Correspondences between the Classical Electrostatic Thomson Problem and Atomic Electronic Structure
LaFave, Tim
2014-01-01
Correspondences between the Thomson Problem and atomic electron shell-filling patterns are observed as systematic non-uniformities in the distribution of potential energy necessary to change configurations of $N\\le 100$ electrons into discrete geometries of neighboring $N-1$ systems. These non-uniformities yield electron energy pairs, intra-subshell pattern similarities with empirical ionization energy, and a salient pattern that coincides with size-normalized empirical ionization energies. Spatial symmetry limitations on discrete charges constrained to a spherical volume are conjectured as underlying physical mechanisms responsible for shell-filling patterns in atomic electronic structure and the Periodic Law.
Mariani, Elisabetta; Kaercher, Pamela; Mecklenburgh, Julian; Wheeler, John
2016-04-01
Perovskite minerals form an important mineral group that has applications in Earth science and emerging alternative energy technologies, however crystallographic quantification of these minerals with electron backscatter diffraction (EBSD) is not accurate due to pseudosymmetry problems. The silicate perovskite Bridgmanite, (Mg,Fe)SiO3, is understood to be the dominant phase in the Earth's lower mantle. Gaining insight into its physical and rheological properties is therefore vital to understand the dynamics of the Earth's deep interior. Rock deformation experiments on analogue perovskite phases, for example (Ca,Sr)TiO3, combined with quantitative microstructural analyses of the recovered samples by EBSD, yield datasets that can reveal what deformation mechanisms may dominate the flow of perovskite in the lower mantle. Additionally, perovskite structures have important technological applications as new, suitable cathodes for the operation of more efficient and environmentally-friendly solid oxide fuel cells (SOFC). In recent years they have also been recognised as a potential substitute for silicon in the next generation of photovoltaic cells for the construction of economic and energy efficient solar panels. EBSD has the potential to be a valuable tool for the study of crystal orientations achieved in perovskite substrates as crystal alignment has a direct control on the properties of these materials. However, perovskite structures currently present us with challenges during the automated indexing of Kikuchi bands in electron backscatter diffraction patterns (EBSPs). Such challenges are represented by the pseudosymmetric character of perovskites, where atoms are subtly displaced (0.005 nm to 0.05 nm) from their higher symmetry positions. In orthorhombic Pbnm perovskites, for example, pseudosymmetry may be evaluated from the c/a unit cell parameter ratio, which is very close to 1. Two main types of distortions from the higher symmetry structure are recognised: a
Locally self-consistent Green’s function approach to the electronic structure problem
Abrikosov, I.A.; Simak, S.I.; Johansson, B.;
1997-01-01
The locally self-consistent Green's function (LSGF) method is an order-N method for calculation of the electronic structure of systems with an arbitrary distribution of atoms of different kinds on an underlying crystal lattice. For each atom Dyson's equation is used to solve the electronic multiple...
Schiffmann, Florian; VandeVondele, Joost, E-mail: Joost.VandeVondele@mat.ethz.ch [Nanoscale Simulations, Department of Materials, ETH Zürich, Wolfgang-Pauli-Str. 27, CH-8093 Zürich (Switzerland)
2015-06-28
We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling’s iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.
Roman F. Nalewajski
2002-04-01
Full Text Available Abstract: Recent studies on applications of the information theoretic concepts to molecular systems are reviewed. This survey covers the information theory basis of the Hirshfeld partitioning of molecular electron densities, its generalization to many electron probabilities, the local information distance analysis of molecular charge distributions, the charge transfer descriptors of the donor-acceptor reactive systems, the elements of a Ã¢Â€ÂœthermodynamicÃ¢Â€Â description of molecular charge displacements, both Ã¢Â€ÂœverticalÃ¢Â€Â (between molecular fragments for the fixed overall density and Ã¢Â€ÂœhorizontalÃ¢Â€Â (involving different molecular densities, with the entropic representation description provided by the information theory. The average uncertainty measures of bond multiplicities in molecular Ã¢Â€ÂœcommunicationÃ¢Â€Â systems are also briefly summarized. After an overview of alternative indicators of the information distance (entropy deficiency, missing information between probability distributions the properties of the Ã¢Â€ÂœstockholderÃ¢Â€Â densities, which minimize the entropy deficiency relative to the promolecule reference, are summarized. In particular, the surprisal analysis of molecular densities is advocated as an attractive information-theoretic tool in the electronic structure theory, supplementary to the familiar density difference diagrams. The subsystem information density equalization rules satisfied by the Hirshfeld molecular fragments are emphasized: the local values of alternative information distance densities of subsystems are equal to the corresponding global value, characterizing the molecule as a whole. These local measures of the information content are semi-quantitatively related to the molecular density difference function. In the density functional theory the effective external potentials of molecular fragments are defined, for which
Alloul, H. [Paris-11 Univ., 91 - Orsay (France). Lab. de Physique des Solides
2007-07-01
The diversity of the macroscopic properties of solids like magnetism or superconductivity stems from the quantum states of electrons. Today only the experimental approach reveals the spectacular effects of these properties but basic concepts of quantum mechanics and of statistical physics are necessary to give an account of the link between the microscopic scale and the macroscopic world. The simple approach involving independent electrons gives a description of the electronic structure as energy bands that explains the existence of metals, isolators and semi-conductors. Magnetism and superconductivity can be understood only by taking into account the existence of correlations between the electrons in the solids. The first tome presents the formalism of quantum mechanics applied to the system formed by nuclei and the electrons in solids. Different issues like electronic structures in solids, electron transport, the microscopic origin of superconductivity, the magnetism of isolators, the dynamics of spin and magnetic resonance are explained. The second volume can be divided into 2 parts, the first part giving the keys of the questions arisen in the first volume while the second part propose a series of problems (with keys). These problems illustrate the topics presented in the first volume and deal with issues like optical properties of solids, electron bands, Peierls transition, phonons in solids, isolator-metal transition, cyclotron resonance, superconductivity of NbSe{sub 2}, electronic properties of La{sub 2}CuO{sub 4}, or the magnetism of thin films. (A.C.)
Structural Identification Problem
Suvorov Aleksei
2016-01-01
Full Text Available The identification problem of the existing structures though the Quasi-Newton and its modification, Trust region algorithms is discussed. For the structural problems, which could be represented by means of the mathematical modelling of the finite element code discussed method is extremely useful. The nonlinear minimization problem of the L2 norm for the structures with linear elastic behaviour is solved by using of the Optimization Toolbox of Matlab. The direct and inverse procedures for the composition of the desired function to minimize are illustrated for the spatial 3D truss structure as well as for the problem of plane finite elements. The truss identification problem is solved with 2 and 3 unknown parameters in order to compare the computational efforts and for the graphical purposes. The particular commands of the Matlab codes are present in this paper.
Henderson, Richard; McMullan, Greg
2013-01-01
Theoretical considerations together with simulations of single-particle electron cryomicroscopy images of biological assemblies in ice demonstrate that atomic structures should be obtainable from images of a few thousand asymmetric units, provided the molecular weight of the whole assembly being studied is greater than the minimum needed for accurate position and orientation determination. However, with present methods of specimen preparation and current microscope and detector...
Problems in structural inorganic chemistry
Li, Wai-Kee; Mak, Thomas Chung Wai; Mak, Kendrew Kin Wah
2013-01-01
This book consists of over 300 problems (and their solutions) in structural inorganic chemistry at the senior undergraduate and beginning graduate level. The topics covered comprise Atomic and Molecular Electronic States, Atomic Orbitals, Hybrid Orbitals, Molecular Symmetry, Molecular Geometry and Bonding, Crystal Field Theory, Molecular Orbital Theory, Vibrational Spectroscopy, and Crystal Structure. The central theme running through these topics is symmetry, molecular or crystalline. The problems collected in this volume originate in examination papers and take-home assignments that have been part of the teaching of the book's two senior authors' at The Chinese University of Hong Kong over the past four decades. The authors' courses include Chemical Bonding, Elementary Quantum Chemistry, Advanced Inorganic Chemistry, X-Ray Crystallography, etc. The problems have been tested by generations of students taking these courses.
Molecular electronic-structure theory
Helgaker, Trygve; Jorgensen, Poul
2013-01-01
Ab initio quantum chemistry is increasingly paired with computational methods to solve intractable problems in chemistry and molecular physics. Now in a paperback edition, this comprehensive and technical work covers all the important aspects of modern molecular electronic-structure theory, clearly explaining quantum-mechanical methods and applications to molecular equilibrium structure, atomization energies, and reaction enthalpies. Extensive numerical examples illustrate each method described. An excellent resource for researchers in quantum chemistry and anyone interested in the theory and its applications.
Problems of reliability of electronic components
Vyacheslav A. Kharchenko
2015-09-01
Full Text Available This paper describes the problem of increasing the reliability of electronic components (EC used for the fabrication of high-tech products. Two main ways of solving the problem are considered based on analysis of published data. One approach is rejection of EC at the input control using special testing methods combined with burn-in test program. This testing reveals components with “hidden defects”, counterfeit parts and components with incompatible construction materials with both internal and external service conditions. The other approach considers the feature of creating EC with nanoscale parameters. In this case the modular principle is applied for the design of devices that allows significantly reducing the loads on single elements and malfunction of a discrete module causes its disconnection from the scheme followed by reconfiguration of the EC structure. We show that in general the problem of increasing reliability is a complex task related to developing an optimum structure of IC elements, informed choice of materials, testing and optimization of circuit solutions.
Collaborative problem structuring using MARVEL
Veldhuis, G.A.; Scheepstal, P.G.M. van; Rouwette, E.; Logtens, T.W.A.
2015-01-01
When faced with wicked and messy problems, practitioners can rely on a variety of problem structuring methods (PSMs). Although previous efforts have been made to combine such methods with simulation, currently, few exist that integrate a simulation capability within problem structuring. Our
Molecular electronic-structure theory
Helgaker, Trygve; Olsen, Jeppe
2014-01-01
Ab initio quantum chemistry has emerged as an important tool in chemical research and is appliced to a wide variety of problems in chemistry and molecular physics. Recent developments of computational methods have enabled previously intractable chemical problems to be solved using rigorous quantum-mechanical methods. This is the first comprehensive, up-to-date and technical work to cover all the important aspects of modern molecular electronic-structure theory. Topics covered in the book include: * Second quantization with spin adaptation * Gaussian basis sets and molecular-integral evaluati
Gagarin, S.G.; Kovtun, A.P.; Krichko, A.A.; Sachenko, V.P.
1979-10-01
Computer calculations of the electron structure of palladium sulfide were carried out by using the diffuse electron wave self-consistent-field quantum chemical method with the X/sub ..cap alpha../ approximation of exchange interaction. The energies of valence molecular orbitals and their distributions within model clusters, PdS/sub 4/(-6) or Pd/sub 6/S/sub 8/(-4), were compared with experimental data previously obtained by X-ray photoelectron and exo-electronic emission spectral techniques. Catalyst structure representation by the minimal cluster PdS/sub 4/ was only sufficient to qualitatively describe the covalent character of the chemical bonds in the catalysts. Extension of the cluster to account for the interaction between atoms of adjacent crystalline cells yielded satisfactory predictions of the experimental spectra and structural particularities responsible for the catalytic properties of palladium sulfide in hydrogenation of unsaturated compounds.
Structural Dynamics of Electronic Systems
Suhir, E.
2013-03-01
The published work on analytical ("mathematical") and computer-aided, primarily finite-element-analysis (FEA) based, predictive modeling of the dynamic response of electronic systems to shocks and vibrations is reviewed. While understanding the physics of and the ability to predict the response of an electronic structure to dynamic loading has been always of significant importance in military, avionic, aeronautic, automotive and maritime electronics, during the last decade this problem has become especially important also in commercial, and, particularly, in portable electronics in connection with accelerated testing of various surface mount technology (SMT) systems on the board level. The emphasis of the review is on the nonlinear shock-excited vibrations of flexible printed circuit boards (PCBs) experiencing shock loading applied to their support contours during drop tests. At the end of the review we provide, as a suitable and useful illustration, the exact solution to a highly nonlinear problem of the dynamic response of a "flexible-and-heavy" PCB to an impact load applied to its support contour during drop testing.
The electronic structures of solids
Coles, B R
2013-01-01
The Electronic Structures of Solids aims to provide students of solid state physics with the essential concepts they will need in considering properties of solids that depend on their electronic structures and idea of the electronic character of particular materials and groups of materials. The book first discusses the electronic structure of atoms, including hydrogen atom and many-electron atom. The text also underscores bonding between atoms and electrons in metals. Discussions focus on bonding energies and structures in the solid elements, eigenstates of free-electron gas, and electrical co
Block Tridiagonal Matrices in Electronic Structure Calculations
Petersen, Dan Erik
This thesis focuses on some of the numerical aspects of the treatment of the electronic structure problem, in particular that of determining the ground state electronic density for the non–equilibrium Green’s function formulation of two–probe systems and the calculation of transmission in the Lan...
Electron conductance in curved quantum structures
Willatzen, Morten; Gravesen, Jens
2010-01-01
A differential-geometry analysis is employed to investigate the transmission of electrons through a curved quantum-wire structure. Although the problem is a three-dimensional spatial problem, the Schrodinger equation can be separated into three general coordinates. Hence, the proposed method...
Sheng Chun-Qi; Wang Peng; Shen Ying; Li Yan-Jun; Zhang Wen-Hua; Xu Fa-Qiang; Zhu Jun-Fa; Li Hong-Nian; Lai Guo-Qiao
2012-01-01
We have studied the electronic structure of [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) using synchrotron radiation photoelectron spectroscopy (PES) measurements and first-principles calculations.The PES spectrum of the entire occupied valence band is reported,which exhibits abundant spectral features from the Fermi level to ～ 24 eV binding energy. All the spectral features are broadened as compared with the cases of C60. The reasons for the broadening are analysed by comparing the experimental data with the calculated energy levels and density of states.Special attention is paid to the analysis of the C60 highest occupied molecular orbital (HOMO)-1 derived states,which can play a crucial role in the bonding at the interfaces of PCBM/polymer blenders or PCBM/electrodes.Besides the well-known energy level splitting of the C60 backbone caused by the lowered symmetry,C 2p states from the side chain mix or hybridize with the molecular orbitals of parent C60.The contribution of the O 2p states can substantially modify the PES spectrum.
The Electronic Structure of Calcium
Jan, J.-P.; Skriver, Hans Lomholt
1981-01-01
The electronic structure of calcium under pressure is re-examined by means of self-consistent energy band calculations based on the local density approximation and using the linear muffin-tin orbitals (LMTO) method with corrections to the atomic sphere approximation included. At zero pressure.......149 Ryd, respectively, relative to the s band, give the best possible agreement. Under increasing pressure the s and p electrons are found to transfer into the d band, and Ca undergoes metal-semimetal-metal electronic transitions. Calculations of the bandstructure and the electronic pressure, including...
Ballistic transport and electronic structure
Schep, Kees M.; Kelly, Paul J.; Bauer, Gerrit E.W.
1998-01-01
The role of the electronic structure in determining the transport properties of ballistic point contacts is studied. The conductance in the ballistic regime is related to simple geometrical projections of the Fermi surface. The essential physics is first clarified for simple models. For real
Montero, E.; Gonzalez, M. J.
2009-01-01
Problem-based learning has been at the core of significant developments in engineering education in recent years. This term refers to any learning environment in which the problem drives the learning, because it is posed in such a way that students realize they need to acquire new knowledge before the problem can be solved. This paper presents the…
Montero, E.; Gonzalez, M. J.
2009-01-01
Problem-based learning has been at the core of significant developments in engineering education in recent years. This term refers to any learning environment in which the problem drives the learning, because it is posed in such a way that students realize they need to acquire new knowledge before the problem can be solved. This paper presents the…
Electronic structure of tin monosulfide
Bletskan, D. I.; Bletskan, M. M.; Glukhov, K. E.
2017-01-01
The band structure of three-dimensional and two-dimensional tin monosulfide was calculated by the density functional method in LDA and LDA+U approximations. Group-theoretical analysis of the electronic band structure of SnS crystallized in the orthorhombic structure with space group D2h16- Pcmn is carried out, the symmetry of wave functions of the valence band and the bottom of the conduction band is found. The selection rules for direct and indirect optical transitions at different incident light polarization are determined. The group-theoretical analysis of energy states of the three-dimensional and two-dimensional SnS structures explains the formation of the band structure including the Davydov splitting. The calculated total density of states is compared with the known experimental XPS and UPS spectra, providing the assignment of their main features.
Electronic Structure of Lithium Tetraborate
2010-06-01
Czochralski crystal growth method [1, 2] were the samples used for this research. Li2B4O7 To ensure results repeatability, two different samples for both...tetraborate is a strongly correlated electron semiconductor, the methods for accurately calculating the detailed band structure, to include the band...Instrum. Methods Phys. Res. A 591, 530 (2008). 11. J. Uher, S. Pospisil, V. Linhart, and M. Schieber, "Efficiency of composite boron nitride
NOT REAL PROBLEMS, BUT UNKNOWN ELECTRONIC DEVICES
Julio Carabaña Morales
2014-05-01
Full Text Available According to PISA 2012, Spanish students did score still worse in Problem Solving than in Reading, Mathematics and Science, a result that has produced a certain alarm and a lot of diagnoses and remedies. In this paper, I first use OCDE’s data and analyses to show that the main cause of this difference among Problem Solving and Reading, Mathematics and Science has been the Computer Based Administration of the Problem Solving test. Second, I suggest some hypotheses about why the OCDE ignores its own finding about the lack of validity of this test.
Problem Resolution through Electronic Mail: A Five-Step Model.
Grandgenett, Neal; Grandgenett, Don
2001-01-01
Discusses the use of electronic mail within the general resolution and management of administrative problems and emphasizes the need for careful attention to problem definition and clarity of language. Presents a research-based five-step model for the effective use of electronic mail based on experiences at the University of Nebraska at Omaha.…
RESEARCH ON NONLINEAR PROBLEMS IN STRUCTURAL DYNAMICS.
Research on nonlinear problems structural dynamics is briefly summarized. Panel flutter was investigated to make a critical comparison between theory...panel flutter in aerospace vehicles, plausible simplifying assumptions are examined in the light of experimental results. Structural dynamics research
Inference problems in structural biology
Olsson, Simon
The structure and dynamics of biological molecules are essential for their function. Consequently, a wealth of experimental techniques have been developed to study these features. However, while experiments yield detailed information about geometrical features of molecules, this information is of...
Inference problems in structural biology
Olsson, Simon
The structure and dynamics of biological molecules are essential for their function. Consequently, a wealth of experimental techniques have been developed to study these features. However, while experiments yield detailed information about geometrical features of molecules, this information is of...
Problems in single-particle dynamics specific to electrons
Renieri, A
1977-01-01
The author investigates the specific problems related to the electron motion in a circular high-energy accelerator. The main difference between electrons and protons (or other heavy particles) is the synchrotron radiation energy loss. This phenomenon is negligible for heavy particles, but not for electrons. (5 refs).
Inverse Eigenvalue Problem in Structural Dynamics Design
Huiqing Xie; Hua Dai
2006-01-01
A kind of inverse eigenvalue problem in structural dynamics design is considered. The problem is formulated as an optimization problem. The properties of this problem are analyzed, and the existence of the optimum solution is proved. The directional derivative of the objective function is obtained and a necessary condition for a point to be a local minimum point is given. Then a numerical algorithm for solving the problem is presented and a plane-truss problem is discussed to show the applications of the theories and the algorithm.
Electronic structure of spin systems
Saha-Dasgupta, Tanusri
2016-04-15
Highlights: • We review the theoretical modeling of quantum spin systems. • We apply the Nth order muffin-tin orbital electronic structure method. • The method shows the importance of chemistry in the modeling. • CuTe{sub 2}O{sub 5} showed a 2-dimensional coupled spin dimer behavior. • Ti substituted Zn{sub 2}VO(PO{sub 4}){sub 2} showed spin gap behavior. - Abstract: Low-dimensional quantum spin systems, characterized by their unconventional magnetic properties, have attracted much attention. Synthesis of materials appropriate to various classes within these systems has made this field very attractive and a site of many activities. The experimental results like susceptibility data are fitted with the theoretical model to derive the underlying spin Hamiltonian. However, often such a fitting procedure which requires correct guess of the assumed spin Hamiltonian leads to ambiguity in deciding the representative model. In this review article, we will describe how electronic structure calculation within the framework of Nth order muffin-tin orbital (NMTO) based Wannier function technique can be utilized to identify the underlying spin model for a large number of such compounds. We will show examples from compounds belonging to vanadates and cuprates.
Some Modern Problems in Structural Engineering Dynamics
I. Elishakoff
2010-01-01
Full Text Available This review paper deals with two problems in structural engineering dynamics; one is deterministic, the other is of stochastic nature. One problem is linear, the other is nonlinear. Authors have a biased preferential view on these problems because of their active involvement in the discussed research topics. Still, these two problems reflect, at least in a small manner, some developments in this vast and fascinating field. The first part deals with deterministic linear vibrations of double-walled carbon nanotubes either in classical or refined setting; the second part is devoted to the nonlinear random vibrations of structures.
Isogeometric analysis in electronic structure calculations
Cimrman, Robert; Kolman, Radek; Tůma, Miroslav; Vackář, Jiří
2016-01-01
In electronic structure calculations, various material properties can be obtained by means of computing the total energy of a system as well as derivatives of the total energy w.r.t. atomic positions. The derivatives, also known as Hellman-Feynman forces, require, because of practical computational reasons, the discretized charge density and wave functions having continuous second derivatives in the whole solution domain. We describe an application of isogeometric analysis (IGA), a spline modification of finite element method (FEM), to achieve the required continuity. The novelty of our approach is in employing the technique of B\\'ezier extraction to add the IGA capabilities to our FEM based code for ab-initio calculations of electronic states of non-periodic systems within the density-functional framework, built upon the open source finite element package SfePy. We compare FEM and IGA in benchmark problems and several numerical results are presented.
Halogen versus halide electronic structure
Willem-Jan; van; Zeist; F.Matthias; Bickelhaupt
2010-01-01
Halide anions X-are known to show a decreasing proton affinity(PA),as X descends in the periodic table along series F,Cl,Br and I.But it is also well-known that,along this series,the halogen atom X becomes less electronegative(or more electropositive).This corresponds to an increasing energy of the valence np atomic orbital(AO) which,somewhat contradictorily,suggests that the electron donor capability and thus the PA of the halides should increase along the series F,Cl,Br,I.To reconcile these contradictory observations,we have carried out a detailed theoretical analysis of the electronic structure and bonding capability of the halide anions X-as well as the halogen radicals X-,using the molecular orbital(MO) models contained in Kohn-Sham density functional theory(DFT,at SAOP/TZ2P as well as OLYP/TZ2P levels) and ab initio theory(at the HF/TZ2P level).We also resolve an apparent intrinsic contradiction in Hartree-Fock theory between orbital-energy and PA trends.The results of our analyses are of direct relevance for understanding elementary organic reactions such as nucleophilic substitution(SN2) and base-induced elimination(E2) reactions.
Hilbert space renormalization for the many-electron problem
Li, Zhendong
2015-01-01
Renormalization is a powerful concept in the many-body problem. Inspired by the highly successful density matrix renormalization group (DMRG) algorithm, and the quantum chemical graphical representation of configuration space, we introduce a new theoretical tool: Hilbert space renormalization, to describe many-electron correlations. While in DMRG, the many-body states in nested Fock subspaces are successively renormalized, in Hilbert space renormalization, many-body states in nested Hilbert subspaces undergo renormalization. This provides a new way to classify and combine configurations. The underlying wavefunction ansatz, namely the Hilbert space matrix product state (HS-MPS), has a very rich and flexible mathematical structure. It provides low-rank tensor approximations to any configuration interaction (CI) space through restricting either the 'physical indices' or the coupling rules in the HS-MPS. Alternatively, simply truncating the 'virtual dimension' of the HS-MPS leads to a family of size-extensive wav...
On the Cauchy Problem Describing an Electron-Phonon Interaction
Jo(a)o-Paulo DIAS; Mário FIGUEIRA; Filipe OLIVEIRA
2011-01-01
In this paper, a model is derived to describe a quartic anharmonic interatomic interaction with an external potential involving a pair electron-phonon. The authors study the corresponding Cauchy Problem in the semilinear and quasilinear cases.
Denlinger, J. D.; Rossnagel, Kai; Allen, J. W.; Huxley, A. D.; Flouquet, J.
2003-03-01
UGe2 is of high current interest in connection with the possible role of ferromagnetic fluctuations in its pressure induced superconductivity, for which the Fermi surface (FS) is thought to be important. The band structure and FS contours of a single crystal have been measured using resonant angle-resolved photoemission near the U 5d to 5f edge. Quantitative comparisons to available band structure calculations and to magneto-oscillaory measurements will be presented. Discrepancies with theory are generically similar to those(J.D. Denlinger et al.), J. Electron Spectrosc. Relat. Phenom. 117-118, 347 (2001). found for heavy Fermion URu_2Si2 in that the underlying non-f bands appear to play the major role in defining the FS and in determining the k-space location of 5f spectral weight, in contrast to the important role of actual f-bands in the theory. Supported by the U.S. NSF at U. Mich. (DMR-9971611) and by the U.S. DOE at U. Mich. (DE-FG02-90ER45416) and at the Advanced Light Source (DE-AC03-76SF00098).
Correlated electronic structure of CeN
Panda, S.K., E-mail: swarup.panda@physics.uu.se [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); Di Marco, I. [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); Delin, A. [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); KTH Royal Institute of Technology, School of Information and Communication Technology, Department of Materials and Nano Physics, Electrum 229, SE-164 40 Kista (Sweden); KTH Royal Institute of Technology, Swedish e-Science Research Center (SeRC), SE-100 44 Stockholm (Sweden); Eriksson, O., E-mail: olle.eriksson@physics.uu.se [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden)
2016-04-15
Highlights: • The electronic structure of CeN is studied within the GGA+DMFT approach using SPTF and Hubbard I approximation. • 4f spectral functions from SPTF and Hubbard I are coupled to explain the various spectroscopic manifestations of CeN. • The calculated XPS and BIS spectra show good agreement with the corresponding experimental spectra. • The contribution of the various l-states and the importance of cross-sections for the photoemission process are analyzed. - Abstract: We have studied in detail the electronic structure of CeN including spin orbit coupling (SOC) and electron–electron interaction, within the dynamical mean-field theory combined with density-functional theory in generalized gradient approximation (GGA+DMFT). The effective impurity problem has been solved through the spin-polarized T-matrix fluctuation-exchange (SPTF) solver and the Hubbard I approximation (HIA). The calculated l-projected atomic partial densities of states and the converged potential were used to obtain the X-ray-photoemission-spectra (XPS) and Bremstrahlung Isochromat spectra (BIS). Following the spirit of Gunnarsson–Schonhammer model, we have coupled the SPTF and HIA 4f spectral functions to explain the various spectroscopic manifestations of CeN. Our computed spectra in such a coupled scheme explain the experimental data remarkably well, establishing the validity of our theoretical model in analyzing the electronic structure of CeN. The contribution of the various l-states in the total spectra and the importance of cross sections are also analyzed in detail.
Hilbert space renormalization for the many-electron problem.
Li, Zhendong; Chan, Garnet Kin-Lic
2016-02-28
Renormalization is a powerful concept in the many-body problem. Inspired by the highly successful density matrix renormalization group (DMRG) algorithm, and the quantum chemical graphical representation of configuration space, we introduce a new theoretical tool: Hilbert space renormalization, to describe many-electron correlations. While in DMRG, the many-body states in nested Fock subspaces are successively renormalized, in Hilbert space renormalization, many-body states in nested Hilbert subspaces undergo renormalization. This provides a new way to classify and combine configurations. The underlying wavefunction Ansatz, namely, the Hilbert space matrix product state (HS-MPS), has a very rich and flexible mathematical structure. It provides low-rank tensor approximations to any configuration interaction (CI) space through restricting either the "physical indices" or the coupling rules in the HS-MPS. Alternatively, simply truncating the "virtual dimension" of the HS-MPS leads to a family of size-extensive wave function Ansätze that can be used efficiently in variational calculations. We make formal and numerical comparisons between the HS-MPS, the traditional Fock-space MPS used in DMRG, and traditional CI approximations. The analysis and results shed light on fundamental aspects of the efficient representation of many-electron wavefunctions through the renormalization of many-body states.
Electronic structure and magnetic anisotropy of CrO_2
Toropova, A.; Kotliar, G.; Savrasov, S. Y.; Oudovenko, V. S.
2004-01-01
The problem of importance of strong correlations for the electronic structure, transport and magnetic properties of half--metallic ferromagnetic CrO_2 is addressed by performing density functional electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. It is shown that the corresponding low--temperature experimental data are best fitted without accounting for the Hubbard U corrections. We conclude that the ordered phase of CrO$_2 is...
Electronic structure of pesticides: 1. Organochlorine insecticides
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Kovac, Branka [Physical Chemistry Division, ' R. Boskovic' Institute, HR-10000 Zagreb (Croatia)
2011-11-15
Highlights: {yields} Electronic structure of several organochlorine insecticides has been determined by UV photoelectron spectroscopy and high-level ab initio calculations. {yields} The electronic structure obtained from spectra has been related to their biological activity. {yields} The molecular modes of binding to appropriate receptors are rationalized in view of the molecule's electronic structure and conformational flexibility. - Abstract: The electronic structures of six organochlorine insecticides: {gamma}-lindane (I), aldrin (II), dieldrin (III), DDD (IV), DDE (V) and DDT (VI) have been investigated by UV photoelectron spectroscopy (UPS), quantum chemical calculations and comparison with molecular modelling studies. Their electronic and molecular structures are discussed in order to rationalize their biological activity. In this work we relate the biological activity of these insecticides to their experimentally observed electronic and molecular structures.
Electronic and chemical properties of graphene-based structures:
Vanin, Marco
In the present thesis several aspects of graphene-based structures have been investigated using density functional theory calculations to solve the electronic structure problem. A review of the implementation of a localized basis-set within the projector augmented wave method - the way of describ...... are attractive candidates although issues regarding the poisoning of the active site remain to be addressed....
Electronic structure of herbicides: Atrazine and bromoxynil
Novak, Igor; Kovač, Branka
2011-06-01
The electronic structures of herbicides atrazine and bromoxynil have been investigated by UV photoelectron spectroscopy (UPS), quantum chemical calculations and comparison with X-ray diffraction, molecular docking and molecular dynamics studies. Their electronic and molecular structures are discussed in the context of their biological activity. This is the first report which correlates the molecular mechanism of biological activity of these herbicides with their experimentally determined electronic and molecular structures.
An electronic study guide for problem-based learning.
Mooney, G A; Bligh, J G; Leinster, S F; Warenius, H M
1995-11-01
This paper describes the development and structure of an Electronic Study Guide for Oncology (LETSGO) for undergraduate medical students. LETSGO is aimed at clinical students learning about cancer. The subject of the guide is breast cancer and learning objectives cover structure and function, behavioural science, public health and epidemiology and professional and personal values. LETSGO is designed to follow the steps used in problem-based learning. The student is encouraged to carry out individual brainstorming around cases with the issues identified acting as the first step in an educational audit loop. Clear definition of prior knowledge is available by way of interactive features, and hyper-text links to core text and diagrams (including microscopic sections) precede definition of both broad aims and objectives for the module and specific objectives for assessment purposes. Core knowledge is available via hyper-text links. Assessment has three components: open ended questions asking for free text responses linking to 'model' answers; extended matching items linking to 'model' answers and providing peer-referenced feedback as a bar-chart distribution, and an educational audit loop referring back to the original issues identified at the beginning of the package in brainstorming. Clear mapping throughout the guide is a major feature and the student's progress is clearly displayed at each stage of the guide. The program provides dynamic access to the student's existing knowledge base and stimulates new learning based on the student's own learning needs.
Solution of a multiple-scattering inverse problem: electron diffraction from surfaces.
Saldin, D K; Seubert, A; Heinz, K
2002-03-18
We present a solution to the multiple-scattering inverse problem for low-energy electron diffraction that enables the determination of the three-dimensional atomic structure of an entire surface unit cell directly from measured data. The solution requires a knowledge of the structure of the underlying bulk crystal and is implemented by a maximum entropy algorithm.
Pattern matching approach to pseudosymmetry problems in electron backscatter diffraction.
Nolze, Gert; Winkelmann, Aimo; Boyle, Alan P
2016-01-01
We demonstrate an approach to overcome Kikuchi pattern misindexing problems caused by crystallographic pseudosymmetry in electron backscatter diffraction (EBSD) measurements. Based on the quantitative comparison of experimentally measured Kikuchi patterns with dynamical electron diffraction simulations, the algorithm identifies the best-fit orientation from a set of pseudosymmetric candidates. Using measurements on framboidal pyrite (FeS2) as an example, we also show the improvement of the orientation precision using this approach.
Electronic structure and tautomerism of thioamides
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); McGlynn, Sean P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2016-05-15
Highlights: • Electronic structure of thioamide group and its relation to Lewis basicity. • Tautomerism of the (thio)amide groups. • Substituent effects on the electronic structure of (thio)amide group. - Abstract: The electronic structures of several thioamides have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of thioamide derivatives are discussed. The predominant tautomers in the gas phase are of keto–(thio)keto form. The addition of cyclohexanone moiety to the thioamide group enhances the Lewis base character of the sulfur atom. The addition of phenyl group to the (thio)amide group significantly affects its electronic structure.
Electron tomography of dislocation structures
Liu, G.S.; House, S.D.; Kacher, J. [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St., Urbana, IL 61801 (United States); Tanaka, M.; Higashida, K. [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Robertson, I.M., E-mail: irobertson@wisc.edu [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St., Urbana, IL 61801 (United States); Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706 (United States)
2014-01-15
Recent developments in the application of electron tomography for characterizing microstructures in crystalline solids are described. The underlying principles for electron tomography are presented in the context of typical challenges in adapting the technique to crystalline systems and in using diffraction contrast imaging conditions. Methods for overcoming the limitations associated with the angular range, the number of acquired images, and uniformity of image contrast are introduced. In addition, a method for incorporating the real space coordinate system into the tomogram is presented. As the approach emphasizes development of experimental solutions to the challenges, the solutions developed and implemented are presented in the form of examples.
Scattering problems involving electrons, photons, and Dirac fermions
Snyman, Izak
2008-01-01
The theoretical foundation for the work reported here is provided by Landauer's scattering theory of electron transport. The three main ingredients of a scattering problem are (1) a set of reservoirs that emit and absorb particles, (2) the particles themselves, that propagate as waves between the re
Majorana solutions to the two-electron problem
Esposito, S
2012-01-01
A review of the known different methods and results devised to study the two-electron atom problem, appeared in the early years of quantum mechanics, is given, with particular reference to the calculations of the ground state energy of helium. This is supplemented by several, unpublished results obtained around the same years by Ettore Majorana, which results did not convey in his published papers on the argument, and thus remained unknown until now. Particularly interesting, even for current research in atomic and nuclear physics, is a general variant of the variational method, developed by Majorana in order to take directly into account, already in the trial wavefunction, the action of the full Hamiltonian operator of a given quantum system. Moreover, notable calculations specialized to the study of the two-electron problem show the introduction of the remarkable concept of an effective nuclear charge different for the two electrons (thus generalizing previous known results), and an application of the pertu...
An electronic structure perspective of graphene interfaces
Schultz, Brian J.; Dennis, Robert V.; Lee, Vincent; Banerjee, Sarbajit
2014-03-01
The unusual electronic structure of graphene characterized by linear energy dispersion of bands adjacent to the Fermi level underpins its remarkable transport properties. However, for practical device integration, graphene will need to be interfaced with other materials: 2D layered structures, metals (as ad-atoms, nanoparticles, extended surfaces, and patterned metamaterial geometries), dielectrics, organics, or hybrid structures that in turn are constituted from various inorganic or organic components. The structural complexity at these nanoscale interfaces holds much promise for manifestation of novel emergent phenomena and provides a means to modulate the electronic structure of graphene. In this feature article, we review the modifications to the electronic structure of graphene induced upon interfacing with disparate types of materials with an emphasis on iterative learnings from theoretical calculations and electronic spectroscopy (X-ray absorption fine structure (XAFS) spectroscopy, scanning transmission X-ray microscopy (STXM), angle-resolved photoemission spectroscopy (ARPES), and X-ray magnetic circular dichroism (XMCD)). We discuss approaches for engineering and modulating a bandgap in graphene through interfacial hybridization, outline experimental methods for examining electronic structure at interfaces, and overview device implications of engineered interfaces. A unified view of how geometric and electronic structure are correlated at interfaces will provide a rational means for designing heterostructures exhibiting emergent physical phenomena with implications for plasmonics, photonics, spintronics, and engineered polymer and metal matrix composites.
Electronic Structure of Doped Trans-Polyacetylene
无
2002-01-01
The behavior of electronic structures of doped trans-polyacetylene is revealed by a simplemethod. (C24H26)+n is used to simulate p-type doped trans-polyacetylene at various doping concentrations.The electronic structure is calculated by CNDO/2 method. These calculations show that at low doping lev-el, the decrease of electronic energy compensates the increase of elastic energy, thus the bond alternationexists, and the charge carriers are solitons. When doping level is high, the increase of elastic energy islarger than the decrease of electronic energy, the bond alternation disappears, solitons no longer exist,and polyacetylene is in a metalic state.
Electron-Hole Counting Approach to Surface Atomic Structure
Chadi, D. J.
The observed reconstructions of III-V semiconductor surfaces are shown to be consistent with constraints imposed by a simple "electron-hole" counting rule proposed by Pashley. The rule ensures that the predicted surfaces are nonmetallic, nonpolar, and at least, metastable since the compensation of the "donor" electrons leaves no occupied states in the upper part of the band gap which can easily induce other reconstructions. Applications of the method to the problem of surface structure and passivation are examined.
Application and electronic structure of high-permittivity dielectrics
Perevalov, Timofei V; Gritsenko, Vladimir A [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)
2010-09-07
Major applications of high-permittivity dielectric materials in silicon devices are reviewed. The basics and software implementations of the electron density functional method are considered. Results of first-principle calculations of the electronic structure are analyzed for the three most important and promising high-permittivity dielectrics, Al{sub 2}O{sub 3}, HfO{sub 2}, and TiO{sub 2}. (reviews of topical problems)
Complex structures of dense lithium: Electronic origin
Degtyareva, V. F.
2016-11-01
Lithium—the lightest alkali metal exhibits unexpected structures and electronic behavior at high pressures. Like the heavier alkali metals, Li is bcc at ambient pressure and transforms first to fcc (at 7.5 GPa). The post-fcc high-pressure form Li-cI 16 (at 40-60 GPa) is similar to Na-cI 16 and related to more complex structures of heavy alkalis Rb-oC52 and Cs- oC84. The other high pressure phases for Li (oC88, oC40, oC24) observed at pressures up to 130 GPa are found only in Li. The different route of Li high-pressure structures correlates with its special electronic configuration containing the only 3 electrons (at 1s and 2s levels). Crystal structures for Li are analyzed within the model of Fermi sphere-Brillouin zone interactions. Stability of post-fcc structures for Li are supported by the Hume-Rothery arguments when new diffraction plains appear close to the Fermi level producing pseudogaps near the Fermi level and decreasing the crystal energy. The filling of Brillouin-Jones zones by electron states for a given structure defines the physical properties as optical reflectivity, electrical resistivity and superconductivity. To understand the complexity of structural and physical properties of Li above 60 GPa it is necessary to assume the valence electron band overlap with the core electrons and increase the valence electron count under compression.
Banded electron structures in the plasmasphere
Burke, W.J.; Rubin, A.G.; Hardy, D.A.; Holeman, E.G.
1995-05-01
The low-energy plasma analyzer on CRRES has detected significant fluxes of 10-eV to 30-keV electrons trapped on plasmaspheric field lines. On energy versus time spectrograms these electrons appear as banded structures that can span the 2 < L < 6 range of magnetic shells. The authors present an example of banded electron structures, encountered in the nightside plasmasphere during the magnetically quiet January 30, 1991. Empirical analysis suggests that two clouds of low energy electrons were injected from the plasma sheet to L < 4 on January 26 and 27 while the convective electric field was elevated. The energies of electrons in the first cloud were greater than those in the second. DMSP F8 measurements show that after the second injection, the polar cap potential rapidly decreased from >50 to <20 kY. Subsequent encounters with the lower energy cloud on alternating CRRES orbits over the next 2 days showed a progressive, earthward movement of the electrons, inner boundary. Whistler and electron cyclotron harmonic emissions accompanied the most intense manifestations of cloud electrons. The simplest explanation of these measurements is that after initial injection, the AIfven boundary moved Outward, leaving the cloud electrons on closed drift paths. Subsequent fluctuations of the convective electric field penetrated the plasmasphere, transporting cloud elements inward. The magnetic shell distribution of electron temperatures in one of the banded structures suggests that radiative energy losses may be comparable in magnitude to gains due to adiabatic compression.
Electronic structure and tautomerism of aryl ketones
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); Šket, Boris, E-mail: Boris.Sket@fkkt.uni-lj.si [Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 (Slovenia); McGlynn, S.P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2015-07-15
Graphical abstract: Photoelectron spectroscopy, tautomerism. - Highlights: • UV photoelectron spectroscopy of aryl ketones. • The relative stability of tautomers and their electronic structures. • The factors influencing tautomerism. - Abstract: The electronic structures of several aryl ketones (AK) and their α-halo derivatives have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of the AK derivatives are discussed.
Removal of Vesicle Structures from Transmission Electron Microscope Images
Jensen, Katrine Hommelhoff; Sigworth, Fred; Brandt, Sami Sebastian
2015-01-01
In this paper, we address the problem of imaging membrane proteins for single-particle cryo-electron microscopy reconstruction of the isolated protein structure. More precisely, we propose a method for learning and removing the interfering vesicle signals from the micrograph, prior to reconstruct...
Electronic Structure of the Actinide Metals
Johansson, B.; Skriver, Hans Lomholt
1982-01-01
Some recent experimental photoelectron spectroscopic results for the actinide metals are reviewed and compared with the theoretical picture of the basic electronic structure that has been developed for the actinides during the last decade. In particular the experimental data confirm the change from...... itinerant to localized 5f electron behaviour calculated to take place between plutonium and americium. From experimental data it is shown that the screening of deep core-holes is due to 5f electrons for the lighter actinide elements and 6d electrons for the heavier elements. A simplified model for the full...... LMTO electronic structure calculations is introduced. In this model the spd and 5f electronic contributions are treated as separable entities. It is shown that the model reproduces quite well the results from the full treatment. The equilibrium volume, cohesive energy and bulk modulus are calculated...
Epitaxial graphene electronic structure and transport
De Heer, Walt A; Berger, Claire; Wu Xiaosong; Sprinkle, Mike; Hu Yike; Ruan Ming; First, Phillip N [School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Stroscio, Joseph A [Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD 20899 (United States); Haddon, Robert [Center for Nanoscale Science and Engineering, Departments of Chemistry and Chemical and Environmental Engineering, University of California, Riverside, CA 92521 (United States); Piot, Benjamin; Faugeras, Clement; Potemski, Marek [LNCMI -CNRS, Grenoble, 38042 Cedex 9 (France); Moon, Jeong-Sun, E-mail: walt.deheer@physics.gateh.ed [HRL Laboratories LLC, Malibu, CA 90265 (United States)
2010-09-22
Since its inception in 2001, the science and technology of epitaxial graphene on hexagonal silicon carbide has matured into a major international effort and is poised to become the first carbon electronics platform. A historical perspective is presented and the unique electronic properties of single and multilayered epitaxial graphenes on electronics grade silicon carbide are reviewed. Early results on transport and the field effect in Si-face grown graphene monolayers provided proof-of-principle demonstrations. Besides monolayer epitaxial graphene, attention is given to C-face grown multilayer graphene, which consists of electronically decoupled graphene sheets. Production, structure and electronic structure are reviewed. The electronic properties, interrogated using a wide variety of surface, electrical and optical probes, are discussed. An overview is given of recent developments of several device prototypes including resistance standards based on epitaxial graphene quantum Hall devices and new ultrahigh frequency analogue epitaxial graphene amplifiers.
Electronic structure of Fe-based superconductors
Kalobaran Maiti
2015-06-01
Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the dominant role of states in their electronic properties, which is significantly different from the cuprate superconductors. In this article, some of our studies of the electronic structure of these fascinating systems employing high-resolution photoemission spectroscopy is reviewed. The combined effect of electron correlation and covalency reveals an interesting scenario in their electronic structure. The contribution of ligand states at the Fermi level is found to be much more significant than indicated in earlier studies. Temperature evolution of the energy bands reveals the signature of transition akin to Lifshitz transition in these systems.
