E1 decays to the yrast band and of the anomalous behavior of their dynamical moment of inertia. It is also shown that the onset of supederformation affects considerably the structure of the giant resonances and greatly enhances the collectivity of the low-lying scissors mode. (author)
Greenberg, J.; Guess, C. J.; Tandel, S.; Chowdhury, P.; Carpenter, M. P.; Hartley, D. J.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Seweryniak, D.; Shirwadkar, U.; Wang, X.; Zhu, S.
2015-10-01
Studying the structure of rotational bands in 172W is valuable for gaining a better understanding of deformed nuclei. Highly excited states of the isotope were populated from a 230 MeV 50Ti beam incident on a 128Te target at Argonne National Laboratory using the ATLAS accelerator. γ emissions from 172W in the range were measured using Compton suppressed germanium detectors in the Gammasphere array. Using this data, three new rotational bands were found, and several other bands were expanded. Swarthmore College Summer Research Fellowship.
Modeling charged defects inside density functional theory band gaps
Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem
On-Site was developed to provide modelers and model reviewers with prepackaged tools ("calculators") for performing site assessment calculations. The philosophy behind OnSite is that the convenience of the prepackaged calculators helps provide consistency for simple calculations,...
Electronic structures of the silicide carbides Tm2Fe2Si2C, Th2Re2Si2C, and ThFe2SiC and the carbide Ho2Cr2C3 were calculated, using the extended Hueckel tight binding method, to probe the d-electron counts of their transition metal atoms M (Cr, Fe, Re) the bonding of their linear M-C-M (M = Cr, Fe, Re) units. The nature of the short interlayer X hor-ellipsis X (X = C, Si) bonds in Tm2Fe2Si2C, Th2Re2Si2C, and Ho2Cr2C3 was also examined. The study shows that the M-C bonds of the M-C-M units exist as double bonds. There is significant bonding in the interlayer Si hor-ellipsis Si contacts of the silicide carbides R2M2Si2C (M = Fe, Re). The transition-metal atoms exist as d10 ions in Tm2Fe2Si2C and Th2Re2Si2C. The d-electron count is slightly lower than d10 in ThFe2SiC and close to d5 in Ho2Cr2C3
Photonic band structure of two-dimensional metal/dielectric photonic crystals
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. (paper)
Spin susceptibility of Anderson impurities in arbitrary conduction bands
Fang, Tie-Feng; Tong, Ning-Hua; Cao, Zhan; Sun, Qing-Feng; Luo, Hong-Gang
2015-10-01
Spin susceptibility of Anderson impurities is a key quantity in understanding the physics of Kondo screening. Traditional numerical renormalization group (NRG) calculation of the impurity contribution χimp to susceptibility, defined originally by Wilson in a flat wide band, has been generalized before to structured conduction bands. The results brought about non-Fermi-liquid and diamagnetic Kondo behaviors in χimp, even when the bands are not gapped at the Fermi energy. Here, we use the full density-matrix (FDM) NRG to present high-quality data for the local susceptibility χloc and to compare them with χimp obtained by the traditional NRG. Our results indicate that those exotic behaviors observed in χimp are unphysical. Instead, the low-energy excitations of the impurity in arbitrary bands only without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We also demonstrate that unlike the traditional NRG yielding χloc less accurate than χimp, the FDM method allows a high-precision dynamical calculation of χloc at much reduced computational cost, with an accuracy at least one order higher than χimp. Moreover, artifacts in the FDM algorithm to χimp and origins of the spurious non-Fermi-liquid and diamagnetic features are clarified. Our work provides an efficient high-precision algorithm to calculate the spin susceptibility of impurity for arbitrary structured bands, while negating the applicability of Wilson's definition to such cases.
Mason, Brian D.