Problems of linear electron (polaron) transport theory in semiconductors
Klinger, M I
1979-01-01
Problems of Linear Electron (Polaron) Transport Theory in Semiconductors summarizes and discusses the development of areas in electron transport theory in semiconductors, with emphasis on the fundamental aspects of the theory and the essential physical nature of the transport processes. The book is organized into three parts. Part I focuses on some general topics in the theory of transport phenomena: the general dynamical theory of linear transport in dissipative systems (Kubo formulae) and the phenomenological theory. Part II deals with the theory of polaron transport in a crystalline semicon
Structure of Wet Specimens in Electron Microscopy
Parsons, D. F.
1974-01-01
Discussed are past work and recent advances in the use of electron microscopes for viewing structures immersed in gas and liquid. Improved environmental chambers make it possible to examine wet specimens easily. (Author/RH)
Structure of Wet Specimens in Electron Microscopy
Parsons, D. F.
1974-01-01
Discussed are past work and recent advances in the use of electron microscopes for viewing structures immersed in gas and liquid. Improved environmental chambers make it possible to examine wet specimens easily. (Author/RH)
Computational Chemistry Using Modern Electronic Structure Methods
Bell, Stephen; Dines, Trevor J.; Chowdhry, Babur Z.; Withnall, Robert
2007-01-01
Various modern electronic structure methods are now days used to teach computational chemistry to undergraduate students. Such quantum calculations can now be easily used even for large size molecules.
Slebarski, A.; Orzechowska, M.; Wrona, A.; Szade, J.; Jezierski, A.
2000-02-01
We report on structural measurements on and electronic structure investigations of the alloyed compounds ZrNiSn, TiNiSn, CeNiSn and CeRhSb. We present measurements of lattice parameters as a function of temperature and analysis of a (T ) and its relation to icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> T , icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> being the magnetic susceptibility. We observed a linear dependence of a (T ) versus icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> T for Zr, Ti and Ce alloys (for orthorhombic Ce alloys, the lattice parameters a , b and c scale linearly with icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> T ). The x-ray photoelectron and ultraviolet photoemission spectra are further compared to the density of states, obtained from band-structure calculations.
Electronic money in russia: current state and problems of development
T. G. Bondarenko
2016-01-01
Full Text Available Article is devoted to urgent problems of non-cash methods of calculation development by using electronic money – as one of the modern economically developed state strategic tasks. On modern economic science strong influence appears informatization process. The control expansion tendency, influence and distribution of commerce due to informatization of society led to emergence of the new phenomenon – information economy. Information economy brought new economic events which owing to their novelty are insufficiently studied to life. It is possible to carry electronic money to such phenomena of modern network economy Relevance and, in our opinion, timeliness of this scientific work, consisting in novelty of this non-cash payment method, its prospects and innovation within non-cash methods of calculations. Authors set as the purpose – studying of problems and the prospects of development of electronic money in the Russian Federation. In article theoretical bases of electronic money functioning are described. Determinations and classifications dismissed non-cash a method, and also the principles of electronic money functioning are considered, the questions of their historical development are raised.Authors analyzed statistical data on development of electronic services and channels of their using. Features, benefits and shortcomings of the current state of the market of electronic money are studied. The emphasis on that fact that in modern conditions considerable number of economic actors perform the activities, both in the real environment of economy, and within the virtual environment that promotes expansion of methods of their customer interaction by means of technical devices of personal computers, mobile phones is placed. In article common problems and tendencies of payments with using an electronic money are designated, the research on assessment of the current state and the prospects of electronic money
Visual problems among electronic and jewelry workers in Thailand.
Untimanon, Orrapan; Pacharatrakul, Wanpen; Boonmeepong, Kowit; Thammagarun, Ladda; Laemun, Nuttapong; Taptagaporn, Sasitorn; Chongsuvivatwong, Virasakdi
2006-09-01
In the processes of electronic and jewelry manufacturing, workers are employed to use their skill in tiny visual tasks (1-3 mm) and near visual distances (development and implementation of guidelines in the selected factories; and 3) a resurvey to document the change. The baseline survey was conducted in Samutprakan Province during October to December, 2003. Ninety-five percent of the sampled workers were female with an average age of 26.2 yr. Fifty-two percent of the workers had at least one kind of vision problem that might have affected their work performance, and 48.3% of the work sites had substandard illumination levels. The intervention included improvement of lighting conditions, the introduction of short breaks, and correction of visual performance problems. After the intervention, the inadequate lighting problem went down to 24.5%. All factories took a rest break and 20.5% of the workers with inadequate visual performance had corrected their vision in the intervention period. Comparing pre-intervention status with the end of the program, the Critical Fusion Frequency (CFF) at one hour and two hours of work were improved with statistical significance among the electronic but not the jewelry workers. In conclusion, visual problems among vision intensive industrial workers are common. Intervention programs partially but significantly improved the situation.
Menstrual problems in university students: an electronic mail survey.
Anastasakis, E; Kingman, C E; Lee, C A; Economides, D L; Kadir, R A
2008-01-01
To establish the prevalence of menstrual-related problems among university students. A questionnaire regarding gynecological, bleeding and family history was sent by electronic mail (e-mail) to all female students attending University College London (UCL). A total of 767 students aged 18-39 years replied; 71% had a regular menstrual cycle. One in three (n = 264) had received some treatment for their menstrual periods (such as the combined oral contraceptive pill or simple analgesia). Those with heavy or painful periods were more likely to feel that their menstrual problems had a substantial impact on their academic and social life; however, even among those with light periods, one in every four females felt that their life was considerably affected. A considerable prevalence of menstrual-related problems was demonstrated among this young healthy population. Additionally, the use of e-mail could present potential benefits as a research medium for this kind of study.
The relativistic inverse stellar structure problem
Lindblom, Lee [Theoretical Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
2014-01-14
The observable macroscopic properties of relativistic stars (whose equations of state are known) can be predicted by solving the stellar structure equations that follow from Einstein’s equation. For neutron stars, however, our knowledge of the equation of state is poor, so the direct stellar structure problem can not be solved without modeling the highest density part of the equation of state in some way. This talk will describe recent work on developing a model independent approach to determining the high-density neutron-star equation of state by solving an inverse stellar structure problem. This method uses the fact that Einstein’s equation provides a deterministic relationship between the equation of state and the macroscopic observables of the stars which are composed of that material. This talk illustrates how this method will be able to determine the high-density part of the neutron-star equation of state with few percent accuracy when high quality measurements of the masses and radii of just two or three neutron stars become available. This talk will also show that this method can be used with measurements of other macroscopic observables, like the masses and tidal deformabilities, which can (in principle) be measured by gravitational wave observations of binary neutron-star mergers.
The Relativistic Inverse Stellar Structure Problem
Lindblom, Lee
2014-01-01
The observable macroscopic properties of relativistic stars (whose equations of state are known) can be predicted by solving the stellar structure equations that follow from Einstein's equation. For neutron stars, however, our knowledge of the equation of state is poor, so the direct stellar structure problem can not be solved without modeling the highest density part of the equation of state in some way. This talk will describe recent work on developing a model independent approach to determining the high-density neutron-star equation of state by solving an inverse stellar structure problem. This method uses the fact that Einstein's equation provides a deterministic relationship between the equation of state and the macroscopic observables of the stars which are composed of that material. This talk illustrates how this method will be able to determine the high-density part of the neutron-star equation of state with few percent accuracy when high quality measurements of the masses and radii of just two or thr...
Frameworks in Problems of Structural Identification Systems
Nikolay Karabutov
2017-01-01
Full Text Available The new approach to structural identification of nonlinear dynamic systems under uncertainty is proposed. It is based on the analysis of virtual frameworks (VF, reflecting a state of a nonlinear part system. Construction VF is based on obtaining special an informational set describing a steady state of a nonlinear dynamic system. Introduction VF demands an estimation of structural identifiability of a system. This concept is associated with nonlinearity of system and properties VF. The method of an estimation of structural identifiability is proposed. The appearance of the insignificant virtual frameworks, not satisfying to the condition of structural identifiability, is considered. Algorithms for an estimation of a nonlinearity class on the basis of the analysis of sector sets are proposed. Methods and procedures of the estimation of framework single-valued and multiple -valued nonlinearities are proposed. The method of the structurally-frequency analysis is proposed and applied to validate the obtained solutions. VF is proposed for identification of an order and a spectrum of eigenvalues of a linear dynamic system. The possibility of application VF for the problem solving of identification static systems is shown
Electronic structure and magnetic anisotropy of CrO2
Toropova, A.; Kotliar, G.; Savrasov, S. Y.; Oudovenko, V. S.
2005-05-01
The problem of importance of strong correlations for the electronic structure, transport, and magnetic properties of half-metallic ferromagnetic CrO2 is addressed by performing density functional electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. It is shown that the corresponding low-temperature experimental data are best fitted without accounting for the Hubbard U corrections. We conclude that the ordered phase of CrO2 is weakly correlated.
Electronic structure and bonding in hydroxocobalamin
Ouyang, Lizhi; Rulis, Paul; Ching, Wai-Y.; Slouf, Miroslav; Nardin, Giorgio; Randaccio, Lucio
2005-05-01
The electronic structure of hydroxocobalamin (OHCbl) has been calculated by a density functional method, using the orthogonalized linear combination of the atomic orbitals method (OLCAO). The X-ray crystal structure has been determined from synchrotron X-ray diffraction data and the geometry determined was used in the calculations. Comparison with the recently reported electronic structures of cyanocobalamin (CNCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) shows that Mulliken charges ( Q*) and bond orders (BO) vary only on the axial fragment.
Long-Lived Vortex Structures in Collisional Pure and Gas-Discharge Nonneutral Electron Plasmas
Kervalishvili, N. A.
2013-01-01
The analysis of experimental investigations of equilibrium, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas during the time much more than the electron-neutral collision time has been carried out. The problem of long confinement of the column of pure electron plasma in Penning-Malmberg trap is considered. The mechanism of stability of long-lived vortex structure in gas-discharge nonneutral electron plasma is investigated. The collap...
Computational strategies to address chromatin structure problems
Perišić, Ognjen; Schlick, Tamar
2016-06-01
While the genetic information is contained in double helical DNA, gene expression is a complex multilevel process that involves various functional units, from nucleosomes to fully formed chromatin fibers accompanied by a host of various chromatin binding enzymes. The chromatin fiber is a polymer composed of histone protein complexes upon which DNA wraps, like yarn upon many spools. The nature of chromatin structure has been an open question since the beginning of modern molecular biology. Many experiments have shown that the chromatin fiber is a highly dynamic entity with pronounced structural diversity that includes properties of idealized zig-zag and solenoid models, as well as other motifs. This diversity can produce a high packing ratio and thus inhibit access to a majority of the wound DNA. Despite much research, chromatin’s dynamic structure has not yet been fully described. Long stretches of chromatin fibers exhibit puzzling dynamic behavior that requires interpretation in the light of gene expression patterns in various tissue and organisms. The properties of chromatin fiber can be investigated with experimental techniques, like in vitro biochemistry, in vivo imagining, and high-throughput chromosome capture technology. Those techniques provide useful insights into the fiber’s structure and dynamics, but they are limited in resolution and scope, especially regarding compact fibers and chromosomes in the cellular milieu. Complementary but specialized modeling techniques are needed to handle large floppy polymers such as the chromatin fiber. In this review, we discuss current approaches in the chromatin structure field with an emphasis on modeling, such as molecular dynamics and coarse-grained computational approaches. Combinations of these computational techniques complement experiments and address many relevant biological problems, as we will illustrate with special focus on epigenetic modulation of chromatin structure.
Electronic structure and polarizability of metallic nanoshells
Prodan, E.; Nordlander, P.
2002-01-01
An efficient method for the calculation of the electronic structure of metallic nanoshells is developed. The method is applied to a large nanoshell (of 10 nm in diameter) containing more than 2.5×10 4 conduction electrons. The calculations show that the density of states of the nanoshell is relatively bulk-like. The frequency dependent polarizability is calculated and shown to display strong confinement effects and features similar to what is predicted by semi-classical electrodynamic theory.
Structural and electronic properties for atomic clusters
Sun, Yan
We have studied the structural and electronic properties for different groups of atomic clusters by doing a global search on the potential energy surface using the Taboo Search in Descriptors Space (TSDS) method and calculating the energies with Kohn-Sham Density Functional Theory (KS-DFT). Our goal was to find the structural and electronic principles for predicting the structure and stability of clusters. For Ben (n = 3--20), we have found that the evolution of geometric and electronic properties with size reflects a change in the nature of the bonding from van der Waals to metallic and then bulk-like. The cluster sizes with extra stability agree well with the predictions of the jellium model. In the 4d series of transition metal (TM) clusters, as the d-type bonding becomes more important, the preferred geometric structure changes from icosahedral (Y, Zr), to distorted compact structures (Nb, Mo), and FCC or simple cubic crystal fragments (Tc, Ru, Rh) due to the localized nature of the d-type orbital. Analysis of relative isomer energies and their electronic density of states suggest that these clusters tend to follow a maximum hardness principle (MHP). For A4B12 clusters (A is divalent, B is monovalent), we found unusually large (on average 1.95 eV) HOMO-LUMO gap values. This shows the extra stability at an electronic closed shell (20 electrons) predicted by the jellium model. The importance of symmetry, closed electronic and ionic shells in stability is shown by the relative stability of homotops of Mg4Ag12 which also provides support for the hypothesis that clusters that satisfy more than one stability criterion ("double magic") should be particularly stable.
Pedro GARCÍA GALLEGO; Sanjosé López, Vicente; SOLAZ-PORTOLÉS, Joan Josep
2015-01-01
This study analyses the influence of academic level, academic itinerary, word problem’s context and structure, capturing problem structure, and using analogies on problem-solving. A factorial design was used with one within-subjects variable and several between-subjects variables, which have been selected depending on the hypothesis in question. Two types of booklets containing two word problems and questions about capturing problem structure and using analogies in problem solving, were admin...
Electronic Structure of Gadolinium Calcium Oxoborate
Nelson, A; Adams, J; Schaffers, K
2004-07-01
Gadolinium calcium oxoborate (GdCOB) is a nonlinear optical material that belongs to the calcium--rare-earth (R) oxoborate family, with general composition Ca{sub 4}RO(BO{sub 3}){sub 3} (R{sup 3+} = La, Sm, Gd, Lu, Y). X-ray photoemission was applied to study the valence band electronic structure and surface chemistry of this material. High resolution photoemission measurements on the valence band electronic structure and Gd 3d and 4d, Ca 2p, B 1s and O 1s core lines were used to evaluate the surface and near surface chemistry. These results provide measurements of the valence band electronic structure and surface chemistry of this rare-earth oxoborate.
The Electronic Structure of Heavy Element Complexes
Bursten, Bruce E.
2000-07-25
The area of study is the bonding in heavy element complexes, and the application of more sophisticated electronic structure theories. Progress is recounted in several areas: (a) technological advances and current methodologies - Relativistic effects are extremely important in gaining an understanding of the electronic structure of compounds of the actinides, transactinides, and other heavy elements. Therefore, a major part of the continual benchmarking was the proper inclusion of the appropriate relativistic effects for the properties under study. (b) specific applications - These include organoactinide sandwich complexes, CO activation by actinide atoms, and theoretical studies of molecules of the transactinide elements. Finally, specific directions in proposed research are described.
Electronic structure and magnetism in actinide compounds
Durakiewicz, T. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)]. E-mail: tomasz@lanl.gov; Joyce, J.J. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Lander, G.H. [JRC, Institute of Transuranium Elements, Postfach 2340, 76125 Karlsruhe (Germany); Olson, C.G. [Ames Laboratory, Iowa State University, Ames, Iowa 5011 (United States); Butterfield, M.T. [Lawrence Livermoore National Laboratory, Livermoore, CA 94550 (United States); Guziewicz, E. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Batista, C.D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Arko, A.J. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Morales, L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Mattenberger, K. [Laboratorium fur Festkorperphysik, ETH, CH-8093, Zurich (Switzerland); Vogt, O. [Laboratorium fur Festkorperphysik, ETH, CH-8093, Zurich (Switzerland)
2006-05-01
A close relationship between electronic structure and magnetic properties is observed in actinide compounds. The exact nature of this relationship is under investigation. We present examples of a direct link between electronic structure and ordered magnetic moment and/or magnetization. Specifically, results obtained for cubic U, Np and Pu compounds and quasi-2D U compounds are be presented. In the case of cubic compounds, a direct relationship between binding energy of valence band features and magnetic moment will be discussed. A Stoner-like mechanism and simple mean-field explanation is proposed for ferromagnetic UTe.
Electronic Properties in a Hierarchical Multilayer Structure
ZHU Chen-Ping; XIONG Shi-Jie
2001-01-01
We investigate electronic properties of a hierarchical multilayer structure consisting of stacking of barriers and wells. The structure is formed in a sequence of generations, each of which is constructed with the same pattern but with the previous generation as the basic building blocks. We calculate the transmission spectrum which shows the multifractal behavior for systems with large generation index. From the analysis of the average resistivity and the multifractal structure of the wavefunctions, we show that there exist different types of states exhibiting extended, localized and intermediate characteristics. The degree of localization is sensitive to the variation of the structural parameters.Suggestion of the possible experimental realization is discussed.
Writing Electron Dot Structures: Abstract of Issue 9905M
Magnell, Kenneth R.
1999-10-01
Writing Electron Dot Structures is a computer program for Mac OS that provides drill with feedback for students learning to write electron dot structures. While designed for students in the first year of college general chemistry it may also be used by high school chemistry students. A systematic method similar to that found in many general chemistry texts is employed: determine the number of valence shell electrons, select the central atom, construct a skeleton, add electrons to complete octets, examine the structure for resonance forms. During the construction of a structure, the student has the option of quitting, selecting another formula, or returning to a previous step. If an incorrect number of electrons is entered the student may not proceed until the correct number is entered. The symbol entered for the central atom must follow accepted upper/lower case practice, and entry of the correct symbol must be accomplished before proceeding to the next step. A periodic table is accessible and feedback provides assistance for these steps. Construction of the skeleton begins with the placement of the central atom. Atoms can be added, moved, or removed. Prompts and feedback keep the student informed of progress and problems. A correct skeleton is required before proceeding to the next step. Completion of the structure begins with the addition of electron pairs to form the required bonds. Remaining electrons are added to complete the formation of multiple bonds, assure compliance with the octet rule, and form expanded octets. Resonance forms are made by moving or removing and replacing electron pairs in the existing skeleton. Prompts and feedback guide the student through this process. A running tally of bond pairs, unshared pairs, octets, electrons used, and electrons remaining is provided during this step. Screens from Writing Electron Dot Structures Hardware and Software Requirements Hardware and software requirements for Writing Electron Dot Structures are shown
Electrical and electronic waste: a global environmental problem.
Ramesh Babu, Balakrishnan; Parande, Anand Kuber; Ahmed Basha, Chiya
2007-08-01
The production of electrical and electronic equipment (EEE) is one of the fastest growing global manufacturing activities. This development has resulted in an increase of waste electric and electronic equipment (WEEE). Rapid economic growth, coupled with urbanization and growing demand for consumer goods, has increased both the consumption of EEE and the production of WEEE, which can be a source of hazardous wastes that pose a risk to the environment and to sustainable economic growth. To address potential environmental problems that could stem from improper management of WEEE, many countries and organizations have drafted national legislation to improve the reuse, recycling and other forms of material recovery from WEEE to reduce the amount and types of materials disposed in landfills. Recycling of waste electric and electronic equipment is important not only to reduce the amount of waste requiring treatment, but also to promote the recovery of valuable materials. EEE is diverse and complex with respect to the materials and components used and waste streams from the manufacturing processes. Characterization of these wastes is of paramount importance for developing a cost-effective and environmentally sound recycling system. This paper offers an overview of electrical and e-waste recycling, including a description of how it is generated and classified, strategies and technologies for recovering materials, and new scientific developments related to these activities. Finally, the e-waste recycling industry in India is also discussed.
Structure of conduction electrons on polysilanes
Ichikawa, Tsuneki [Hokkaido Univ., Sapporo (Japan); Kumagai, Jun
1998-10-01
The orbital structures of conduction electrons on permethylated oligosilane, Si{sub 2n}(CH{sub 3}){sub 2n+2}(n = 2 - 8), and poly(cyclohexylmethylsilane) have been determined by the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms. Quantum-chemical calculations suggest that Anderson localization due to fluctuation of {sigma} conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole. (author)
The Electronic Structure Effect in Heterogeneous Catalysis
Nilsson, A.; Pettersson, L. G. M.; Hammer, Bjørk
2005-01-01
Using a combination of density functional theory calculations and X-ray emission and absorption spectroscopy for nitrogen on Cu and Ni surfaces, a detailed picture is given of the chemisorption bond. It is suggested that the adsorption bond strength and hence the activity of transition metal...... surfaces as catalysts for chemical reactions can be related to certain characteristics of the surface electronic structure....
The electronic structure of antiferromagnetic chromium
Skriver, Hans Lomholt
1981-01-01
The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...
Nicolaides, Cleanthes A
2016-01-01
The paper summarizes elements of theories and computational methods that we have constructed and applied over the years for the nonperturbative solution of many electron problems, in the absence or presence of strong external fields, concerning resonance and nonstationary states with a variety of electronic structures.
Nonlinear eigenvalue problems with semipositone structure
Alfonso Castro
2000-10-01
Full Text Available In this paper we summarize the developments of semipositone problems to date, including very recent results on semipositone systems. We also discuss applications and open problems.
[Structured electronic consultation letter for shoulder disorders].
Paloneva, Juha; Oikari, Marjo; Ylinen, Jari; Ingalsuo, Minna; Ilkka, Kunnamo; Ilkka, Kiviranta
2012-01-01
Referral to a specialist has a significant influence on management of the patient and costs associated with the treatments. However, development and research of the process by which patients are referred has been almost neglected. Expectations considering the purpose, contents, and timing of the referral of the consulting physician and the consultant do not always meet. A structured, electronic consultation letter was developed to respond this need. Functionality and interactivity are the key elements of the referral, including (1) an electronic referral letter to a specialist, (2) interactive education in clinical examination and management of shoulder disorders, and (3) an instrument of clinical examination and documentation of shoulder disorders.
Electronic media, violence, and adolescents: an emerging public health problem.
David-Ferdon, Corinne; Hertz, Marci Feldman
2007-12-01
Adolescents' access to and use of new media technology (e.g., cell phone, personal data assistant, computer for Internet access) are on the rise, and this explosion of technology brings with it potential benefits and risks. Attention is growing about the risk of adolescents to become victims of aggression perpetrated by peers with new technology. In September 2006, the Centers for Disease Control and Prevention convened a panel of experts in technology and youth aggression to examine this specific risk. This special issue of the Journal of Adolescent Health presents the data and recommendations for future directions discussed at the meeting. The articles in the Journal support the argument that electronic aggression is an emerging public health problem in need of additional prevalence and etiological research to support the development and evaluation of effective prevention programs.
Topological structures of boundary value problems in block elements
Babeshko, V. A.; Evdokimova, O. V.; Babeshko, O. M.
2016-10-01
Block structures are considered; a boundary value problem for a system of inhomogeneous partial differential equations with constant coefficients is formulated in each block of a structure. The problem of matching solutions to boundary value problems in blocks with each other by topological study of the properties of solutions in the block structure is examined in the conditions of correct solvability of boundary value problems in blocks of the block structure. Some new properties of solutions to boundary value problems in block structures are found that are important for applications.
Electronic Structure of Strongly Correlated Materials
Anisimov, Vladimir
2010-01-01
Electronic structure and physical properties of strongly correlated materials containing elements with partially filled 3d, 4d, 4f and 5f electronic shells is analyzed by Dynamical Mean-Field Theory (DMFT). DMFT is the most universal and effective tool used for the theoretical investigation of electronic states with strong correlation effects. In the present book the basics of the method are given and its application to various material classes is shown. The book is aimed at a broad readership: theoretical physicists and experimentalists studying strongly correlated systems. It also serves as a handbook for students and all those who want to be acquainted with fast developing filed of condensed matter physics.
Electronic structure calculations on helical conducting polymers.
Ripoll, Juan D; Serna, Andrei; Guerra, Doris; Restrepo, Albeiro
2010-10-21
We present a study of the electronic structure and derived properties of polyfurane (PFu), polypyrrol (PPy), and polythiophene (PTh). Two spatial arrangements are considered: trans chain (tc-PFu, tc-PPy, tc-PTh) and cis α-helical (α-PFu, α-PPy, α-PTh). Even at the small sizes considered here, helical conformations appear to be stable. Band gaps of pure, undoped oligomers fall into the semiconductor range. Density of states (DOS) analysis suggest dense valence and conduction bands. Bond length alternation analysis predicts almost complete delocalization of the π clouds in all spatial arrangements. Doping with electron donors or electron-withdrawing impurities reduces all band gaps close to the metallic regime in addition to increasing the DOS for the valence and conduction bands.
Electrons and photons in periodic structures
Pedersen, Jesper Goor
applications both in terms of spontaneous emission control and for slow light propagation. We first consider antidot lattices, periodic modulations of the potential of an electron gas. We demonstrate that such structures may serve as an interesting platform for quantum information processing. In particular, we......This thesis concerns various theoretical proposals for engineering dispersion relations of photons and electrons for particular applications. The common concept is the use of a periodic modulation to induce new phenomena on length scales comparable with the periodicity of the modulation...... periodic modulation of an electron gas leads to the emergence of localized defect states with energies within the band gap, where no propagating modes exist. Secondly, the divergence of the photonic density of states near a photonic band gap leads to strongly modified light-matter interactions, which has...
Electronic band structures of binary skutterudites
Khan, Banaras [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Aliabad, H.A. Rahnamaye [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Saifullah [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Jalali-Asadabadi, S. [Department of Physics, Faculty of Science, University of Isfahan (UI), 81744 Isfahan (Iran, Islamic Republic of); Khan, Imad [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Ahmad, Iftikhar, E-mail: ahma5532@gmail.com [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan)
2015-10-25
The electronic properties of complex binary skutterudites, MX{sub 3} (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. - Highlights: • Theoretical and experimental electronic band structures of binary skutterudites are reviewed. • The literature reveals that none of the existing theoretical results are consistent with the experiments. • GW, regular and non-regular TB-mBJ methods are used to reproduce the correct results. • The GW and regular TB-mBJ results are better than the available results in literature. • However, non-regular TB-mBJ reproduces the correct experimental band structures.
Electronic structure studies of topological materials
Zhou, Shuyun
Three-dimensional (3D) Dirac fermions are a new class of topological quantum materials. In 3D Dirac semimetals, the conduction and valence bands touch each other at discrete points in the momentum space and show linear dispersions along all momentum directions, forming 3D Dirac cones which are protected by the crystal symmetry. Here I will present our recent studies of the electronic structures of novel materials which host 3D Dirac fermions by using angle-resolved photoemission spectroscopy.
P Modak; R S Rao; B K Godwal; S K Sikka
2002-05-01
Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated (F) and the experimental speciﬁc heat data. The c is found to be 24.7 K.
On Electronic Structure Engineering and Thermoelectric Performance
Jeong, Changwook; Lundstrom, Mark S.
2011-01-01
In this paper, we address the question of how to engineer the electronic structure to enhance the performance of a thermoelectric material. We examine several different materials and show that all of them, even those for which giant Seebeck coefficients have been predicted, display a value that is expected from conventional thermoelectric theory. For molecular thermoelectrics, we show that the detailed lineshape plays an important role. Finally, using III-V alloy semiconductors as a model sys...
Electronic structure of hcp transition metals
Jepsen, O.; Andersen, O. Krogh; Mackintosh, A. R.
1975-01-01
Using the linear muffin-tin-orbital method described in the previous paper, we have calculated the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os. We show how the band structures of these metals may be synthesized from the sp and d bands, and illustrate the effects...... mRy. Very small pieces of Fermi surface, which have not yet been observed experimentally, are predicted for Os. The limited amount of experimental information available for Zr can be fairly satisfactorily interpreted if the calculated d bands are raised by about 10-20 mRy relative to the sp bands...
Structural dynamics of electronic and photonic systems
Suhir, Ephraim; Steinberg, David S
2011-01-01
The proposed book will offer comprehensive and versatile methodologies and recommendations on how to determine dynamic characteristics of typical micro- and opto-electronic structural elements (printed circuit boards, solder joints, heavy devices, etc.) and how to design a viable and reliable structure that would be able to withstand high-level dynamic loading. Particular attention will be given to portable devices and systems designed for operation in harsh environments (such as automotive, aerospace, military, etc.) In-depth discussion from a mechanical engineer's viewpoint will be conducte
Electronic structure investigation of biphenylene films
Totani, R.; Grazioli, C.; Zhang, T.; Bidermane, I.; Lüder, J.; de Simone, M.; Coreno, M.; Brena, B.; Lozzi, L.; Puglia, C.
2017-02-01
Photoelectron Spectroscopy (PS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The obtained results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, NEXAFS measurements allowed characterizing the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction.
Long-Lived Vortex Structures in Collisional Pure and Gas-Discharge Nonneutral Electron Plasmas
Kervalishvili, N A
2013-01-01
The analysis of experimental investigations of equilibrium, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas during the time much more than the electron-neutral collision time has been carried out. The problem of long confinement of the column of pure electron plasma in Penning-Malmberg trap is considered. The mechanism of stability of long-lived vortex structure in gas-discharge nonneutral electron plasma is investigated. The collapse of electron sheath in gas-discharge nonneutral electron plasma in Penning cell at high pressures of neutral gas is described. The interaction between the stable vortex structure and the annular electron sheath, and the action of vortex structures on the transport of electrons along and across the magnetic field are discussed.
The structure of algebraic problem in high schools
Chio, José Angel
2010-01-01
Full Text Available The paper is aimed at discussing the importance of pupil’s knowledge of algebraic problem structure. The research started by diagnosing pupil’s actual command of algebraic problem structure. Finally suggestions to teachers of mathematics for facing difficulties in solving problems are given.
Eyring, LeRoy
1980-01-01
Describes methods for using the high-resolution electron microscope in conjunction with other tools to reveal the identity and environment of atoms. Problems discussed include the ultimate structure of real crystalline solids including defect structure and the mechanisms of chemical reactions. (CS)
Reconfiguration of Analog Electronics for Extreme Environments: Problem or Solution?
Stoica, Adrian; Zebulum, Ricardo; Keymeulen, Didier; Guo, Xin
2005-01-01
This paper argues in favor of adaptive reconfiguration as a technique to expand the operational envelope of analog electronics for extreme environments (EE). In addition to hardening-by-process and hardening-by-design, "hardening-by-reconfiguration", when applicable, could be used to mitigate drifts, degradation, or damage on electronic devices (chips) in EE, by using re-configurable devices and an adaptive self-reconfiguration of their circuit topology. Conventional circuit design exploits device characteristics within a certain temperature/radiation range; when that is exceeded, the circuit function degrades. On a reconfigurable device, although component parameters change in EE, as long as devices still operate, albeit degraded, a new circuit design, suitable for new parameter values, may be mapped into the reconfigurable structure to recover the initial circuit function. Partly degraded resources are still used, while completely damaged resources are bypassed. Designs suitable for various environmental conditions can be determined prior to operation or can be determined in-situ, by adaptive reconfiguration algorithms running on built-in digital controllers. Laboratory demonstrations of this technique were performed by JPL in several independent experiments in which bulk CMOS reconfigurable devices were exposed to, and degraded by, low temperatures (approx. 196 C), high temperatures (approx.300 C) or radiation (300kRad TID), and then recovered by adaptive reconfiguration using evolutionary search algorithms. Taking this technology from Technology Readiness Level (TRL) 3 to TRL 5 is the target of a current NASA project.
Thermal transfer structures coupling electronics card(s) to coolant-cooled structure(s)
David, Milnes P; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Parida, Pritish R; Schmidt, Roger R
2014-12-16
Cooling apparatuses and coolant-cooled electronic systems are provided which include thermal transfer structures configured to engage with a spring force one or more electronics cards with docking of the electronics card(s) within a respective socket(s) of the electronic system. A thermal transfer structure of the cooling apparatus includes a thermal spreader having a first thermal conduction surface, and a thermally conductive spring assembly coupled to the conduction surface of the thermal spreader and positioned and configured to reside between and physically couple a first surface of an electronics card to the first surface of the thermal spreader with docking of the electronics card within a socket of the electronic system. The thermal transfer structure is, in one embodiment, metallurgically bonded to a coolant-cooled structure and facilitates transfer of heat from the electronics card to coolant flowing through the coolant-cooled structure.
Electronic structure study of strongly correlated Mott-insulators
Yin, Quan
Strongly correlated electronic systems have presented the most challenging problems to condensed matter theorists for many years and this continues to be the case. They are complicated materials with active d or f orbitals, whose valence electrons are in the intermediate region between itinerant (band-like) and highly localized (atomic-like) limits, which demand genuine many-body treatment. Although dealing with strongly correlated systems is a notorious problem, they have drawn broad interests of both theoretical and experimental condensed matter physicists, with intensive studies carried out in the past and present. This is due to the most exotic properties associated with strongly correlated materials, such as high-temperature superconductivity, metal-insulator transition, volume collapse, Kondo effect, colossal magnetoresistance, and many others. Although density functional theory (DFT) within local density approximation (LDA) is very successful in describing a wide range of materials, it encounters difficulty in predicting strongly correlated systems. Traditionally, they have been studied by model Hamiltonians with empirical parameters. The development of dynamical mean field theory (DMFT) and its marriage to DFT have brought new hope for first-principle study of strongly correlated systems. In this work, electronic structures of select strongly correlated systems are studied using LDA+DMFT. As theoretical backgrounds, reviews of DFT and DMFT are given in the first few chapters, where we also introduce the philosophy and workflow of LDA+DMFT. In the following chapters, applications to transition metal oxides, undoped high-temperature superconductors and actinide oxides are presented, where electronic structures of these materials and other properties derived from electronic structures are calculated and compared with experiments where available. Generally good agreements have been found between theory and experiments.
Electronic structure investigation of novel superconductors
Buling, Anna
2014-05-15
The discovery of superconductivity in iron-based pnictides in 2008 gave rise to a high advance in the research of high-temperature superconductors. But up to now there is no generally admitted theory of the non-BCS mechanism of these superconductors. The electron and hole doped Ba122 (BaFe{sub 2}As{sub 2}) compounds investigated in this thesis are supposed to be suitable model systems for studying the electronic behavior in order to shed light on the superconducting mechanisms. The 3d-transition metal doped Ba122 compounds are investigated using the X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and X-ray magnetic circular dichroism (XMCD), while the completely hole doped K122 is observed using XPS. The experimental measurements are complemented by theoretical calculations. A further new class of superconductors is represented by the electride 12CaO*7Al{sub 2}O{sub 3}: Here superconductivity can be realized by electrons accommodated in the crystallographic sub-nanometer-sized cavities, while the mother compound is a wide band gap insulator. Electronic structure investigations, represented by XPS, XAS and resonant X-ray photoelectron spectroscopy (ResPES), carried out in this work, should help to illuminate this unconventional superconductivity and resolve a debate of competing models for explaining the existence of superconductivity in this compound.
Electromagnetic Radiation of Electrons in Periodic Structures
Potylitsyn, Alexander Petrovich
2011-01-01
Periodic magnetic structures (undulators) are widely used in accelerators to generate monochromatic undulator radiation (UR) in the range from far infrared to the hard X-ray region. Another periodic crystalline structure is used to produce quasimonochromatic polarized photon beams via the coherent bremsstrahlung mechanism (CBS). Due to such characteristics as monochromaticity, polarization and adjustability, these types of radiation is of large interest for applied and basic research of accelerator-emitted radiation. The book provides a detailed overview of the fundamental principles behind electromagnetic radiation emitted from accelerated charged particles (e.g. UR, CBS, radiation of fast electrons in Laser flash fields) as well as a unified description of relatively new radiation mechanisms which attracted great interest in recent years. This are the so-called polarization radiation excited by the Coulomb field of incident particles in periodic structures, parametric X-rays, resonant transition radiation a...
Electronic structure interpolation via atomic orbitals.
Chen, Mohan; Guo, G-C; He, Lixin
2011-08-17
We present an efficient scheme for accurate electronic structure interpolation based on systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse k-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals algorithms. We find that usually 16-25 orbitals per atom can give an accuracy of about 10 meV compared to the full ab initio calculations, and the accuracy can be systematically improved by using more atomic orbitals. The scheme is easy to implement and robust, and works equally well for metallic systems and systems with complicated band structures. Furthermore, the atomic orbitals have much better transferability than Shirley's basis and Wannier functions, which is very useful for perturbation calculations.
Electronic structure and bonding in crystalline peroxides
Königstein, Markus; Sokol, Alexei A.; Catlow, C. Richard A.
1999-08-01
Hartree-Fock and density-functional PW91 theories as realized in the CRYSTAL95 code have been applied to investigate the structural and electronic properties of Ba, Sr, and Ca peroxide materials with the calcium carbide crystal structure, results for which are compared with those for the corresponding oxides. Special attention is paid to the stabilization of the peroxide molecular ion O2-2 in the ionic environment provided by the lattice, and to chemical bonding effects. In order to describe the covalent bonding within the O2-2 ion and the polarization of the O- ion in the crystal electrostatic field, it is essential to include an account of the effects of electron correlation. The PW91 density functional has allowed us to reproduce the crystallographic parameters within a 3% error. The chemical bonding within the peroxide molecular ion has a complex nature with a balance between the weak covalent bond of σz type and the strong electrostatic repulsion of the closed-shell electron groups occupying O 2s and O 2px and 2py states. Compression of the peroxide ion in the ionic crystals gives rise to an excessive overlap of the O 2s closed shells of the two O- ions of a peroxide molecular ion O2-2, which in turn determines the antibonding character of the interaction and chemical bonding in the O2-2 molecular ion.
Photoelectron spectroscopy bulk and surface electronic structures
Suga, Shigemasa
2014-01-01
Photoelectron spectroscopy is now becoming more and more required to investigate electronic structures of various solid materials in the bulk, on surfaces as well as at buried interfaces. The energy resolution was much improved in the last decade down to 1 meV in the low photon energy region. Now this technique is available from a few eV up to 10 keV by use of lasers, electron cyclotron resonance lamps in addition to synchrotron radiation and X-ray tubes. High resolution angle resolved photoelectron spectroscopy (ARPES) is now widely applied to band mapping of materials. It attracts a wide attention from both fundamental science and material engineering. Studies of the dynamics of excited states are feasible by time of flight spectroscopy with fully utilizing the pulse structures of synchrotron radiation as well as lasers including the free electron lasers (FEL). Spin resolved studies also made dramatic progress by using higher efficiency spin detectors and two dimensional spin detectors. Polarization depend...
Gradient type optimization methods for electronic structure calculations
Zhang, Xin; Wen, Zaiwen; Zhou, Aihui
2013-01-01
The density functional theory (DFT) in electronic structure calculations can be formulated as either a nonlinear eigenvalue or direct minimization problem. The most widely used approach for solving the former is the so-called self-consistent field (SCF) iteration. A common observation is that the convergence of SCF is not clear theoretically while approaches with convergence guarantee for solving the latter are often not competitive to SCF numerically. In this paper, we study gradient type methods for solving the direct minimization problem by constructing new iterations along the gradient on the Stiefel manifold. Global convergence (i.e., convergence to a stationary point from any initial solution) as well as local convergence rate follows from the standard theory for optimization on manifold directly. A major computational advantage is that the computation of linear eigenvalue problems is no longer needed. The main costs of our approaches arise from the assembling of the total energy functional and its grad...
Problems with readings of electronic tagged sheep in dairy flocks
Antun Kostelić
2010-01-01
Full Text Available Reliable traceability system in animal production is a crucial part for protection of animal and human health. Small ruminants are usually ear’ tagged but this tagging system especially in extensive production systems is not reliable. The use of Radio Frequency Indentifying Devices (RFID, or electronic identification is more suitable. Ruminal boluses (Rumitag 20 gr, hdx are first chosen for ruminant tagging because they are easy and early applicable, easy to read and fraud resistant but they encounter some problems, mainly reading failure. In our trial we investigated reading failure on one sheep dairy farm. Six hundred and eight sheep have been milked during the trial and read for four times during milking. In all four readings we had quite high reading failure in comparison to other author findings. Probable cause for this very high failure could be the use of hand held readers in crowded environment which caused lot of double reading. This means that reading protocol should be improved. Unfortunately we did not have fixed reader so we could not compare readings.
Electronic Structure of Buried Interfaces - Oral Presentation
Porter, Zachary [SLAC National Accelerator Lab., Menlo Park, CA (United States)
2015-08-25
In the electronics behind computer memory storage, the speed and size are dictated by the performance of permanent magnets inside devices called read heads. Complicated magnets made of stacked layers of thin films can be engineered to have properties that yield more energy storage and faster switching times compared to conventional iron or cobalt magnets. The reason is that magnetism is a result of subtle interactions amongst electrons; just how neurons come together on large scales to make cat brains and dog brains, ensembles of electrons interact and become ferromagnets and paramagnets. These interactions make magnets too difficult to study in their entirety, so I focus on the interfaces between layers, which are responsible for the coupling materials physicists hope to exploit to produce next-generation magnets. This project, I study a transition metal oxide material called LSCO, Lanthanum Cobaltite, which can be a paramagnet or a ferromagnet depending on how you tweak the electronic structure. It exhibits an exciting behavior: its sum is greater than the sum of its parts. When another similar material called a LSMO, Lanthanum Manganite, is grown on top of it, their interface has a different type of magnetism from the LSCO or the LSMO! I hope to explain this by demonstrating differently charged ions in the interface. The typical method for quantifying this is x-ray absorption, but all conventional techniques look at every layer simultaneously, averaging the interfaces and the LSCO layers that we want to characterize separately. Instead, I must use a new reflectivity technique, which tracks the intensity of reflected x-rays at different angles, at energies near the absorption peaks of certain elements, to track changes in the electronic structure of the material. The samples were grown by collaborators at the Takamura group at U.C. Davis and probed with this “resonant reflectivity” technique on Beamline 2-1 at the Stanford Synchrotron Radiation Lightsource
Surface structure and electronic properties of materials
Siekhaus, W. J.; Somorjai, G. A.
1975-01-01
A surface potential model is developed to explain dopant effects on chemical vapor deposition. Auger analysis of the interaction between allotropic forms of carbon and silicon films has shown Si-C formation for all forms by glassy carbon. LEED intensity measurements have been used to determine the mean square displacement of surface atoms of silicon single crystals, and electron loss spectroscopy has shown the effect of structure and impurities on surface states located within the band gap. A thin film of Al has been used to enhance film crystallinity at low temperature.
Electronic structure of cobalt nanocrystals suspended inliquid
Liu, Hongjian; Guo, Jinghua; Yin, Yadong; Augustsson, Andreas; Dong, Chungli; Nordgren, Joseph; Chang, Chinglin; Alivisatos, Paul; Thornton, Geoff; Ogletree, D. Frank; Requejo, Felix G.; de Groot, Frank; Salmeron, Miquel
2007-07-16
The electronic structure of cobalt nanocrystals suspended in liquid as a function of size has been investigated using in-situ x-ray absorption and emission spectroscopy. A sharp absorption peak associated with the ligand molecules is found that increases in intensity upon reducing the nanocrystal size. X-ray Raman features due to d-d and to charge-transfer excitations of ligand molecules are identified. The study reveals the local symmetry of the surface of {var_epsilon}-Co phase nanocrystals, which originates from a dynamic interaction between Co nanocrystals and surfactant + solvent molecules.
Atomic Reference Data for Electronic Structure Calculations
Kotochigova, S; Shirley, E L
We have generated data for atomic electronic structure calculations, to provide a standard reference for results of specified accuracy under commonly used approximations. Results are presented here for total energies and orbital energy eigenvalues for all atoms from H to U, at microHartree accuracy in the total energy, as computed in the local-density approximation (LDA) the local-spin-density approximation (LSD); the relativistic local-density approximation (RLDA); and scalar-relativistic local-density approximation (ScRLDA).
Electronic golden structure of the periodic chart
Malinowski, Leonard J. [Interdisciplinary Research Club, Monroeville, PA (United States)], E-mail: LJMalinowski@gmail.com
2009-11-15
The golden ratio has been studied since the ancient Greeks due to its inherent symmetry and aesthetic beauty, especially in the five Platonic Solids. The golden mean is now established as a pillar of El Naschie's E infinity where it achieves the physical manifestation of 0.618 034 MeV. The largest atomic electron orbital total energies average to the golden mean energy. This paper examines the golden ratio in order to expand upon a century old attempt to produce a relatively static, visual, geometric model of atomic structure.
The electronic structure of impurities in semiconductors
Nylandsted larsen, A; Svane, A
2002-01-01
The electronic structure of isolated substitutional or interstitial impurities in group IV, IV-IV, and III-V compound semiconductors will be studied. Mössbauer spectroscopy will be used to investigate the incorporation of the implanted isotopes on the proper lattice sites. The data can be directly compared to theoretical calculations using the LMTO scheme. Deep level transient spectroscopy will be used to identify the band gap levels introduced by metallic impurities, mainly in Si~and~Si$ _{x}$Ge$_{1-x}$. \\\\ \\\\
Lattice Boltzmann Model for Electronic Structure Simulations
Mendoza, M; Succi, S
2015-01-01
Recently, a new connection between density functional theory and kinetic theory has been proposed. In particular, it was shown that the Kohn-Sham (KS) equations can be reformulated as a macroscopic limit of the steady-state solution of a suitable single-particle kinetic equation. By using a discrete version of this new formalism, the exchange and correlation energies of simple atoms and the geometrical configuration of the methane molecule were calculated accurately. Here, we discuss the main ideas behind the lattice kinetic approach to electronic structure computations, offer some considerations for prospective extensions, and also show additional numerical results, namely the geometrical configuration of the water molecule.
Electronic structure and magnetism of complex materials
Papaconstantopoulos, D A
2003-01-01
Recent developments in electronic structure theory have led to a new understanding of magnetic materials at the microscopic level. This enables a truly first-principles approach to investigations of technologically important magnetic materials. Among these advances have been practical schemes for handling non-collinear magnetic systems, including relativity, understanding of the origins and role of orbital magnetism within band structure formalisms, density functional approaches for magnons and low-lying spin excitations, understanding of the interplay of orbital, spin and lattice orderings in complex oxides, transport theories for layered systems, and the theory of magnetic interactions in doped semiconductors. The book covers these recent developments with review articles by some of the main originators of these advances.
Electrons and photons in periodic structures
Pedersen, Jesper Goor
This thesis concerns various theoretical proposals for engineering dispersion relations of photons and electrons for particular applications. The common concept is the use of a periodic modulation to induce new phenomena on length scales comparable with the periodicity of the modulation. In parti......This thesis concerns various theoretical proposals for engineering dispersion relations of photons and electrons for particular applications. The common concept is the use of a periodic modulation to induce new phenomena on length scales comparable with the periodicity of the modulation...... periodic modulation of an electron gas leads to the emergence of localized defect states with energies within the band gap, where no propagating modes exist. Secondly, the divergence of the photonic density of states near a photonic band gap leads to strongly modified light-matter interactions, which has...... the way for graphene transistors. Photonic band gaps can be engineered using structures with a periodic modulations of the refractive index, commonly referred to as photonic crystal. We discuss the application of photonic crystals to slow light phenomena, where advantage is taken of the divergence...
Analysis of boron carbides' electronic structure
Howard, Iris A.; Beckel, Charles L.
1986-01-01
The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.
Oliveira, Micael
The CECAM Electronic Structure Library (ESL) is a community-driven effort to segregate shared pieces of software as libraries that could be contributed and used by the community. Besides allowing to share the burden of developing and maintaining complex pieces of software, these can also become a target for re-coding by software engineers as hardware evolves, ensuring that electronic structure codes remain at the forefront of HPC trends. In a series of workshops hosted at the CECAM HQ in Lausanne, the tools and infrastructure for the project were prepared, and the first contributions were included and made available online (http://esl.cecam.org). In this talk I will present the different aspects and aims of the ESL and how these can be useful for the electronic structure community.
Problems and Projects Based Approach For Analog Electronic Circuits' Course
Vahé Nerguizian
2009-04-01
Full Text Available New educational methods and approaches are recently introduced and implemented at several North American and European universities using Problems and Projects Based Approach (PPBA. The PPBA employs a teaching technique based mostly on competences/skills rather than only on knowledge. This method has been implemented and proven by several pedagogical instructors and authors at several educational institutions. This approach is used at different disciplines such as medicine, biology, engineering and many others. It has the advantage to improve the student's skills and the knowledge retention rate, and reflects the 21st century industrial/company needs and demands. Before implementing this approach to a course, a good resources preparation and planning is needed upfront by the responsible or instructor of the course to achieve the course and students related objectives. This paper presents the preparation, the generated documentation and the implementation of a pilot project utilizing PPBA education for a second year undergraduate electronic course over a complete semester, and for two different class groups (morning and evening groups. The outcome of this project (achieved goals, observed difficulties and lessons learned is presented based on different tools such as students 'in class' communication and feedback, different course evaluation forms and the professor/instructor feedback. Resources, challenges, difficulties and recommendations are also assessed and presented. The impact, the effect and the results (during and at the end of the academic fall session of the PPBA on students and instructor are discussed, validated, managed and communicated to help other instructor in taking appropriate approach decisions with respect to this new educational approach compared to the classical one.
Structure and navigation for electronic publishing
Tillinghast, John; Beretta, Giordano B.
1998-01-01
The sudden explosion of the World Wide Web as a new publication medium has given a dramatic boost to the electronic publishing industry, which previously was a limited market centered around CD-ROMs and on-line databases. While the phenomenon has parallels to the advent of the tabloid press in the middle of last century, the electronic nature of the medium brings with it the typical characteristic of 4th wave media, namely the acceleration in its propagation speed and the volume of information. Consequently, e-publications are even flatter than print media; Shakespeare's Romeo and Juliet share the same computer screen with a home-made plagiarized copy of Deep Throat. The most touted tool for locating useful information on the World Wide Web is the search engine. However, due to the medium's flatness, sought information is drowned in a sea of useless information. A better solution is to build tools that allow authors to structure information so that it can easily be navigated. We experimented with the use of ontologies as a tool to formulate structures for information about a specific topic, so that related concepts are placed in adjacent locations and can easily be navigated using simple and ergonomic user models. We describe our effort in building a World Wide Web based photo album that is shared among a small network of people.
Particle Swarm Optimization for Structural Design Problems
Hamit SARUHAN
2010-02-01
Full Text Available The aim of this paper is to employ the Particle Swarm Optimization (PSO technique to a mechanical engineering design problem which is minimizing the volume of a cantilevered beam subject to bending strength constraints. Mechanical engineering design problems are complex activities which are computing capability are more and more required. The most of these problems are solved by conventional mathematical programming techniques that require gradient information. These techniques have several drawbacks from which the main one is becoming trapped in local optima. As an alternative to gradient-based techniques, the PSO does not require the evaluation of gradients of the objective function. The PSO algorithm employs the generation of guided random positions when they search for the global optimum point. The PSO which is a nature inspired heuristics search technique imitates the social behavior of bird flocking. The results obtained by the PSO are compared with Mathematical Programming (MP. It is demonstrated that the PSO performed and obtained better convergence reliability on the global optimum point than the MP. Using the MP, the volume of 2961000 mm3 was obtained while the beam volume of 2945345 mm3 was obtained by the PSO.
Dichotomy for tree-structured trigraph list homomorphism problems
Feder, Tomás; Schell, David G; Stacho, Juraj
2010-01-01
Trigraph list homomorphism problems (also known as list matrix partition problems) have generated recent interest, partly because there are concrete problems that are not known to be polynomial time solvable or NP-complete. Thus while digraph list homomorphism problems enjoy dichotomy (each problem is NP-complete or polynomial time solvable), such dichotomy is not necessarily expected for trigraph list homomorphism problems. However, in this paper, we identify a large class of trigraphs for which list homomorphism problems do exhibit a dichotomy. They consist of trigraphs with a tree-like structure, and, in particular, include all trigraphs whose underlying graphs are trees. In fact, we show that for these tree-like trigraphs, the trigraph list homomorphism problem is polynomially equivalent to a related digraph list homomorphism problem. We also describe a few examples illustrating that our conditions defining tree-like trigraphs are not unnatural, as relaxing them may lead to harder problems.
Structured collaboration versus individual learning in solving physics problems
Harskamp, Egbert; Ding, Ning
2006-01-01
The research issue in this study is how to structure collaborative learning so that it improves solving physics problems more than individual learning. Structured collaborative learning has been compared with individual learning environments with Schoenfeld's problem-solving episodes. Students took
Structuring and assessing large and complex decision problems using MCDA
Barfod, Michael Bruhn
This paper presents an approach for the structuring and assessing of large and complex decision problems using multi-criteria decision analysis (MCDA). The MCDA problem is structured in a decision tree and assessed using the REMBRANDT technique featuring a procedure for limiting the number of pair...
Reversible Hydrogen Storage Materials – Structure, Chemistry, and Electronic Structure
Robertson, Ian M. [University of Wisconsin-Madison; Johnson, Duane D. [Ames Lab., Iowa
2014-06-21
To understand the processes involved in the uptake and release of hydrogen from candidate light-weight metal hydride storage systems, a combination of materials characterization techniques and first principle calculation methods have been employed. In addition to conventional microstructural characterization in the transmission electron microscope, which provides projected information about the through thickness microstructure, electron tomography methods were employed to determine the three-dimensional spatial distribution of catalyst species for select systems both before and after dehydrogenation. Catalyst species identification as well as compositional analysis of the storage material before and after hydrogen charging and discharging was performed using a combination of energy dispersive spectroscopy, EDS, and electron energy loss spectroscopy, EELS. The characterization effort was coupled with first-principles, electronic-structure and thermodynamic techniques to predict and assess meta-stable and stable phases, reaction pathways, and thermodynamic and kinetic barriers. Systems studied included:NaAlH4, CaH2/CaB6 and Ca(BH4)2, MgH2/MgB2, Ni-Catalyzed Magnesium Hydride, TiH2-Catalyzed Magnesium Hydride, LiBH4, Aluminum-based systems and Aluminum
A dressing of zero-range potentials and electron-molecule scattering problem at low energies
Leble, S B
2002-01-01
A dressing of a nonspherical potential, which includes $n$ zero range potentials, is considered. The dressing technique is used to improve ZRP model. Concepts of the partial waves and partial phases for non-spherical potential are used in order to perform Darboux transformation. The problem of scattering on the regular $\\hbox{X}_n$ and $\\hbox{YX}_n$ structures is studied. The possibilities of dressed ZRP are illustrated by model calculation of the low-energy electron-Silane ($\\hbox{SiH}_4$) scattering. The results are discussed. Key words: multiple scattering, silane, zero range potential.
Microscopical Studies of Structural and Electronic Properties of Semiconductors
2002-01-01
The electronic and structural properties of point defects in semiconductors, e.g. radiation defects, impurities or passivating defects can excellently be studied by the hyperfine technique of Perturbed Angular Correlation (PAC). The serious limitation of this method, the small number of chemically different radioactive PAC probe atoms can be widely overcome by means of ISOLDE. Providing shortliving isotopes, which represent common dopants as well as suitable PAC probe atoms, the ISOLDE facility enables a much broader application of PAC to problems in semiconductor physics.\\\\ Using the probe atom $^{111m}$ Cd , the whole class of III-V compounds becomes accessible for PAC investigations. First successful experiments in GaAs, InP and GaP have been performed, concerning impurity complex formation and plasma induced defects. In Si and Ge, the electronic properties~-~especially their influence on acceptor-donor interaction~-~could be exemplarily st...
CUDA Parallel Algorithms for Forward and Inverse Structural Gravity Problems
2015-01-01
This paper describes usage of CUDA parallelization scheme for forward and inverse gravity problems for structural boundaries. Forward problem is calculated using the finite elements approach. This means that the whole calculation volume is split into parallelepipeds and then the gravity effect of each is calculated using known formula. Inverse problem solution is found using iteration local corrections method. This method requires only forward problem calculation on each iteration and does no...
Solving Fluid Structure Interaction Problems with an Immersed Boundary Method
Barad, Michael F.; Brehm, Christoph; Kiris, Cetin C.
2016-01-01
An immersed boundary method for the compressible Navier-Stokes equations can be used for moving boundary problems as well as fully coupled fluid-structure interaction is presented. The underlying Cartesian immersed boundary method of the Launch Ascent and Vehicle Aerodynamics (LAVA) framework, based on the locally stabilized immersed boundary method previously presented by the authors, is extended to account for unsteady boundary motion and coupled to linear and geometrically nonlinear structural finite element solvers. The approach is validated for moving boundary problems with prescribed body motion and fully coupled fluid structure interaction problems. Keywords: Immersed Boundary Method, Higher-Order Finite Difference Method, Fluid Structure Interaction.
Time Collocation Method for Structural Dynamic Problems
TANG Chen; LUO Tao; YAN Haiqing; GU Xiaohui
2005-01-01
In order to achieve highly accurate and efficient numerical calculations of structural dynamics, time collocation method is presented. For a given time interval, the numerical solution of the method is approximated by a polynomial. The polynomial coefficients are evaluated by solving algebraic equation. Once the polynomial coefficients are evaluated, the numerical solutions at any time in the interval can be easily calculated. New formulae are derived for the polynomial coefficients,which are more practical and succinct than those previously given. Two structural dynamic equations are calculated by the proposed method. The numerical solutions are compared with the traditional fourth-order Runge-Kutta method. The results show that the method proposed is highly accurate and computationally efficient. In addition, an important advantage of the method is the simplicity in software programming.
Electron Liquids in Semiconductor Quantum Structures
Aron Pinczuk
2009-05-25
The groups led by Stormer and Pinczuk have focused this project on goals that seek the elucidation of novel many-particle effects that emerge in two-dimensional electron systems (2DES) as the result from fundamental quantum interactions. This experimental research is conducted under extreme conditions of temperature and magnetic field. From the materials point of view, the ultra-high mobility systems in GaAs/AlGaAs quantum structures continue to be at the forefront of this research. The newcomer materials are based on graphene, a single atomic layer of graphite. The graphene research is attracting enormous attention from many communities involved in condensed matter research. The investigated many-particle phenomena include the integer and fractional quantum Hall effect, composite fermions, and Dirac fermions, and a diverse group of electron solid and liquid crystal phases. The Stormer group performed magneto-transport experiments and far-infrared spectroscopy, while the Pinczuk group explores manifestations of such phases in optical spectra.
Multigrid Methods in Electronic Structure Calculations
Briggs, E L; Bernholc, J
1996-01-01
We describe a set of techniques for performing large scale ab initio calculations using multigrid accelerations and a real-space grid as a basis. The multigrid methods provide effective convergence acceleration and preconditioning on all length scales, thereby permitting efficient calculations for ill-conditioned systems with long length scales or high energy cut-offs. We discuss specific implementations of multigrid and real-space algorithms for electronic structure calculations, including an efficient multigrid-accelerated solver for Kohn-Sham equations, compact yet accurate discretization schemes for the Kohn-Sham and Poisson equations, optimized pseudo\\-potentials for real-space calculations, efficacious computation of ionic forces, and a complex-wavefunction implementation for arbitrary sampling of the Brillioun zone. A particular strength of a real-space multigrid approach is its ready adaptability to massively parallel computer architectures, and we present an implementation for the Cray-T3D with essen...
Electronic Structure and Catalysis on Metal Surfaces
Greeley, Jeff; Norskov, Jens K.; Mavrikakis, Manos
2002-10-01
The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid in the establishment of chemisorption trends across the transition metals, in the characterization of reaction pathways on individual metals, and in the design of novel catalysts. First principles studies provide an excellent fundamental complement to experimental investigations of the above phenomena and can often allow the elucidation of important mechanistic details that would be difficult, if not impossible, to determine from experiments alone.
Electronic structures of reconstructed zigzag silicene nanoribbons
Ding, Yi, E-mail: dingyi2001@tsinghua.org.cn, E-mail: wangyanli-04@tsinghua.org.cn [Department of Physics, Hangzhou Normal University, Hangzhou, Zhejiang 310036 (China); Wang, Yanli, E-mail: dingyi2001@tsinghua.org.cn, E-mail: wangyanli-04@tsinghua.org.cn [Department of Physics, Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Xiasha College Park, Hangzhou, Zhejiang 310018 (China)
2014-02-24
Edge states and magnetism are crucial for spintronic applications of nanoribbons. Here, using first-principles calculations, we explore structural stabilities and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with Klein and pentagon-heptagon reconstructions. Comparing to unreconstructed zigzag edges, deformed bare pentagon-heptagon ones are favored under H-poor conditions, while H-rich surroundings stabilize di-hydrogenated Klein edges. These Klein edges have analogous magnetism to zigzag ones, which also possess the electric-field-induced half-metallicity of nanoribbons. Moreover, diverse magnetic states can be achieved by asymmetric Klein and zigzag edges into ZSiNRs, which could be transformed from antiferromagnetic-semiconductors to bipolar spin-gapless-semiconductors and ferromagnetic-metals depending on edge hydrogenations.
Chen, Duan; Wei, Guo-Wei
2010-01-01
The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano scale. By optimization of the energy functional, we derive consistently-coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I-V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical convergence
Chen, Duan; Wei, Guo-Wei
2010-06-01
The miniaturization of nano-scale electronic devices, such as metal oxide semiconductor field effect transistors (MOSFETs), has given rise to a pressing demand in the new theoretical understanding and practical tactic for dealing with quantum mechanical effects in integrated circuits. Modeling and simulation of this class of problems have emerged as an important topic in applied and computational mathematics. This work presents mathematical models and computational algorithms for the simulation of nano-scale MOSFETs. We introduce a unified two-scale energy functional to describe the electrons and the continuum electrostatic potential of the nano-electronic device. This framework enables us to put microscopic and macroscopic descriptions in an equal footing at nano-scale. By optimization of the energy functional, we derive consistently coupled Poisson-Kohn-Sham equations. Additionally, layered structures are crucial to the electrostatic and transport properties of nano-transistors. A material interface model is proposed for more accurate description of the electrostatics governed by the Poisson equation. Finally, a new individual dopant model that utilizes the Dirac delta function is proposed to understand the random doping effect in nano-electronic devices. Two mathematical algorithms, the matched interface and boundary (MIB) method and the Dirichlet-to-Neumann mapping (DNM) technique, are introduced to improve the computational efficiency of nano-device simulations. Electronic structures are computed via subband decomposition and the transport properties, such as the I- V curves and electron density, are evaluated via the non-equilibrium Green's functions (NEGF) formalism. Two distinct device configurations, a double-gate MOSFET and a four-gate MOSFET, are considered in our three-dimensional numerical simulations. For these devices, the current fluctuation and voltage threshold lowering effect induced by the discrete dopant model are explored. Numerical
Temperature dependence of the electronic structure of semiconductors and insulators
Poncé, S., E-mail: samuel.pon@gmail.com; Gillet, Y.; Laflamme Janssen, J.; Gonze, X. [European Theoretical Spectroscopy Facility and Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Chemin des étoiles 8, bte L07.03.01, B-1348 Louvain-la-neuve (Belgium); Marini, A. [Consiglio Nazionale delle Ricerche (CNR), Via Salaria Km 29.3, CP 10, 00016 Monterotondo Stazione (Italy); Verstraete, M. [European Theoretical Spectroscopy Facility and Physique des matériaux et nanostructures, Université de Liège, Allée du 6 Août 17, B-4000 Liège (Belgium)
2015-09-14
The renormalization of electronic eigenenergies due to electron-phonon coupling (temperature dependence and zero-point motion effect) is sizable in many materials with light atoms. This effect, often neglected in ab initio calculations, can be computed using the perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic harmonic approximation. After a short description of the recent progresses in this field and a brief overview of the theory, we focus on the issue of phonon wavevector sampling convergence, until now poorly understood. Indeed, the renormalization is obtained numerically through a slowly converging q-point integration. For non-zero Born effective charges, we show that a divergence appears in the electron-phonon matrix elements at q → Γ, leading to a divergence of the adiabatic renormalization at band extrema. This problem is exacerbated by the slow convergence of Born effective charges with electronic wavevector sampling, which leaves residual Born effective charges in ab initio calculations on materials that are physically devoid of such charges. Here, we propose a solution that improves this convergence. However, for materials where Born effective charges are physically non-zero, the divergence of the renormalization indicates a breakdown of the adiabatic harmonic approximation, which we assess here by switching to the non-adiabatic harmonic approximation. Also, we study the convergence behavior of the renormalization and develop reliable extrapolation schemes to obtain the converged results. Finally, the adiabatic and non-adiabatic theories, with corrections for the slow Born effective charge convergence problem (and the associated divergence) are applied to the study of five semiconductors and insulators: α-AlN, β-AlN, BN, diamond, and silicon. For these five materials, we present the zero-point renormalization, temperature dependence, phonon-induced lifetime broadening, and the renormalized electronic band structure.
Kervalishvili, N A
2015-01-01
The nonperturbing experimental methods have been described, by means of which the solitary vortex structures in gas-discharge nonneutral electron plasma were detected and investigated. The comparison with the experimental methods used in devices with pure electron plasma was made. The problems of shielding the electrostatic perturbations in nonneutral plasmas were considered.
Comparison of some multireference electronic structure methods in illustrative applications
无
2010-01-01
The performances of several multireference electronic structure methods including complete active space self-consistent field (CASSCF)-based second-order perturbation theory (CASPT2), multireference configuration interaction with single and double excitations (MR-CISD), MR-CISD with the Davidson correction (MR-CISD+Q), and the CASSCF-based block-correlated coupled cluster method (CAS-BCCC4) we developed recently are compared by applying them to study several different chemical problems involving computation of ground state potential energy surfaces, the singlet-triplet gaps in diradicals, reaction barriers, and the excitation energies of low-lying excited states. Comparison with the results from other highly accurate theoretical methods or the available experimental data demonstrate that for all the problems studied, the overall performance of CAS-BCCC4 is competitive with that of MR-CISD+Q, and better than that of CASPT2 and MR-CISD methods. Thus the CAS-BCCC4 approach is expected to be a promising theoretical method for quantitative descriptions of the electronic structures of molecules with noticeable multireference character.
Conjugated Polymers for Organic Electronics: Structural and Electronic Characteristics
Rafael C. González-Cano; López Navarrete, Juan T.; Ruiz Delgado, M. Carmen
2016-01-01
The use of organic materials to design electronic devices has actually presented a broad interest for because they constitute an ecological and suitable resource for our current "electronic world". These materials provide several advantages (low cost, light weight, good flexibility and solubility to be easily printed) that cannot be afforded with silicium. They can also potentially interact with biological systems, something impossible with inorganic devices. Between these materials we can in...
Fanelli, D.; Öktem, O.
2008-02-01
This review of the development and current status of electron tomography deals mainly with the mathematical and algorithmic aspects. After a very brief description of the role of electron tomography in structural biology, we turn our attention to the derivation of the forward operator. Starting from the Schrödinger equation, the electron-specimen interaction is modelled as a diffraction tomography problem and the picture is completed by adding a description of the optical system of the transmission electron microscope. The first-order Born approximation enables one to explicitly express the intensity for any finite wavenumber in terms of the propagation operator acting on the specimen convolved with a point spread function, derived from the optics in the transmission electron microscope. Next, we focus on the difficulties that cause the reconstruction problem to be quite challenging. Special emphasis is put on explaining the extremely low signal-to-noise ratio in the data combined with the incomplete data problems, which lead to severe ill-posedness. The next step is to derive the standard phase contrast model used in the electron tomography community. The above-mentioned expression for the intensity generalizes the standard phase contrast model which can be obtained by replacing the propagation operator by its high-energy limit, the x-ray transform, as the wavenumber tends to infinity. The importance of more carefully including the wave nature of the electron-specimen interaction is supported by performing an asymptotic analysis of the intensity as the wavenumber tends to infinity. Next we provide an overview of the various reconstruction methods that have been employed in electron tomography and we conclude by mentioning a number of open problems. Besides providing an introduction to electron tomography written in the 'language of inverse problems', the authors hope to raise interest among experts in integral geometry and regularization theory for the
Quantum Mechanical Hysteresis and the Electron Transfer Problem
Etchegoin, P G
2004-01-01
We study a simple quantum mechanical symmetric donor-acceptor model for electron transfer (ET) with coupling to internal deformations. The model contains several basic properties found in biological ET in enzymes and photosynthetic centers; it produces tunnelling with hysteresis thus providing a simple explanation for the slowness of the reversed rate and the near 100% efficiency of ET in many biological systems. The model also provides a conceptual framework for the development of molecular electronics memory elements based on electrostatic architectures.
Structured Sparsity Regularization Approach to the EEG Inverse Problem
Montoya-Martinez, Jair; Artes-Rodriguez, Antonio; Hansen, Lars Kai
2012-01-01
Localization of brain activity involves solving the EEG inverse problem, which is an undetermined ill-posed problem. We propose a novel approach consisting in estimating, using structured sparsity regularization techniques, the Brain Electrical Sources (BES) matrix directly in the spatio-temporal......Localization of brain activity involves solving the EEG inverse problem, which is an undetermined ill-posed problem. We propose a novel approach consisting in estimating, using structured sparsity regularization techniques, the Brain Electrical Sources (BES) matrix directly in the spatio...
Structural qualia: a solution to the hard problem of consciousness
Kristjan eLoorits
2014-03-01
Full Text Available The hard problem of consciousness has been often claimed to be unsolvable by the methods of traditional empirical sciences. It has been argued that all the objects of empirical sciences can be fully analyzed in structural terms but that consciousness is (or has something over and above its structure. However, modern neuroscience has introduced a theoretical framework in which also the apparently non-structural aspects of consciousness, namely the so called qualia or qualitative properties, can be analyzed in structural terms. That framework allows us to see qualia as something compositional with internal structures that fully determine their qualitative nature. Moreover, those internal structures can be identified which certain neural patterns. Thus consciousness as a whole can be seen as a complex neural pattern that misperceives some of its own highly complex structural properties as monadic and qualitative. Such neural pattern is analyzable in fully structural terms and thereby the hard problem is solved.
Structural qualia: a solution to the hard problem of consciousness
Loorits, Kristjan
2014-01-01
The hard problem of consciousness has been often claimed to be unsolvable by the methods of traditional empirical sciences. It has been argued that all the objects of empirical sciences can be fully analyzed in structural terms but that consciousness is (or has) something over and above its structure. However, modern neuroscience has introduced a theoretical framework in which also the apparently non-structural aspects of consciousness, namely the so called qualia or qualitative properties, can be analyzed in structural terms. That framework allows us to see qualia as something compositional with internal structures that fully determine their qualitative nature. Moreover, those internal structures can be identified which certain neural patterns. Thus consciousness as a whole can be seen as a complex neural pattern that misperceives some of its own highly complex structural properties as monadic and qualitative. Such neural pattern is analyzable in fully structural terms and thereby the hard problem is solved. PMID:24672510
Applicability Problem in Optimum Reinforced Concrete Structures Design
Ashara Assedeq
2016-01-01
Full Text Available Optimum reinforced concrete structures design is very complex problem, not only considering exactness of calculus but also because of questionable applicability of existing methods in practice. This paper presents the main theoretical mathematical and physical features of the problem formulation as well as the review and analysis of existing methods and solutions considering their exactness and applicability.
Quantum Mechanical Square Root Speedup in a Structured Search Problem
Farhi, E; Farhi, Edward; Gutmann, Sam
1997-01-01
An unstructured search for one item out of N can be performed quantum mechanically in time of order square root of N whereas classically this requires of order N steps. This raises the question of whether square root speedup persists in problems with more structure. In this note we focus on one example of a structured problem and find a quantum algorithm which takes time of order the square root of the classical time.
Experimental Electronic Structure of Be_2C
Tsuei, K.-D.; Tzeng, C.-T.; Lo, W.-S.; Yuh, J.-Y.; Chu, R.-Y.
1998-03-01
The insulating Be_2C thin films have been successfully prepared on a Be surface. LEED pattern shows that the films have (100) orientation along the surface normal. We have used angle-resolved photoemission to map out the occupied bulk band dispersion along Γ-X direction. The band gap edges at X point are 6.5 and 11.7 eV below the valence band maximum which is located at Γ point. These values are in good agreement with theoretical calculations. [1,2] In addition two surface states are observed. One is 0.5 eV above VBM. The other is located at 9.5 eV below VBM in the middle of the band gap at X point. The unoccupied bulk electronic structure is measured using C 1s near edge x-ray absorption spectroscopy. The spectrum is similar in shape to an energy loss spectrum [3] and p-PDOS from the calculation, [2] while the relative peak positions are different. [1] J.L. Corkill and M.L. Cohen, Phy. Rev. B 48, 17138 (1993). [2] C.H. Lee, W.R. Lambrecht, and B. Segall, Phys. Rev. B 51, 10392 (1995). [3] M.M. Disko, J.C.H. Spence, O.F. Sankey, and D. Saldin, Phys. Rev. B 33, 5642 (1986).
Sorzano, C O S; Vargas, J; de la Rosa-Trevín, J M; Otón, J; Álvarez-Cabrera, A L; Abrishami, V; Sesmero, E; Marabini, R; Carazo, J M
2015-03-01
Cryo Electron Microscopy is a powerful Structural Biology technique, allowing the elucidation of the three-dimensional structure of biological macromolecules. In particular, the structural study of purified macromolecules -often referred as Single Particle Analysis(SPA)- is normally performed through an iterative process that needs a first estimation of the three-dimensional structure that is progressively refined using experimental data. It is well-known the local optimisation nature of this refinement, so that the initial choice of this first structure may substantially change the final result. Computational algorithms aiming to providing this first structure already exist. However, the question is far from settled and more robust algorithms are still needed so that the refinement process can be performed with sufficient guarantees. In this article we present a new algorithm that addresses the initial volume problem in SPA by setting it in a Weighted Least Squares framework and calculating the weights through a statistical approach based on the cumulative density function of different image similarity measures. We show that the new algorithm is significantly more robust than other state-of-the-art algorithms currently in use in the field. The algorithm is available as part of the software suite Xmipp (http://xmipp.cnb.csic.es) and Scipion (http://scipion.cnb.csic.es) under the name "Significant".
Electronic Interests and Behaviours Associated with Gambling Problems
Phillips, James G.; Ogeil, Rowan P.; Blaszczynski, Alex
2012-01-01
Multiple computing devices continue to develop capabilities that support online gambling, resulting in the need to evaluate the extent that this trend will contribute to gambling problems. A sample of 1,141 participants completed an online survey assessing interest in and difficulties limiting use of digital services. Questionnaire items measured…
Electronic structure and dynamics of nitrosyl porphyrins.
Scheidt, W Robert; Barabanschikov, Alexander; Pavlik, Jeffrey W; Silvernail, Nathan J; Sage, J Timothy
2010-07-19
functionals are not fully successful at capturing the trans interaction between the axial NO and imidazole ligands. This supports previous conclusions that heme-NO complexes exhibit an unusual degree of variability with respect to the computational method, and we speculate that this variability hints at a genuine electronic instability that a protein can exploit to tune its reactivity. We anticipate that ongoing characterization of heme-NO complexes will deepen our understanding of their structure, dynamics, and reactivity.
Graph-based linear scaling electronic structure theory
Niklasson, Anders M N; Negre, Christian F A; Cawkwell, Marc J; Swart, Pieter J; Mohd-Yusof, Jamal; Germann, Timothy C; Wall, Michael E; Bock, Nicolas; Djidjev, Hristo
2016-01-01
We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations.
ELECTRONIC STRUCTURE OF CLUSTER ASSEMBLED Al12C (Si) SOLID
QUAN HONG-JUN; GONG XIN-GAO
2000-01-01
The electronic structures of the cluster-assembled solid Al12C (Si) are studied by the ab initio method. We find that Al12C (Si) can solidify into a van der Waals solid. The electronic band structures show very weak dispersion. The main features in the electronic structure of cluster are retained in the solid, and an energy gap up to about 1.5 eV is observed for Al12C and Al12Si solids.
Solving Tensor Structured Problems with Computational Tensor Algebra
Morozov, Oleksii
2010-01-01
Since its introduction by Gauss, Matrix Algebra has facilitated understanding of scientific problems, hiding distracting details and finding more elegant and efficient ways of computational solving. Today's largest problems, which often originate from multidimensional data, might profit from even higher levels of abstraction. We developed a framework for solving tensor structured problems with tensor algebra that unifies concepts from tensor analysis, multilinear algebra and multidimensional signal processing. In contrast to the conventional matrix approach, it allows the formulation of multidimensional problems, in a multidimensional way, preserving structure and data coherence; and the implementation of automated optimizations of solving algorithms, based on the commutativity of all tensor operations. Its ability to handle large scientific tasks is showcased by a real-world, 4D medical imaging problem, with more than 30 million unknown parameters solved on a current, inexpensive hardware. This significantly...
LINGUISTIC MECHANISM OF HYPERMEDIA STRUCTURE IN MULTIMEDIA ELECTRONIC ATLAS
无
2000-01-01
With hypermedia technology the structure of a publication can be re-arranged to accommodate more easy cognition of the idea and concept by linking the concepts which are represented by different media forms into an integrated concept.Essentially,multimedia electronic atlas is a kind of electronic publication,which has many common characters with ordinary CD-ROM publications.For the deeper exploration of electronic atlas it is very important to understand the internal and general structure of the new media structure.The aim of this paper is to discuss the internal structure of multimedia electronic atlas as a whole by applying the methodology of linguistics.
Exploiting problem structure in a genetic algorithm approach to a nurse rostering problem
Uwe, Aickelin
2008-01-01
There is considerable interest in the use of genetic algorithms to solve problems arising in the areas of scheduling and timetabling. However, the classical genetic algorithm paradigm is not well equipped to handle the conflict between objectives and constraints that typically occurs in such problems. In order to overcome this, successful implementations frequently make use of problem specific knowledge. This paper is concerned with the development of a GA for a nurse rostering problem at a major UK hospital. The structure of the constraints is used as the basis for a co-evolutionary strategy using co-operating sub-populations. Problem specific knowledge is also used to define a system of incentives and disincentives, and a complementary mutation operator. Empirical results based on 52 weeks of live data show how these features are able to improve an unsuccessful canonical GA to the point where it is able to provide a practical solution to the problem
Dramatic changes in electronic structure revealed by fractionally charged nuclei
Cohen, Aron J. [Department of Chemistry, Lensfield Rd., University of Cambridge, Cambridge CB2 1EW (United Kingdom); Mori-Sánchez, Paula, E-mail: paula.mori@uam.es [Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid (Spain)
2014-01-28
Discontinuous changes in the electronic structure upon infinitesimal changes to the Hamiltonian are demonstrated. These are revealed in one and two electron molecular systems by full configuration interaction (FCI) calculations when the realm of the nuclear charge is extended to be fractional. FCI electron densities in these systems show dramatic changes in real space and illustrate the transfer, hopping, and removal of electrons. This is due to the particle nature of electrons seen in stretched systems and is a manifestation of an energy derivative discontinuity at constant number of electrons. Dramatic errors of density functional theory densities are seen in real space as this physics is missing from currently used approximations. The movements of electrons in these simple systems encapsulate those in real physical processes, from chemical reactions to electron transport and pose a great challenge for the development of new electronic structure methods.
Dramatic changes in electronic structure revealed by fractionally charged nuclei
Cohen, Aron J.; Mori-Sánchez, Paula
2014-01-01
Discontinuous changes in the electronic structure upon infinitesimal changes to the Hamiltonian are demonstrated. These are revealed in one and two electron molecular systems by full configuration interaction (FCI) calculations when the realm of the nuclear charge is extended to be fractional. FCI electron densities in these systems show dramatic changes in real space and illustrate the transfer, hopping, and removal of electrons. This is due to the particle nature of electrons seen in stretched systems and is a manifestation of an energy derivative discontinuity at constant number of electrons. Dramatic errors of density functional theory densities are seen in real space as this physics is missing from currently used approximations. The movements of electrons in these simple systems encapsulate those in real physical processes, from chemical reactions to electron transport and pose a great challenge for the development of new electronic structure methods.
Electronic-structural dynamics in graphene
Isabella Gierz
2016-09-01
meV, a transient enhancement of the electron-phonon coupling constant is observed, providing interesting perspective for experiments that report light-enhanced superconductivity in doped fullerites in which a similar lattice mode was excited. All the studies reviewed here have important implications for applications of graphene in optoelectronic devices and for the dynamical engineering of electronic properties with light.
Electronic Structure of the Bismuth Family of High Temperature Superconductors
Dunn, Lisa
2002-03-07
High temperature superconductivity remains the central intellectual problem in condensed matter physics fifteen years after its discovery. Angle resolved photoemission spectroscopy (ARPES) directly probes the electronic structure, and has played an important role in the field of high temperature superconductors. With the recent advances in sample growth and the photoemission technique, we are able to study the electronic structure in great detail, and address regimes that were previously inaccessible. This thesis work contains systematic photoemission studies of the electronic structure of the Bi-family of high temperature superconductors, which include the single-layer system (Bi2201), the bi-layer system (Bi2212), and the tri-layer system (Bi2223). We show that, unlike conventional BCS superconductors, phase coherence information emerges in the single particle excitation spectrum of high temperature superconductors as the superconducting peak in Bi2212. The universality and various properties of this superconducting peak are studied in various systems. We argue that the origin of the superconducting peak may provide the key to understanding the mechanism of High-Tc superconductors. In addition, we identified a new experimental energy scale in the bilayer material, the anisotropic intra-bilayer coupling energy. For a long time, it was predicted that this energy scale would cause bilayer band splitting. We observe this phenomenon, for the first time, in heavily overdoped Bi2212. This new observation requires the revision of the previous picture of the electronic excitation in the Brillouin zone boundary. As the first ARPES study of a trilayer system, various detailed electronic proper- ties of Bi2223 are examined. We show that, comparing with Bi2212, both superconducting gap and relative superconducting peak intensity become larger in Bi2223, however, the strength of the interlayer coupling within each unit cell is possibly weaker. These results suggest that the
Electronic structure of atoms: atomic spectroscopy information system
Kazakov, V. V.; Kazakov, V. G.; Kovalev, V. S.; Meshkov, O. I.; Yatsenko, A. S.
2017-10-01
The article presents a Russian atomic spectroscopy, information system electronic structure of atoms (IS ESA) (http://grotrian.nsu.ru), and describes its main features and options to support research and training. The database contains over 234 000 records, great attention paid to experimental data and uniform filling of the database for all atomic numbers Z, including classified levels and transitions of rare earth and transuranic elements and their ions. Original means of visualization of scientific data in the form of spectrograms and Grotrian diagrams have been proposed. Presentation of spectral data in the form of interactive color charts facilitates understanding and analysis of properties of atomic systems. The use of the spectral data of the IS ESA together with its functionality is effective for solving various scientific problems and training of specialists.
Atomic and electronic structure of surfaces theoretical foundations
Lannoo, Michel
1991-01-01
Surfaces and interfaces play an increasingly important role in today's solid state devices. In this book the reader is introduced, in a didactic manner, to the essential theoretical aspects of the atomic and electronic structure of surfaces and interfaces. The book does not pretend to give a complete overview of contemporary problems and methods. Instead, the authors strive to provide simple but qualitatively useful arguments that apply to a wide variety of cases. The emphasis of the book is on semiconductor surfaces and interfaces but it also includes a thorough treatment of transition metals, a general discussion of phonon dispersion curves, and examples of large computational calculations. The exercises accompanying every chapter will be of great benefit to the student.
CIF2Cell: Generating geometries for electronic structure programs
Björkman, Torbjörn
2011-05-01
The CIF2Cell program generates the geometrical setup for a number of electronic structure programs based on the crystallographic information in a Crystallographic Information Framework (CIF) file. The program will retrieve the space group number, Wyckoff positions and crystallographic parameters, make a sensible choice for Bravais lattice vectors (primitive or principal cell) and generate all atomic positions. Supercells can be generated and alloys are handled gracefully. The code currently has output interfaces to the electronic structure programs ABINIT, CASTEP, CPMD, Crystal, Elk, Exciting, EMTO, Fleur, RSPt, Siesta and VASP. Program summaryProgram title: CIF2Cell Catalogue identifier: AEIM_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIM_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU GPL version 3 No. of lines in distributed program, including test data, etc.: 12 691 No. of bytes in distributed program, including test data, etc.: 74 933 Distribution format: tar.gz Programming language: Python (versions 2.4-2.7) Computer: Any computer that can run Python (versions 2.4-2.7) Operating system: Any operating system that can run Python (versions 2.4-2.7) Classification: 7.3, 7.8, 8 External routines: PyCIFRW [1] Nature of problem: Generate the geometrical setup of a crystallographic cell for a variety of electronic structure programs from data contained in a CIF file. Solution method: The CIF file is parsed using routines contained in the library PyCIFRW [1], and crystallographic as well as bibliographic information is extracted. The program then generates the principal cell from symmetry information, crystal parameters, space group number and Wyckoff sites. Reduction to a primitive cell is then performed, and the resulting cell is output to suitably named files along with documentation of the information source generated from any bibliographic information contained in the CIF
Electronic structure of heterocyclic ring chain polymers
Brocks, Geert; Tol, Arie
1999-01-01
The band gaps, ionization potentials and electron affinities of conjugated chain polymers comprising heterocyclic aromatic rings are studied systematically as a function of atomic substitutions with N, O and S using first principles density functional calculations.
Efficient electronic structure methods applied to metal nanoparticles
Larsen, Ask Hjorth
Nano-scale structures are increasingly applied in the design of catalysts and electronic devices. A theoretical understanding of the basic properties of such systems is enabled through modern electronic structure methods such as density functional theory. This thesis describes the development...... more strongly than large ones. This can be understood mostly as a geometric eect. Convergence of chemisorption energies within 0.1 eV of bulk values happens at about 200 atoms for Pt and 600 atoms for Au. Particularly for O on Au, large variations due to electronic effects are seen for smaller clusters....... The basis set method is used to study the electronic effects for the contiguous range of clusters up to several hundred atoms. The s-electrons hybridize to form electronic shells consistent with the jellium model, leading to electronic magic numbers for clusters with full shells. Large electronic gaps...
Structure problems in the analog computation; Problemes de structure dans le calcul analogique
Braffort, P.L. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1957-07-01
The recent mathematical development showed the importance of elementary structures (algebraic, topological, etc.) in abeyance under the great domains of classical analysis. Such structures in analog computation are put in evidence and possible development of applied mathematics are discussed. It also studied the topological structures of the standard representation of analog schemes such as additional triangles, integrators, phase inverters and functions generators. The analog method gives only the function of the variable: time, as results of its computations. But the course of computation, for systems including reactive circuits, introduces order structures which are called 'chronological'. Finally, it showed that the approximation methods of ordinary numerical and digital computation present the same structure as these analog computation. The structure analysis permits fruitful comparisons between the several domains of applied mathematics and suggests new important domains of application for analog method. (M.P.)
QWalk: A Quantum Monte Carlo Program for Electronic Structure
Wagner, Lucas K; Mitas, Lubos
2007-01-01
We describe QWalk, a new computational package capable of performing Quantum Monte Carlo electronic structure calculations for molecules and solids with many electrons. We describe the structure of the program and its implementation of Quantum Monte Carlo methods. It is open-source, licensed under the GPL, and available at the web site http://www.qwalk.org
Electronic structure of hybrid interfaces for polymer-based electronics.
Fahlman, M; Crispin, A; Crispin, X; Henze, S K M; de Jong, M P; Osikowicz, W; Tengstedt, C; Salaneck, W R
2007-05-08
The fundamentals of the energy level alignment at anode and cathode electrodes in organic electronics are described. We focus on two different models that treat weakly interacting organic/metal (and organic/organic) interfaces: the induced density of interfacial states model and the so-called integer charge transfer model. The two models are compared and evaluated, mainly using photoelectron spectroscopy data of the energy level alignment of conjugated polymers and molecules at various organic/metal and organic/organic interfaces. We show that two different alignment regimes are generally observed: (i) vacuum level alignment, which corresponds to the lack of vacuum level offsets (Schottky-Mott limit) and hence the lack of charge transfer across the interface, and (ii) Fermi level pinning where the resulting work function of an organic/metal and organic/organic bilayer is independent of the substrate work function and an interface dipole is formed due to charge transfer across the interface. We argue that the experimental results are best described by the integer charge transfer model which predicts the vacuum level alignment when the substrate work function is above the positive charge transfer level and below the negative charge transfer level of the conjugated material. The model further predicts Fermi level pinning to the positive (negative) charge transfer level when the substrate work function is below (above) the positive (negative) charge transfer level. The nature of the integer charge transfer levels depend on the materials system: for conjugated large molecules and polymers, the integer charge transfer states are polarons or bipolarons; for small molecules' highest occupied and lowest unoccupied molecular orbitals and for crystalline systems, the relevant levels are the valence and conduction band edges. Finally, limits and further improvements to the integer charge transfer model are discussed as well as the impact on device design.