1995-03-01
results is presented. Of the remaining 96 systems, 66 have been detected by speckle interferometry, 13 for the first time, and 17 new orbits have been calculated. Of these orbits, five (HR 793 = Bla Aa, ADS 3608 = A 1844, HR 3880 = McA 34, HR 5652 = B 2531 Aa, HR 7776 = $\\beta$ Cap) have improved elements over previous orbit calculations, four (BD$+$24~1805 = Cou 929, ADS 17052 = A 2700, HR 9041 = Fin 359, ADS 17111 = A 2100) have previous but significantly different orbits, five (HR 132 = McA 1 Aa, HR 1808 = McA 19 Aa, HR 2343 = Btz Aa, HR 8060 = Fin 328, HR 8704 = McA 73) are first orbits, and three (HR 763 = McA 7, HR 2130 = McA 24, HR 2846 = McA 30 Aa) are first orbits of spectroscopic binaries. The occultation catalog, speckle measures, and new orbits will be presented in subsequent CHARA publications. The detection of occultation binaries by speckle interferometry seems to be predictable, however, there appear to be a small sample of occultation binaries which cannot be detected. These may be spurious. Lunar occultation measures place a good limit on $\\Delta$m for speckle of about 3.0. CHARA hopes to complete a survey of all occultation objects with current scheduled runs which should result in a further five to ten objects resolved for the first time. While the rate of occultation measures has dropped significantly, they are still continuing to provide useful complementary data for other binary star methods. (SECTION: Dissertation Summaries)
Exact two-component relativistic energy band theory and application
An exact two-component (X2C) relativistic density functional theory in terms of atom-centered basis functions is proposed for relativistic calculations of band structures and structural properties of periodic systems containing heavy elements. Due to finite radial extensions of the local basis functions, the periodic calculation is very much the same as a molecular calculation, except only for an Ewald summation for the Coulomb potential of fluctuating periodic monopoles. For comparison, the nonrelativistic and spin-free X2C counterparts are also implemented in parallel. As a first and pilot application, the band gaps, lattice constants, cohesive energies, and bulk moduli of AgX (X = Cl, Br, I) are calculated to compare with other theoretical results
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.
Exact two-component relativistic energy band theory and application
Zhao, Rundong; Zhang, Yong; Xiao, Yunlong; Liu, Wenjian, E-mail: liuwj@pku.edu.cn [Beijing National Laboratory for Molecular Sciences, Institute of Theoretical and Computational Chemistry, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, and Center for Computational Science and Engineering, Peking University, Beijing 100871 (China)
2016-01-28
An exact two-component (X2C) relativistic density functional theory in terms of atom-centered basis functions is proposed for relativistic calculations of band structures and structural properties of periodic systems containing heavy elements. Due to finite radial extensions of the local basis functions, the periodic calculation is very much the same as a molecular calculation, except only for an Ewald summation for the Coulomb potential of fluctuating periodic monopoles. For comparison, the nonrelativistic and spin-free X2C counterparts are also implemented in parallel. As a first and pilot application, the band gaps, lattice constants, cohesive energies, and bulk moduli of AgX (X = Cl, Br, I) are calculated to compare with other theoretical results.
Superdeformed bands of odd nuclei in A=190 region in the quasiparticle picture
Properties of the superdeformed (SD) bands of 195Pb and 193Hg have been studied by the cranked Hartree-Fock-Bogoliubov method. The calculations reproduce the flat behavior of the dynamical moment of inertia of two of the SD bands of 195Pb measured recently. Possible configuration assignments for the observed bands 3 and 4 of 195Pb are discussed. The two interacting SD bands of 193Hg have also been calculated. The analysis confirms the superiority of a density-dependent pairing force over a seniority pairing interaction. (author)
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...
First principle study of band structure of SrMO3 perovskites
Daga, Avinash; Sharma, Smita
2016-05-01
First principle study of band structure calculations in the local density approximations (LDA) as well as in the generalized gradient approximations (GGA) have been used to determine the electronic structure of SrMO3 where M stands for Ti, Zr and Mo. Occurrence of band gap proves SrTiO3 and SrZrO3 to be insulating. A small band gap is observed in SrMoO3 perovskite signifies it to be metallic. Band structures are found to compare well with the available data in the literature showing the relevance of this approach. ABINIT computer code has been used to carry out all the calculations.
Some parallel banded system solvers
Dongarra, J.J.; Sameh, A.H.
1984-12-01
This paper describes algorithms for solving narrow banded systems and the Helmholtz difference equations that are suitable for multiprocessing systems. The organization of the algorithms highlight the large grain parallelism inherent in the problems. 13 references, 5 tables.
Audio watermarking based on psychoacoustic model and critical band wavelet transform
TAO Zhi; ZHAO Heming; GU Jihua; WU Di
2007-01-01
Watermark embedding algorithm based on critical band wavelet transform of digital audio signal is proposed in this paper. The masking threshold for each audio signal segment was calculated on the basic of psychoacoustic model. According to the similarity between critical band of human auditory system and critical band wavelet transform, a watermark was embedded into the low-band and mid-band coefficients of digital wavelet. The embedding strength was adaptively controlled by the masking threshold. The experiment results show that the embedded watermark signal is inaudible, and the watermarked audio signal has good robustness against many attacks such as compression, noise, re-sampling, low-pass filtering.