Topology optimization for acoustic-structure interaction problems
Yoon, Gil Ho; Jensen, Jakob Søndergaard; Sigmund, Ole
2006-01-01
We propose a gradient based topology optimization algorithm for acoustic-structure (vibro-acoustic) interaction problems without an explicit interfacing boundary representation. In acoustic-structure interaction problems, the pressure field and the displacement field are governed by the Helmholtz...... to subdomain interfaces evolving during the optimization process. In this paper, we propose to use a mixed finite element formulation with displacements and pressure as primary variables (u/p formulation) which eliminates the need for explicit boundary representation. In order to describe the Helmholtz...
Model reduction for optimization of structural-acoustic coupling problems
Creixell Mediante, Ester; Jensen, Jakob Søndergaard; Brunskog, Jonas;
2016-01-01
, which becomes highly time consuming since many iterations may be required. The use of model reduction techniques to speed up the computations is studied in this work. The Component Mode Synthesis (CMS) method and the Multi-Model Reduction (MMR) method are adapted for problems with structure......Fully coupled structural-acoustic models of complex systems, such as those used in the hearing aid field, may have several hundreds of thousands of nodes. When there is a strong structure-acoustic interaction, performing optimization on one part requires the complete model to be taken into account...
Moeck, Peter; Rouvimov, Sergei; Nicolopoulos, Stavros
2009-09-01
Precession electron diffraction (PED) in a transmission electron microscope (TEM) is discussed in order to illustrate its utility for structural fingerprinting of nanocrystals. While individual nanocrystals may be fingerprinted structurally from PED spot patterns, ensembles of nanocrystals may be fingerprinted from powder PED ring patterns.
On the electronic structure of fullerene anions
Bergomi, L.; Jolicoeur, T. (CEA Centre d' Etudes de Saclay, 91 - Gif-sur-Yvette (France). Service de Physique Theorique)
1994-02-03
The authors study the electronic states of isolated fullerene anions C[sub 60][sup n-] (1 [<=] n [<=] 6) taking into account the effective interaction between electrons due to exchange of intramolecular phonons. If the vibronic coupling is strong enough such an effect may overwhelm Hund's rule and lead to an ordering of levels that can be interpreted as on-ball pairing, in a manner similar to the pairing in atomic nuclei. The authors suggest that such effects may be sought in solutions of fulleride ions and discuss recent experimental results.
Sutirman; Muhyadi; Surjono, Herman Dwi
2017-01-01
This study aims to investigate the learning implementation of electronic filing and problems faced by teachers in learning implementing of electronic filing. This study is a descriptive research with qualitative approach. Collecting data used interview and documentation techniques. The research subjects consisted of 29 teachers who teach Filing…
Structural simplicity and complexity of compressed calcium: electronic origin.
Degtyareva, Valentina F
2014-06-01
A simple cubic structure with one atom in the unit cell found in compressed calcium is counterintuitive to the traditional view of a tendency towards densely packed structures with an increase in pressure. To understand this unusual transformation it is necessary to assume electron transfer from the outer core band to the valence band, and an increase of valence electron number for calcium from 2 to ∼ 3.5. This assumption is supported by the Fermi sphere-Brillouin zone interaction model that increases under compression. The recently found structure of Ca-VII with a tetragonal cell containing 32 atoms (tI32) is similar to that in the intermetallic compound In5Bi3 with 3.75 valence electrons per atom. Structural relations are analyzed in terms of electronic structure resemblance. Correlations of structure and physical properties of Ca are discussed.
Electron crystallography for structural and functional studies of membrane proteins.
Fujiyoshi, Yoshinori
2011-01-01
Membrane proteins are important research targets for basic biological sciences and drug design, but studies of their structure and function are considered difficult to perform. Studies of membrane structures have been greatly facilitated by technological and instrumental advancements in electron microscopy together with methodological advancements in biology. Electron crystallography is especially useful in studying the structure and function of membrane proteins. Electron crystallography is now an established method of analyzing the structures of membrane proteins in lipid bilayers, which resembles their natural biological environment. To better understand the neural system function from a structural point of view, we developed the cryo-electron microscope with a helium-cooled specimen stage, which allows for analysis of the structures of membrane proteins at a resolution higher than 3 Å. This review introduces recent instrumental advances in cryo-electron microscopy and presents some examples of structure analyses of membrane proteins, such as bacteriorhodopsin, water channels and gap junction channels. This review has two objectives: first, to provide a personal historical background to describe how we came to develop the cryo-electron microscope and second, to discuss some of the technology required for the structural analysis of membrane proteins based on cryo-electron microscopy.
Electronic Structures of LNA Phosphorothioate Oligonucleotides
Bohr, Henrik G.; Shim, Irene; Stein, Cy
2017-01-01
or differentiate between the individual PS diastereoisomers determined by the position of sulfur atoms. Rules are derived from the electronic calculations of these molecules and include the effects of the phosphorothioate chirality and formation of electrostatic potential surfaces. Physical and electrochemical...
Electronic Properties of low dimensional structures
Bendounan, Azzedine
2010-01-01
Exotic phenomena about the behavior of electrons inside the solid were a long time ago predicted by the quantum mechanic physics and are only recently experimentally observed, in particular for systems of extremely reduced dimensions. Here, I report on recent experimental observation of fundamental effect concerning the dispersion properties of the surface state influenced by the presence of surface reconstruction.
Orbital Models and Electronic Structure Theory
Linderberg, Jan
2012-01-01
This tribute to the work by Carl Johan Ballhausen focuses on the emergence of quantitative means for the study of the electronic properties of complexes and molecules. Development, refinement and application of the orbital picture elucidated electric and magnetic features of ranges of molecules...
THEORETICAL STUDY ON ELECTRONIC STRUCTURES AND ...
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method and density function theory (DFT) at B3LYP/6-31G(d) level. ... and the increase in the number of thiophene rings in the derivatives lead to the decrease ... At the same time, the first absorptions in the electronic spectra and the stretching ...
Towards Structural Testing of Superconductor Electronics
Arun, A.J.; Kerkhoff, Hans G.
2003-01-01
Many of the semiconductor technologies are already facing limitations while new-generation data and telecommunication systems are implemented. Although in its infancy, superconductor electronics (SCE) is capable of handling some of these high-end tasks. We have started a defect-oriented test
Mixing Problem Based Learning And Conventional Teaching Methods In An Analog Electronics Course
Podges, J.M.; Kommers, P.A.M.; Winnips, K.; Joolingen, van W.R.
2014-01-01
This study, undertaken at the Walter Sisulu University of Technology (WSU) in South Africa, describes how problem-based learning (PBL) affects the first year ‘analog electronics course’, when PBL and the lecturing mode is compared. Problems were designed to match real-life situations. Data betwee
Mixing Problem Based Learning And Conventional Teaching Methods In An Analog Electronics Course
Podges, J.M.; Kommers, Petrus A.M.; Winnips, K.; van Joolingen, Wouter
2014-01-01
This study, undertaken at the Walter Sisulu University of Technology (WSU) in South Africa, describes how problem-based learning (PBL) affects the first year ‘analog electronics course’, when PBL and the lecturing mode is compared. Problems were designed to match real-life situations. Data between
An Electronic Library-Based Learning Environment for Supporting Web-Based Problem-Solving Activities
Tsai, Pei-Shan; Hwang, Gwo-Jen; Tsai, Chin-Chung; Hung, Chun-Ming; Huang, Iwen
2012-01-01
This study aims to develop an electronic library-based learning environment to support teachers in developing web-based problem-solving activities and analyzing the online problem-solving behaviors of students. Two experiments were performed in this study. In study 1, an experiment on 103 elementary and high school teachers (the learning activity…
High resolution inelastic electron scattering and nuclear structure
Blok, H. B.; Heisenberg, J. H.
Thanks to the improved characteristics of the experimental set-up electron scattering has become an excellent tool to study the structure of the nucleus. After describing globally how the nuclear structure enters in the formalism of (e,e') reactions and how the high experimental resolution is obtained, several examples of the use of electron scattering for the study of specific nuclear structure questions are discussed.
Electron vortex magnetic holes: a nonlinear coherent plasma structure
Haynes, Christopher T; Camporeale, Enrico; Sundberg, Torbjorn
2014-01-01
We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional PIC simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is ...
Anionic substituent control of the electronic structure of aromatic nitrenes.
Rau, Nathan J; Welles, Emily A; Wenthold, Paul G
2013-01-16
The electronic structures of phenylnitrenes with anionic π-donating substituents are investigated by using mass spectrometry and electronic structure calculations. Reactions of para-CH(2)(-)-substituted phenylnitrene, formed by dissociative deprotonation of p-azidotoluene, with CS(2) and NO indicate that it has a closed-shell singlet ground state, whereas reactions of p-oxidophenylnitrene formed by dissociative deprotonation of p-azidophenol indicate either a triplet ground state or a singlet with a small singlet-triplet splitting. The ground electronic state assignments based on ion reactivity are consistent with electronic structure calculations. The stability of the closed-shell singlet states in nitrenes is shown by Natural Resonance Theory to be very sensitive to the amount of deprotonated-imine character in the wave function, such that large changes in state energies can be achieved by small modifications of the electronic structure.
The Similar Structures and Control Problems of Complex Systems
无
2002-01-01
In this paper, the naturally evolving complex systems, such as biotic and social ones, are considered. Focusing on their structures, a feature is noteworthy, i.e., the similarity in structures. The relations between the functions and behaviors of these systems and their similar structures will be studied. Owing to the management of social systems and the course of evolution of biotic systems may be regarded as control processes, the researches will be within the scope of control problems. Moreover, since it is difficult to model for biotic and social systems, it will start with the control problems of complex systems, possessing similar structures, in engineering.The obtained results show that for either linear or nonlinear systems and for a lot of control problemssimilar structures lead to a series of simplifications. In general, the original system may be decomposed into reduced amount of subsystems with lower dimensions and simpler structures. By virtue of such subsystems, the control problems of original system can be solved more simply.At last, it turns round to observe the biotic and social systems and some analyses are given.
Sensitivity analysis of fluid-structure interaction problems
Etienne, S.; Pelletier, D. [Ecole Polytechnique de Montreal, Montreal, Quebec (Canada)]. E-mail: stephane.etienne@polymtl.ca
2004-07-01
Interactions between solids and fluids (FSI) have been a topic of interest for engineers for many years. The behavior of vessels subject to wave loads, of planes in flight condition as well as submarine or transmission lines are but a few examples. In an attempt to address these problems, the present paper presents a formulation which allows to treat interactions between an incompressible flow and a structure undergoing large displacements. We assume existence and unicity of the solution. The interested reader is referred, for a mathematical discussion of existence and unicity. The approach to coupling can be addressed in two ways: weakly-coupled methods for which algorithms for structure and fluid are segregated, as is commonly done for simplicity and often because engineers have access to existing structural and fluid codes; and tightly-coupled or monolithic methods, for which the formulation guarantees satisfaction of equilibrium of the interface between the fluid and the solid. The latter has been chosen as it allows for quadratic convergence of Newton's method. The paper begins with the description of the steady state governing equations for laminar incompressible fluids, hyperelastic solid behaviour, pseudo-solid mapping and fluid-structure interfaces. The weak forms of the equations are then presented. We proceed with the description of the continuous sensitivity equations for fluid-structure interactions problems. The following sections detail the adaptive finite element procedure for the fluid-structure interaction and sensitivity problems. Results are presented and the paper ends with conclusions and discussions. (author)
Syntheses and electronic structures of decamethylmetallocenes
Robbins, J.L.
1981-04-01
The synthesis of decamethylmanganocene ((eta-C/sub 5/(CH/sub 3/)/sub 5/)/sub 2/Mn or (Me/sub 5/Cp)/sub 2/Mn)) is described. Magnetic susceptibility and electron paramagnetic resonance (EPR) studies show that (Me/sub 5/Cp)/sub 2/Mn is a low-spin, 17-electron compound with an orbitally degenerate, /sup 2/E/sub 2g/ (e/sub 2g//sup 3/ a/sub 1g//sup 2/) ground state. An x-ray crystallographic study of (Me/sub 5/Cp)/sub 2/Mn shows that it is a monomeric, D/sub 5d/ decamethylmetallocene with metal to ring carbon distances that are about 0.3 A shorter than those determined for high-spin manganocenes. The syntheses of new (Me/sub 5/Cp)/sub 2/M (M = Mg,V,Cr,Co, and Ni) and ((Me/sub 5/Cp)/sub 2/M)PF/sub 6/ (M = Cr,Co, and Ni) compounds are described. In addition, a preparative route to a novel, dicationic decamethylmetallocene, ((Me/sub 5/Cp)/sub 2/Ni)(PF/sub 6/)/sub 2/ is reported. Infrared, nuclear magnetic resonance, magnetic susceptibility, and/or x-ray crystallographic studies indicate that all the above compounds are D/sub 5d/ or D/sub 5h/ decamethylmetallocenes with low-spin electronic configurations. Cyclic voltammetry studies verify the reversibility and the one-electron nature of the (Me/sub 5/Cp)/sub 2/M ..-->.. ((Me/sub 5/Cp)/sub 2/M)/sup +/ (M = Cr,Mn,Fe,Co,Ni), ((Me/sub 5/Cp)/sub 2/Mn)/sup -/ ..-->.. (Me/sub 5/Cp)/sub 2/Mn and ((Me/sub 5/Cp)/sub 2/Ni)/sup +/ ..-->.. (Me/sub 5/Cp)/sub 2/Ni)/sup 2 +/ redox reactions. These studies reveal that the neutral decamethylmetallocenes are much more easily oxidized than their metallocene counterparts. This result attests to the electron-donating properties of the ten substituent methyl groups. Proton and carbon-13 NMR data are reported for the diamagnetic Mg(II), Mn(I), Fe(II), Co(III), and Ni(IV) decamethylmetallocenes and for ((Me/sub 5/Cp)/sub 2/V(CO)/sub 2/)/sup +/. The uv-visible absorption spectra of the 15-, 18- and 20- electron decamethylmetallocenes are also reported.
Structural analysis for diagnosis with application to ship propulsion problem
Izadi-Zamanabadi, Roozbeh; Blanke, Mogens
2002-01-01
Aiming at design of algorithms for fault diagnosis, structural analysis of systems offers concise yet easy overall analysis. Graph-based matching, which is the essential tech-nique to obtain redundant information for diagnosis, is reconsidered in this paper. Matching is reformulated as a problem ...
Structural analysis for diagnosis with application to ship propulsion problem
Izadi-Zamanabadi, Roozbeh; Blanke, Mogens
2002-01-01
Aiming at design of algorithms for fault diagnosis, structural analysis of systems offers concise yet easy overall analysis. Graph-based matching, which is the essential tech-nique to obtain redundant information for diagnosis, is reconsidered in this paper. Matching is reformulated as a problem...
Cimrman, Robert; Kolman, Radek; Tůma, Miroslav; Vackář, Jiří
2015-01-01
We compare convergence of isogeometric analysis (IGA), a spline modification of finite element method (FEM), with FEM in the context of our real space code for ab-initio electronic structure calculations of non-periodic systems. The convergence is studied on simple sub-problems that appear within the density functional theory approximation to the Schr\\"odinger equation: the Poisson problem and the generalized eigenvalue problem. We also outline the complete iterative algorithm seeking a fixed point of the charge density of a system of atoms or molecules, and study IGA/FEM convergence on a benchmark problem of nitrogen atom.
Crystal structure from one-electron theory
Skriver, H. L.
1985-01-01
The authors have studied the crystal structure of all the 3d, 4d, and 5d transition metals at zero pressure and temperature by means of the linear muffin-tin orbital method and Andersen's force theorem. They find that, although the structural energy differences seem to be overestimated by the the......The authors have studied the crystal structure of all the 3d, 4d, and 5d transition metals at zero pressure and temperature by means of the linear muffin-tin orbital method and Andersen's force theorem. They find that, although the structural energy differences seem to be overestimated...... by the theory, the predicted crystal structures are in accord with experiment in all cases except 79Au. In addition, they have investigated the effect of pressure upon the alkali metals (3Li, 11Na, 37Rb, 55Cs) and selected lanthanide metals (57La, 58Ce, 71Lu) and actinide metals (90Th, 91Pa). In these cases...
Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics.
Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios
2016-10-31
In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.
CISM Second Meeting on Unilateral Problems in Structural Analysis
Maceri, F
1987-01-01
The volume collects the contributions presented at the second meeting on Unilateral Problems, organized by CISM and held near Udine in June 1985. It gives an updated account of the state-of-the-art in the field of unilateral problems, with an outlook on open problems and on perspectives of application to structural analysis. The topic is presently the object of growing interest and is undergoing very rapid development. One of the most noticeable characteristics of unilateral problems is their interdisciplinary nature; they involve sophisticated mathematics, fundamental questions in mechanics, modern techniques in numerical analysis, re-inspection of the present knowledge of physical phenomena, and engineering applications. This volume succeeds in collecting and coordinating contributions from all these areas. For this reason, it is an excellent source of information for researchers working in the field.
d0 Perovskite-Semiconductor Electronic Structure
Bistritzer, R.; Khalsa, G.; MacDonald, A. H.
2010-01-01
We address the low-energy effective Hamiltonian of electron doped d0 perovskite semiconductors in cubic and tetragonal phases using the k*p method. The Hamiltonian depends on the spin-orbit interaction strength, on the temperature-dependent tetragonal distortion, and on a set of effective-mass parameters whose number is determined by the symmetry of the crystal. We explain how these parameters can be extracted from angle resolved photo-emission, Raman spectroscopy, and magneto-transport measu...
Towards Structural Testing of Superconductor Electronics
Arun, A.J.; Kerkhoff, Hans G.
2003-01-01
Many of the semiconductor technologies are already facing limitations while new-generation data and telecommunication systems are implemented. Although in its infancy, superconductor electronics (SCE) is capable of handling some of these high-end tasks. We have started a defect-oriented test methodology for SCE, so that reliable systems can be implemented in this technology. In this paper, the details of the study on the Rapid Single-Flux Quantum (RSFQ) process are presented. We present commo...
Mahmoudian, Morteza
1980-01-01
Language is viewed as a nonhomogeneous hierarchical system, where complex correlations between a psychological/social dimension (external) and a linguistic dimension (internal) permit measurements of the stability and acceptability of its structures. Frequency of occurrence and integration in the system are presented as the key factors in the…
Electronic structures and physical properties of pure aluminum metal
谢佑卿; 刘心笔
1999-01-01
By one-atom theory, the electronic structure of pure Al metal with f.c.c, structure has been determined to be [Ne]（3sc）1.8790（3pc）0.4982（3sf+3pf）0.6228. According to this electronic structure, the potential curve, lattice constant, cohesive energy, elastisity, and the temperature dependence of the linear thermal expansion coefficients have been calculated. The electronic structures and characteristic properties of Al metals with b. c. c., h.c.p. structures and liquid have been studied. It is argued that the pure Al metal with f. c.c. structure can exist naturally, but with b. c. c.and h. c.p. structures cannot.##属性不符
Quantum inferring acausal structures and the Monty Hall problem
Kurzyk, Dariusz; Glos, Adam
2016-09-01
This paper presents a quantum version of the Monty Hall problem based upon the quantum inferring acausal structures, which can be identified with generalization of Bayesian networks. Considered structures are expressed in formalism of quantum information theory, where density operators are identified with quantum generalization of probability distributions. Conditional relations between quantum counterpart of random variables are described by quantum conditional operators. Presented quantum inferring structures are used to construct a model inspired by scenario of well-known Monty Hall game, where we show the differences between classical and quantum Bayesian reasoning.
Spatially-Structured Sharing Technique for Multimodal Problems
Grant Dick; Peter Whigham
2008-01-01
Spatially-structured populations are one approach to increasing genetic diversity in an evolutionary algorithm (EA). However, they are suscptible to convergence to a single peak in a multimodal fitness landscape. Niching methods, such as fitness sharing, allow an EA to maintain multiple solutions in a single population, however they have rarely been used in conjunction with spatially-structured populations. This paper introduces local sharing, a method that applies sharing to the overlapping demes of a spatially-structured population. The combination of these two methods succeeds in maintaining multiple solutions in problems that have previously proved difficult for sharing alone (and vice-versa).
One-Electron Theory of Metals. Cohesive and Structural Properties
Skriver, Hans Lomholt
by means of the Linear Muffin-Tin Orbital (LMTO) method. It has been the goal of the work to establish how well this one-electron approach describes physical properties such as the crystal structures of the transition metals, the structural phase transitions in the alkali, alkaline earth, and rare earth......The work described in the report r.nd the 16 accompanying publications is based upon a one-electron theory obtained within the local approximation to density-functional theory, and deals with the ground state of metals as obtained from selfconsistent electronic-structure calculations performed...
Structural problems of mining region innovative development (Kuzbass, Western Siberia
Dotsenko Elena
2017-01-01
Full Text Available At present, the issues of overcoming the negative structural shift in Russian economy, accelerating economic growth, reducing technological and social- and-economic gap between Russia and the developed countries are strategically important. Modern structure of Russian economy which had been developed as a part of market model does not generate the innovative type of development. In this situation, mining regions, the structure of which was formed in the early 20th century and is represented by the extractive industries, are undergoing the greatest problems of innovative development. Therefore, despite high urbanization and industrial development level the economy of Kuzbass (Western Siberia, Russia is characterized by significant structural problems. They are associated with primary extractive nature of the regional industry, in which coal and iron ore, metallurgical and chemical industries dominate. They highly depend on Russian and global market of raw materials, widely use low-productive technologies, and they are characterized by high level of fixed capital depreciation and insufficient pace of innovative infrastructure development. The solution of the structural problems of economic development of mining region is connected with technological modernization of extractive industries and use of modern materials for the production of high-tech products.
Topology optimization of coated structures and material interface problems
Clausen, Anders; Aage, Niels; Sigmund, Ole
2015-01-01
This paper presents a novel method for including coated structures and prescribed material interface properties into the minimum compliance topology optimization problem. Several elements of the method are applicable to a broader range of interface problems. The approach extends the standard SIMP...... method by including the normalized norm of the spatial gradient of the design field into the material interpolation function, enforcing coating material at interfaces by attributing particular properties. The length scales of the base structure and the coating are separated by introducing a two......-step filtering/projection approach. The modeled coating thickness is derived analytically, and the coating is shown to be accurately controlled and applied in a highly uniform manner over the structure. An alternative interpretation of the model is to perform single-material design for additive manufacturing...
Topology optimization of coated structures and material interface problems
Clausen, Anders; Aage, Niels; Sigmund, Ole
2015-01-01
This paper presents a novel method for including coated structures and prescribed material interface properties into the minimum compliance topology optimization problem. Several elements of the method are applicable to a broader range of interface problems. The approach extends the standard SIMP...... method by including the normalized norm of the spatial gradient of the design field into the material interpolation function, enforcing coating material at interfaces by attributing particular properties. The length scales of the base structure and the coating are separated by introducing a two......-step filtering/projection approach. The modeled coating thickness is derived analytically, and the coating is shown to be accurately controlled and applied in a highly uniform manner over the structure. An alternative interpretation of the model is to perform single-material design for additive manufacturing...
Waal, van de B.W.
1999-01-01
An up-to-date overview of recent developments in the structure elucidation of large ArN-clusters (103
Electronic Structure of Pi Systems: Part III--Applications in Spectroscopy and Chemical Reactivity.
Fox, Marye Anne; Matsen, F. A.
1985-01-01
Shows that electronic structure diagrams make more accurate predictions of spectral properties and chemical reactivity for simple pi systems than do either Huckel molecular orbital or valence bond theory alone. Topics addressed include absorption and photoelectron spectra, spin density distribution in radicals, and several problems regarding…
Electron beam joining of structural ceramics
Turman, B.N.; Glass, S.J.; Halbleib, J.A.; Helmich, D.R.; Loehman, R.E.
1995-04-01
Feasibility of ceramic joining using a high energy (10 MeV) electron beam. The experiments used refractory metals as bonding materials in buried interfaces between Si{sub 3}N{sub 4} pieces. Because the heat capacity of the metal bonding layer is much lower than the ceramic, the metal reaches much higher temperatures than the adjoining ceramic. Using the right combination of beam parameters allows the metal to be melted without causing the adjoining ceramics to melt or decompose. Beam energy deposition and thermal simulations were performed to guide the experiments. Joints were shear tested and interfaces between the metal and the ceramic were examined to identify the bonding mechanism. Specimens joined by electron beams were compared to specimens produced by hot-pressing. Similar reactions occurred using both processes. Reactions between the metal and ceramic produced silicides that bond the metal to the ceramic. The molybdenum silicide reaction products appeared to be more brittle than the platinum silicides. Si{sub 3}N{sub 4} was also joined to Si{sub 3} N{sub 4} directly. The bonding appears to have been produced by the flow of intergranular glass into the interface. Shear strength was similar to the metal bonded specimens. Bend specimens Of Si{sub 3}N{sub 4} were exposed to electron beams with similar parameters to those used in joining experiments to determine how beam exposure degrades the strength. Damage was macroscopic in nature with craters being tonned by material ablation, and cracking occurring due to excessive thermal stresses. Si was also observed on the surface indicating the Si{sub 3}N{sub 4} was decomposing. Bend strength after exposure was 62% of the asreceived strength. No obvious microstructural differences were observed in the material close to the damaged region compared to material in regions far away from the damage.
Writing silica structures in liquid with scanning transmission electron microscopy.
van de Put, Marcel W P; Carcouët, Camille C M C; Bomans, Paul H H; Friedrich, Heiner; de Jonge, Niels; Sommerdijk, Nico A J M
2015-02-04
Silica nanoparticles are imaged in solution with scanning transmission electron microscopy (STEM) using a liquid cell with silicon nitride (SiN) membrane windows. The STEM images reveal that silica structures are deposited in well-defined patches on the upper SiN membranes upon electron beam irradiation. The thickness of the deposits is linear with the applied electron dose. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrate that the deposited patches are a result of the merging of the original 20 nm-diameter nanoparticles, and that the related surface roughness depends on the electron dose rate used. Using this approach, sub-micrometer scale structures are written on the SiN in liquid by controlling the electron exposure as function of the lateral position.
A framework for solving ill-structured community problems
Keller, William Cotesworth
A multifaceted protocol for solving ill-structured community problems has been developed. It embodies the lessons learned from the past by refining and extending features of previous models from the systems thinkers, and the fields of behavioral decision making and creative problem solving. The protocol also embraces additional features needed to address the unique aspects of community decision situations. The essential elements of the protocol are participants from the community, a problem-solving process, a systems picture, a facilitator, a modified Delphi method of communications, and technical expertise. This interdisciplinary framework has been tested by a quasi experiment with a real world community problem (the high cost of electrical power on Long Island, NY). Results indicate the protocol can enable members of the community to understand a complicated, ill-structured problem and guide them to action to solve the issue. However, the framework takes time (over one year in the test case) and will be inappropriate for crises where quick action is needed.
Nodal Structure of the Electronic Wigner Function
Schmider, Hartmut; Dahl, Jens Peder
1996-01-01
On the example of several atomic and small molecular systems, the regular behavior of nodal patterns in the electronic one-particle reduced Wigner function is demonstrated. An expression found earlier relates the nodal pattern solely to the dot-product of the position and the momentum vector......, if both arguments are large. An argument analogous to the ``bond-oscillatory principle'' for momentum densities links the nuclear framework in a molecule to an additional oscillatory term in momenta parallel to bonds. It is shown that these are visible in the Wigner function in terms of characteristic...
MSClique: Multiple Structure Discovery through the Maximum Weighted Clique Problem.
Sanroma, Gerard; Penate-Sanchez, Adrian; Alquézar, René; Serratosa, Francesc; Moreno-Noguer, Francesc; Andrade-Cetto, Juan; González Ballester, Miguel Ángel
2016-01-01
We present a novel approach for feature correspondence and multiple structure discovery in computer vision. In contrast to existing methods, we exploit the fact that point-sets on the same structure usually lie close to each other, thus forming clusters in the image. Given a pair of input images, we initially extract points of interest and extract hierarchical representations by agglomerative clustering. We use the maximum weighted clique problem to find the set of corresponding clusters with maximum number of inliers representing the multiple structures at the correct scales. Our method is parameter-free and only needs two sets of points along with their tentative correspondences, thus being extremely easy to use. We demonstrate the effectiveness of our method in multiple-structure fitting experiments in both publicly available and in-house datasets. As shown in the experiments, our approach finds a higher number of structures containing fewer outliers compared to state-of-the-art methods.
Regularizing the molecular potential in electronic structure calculations. II. Many-body methods
Bischoff, Florian A., E-mail: florian.bischoff@hu-berlin.de [Institut für Chemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin (Germany)
2014-11-14
In Paper I of this series [F. A. Bischoff, “Regularizing the molecular potential in electronic structure calculations. I. SCF methods,” J. Chem. Phys. 141, 184105 (2014)] a regularized molecular Hamilton operator for electronic structure calculations was derived and its properties in SCF calculations were studied. The regularization was achieved using a correlation factor that models the electron-nuclear cusp. In the present study we extend the regularization to correlated methods, in particular the exact solution of the two-electron problem, as well as second-order many body perturbation theory. The nuclear and electronic correlation factors lead to computations with a smaller memory footprint because the singularities are removed from the working equations, which allows coarser grid resolution while maintaining the precision. Numerical examples are given.
Basis functions for electronic structure calculations on spheres
Gill, Peter M W; Agboola, Davids
2014-01-01
We introduce a new basis function (the spherical gaussian) for electronic structure calculations on spheres of any dimension $D$. We find \\alert{general} expressions for the one- and two-electron integrals and propose an efficient computational algorithm incorporating the Cauchy-Schwarz bound. Using numerical calculations for the $D = 2$ case, we show that spherical gaussians are more efficient than spherical harmonics when the electrons are strongly localized.
Electronic structure and equilibrium properties of hcp titanium and zirconium
B P Panda
2012-08-01
The electronic structures of hexagonal-close-packed divalent titanium (3-d) and zirconium (4-d) transition metals are studied by using a non-local model potential method. From the present calculation of energy bands, Fermi energy, density of states and the electronic heat capacity of these two metals are determined and compared with the existing results in the literature.
Electron vortex magnetic holes: A nonlinear coherent plasma structure
Haynes, C.T.; Burgess, D.; Camporeale, E.; Sundberg, T.
2015-01-01
We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic
Electronic Structure of Au25 Clusters: Between Discrete and Continuous
Katsiev, Khabiboulakh
2016-07-15
Here, an approach based on synchrotron resonant photoemission is emplyed to explore the transition between quantization and hybridization of the electronic structure in atomically precise ligand-stabilized nanoparticles. While the presence of ligands maintains quantization in Au25 clusters, their removal renders increased hybridization of the electronic states at the vicinity of the Fermi level. These observations are supported by DFT studies.
Structure functions in electron-nucleon deep inelastic scattering
Saleem, M.; Fazal-E-Aleem (University of the Punjab, Lahore (Pakistan). Dept. of Physics)
1982-06-26
The phenomenological expressions for the structure functions in electron-nucleon deep inelastic scattering are proposed and are shown to satisfy the experimental data as well as a number of sum rules.
Electron Diffraction Determination of Nanoscale Structures
Parks, Joel H
2013-03-01
Dominant research results on adsorption on gold clusters are reviewed, including adsorption of H{sub 2}O and O{sub 2} on gold cluster cations and anions, kinetics of CO adsorption to middle sized gold cluster cations, adsorption of CO on Au{sub n}{sup +} with induced changes in structure, and H{sub 2}O enhancement of CO adsorption.
Dornburg, Courtney C; Stevens, Susan M; Hendrickson, Stacey M L; Davidson, George S
2009-08-01
An experiment was conducted to compare the effectiveness of individual versus group electronic brainstorming to address difficult, real-world challenges. Although industrial reliance on electronic communications has become ubiquitous, empirical and theoretical understanding of the bounds of its effectiveness have been limited. Previous research using short-term laboratory experiments have engaged small groups of students in answering questions irrelevant to an industrial setting. The present experiment extends current findings beyond the laboratory to larger groups of real-world employees addressing organization-relevant challenges during the course of 4 days. Employees and contractors at a national laboratory participated, either in a group setting or individually, in an electronic brainstorm to pose solutions to a real-world problem. The data demonstrate that (for this design) individuals perform at least as well as groups in producing quantity of electronic ideas, regardless of brainstorming duration. However, when judged with respect to quality along three dimensions (originality, feasibility, and effectiveness), the individuals significantly (p < .05) outperformed the group. When quality is used to benchmark success, these data indicate that work-relevant challenges are better solved by aggregating electronic individual responses rather than by electronically convening a group. This research suggests that industrial reliance on electronic problem-solving groups should be tempered, and large nominal groups may be more appropriate corporate problem-solving vehicles.
Tailoring electronic structure of polyazomethines thin films
J. Weszka
2010-09-01
Full Text Available Purpose: The aim of this work is to show how electronic properties of polyazomethine thin films deposited by chemical vapor deposition method (CVD can be tailored by manipulating technological parameters of pristine films preparation as well as modifying them while the as-prepared films put into iodine atmosphere.Design/methodology/approach: The recent achievements in the field of designing and preparation methods to be used while preparing polymer photovoltaic solar cells or optoelectronic devices.Findings: The method used allow for pure pristine polymer thin films to be prtepared without any unintentional doping taking place during prepoaration methods. This is a method based on polycondensation process, where polymer chain developing is running directly due to chemical reaction between molecules of bifunctional monomers. The method applied to prepare thin films of polyazomethines takes advantage of monomer transporting by mreans of neutral transport agent as pure argon is.Research limitations/implications: The main disadvantage of alternately conjugated polymers seems to be quite low mobility of charge carrier that is expected to be a consequence of their backbone being built up of sp2 hybridized carbon and nitrogen atoms. Varying technological conditions towards increasing reagents mass transport to the substrate is expected to give such polyazomethine thin films organization that phenylene rin stacking can result in special π electron systems rather than linear ones as it is the case.Originality/value: Our results supply with original possibilities which can be useful in ooking for good polymer materials for optoelectronic and photovoltaic applications. These results have been gained on polyazomethine thin films but their being isoelectronic counterpart to widely used poly p-phenylene vinylene may be very convenient to develop high efficiency polymer solar cells
Data Structures: Sequence Problems, Range Queries, and Fault Tolerance
Jørgensen, Allan Grønlund
for a range of sequence analysis problems that have risen from applications in pattern matching, bioinformatics, and data mining. On a high level, each problem is dened by a function and some constraints and the job at hand is to locate subsequences that score high with this function and are not invalidated...... a certain function on the elements in a given query subsequence. There are many types of functions that has been considered in connection with input from dierent sources. The input could be ip-data sorted by ip-address, real estate prices sorted by zip code, advertising cost sorted by time etc. We consider...... data structures for two classic statistics functions, namely median and mode. Finally, Part III investigates fault tolerant algorithms and data structures. This deals with the trend of avoiding elaborate error checking and correction circuitry that would impose non-negligible costs in terms of hardware...
Topology optimization for acoustic-structure interaction problems
Yoon, Gil Ho; Jensen, Jakob Søndergaard; Sigmund, Ole
2006-01-01
We propose a gradient based topology optimization algorithm for acoustic-structure (vibro-acoustic) interaction problems without an explicit interfacing boundary representation. In acoustic-structure interaction problems, the pressure field and the displacement field are governed by the Helmholtz...... equation and the linear elasticity equation, respectively, and it is necessary that the governing equations should be properly evolved with respect to the design variables in the design domain. Moreover, all the boundary conditions obtained by computing surface coupling integrals should be properly imposed...... to subdomain interfaces evolving during the optimization process. In this paper, we propose to use a mixed finite element formulation with displacements and pressure as primary variables (u/p formulation) which eliminates the need for explicit boundary representation. In order to describe the Helmholtz...
Center of Gravity within the Ill-Structured Problem
2012-05-04
one of the most important tasks during the early stages of planning. 25 It is critical to understand that the purpose of identifying the enemy’s...train to them. Planning exercises within ill-structure problems need to be incorporated at all levels of command and training. It will do us little...theories when he said, We wanted to show that every age had its own kind of war, its own limiting conditions, and own peculiar preconceptions
Contrast structure for singular singularly perturbed boundary value problem
王爱峰; 倪明康
2014-01-01
The step-type contrast structure for a singular singularly perturbed problem is shown. By use of the method of boundary function, the formal asymptotic expansion is constructed. At the same time, based on sewing orbit smooth, the existence of the step-type solution and the uniform validity of the asymptotic expansion are proved. Finally, an example is given to demonstrate the effectiveness of the present results.
Electronic structure and magnetism of ThFeAsN
Wang, Guangtao; Shi, Xianbiao
2016-03-01
The electronic structure and magnetic properties of ThFeAsN, a newly discovered superconductor, are investigated by means of first-principles calculations. ThFeAsN shares electronic structure and magnetic properties similar to those of LaOFeAs. Its calculated ground state is the stripe antiferromagnetic state. The hole-like Fermi surfaces (FSs) along the Γ\\text-Z line largely overlap with the electron-like FS along the M\\text-A line with the vector q= (π, π, 0) . Such significant FS nesting induces a peak of the bare susceptibility χ0(q ) at the M-point.
Electronic structure of EuFe2As2.
Adhikary, Ganesh; Sahadev, Nishaina; Biswas, Deepnarayan; Bindu, R; Kumar, Neeraj; Thamizhavel, A; Dhar, S K; Maiti, Kalobaran
2013-06-01
Employing high resolution photoemission spectroscopy, we studied the temperature evolution of the electronic structure of EuFe2As2, a unique pnictide, where antiferromagnetism of the Eu layer survives within the superconducting phase due to 'FeAs' layers, achieved via substitution and/or pressure. High energy and angle resolution helped to reveal the signature of peak-dip features, having significant p orbital character and spin density wave transition induced band folding in the electronic structure. A significant spectral weight redistribution is observed below 20 K manifesting the influence of antiferromagnetic order on the conduction electrons.
Solitary structures with ion and electron thermal anisotropy
Khusroo, Murchana
2015-01-01
Formation of electrostatic solitary structures are analysed for a magnetised plasma with ion and electron thermal anisotropies. The ion thermal anisotropy is modelled with the help of the Chew-Goldberger-Low (CGL) double adiabatic equations of state while the electrons are treated as inertia-less species with an anisotropic bi-Maxwellian velocity distribution function. A negative electron thermal anisotropy $(T_{e\\perp}/T_e{\\parallel}>1)$ is found to help form large amplitude solitary structures which are in agreement with observational data.
Electronic structure calculations of ESR parameters of melanin units.
Batagin-Neto, Augusto; Bronze-Uhle, Erika Soares; Graeff, Carlos Frederico de Oliveira
2015-03-21
Melanins represent an important class of natural pigments present in plants and animals that are currently considered to be promising materials for applications in optic and electronic devices. Despite their interesting properties, some of the basic features of melanins are not satisfactorily understood, including the origin of their intrinsic paramagnetism. A number of experiments have been performed to investigate the electron spin resonance (ESR) response of melanin derivatives, but until now, there has been no consensus regarding the real structure of the paramagnetic centers involved. In this work, we have employed electronic structure calculations to evaluate the ESR parameters of distinct melanin monomers and dimers in order to identify the possible structures associated with unpaired spins in this biopolymer. The g-factors and hyperfine constants of the cationic, anionic and radicalar structures were investigated. The results confirm the existence of at least two distinct paramagnetic centers in melanin structure, identifying the chemical species associated with them and their roles in electrical conductivity.
Radiation of relativistic electrons in a periodic wire structure
Soboleva, V.V., E-mail: sobolevaveronica@mail.ru; Naumenko, G.A.; Bleko, V.V.
2015-07-15
We present in this work the experimental investigation of the interaction of relativistic electron field with periodic wire structures. We used two types of the targets in experiments: flat wire target and sandwich wire target that represent the right triangular prism. The measurements were done in millimeter wavelength region (10–40 mm) on the relativistic electron beam with energy of 6.2 MeV in far-field zone. We showed that bunched electron beam passing near wire metamaterial prism generates coherent Cherenkov radiation. The experiments with flat wire target were carried out in two geometries. In the first geometry the electron beam passed close to the flat wire target surface. In the second case the electron beam passed through the flat wire structure with generation of a coherent backward transition radiation (CBTR). The comparison of the Cherenkov radiation intensity and BTR intensity from the flat wire target and from the flat conductive target (conventional BTR) was made.
Structural complexities in the active layers of organic electronics.
Lee, Stephanie S; Loo, Yueh-Lin
2010-01-01
The field of organic electronics has progressed rapidly in recent years. However, understanding the direct structure-function relationships between the morphology in electrically active layers and the performance of devices composed of these materials has proven difficult. The morphology of active layers in organic electronics is inherently complex, with heterogeneities existing across multiple length scales, from subnanometer to micron and millimeter range. A major challenge still facing the organic electronics community is understanding how the morphology across all of the length scales in active layers collectively determines the device performance of organic electronics. In this review we highlight experiments that have contributed to the elucidation of structure-function relationships in organic electronics and also point to areas in which knowledge of such relationships is still lacking. Such knowledge will lead to the ability to select active materials on the basis of their inherent properties for the fabrication of devices with prespecified characteristics.
Electronic structure of nanograin barium titanate ceramics
DENG Xiangyun; WANG Xiaohui; LI Dejun; LI Longtu
2007-01-01
The density of states and band structure of 20 nm barium titanate(BaTiO3,BT)ceramics are investigated by first-principles calculation.The full potential linearized augmented plane wave(FLAPW)method is used and the exchange correlation effects are treated by the generalized gradient approximation(GGA).The results show that there is substantial hybridization between the Ti 3d and O 2p states in 20 nm BT ceramics and the interaction between barium and oxygen is typically ionic.
Mangion, Ian; Liu, Yizhou; Reibarkh, Mikhail; Williamson, R Thomas; Welch, Christopher J
2016-08-19
As new chemical methodologies driven by single-electron chemistry emerge, process and analytical chemists must develop approaches to rapidly solve problems in this nontraditional arena. Electron paramagnetic resonance spectroscopy has been long known as a preferred technique for the study of paramagnetic species. However, it is only recently finding application in contemporary pharmaceutical development, both to study reactions and to track the presence of undesired impurities. Several case studies are presented here to illustrate its utility in modern pharmaceutical development efforts.
MATERIALS WITH COMPLEX ELECTRONIC/ATOMIC STRUCTURES
D. M. PARKIN; L. CHEN; ET AL
2000-09-01
We explored both experimentally and theoretically the behavior of materials at stresses close to their theoretical strength. This involves the preparation of ultra fine scale structures by a variety of fabrication methods. In the past year work has concentrated on wire drawing of in situ composites such as Cu-Ag and Cu-Nb. Materials were also fabricated by melting alloys in glass and drawing them into filaments at high temperatures by a method known as Taylor wire technique. Cu-Ag microwires have been drawn by this technique to produce wires 10 {micro}m in diameter that consist of nanoscale grains of supersaturated solid solution. Organogels formed from novel organic gelators containing cholesterol tethered to squaraine dyes or trans-stilbene derivatives have been studied from several different perspectives. The two types of molecules are active toward several organic liquids, gelling in some cases at w/w percentages as low as 0.1. While relatively robust, acroscopically dry gels are formed in several cases, studies with a variety of probes indicate that much of the solvent may exist in domains that are essentially liquid-like in terms of their microenvironment. The gels have been imaged by atomic force microscopy and conventional and fluorescence microscopy, monitoring both the gelator fluorescence in the case of the stilbene-cholesterol gels and, the fluorescence of solutes dissolved in the solvent. Remarkably, our findings show that several of the gels are composed of similarly appearing fibrous structures visible at the nano-, micro-, and macroscale.
Complex band structure and superlattice electronic states
Schulman, J. N.; McGill, T. C.
1981-04-01
The complex band structures of the bulk materials which constitute the alternating layer (001) semiconductor-semiconductor superlattice are investigated. The complex bands near the center of the Brillouin zone in the [001] direction are studied in detail. The decay lengths of superlattice states whose energies lie in the bulk band gaps of one of the semiconductors are determined from the dispersion curves of these bands for imaginary k-->. This method is applied using a tight-binding band-structure calculation to two superlattices: the AlAs-GaAs superlattice and the CdTe-HgTe superlattice. The decay lengths of AlAs-GaAs superlattice conduction-band minimum states are found to be substantially shorter than those for the CdTe-HgTe superlattice. These differences in the decay of the states in the two superlattices result in differences in the variation of the conduction-band effective masses with the thickness of the AlAs and CdTe layers. The conduction-band effective masses increase more rapidly with AlAs thickness in the AlAs-GaAs superlattice than with CdTe thickness in the CdTe-HgTe superlattice.
Electronic structure of a graphene superlattice with massive Dirac fermions
Lima, Jonas R. F., E-mail: jonas.iasd@gmail.com [Instituto de Ciencia de Materiales de Madrid (CSIC) - Cantoblanco, Madrid 28049 (Spain)
2015-02-28
We study the electronic and transport properties of a graphene-based superlattice theoretically by using an effective Dirac equation. The superlattice consists of a periodic potential applied on a single-layer graphene deposited on a substrate that opens an energy gap of 2Δ in its electronic structure. We find that extra Dirac points appear in the electronic band structure under certain conditions, so it is possible to close the gap between the conduction and valence minibands. We show that the energy gap E{sub g} can be tuned in the range 0 ≤ E{sub g} ≤ 2Δ by changing the periodic potential. We analyze the low energy electronic structure around the contact points and find that the effective Fermi velocity in very anisotropic and depends on the energy gap. We show that the extra Dirac points obtained here behave differently compared to previously studied systems.
Electron Crystallographic Study on Structure Determination for Minute Crystals
LI Fanghua; FAN Haifu; WAN Zhenghua; HU Jianjun; TANG Dong
2007-01-01
@@ In the 1970s the development of high-resolution electron microscopy (HREM) provided a new approach to structure determination for minute crystals, which is thoroughly different from the diffraction methods.However, the previous method of trial and error has its own limits, such as some preliminary structural information must be known in advance; the crystals must be sufficient strong under the electron beam irradiation;and not all atoms can be seen in the image. Two ideas were proposed to initiate the present research project:one is to transform an arbitrary image into the crystal structure map, and the other is to enhance the image resolution by combining the information contained in the image and the corresponding electron diffraction pattern. These ideas have been realized via the combination of electron microscopy and diffraction crystallography.
Briggs, E L; Bernholc, J
2015-01-01
A parallel implementation of an eigensolver designed for electronic structure calculations is presented. The method is applicable to computational tasks that solve a sequence of eigenvalue problems where the solution for a particular iteration is similar but not identical to the solution from the previous iteration. Such problems occur frequently when performing electronic structure calculations in which the eigenvectors are solutions to the Kohn-Sham equations. The eigenvectors are represented in some type of basis but the problem sizes are normally too large for direct diagonalization in that basis. Instead a subspace diagonalization procedure is employed in which matrix elements of the Hamiltonian operator are generated and the eigenvalues and eigenvectors of the resulting reduced matrix are obtained using a standard eigensolver from a package such as LAPACK or SCALAPACK. While this method works well and is widely used, the standard eigensolvers scale poorly on massively parallel computer systems for the m...
Quantum chemistry the development of ab initio methods in molecular electronic structure theory
Schaefer III, Henry F
2004-01-01
This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi
The stabilities and electron structures of Al-Mg clusters with 18 and 20 valence electrons
Yang, Huihui; Chen, Hongshan
2017-07-01
The spherical jellium model predicts that metal clusters having 18 and 20 valence electrons correspond to the magic numbers and will show specific stabilities. We explore in detail the geometric structures, stabilities and electronic structures of Al-Mg clusters containing 18 and 20 valence electrons by using genetic algorithm combined with density functional theories. The stabilities of the clusters are governed by the electronic configurations and Mg/Al ratios. The clusters with lower Mg/Al ratios are more stable. The molecular orbitals accord with the shell structures predicted by the jellium model but the 2S level interweaves with the 1D levels and the 2S and 1D orbitals form a subgroup. The clusters having 20 valence electrons form closed 1S21P61D102S2 shells and show enhanced stability. The Al-Mg clusters with a valence electron count of 18 do not form closed shells because one 1D orbital is unoccupied. The ionization potential and electron affinity are closely related to the electronic configurations; their values are determined by the subgroups the HOMO or LUMO belong to. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80042-9
Electron states in curved quantum structures with varying radius
Gravesen, Jens; Willatzen, Morten
2008-01-01
The influence of size and shape is investigated for quantum-dot electronic states and intra-band oscillator strengths adapting a method originally due to Stevenson. The present work solves the one-band envelope-function problem for conduction-band eigenstates in the framework of k⋅p theory using ...
Structure Identification in High-Resolution Transmission Electron Microscopic Images
Vestergaard, Jacob Schack; Kling, Jens; Dahl, Anders Bjorholm
2014-01-01
A connection between microscopic structure and macroscopic properties is expected for almost all material systems. High-resolution transmission electron microscopy is a technique offering insight into the atomic structure, but the analysis of large image series can be time consuming. The present ...
Electronic structures and properties of Ti, Zr and Hf metals
无
2001-01-01
The electronic structures of pure Ti, Zr and Hf metals with hcp structure were determined by one-atom (OA) theory. According to the electronic structures of these metals,their potential curves, cohesive energies, lattice constants, elasticities and the temperature dependence of linear thermal expansion coefficients were calculated. The electronic structures and characteristic properties of these metals with bcc and fcc structures and liquids were also studied. The results show that the electronic structures of Ti, Zr and Hf metals are respectively [Ar](3dn)0.481 0(3dc)2.085 7(4sc)1.000 0(4sf)0.433 3, [Kr](4dn)0.396 8(4dc)2.142 8(5sc)1.262 0(5sf)0.198 4, [Xe](5dn)0.368 0(5dc)2.041 4(6sc)1.406 6(6sf)0.184 0. It is explained why the pure Ti, Zr and Hf metals with hcp and bcc structures can exist naturally, while those with fcc structure can not.
Electronic shell structure and chemisorption on gold nanoparticles
Larsen, Ask Hjorth; Kleis, Jesper; Thygesen, Kristian Sommer
2011-01-01
to distort considerably, creating large band gaps at the Fermi level. For up to 200 atoms we consider structures generated with a simple EMT potential and clusters based on cuboctahedra and icosahedra. All types of cluster geometry exhibit jelliumlike electronic shell structure. We calculate adsorption...
Electron vortex magnetic holes: A nonlinear coherent plasma structure
Haynes, Christopher T.; Burgess, David; Camporeale, Enrico; Sundberg, Torbjorn
2015-01-01
We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.
Electron vortex magnetic holes: A nonlinear coherent plasma structure
Haynes, Christopher T., E-mail: c.t.haynes@qmul.ac.uk; Burgess, David; Sundberg, Torbjorn [School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Camporeale, Enrico [Multiscale Dynamics, Centrum Wiskunde and Informatica (CWI), Amsterdam (Netherlands)
2015-01-15
We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.
Orbital approach to the electronic structure of solids
Canadell, Enric; Iung, Christophe
2012-01-01
This book provides an intuitive yet sound understanding of how structure and properties of solids may be related. The natural link is provided by the band theory approach to the electronic structure of solids. The chemically insightful concept of orbital interaction and the essential machinery of band theory are used throughout the book to build links between the crystal and electronic structure of periodic systems. In such a way, it is shown how important tools for understandingproperties of solids like the density of states, the Fermi surface etc. can be qualitatively sketched and used to ei
Bohr's Electron was Problematic for Einstein: String Theory Solved the Problem
Webb, William
2013-04-01
Neils Bohr's 1913 model of the hydrogen electron was problematic for Albert Einstein. Bohr's electron rotates with positive kinetic energies +K but has addition negative potential energies - 2K. The total net energy is thus always negative with value - K. Einstein's special relativity requires energies to be positive. There's a Bohr negative energy conflict with Einstein's positive energy requirement. The two men debated the problem. Both would have preferred a different electron model having only positive energies. Bohr and Einstein couldn't find such a model. But Murray Gell-Mann did! In the 1960's, Gell-Mann introduced his loop-shaped string-like electron. Now, analysis with string theory shows that the hydrogen electron is a loop of string-like material with a length equal to the circumference of the circular orbit it occupies. It rotates like a lariat around its centered proton. This loop-shape has no negative potential energies: only positive +K relativistic kinetic energies. Waves induced on loop-shaped electrons propagate their energy at a speed matching the tangential speed of rotation. With matching wave speed and only positive kinetic energies, this loop-shaped electron model is uniquely suited to be governed by the Einstein relativistic equation for total mass-energy. Its calculated photon emissions are all in excellent agreement with experimental data and, of course, in agreement with those -K calculations by Neils Bohr 100 years ago. Problem solved!
Extended ALE Method for fluid-structure interaction problems with large structural displacements
Basting, Steffen; Quaini, Annalisa; Čanić, Sunčica; Glowinski, Roland
2017-02-01
Standard Arbitrary Lagrangian-Eulerian (ALE) methods for the simulation of fluid-structure interaction (FSI) problems fail due to excessive mesh deformations when the structural displacement is large. We propose a method that successfully deals with this problem, keeping the same mesh connectivity while enforcing mesh alignment with the structure. The proposed Extended ALE Method relies on a variational mesh optimization technique, where mesh alignment with the structure is achieved via a constraint. This gives rise to a constrained optimization problem for mesh optimization, which is solved whenever the mesh quality deteriorates. The performance of the proposed Extended ALE Method is demonstrated on a series of numerical examples involving 2D FSI problems with large displacements. Two-way coupling between the fluid and structure is considered in all the examples. The FSI problems are solved using either a Dirichlet-Neumann algorithm, or a Robin-Neumann algorithm. The Dirichlet-Neumann algorithm is enhanced by an adaptive relaxation procedure based on Aitken's acceleration. We show that the proposed method has excellent performance in problems with large displacements, and that it agrees well with a standard ALE method in problems with mild displacement.
Geometric and Electronic Structure of Closed Graphene Edges
Lopez-Benzanilla, Alejandro [Oak Ridge National Laboratory (ORNL); Campos-Delgado, Jessica [IPICyT; Sumpter, Bobby G [ORNL; Baptista, Daniel [National Institute of Metrology, Duque de Caxias, Brazil; Hayashi, Takuya [Institute of Carbon Science and Technology, Shinshu Unversity; Kim, Y A [Shinshu University; Muramatsu, H [Shinshu University; Endo, M [Shinshu University; Achete, Carlos [National Institute of Metrology, Duque de Caxias, Brazil; Terrones, M. [Universidad Carlos III, Madrid, Spain; Meunier, Vincent [ORNL
2012-01-01
We report theoretical and experimental results on single and multiple looped graphene sheets. Experimental images of stable closed-edge structures in few-layer graphene samples obtained by high-resolution transmission electron microscopy (HRTEM) are compared with first- principles density functional theory calculations. We demonstrate that the electronic structure of a graphene nanoribbon is not significantly perturbed upon closing. By contrast, a significant modulation of the electronic structure is observed for closed-edge graphene structures deposited on a planar graphene substrate. This effect is due to an enhanced reactivity of the looped (coalesced) edges observed experimentally. The coexistence of different degrees of curvature in the graphene sheet induced by folding indicates that these materials could be used for surface chemistry engineering.
Design Considerations for Optimized Lateral Spring Structures for Wearable Electronics
Hussain, Aftab M.
2016-03-07
The market for wearable electronics has been gaining momentum in the recent years. For completely electronic wearable textiles with integrated sensors, actuators, computing units and communication circuitry, it is important that there is significant stretchability. This stretchability can be obtained by introducing periodic stretchable structures between the electronic circuits. In this work, we derive the equations and constraints governing the stretchability in horseshoe lateral spring structures. We have derived the optimum design and the parameters therein, to help develop the best spring structures for a given stretchability. We have also developed a figure of merit, called area efficiency of stretchability, to compare all twodimensional stretchable systems. Finally, we experimentally verify the validity of our equations by fabricating a metal/polymer bilayer thin film based stretchable horseshoe lateral spring structures. We obtain a stretchability of 1.875 which is comparable to the theoretical maxima of 2.01 for the given parameters.
Real-time feedback from iterative electronic structure calculations
Vaucher, Alain C; Reiher, Markus
2015-01-01
Real-time feedback from iterative electronic structure calculations requires to mediate between the inherently unpredictable execution times of the iterative algorithm employed and the necessity to provide data in fixed and short time intervals for real-time rendering. We introduce the concept of a mediator as a component able to deal with infrequent and unpredictable reference data to generate reliable feedback. In the context of real-time quantum chemistry, the mediator takes the form of a surrogate potential that has the same local shape as the first-principles potential and can be evaluated efficiently to deliver atomic forces as real-time feedback. The surrogate potential is updated continuously by electronic structure calculations and guarantees to provide a reliable response to the operator for any molecular structure. To demonstrate the application of iterative electronic structure methods in real-time reactivity exploration, we implement self-consistent semi-empirical methods as the data source and a...
Studies on electronic structure of GaN(0001) surface
Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K
2002-01-01
An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized
Structure of a bacterial cell surface decaheme electron conduit.
Clarke, Thomas A; Edwards, Marcus J; Gates, Andrew J; Hall, Andrea; White, Gaye F; Bradley, Justin; Reardon, Catherine L; Shi, Liang; Beliaev, Alexander S; Marshall, Matthew J; Wang, Zheming; Watmough, Nicholas J; Fredrickson, James K; Zachara, John M; Butt, Julea N; Richardson, David J
2011-06-07
Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves decaheme cytochromes that are located on the bacterial cell surface at the termini of trans-outer-membrane electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular intercytochrome electron exchange along "nanowire" appendages. We present a 3.2-Å crystal structure of one of these decaheme cytochromes, MtrF, that allows the spatial organization of the 10 hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65-Å octaheme chain transects the length of the protein and is bisected by a planar 45-Å tetraheme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g., minerals), soluble substrates (e.g., flavins), and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.
Snap-Through Buckling Problem of Spherical Shell Structure
Sumirin Sumirin
2014-12-01
Full Text Available This paper presents results of a numerical study on the nonlinear behavior of shells undergoing snap-through instability. This research investigates the problem of snap-through buckling of spherical shells applying nonlinear finite element analysis utilizing ANSYS Program. The shell structure was modeled by axisymmetric thin shell of finite elements. Shells undergoing snap-through buckling meet with significant geometric change of their physical configuration, i.e. enduring large deflections during their deformation process. Therefore snap-through buckling of shells basically is a nonlinear problem. Nonlinear numerical operations need to be applied in their analysis. The problem was solved by a scheme of incremental iterative procedures applying Newton-Raphson method in combination with the known line search as well as the arc- length methods. The effects of thickness and depth variation of the shell is taken care of by considering their geometrical parameter l. The results of this study reveal that spherical shell structures subjected to pressure loading experience snap-through instability for values of l≥2.15. A form of ‘turn-back’ of the load-displacement curve took place at load levels prior to the achievement of the critical point. This phenomenon was observed for values of l=5.0 to l=7.0.
Generalized Artificial Life Structure for Time-dependent Problems
TSAU Minhe; KAO Weiwen; CHANG Albert
2009-01-01
In recent years, more attention has been paid on artificial life researches. Artificial life(AL) is a research on regulating gene parameters of digital organisms under complicated problematic environments through natural selections and evolutions to achieve the final emergence of intelligence. Most recent studies focused on solving certain real problems by artificial life methods, yet without much address on the AL life basic mechanism. The real problems are often very complicated, and the proposed methods sometimes seem too simple to handle those problems. This study proposed a new approach in AL research, named "generalized artificial life structure(GALS)", in which the traditional "gene bits" in genetic algorithms is first replaced by "gene parameters", which could appear anywhere in GALS. A modeling procedure is taken to normalize the input data, and AL "tissue" is innovated to make AL more complex. GALS is anticipated to contribute significantly to the fitness of AL evolution. The formation of"tissue" begins with some different AL basic cells, and then tissue is produced by the casual selections of one or several of these cells. As a result, the gene parameters, represented by "tissues", could become highly diversified. This diversification should have obvious effects on improving gene fitness. This study took the innovative method of GALS in a stock forecasting problem under a carefully designed manipulating platform. And the researching results verify that the GALS is successful in improving the gene evolution fitness.
The readiness of SNOMED problem list concepts for meaningful use of electronic health records.
Agrawal, Ankur; He, Zhe; Perl, Yehoshua; Wei, Duo; Halper, Michael; Elhanan, Gai; Chen, Yan
2013-06-01
By 2015, SNOMED CT (SCT) will become the USA's standard for encoding diagnoses and problem lists in electronic health records (EHRs). To facilitate this effort, the National Library of Medicine has published the "SCT Clinical Observations Recording and Encoding" and the "Veterans Health Administration and Kaiser Permanente" problem lists (collectively, the "PL"). The PL is studied in regard to its readiness to support meaningful use of EHRs. In particular, we wish to determine if inconsistencies appearing in SCT, in general, occur as frequently in the PL, and whether further quality-assurance (QA) efforts on the PL are required. A study is conducted where two random samples of SCT concepts are compared. The first consists of concepts strictly from the PL and the second contains general SCT concepts distributed proportionally to the PL's in terms of their hierarchies. Each sample is analyzed for its percentage of primitive concepts and for frequency of modeling errors of various severity levels as quality measures. A simple structural indicator, namely, the number of parents, is suggested to locate high likelihood inconsistencies in hierarchical relationships. The effectiveness of this indicator is evaluated. PL concepts are found to be slightly better than other concepts in the respective SCT hierarchies with regards to the quality measure of the percentage of primitive concepts and the frequency of modeling errors. There were 58% primitive concepts in the PL sample versus 62% in the control sample. The structural indicator of number of parents is shown to be statistically significant in its ability to identify concepts having a higher likelihood of inconsistencies in their hierarchical relationships. The absolute number of errors in the group of concepts having 1-3 parents was shown to be significantly lower than that for concepts with 4-6 parents and those with 7 or more parents based on Chi-squared analyses. PL concepts suffer from the same issues as general SCT
The Gaseous Electronics Conference in its seventh decade: some new problems in an old field
Gay, Timothy
2015-09-01
Our understanding of scattering processes involving atoms and molecules is the foundation of the science of gaseous electronics. As fields of physics and chemistry, both atomic and molecular collisions and gaseous electronics originated in the early 20th century, and they have developed symbiotically and in parallel since then. Despite a century of progress since the Franck-Hertz experiment however, it is fair to say that the field of atomic and molecular collisions is old and well-explored, but not mature. While the electron-atomic hydrogen problem has been solved in complete detail, there are large regions in the ``great outback'' of the periodic table where either theory or experiment (or both) are nonexistent, or there is little correlation between the two. The problem becomes dramatically worse with molecules, including those with just one atom too many. As applications of gaseous electronics have become both more sophisticated and more complicated, the demands for basic, accurate cross section data, especially for heavy, polyatomic molecular constituents, have escalated accordingly. This talk will review the status of our theoretical understanding of atomic and molecular collisions, and will present several case studies involving targets of He, H2, Zn, H2O, and C10H15IO to illustrate current problems in the field. We will also consider crucial needs for basic collisional data in recent applied plasma science problems. Work supported by the NSF through Grant PHY-1505794.
Yulia V. Dementieva
2016-01-01
Full Text Available The aim of the study is the description of the main problems of formation of the student’s electronic portfolio in the conditions of realization of Federal State Educational Standards of the Higher Education (FSES of HE.Methods.Theoretical analysis of scientific literature concerning the subject under discussion; monitoring of existing practices in modern Russian Universities procedures for the formation and maintenance of students electronic portfolio.Results. The author describes the main problems of the electronic students’ portfolio formation; some ways of solving described problems are offered.Scientific novelty concludes in the formation of key ideas of the electronic students’ portfolio based on the understanding of requirements of Federal State Educational Standards of Higher Education for the results of mastering educational programs. They are the formation of general cultural, general professional and professional competences.Practical significance. The researching results will become the theoretical basis for the systematic organization of the process of creating and maintaining an electronic students’ portfolio during the whole period of their studying at the university; the researching results can become a basis for methodological developments.
Structure of Matter An Introductory Course with Problems and Solutions
Rigamonti, Attilio
2009-01-01
This is the second edition of this textbook, the original of which was published in 2007. Initial undergraduate studies in physics are usually in an organized format devoted to elementary aspects, which is then followed by advanced programmes in specialized fields. A difficult task is to provide a formative introduction in the early period, suitable as a base for courses more complex, thus bridging the wide gap between elementary physics and topics pertaining to research activities. This textbook remains an endeavour toward that goal, and is based on a mixture of simplified institutional theory and solved problems. In this way, the hope is to provide physical insight, basic knowledge and motivation, without impeding advanced learning. The choice has been to limit the focus to key concepts and to those aspects most typical of atoms, molecules and compounds, by looking at the basic, structural components, without paying detailed attention to the properties possessed by them. Problems are intertwined with formal...
Structure of Matter An Introductory Course with Problems and Solutions
Rigamonti, Attilio
2007-01-01
This is the second edition of this textbook, the original of which was published in 2007. Initial undergraduate studies in physics are usually in an organized format devoted to elementary aspects, which is then followed by advanced programmes in specialized fields. A difficult task is to provide a formative introduction in the early period, suitable as a base for courses more complex, thus bridging the wide gap between elementary physics and topics pertaining to research activities. This textbook remains an endeavour toward that goal, and is based on a mixture of simplified institutional theory and solved problems. In this way, the hope is to provide physical insight, basic knowledge and motivation, without impeding advanced learning. The choice has been to limit the focus to key concepts and to those aspects most typical of atoms, molecules and compounds, by looking at the basic, structural components, without paying detailed attention to the properties possessed by them. Problems are intertwined with formal...
Variability of Protein Structure Models from Electron Microscopy.
Monroe, Lyman; Terashi, Genki; Kihara, Daisuke
2017-03-02
An increasing number of biomolecular structures are solved by electron microscopy (EM). However, the quality of structure models determined from EM maps vary substantially. To understand to what extent structure models are supported by information embedded in EM maps, we used two computational structure refinement methods to examine how much structures can be refined using a dataset of 49 maps with accompanying structure models. The extent of structure modification as well as the disagreement between refinement models produced by the two computational methods scaled inversely with the global and the local map resolutions. A general quantitative estimation of deviations of structures for particular map resolutions are provided. Our results indicate that the observed discrepancy between the deposited map and the refined models is due to the lack of structural information present in EM maps and thus these annotations must be used with caution for further applications.
Electron Structure: Shape, Size and GPDs in QED
Miller, Gerald A
2014-01-01
The shape of the electron is studied using lowest-order perturbation theory. Quantities used to probe the structure of the proton: form factors, generalized parton distributions, transverse densities, Wigner distributions and the angular momentum content are computed for the electron-photon component of the electron wave function. The influence of longitudinally polarized photons, demanded by the need for infrared regularization via a non-zero photon mass, is included. The appropriate value of the photon mass depends on experimental conditions, and consequently the size of the electron (as defined by the slope of its Dirac form factor) bound in a hydrogen atom is found to be about four times larger than when the electron is free. The shape of the electron, as determined from the transverse density and generalized parton distributions is shown to not be round, and the free electron is shown to be far less round than the bound electron. An electron distribution function (analogous to the quark distribution func...
Spin structure of electron subbands in (110)-grown quantum wells
Nestoklon, M. O.; Tarasenko, S. A. [Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); Jancu, J.-M. [FOTON-INSA Laboratory, UMR 6082 au CNRS, INSA de Rennes, 35043 Rennes Cedex (France); Voisin, P. [CNRS-Laboratoire de Photonique et de Nanostructures, 91460 Marcoussis (France)
2013-12-04
We present the theory of fine structure of electron states in symmetric and asymmetric zinc-blende-type quantum wells with the (110) crystallographic orientation. By combining the symmetry analysis, sp{sup 3}d{sup 5}s* tight-binding method, and envelope-function approach we obtain quantitative description of in-plane wave vector, well width and applied electric field dependencies of the zero-magnetic-field spin splitting of electron subbands and extract spin-orbit-coupling parameters.
Electronic Structure of High-Pressure Alumina Polymorphs
LIU Xiao-Lei; DUAN Wen-Hui; GU Bing-Lin
2000-01-01
Electronic properties are investigated for three alumina polymorphs (corundum, Rb2 O3 (Ⅱ) and Pbnm perovskite),which are predicted as the stable structures under different pressure range, by means of the first-principles molecular dynamics method within local density functional framework. The similarity in electronic properties of the polymorphs of alumina is observed. The effect of possible phase transitions on ruby (Cr+3-doped Al2 O3)fluorescences is discussed.
Many-Body Electronic Structure of Curium metal
Toropova, Antonina; Haule, Kristjan; Kotliar, Gabriel
2006-03-01
We report computer-based simulations for the many-body electronic structure of Curium metal. Cm belongs to the actinide series and has a half-filled shell with seven 5f electrons. As a function of pressure, curium exhibits five different crystallographic phases. At low temperatures all phases demonstrate either antiferromagnetic or ferrimagnetic ordering. In this study we perform LDA+DMFT calculations for the antiferromagnetic state of high-pressure fcc modification of Curium metal.
Electron Crystallography Novel Approaches for Structure Determination of Nanosized Materials
Weirich, Thomas E; Zou, Xiaodong
2006-01-01
During the last decade we have been witness to several exciting achievements in electron crystallography. This includes structural and charge density studies on organic molecules complicated inorganic and metallic materials in the amorphous, nano-, meso- and quasi-crystalline state and also development of new software, tailor-made for the special needs of electron crystallography. Moreover, these developments have been accompanied by a now available new generation of computer controlled electron microscopes equipped with high-coherent field-emission sources, cryo-specimen holders, ultra-fast CCD cameras, imaging plates, energy filters and even correctors for electron optical distortions. Thus, a fast and semi-automatic data acquisition from small sample areas, similar to what we today know from imaging plates diffraction systems in X-ray crystallography, can be envisioned for the very near future. This progress clearly shows that the contribution of electron crystallography is quite unique, as it enables to r...
Atomic and electronic structure of exfoliated black phosphorus
Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
2015-11-15
Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.
Electron confinement in thin metal films. Structure, morphology and interactions
Dil, J.H.
2006-05-15
This thesis investigates the interplay between reduced dimensionality, electronic structure, and interface effects in ultrathin metal layers (Pb, In, Al) on a variety of substrates (Si, Cu, graphite). These layers can be grown with such a perfection that electron confinement in the direction normal to the film leads to the occurrence of quantum well states in their valence bands. These quantum well states are studied in detail, and their behaviour with film thickness, on different substrates, and other parameters of growth are used here to characterise a variety of physical properties of such nanoscale systems. The sections of the thesis deal with a determination of quantum well state energies for a large data set on different systems, the interplay between film morphology and electronic structure, and the influence of substrate electronic structure on their band shape; finally, new ground is broken by demonstrating electron localization and correlation effects, and the possibility to measure the influence of electron-phonon coupling in bulk bands. (orig.)
Electronic Structure of Dense Plasmas by X-Ray Scattering
Gregori, G; Glenzer, S H; Rogers, F J; Pollaine, S M; Froula, D H; Blancard, C; Faussurier, G; Renaudin, P; Kuhlbrodt, S; Redmer, R; Landen, O L
2003-10-07
We present an improved analytical expression for the x-ray dynamic structure factor from a dense plasma which includes the effects of weakly bound electrons. This result can be applied to describe scattering from low to moderate Z plasmas, and it covers the entire range of plasma conditions that can be found in inertial confinement fusion experiments, from ideal to degenerate up to moderately coupled systems. We use our theory to interpret x-ray scattering experiments from solid density carbon plasma and to extract accurate measurements of electron temperature, electron density and charge state. We use our experimental results to validate various equation-of-state models for carbon plasmas.
Quasiparticle GW calculations within the GPAW electronic structure code
Hüser, Falco
The GPAW electronic structure code, developed at the physics department at the Technical University of Denmark, is used today by researchers all over the world to model the structural, electronic, optical and chemical properties of materials. They address fundamental questions in material science...... and use their knowledge to design new materials for a vast range of applications. Todays hottest topics are, amongst many others, better materials for energy conversion (e.g. solar cells), energy storage (batteries) and catalysts for the removal of environmentally dangerous exhausts. The mentioned...... properties are to a large extent governed by the physics on the atomic scale, that means pure quantum mechanics. For many decades, Density Functional Theory has been the computational method of choice, since it provides a fairly easy and yet accurate way of determining electronic structures and related...
Atomic structure and electronic states of extended defects in silicon
Riedel, F; Schröter, W
2002-01-01
Defects in silicon like dislocations, grain boundaries, silicide precipitates, etc. are spatially extended and associated with a large number of electronic states in the band gap. Our knowledge on the relation between atomic structure and electronic states of these extended defects presently starts to grow by applying high-resolution electron microscopy (HRTEM) and deep level transient spectroscopy (DLTS) in combination with numerical simulations. While by means of HRTEM details of structure can be studied, DLTS has been shown to allow for a classification of extended defect states into bandlike and localized. Moreover, this method opens the perspective to distinguish between trap-like and recombination-like electrical activity. In this paper, we emphasize the particular role of nickel and copper silicide precipitates, since in their cases structural features could be successfully related to specific DLTS line characteristics. Rapid quenching from high diffusion temperatures prevents decoration of platelet-sh...
Structural and electronic properties of dense liquid and amorphous nitrogen
Boates, B; Bonev, S A
2011-02-11
We present first-principles calculations of the structural and electronic properties of liquid nitrogen in the pressure-temperature range of 0-200 GPa and 2000-6000 K. The molecular-polymerization and molecular-atomic liquid phase boundaries have been mapped over this region. We find the polymeric liquid to be metallic, similar to what has been reported for the higher-temperature atomic fluid. An explanation of the electronic properties is given based on the structure and bonding character of the transformed liquids. We discuss the structural and bonding differences between the polymeric liquid and insulating solid cubic-gauche nitrogen to explain the differences in their electronic properties. Furthermore, we discuss the mechanism responsible for charge transport in polymeric nitrogen systems to explain the conductivity of the polymeric fluid and the semi-conducting nature of low-temperature amorphous nitrogen.
Electron crystallography--the waking beauty of structural biology.
Pope, Christopher R; Unger, Vinzenz M
2012-08-01
Since its debut in the mid 1970s, electron crystallography has been a valuable alternative in the structure determination of biological macromolecules. Its reliance on single-layered or double-layered two-dimensionally ordered arrays and the ability to obtain structural information from small and disordered crystals make this approach particularly useful for the study of membrane proteins in a lipid bilayer environment. Despite its unique advantages, technological hurdles have kept electron crystallography from reaching its full potential. Addressing the issues, recent initiatives developed high-throughput pipelines for crystallization and screening. Adding progress in automating data collection, image analysis and phase extension methods, electron crystallography is poised to raise its profile and may lead the way in exploring the structural biology of macromolecular complexes.
Molecular and Electronic Structure of n-Alkyl Cyanobiphenyl Nematogens
Risser, Steven M.(TEXAS A and M UNIVERSITY); Ferris, Kim F.(BATTELLE (PACIFIC NW LAB))
2001-12-01
First principle electronic structure calculations (ab-initio and density functional) were performed on a series of substituted cyanobiphenyls to examine the structural and electronic properties as a function of the alkyl tail length and changes in torsion angle about the central bond connecting the rings. We find good agreement between our results and previous electronic structure studies for the optimized torsion angle between phenyls in the cyanobiphenyls, and changes in dipole moment for the cyanobiphenyls. We also find the torsion angle and rotational barriers in cyanobiphenyls to be similar to that in simple biphenyl. However, we find large discrepancies with the recent density functional calculations that reported a much smaller torsion angle in the syanobiphenyls.
Structure of matter an introductory course with problems and solutions
Rigamonti, Attilio
2015-01-01
This textbook, now in its third edition, provides a formative introduction to the structure of matter that will serve as a sound basis for students proceeding to more complex courses, thus bridging the gap between elementary physics and topics pertaining to research activities. The focus is deliberately limited to key concepts of atoms, molecules and solids, examining the basic structural aspects without paying detailed attention to the related properties. For many topics the aim has been to start from the beginning and to guide the reader to the threshold of advanced research. This edition includes four new chapters dealing with relevant phases of solid matter (magnetic, electric and superconductive) and the related phase transitions. The book is based on a mixture of theory and solved problems that are integrated into the formal presentation of the arguments. Readers will find it invaluable in enabling them to acquire basic knowledge in the wide and wonderful field of condensed matter and to understand how ...
Structural and luminescent properties of electron-irradiated silicon
Sobolev, N. A.; Aruev, P. N.; Kalyadin, A. E.; Shek, E. I.; Zabrodskiy, V. V.; Loshachenko, A. S.; Shtel`makh, K. F.; Vdovin, V. I.; Xiang, Luelue; Yang, Deren
2014-02-01
Structural defects induced by electron irradiation of p-Cz-Si wafers were identified. The influence of the annealing conditions in a chlorine-containing atmosphere on the structural and luminescent properties of the samples was examined. Light-emitting diodes based on electron-irradiated and high-temperature-annealed wafers were fabricated by a vapour-phase epitaxy technique and their luminescence properties were studied. A high-intensity dislocation-related D1 line was observed at 1.6 μm in the room-temperature electroluminescence spectrum.
Structural and luminescent properties of electron-irradiated silicon
Sobolev, N. A.; Loshachenko, A. S. [Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia and Fok Institute of Physics, St. Petersburg State University, 198504 St. Petersburg (Russian Federation); Aruev, P. N.; Kalyadin, A. E.; Shek, E. I.; Zabrodskiy, V. V. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Shtel' makh, K. F. [Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia and St. Petersburg State Technical University, 195251 St. Petersburg (Russian Federation); Vdovin, V. I. [Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation); Xiang, Luelue; Yang, Deren [State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, 310027 Hangzhou (China)
2014-02-21
Structural defects induced by electron irradiation of p-Cz-Si wafers were identified. The influence of the annealing conditions in a chlorine-containing atmosphere on the structural and luminescent properties of the samples was examined. Light-emitting diodes based on electron-irradiated and high-temperature-annealed wafers were fabricated by a vapour-phase epitaxy technique and their luminescence properties were studied. A high-intensity dislocation-related D1 line was observed at 1.6 μm in the room-temperature electroluminescence spectrum.
The electronic structure and chemical bonding of vitamin B12
Kurmaev, E. Z.; Moewes, A.; Ouyang, L.; Randaccio, L.; Rulis, P.; Ching, W. Y.; Bach, M.; Neumann, M.
2003-05-01
The electronic structure and chemical bonding of vitamin B12 (cyanocobalamin) and B12-derivative (methylcobalamin) are studied by means of X-ray emission (XES) and photoelectron (XPS) spectroscopy. The obtained results are compared with ab initio electronic structure calculations using the orthogonalized linear combination of the atomic orbital method (OLCAO). We show that the chemical bonding in vitamin B12 is characterized by the strong Co-C bond and relatively weak axial Co-N bond. It is further confirmed that the Co-C bond in cyanocobalamin is stronger than that of methylcobalamin resulting in their different biological activity.
Polymeric Thin Films for Organic Electronics: Properties and Adaptive Structures
Bruno Pignataro
2013-03-01
Full Text Available This review deals with the correlation between morphology, structure and performance of organic electronic devices including thin film transistors and solar cells. In particular, we report on solution processed devices going into the role of the 3D supramolecular organization in determining their electronic properties. A selection of case studies from recent literature are reviewed, relying on solution methods for organic thin-film deposition which allow fine control of the supramolecular aggregation of polymers confined at surfaces in nanoscopic layers. A special focus is given to issues exploiting morphological structures stemming from the intrinsic polymeric dynamic adaptation under non-equilibrium conditions.
Electromagnetic Structure and Electron Acceleration in Shock–Shock Interaction
Nakanotani, Masaru; Matsukiyo, Shuichi; Hada, Tohru; Mazelle, Christian X.
2017-09-01
A shock–shock interaction is investigated by using a one-dimensional full particle-in-cell simulation. The simulation reproduces the collision of two symmetrical high Mach number quasi-perpendicular shocks. The basic structure of the shocks and ion dynamics is similar to that obtained by previous hybrid simulations. The new aspects obtained here are as follows. Electrons are already strongly accelerated before the two shocks collide through multiple reflection. The reflected electrons self-generate waves upstream between the two shocks before they collide. The waves far upstream are generated through the right-hand resonant instability with the anomalous Doppler effect. The waves generated near the shock are due to firehose instability and have much larger amplitudes than those due to the resonant instability. The high-energy electrons are efficiently scattered by the waves so that some of them gain large pitch angles. Those electrons can be easily reflected at the shock of the other side. The accelerated electrons form a power-law energy spectrum. Due to the accelerated electrons, the pressure of upstream electrons increases with time. This appears to cause the deceleration of the approaching shock speed. The accelerated electrons having sufficiently large Larmor radii are further accelerated through the similar mechanism working for ions when the two shocks are colliding.
Quantum Implementation of Unitary Coupled Cluster for Simulating Molecular Electronic Structure
Shen, Yangchao; Zhang, Shuaining; Zhang, Jing-Ning; Yung, Man-Hong; Kim, Kihwan
2015-01-01
Quantum simulation represents an efficient solution to a certain classically intractable problem in various research area including quantum chemistry. The central problem of quantum chemistry is to determine the electronic structure and the ground-state energy of atoms and molecules. The exact classical calculation of the problem is demanding even for molecules with moderate size due to the "exponential catastrophe." To deal with such quantum chemistry problem, the coupled-cluster methods have been successfully developed, which are considered to be the current "gold standard" in classical computational chemistry. However, the coupled-cluster ansatz is built with non-unitary operation, which leads to drawbacks such as lacking variational bound of ground-state energy. The unitary version of the coupled-cluster methods would perfectly address the problem, whereas it is classically inefficient without proper truncation of the infinite series expansion. It has been a long-standing challenge to build an efficient c...
Koupilová, Zdeňka; Mandíková, Dana; Snětinová, Marie
2017-09-01
Ten years ago we started to develop a Collection of Fully Solved Problems aimed at introductory undergraduate and high school level students. The collection is specially designed to encourage students in an active approach to problem solving, e.g. to solve at least some parts of a problem on their own. Nowadays the Collection contains about 800 fully solved problems in physics in Czech and nearly 180 problems in English. It has several hundreds of unique visitors per school day. Based on user feedback, the collection is used by students mainly for their home study and by teachers as a supplementary material. The creation of the structured solution of the physics problems has proved to be a beneficial activity for prospective physics teachers (students of our department).
Zhang, P; Wang, H Y; Li, Y G; Mao, S F; Ding, Z J
2012-01-01
Monte Carlo simulation methods for the study of electron beam interaction with solids have been mostly concerned with specimens of simple geometry. In this article, we propose a simulation algorithm for treating arbitrary complex structures in a real sample. The method is based on a finite element triangular mesh modeling of sample geometry and a space subdivision for accelerating simulation. Simulation of secondary electron image in scanning electron microscopy has been performed for gold particles on a carbon substrate. Comparison of the simulation result with an experiment image confirms that this method is effective to model complex morphology of a real sample.
Free electron laser-driven ultrafast rearrangement of the electronic structure in Ti
E. Principi
2016-03-01
Full Text Available High-energy density extreme ultraviolet radiation delivered by the FERMI seeded free-electron laser has been used to create an exotic nonequilibrium state of matter in a titanium sample characterized by a highly excited electron subsystem at temperatures in excess of 10 eV and a cold solid-density ion lattice. The obtained transient state has been investigated through ultrafast absorption spectroscopy across the Ti M2,3-edge revealing a drastic rearrangement of the sample electronic structure around the Fermi level occurring on a time scale of about 100 fs.
Measurement of the Electron Structure Function at LEP energies
Abdallah, J; Adam, W; Adzic, P; Albrecht, T; Alemany-Fernandez, R; Allmendinger, T; Allport, P P; Amaldi, U; Amapane, N; Amato, S; Anashkin, E; Andreazza, A; Andringa, S; Anjos, N; Antilogus, P; Apel, W-D; Arnoud, Y; Ask, S; Asman, B; Augustin, J E; Augustinus, A; Baillon, P; Ballestrero, A; Bambade, P; Barbier, R; Bardin, D; Barker, G J; Baroncelli, A; Battaglia, M; Baubillier, M; Becks, K-H; Begalli, M; Behrmann, A; Ben-Haim, E; Benekos, N; Benvenuti, A; Berat, C; Berggren, M; Bertrand, D; Besancon, M; Besson, N; Bloch, D; Blom, M; Bluj, M; Bonesini, M; Boonekamp, M; Booth, P S L; Borisov, G; Botner, O; Bouquet, B; Bowcock, T J V; Boyko, I; Bracko, M; Brenner, R; Brodet, E; Bruckman, P; Brunet, J M; Buschbeck, B; Buschmann, P; Calvi, M; Camporesi, T; Canale, V; Carena, F; Castro, N; Cavallo, F; Chapkin, M; Charpentier, Ph; Checchia, P; Chierici, R; Chliapnikov, P; Chudoba, J; Chung, S U; Cieslik, K; Collins, P; Contri, R; Cosme, G; Cossutti, F; Costa, M J; Crennell, D; Cuevas, J; D'Hondt, J; da Silva, T; Da Silva, W; Della Ricca, G; De Angelis, A; De Boer, W; De Clercq, C; De Lotto, B; De Maria, N; De Min, A; de Paula, L; Di Ciaccio, L; Di Simone, A; Doroba, K; Drees, J; Eigen, G; Ekelof, T; Ellert, M; Elsing, M; Espirito Santo, M C; Fanourakis, G; Fassouliotis, D; Feindt, M; Fernandez, J; Ferrer, A; Ferro, F; Flagmeyer, U; Foeth, H; Fokitis, E; Fulda-Quenzer, F; Fuster, J; Gandelman, M; Garcia, C; Gavillet, Ph; Gazis, E; Gokieli, R; Golob, B; Gomez-Ceballos, G; Goncalves, P; Graziani, E; Grosdidier, G; Grzelak, K; Guy, J; Haag, C; Hallgren, A; Hamacher, K; Hamilton, K; Haug, S; Hauler, F; Hedberg, V; Hennecke, M; Hoffman, J; Holmgren, S-O; Holt, P J; Houlden, M A; Jackson, J N; Jarlskog, G; Jarry, P; Jeans, D; Johansson, E K; Jonsson, P; Joram, C; Jungermann, L; Kapusta, F; Katsanevas, S; Katsoufis, E; Kernel, G; Kersevan, B P; Kerzel, U; King, B T; Kjaer, N J; Kluit, P; Kokkinias, P; Kourkoumelis, C; Kouznetsov, O; Krumstein, Z; Kucharczyk, M; Lamsa, J; Leder, G; Ledroit, F; Leinonen, L; Leitner, R; Lemonne, J; Lepeltier, V; Lesiak, T; Liebig, W; Liko, D; Lipniacka, A; Lopes, J H; Lopez, J M; Loukas, D; Lutz, P; Lyons, L; MacNaughton, J; Malek, A; Maltezos, S; Mandl, F; Marco, J; Marco, R; Marechal, B; Margoni, M; Marin, J-C; Mariotti, C; Markou, A; Martinez-Rivero, C; Masik, J; Mastroyiannopoulos, N; Matorras, F; Matteuzzi, C; Mazzucato, F; Mazzucato, M; Mc Nulty, R; Meroni, C; Migliore, E; Mitaroff, W; Mjoernmark, U; Moa, T; Moch, M; Moenig, K; Monge, R; Montenegro, J; Moraes, D; Moreno, S; Morettini, P; Mueller, U; Muenich, K; Mulders, M; Mundim, L; Murray, W; Muryn, B; Myatt, G; Myklebust, T; Nassiakou, M; Navarria, F; Nawrocki, K; Nemecek, S; Nicolaidou, R; Nikolenko, M; Oblakowska-Mucha, A; Obraztsov, V; Olshevski, A; Onofre, A; Orava, R; Osterberg, K; Ouraou, A; Oyanguren, A; Paganoni, M; Paiano, S; Palacios, J P; Palka, H; Papadopoulou, Th D; Pape, L; Parkes, C; Parodi, F; Parzefall, U; Passeri, A; Passon, O; Peralta, L; Perepelitsa, V; Perrotta, A; Petrolini, A; Piedra, J; Pieri, L; Pierre, F; Pimenta, M; Piotto, E; Podobnik, T; Poireau, V; Pol, M E; Polok, G; Pozdniakov, V; Pukhaeva, N; Pullia, A; Radojicic, D; Rebecchi, P; Rehn, J; Reid, D; Reinhardt, R; Renton, P; Richard, F; Ridky, J; Rivero, M; Rodriguez, D; Romero, A; Ronchese, P; Roudeau, P; Rovelli, T; Ruhlmann-Kleider, V; Ryabtchikov, D; Sadovsky, A; Salmi, L; Salt, J; Sander, C; Savoy-Navarro, A; Schwickerath, U; Sekulin, R; Siebel, M; Sisakian, A; Slominski, W; Smadja, G; Smirnova, O; Sokolov, A; Sopczak, A; Sosnowski, R; Spassov, T; Stanitzki, M; Stocchi, A; Strauss, J; Stugu, B; Szczekowski, M; Szeptycka, M; Szumlak, T; Szwed, J; Tabarelli, T; Tegenfeldt, F; Timmermans, J; Tkatchev, L; Tobin, M; Todorovova, S; Tome, B; Tonazzo, A; Tortosa, P; Travnicek, P; Treille, D; Tristram, G; Trochimczuk, M; Troncon, C; Turluer, M L; Tyapkin, I A; Tyapkin, P; Tzamarias, S; Uvarov, V; Valenti, G; Van Dam, P; Van Eldik, J; van Remortel, N; Van Vulpen, I; Vegni, G; Veloso, F; Venus, W; Verdier, P; Verzi, V; Vilanova, D; Vitale, L; Vrba, V; Wahlen, H; Washbrook, A J; Weiser, C; Wicke, D; Wickens, J; Wilkinson, G; Winter, M; Witek, M; Yushchenko, O; Zalewska, A; Zalewski, P; Zavrtanik, D; Zhuravlov, V; Zimin, N I; Zintchenko, A; Zupan, M
2010-01-01
The hadronic part of the Electron Structure Function (ESF) has been measured for the first time, using e+e- data collected by the DELPHI experiment at LEP, at centre-of-mass energies sqrt(s) = 91.2-209.5 GeV. The data analysis is simpler than that of the measurement of the photon structure function. The ESF data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the quasi-real photon virtuality contribution is significant. The presented data can serve as a cross-check of the photon structure function analyses and help in refining existing parametrizations.