Multi-band effects on Fulde-Ferrell-Larkin-Ovchinnikov states of Pauli-limited superconductors
Takahashi, Masahiro; Mizushima, Takeshi; Machida, Kazushige
2014-01-01
Multi-band effects on Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states of a Pauli-limiting two-band superconductor are studied theoretically, based on self-consistent calculations of the Bogoliubov-de Gennes equation. First, we examine the phase diagrams of two-band systems with a passive band in which the intraband pairing interaction is absent and superconductivity is induced by a Cooper pair tunneling from an active band. It is demonstrated that the temperature of the Lifshitz point at which...
Effects of inclusion shapes on the band gaps in two-dimensional piezoelectric phononic crystals
In this paper, the elastic wave propagation in piezoelectric phononic crystals with several inclusion shapes is investigated by taking the electromechanical coupling into account. The band structures for five different shapes of scatterers (regular triangle, square, hexagon, circle, and oval) with square lattice are calculated using the plane-wave expansion method. The effects of the inclusion shapes on the normalized band width are discussed. The largest complete band gap is obtained by selecting the scatterers with the same symmetry of lattice for the first band gap, but this rule is not valid for the second band gap
Band gap engineering strategy via polarization rotation in perovskite ferroelectrics
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
A.V. Strizhachenko
2010-01-01
Full Text Available Original design of the narrow-band compact filters based on the high-quality waveguide-dielectric resonator with anisotropic materials has been presented in this work. Designed filters satisfy the contradictory requirements: they provide the narrow frequency band (0.05 ÷ 0.1 % of the main frequency f0 and the low initial losses α0 ≤ 1 dB.
High spin states in 196Hg have been populated in the 198Pt(α,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.
Coupling effect of quantum wells on band structure
Jie, Chen; Weiyou, Zeng
2015-10-01
The coupling effects of quantum wells on band structure are numerically investigated by using the Matlab programming language. In a one dimensional finite quantum well with the potential barrier V0, the calculation is performed by increasing the number of inserted barriers with the same height Vb, and by, respectively, varying the thickness ratio of separated wells to inserted barriers and the height ratio of Vb to V0. Our calculations show that coupling is strongly influenced by the above parameters of the inserted barriers and wells. When these variables change, the width of the energy bands and gaps can be tuned. Our investigation shows that it is possible for quantum wells to achieve the desired width of the bands and gaps.
Band Anticrossing in Dilute Germanium Carbides Using Hybrid Density Functionals
Stephenson, Chad A.; O'brien, William A.; Qi, Meng; Penninger, Michael; Schneider, William F.; Wistey, Mark A.
2016-04-01
Dilute germanium carbides (Ge1- x C x ) offer a direct bandgap for compact silicon photonics, but widely varying properties have been reported. This work reports improved band structure calculations for Ge1- x C x using ab initio simulations that employ the HSE06 exchange-correlation density functional. Contrary to Vegard's law, the conduction band minimum at Γ is consistently found to decrease with increasing C content, while L and X valleys change much more slowly. The calculated Ge bandgap is within 11% of experimental values. A decrease in energy at the Γ conduction band valley of (170 meV ± 50)/%C is predicted, leading to a direct bandgap for x > 0.008. These results indicate a promising material for Group IV lasers.
Coupling effect of quantum wells on band structure
The coupling effects of quantum wells on band structure are numerically investigated by using the Matlab programming language. In a one dimensional finite quantum well with the potential barrier V0, the calculation is performed by increasing the number of inserted barriers with the same height Vb, and by, respectively, varying the thickness ratio of separated wells to inserted barriers and the height ratio of Vb to V0. Our calculations show that coupling is strongly influenced by the above parameters of the inserted barriers and wells. When these variables change, the width of the energy bands and gaps can be tuned. Our investigation shows that it is possible for quantum wells to achieve the desired width of the bands and gaps. (paper)
Band gap bowing in quaternary nitride semiconducting alloys
Gorczyka, Isabela; Suski, T.; Christensen, Niels Egede;
2011-01-01
Structural properties of InxGayAl1−x−yN alloys are derived from total-energy minimization within the local-density approximation (LDA). The electronic properties are studied by band structure calculations including a semiempirical correction for the “LDA gap error.” The effects of varying the...
Band loss by nestling mourning doves
Kaczynski, C.F.; Kiel, W.H.
1963-01-01
Nestling mourning doves (Zenaidura macroura) were banded and checked for band loss prior to fledging at Parchman, Mississippi, during the months of June-August, 1960. Three hundred seventy-seven nestlings 4-6 days of age were banded, 117 with size 3 bands, 120 with size 3A bands, and 140 with size 3A bands secured by Dalzoflex tape. Two hundred twenty nestlings 7-9 days of age were banded, 114 with size 3 bands and 106 with size 3A bands. In the 4- to 6-day age group, 66.3 percent of the size 3A bands were lost. This was a statistically significant departure from the 7.7 percent loss of size 3 bands. No taped bands were lost. However, predators ate 13.8 percent of the nestlings with taped bands and significantly fewer of the nestlings banded without tape. In the 4- to 6-day age group, percentages of nestlings known to be available for band recovery at 9 days or older were: size 3, 69.2 percent; size 3A with tape, 59.0 percent; size 3A, 25.8 percent. In the 7-to 9-day age group, there was a 3.3 percent loss of size 3A bands and no loss of size 3 bands. The minimum age at which nestlings were banded without subsequent loss of bands was 6 days for size 3 and 8 days for size 3A.