Electronic structure of disordered alloys, surfaces and interfaces
Turek, Ilja; Kudrnovský, Josef; Šob, Mojmír; Weinberger, Peter
1997-01-01
At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use ...
Electronic structure of nitrides PuN and UN
Lukoyanov, A. V., E-mail: lukoyanov@imp.uran.ru; Anisimov, V. I. [Russian Academy of Sciences, Mikheev Institute of Metal Physics, Ural Branch (Russian Federation)
2016-11-15
The electronic structure of uranium and plutonium nitrides in ambient conditions and under pressure is investigated using the LDA + U + SO band method taking into account the spin–orbit coupling and the strong correlations of 5f electrons of actinoid ions. The parameters of these interactions for the equilibrium cubic structure are calculated additionally. The application of pressure reduces the magnetic moment in PuN due to predominance of the f{sup 6} configuration and the jj-type coupling. An increase in the occupancy of the 5f state in UN leads to a decrease in the magnetic moment, which is also detected in the trigonal structure of the UN{sub x} β phase (La{sub 2}O{sub 3}-type structure). The theoretical results are in good agreement with the available experimental data.
A periodic structure for electronic signals and demonstration of electronic lasing
Doiron, Serge; Giller, Christophe; Beaudoin, Normand; Haché, Alain
2008-11-01
A sequence of electronic phase shifters and partial reflectors/transmitters is shown to form a true periodic scattering structure for electronic signals, complete with stop bands, interference, and dispersion effects. An experimental demonstration at 1kHz is made with supporting theoretical results. As with conventional periodic media, sharp defect modes in the forbidden band arise when the periodicity is broken. When gain is added to the structure, a type of lasing action is observed that in almost every aspect is similar to conventional lasers.
Integrated electronic system for ultrasonic structural health monitoring
Ruiz González, Mariano; Monje, Pedro María; Casado, Luciano; Aranguren, Gerardo; Cokonaj, Valerijan; Barrera Lopez de Turiso, Eduardo
2012-01-01
A fully integrated on-board electronic system that can perform in-situ structural health monitoring (SHM) of aircraft?s structures using specifically designed equipment for SHM based on guided wave ultrasonic method or Lamb waves? method is introduced. This equipment is called Phased Array Monitoring for Enhanced Life Assessment (PAMELA III) and is an essential part of overall PAMELA SHM? system. PAMELA III can generate any kind of excitation signals, acquire the response signals that propaga...
A proposal to first principles electronic structure calculation: Symbolic-Numeric method
Kikuchi, Akihito
2012-01-01
This study proposes an approach toward the first principles electronic structure calculation with the aid of symbolic-numeric solving. The symbolic computation enables us to express the Hartree-Fock-Roothaan equation in an analytic form and approximate it as a set of polynomial equations. By use of the Grobner basis technique, the polynomial equations are transformed into other ones which have identical roots. The converted equations take more convenient forms which will simplify numerical procedures, from which we can derive necessary physical properties in order, in an a la carte way. This method enables us to solve the electronic structure calculation, the optimization of any kind, or the inverse problem as a forward problem in a unified way, in which there is no need for iterative self-consistent procedures with trials and errors.
Electronic structures of long periodic stacking order structures in Mg: A first-principles study
Wang, William Yi, E-mail: yuw129@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Shang, Shun Li; Wang, Yi [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Darling, Kristopher A. [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kecskes, Laszlo J. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-B, Aberdeen Proving Ground, MD 21005 (United States); Mathaudhu, Suveen N. [Materials Science Division, U.S. Army Research Office, Research Triangle Park, NC 27709 (United States); Hui, Xi Dong [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Liu, Zi-Kui, E-mail: dr.liu@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)
2014-02-15
Graphical abstract: -- Highlight: • Formation energies of the LPSOs (γ{sub LPSO}) can be scaled with respect to the formation energy of I2. • γ{sub LPSO} depends on the number of fault layers. • Electron structures of the 10H, 14H, 18R and 24R originate from those of I2. • Electron structure and formation energy of the 6H are between those of I1 and I2. -- Abstract: Long period stacking order (LPSO) structures, such as 6H, 10H, 14H, 18R and 24R, play significant roles in enhancing the mechanical properties of Mg alloys and have been largely investigated separately. In the present work, through detailed investigations of deformation electron density, we show that the electron structures of 10H, 14H, 18R and 24R LPSO structures in Mg originate from those of deformation stacking faults in Mg, and their formation energies can be scaled with respect to formation energy and the number of layers of deformation stacking faults, while the electron structure and formation energy of the 6H LPSO structure are between those of deformation and growth stacking faults. The simulated images of high resolution transmission electron microscopy compare well with experimental observed ones. The understanding of LPSO structures in Mg enables future quantitative investigations of effects of alloying elements on properties of LPSO structures and Mg alloys.
Fast electron scattering as a tool to study target structure
Amusia, M Ya
2006-01-01
We concentrate on several relatively new aspects of the study of fast electron scattering by atoms and atom-like objects, namely endohedral atoms and fullerenes. We show that the corresponding cross sections, being expressed via so-called Generalized Oscillator Strengths (GOS), give information on the electronic structure of the target and on the role of electron correlations in it. We consider what sort of information became available when analyzing the dependence of GOS upon their multipolarity, transferred momentum and energy. We demonstrate the role of nondipole corrections in the small-angle fast-electron inelastic scattering. There dipole contribution dominates while non-dipole corrections can be considerably and controllably enhanced as compared to the case of low and medium energy photoionization. We show also that analyses of GOS for discrete level excitations permit to clarify their multipolarity. The results of calculations of Compton excitation and ionization cross-sections for noble gas atoms are...
Combining UV photodissociation with electron transfer for peptide structure analysis.
Shaffer, Christopher J; Marek, Ales; Pepin, Robert; Slovakova, Kristina; Turecek, Frantisek
2015-03-01
The combination of near-UV photodissociation with electron transfer and collisional activation provides a new tool for structure investigation of isolated peptide ions and reactive intermediates. Two new types of pulse experiments are reported. In the first one called UV/Vis photodissociation-electron transfer dissociation (UVPD-ETD), diazirine-labeled peptide ions are shown to undergo photodissociation in the gas phase to form new covalent bonds, guided by the ion conformation, and the products are analyzed by electron transfer dissociation. In the second experiment, called ETD-UVPD wherein synthetic labels are not necessary, electron transfer forms new cation-peptide radical chromophores that absorb at 355 nm and undergo specific backbone photodissociation reactions. The new method is applied to distinguish isomeric ions produced by ETD of arginine containing peptides. Copyright © 2015 John Wiley & Sons, Ltd.
Highlighting material structure with transmission electron diffraction correlation coefficient maps.
Kiss, Ákos K; Rauch, Edgar F; Lábár, János L
2016-04-01
Correlation coefficient maps are constructed by computing the differences between neighboring diffraction patterns collected in a transmission electron microscope in scanning mode. The maps are shown to highlight material structural features like grain boundaries, second phase particles or dislocations. The inclination of the inner crystal interfaces are directly deduced from the resulting contrast.
Electronic origin of structural transition in 122 Fe based superconductors
Ghosh, Haranath; Sen, Smritijit; Ghosh, Abyay
2017-03-01
Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies Edxz, Edyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.
Electronic structure of heavy fermions: narrow temperature-independent bands
Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Thompson, J.D.; Smith, J.L. [Los Alamos National Lab., NM (United States); Moshopoulou, E.; Fisk, Z. [NHMFL, Florida State Univ., Tallahassee, FL (United States); Menovsky, A.A. [Amsterdam Univ. (Netherlands). Natuurkundig Lab.; Canfield, P.C.; Olson, C.G. [Iowa State Univ., Ames, IA (United States). Ames Lab.
1997-02-01
The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from ARPES data reported here for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable. (orig.).
The electronic structure of heavy fermions: Narrow temperature independent bands
Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B. [and others
1996-08-01
The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.
Electronic structures and optical properties of two anthracene derivatives
ZHANG Peng; XIA Baohui; SUN Yinghui; YANG Bing; TIAN Wenjing; WANG Yue; ZHANG Guo
2006-01-01
The electronic structures and the optical properties of two anthracene derivatives, DBMA and DAA, are investigated by both experimental techniques and quantum chemical calculations. The cyclic voltammetry and differential pulse polarograph measurement revealed that the introduction of benzol-imidazol and pyrrolo-pyridine group on the anthracene block can affect the electrochemical behavior of DBMA and DAA. Both UV/visible absorption and emission spectra of DBMA and DAA are red-shifted in contrast to the unsubstituted anthracene, so that the anthracene derivatives emit at blue-green region and the luminescence yields are remarkably elevated (over 90%). The B3LYP/6-31G theoretical calculations explored that the electronic structures of the anthracene derivatives are perturbed by the side substitutes on the anthracene block, and the slight variation of the electronic structures results in the enhanced electron accepting ability and the decrease of the HOMO-LUMO energy gap,which is the origin of the emission to be shifted to blue-green region. The non-planar geometry structures of DBMA and DAA are responsible for the excellent luminescence yields.
ELECTRONIC-STRUCTURE OF LI-DOPED NIO
VANELP, J; ESKES, H; KUIPER, P; SAWATZKY, GA
1992-01-01
The electronic structure of Li(x)Ni1-xO has been investigated using x-ray photoemission spectroscopy (XPS), bremsstrahlung isochromat spectroscopy (BIS), and model-Hamiltonian cluster calculations. The measurements support the conclusion that the Li-doped holes have mainly oxygen character. The
Structural preablation dynamics of graphite observed by ultrafast electron crystallography
Carbone, Fabrizio; Baum, Peter; Rudolf, Petra; Zewail, Ahmed H.
2008-01-01
By means of time-resolved electron crystallography, we report direct observation of the structural dynamics of graphite, providing new insights into the processes involving coherent lattice motions and ultrafast graphene ablation. When graphite is excited by an ultrashort laser pulse, the excited
Electronic-Structure-Based Design of Ordered Alloys
Bligaard, Thomas; Andersson, M.P.; Jacobsen, Karsten Wedel
2006-01-01
We describe some recent advances in the methodology of using electronic structure calculations for materials design. The methods have been developed for the design of ordered metallic alloys and metal alloy catalysts, but the considerations we present are relevant for the atomic-scale computation...
Electronic structure of Fe- vs. Ru-based dye molecules
Johnson, Phillip S.; Cook, Peter L.; Zegkinoglou, Ioannis;
2013-01-01
In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold...
Atomic and electronic structure of MoS2 nanoparticles
Bollinger, Mikkel; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet
2003-01-01
at the edges. The electronic structure of the edge states is studied and we discuss their influence on the chemical properties of the edges. In particular, we study the reactivity towards hydrogen and show that hydrogen may form stable chemical bonds with both the two low-Miller indexed edges of MoS2. A model...
Structural and electronic properties of perylene from first principles calculations.
Fedorov, I A; Zhuravlev, Y N; Berveno, V P
2013-03-07
The electronic structure of crystalline perylene has been investigated within the framework of density functional theory including van der Waals interactions. The computations of the lattice parameters and cohesive energy have good agreement with experimental values. We have also calculated the binding distance and energy of perylene dimers, using different schemes, which include van der Waals interactions.
CLOPW: a mixed basis set full potential electronic structure method
Bekker, Hermie Gerhard
1997-01-01
This thesis is about the development of the full potental CLOPW package for electronic structure calculations. Chapter 1 provides the necessary background in the theory of solid state physics. It gives a short overview of the effective one particle model as commonly used in solid state physics. It a
Three real-space discretization techniques in electronic structure calculations
Torsti, T; Eirola, T; Enkovaara, J; Hakala, T; Havu, P; Havu, [No Value; Hoynalanmaa, T; Ignatius, J; Lyly, M; Makkonen, [No Value; Rantala, TT; Ruokolainen, J; Ruotsalainen, K; Rasanen, E; Saarikoski, H; Puska, MJ
2006-01-01
A characteristic feature of the state-of-the-art of real-space methods in electronic structure calculations is the diversity of the techniques used in the discretization of the relevant partial differential equations. In this context, the main approaches include finite-difference methods, various ty
Topographic mapping of oral structures - problems and applications in prosthodontics
Young, John M.; Altschuler, Bruce R.
1981-10-01
The diagnosis and treatment of malocclusion, and the proper design of restorations and prostheses, requires the determination of surface topography of the teeth and related oral structures. Surface contour measurements involve not only affected teeth, but adjacent and opposing surface contours composing a complexly interacting occlusal system. No a priori knowledge is predictable as dental structures are largely asymmetrical, non-repetitive, and non-uniform curvatures in 3-D space. Present diagnosis, treatment planning, and fabrication relies entirely on the generation of physical replicas during each stage of treatment. Fabrication is limited to materials that lend themselves to casting or coating, and to hand fitting and finishing. Inspection is primarily by vision and patient perceptual feedback. Production methods are time-consuming. Prostheses are entirely custom designed by manual methods, require costly skilled technical labor, and do not lend themselves to centralization. The potential improvement in diagnostic techniques, improved patient care, increased productivity, and cost-savings in material and man-hours that could result, if rapid and accurate remote measurement and numerical (automated) fabrication methods were devised, would be significant. The unique problems of mapping oral structures, and specific limitations in materials and methods, are reviewed.
Electronic structure and magnetism of samarium and neodymium adatoms on free-standing graphene
Kozub, Agnieszka L.; Shick, Alexander B.; Máca, František; Kolorenč, Jindřich; Lichtenstein, Alexander I.
2016-09-01
The electronic structure of selected rare-earth atoms adsorbed on a free-standing graphene was investigated using methods beyond the conventional density functional theory (DFT+U , DFT+HIA, and DFT+ED). The influence of the electron correlations and the spin-orbit coupling on the magnetic properties has been examined. The DFT+U method predicts both atoms to carry local magnetic moments (spin and orbital) contrary to a nonmagnetic f6 (J =0 ) ground-state configuration of Sm in the gas phase. Application of DFT +Hubbard-I (HIA) and DFT +exact diagonalization (ED) methods cures this problem, and yields a nonmagnetic ground state with six f electrons and J =0 for the Sm adatom. Our calculations show that Nd adatom remains magnetic, with four localized f electrons and J =4.0 . These conclusions could be verified by STM and XAS experiments.
AMORPHOUS SILICON ELECTRONIC STRUCTURE MODELING AND BASIC ELECTRO-PHYSICAL PARAMETERS CALCULATION
B. A. Golodenko
2014-01-01
Full Text Available Summary. The amorphous semiconductor has any unique processing characteristics and it is perspective material for electronic engineering. However, we have not authentic information about they atomic structure and it is essential knot for execution calculation they electronic states and electro physical properties. The author's methods give to us decision such problem. This method allowed to calculation the amorphous silicon modeling cluster atomics Cartesian coordinates, determined spectrum and density its electronic states and calculation the basics electro physical properties of the modeling cluster. At that determined numerical means of the energy gap, energy Fermi, electron concentration inside valence and conduction band for modeling cluster. The find results provides real ability for purposeful control to type and amorphous semiconductor charge carriers concentration and else provides relation between atomic construction and other amorphous substance physical properties, for example, heat capacity, magnetic susceptibility and other thermodynamic sizes.
Structural and Electronic Investigations of Complex Intermetallic Compounds
Ko, Hyunjin [Iowa State Univ., Ames, IA (United States)
2008-01-01
In solid state chemistry, numerous investigations have been attempted to address the relationships between chemical structure and physical properties. Such questions include: (1) How can we understand the driving forces of the atomic arrangements in complex solids that exhibit interesting chemical and physical properties? (2) How do different elements distribute themselves in a solid-state structure? (3) Can we develop a chemical understanding to predict the effects of valence electron concentration on the structures and magnetic ordering of systems by both experimental and theoretical means? Although these issues are relevant to various compound classes, intermetallic compounds are especially interesting and well suited for a joint experimental and theoretical effort. For intermetallic compounds, the questions listed above are difficult to answer since many of the constituent atoms simply do not crystallize in the same manner as in their separate, elemental structures. Also, theoretical studies suggest that the energy differences between various structural alternatives are small. For example, Al and Ga both belong in the same group on the Periodic Table of Elements and share many similar chemical properties. Al crystallizes in the fcc lattice with 4 atoms per unit cell and Ga crystallizes in an orthorhombic unit cell lattice with 8 atoms per unit cell, which are both fairly simple structures (Figure 1). However, when combined with Mn, which itself has a very complex cubic crystal structure with 58 atoms per unit cell, the resulting intermetallic compounds crystallize in a completely different fashion. At the 1:1 stoichiometry, MnAl forms a very simple tetragonal lattice with two atoms per primitive unit cell, while MnGa crystallizes in a complicated rhombohedral unit cell with 26 atoms within the primitive unit cell. The mechanisms influencing the arrangements of atoms in numerous crystal structures have been studied theoretically by calculating electronic
Subotnik, Joseph E; Alguire, Ethan C; Ou, Qi; Landry, Brian R; Fatehi, Shervin
2015-05-19
Electronically photoexcited dynamics are complicated because there are so many different relaxation pathways: fluorescence, phosphorescence, radiationless decay, electon transfer, etc. In practice, to model photoexcited systems is a very difficult enterprise, requiring accurate and very efficient tools in both electronic structure theory and nonadiabatic chemical dynamics. Moreover, these theoretical tools are not traditional tools. On the one hand, the electronic structure tools involve couplings between electonic states (rather than typical single state energies and gradients). On the other hand, the dynamics tools involve propagating nuclei on multiple potential energy surfaces (rather than the usual ground state dynamics). In this Account, we review recent developments in electronic structure theory as directly applicable for modeling photoexcited systems. In particular, we focus on how one may evaluate the couplings between two different electronic states. These couplings come in two flavors. If we order states energetically, the resulting adiabatic states are coupled via derivative couplings. Derivative couplings capture how electronic wave functions change as a function of nuclear geometry and can usually be calculated with straightforward tools from analytic gradient theory. One nuance arises, however, in the context of time-dependent density functional theory (TD-DFT): how do we evaluate derivative couplings between TD-DFT excited states (which are tricky, because no wave function is available)? This conundrum was recently solved, and we review the solution below. We also discuss the solution to a second, pesky problem of origin dependence, whereby the derivative couplings do not (strictly) satisfy translation variance, which can lead to a lack of momentum conservation. Apart from adiabatic states, if we order states according to their electronic character, the resulting diabatic states are coupled via electronic or diabatic couplings. The couplings
Nanographene and graphene edges: electronic structure and nanofabrication.
Fujii, Shintaro; Enoki, Toshiaki
2013-10-15
Graphene can be referred to as an infinite polycyclic aromatic hydrocarbon (PAH) consisting of an infinite number of benzene rings fused together. However, at the nanoscale, nanographene's properties lie in between those of bulk graphene and large PAH molecules, and its electronic properties depend on the influence of the edges, which disrupt the infinite π-electron system. The resulting modulation of the electronic states depends on whether the nanographene edge is the armchair or zigzag type, corresponding to the two fundamental crystal axes. In this Account, we report the results of fabricating both types of edges in the nanographene system and characterizing their electronic properties using a scanning probe microscope. We first introduce the theoretical background to understand the two types of finite size effects on the electronic states of nanographene (i) the standing wave state and (ii) the edge state which correspond to the armchair and zigzag edges, respectively. Most importantly, characterizing the standing wave and edge states could play a crucial role in understanding the chemical reactivity, thermodynamic stability and magnetism of nanosized graphene--important knowledge in the design and realization of promising functionalized nanocarbon materials. In the second part, we present scanning probe microscopic characterization of both edge types to experimentally characterize the two electronic states. As predicted, we find the armchair-edged nanographene to have an energetically stable electronic pattern. The zigzag-edged nanographene shows a nonbonding (π radical) pattern, which is the source of the material's electronic and magnetic properties and its chemical activity. Precise control of the edge geometry is a practical requirement to control the electronic structure. We show that we can fabricate the energetically unstable zigzag edges using scanning probe manipulation techniques, and we discuss challenges in using these techniques for that
Ab initio calculations of yttrium nitride: structural and electronic properties
Zerroug, S.; Ali Sahraoui, F. [Universite Ferhat Abbas, Laboratoire d' Optoelectronique et Composants, Departement de Physique, Setif (Algeria); Bouarissa, N. [King Khalid University, Department of Physics, Faculty of Science, P.O. Box 9004, Abha (Saudi Arabia)
2009-11-15
Using first principles total energy calculations within the full-potential linearized augmented plane wave method, we have studied the structural and electronic properties of yttrium nitride (YN) in the three phases, namely wurtzite, caesium chloride and rocksalt structures. The calculations are performed at zero and under hydrostatic pressure. In agreement with previous findings, it is found that the favored phase for YN is the rocksalt-like structure. We predict that at zero pressure YN in the rocksalt structure is a semiconductor with an indirect bandgap of 0.8 eV. A phase transition from a rocksalt to a caesium chloride structure is found to occur at {proportional_to}134 GPa. Besides, a transition from an indirect ({gamma}-X) bandgap semiconductor to a direct (X-X) one is predicted at pressure of {proportional_to}84 GPa. For the electron effective mass of rocksalt YN, these are the first results, to our knowledge. The information derived from the present study may be useful for the use of YN as an active layer in electronic devices such as diodes and transistors. (orig.)
Computational Electronic Structure of Antiferromagnetic Centers in Metalloproteins.
Rodriguez, Jorge H.
2003-03-01
Nature uses the properties of transition metal ions to carry out a variety of functions associated with vital life processes such as respiration and the transport of oxygen. Oxo-bridged diiron centers are intriguing structural motifs which are present in dioxygen transporting proteins and display antiferromagnetic ordering. We have performed a comprehensive study of the electronic structure and magnetic properties of structurally characterized models for diiron-oxo proteins. Results from Kohn-Sham density functional theory show that the models are antiferromagnetically coupled in agreement with experiment. The physical origin of the spin coupling has been elucidated as the main superexchange pathways responsible for magnetic ordering have been identified. In addition, the exchange constants that parameterize the Heisenberg Hamiltonian, H=JS_1.S_2, have been predicted in excellent agreement with experiment. Our results are important for establishing correlations between electronic structure and biomolecular function and show that computational electronic structure can be used as a powerful tool for the investigation of biomolecular magnetism.
Electronic structure tuning via surface modification in semimetallic nanowires
Sanchez-Soares, Alfonso; O'Donnell, Conor; Greer, James C.
2016-12-01
Electronic structure properties of nanowires (NWs) with diameters of 1.5 and 3 nm based on semimetallic α -Sn are investigated by employing density functional theory and perturbative GW methods. We explore the dependence of electron affinity, band structure, and band-gap values with crystallographic orientation, NW cross-sectional size, and surface passivants of varying electronegativity. We consider four chemical terminations in our study: methyl (CH3), hydrogen (H ), hydroxyl (OH ), and fluorine (F ). Results suggest a high degree of elasticity of Sn-Sn bonds within the Sn NWs' cores with no significant structural variations for nanowires with different surface passivants. Direct band gaps at Brillouin-zone centers are found for most studied structures with quasiparticle corrected band-gap magnitudes ranging from 0.25 to 3.54 eV in 1.5-nm-diameter structures, indicating an exceptional range of properties for semimetal NWs below the semimetal-to-semiconductor transition. Band-gap variations induced by changes in surface passivants indicate the possibility of realizing semimetal-semiconductor interfaces in NWs with constant cross-section and crystallographic orientation, allowing the design of novel dopant-free NW-based electronic devices.
Electronic structure of graphene on Ni surfaces with different orientation
Pudikov, D.A., E-mail: gelbry@gmail.com; Zhizhin, E.V.; Rybkin, A.G.; Rybkina, A.A.; Zhukov, Y.M.; Vilkov, O. Yu.; Shikin, A.M.
2016-08-15
An experimental study of the graphene, synthesized by propylene cracking on Ni surfaces with different orientation: (100) and (111), using angle-resolved photoemission, has been performed. It has been shown that graphene on Ni(111) had a perfect lateral structure due to consistency of their lattices, whereas graphene/Ni(100) consisted of a lot of domains. For both systems electronic structure was quite similar and demonstrated a strong bonding of graphene to the underlying Ni surface. After Au intercalation the electronic structure of graphene in both systems was shifted to the Fermi level and became linear in the vicinity of the K point of the Brillouin zone. - Highlights: • Graphene on Ni(111) is well-ordered, whereas on Ni(100) – multi-domain. • Graphene on Ni(111) and Ni(100) is strongly bonded with substrate. • Intercalation of Au atoms restores the linearity in dispersion and makes graphene quasi-free on both Ni(100) and Ni(111).
Electronic structure of α-oligothiophenes with various substituents
Vikramaditya, Talapunur; Saisudhakar, Mukka; Sumithra, Kanakamma
2015-02-01
Density functional theory is employed to investigate the effect of various substituents on the electronic structure of α-oligothiophenes. The effect of electron donating and withdrawing groups of oligothiophenes in the regio regular HT-HT form is studied. Depending on the type of substituent and the substitution pattern, large differences in the delocalization pattern are observed between the substituted and unsubstituted oligomers. It is found that the band gaps critically depend on the chemical structure and regioselectivity of the building blocks. For the 3-substitued systems, electron donating and electron withdrawing substituents are shown to decrease and increase band gaps respectively compared to unsubstituted systems. There are charge separation effects introduced as a result of lack of symmetry in some of the substituted oligothiophenes. A new strategy is explained to achieve low band gap materials by making use of the regioselective form with lesser symmetry. Push-pull substitution with an electron donor at one end of the conjugation and an acceptor the other end is also investigated. Comparisons of band gaps of the substituted oligothiophenes with the corresponding polymeric systems are also done.
XUJungang; WANGHongan; DAIGuozhong
2004-01-01
Currently, the world is in the times that knowledge economy is growing up rapidly. The gathering, sharing, using and spreading of information have become key factors of influencing competition capability of one enterprise; at the same time, information technologies that support distributed computing and information sharing appear one after the other. Therefore, distributed computing will become an inevitable trend of development of enterprise informatization. As one part of the construction industry, the housing industry is emerging as a new application frontier for information technologies. According to the applications of information technologies in the housing industry, this paper puts forth a Problem Solving Environment for electronic commerce and collaborative work, electronic-PSE (e-PSE), which is an Intranet/Internet platform for solving many problems existing in the housing industry, such as building of virtual organization, system integration, development of new Internet/Intranet application and so on. The information infrastructure framework of e-PSE is presented, whichi ncludes two modules: XML-based electronic commerce platform (XECP), XML-based collaborative work platform(XCWP). XECP provides solutions for integration of construction system and electronic commerce system; XCWP provides solutions for building of virtual organization and implementation of collaborative work of partners. At last,conclusions and prospects are presented.
Electronic structure of multi-walled carbon fullerenes
Doore, Keith; Cook, Matthew; Clausen, Eric; Lukashev, Pavel V.; Kidd, Tim E.; Stollenwerk, Andrew J.
2017-02-01
Despite an enormous amount of research on carbon based nanostructures, relatively little is known about the electronic structure of multi-walled carbon fullerenes, also known as carbon onions. In part, this is due to the very high computational expense involved in estimating electronic structure of large molecules. At the same time, experimentally, the exact crystal structure of the carbon onion is usually unknown, and therefore one relies on qualitative arguments only. In this work we present the results of a computational study on a series of multi-walled fullerenes and compare their electronic structures to experimental data. Experimentally, the carbon onions were fabricated using ultrasonic agitation of isopropanol alcohol and deposited onto the surface of highly ordered pyrolytic graphite using a drop cast method. Scanning tunneling microscopy images indicate that the carbon onions produced using this technique are ellipsoidal with dimensions on the order of 10 nm. The majority of differential tunneling spectra acquired on individual carbon onions are similar to that of graphite with the addition of molecular-like peaks, indicating that these particles span the transition between molecules and bulk crystals. A smaller, yet sizable number exhibited a semiconducting gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels. These results are compared with the electronic structure of different carbon onion configurations calculated using first-principles. Similar to the experimental results, the majority of these configurations are metallic with a minority behaving as semiconductors. Analysis of the configurations investigated here reveals that each carbon onion exhibiting an energy band gap consisted only of non-metallic fullerene layers, indicating that the interlayer interaction is not significant enough to affect the total density of states in these structures.
Characterization of strained semiconductor structures using transmission electron microscopy
Oezdoel, Vasfi Burak
2011-08-15
Today's state-of-the-art semiconductor electronic devices utilize the charge transport within very small volumes of the active device regions. The structural, chemical and optical material properties in these small dimensions can critically affect the performance of these devices. The present thesis is focused on the nanometer scale characterization of the strain state in semiconductor structures using transmission electron microscopy (TEM). Although high-resolution TEM has shown to provide the required accuracy at the nanometer scale, optimization of imaging conditions is necessary for accurate strain measurements. An alternative HRTEM method based on strain mapping on complex-valued exit face wave functions is developed to reduce the artifacts arising from objective lens aberrations. However, a much larger field of view is crucial for mapping strain in the active regions of complex structures like latest generation metal-oxide-semiconductor field-effect transistors (MOSFETs). To overcome this, a complementary approach based on electron holography is proposed. The technique relies on the reconstruction of the phase shifts in the diffracted electron beams from a focal series of dark-field images using recently developed exit-face wave function reconstruction algorithm. Combining high spatial resolution, better than 1 nm, with a field of view of about 1 {mu}m in each dimension, simultaneous strain measurements on the array of MOSFETs are possible. Owing to the much lower electron doses used in holography experiments when compared to conventional quantitative methods, the proposed approach allows to map compositional distribution in electron beam sensitive materials such as InGaN heterostructures without alteration of the original morphology and chemical composition. Moreover, dark-field holography experiments can be performed on thicker specimens than the ones required for high-resolution TEM, which in turn reduces the thin foil relaxation. (orig.)
Toward the origin of exciton electronic structure in phycobiliproteins
Womick, Jordan M.; Miller, Stephen A.; Moran, Andrew M.
2010-07-01
Femtosecond laser spectroscopies are used to examine the electronic structures of two proteins found in the phycobilisome antenna of cyanobacteria, allophycocyanin (APC) and C-phycocyanin (CPC). The wave function composition involving the pairs of phycocyanobilin pigments (i.e., dimers) found in both proteins is the primary focus of this investigation. Despite their similar geometries, earlier experimental studies conducted in our laboratory and elsewhere observe clear signatures of exciton electronic structure in APC but not CPC. This issue is further investigated here using new experiments. Transient grating (TG) experiments employing broadband quasicontinuum probe pulses find a redshift in the signal spectrum of APC, which is almost twice that of CPC. Dynamics in the TG signal spectra suggest that the sub-100 fs dynamics in APC and CPC are respectively dominated by internal conversion and nuclear relaxation. A specialized technique, intraband electronic coherence spectroscopy (IECS), photoexcites electronic and nuclear coherences with nearly full suppression of signals corresponding to electronic populations. The main conclusion drawn by IECS is that dephasing of intraband electronic coherences in APC occurs in less than 25 fs. This result rules out correlated pigment fluctuations as the mechanism enabling exciton formation in APC and leads us to propose that the large Franck-Condon factors of APC promote wave function delocalization in the vibronic basis. For illustration, we compute the Hamiltonian matrix elements involving the electronic origin of the α84 pigment and the first excited vibronic level of the β84 pigment associated with a hydrogen out-of-plane wagging mode at 800 cm-1. For this pair of vibronic states, the -51 cm-1 coupling is larger than the 40 cm-1 energy gap, thereby making wave function delocalization a feasible prospect. By contrast, CPC possesses no pair of vibronic levels for which the intermolecular coupling is larger than the energy
Problem statement for optimal design of steel structures
Ginzburg Aleksandr Vital'evich
2014-07-01
Full Text Available The presented article considers the following complex of tasks. The main stages of the life cycle of a building construction with the indication of process entrance and process exit are described. Requirements imposed on steel constructions are considered. The optimum range of application for steel designs is specified, as well as merits and demerits of a design material. The nomenclature of metal designs is listed - the block diagram is constructed. Possible optimality criteria of steel designs, offered by various authors for various types of constructions are considered. It is established that most often the criterion of a minimum of design mass is accepted as criterion of optimality; more rarely - a minimum of the given expenses, a minimum of a design cost in business. In the present article special attention is paid to a type of objective function of optimization problem. It is also established that depending on the accepted optimality criterion, the use of different types of functions is possible. This complexity of objective function depends on completeness of optimality criterion application. In the work the authors consider the following objective functions: the mass of the main element of a design; objective function by criterion of factory cost; objective function by criterion of cost in business. According to these examples it can be seen that objective functions by the criteria of labor expenses for production of designs are generally non-linear, which complicates solving the optimization problem. Another important factor influencing the problem of optimal design solution for steel designs, which is analyzed, is account for operating restrictions. In the article 8 groups of restrictions are analyzed. Attempts to completely account for the parameters of objective function optimized by particular optimality criteria, taking into account all the operating restrictions, considerably complicates the problem of designing. For solving this
A new parametrizable model of molecular electronic structure
Laikov, Dimitri N
2011-01-01
A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the paramtrization procedure -- making a direct link...
Research Projects in Physics: A Mechanism for Teaching Ill-Structured Problem Solving
Milbourne, Jeff; Bennett, Jonathan
2017-10-01
Physics education research has a tradition of studying problem solving, exploring themes such as physical intuition and differences between expert and novice problem solvers. However, most of this work has focused on traditional, or well-structured, problems, similar to what might appear in a textbook. Less work has been done with open-ended, or ill-structured, problems, similar to the types of problems students might face in their professional lives. Given the national discourse on educational system reform aligned with 21st century skills, including problem solving, it is critical to provide educational experiences that help students learn to solve all types of problems, including ill-structured problems.
Owens, Jonathan R.
In this work, we first present two powerful methods for understanding the electronic, structural, conducting, and energetic properties of nano-materials: density functional theory (DFT) and quantum transport. The basics of the theory and background of both methods are discussed thoroughly. After establishing a firm foundation, we turn our attention to using these tools to solve practical problems, often in collaboration with experimental colleagues. The first two projects pertain to nitrogen doping in graphene nanoribbons (GNRs). We study nitrogen doping in two different schema: concentration-based (N_x-doped) and structural based (N_2. {AA}-doped). Concentration based doping is explored in the context of experimental measurements of IV curves on GNRs with differing dopant concentrations. These results show a shift towards semi-conducting behavior with an increase in dopant concentration. We combine first principles calculations (DFT) and transport calculations in the Landauer formalism to compute the density-of-states (DOS) and transport curves for various dopant concentrations (0.46%, 1.39%, 1.89%, and 2.31%), which corroborate the experimental observations. The N_2. {AA}-doped GNR study was inspired by experimental observation of an atomically precise nitrogen doping scheme in bulk graphene. Experimental STM images, combined with simulated STM images, revealed that the majority (80%) of doping sites consist of nitrogen atoms on neighboring sites of the same sublattice (A) in graphene, hence N_2. {AA} doping. We examine this doping scheme applied to zigzag and armchair GNRs under different orientations of the dopants. We present spin-resolved charge densities, energetics, transport, DOS, and simulated STM images for all four systems studied. Our results show the possibility of spin-filtered devices and the STM images provide an aid in helping experimentalist identify the dopant patterns, if these GNRs are fabricated. We next venture to explain different observed
Electronic structure of superlattices of graphene and hexagonal boron nitride
Kaloni, Thaneshwor P.
2011-11-14
We study the electronic structure of superlattices consisting of graphene and hexagonal boron nitride slabs, using ab initio density functional theory. We find that the system favors a short C–B bond length at the interface between the two component materials. A sizeable band gap at the Dirac point is opened for superlattices with single graphene layers but not for superlattices with graphene bilayers. The system is promising for applications in electronic devices such as field effect transistors and metal-oxide semiconductors.
Electronic structure and thermoelectric transport of black phosphorus
Craco, L.; Pereira, T. A. da Silva; Leoni, S.
2017-08-01
We investigate anisotropic electronic structure and thermal transport properties of bulk black phosphorus (BP). Using density functional dynamical mean-field theory we first derive a correlation-induced electronic reconstruction, showing band-selective Kondoesque physics in this elemental p -band material. The resulting correlated picture is expected to shed light onto the temperature and doping dependent evolution of resistivity, Seebeck coefficient, and thermal conductivity, as seen in experiments on bulk single crystal BP. Therein, large anisotropic particle-hole excitations are key to consistently understand thermoelectric transport responses of pure and doped BP.
Electronic States in Quasi-one-Dimensional Copolymeric Sandwich Structures
刘德胜; 王鹿霞; 魏建华; 郑斌; 解士杰; 韩圣浩; 梅良模
2001-01-01
The electronic properties of xPA/nPPP/yPA sandwiched copo]ymers with a well-barrier-well structure have been studied by using a tight-binding calculation. It was found that the electronic properties of the neutral states of these sandwiched copolymers are sensitive to the constitutions of PPP and PA monomers and the interface coupling between PA and PPP. It is verified that the quantum tunnelling effect will occur at the lowest conductive state of xPA/nPPP/xPA copolymers.
Electronic structure and ionicity of actinide oxides from first principles
Petit, Leon; Svane, Axel; Szotek, Z.
2010-01-01
The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, which...... in the actinide dioxides is discussed, and it is found that the dioxide is the most stable oxide for the actinides from Np onward. Our study reveals a strong link between preferred oxidation number and degree of localization which is confirmed by comparing to the ground-state configurations of the corresponding...
Structures of quantum 2D electron-hole plasmas
Filinov, V S; Fehske, H; Levashov, P R; Fortov, V E
2008-01-01
We investigate structures of 2D quantum electron-hole (e-h) plasmas by the direct path integral Monte Carlo method (PIMC) in a wide range of temperature, density and hole-to-electron mass ratio. Our simulation includes a region of appearance and decay of the bound states (excitons and biexcitons), the Mott transition from the neutral e-h plasma to metallic-like clusters, formation from clusters the hexatic-like liquid and formation of the crystal-like lattice.
Sergeyev, Yaroslav D; Grimaldi, Domenico; Molinaro, Anna
2011-01-01
In this paper we introduce a common problem in electronic measurements and electrical engineering: finding the first root from the left of an equation in the presence of some initial conditions. We present examples of electrotechnical devices (analog signal filtering), where it is necessary to solve it. Two new methods for solving this problem, based on global optimization ideas, are introduced. The first uses the exact a priori given global Lipschitz constant for the first derivative. The second method adaptively estimates local Lipschitz constants during the search. Both algorithms either find the first root from the left or determine the global minimizers (in the case when the objective function has no roots). Sufficient conditions for convergence of the new methods to the desired solution are established in both cases. The results of numerical experiments for real problems and a set of test functions are also presented.
Solving Optimal Control Problems by Exploiting Inherent Dynamical Systems Structures
Flaßkamp, Kathrin; Ober-Blöbaum, Sina; Kobilarov, Marin
2012-08-01
Computing globally efficient solutions is a major challenge in optimal control of nonlinear dynamical systems. This work proposes a method combining local optimization and motion planning techniques based on exploiting inherent dynamical systems structures, such as symmetries and invariant manifolds. Prior to the optimal control, the dynamical system is analyzed for structural properties that can be used to compute pieces of trajectories that are stored in a motion planning library. In the context of mechanical systems, these motion planning candidates, termed primitives, are given by relative equilibria induced by symmetries and motions on stable or unstable manifolds of e.g. fixed points in the natural dynamics. The existence of controlled relative equilibria is studied through Lagrangian mechanics and symmetry reduction techniques. The proposed framework can be used to solve boundary value problems by performing a search in the space of sequences of motion primitives connected using optimized maneuvers. The optimal sequence can be used as an admissible initial guess for a post-optimization. The approach is illustrated by two numerical examples, the single and the double spherical pendula, which demonstrates its benefit compared to standard local optimization techniques.
Electronic phases of substances. Phase transitions with change of electron and crystalline structure
Nadykto Boris
2015-01-01
Full Text Available There is plenty of experimental data on high-pressure phase transformations in various materials. Variations in materials characteristics (for example, equilibrium density and bulk modulus, while the crystalline structure remains unchanged, are indicative of energy variations in outer-shell electrons of solid atoms. In experiments with crystalline structure variations, the dependence of pressure on density in some cases can be described by the same curve, the parameters of which are independent of the crystalline structure. Examples of such transformations in some materials at static compression and in shock-wave experiments are given.
Atomic and Electronic Structures of Zr Atomic Chains
林益寿; 李爱玉; 朱梓忠
2004-01-01
The atomic, binding and electronic structures of very thin Zr chains are studied by the first-principles densityfunctional method. The present calculations reveal that zirconium can form planar chains in zigzag, dimer and ladder structures. The zigzag geometry has two minima. The most stable geometry is the zigzag one with a unit cell rather close to equilateral triangles with four nearest neighbours. The other stable zigzag structure has a wide bond angle and allows for two nearest neighbours. An intermediary structure has the ladder geometry and is formed by two strands. The dimer structure is also found to be more stable than the truly linear chain. All these planar geometries are more favourable energetically than the linear chain. We also show that by going from Zr bulk to a Zr chain, the characters of bonding do not change significantly.
Electronic and Thermal Properties of Graphene and Carbon Structures
Anthony, Gilmore; Khatun, Mahfuza
2011-10-01
We will present the general properties of carbon structures. The research involves the study of carbon structures: Graphene, Graphene nanoribbons (GNRs), and Carbon Nanotubes (CNTs). A review of electrical and thermal conduction phenomena of the structures will be discussed. Particularly carbon nanoribbons and CNTs have many interesting physical properties, and have the potential for device applications. Our research interests include the study of electronic structures, electrical and thermal transport properties of the carbon structures. Results are produced analytically as well as by simulation. The numerical simulations are conducted using various tools such as Visual Molecular Dynamics (VMD), Large Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), NanoHub at Purdue University and the Beowulf Cluster at Ball State University.
Fluctuation electron microscopy studies of complex structured materials
Zhao, Gongpu; Rougée, Annick; Buseck, Peter; Treacy, Michael
2008-03-01
Fluctuation electron microscopy (FEM) is a hybrid imaging-diffraction technique. This technique is particularly sensitive to paracrystalline structures of dimension 0.5-2 nm, which are difficult to detect by either imaging or diffraction techniques alone. It has been successfully deployed to study paracrystalline structures in amorphous silicon, germanium thin film. This technique has also been used to study metallic glasses and oxide glasses. Until now, FEM has not been used to study disordered geological materials. In this talk we present our FEM studies of shungite, a naturally occurring disordered carbonaceous material, reveal that trace quantities of tightly curved graphene structures such as C60, or fragments of C60, is present in shungite. We also present results from our study of metamict zircon, whose crystal structure is destroyed by self-radiation during naturally occurring α decay events. Work is in progress to study the structural evolution during the metamictization process.
Structural and electronic effects resulting from metal-flavin ligation.
Clarke, M J; Dowling, M G; Garafalo, A R; Brennan, T F
1980-04-25
The synthesis and physical properties of a model metalloflavin complex, [(10-methylisoalloxazine)-(NH3)4Ru](PF6)2 . 2H2O are reported. The structure of this stable, enantiomeric compound was elucidated by x-ray diffraction methods with a final unweighted R value of 0.054. Crystals belong to the triclinic space group P1 with unit cell dimensions: a = 9.631, b = 10.618, c = 13.216 A; alpha = 113.86, beta = 100.19, gamma = 94.12 degrees. Chelation of the metal ion to the flavin occurs at the N(5) and O(4) positions, with a short Ru-N(5) bond distance of 1.979 A. Steric and electronic factors induce a 9.9 degrees bend in the isoalloxazine ring system and a significant lengthening of the C(4a)-N(5) bond. The flavin absorption bands shift significantly toward lower energy on complexation and a new band occurs at 617 nm. These absorptions are pH-dependent and pK alpha values for the complex are 0.6 and 7.4. The spectra of this complex exhibit similarities to that of metallosemiquinone species and arguments are made that a significant amount of electron density is donated to the pi-system of the flavin. Proton NMR studies suggest enhanced electron density at the N(10) position, probably occurring through backbonding interactions. Cyclic voltametry studies are also consistent with substantial metal to ligand pi-electron donation, since it is significantly more difficult to reduce the coordinated flavin relative to the free ligand under the same conditions. Moreover, the complexed flavin accepts electrons in 1-electron rather than 2-electron steps. Spectroelectrochemical studies on the 1-electron reduced complex indicate a similarity with other M(II)-F1 species.
Kervalishvili, N A
2015-01-01
The results of experimental investigations of electron ejection from gas-discharge nonneutral electron plasma at the formation and radial oscillations of vortex structure have been presented. The electrons are injected from the vortex structure and the adjacent region of electron sheath in the form of pulses the duration and periodicity of which are determined by the processes of evolution and dynamics of this structure. The possible mechanisms of pulse ejection of electrons are considered. The influence of electron ejection on other processes in discharge electron sheath is analyzed.
Real-time feedback from iterative electronic structure calculations.
Vaucher, Alain C; Haag, Moritz P; Reiher, Markus
2016-04-05
Real-time feedback from iterative electronic structure calculations requires to mediate between the inherently unpredictable execution times of the iterative algorithm used and the necessity to provide data in fixed and short time intervals for real-time rendering. We introduce the concept of a mediator as a component able to deal with infrequent and unpredictable reference data to generate reliable feedback. In the context of real-time quantum chemistry, the mediator takes the form of a surrogate potential that has the same local shape as the first-principles potential and can be evaluated efficiently to deliver atomic forces as real-time feedback. The surrogate potential is updated continuously by electronic structure calculations and guarantees to provide a reliable response to the operator for any molecular structure. To demonstrate the application of iterative electronic structure methods in real-time reactivity exploration, we implement self-consistent semiempirical methods as the data source and apply the surrogate-potential mediator to deliver reliable real-time feedback.
Electronic structure and insulating gap in epitaxial VO2 polymorphs
Shinbuhm Lee
2015-12-01
Full Text Available Determining the origin of the insulating gap in the monoclinic V O2(M1 is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating V O2(A and V O2(B thin films to better understand the insulating phase of VO2. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO2 phases. By x-ray absorption and optical spectroscopy, we find that the shift of unoccupied t2g orbitals away from the Fermi level is a common feature, which plays an important role for the insulating behavior in VO2 polymorphs. The distinct splitting of the half-filled t2g orbital is observed only in the M1 phase, widening the bandgap up to ∼0.6 eV. Our approach of comparing all three insulating VO2 phases provides insight into a better understanding of the electronic structure and the origin of the insulating gap in VO2.
Compressed Sensing Electron Tomography for Determining Biological Structure
Guay, Matthew D.; Czaja, Wojciech; Aronova, Maria A.; Leapman, Richard D.
2016-06-01
There has been growing interest in applying compressed sensing (CS) theory and practice to reconstruct 3D volumes at the nanoscale from electron tomography datasets of inorganic materials, based on known sparsity in the structure of interest. Here we explore the application of CS for visualizing the 3D structure of biological specimens from tomographic tilt series acquired in the scanning transmission electron microscope (STEM). CS-ET reconstructions match or outperform commonly used alternative methods in full and undersampled tomogram recovery, but with less significant performance gains than observed for the imaging of inorganic materials. We propose that this disparity stems from the increased structural complexity of biological systems, as supported by theoretical CS sampling considerations and numerical results in simulated phantom datasets. A detailed analysis of the efficacy of CS-ET for undersampled recovery is therefore complicated by the structure of the object being imaged. The numerical nonlinear decoding process of CS shares strong connections with popular regularized least-squares methods, and the use of such numerical recovery techniques for mitigating artifacts and denoising in reconstructions of fully sampled datasets remains advantageous. This article provides a link to the software that has been developed for CS-ET reconstruction of electron tomographic data sets.
Electronic structure and electron energy-loss spectroscopy of ZrO2 zirconia
Dash, L. K.; Vast, Nathalie; Baranek, Philippe; Cheynet, Marie-Claude; Reining, Lucia
2004-12-01
The atomic and electronic structures of zirconia are calculated within density functional theory, and their evolution is analyzed as the crystal-field symmetry changes from tetrahedral [cubic (c-ZrO2) and tetragonal (t-ZrO2) phases] to octahedral (hypothetical rutile ZrO2 ), to a mixing of these symmetries (monoclinic phase, m-ZrO2 ). We find that the theoretical bulk modulus in c-ZrO2 is 30% larger than the experimental value, showing that the introduction of yttria in zirconia has a significant effect. Electronic structure fingerprints which characterize each phase from their electronic spectra are identified. We have carried out electron energy-loss spectroscopy experiments at low momentum transfer and compared these results to the theoretical spectra calculated within the random phase approximation. We show a dependence of the valence and 4p ( N2,3 edge) plasmons on the crystal structure, the dependence of the latter being brought into the spectra by local-field effects. Last, we attribute low energy excitations observed in EELS of m-ZrO2 to defect states 2eV above the top of the intrinsic valence band, and the EELS fundamental band gap value is reconciled with the 5.2 or 5.8eV gaps determined by vacuum ultraviolet spectroscopy.
Schwingenschlögl, Udo
2009-12-01
Motivated by a RIXS study of Wakimoto, et al.(Phys. Rev. Lett., 102 (2009) 157001) we use density functional theory to analyze the magnetic order in the nickelate La5/3Sr1/3NiO4 and the details of its crystal and electronic structure. We compare the generalized gradient approximation to the hybrid functional approach of exact exchange for correlated electrons (EECE). In contrast to the former, the latter reproduces the insulating state of the compound and the midgap states. The EECE approach, in general, appears to be appropriate for describing stripe phases in systems with orbital degrees of freedom. Copyright © EPLA, 2009.
Decay properties of spectral projectors with applications to electronic structure
Benzi, Michele; Razouk, Nader
2012-01-01
Motivated by applications in quantum chemistry and solid state physics, we apply general results from approximation theory and matrix analysis to the study of the decay properties of spectral projectors associated with large and sparse Hermitian matrices. Our theory leads to a rigorous proof of the exponential off-diagonal decay ("nearsightedness") for the density matrix of gapped systems at zero electronic temperature in both orthogonal and non-orthogonal representations, thus providing a firm theoretical basis for the possibility of linear scaling methods in electronic structure calculations for non-metallic systems. We further discuss the case of density matrices for metallic systems at positive electronic temperature. A few other possible applications are also discussed.
Valence electronic structure of tantalum carbide and nitride
FAN; ChangZeng
2007-01-01
The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.……
Valence electronic structure of tantalum carbide and nitride
无
2007-01-01
@@ The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.
Electronic Structures of Silicene Doped with Galium: First Principle study
Pamungkas Mauludi Ariesto
2015-01-01
Full Text Available Following the success of graphene which possesses unique and superior properties, 2D material other than graphene become centre of interest of material scientists.Silicene, which has the same crystal structure as graphene but consist of silicon atoms rather than carbon become intriguing material due to domination of silicon as main material of electronic component. It is common to enhance electronic properties of semiconductor by adding dopant atoms. The electronic properties of Silicene doped with Gallium are investigated using first principle calculation based on density functional theory (DFT.Ga doping changes character of silicene from semimetal to conductor except silicene with Ga doping on S-site (Ga atom substitutes one Si atom which lead to semiconductor.
Electronic structures of nickel metal with hydrogen impurity
冯艳全; 王崇愚; 陈能宽
2001-01-01
By using a first-principles numerical method, the electronic structures of face-centered cubic Ni doped with H, H+ and H- are investigated. In two adopted cluster models, H occupies the centers of octahedron and tetrahedron as interstitial. It was found that the former is preferentially occupied. The constructed Ni-H, Ni-H+ and Ni-H- bonds are only slightly different due to electron flowing. The residual (doping H-) or insufficient (doping H+) electrons are basically absorbed or supplied by the further matrix atoms. The additions induce a strong reduction of the interactions between their first neighbor atoms, but a weaker alteration of those between their first and second neighbors, which is the expression of hydrogen local effect and can be regarded as an explanation of hydrogen embrittlement.
Perspective: Explicitly correlated electronic structure theory for complex systems
Grüneis, Andreas; Hirata, So; Ohnishi, Yu-ya; Ten-no, Seiichiro
2017-02-01
The explicitly correlated approach is one of the most important breakthroughs in ab initio electronic structure theory, providing arguably the most compact, accurate, and efficient ansatz for describing the correlated motion of electrons. Since Hylleraas first used an explicitly correlated wave function for the He atom in 1929, numerous attempts have been made to tackle the significant challenges involved in constructing practical explicitly correlated methods that are applicable to larger systems. These include identifying suitable mathematical forms of a correlated wave function and an efficient evaluation of many-electron integrals. R12 theory, which employs the resolution of the identity approximation, emerged in 1985, followed by the introduction of novel correlation factors and wave function ansätze, leading to the establishment of F12 theory in the 2000s. Rapid progress in recent years has significantly extended the application range of explicitly correlated theory, offering the potential of an accurate wave-function treatment of complex systems such as photosystems and semiconductors. This perspective surveys explicitly correlated electronic structure theory, with an emphasis on recent stochastic and deterministic approaches that hold significant promise for applications to large and complex systems including solids.
Electronic Structure and Stability of C20 Isomers
曹则贤
2001-01-01
The electronic structure of the C20 cluster in monocyclic ring, bowl and fullerene isomers has been calculated using the tight-binding scheme developed by Harrison, starting in particular from the sp2.803-hybrids for the fullerene structure. The study of energetics predicts the fullerene to be the ground state with the bowl and ring lying over 1.32 and 3.35 eV higher in energy. The total energies will be lowered by Peierls or Jahn-Teller distortion, but the energetic ordering remains unchanged. It is also shown that the range of valence electron, the level difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as the σ - π gap, which are less sensitive to the exact geometry, vary in the ring, bowl and fullerene sequence.
Structural and electronic properties of arsenic nitrogen monolayer
Liu, Pei; Nie, Yao-zhuang; Xia, Qing-lin; Guo, Guang-hua
2017-03-01
We present our first-principles calculations of a new two-dimensional material, arsenic nitrogen monolayer. The structural, electronic, and mechanical properties are investigated in detail by means of density functional theory computations. The calculated binding energy and the phonon spectra demonstrate that the AsN can form stable monolayer in puckered honeycomb structure. It is a semiconductor with indirect band gap of 0.73 eV, and displays highly anisotropic mechanical properties. Strain has obvious influence on the electronic properties of AsN monolayer. It is found that in the armchair direction, a moderate compression strain (-12%) can trigger an indirect to direct band gap transition and a tensile strain of 18% can make the AsN becoming a stable metal. In the zigzag direction, a rather smaller strain than armchair direction (12% for compression and 8% for stretch) can induce the indirect band gap to metal transition.
Electronic structure of spontaneously strained graphene on hexagonal boron nitride
San-Jose, Pablo; Gutiérrez-Rubio, A.; Sturla, Mauricio; Guinea, Francisco
2014-09-01
Hexagonal boron nitride substrates have been shown to dramatically improve the electric properties of graphene. Recently, it has been observed that when the two honeycomb crystals are close to perfect alignment, strong lattice distortions develop in graphene due to the moiré adhesion landscape. Simultaneously, a gap opens at the Dirac point. Here, we derive a simple low-energy electronic model for graphene aligned with the substrate, taking into account spontaneous strains at equilibrium and pseudogauge fields. We carry out a detailed characterization of the modified band structure, gap, local and global density of states, and band topology in terms of physical parameters. We show that the overall electronic structure is strongly modified by the spontaneous strains.
Strongly correlated electron materials. I. Theory of the quasiparticle structure
Lopez-Aguilar, F.; Costa-Quintana, J.; Puig-Puig, L. (Departamento de Fisica, Grupo de Electromagnetismo, Universidad Autonoma de Barcelona, Bellaterra, E-08193 Barcelona (Spain))
1993-07-01
In this paper we give a method for analyzing the renormalized electronic structure of the Hubbard systems. The first step is the determination of effective interactions from the random-phase approximation (RPA) and from an extended RPA (ERPA) that introduces vertex effects within the bubble polarization. The second step is the determination of the density of states deduced from the spectral functions. Its analysis leads us to conclude that these systems can exhibit three types of resonances in their electronic structures: the lower-, middle-, and upper-energy resonances. Furthermore, we analyze the conditions for which there is only one type of resonance and the causes that lead to the disappearance of the heavy-fermion state. We finally introduce the RPA and ERPA effective interactions within the strong-coupling theory and we give the conditions for obtaining coupling and superconductivity.
Phase Diagram and Electronic Structure of Praseodymium and Plutonium
Lanatà, Nicola; Yao, Yongxin; Wang, Cai-Zhuang; Ho, Kai-Ming; Kotliar, Gabriel
2015-01-01
We develop a new implementation of the Gutzwiller approximation in combination with the local density approximation, which enables us to study complex 4 f and 5 f systems beyond the reach of previous approaches. We calculate from first principles the zero-temperature phase diagram and electronic structure of Pr and Pu, finding good agreement with the experiments. Our study of Pr indicates that its pressure-induced volume-collapse transition would not occur without change of lattice structure—contrarily to Ce. Our study of Pu shows that the most important effect originating the differentiation between the equilibrium densities of its allotropes is the competition between the Peierls effect and the Madelung interaction and not the dependence of the electron correlations on the lattice structure.
Electronic Structure and Geometries of Small Compound Metal Clusters
NONE
1999-04-14
During the tenure of the DOE grant DE-FG05-87EI145316 we have concentrated on equilibrium geometries, stability, and the electronic structure of transition metal-carbon clusters (met-cars), clusters designed to mimic the chemistry of atoms, and reactivity of homo-nuclear metal clusters and ions with various reactant molecules. It is difficult to describe all the research the authors have accomplished as they have published 38 papers. In this report, they outline briefly the salient features of their work on the following topics: (1) Designer Clusters: Building Blocks for a New Class of Solids; (2) Atomic Structure, Stability, and Electronic Properties of Metallo-Carbohedrenes; (3) Reactivity of Metal Clusters with H{sub 2} and NO; and (4) Anomalous Spectroscopy of Li{sub 4} Clusters.
Electronic Structure and Geometries of Small Compound Metal Clusters
NONE
1999-04-14
During the tenure of the DOE grant DE-FG05-87EI145316 we have concentrated on equilibrium geometries, stability, and the electronic structure of transition metal-carbon clusters (met-cars), clusters designed to mimic the chemistry of atoms, and reactivity of homo-nuclear metal clusters and ions with various reactant molecules. It is difficult to describe all the research the authors have accomplished as they have published 38 papers. In this report, they outline briefly the salient features of their work on the following topics: (1) Designer Clusters: Building Blocks for a New Class of Solids; (2) Atomic Structure, Stability, and Electronic Properties of Metallo-Carbohedrenes; (3) Reactivity of Metal Clusters with H{sub 2} and NO; and (4) Anomalous Spectroscopy of Li{sub 4} Clusters.
Electronic Structure of Silicon Nanowires Matrix from Ab Initio Calculations.
Monastyrskii, Liubomyr S; Boyko, Yaroslav V; Sokolovskii, Bogdan S; Potashnyk, Vasylyna Ya
2016-12-01
An investigation of the model of porous silicon in the form of periodic set of silicon nanowires has been carried out. The electronic energy structure was studied using a first-principle band method-the method of pseudopotentials (ultrasoft potentials in the basis of plane waves) and linearized mode of the method of combined pseudopotentials. Due to the use of hybrid exchange-correlation potentials (B3LYP), the quantitative agreement of the calculated value of band gap in the bulk material with experimental data is achieved. The obtained results show that passivation of dangling bonds with hydrogen atoms leads to substantial transformation of electronic energy structure. At complete passivation of the dangling silicon bonds by hydrogen atoms, the band gap value takes the magnitude which substantially exceeds that for bulk silicon. The incomplete passivation gives rise to opposite effect when the band gap value decreases down the semimetallic range.
Electronic shell and supershell structure in graphene flakes
Manninen, M; Akola, J
2008-01-01
We use a simple tight-binding (TB) model to study electronic properties of free graphene flakes. Valence electrons of triangular graphene flakes show a shell and supershell structure which follows an analytical expression derived from the solution of the wave equation for triangular cavity. However, the solution has different selection rules for triangles with armchair and zigzag edges, and roughly 40000 atoms are needed to see clearly the first supershell oscillation. In the case of spherical flakes, the edge states of the zigzag regions dominate the shell structure which is thus sensitive to the flake diameter and center. A potential well that is made with external gates cannot have true bound states in graphene due to the zero energy band gap. However, it can cause strong resonances in the conduction band.
Electronic Structure Rearrangements in Hybrid Ribozyme/Protein Catalysis
Kang, Jiyoung; Kino, Hiori; Field, Martin J.; Tateno, Masaru
2017-04-01
We analyzed the electronic structural changes that occur in the reaction cycle of a biological catalyst composed of RNA and protein, and elucidated the dynamical rearrangements of the electronic structure that was obtained from our previous study in which ab initio quantum mechanics/molecular mechanics molecular dynamics simulations were performed. Notable results that we obtained include the generation of a reactive HOMO that is responsible for bond formation in the initial stages of the reaction, and the appearance of a reactive LUMO that is involved in the bond rupture that leads to products. We denote these changes as dynamical induction of the reactive HOMO (DIRH) and LUMO (DIRL), respectively. Interestingly, we also find that the induction of the reactive HOMO is enhanced by the formation of a low-barrier hydrogen bond (LBHB), which, to the best of our knowledge, represents a novel role for LBHBs in enzymatic systems.
Electronic structure of the radical-cations of phenothiazine and its structural analogs
Turchaninov, V.K.; Ermikov, A.F.; Shagun, V.A.
1986-09-20
The electronic structure of the radical-cations of phenothiazine and some of its derivatives and heteroanalogs was investigated by electronic absorption spectroscopy. On the basis of the obtained results and also of the data from photoelectron spectroscopy of the parent molecules, quantum-chemical calculations (MINDO/3), and published data it was concluded that the occupied molecular orbitals of the excess-..pi.. heteroatomic system exhibit different sensitivities to hole formation. It is suggested that this is due to the different degrees of delocalization of the unpaired electron in the ground and electronically excited states of the radical cation of such molecules.
Phosphorene Nanoribbons: Electronic Structure and Electric Field Modulation
Soleimanikahnoj, Sina; Knezevic, Irena
Phosphorene, a newcomer among the 2D van der Waals materials, has attracted the attention of many scientists due to its promising electronic properties. Monolayer phosphorene has a direct band gap of 2 eV located at the Gamma point of the Brillouin zone. Increasing the number of layers reduces the bandgap due to the van der Waals interaction. The direct nature of the bandgap makes phosphorene particularly favorable for electronic transport and optoelectronic applications. While multilayer phosphorene sheets have been studied, the electronic properties of their 1D counterparts are still unexplored. An accurate tight-binding model was recently proposed for multilayer phosphorene nanoribbons. Employing this model along with the non-equilibrium Green's function method, we calculate the band structure and electronic properties of phosphorene nanoribbons. We show that, depending on the edge termination, phosphorene nanoribbons can be metallic or semiconducting. Our analysis also shows that the electronic properties of phosphorene nanoribbons are highly tunable by in-plane and out-of-plane electric fields. In metallic ribbons, the conductance can be switched off by a threshold electric field, similar to field effect devices. Support by the NSF through the University of Wisconsin MRSEC Seed (NSF Award DMR-1121288).
Analysis of some integrals arising in the atomic three-electron problem
King, Frederick W.
1991-12-01
A detailed analysis is presented for the evaluation of atomic integrals of the form Fri1rj2rk3r-223rm31r12 ne-αr1-βr2-γr3dr1 dr2 dr3, which arise in several contexts of the three-electron atomic problem. All convergent integrals with i>=-2, j>=-2, k>=-2, m>=-1, and n>=-1 are examined. These integrals are solved by two distinct procedures. A majority of the integrals can be evaluated by a reduction of the three-electron integrals to integrals arising in the atomic two-electron integral problem. A second approach allows all integrals with the aforementioned indices to be evaluated by the use of Sack's expansion [J. Math. Phys. 5, 245 (1964)] of the interelectronic separation, which leads to a reduction of the above nine-dimensional integrals to a set of three-dimensional integrals. A discussion is given for the numerical evaluation of the three-dimensional integrals that arise.
Electronic structure of ternary hydrides based on light elements
Orgaz, E. [Departamento de Fisica y Quimica Teorica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, CP 04510 Coyoacan, Mexico, D.F. (Mexico)]. E-mail: orgaz@eros.pquim.unam.mx; Membrillo, A. [Departamento de Fisica y Quimica Teorica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, CP 04510 Coyoacan, Mexico, D.F. (Mexico); Castaneda, R. [Departamento de Fisica y Quimica Teorica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, CP 04510 Coyoacan, Mexico, D.F. (Mexico); Aburto, A. [Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, CP 04510 Coyoacan, Mexico, D.F. (Mexico)
2005-12-08
Ternary hydrides based on light elements are interesting owing to the high available energy density. In this work we focused into the electronic structure of a series of known systems having the general formula AMH{sub 4}(A=Li,Na,M=B,Al). We computed the energy bands and the total and partial density of states using the linear-augmented plane waves method. In this report, we discuss the chemical bonding in this series of complex hydrides.
Final Technical Report: Electronic Structure Workshop (ES13)
Zhang, Shiwei [College of William and Mary, Williamsburg, VA (United States)
2015-02-26
The 25th Annual Workshop on Recent Developments in Electronic Structure Methods (ES2013) was successfully held at the College of William & Mary in Williamsburg VA on June 11-14, 2013. The workshop website is at http://es13.wm.edu/ , which contains updated information on the workshop and a permanent archive of the scientific contents. DOE's continued support has been instrumental to the success of the workshop.
Structured electron beams from nano-engineered cathodes
Lueangaramwong, A. [NICADD, DeKalb; Mihalcea, D. [NICADD, DeKalb; Andonian, G. [RadiaBeam Tech.; Piot, P. [Fermilab
2017-03-07
The ability to engineer cathodes at the nano-scale have open new possibilities such as enhancing quantum eciency via surface-plasmon excitation, forming ultra-low-emittance beams, or producing structured electron beams. In this paper we present numerical investigations of the beam dynamics associated to this class of cathode in the weak- and strong-field regimes.We finally discuss the possible applications of some of the achievable cathode patterns when coupled with other phase space manipulations.
Electronic structure and superconductivity of FeSe-related superconductors.
Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J
2015-05-13
FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.
Electron spectra and structure of atomic and molecular clusters
Dehmer, Patricia M.
1980-01-01
Changes in electronic structure that occur during the stepwise transition from gas phase monomers to large clusters which resemble the condensed phase were studied. This basic information on weakly bound clusters is critical to the understanding of such phenomena as nucleation, aerosol formation, catalysis, and gas-to-particle conversion, yet there exist almost no experimental data on neutral particle energy levels or binding energies as a function of cluster size. (GHT)
Structured electron beams from nano-engineered cathodes
Lueangaramwong, A.; Mihalcea, D.; Andonian, G.; Piot, P.
2017-03-01
The ability to engineer cathodes at the nano-scale have opened new possibilities such as enhancing quantum efficiency via surface-plasmon excitation, forming ultra-low-emittance beams, or producing structured electron beams. In this paper, we present numerical investigations of the beam dynamics associated with this class of cathode in the weak- and strong-field regimes. We finally discuss the possible applications of some of the achievable cathode patterns when coupled with other phase space manipulations.
Strain-induced changes to the electronic structure of germanium
Tahini, H. A.
2012-04-17
Density functional theory calculations (DFT) are used to investigate the strain-induced changes to the electronic structure of biaxially strained (parallel to the (001), (110) and (111) planes) and uniaxially strained (along the [001], [110] and [111] directions) germanium (Ge). It is calculated that a moderate uniaxial strain parallel to the [111] direction can efficiently transform Ge to a direct bandgap material with a bandgap energy useful for technological applications. © 2012 IOP Publishing Ltd.
Structural and electronic properties of hydrosilylated silicon surfaces
Baumer, A.
2005-11-15
The structural and electronic properties of alkyl-terminated Si surfaces prepared by thermallyinduced hydrosilylation have been studied in detail in the preceding chapters. Various surfaces have been used for the functionalization ranging from crystalline Si over amorphous hydrogenated Si to nanoscaled materials such as Si nanowires and nanoparticles. In each case, the alkyl-terminated surfaces have been compared to the native oxidized and H-terminated surfaces. (orig.)
Positron studies of surfaces, structure and electronic properties of nanocrystals
Eijt, S. W. H.; Barbiellini, B.; Houtepen, A.J.; Vanmaekelbergh, D.; Mijnarends, P. E.; Bansil, A.
2007-01-01
A brief review is given of recent positron studies of metal and semiconductor nanocrystals. The prospects offered by positron annihilation as a sensitive method to access nanocrystal (NC) properties are described and compared with other experimental methods. The tunability of the electronic structure of nanocrystals underlies their great potential for application in many areas. Owing to their large surface-to-volume ratio, the surfaces and interfaces of NCs play a crucial role in determining ...
DFTB Parameters for the Periodic Table: Part 1, Electronic Structure.
Wahiduzzaman, Mohammad; Oliveira, Augusto F; Philipsen, Pier; Zhechkov, Lyuben; van Lenthe, Erik; Witek, Henryk A; Heine, Thomas
2013-09-10
A parametrization scheme for the electronic part of the density-functional based tight-binding (DFTB) method that covers the periodic table is presented. A semiautomatic parametrization scheme has been developed that uses Kohn-Sham energies and band structure curvatures of real and fictitious homoatomic crystal structures as reference data. A confinement potential is used to tighten the Kohn-Sham orbitals, which includes two free parameters that are used to optimize the performance of the method. The method is tested on more than 100 systems and shows excellent overall performance.
Cellular structural biology as revealed by cryo-electron tomography.
Irobalieva, Rossitza N; Martins, Bruno; Medalia, Ohad
2016-02-01
Understanding the function of cellular machines requires a thorough analysis of the structural elements that underline their function. Electron microscopy (EM) has been pivotal in providing information about cellular ultrastructure, as well as macromolecular organization. Biological materials can be physically fixed by vitrification and imaged with cryo-electron tomography (cryo-ET) in a close-to-native condition. Using this technique, one can acquire three-dimensional (3D) information about the macromolecular architecture of cells, depict unique cellular states and reconstruct molecular networks. Technical advances over the last few years, such as improved sample preparation and electron detection methods, have been instrumental in obtaining data with unprecedented structural details. This presents an exciting opportunity to explore the molecular architecture of both individual cells and multicellular organisms at nanometer to subnanometer resolution. In this Commentary, we focus on the recent developments and in situ applications of cryo-ET to cell and structural biology. © 2016. Published by The Company of Biologists Ltd.
Electronic structure of NiO: Correlation and band effects
Shen, Z. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); List, R.S. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Dessau, D.S.; Wells, B.O. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); Jepsen, O. (Max-Planck-Institute for Solid State Research, D-7000 Stuttgart 80 (Federal Republic of Germany)); Arko, A.J.; Barttlet, R. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Shih, C.K. (Department of Physics, University of Texas, Austin, Texas (USA)); Parmigiani, F. (IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California (USA)); Huang, J.C.; Lindberg, P.A.P. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA))
1991-08-15
We have performed angle-resolved-photoemission experiments and local-density-functional (LDA) band calculations on NiO to study correlation and band effects of this conceptually important compound. Our experimental result suggests a dual nature of the electronic structure of NiO. On the one hand, the LDA band calculation has some relevance to the electronic structure of NiO, and the inclusion of the antiferromagnetic order is essential. For the lower O 2{ital p} bands, the LDA calculation agrees almost perfectly with experimental energy positions and dispersion relations. On the other hand, discrepancies between the experiment and the LDA calculation do exist, especially for the Ni 3{ital d} bands and the O 2{ital p} bands that are heavily mixed with the Ni 3{ital d} bands. It appears that the main discrepancies between the experimental results and the LDA calculation are concentrated in the regions of the insulating gap and the valence-band satellite. In addition to these results, we also report the interesting angle and photon-energy dependence of the satellite emission. The above results show that the angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO.
Transmission electron microscopy in molecular structural biology: A historical survey.
Harris, J Robin
2015-09-01
In this personal, historic account of macromolecular transmission electron microscopy (TEM), published data from the 1940s through to recent times is surveyed, within the context of the remarkable progress that has been achieved during this time period. The evolution of present day molecular structural biology is described in relation to the associated biological disciplines. The contribution of numerous electron microscope pioneers to the development of the subject is discussed. The principal techniques for TEM specimen preparation, thin sectioning, metal shadowing, negative staining and plunge-freezing (vitrification) of thin aqueous samples are described, with a selection of published images to emphasise the virtues of each method. The development of digital image analysis and 3D reconstruction is described in detail as applied to electron crystallography and reconstructions from helical structures, 2D membrane crystals as well as single particle 3D reconstruction of icosahedral viruses and macromolecules. The on-going development of new software, algorithms and approaches is highlighted before specific examples of the historical progress of the structural biology of proteins and viruses are presented.
Structural and electronic properties of arsenic nitrogen monolayer
Liu, Pei; Nie, Yao-zhuang, E-mail: yznie@csu.edu.cn; Xia, Qing-lin; Guo, Guang-hua, E-mail: guogh@mail.csu.edu.cn
2017-03-26
We present our first-principles calculations of a new two-dimensional material, arsenic nitrogen monolayer. The structural, electronic, and mechanical properties are investigated in detail by means of density functional theory computations. The calculated binding energy and the phonon spectra demonstrate that the AsN can form stable monolayer in puckered honeycomb structure. It is a semiconductor with indirect band gap of 0.73 eV, and displays highly anisotropic mechanical properties. Strain has obvious influence on the electronic properties of AsN monolayer. It is found that in the armchair direction, a moderate compression strain (−12%) can trigger an indirect to direct band gap transition and a tensile strain of 18% can make the AsN becoming a stable metal. In the zigzag direction, a rather smaller strain than armchair direction (12% for compression and 8% for stretch) can induce the indirect band gap to metal transition. - Highlights: • A new two-dimensional material, arsenic nitrogen monolayer is predicated by first-principles calculations. • Arsenic nitrogen monolayer displays highly anisotropic mechanical properties. • Electronic structures of arsenic nitrogen monolayer can be effectively manipulated by applied strains.
Arias, E.; Florez, E.; Pérez-Torres, J. F.
2017-06-01
A new algorithm for the determination of equilibrium structures suitable for metal nanoclusters is proposed. The algorithm performs a stochastic search of the minima associated with the nuclear potential energy function restricted to a sphere (similar to the Thomson problem), in order to guess configurations of the nuclear positions. Subsequently, the guessed configurations are further optimized driven by the total energy function using the conventional gradient descent method. This methodology is equivalent to using the valence shell electron pair repulsion model in guessing initial configurations in the traditional molecular quantum chemistry. The framework is illustrated in several clusters of increasing complexity: Cu7, Cu9, and Cu11 as benchmark systems, and Cu38 and Ni9 as novel systems. New equilibrium structures for Cu9, Cu11, Cu38, and Ni9 are reported.
Problems in understanding the structure and assembly of viruses
King, J. [MIT, Cambridge, MA (United States)
1997-12-01
Though viruses infect the cells of all groups of animals, plants, and microorganisms, their structures follow a limited number of general themes; spherical or cylindrical shells built of hundreds of repeated protein subunits enclosing a nucleic acid - DNA or RNA - genome. Since the 1960s it has been known that the protein shells of spherical viruses in fact conform to icosahedral symmetry or to subtle deviations from icosahedral symmetry. The construction of the shell lattices and the transformations they go through in the different stages of the viral life cycle are not fully understood. The shells contain the nucleic in a highly condensed state, of unknown coiling/organization. Features of the well studied bacterial viruses will be reviewed, with examples from adenoviruses, herpesviruses, poliovirus, and HIV. The emergence of new viral disease has led to increased interest in the development of agents which interfere with virus reproduction at the level of the assembly or function of the organized particle. Recently computational approaches to the problem of virus assembly have made important contributions to clarifying shell assembly processes. 1 ref.
Problems of Romanian SMEs with tapping EU structural funds
Gábor HUNYA
2011-06-01
Full Text Available Romanian SMEs can directly benefit from the Sectoral Operational Programme “Increase of Economic Competitiveness” (SOP IEC and some parts of the Regional Operational Programme (ROP in the 2007–2013 period. There has been wide interest for these subsidies on behalf of SMEs but major problems emerged with the implementation of projects. These are mostly related to the poor preparation of the projects, their cumbersome approval and the unfavourable general economic conditions in the country. The paper relies on information compiled by a survey and several focus groups run with SME in early 2011. These reveal that Romanian SMEs are at a rudimentary stage of skills, organization and market knowledge. Their development aims are rather short-term and not very complex. They lack the knowledge, expertise and staff to participate in complex tenders and in application processes which explains their high failure rate with EU financed projects. Learning by doing is, however, improving their skills and capacities. However, the design and structure of the EU programmes are also deficient in supporting the development of SMEs in need of more simple and transparent mechanisms which they can understand and cope with.
Zhou, X.J.
2010-04-30
In addition to the record high superconducting transition temperature (T{sub c}), high temperature cuprate superconductors are characterized by their unusual superconducting properties below T{sub c}, and anomalous normal state properties above T{sub c}. In the superconducting state, although it has long been realized that superconductivity still involves Cooper pairs, as in the traditional BCS theory, the experimentally determined d-wave pairing is different from the usual s-wave pairing found in conventional superconductors. The identification of the pairing mechanism in cuprate superconductors remains an outstanding issue. The normal state properties, particularly in the underdoped region, have been found to be at odd with conventional metals which is usually described by Fermi liquid theory; instead, the normal state at optimal doping fits better with the marginal Fermi liquid phenomenology. Most notable is the observation of the pseudogap state in the underdoped region above T{sub c}. As in other strongly correlated electrons systems, these unusual properties stem from the interplay between electronic, magnetic, lattice and orbital degrees of freedom. Understanding the microscopic process involved in these materials and the interaction of electrons with other entities is essential to understand the mechanism of high temperature superconductivity. Since the discovery of high-T{sub c} superconductivity in cuprates, angle-resolved photoemission spectroscopy (ARPES) has provided key experimental insights in revealing the electronic structure of high temperature superconductors. These include, among others, the earliest identification of dispersion and a large Fermi surface, an anisotropic superconducting gap suggestive of a d-wave order parameter, and an observation of the pseudogap in underdoped samples. In the mean time, this technique itself has experienced a dramatic improvement in its energy and momentum resolutions, leading to a series of new discoveries not
Can an electron gun solve the outstanding problem of magnetosphere-ionosphere connectivity?
Delzanno, Gian Luca; Borovsky, Joseph E.; Thomsen, Michelle F.; Gilchrist, Brian E.; Sanchez, Ennio
2016-07-01
Determining the magnetic connectivity between magnetospheric phenomena and ionospheric phenomena is an outstanding problem of magnetospheric and ionospheric physics. Accurately establishing this connectivity could answer a variety of long-standing questions. The most viable option to solve this is by means of a high-power electron beam fired from a magnetospheric spacecraft and spotted at its magnetic footpoint in the ionosphere. This has technical difficulties. Progress has been made on mitigating the major issue of spacecraft charging. The remaining physics issues are identified, together with the need for a synergistic effort in modeling, laboratory experiments, and, ultimately, testing in space. The goal of this commentary is to stimulate awareness and interest on the magnetosphere-ionosphere connectivity problem and possibly accelerate progress toward its solution.
Stolpe, Mathias; Stidsen, Thomas K.
2005-01-01
of minimizing the weight of a structure subject to displacement and local design-dependent stress constraints. The method iteratively solves a sequence of problems of increasing size of the same type as the original problem. The problems are defined on a design mesh which is initially coarse...... from global optimization, which have only recently become available, for solving the problems in the sequence. Numerical examples of topology design problems of continuum structures with local stress and displacement constraints are presented....
Stolpe, Mathias; Stidsen, Thomas K.
2007-01-01
of minimizing the weight of a structure subject to displacement and local design-dependent stress constraints. The method iteratively treats a sequence of problems of increasing size of the same type as the original problem. The problems are defined on a design mesh which is initially coarse...... from global optimization, which have only recently become available, for solving the problems in the sequence. Numerical examples of topology design problems of continuum structures with local stress and displacement constraints are presented....
Structural, electronic and optical properties of brookite phase titanium dioxide
Samat, M. H.; Taib, M. F. M.; Hassan, O. H.; Yahya, M. Z. A.; Ali, A. M. M.
2017-04-01
Structural, electronic and optical properties of titanium dioxide (TiO2) in brookite phase were studied via first-principles calculations in the framework of density functional theory (DFT). The exchange-correlation functional from local density approximation (LDA) and generalized gradient approximation (GGA) were used to calculate the properties of brookite TiO2. The structural parameters of brookite in orthorhombic structure (Pbca space group) are in good agreement with the previous theoretical and experimental data. The obtained direct band gaps from GGA are slightly higher than LDA. Both LDA and GGA band gaps underestimate the experimental band gap due to the well-known limitation of DFT. The density of states (DOS) displays the hybridization of O 2p and Ti 3d states and Mulliken population analysis presents the net charge of Ti and O atoms in brookite. The dielectric function was also analyzed together with other optical properties such as refractive index, reflectivity, loss function and absorption coefficient. The first-principles calculations on the least studied TiO2 in brookite phase using different exchange-correlation functional from LDA and GGA provide theoretical understanding about its structural, electronic and optical properties. Besides, these results would give a better support for technological applications concerning TiO2 materials using brookite phase.
Semantic Annotation of Complex Text Structures in Problem Reports
Malin, Jane T.; Throop, David R.; Fleming, Land D.
2011-01-01
Text analysis is important for effective information retrieval from databases where the critical information is embedded in text fields. Aerospace safety depends on effective retrieval of relevant and related problem reports for the purpose of trend analysis. The complex text syntax in problem descriptions has limited statistical text mining of problem reports. The presentation describes an intelligent tagging approach that applies syntactic and then semantic analysis to overcome this problem. The tags identify types of problems and equipment that are embedded in the text descriptions. The power of these tags is illustrated in a faceted searching and browsing interface for problem report trending that combines automatically generated tags with database code fields and temporal information.
Ground-state electronic structure of actinide monocarbides and mononitrides
Petit, Leon; Svane, Axel; Szotek, Z.
2009-01-01
The self-interaction corrected local spin-density approximation is used to investigate the ground-state valency configuration of the actinide ions in the actinide monocarbides, AC (A=U,Np,Pu,Am,Cm), and the actinide mononitrides, AN. The electronic structure is characterized by a gradually...... increasing degree of f electron localization from U to Cm, with the tendency toward localization being slightly stronger in the (more ionic) nitrides compared to the (more covalent) carbides. The itinerant band picture is found to be adequate for UC and acceptable for UN, while a more complex manifold...... of competing localized and delocalized f-electron configurations underlies the ground states of NpC, PuC, AmC, NpN, and PuN. The fully localized 5f-electron configuration is realized in CmC (f7), CmN (f7), and AmN (f6). The observed sudden increase in lattice parameter from PuN to AmN is found to be related...
The electronic structure of europium chalcogenides and pnictides
Horne, M [Department of Physics, Keele University, Staffordshire ST5 5DY (United Kingdom); Strange, P [Department of Physics, Keele University, Staffordshire ST5 5DY (United Kingdom); Temmerman, W M [Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Szotek, Z [Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Svane, A [Institute of Physics and Astronomy, University of Aarhus, DK-8000, Aarhus (Denmark); Winter, H [INFP, Forschungzentrum Karlsruhe GmbH, Postfach 3640, D-76021, Karlsruhe (Germany)
2004-07-21
The electronic structure of some europium chalcogenides and pnictides is calculated using the ab initio self-interaction corrected local-spin-density approximation (SIC-LSD). This approach allows both a localized description of the rare earth f-electrons and an itinerant description of s-, p-, and d-electrons. Localizing different numbers of f-electrons on the rare earth atom corresponds to different nominal valencies, and the total energies can be compared, providing a first-principles description of valency. All the chalcogenides are found to be insulators in the ferromagnetic state and to have a divalent configuration. For the pnictides we find that EuN is half-metallic and the rest are normal metals. However, a valence change occurs as we go down the pnictide column of the periodic table. EuN and EuP are trivalent, EuAs is only just trivalent, and EuSb is found to be divalent. Our results suggest that these materials may find applications in spintronic and spin filtering devices.
Electronic Structure of New Superconducting Perovskite MgCNi3
Li CHEN; Hua LI; Liangmo MEI
2004-01-01
The electronic structures of new superconducting perovskite MgCNis and related compounds MgCNi2T (T=Co, Fe,and Cu) have been studied using MS-Xα method. In MgCNi3, the main peak of density of states is located below the Fermi level and dominated by Ni d. From the results of total energy calculations, it was found that the number of Ni valence electron decreases faster for the Fe-doped case than that for the Co-doped case. The valence state of Ni changes from +1.43 in MgCNi2Co to +3.02 in MgCNi2Fe. It was confirmed that Co and Fe dopants in MgCNi3 behave as a source of d-band holes and the suppression of superconductivity occurs faster for the Fe-doped case than that for the Co-doped case. In order to explain the fact that Co and Fe dopants in MgCNi3 behave as a source of d-band holes rather than magnetic scattering centers that quench superconductivity, we have also investigated the effects of electron (Cu) doping on the superconductivity and found that both electron (Cu) doping and hole (Co, Fe)doping quench superconductivity exist. Comparing with the hole (Co) doping, there was no much difference between Cu and Co doping. This suggests that Co and Fe doping do not actas magnetic impurity.
Cellular Electron Cryotomography: Toward Structural Biology In Situ.
Oikonomou, Catherine M; Jensen, Grant J
2017-06-20
Electron cryotomography (ECT) provides three-dimensional views of macromolecular complexes inside cells in a native frozen-hydrated state. Over the last two decades, ECT has revealed the ultrastructure of cells in unprecedented detail. It has also allowed us to visualize the structures of macromolecular machines in their native context inside intact cells. In many cases, such machines cannot be purified intact for in vitro study. In other cases, the function of a structure is lost outside the cell, so that the mechanism can be understood only by observation in situ. In this review, we describe the technique and its history and provide examples of its power when applied to cell biology. We also discuss the integration of ECT with other techniques, including lower-resolution fluorescence imaging and higher-resolution atomic structure determination, to cover the full scale of cellular processes.
Electron Microscopy Structural Insights into CPAP Oligomeric Behavior
Alvarez-Cabrera, Ana L; Delgado, Sandra; Gil-Carton, David
2017-01-01
that represent obtaining the protein in a soluble, homogeneous state for structural studies. Our work constitutes a systematic structural analysis on multiple oligomers of HsCPAP(897)(-1338), using single-particle electron microscopy (EM) of negatively stained (NS) samples. Based on image classification...... into clearly different regular 3D maps (putatively corresponding to dimers and tetramers) and direct observation of individual images representing other complexes of HsCPAP(897-1338) (i.e., putative flexible monomers and higher-order multimers), we report a dynamic oligomeric behavior of this protein, where...... of atomic models into the NS 3D maps at resolutions around 20 Å is performed only to complement our experimental data, allowing us to hypothesize on the oligomeric composition of the different complexes. In this way, the current EM work represents an initial step toward the structural characterization...