Hyperdeformed band in the 36Ar nucleus?
Complete text of publication follows. The exotic shapes of atomic nuclei has attracted much attention recently both from the experimental and from the theoretical sides. E.g. the superdeformed (SD) shape in N = Z nuclei were observed experimentally during the last decade. In particular the SD band of the 36Ar nucleus was detected in 2000 [1]. Following the experimental observation a considerable theoretical effort has been concentrated on this band. In [2] e.g. the possible binary clusterizations of this state was studied systematically. Similar studies have been done also for the ground, and the hyperdeformed band. The latter one had been predicted from alphacluster model calculations [3]. The possible binary cluster-configurations are important not only for the better understanding of the structure of the shape isomers, but also from the viewpoint of predicting the favoured reaction channels to populate these states. This is the straightforward consequence of the close relation between the clusterization and reaction channels. (In fact, a cluster-configuration is defined by the reaction channel in which it can be observed.) One of the interesting conclusions of the work [2] was, that the hyperdeformed (HD) state of the 36Ar nucleus could be populated in the 24Mg+12C and 20Ne+16O reactions. A recent analysis of the 24Mg+12C elastic scattering [4] revealed the fact that the cross section can be described only by supposing resonances on top of the potential scattering. This very careful analysis incorporated phase-shift study, as well as Regge-pole and energy-dependent resonance calculations. The existence of five resonances have been proved, which have angular momenta 2, 4, 6, 7, 8. These states together with the resonances from the 20Ne+16O reactions seem to establish a rotational band, as shown in the upper part of Fig. 1. Its moment of inertia is in a very good agreement with that of the HD shape predicted from alpha-cluster model [3]. The similarity of the
Dosimetry of narrow band UVB treatments
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 (μW/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 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
F. L. Freitas
2016-08-01
Full Text Available We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal AlxGayIn1–x–yN semiconductor alloys, employing a cluster expansion method to account for the inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
The multilayer structure of TiO2/SiO2 (11 layers) as one dimensional photonic crystal (1D PC) has been designed and then fabricated by using asymmetric bipolar pulse DC magnetron sputtering technique for omnidirectional photonic band gap. The experimentally measured photonic band gap (PBG) in the visible region is well matched with the theoretically calculated band structure (ω vs. k) diagram. The experimentally measured omnidirectional reflection band of 44 nm over the incident angle range of 0°-70° is found almost matching within the theoretically calculated band
Bands and Band Termination in 127La%127La转动带及带终止
董保国; Ragna.,I
2000-01-01
The configuration-dependent shell-correction approach with cranked Nilsson potential is employed for explaining the experimental high-spin spectra in 127La. The experimental high spin band with parity and signature (+,-1/2) consists of two parts with a crossing around I=20h. It is most like to have the configuration[02,6], π(h11/2)2v(h11/2)6 and almost reaching the maximum angular momentum at I=47.5 h. It is in normal deformation region with ε2≈0.22 and γ≈0° up to I=40 h and then moving over the γ-plane to termination atγ＝60。． Comparing calculations and experiment, one notes that the bands are seen to spin values where according to calculation they start to go away clearly from yrast, thus this supports our interpretation. There are strongly deformed (or superdeformed) bands with ε2≈0.35 and ν≈0°. They were calculated to become yrast for I=40h making it very unlikely that the observed bands were strongly deformed. However, they represent a challenge for future experiments. Below I＝21.5 Kthe experimental high spin bands appear to have strong pairing interaction since their moments of inertia go down to 10/2 MeV-1 from I=11.5h to I=19.5 h.%用组态相关推转壳模型Nilsson势研究了C．M．Parry组最近用EUROBALL谱仪观测到的127La高自旋态结构．实验上观测的127La的宇称和辛量子数为(π,α)=(+,-1/2)的带自旋达到(83/2)h．理论计算结果表明该带可能具有组态π(h11/2)2v(h11/2)6．并且几乎达到该带的带终止理论预言值 I=47.5h．该带的形变在I≤40h内处于正常形变区(ε2≈0.22，γ≈0°)，随着角动量的增加ν值逐渐增加，直到ν＝60°时带终止．