Structural and electronic properties of carbon nanotubes under hydrostatic pressures
Zhang Ying; Cao Jue-Xian; Yang Wei
2008-01-01
We studied the structural and electronic properties of carbon nanotubes under hydrostatic pressures based on molecular dynamics simulations and first principles band structure calculations.It is found that carbon nanotubes experience a hard-to-soft transition as external pressure increases.The bulk modulus of soft phase is two orders of magnitude smaller than that of hard phase.The band structure calculations show that band gap of (10,0) nanotube increases with the increase of pressure at low pressures. Above a critical pressure (5.70GPa),band gap of (10,0) nanotube drops rapidly and becomes zero at 6.62GPa. Moreover,the calculated charge density shows that a large pressure can induce an sp2-to-sp3 bonding transition,which is confirmed by recent experiments on deformed carbon nanotubes.
Theory of silicon superlattices - Electronic structure and enhanced mobility
Moriarty, J. A.; Krishnamurthy, S.
1983-01-01
A realistic tight-binding band-structure model of silicon superlattices is formulated and used to study systems of potential applied interest, including periodic layered Si-Si(1-x)Ge(x) heterostructures. The results suggest a possible new mechanism for achieving enhanced transverse carrier mobility in such structures: reduced transverse conductivity effective masses associated with the superlattice band structure. For electrons in 100-line-oriented superlattices, a reduced conductivity mass arises intrinsically from the lower symmetry of the superlattice and its unique effect on the indirect bulk silicon band gap. An order of magnitude estimate of the range of mobility enhancement expected from this mechanism appears to be consistent with preliminary experimental results on Si-Si(1-x)Ge(x) superlattices.
Effects of thickness on electronic structure of titanium thin films
Güvenç Akgül
2014-02-01
Effects of thickness on the electronic structure of e-beam evaporated thin titanium films were studied using near-edge X-ray absorption fine structure (NEXAFS) technique at titanium 2,3 edge in total electron yield (TEY) mode and transmission yield mode. Thickness dependence of 2,3 branching ratio (BR) of titanium was investigated and it was found that BR below 3.5 nm shows a strong dependence on film thickness. Mean electron escape depth () in titanium, an important parameter for surface applications, was determined to be = 2.6 ± 0.1 nm using 2,3 resonance intensity variation as a function of film thickness. The average 3/2 white line intensity ratio of titanium was obtained as 0.89 from the ratio of amplitudes of each 3 and 2 peaks and 0.66 from the integrated area under each 3 and 2 peaks. In addition, a theoretical calculation for pure titanium was presented for comparison with experimental data.
Structural Fingerprinting of Nanocrystals in the Transmission Electron Microscope
Rouvimov, Sergei; Plachinda, Pavel; Moeck, Peter
2010-03-01
Three novel strategies for the structurally identification of nanocrystals in a transmission electron microscope are presented. Either a single high-resolution transmission electron microscopy image [1] or a single precession electron diffractogram (PED) [2] may be employed. PEDs from fine-grained crystal powders may also be utilized. Automation of the former two strategies is in progress and shall lead to statistically significant results on ensembles of nanocrystals. Open-access databases such as the Crystallography Open Database which provides more than 81,500 crystal structure data sets [3] or its mainly inorganic and educational subsets [4] may be utilized. [1] http://www.scientificjournals.org/journals 2007/j/of/dissertation.htm [2] P. Moeck and S. Rouvimov, in: {Drugs and the Pharmaceutical Sciences}, Vol. 191, 2009, 270-313 [3] http://cod.ibt.lt, http://www.crystallography.net, http://cod.ensicaen.fr, http://nanocrystallography.org, http://nanocrystallography.net, http://journals.iucr.org/j/issues/2009/04/00/kk5039/kk5039.pdf [4] http://nanocrystallography.research.pdx.edu/CIF-searchable
Multiscale approach to the electronic structure of doped semiconductor surfaces
Sinai, Ofer; Hofmann, Oliver T.; Rinke, Patrick; Scheffler, Matthias; Heimel, Georg; Kronik, Leeor
2015-02-01
The inclusion of the global effects of semiconductor doping poses a unique challenge for first-principles simulations, because the typically low concentration of dopants renders an explicit treatment intractable. Furthermore, the width of the space-charge region (SCR) at charged surfaces often exceeds realistic supercell dimensions. Here, we present a multiscale technique that fully addresses these difficulties. It is based on the introduction of a charged sheet, mimicking the SCR-related field, along with free charge which mimics the bulk charge reservoir, such that the system is neutral overall. These augment a slab comprising "pseudoatoms" possessing a fractional nuclear charge matching the bulk doping concentration. Self-consistency is reached by imposing charge conservation and Fermi level equilibration between the bulk, treated semiclassically, and the electronic states of the slab, which are treated quantum-mechanically. The method, called CREST—the charge-reservoir electrostatic sheet technique—can be used with standard electronic structure codes. We validate CREST using a simple tight-binding model, which allows for comparison of its results with calculations encompassing the full SCR explicitly. Specifically, we show that CREST successfully predicts scenarios spanning the range from no to full Fermi level pinning. We then employ it with density functional theory, obtaining insight into the doping dependence of the electronic structures of the metallic "clean-cleaved" Si(111) surface and its semiconducting (2 ×1 ) reconstructions.
Electronic structure and magnetism in half-Heusler compounds
Nanda, B R K; Dasgupta, I [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400 076 (India)
2003-11-05
In this paper we have applied the full-potential linearized muffin tin orbital method and the tight-binding linearized muffin tin orbital method to investigate in detail the electronic structure and magnetism of a series of half-Heusler compounds XMZ with X = Fe,Co,Ni, M = Ti,V,Nb,Zr,Cr,Mo,Mn and Z Sb,Sn. Our detailed analysis of the electronic structure using various indicators of chemical bonding suggests that covalent hybridization of the higher-valent transition element X with the lower-valent transition element M is the key interaction responsible for the formation of the d-d gap in these systems. However, the presence of the sp-valent element is crucial to provide stability to these systems. The influence of the relative ordering of the atoms in the unit cell on the d-d gap is also investigated. We have also studied in detail some of these systems with more than 18 valence electrons which exhibit novel magnetic properties, namely half-metallic ferro- and ferrimagnetism. We show that the d-d gap in the paramagnetic state, the relatively large X-Sb hybridization and the large exchange splitting of the M atoms are responsible for the half-metallic property of some of these systems.
TCO/metal/TCO structures for energy and flexible electronics
Guillen, C., E-mail: c.guillen@ciemat.es; Herrero, J.
2011-10-31
There is increasing attention paid to improving transparent conductive electrodes for applications in large area photovoltaic devices and displays that are being developed for energy and electronics. To date, transparent and conductive oxides (TCO) based on In{sub 2}O{sub 3}, ZnO, or SnO{sub 2} are commonly used, but advanced devices require new electrodes with lower resistivities than previously achieved and with optical properties superior to those of the present generation. TCO/metal/TCO multilayer structures have emerged as an interesting alternative because they provide optical and electrical characteristics globally superior to those attainable with a single-layer TCO or metal electrode and can be deposited at low temperatures onto inexpensive plastic substrates. Indeed, the fabrication of thin film devices on flexible substrates has substantial interest for application to lightweight products and implementation of roll-to-roll deposition processes that can significantly reduce production costs. In this sense, organic electronics that require low deposition temperatures have the best chance to be the first transferred from conventional glass to inexpensive plastic substrates. The present critical review summarizes current TCO/metal/TCO research results, first analyzed for materials and thickness selection as a function of the optical transmittance and electrical resistance parameters, and then analyzed according to other important properties such as mechanical reliability and thermal and humidity stability. The review concludes with a brief discussion of the results obtained for TCO/metal/TCO structures applied as electrodes in several organic electronic devices.
Electronic structure and hyperfine parameters of substitutional Al and P impurities in silica
Lægsgaard, Jesper; Stokbro, Kurt
2002-01-01
The electronic structure of substitutional Al and P impurities in silica is investigated using supercell calculations within the framework of density functional theory (DFT). Evaluation of hyperfine matrices for the magnetic nuclei facilitates comparison to experimental data. It is found that the......, there is an "asymmetry" between electrons and holes in the electronic states of the silica network: The hole present at the Al impurity goes into a nonbonding O orbital while the extra electron present at the P impurity goes into a P-O antibonding state.......The electronic structure of substitutional Al and P impurities in silica is investigated using supercell calculations within the framework of density functional theory (DFT). Evaluation of hyperfine matrices for the magnetic nuclei facilitates comparison to experimental data. It is found...... that the impaired spin state of substitutional P is well described by the theory, while the unpaired spin state found for substitutional Al is severely at variance with the experimental data. Cluster calculations using both the DFT and the Hartree-Fock approximation indicate that the problem is not caused...
Structural studies of glasses by transmission electron microscopy and electron diffraction
Kashchieva, E.P. [University of Chemical Technology and Metallurgy, Sofia (Bulgaria)
1997-07-01
The purpose of this work is to present information about the applications of transmission electron microscopy (TEM) and electron diffraction (ED) for structural investigations of glasses. TEM investigations have been carried out on some binary and on a large number of ternary borate-telluride systems where glass-forming oxides, oxides of transitional elements and modified oxides of elements from I, II and III groups in the periodic table, are used as third component. The large experimental data given by TEM method allows the fine classification of the micro-heterogeneities. A special case of micro-heterogeneous structure with technological origin occurs near the boundary between the 2 immiscible liquids obtained at macro-phase separation. TEM was also used for the direct observation of the glass structure and we have studied the nano-scale structure of borate glasses obtained at slow and fast cooling of the melts. The ED possesses advantages for analysis of amorphous thin films or micro-pastilles and it is a very useful technique for study in materials containing simultaneously light and heavy elements. A comparison between the possibilities of the 3 diffraction techniques (X-ray diffraction, neutron diffraction and ED) is presented.
The electronic structure of free aluminum clusters: metallicity and plasmons.
Andersson, Tomas; Zhang, Chaofan; Tchaplyguine, Maxim; Svensson, Svante; Mårtensson, Nils; Björneholm, Olle
2012-05-28
The electronic structure of free aluminum clusters with ∼3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms.
The electronic structure of free aluminum clusters: Metallicity and plasmons
Andersson, Tomas; Zhang, Chaofan; Tchaplyguine, Maxim; Svensson, Svante; Mârtensson, Nils; Björneholm, Olle
2012-05-01
The electronic structure of free aluminum clusters with ˜3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms.
Topological signatures in the electronic structure of graphene spirals.
Avdoshenko, Stas M; Koskinen, Pekka; Sevinçli, Haldun; Popov, Alexey A; Rocha, Claudia G
2013-01-01
Topology is familiar mostly from mathematics, but also natural sciences have found its concepts useful. Those concepts have been used to explain several natural phenomena in biology and physics, and they are particularly relevant for the electronic structure description of topological insulators and graphene systems. Here, we introduce topologically distinct graphene forms - graphene spirals - and employ density-functional theory to investigate their geometric and electronic properties. We found that the spiral topology gives rise to an intrinsic Rashba spin-orbit splitting. Through a Hamiltonian constrained by space curvature, graphene spirals have topologically protected states due to time-reversal symmetry. In addition, we argue that the synthesis of such graphene spirals is feasible and can be achieved through advanced bottom-up experimental routes that we indicate in this work.
Structural and Electronic Properties of IV-VI Semiconductor Nanodots
Leitsmann, Roman; Bechstedt, Friedhelm
2008-03-01
The characterization of nanostructure properties versus dimension and surface passivation is of increasing importance for the nanotechnology. Especially the stoichiometry, geometry, and the electronic states of IV-VI semiconductor nanodots are of special interest [1,2]. We use ab initio methods to calculate structural and electronic properties of colloidal IV-VI semiconductor nanodots as a function of the dot diameter. A method to passivate the non-directional dangling bonds at the nanodot surfaces is derived and used to study the confinement effect on the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) states. In addition we take the influence of relativistic (spin-orbit coupling -- SOC ) and excitonic effects into account. While the SOC leads to a considerable decrease of the HOMO-LUMO gap, excitonic effects play a minor role. [1] JACS 128, 10337 (2006) [2] JACS 129, 11354 (2007)
Structure and electronic properties of alkali-C60 nanoclusters.
Rabilloud, Franck
2010-07-08
I investigated the structural and electronic properties of both Na(n)C(60) and Li(n)C(60) (n alkali atoms over the C(60) surface is analyzed. The hypotheses for either an homogeneous coating of the C(60) surface by the alkali atoms or the growth of an alkali droplet not wetting the fullerene surface are discussed. Lithium atoms are found to coat homogeneously the fullerene on the C(60) surface via pentagonal sites, contrary to sodium atoms, which prefer to form 4-atom islands on the surface. The charge transfer, the energetics, and the dipole moments are discussed in relation with available results. The adsorption of alkali atoms on the C(60) surface considerably enhances the capacity of C(60) to accept electrons. The arrangement of lithium atoms seems more favorable for the hydrogen storage than that of sodium atoms.
Ab initio electronic structure and optical conductivity of bismuth tellurohalides
Schwalbe, Sebastian; Starke, Ronald; Schober, Giulio A H; Kortus, Jens
2016-01-01
We investigate the electronic structure, dielectric and optical properties of bismuth tellurohalides BiTeX (X = I, Cl, Br) by means of all-electron density functional theory. In particular, we present the ab initio conductivities and dielectric tensors calculated over a wide frequency range, and compare our results with the recent measurements by Akrap et al. , Makhnev et al. , and Rusinov et al. . We show how the low-frequency branch of the optical conductivity can be used to identify characteristic intra- and interband transitions between the Rashba spin-split bands in all three bismuth tellurohalides. We further calculate the refractive indices and dielectric constants, which in turn are systematically compared to previous predictions and measurements. We expect that our quantitative analysis will contribute to the general assessment of bulk Rashba materials for their potential use in spintronics devices.
Electronic structure of benzene adsorbed on Ni and Cu surfaces
Weinelt, M.; Nilsson, A.; Wassdahl, N. [Uppsala Univ. (Sweden)] [and others
1997-04-01
Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.
Topology optimization of fluid-structure-interaction problems in poroelasticity
Andreasen, Casper Schousboe; Sigmund, Ole
2013-01-01
with the deformation of the elastic skeleton through a macroscopic Darcy-type flow law. The method allows to impose pressure loads for static problems through a one way coupling, while transient problems are fully coupled modeling the interaction between fluid and solid. The material distribution is determined...
The Lunar Internal Structure Model: Problems and Solutions
Nefedyev, Yuri; Gusev, Alexander; Petrova, Natalia; Varaksina, Natalia
The report is devoted the problems of the internal structure and gravitational field of the Moon. New data received from 14 newest instruments installed on low-orbit satellite Kaguya essentially enriched our knowledge of the Moon. Chinese satellite ChagE-1 and Indian Сhandrayan-1 have demonstrated strong potential of China and India in the field of lunar research and obtained new data on gravitational field, mascons, crust, and geochemical composition of the circumlunar space. Internal structure of the Moon: There are some essential arguments in favor of existence of a small-sized Moon’s core made of metallic iron alloyed with a small amount of sulfur and/or oxygen, and availability of hot viscous lower mantle. Structure of gravitational field of the Moon, determined by the comparison of high-precision trajectory measurements by Lunar Prospector (1998- 1999) with the results of laser altimetry obtained by Clementine (1994), as well as with data sets of laser ranging of the Moon (1970-2006), assumes the presence of a metal core. Interpretation of the polar moment value within the framework of chemical, thermal and density models of lunar crust and mantle informed conclusions about the weight and size of the core. LLR analysis of dissipation of rotation of the Moon points at two possible sources of dissipation: monthly solid-state inflows and liquid core, rotation of which differs from viscous-elastic mantle. Liquid (melted) core has its unique impact on the Moon’s rotation. In particular, there are two force moments due to topographical and phase interaction at the boundary between liquid core and elastic mantle (CMB). Liquid core can rotate independently from solid mantle Selenoid satellites (SS) open new and most perspective opportunities in the study of gravitational field and the Moon’s figure. SSs “Moon 10”, “Apollo”, “Clementine”, “Lunar Prospector” trajectory tracking data processing has allowed for identification of coefficients in
Pre-Service Elementary Teachers' Motivation and Ill-Structured Problem Solving in Korea
Kim, Min Kyeong; Cho, Mi Kyung
2016-01-01
This article examines the use and application of an ill-structured problem to pre-service elementary teachers in Korea in order to find implications of pre-service teacher education with regard to contextualized problem solving by analyzing experiences of ill-structured problem solving. Participants were divided into small groups depending on the…
Hong, Jee Yun; Kim, Min Kyeong
2016-01-01
Ill-structured problems can be regarded as one of the measures that meet recent social needs emphasizing students' abilities to solve real-life problems. This study aimed to analyze the mathematical abstraction process in solving such problems, and to identify the mathematical abstraction level ([I] Recognition of mathematical structure through…
Analogical Reasoning as a Decision Support Principle for Weakly-Structured Marketing Problems
N.A.P. Althuizen (Niek)
2006-01-01
textabstractMany marketing problems are weakly-structured. From the psychological literature, we know that analogical reasoning is an effective problem-solving method in weakly-structured decision situations. That is, when confronted with such a problem, one of the first things managers will natural
Electronic structure and superconductivity of MgB2
D M Gaitonde; P Modak; R S Rao; B K Godwal
2003-01-01
Results of ab initio electronic structure calculations on the compound, MgB2, using the FPLAPW method employing GGA for the exchange–correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated, $D(E_F)$ and the experimental specific heat data. The $T_c$ is found to be 37 K. We use a parametrized description of the calculated band structure to obtain the = 0 K values of the London penetration depth and the superconducting coherence length. The penetration depth calculated by us is too small and the coherence length too large as compared to the experimentally determined values of these quantities. This indicates the limitations of a theory that relies only on electronic structure calculations in describing the superconducting state in this material and implies that impurity effects as well as mass renormalization effects need to be included.
Amyloid Structure and Assembly: Insights from Scanning Transmission Electron Microscopy
Goldsbury, C.; Wall, J.; Baxa, U.; Simon, M. N.; Steven, A. C.; Engel, A.; Aebi, U.; Muller, S. A.
2011-01-01
Amyloid fibrils are filamentous protein aggregates implicated in several common diseases such as Alzheimer's disease and type II diabetes. Similar structures are also the molecular principle of the infectious spongiform encephalopathies such as Creutzfeldt-Jakob disease in humans, scrapie in sheep, and of the so-called yeast prions, inherited non-chromosomal elements found in yeast and fungi. Scanning transmission electron microscopy (STEM) is often used to delineate the assembly mechanism and structural properties of amyloid aggregates. In this review we consider specifically contributions and limitations of STEM for the investigation of amyloid assembly pathways, fibril polymorphisms and structural models of amyloid fibrils. This type of microscopy provides the only method to directly measure the mass-per-length (MPL) of individual filaments. Made on both in vitro assembled and ex vivo samples, STEM mass measurements have illuminated the hierarchical relationships between amyloid fibrils and revealed that polymorphic fibrils and various globular oligomers can assemble simultaneously from a single polypeptide. The MPLs also impose strong constraints on possible packing schemes, assisting in molecular model building when combined with high-resolution methods like solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR).
Phase Diagram and Electronic Structure of Praseodymium and Plutonium systems
Yao, Yong-Xin; Nicola, Lanata; Wang, Cai-Zhuang; Kotliar, Gabriel; Ho, Kai-Ming
2015-03-01
We apply a new implementation of LDA +Gutzwiller to calculate the zero-temperature phase diagram and electronic structure of Pr and Pu. Our study of Pr indicates that its pressure-induced volume-collapse transition would not occur without change of lattice structure -- contrarily to Ce. Our study of Pu shows that the most important effect originating the differentiation between the equilibrium densities of its allotropes is the competition between the Peierls effect and the Madelung interaction. However, the proper treatment of electron correlation effects is crucial to reach good agreement with experiment. A similar interplay between correlation effects and bands structure is also displayed in Pr, and might emerge in even greater generality. N.L. and G.K. supported by U.S. DOE BES under Grant No. DE-FG02- 99ER45761. Research at Ames Lab supported by the U.S. DOE, Office of BES, DMSE, Ames Laboratory is operated for the U.S. DOE by Iowa State University under Contract No. DE-AC02-07CH11358.
Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices
Patel, Sahil Jaykumar
Spintronic devices, where information is carried by the quantum spin state of the electron instead of purely its charge, have gained considerable interest for their use in future computing technologies. For optimal performance, a pure spin current, where all electrons have aligned spins, must be generated and transmitted across many interfaces and through many types of materials. While conventional spin sources have historically been elemental ferromagnets, like Fe or Co, these materials pro duce only partially spin polarized currents. To increase the spin polarization of the current, materials like half-metallic ferromagnets, where there is a gap in the minority spin density of states around the Fermi level, or topological insulators, where the current transport is dominated by spin-locked surface states, show promise. A class of materials called Heusler compounds, with electronic structures that range from normal metals, to half metallic ferromagnets, semiconductors, superconductors and even topological insulators, interfaces well with existing device technologies, and through the use of molecular beam epitaxy (MBE) high quality heterostructures and films can be grown. This dissertation examines the electronic structure of surfaces and interfaces of both topological insulator (PtLuSb-- and PtLuBi--) and half-metallic ferromagnet (Co2MnSi-- and Co2FeSi--) III-V semiconductor heterostructures. PtLuSb and PtLuBi growth by MBE was demonstrated on Alx In1--xSb (001) ternaries. PtLuSb (001) surfaces were observed to reconstruct with either (1x3) or c(2x2) unit cells depending on Sb overpressure and substrate temperature. viii The electronic structure of these films was studied by scanning tunneling microscopy/spectroscopy (STM/STS) and photoemission spectroscopy. STS measurements as well as angle resolved photoemission spectropscopy (ARPES) suggest that PtLuSb has a zero-gap or semimetallic band structure. Additionally, the observation of linearly dispersing surface
III - V semiconductor structures for biosensor and molecular electronics applications
Luber, S.M.
2007-01-15
The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging mechanisms either the adsorption of OH- ions on the surface, or the dissociation of OH groups in surface oxides. A comparison between simulation settings and physical device properties indicate the OH- adsorption as the most probable mechanism. In the second part of the present study the suitability of MBE grown III-V semiconductor structures for molecular electronics applications is examined. In doing so, a method to fabricate nanometer separated, coplanar, metallic electrodes based on the cleavage of a supporting AlGaAs-GaAs heterostructure is presented. This is followed
Leble, S B
2004-01-01
A dressing technique is used to improve zero range potential (ZRP) model. We consider a Darboux transformation starting with a ZRP, the result of the "dressing" gives a potential with non-zero range that depends on a seed solution parameters. Concepts of the partial waves and partial phases for non-spherical potential are used in order to perform Darboux transformation. The problem of scattering on the regular X$_{\\hbox{n}}$ and YX$_{\\hbox{n}}$ structures is studied. The results of the low-energy electron-molecule scattering on the dressed ZRPs are illustrated by model calculation for the configuration and parameters of the silane ($\\hbox{SiH}_4$) molecule. \\center{Key words: low-energy scattering, multiple scattering, Ramsauer-Townsend minimum, silane, zero range potential.
PREFACE: MicroTherm' 2013 - Microtechnology and Thermal Problems in Electronics
Lisik, Zbigniew; Raj, Ewa
2014-04-01
MicroTherm is an International Conference on Microtechnology and Thermal Problems in Electronics organised as a cyclic event since 1996. The success of the first seminar, which was devoted mainly to thermal management aspects, and the successive conferences have led us to the tenth edition. Since the first meeting, the scope of the conference has expanded, following the progress of electronics. Now, it covers subjects connected with extreme temperature, electronics, sensors and measurement techniques, modelling, simulation, wide band-gap materials, packaging and reliability, renewable energy sources and photonics with special emphasis on microelectronic technologies. MicroTherm' 2013 was held in Lodz, Poland, on 25-28 June 2013. The programme consistied of invited talks and nine regular sessions in the form of planar discussions and poster presentations, including a Students' Session. The Students' session gave an opportunity for students and young researchers to present their first achievements in the field of science. The next MicroTherm Conference is going to be held on 22-25 June 2015, in Lodz — a beautiful, post-industrial city located in the centre of Poland. Please, feel invited to MicroTherm' 2015 (www.microtherm.dsod.pl). Ewa Raj and Zbigniew Lisik Editors
Dissecting structural and electronic effects in inducible nitric oxide synthase.
Hannibal, Luciana; Page, Richard C; Haque, Mohammad Mahfuzul; Bolisetty, Karthik; Yu, Zhihao; Misra, Saurav; Stuehr, Dennis J
2015-04-01
Nitric oxide synthases (NOSs) are haem-thiolate enzymes that catalyse the conversion of L-arginine (L-Arg) into NO and citrulline. Inducible NOS (iNOS) is responsible for delivery of NO in response to stressors during inflammation. The catalytic performance of iNOS is proposed to rely mainly on the haem midpoint potential and the ability of the substrate L-Arg to provide a hydrogen bond for oxygen activation (O-O scission). We present a study of native iNOS compared with iNOS-mesohaem, and investigate the formation of a low-spin ferric haem-aquo or -hydroxo species (P) in iNOS mutant W188H substituted with mesohaem. iNOS-mesohaem and W188H-mesohaem were stable and dimeric, and presented substrate-binding affinities comparable to those of their native counterparts. Single turnover reactions catalysed by iNOSoxy with L-Arg (first reaction step) or N-hydroxy-L-arginine (second reaction step) showed that mesohaem substitution triggered higher rates of Fe(II)O₂ conversion and altered other key kinetic parameters. We elucidated the first crystal structure of a NOS substituted with mesohaem and found essentially identical features compared with the structure of iNOS carrying native haem. This facilitated the dissection of structural and electronic effects. Mesohaem substitution substantially reduced the build-up of species P in W188H iNOS during catalysis, thus increasing its proficiency towards NO synthesis. The marked structural similarities of iNOSoxy containing native haem or mesohaem indicate that the kinetic behaviour observed in mesohaem-substituted iNOS is most heavily influenced by electronic effects rather than structural alterations.
Mohammed, A
2000-01-01
suppressed by nonradiative recombination centres. The temperatures at which the QW luminescence starts to quench and the activation energies of luminescence quenching are found to depend on excitation conditions, sample quality and QW depth. The results of CL intensity dependence on the excitation intensity revealed that luminescence from good quality QW structures is dominated by radiative recombination processes even at high temperatures during thermal quenching. In contrast, in defected structures non-radiative recombination mechanisms dominate the luminescence properties at all temperatures. Secondary electron images of hexagonal growth hillocks of GaN obtained at a range of electron beam excitation energies vary because of the different signals involved in the imaging. Electron backscatter diffraction measurements have been used for phase identification and lattice constants determination in a strained GaN epilayer. This thesis presents studies on optical and structural characterisation of low dimensiona...
Alloying effect on the electronic structures of hydrogen storage compounds
Yukawa, H.; Moringa, M.; Takahashi, Y. [Nagoya Univ. (Japan). Dept. of Mater. Sci. and Eng.
1997-05-20
The electronic structures of hydrogenated LaNi{sub 5} containing various 3d transition elements were investigated by the DV-X{alpha} molecular orbital method. The hydrogen atom was found to form a strong chemical bond with the Ni rather than the La atoms. The alloying modified the chemical bond strengths between atoms in a small metal octahedron containing a hydrogen atom at the center, resulting in the change in the hydrogen absorption and desorption characteristics of LaNi{sub 5} with alloying. (orig.) 7 refs.
Influence of nonparabolicity on electronic structure of quantum cascade laser
Vuković, Nikola; Milanović, Vitomir; Radovanović, Jelena
2014-06-01
We analyze the influence of nonparabolicity on the bound electronic states in the conduction-band of quantum wells in external electric field. Numerical results, obtained by transfer matrix method are presented for active region of GaAs/Al0.3Ga0.7As quantum cascade laser. The structure was initially optimized by genetic algorithm, using Kane's model of nonparabolicity, with emission wavelength set to λ≈15.1 μm. However, our numerical results indicate the change in lasing wavelength to 14.04 μm when using a more comprehensive description of nonparabolicity.
8th international conference on electronic spectroscopy and structure
Robinson, Art
2000-10-16
Gathering from 33 countries around the world, 408 registrants and a number of local drop-in participants descended on the Clark Kerr Campus of the University of California, Berkeley, from Monday, August 7 through Saturday, August 12, 2000 for the Eighth International Conference on Electronic Structure and Spectroscopy (ICESS8). At the conference, participants benefited from an extensive scientific program comprising more than 100 oral presentations (plenary lectures and invited and contributed talks) and 330 poster presentations, as well as ample time for socializing and a tour of the Advanced Light Source (ALS) at the nearby Lawrence Berkeley National Laboratory.
Design of Carborane Molecular Architectures via Electronic Structure Computations
Josep M. Oliva
2009-01-01
Full Text Available Quantum-mechanical electronic structure computations were employed to explore initial steps towards a comprehensive design of polycarborane architectures through assembly of molecular units. Aspects considered were (i the striking modification of geometrical parameters through substitution, (ii endohedral carboranes and proposed ejection mechanisms for energy/ion/atom/energy storage/transport, (iii the excited state character in single and dimeric molecular units, and (iv higher architectural constructs. A goal of this work is to find optimal architectures where atom/ion/energy/spin transport within carborane superclusters is feasible in order to modernize and improve future photoenergy processes.
Electronic structure and improper electric polarization of samarium orthoferrite
Triguk, V. V.; Makoed, I. I.; Ravinski, A. F.
2016-12-01
The band structure and distributions of the electron and spin densities of samarium orthoferrite have been calculated within the framework of the first-principles density functional theory in the LSDA + U approximation taking into account the collinear antiferromagnetic ordering of the magnetic moments of iron and samarium cations. The possibility of inducing a ferroelectric state at temperatures below the antiferromagnetic ordering temperature of the magnetic sublattice formed by samarium cations has been considered using the results of the group-theoretical analysis. In the high-temperature range, the formation of regions with a spontaneous electric polarization is possible in the presence of additional factors that reduce the symmetry of the crystal.
Electron microscopy analysis of structural changes within white etching areas
Diederichs, Annika Martina; Schwedt, A.; Mayer, J.
2016-01-01
In the present work, crack networks with white etching areas (WEAs) in cross-sections of bearings were investigated by a complementary use of SEM and TEM with the focus on the use of orientation contrast imaging and electron backscatter diffraction (EBSD). Orientation contrast imaging was used...... observed within WEAs. Using EBSD analysis, evidence was obtained that WEA formation and accompanying crack growth are without relation microstructural features. In addition, an inhomogeneous chemical structure of WEA as a result of carbide dissolution is revealed by analytical investigations....
Modern quantum chemistry introduction to advanced electronic structure theory
Szabo, Attila
1996-01-01
The aim of this graduate-level textbook is to present and explain, at other than a superficial level, modem ab initio approaches to the calculation of the electronic structure and properties of molecules. The first three chapters contain introductory material culminating in a thorough discussion of the Hartree-Fock approximation.The remaining four chapters describe a variety of more sophisticated approaches, which improve upon this approximation.Among the highlights of the seven chapters are (1) a review of the mathematics (mostly matrix algebra) required for the rest of the book, (2) an intr
Hamad, Kimberly Sue [Univ. of California, Berkeley, CA (United States)
2000-01-01
Semiconductor nanocrystals are a system which has been the focus of interest due to their size dependent properties and their possible use in technological applications. Many chemical and physical properties vary systematically with the size of the nanocrystal and thus their study enables the investigation of scaling laws. Due to the increasing surface to volume ratio as size is decreased, the surfaces of nanocrystals are expected to have a large influence on their electronic, thermodynamic, and chemical behavior. In spite of their importance, nanocrystal surfaces are still relatively uncharacterized in terms of their structure, electronic properties, bonding, and reactivity. Investigation of nanocrystal surfaces is currently limited by what techniques to use, and which methods are suitable for nanocrystals is still being determined. This work presents experiments using x-ray and electronic spectroscopies to explore the structure, reactivity, and electronic properties of semiconductor (CdSe, InAs) nanocrystals and how they vary with size. Specifically, x-ray absorption near edge spectroscopy (XANES) in conjunction with multiple scattering simulations affords information about the structural disorder present at the surface of the nanocrystal. X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) probe the electronic structure in terms of hole screening, and also give information about band lineups when the nanocrystal is placed in electric contact with a substrate. XPS of the core levels of the nanocrystal as a function of photo-oxidation time yields kinetic data on the oxidation reaction occurring at the surface of the nanocrystal.
Hamad, K.S.
2000-05-01
Semiconductor nanocrystals are a system which has been the focus of interest due to their size dependent properties and their possible use in technological applications. Many chemical and physical properties vary systematically with the size of the nanocrystal and thus their study enables the investigation of scaling laws. Due to the increasing surface to volume ratio as size is decreased, the surfaces of nanocrystals are expected to have a large influence on their electronic, thermodynamic, and chemical behavior. In spite of their importance, nanocrystal surfaces are still relatively uncharacterized in terms of their structure, electronic properties, bonding, and reactivity. Investigation of nanocrystal surfaces is currently limited by what techniques to use, and which methods are suitable for nanocrystals is still being determined. This work presents experiments using x-ray and electronic spectroscopies to explore the structure, reactivity, and electronic properties of semiconductor (CdSe, InAs) nanocrystals and how they vary with size. Specifically, x-ray absorption near edge spectroscopy (XANES) in conjunction with multiple scattering simulations affords information about the structural disorder present at the surface of the nanocrystal. X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) probe the electronic structure in terms of hole screening, and also give information about band lineups when the nanocrystal is placed in electric contact with a substrate. XPS of the core levels of the nanocrystal as a function of photo-oxidation time yields kinetic data on the oxidation reaction occurring at the surface of the nanocrystal.
Electron Beam Freeform Fabrication of Titanium Alloy Gradient Structures
Brice, Craig A.; Newman, John A.; Bird, Richard Keith; Shenoy, Ravi N.; Baughman, James M.; Gupta, Vipul K.
2014-01-01
Historically, the structural optimization of aerospace components has been done through geometric methods. A monolithic material is chosen based on the best compromise between the competing design limiting criteria. Then the structure is geometrically optimized to give the best overall performance using the single material chosen. Functionally graded materials offer the potential to further improve structural efficiency by allowing the material composition and/or microstructural features to spatially vary within a single structure. Thus, local properties could be tailored to the local design limiting criteria. Additive manufacturing techniques enable the fabrication of such graded materials and structures. This paper presents the results of a graded material study using two titanium alloys processed using electron beam freeform fabrication, an additive manufacturing process. The results show that the two alloys uniformly mix at various ratios and the resultant static tensile properties of the mixed alloys behave according to rule-of-mixtures. Additionally, the crack growth behavior across an abrupt change from one alloy to the other shows no discontinuity and the crack smoothly transitions from one crack growth regime into another.
Features for Exploiting Black-Box Optimization Problem Structure
Tierney, Kevin; Malitsky, Yuri; Abell, Tinus
2013-01-01
Black-box optimization (BBO) problems arise in numerous scientic and engineering applications and are characterized by compu- tationally intensive objective functions, which severely limit the number of evaluations that can be performed. We present a robust set of features that analyze the tness...... landscape of BBO problems and show how an algorithm portfolio approach can exploit these general, problem indepen- dent features and outperform the utilization of any single minimization search strategy. We test our methodology on data from the GECCO Workshop on BBO Benchmarking 2012, which contains 21...
Microscopic structures from reduction of continuum nonlinear problems
Lovison, Alberto
2011-01-01
We present an application of the Amann-Zehnder exact finite reduction to a class of nonlinear perturbations of elliptic elasto-static problems. We propose the existence of minmax solutions by applying Ljusternik-Schnirelmann theory to a finite dimensional variational formulation of the problem, based on a suitable spectral cut-off. As a by-product, with a choice of fit variables, we establish a variational equivalence between the above spectral finite description and a discrete mechanical model. By doing so, we decrypt the abstract information encoded in the AZ reduction and give rise to a concrete and finite description of the continuous problem.
A conventional, massively parallel eigensolver for electronic structure theory
Blum, V.; Scheffler, M. [Fritz Haber Institute, Berlin (Germany); Johanni, R.; Lederer, H. [RZ Garching (Germany); Auckenthaler, T.; Huckle, T.; Bungartz, H.J. [TU Muenchen (Germany); Kraemer, L.; Willems, P.; Lang, B. [BU Wuppertal (Germany); Havu, V. [Aalto University, Helsinki (Finland)
2011-07-01
We demonstrate a robust large-scale, massively parallel conventional eigensolver for first-principles theory of molecules and materials. Despite much research into O(N) methods, standard approaches (Kohn-Sham or Hartree-Fock theory and excited-state formalisms) must still rely on conventional but robust O(N{sup 3}) solvers for many system classes, most notably metals. In particular, our eigensolver overcomes parallel scalability limitations where standard implementations of certain steps (reduction to tridiagonal form, solution of reduced tridiagonal eigenproblem) can be a serious bottleneck already for a few hundred CPUs. We demonstrate scalable implementations of these and all other steps of the full generalized eigenvalue problem. Our largest example is a production run with 1046 Pt (heavy-metal) atoms with converged all-electron accuracy in the numeric atom-centered orbital code FHI-aims, but the implementation is generic and should easily be portable to other codes.
Electronic structure calculations toward new potentially AChE inhibitors
de Paula, A. A. N.; Martins, J. B. L.; Gargano, R.; dos Santos, M. L.; Romeiro, L. A. S.
2007-10-01
The main purpose of this study was the use of natural non-isoprenoid phenolic lipid of cashew nut shell liquid from Anacardium occidentale as lead material for generating new potentially candidates of acetylcholinesterase inhibitors. Therefore, we studied the electronic structure of 15 molecules derivatives from the cardanol using the following groups: methyl, acetyl, N, N-dimethylcarbamoyl, N, N-dimethylamine, N, N-diethylamine, piperidine, pyrrolidine, and N-benzylamine. The calculations were performed at RHF level using 6-31G, 6-31G(d), 6-31+G(d) and 6-311G(d,p) basis functions. Among the proposed compounds we found that the structures with substitution by acetyl, N, N-dimethylcarbamoyl, N, N-dimethylamine, and pyrrolidine groups were better correlated to rivastigmine indicating possible activity.
Vibrational structures and long-lasting electronic coherence
Chin, A W; Rosenbach, R; Caycedo-Soler, F; Huelga, S F; Plenio, M B
2012-01-01
Recent observations of beating signals in the excitation energy transfer dynamics of photosynthetic complexes have been interpreted as evidence for sustained coherences that are sufficiently long-lived for energy transport and coherence to coexist. The possibility that coherence may be exploited in biological processes has opened up new avenues of exploration at the interface of physics and biology. The microscopic origin of these long-lived coherences, however, remains to be uncovered. Here we present such a mechanism and verify it by numerically exact simulations of system-environment dynamics. Crucially, the non-trivial spectral structures of the environmental fluctuations and particularly discrete vibrational modes can lead to the generation and sustenance of both oscillatory energy transport and electronic coherence on timescales that are comparable to excitation energy transport. This suggests that the non-trivial structure of protein environments plays a more significant role for coherence in biologica...
Electronic structure of semiconductor-metal-semiconductor heterostructures
Masri, Pierre
For the first time, we present in this article a microscopic self-consistent theory of the electronic structure of semiconductor-metal-semiconductor (SMS) heterostructures. This is done within the framework of a tight-binding approximation. We use a one-band model and a simplified two-band model to describe metal and semiconductor bulk bands, respectively. Results are given for a material-symmetrical and interface-assymetrical SMS structure: this involves the same semiconductors, but different interface polarities (anion- and cation-like interfaces). These results include metal-like states (built-in metal band) and metal-induced semiconductor-like states. The relevance of the charge neutrality condition to this feature and to the determination of the position of the SMS Fermi level is discussed. We also emphasize the confining role of interfaces, with respect to semiconductor-like states, within the semiconductor gap.
Atomic and electronic structure of twin growth defects in magnetite.
Gilks, Daniel; Nedelkoski, Zlatko; Lari, Leonardo; Kuerbanjiang, Balati; Matsuzaki, Kosuke; Susaki, Tomofumi; Kepaptsoglou, Demie; Ramasse, Quentin; Evans, Richard; McKenna, Keith; Lazarov, Vlado K
2016-02-15
We report the existence of a stable twin defect in Fe3O4 thin films. By using aberration corrected scanning transmission electron microscopy and spectroscopy the atomic structure of the twin boundary has been determined. The boundary is confined to the (111) growth plane and it is non-stoichiometric due to a missing Fe octahedral plane. By first principles calculations we show that the local atomic structural configuration of the twin boundary does not change the nature of the superexchange interactions between the two Fe sublattices across the twin grain boundary. Besides decreasing the half-metallic band gap at the boundary the altered atomic stacking at the boundary does not change the overall ferromagnetic (FM) coupling between the grains.
Structure and Electronic Properties of Cerium Orthophosphate: Theory and Experiment
Adelstein, Nicole; Mun, B. Simon; Ray, Hannah; Ross Jr, Phillip; Neaton, Jeffrey; De Jonghe, Lutgard
2010-07-27
Structural and electronic properties of cerium orthophosphate (CePO{sub 4}) are calculated using density functional theory (DFT) with the local spin-density approximation (LSDA+U), with and without gradient corrections (GGA-(PBE)+U), and compared to X-ray diffraction and photoemission spectroscopy measurements. The density of states is found to change significantly as the Hubbard parameter U, which is applied to the Ce 4f states, is varied from 0 to 5 eV. The calculated structural properties are in good agreement with experiment and do not change significantly with U. Choosing U = 3 eV for LDSA provides the best agreement between the calculated density of states and the experimental photoemission spectra.
Embellishing Problem-Solving Examples with Deep Structure Information Facilitates Transfer
Lee, Hee Seung; Betts, Shawn; Anderson, John R.
2017-01-01
Appreciation of problem structure is critical to successful learning. Two experiments investigated effective ways of communicating problem structure in a computer-based learning environment and tested whether verbal instruction is necessary to specify solution steps, when deep structure is already embellished by instructional examples.…
Marek, A; Blum, V; Johanni, R; Havu, V; Lang, B; Auckenthaler, T; Heinecke, A; Bungartz, H-J; Lederer, H
2014-05-28
Obtaining the eigenvalues and eigenvectors of large matrices is a key problem in electronic structure theory and many other areas of computational science. The computational effort formally scales as O(N(3)) with the size of the investigated problem, N (e.g. the electron count in electronic structure theory), and thus often defines the system size limit that practical calculations cannot overcome. In many cases, more than just a small fraction of the possible eigenvalue/eigenvector pairs is needed, so that iterative solution strategies that focus only on a few eigenvalues become ineffective. Likewise, it is not always desirable or practical to circumvent the eigenvalue solution entirely. We here review some current developments regarding dense eigenvalue solvers and then focus on the Eigenvalue soLvers for Petascale Applications (ELPA) library, which facilitates the efficient algebraic solution of symmetric and Hermitian eigenvalue problems for dense matrices that have real-valued and complex-valued matrix entries, respectively, on parallel computer platforms. ELPA addresses standard as well as generalized eigenvalue problems, relying on the well documented matrix layout of the Scalable Linear Algebra PACKage (ScaLAPACK) library but replacing all actual parallel solution steps with subroutines of its own. For these steps, ELPA significantly outperforms the corresponding ScaLAPACK routines and proprietary libraries that implement the ScaLAPACK interface (e.g. Intel's MKL). The most time-critical step is the reduction of the matrix to tridiagonal form and the corresponding backtransformation of the eigenvectors. ELPA offers both a one-step tridiagonalization (successive Householder transformations) and a two-step transformation that is more efficient especially towards larger matrices and larger numbers of CPU cores. ELPA is based on the MPI standard, with an early hybrid MPI-OpenMPI implementation available as well. Scalability beyond 10,000 CPU cores for problem
Structure of the electron momentum density of atomic systems
Romera, E.; Dehesa, J.S. [Granada Univ. (Spain). Dept. de Fisica Moderna; Koga, T. [Department of Applied Chemistry, Muroran Institute of Technology, Muroran, Hokkaido 050 (Japan)
1997-12-01
The present paper addresses the controversial problem on the nonmonotonic behavior of the spherically-averaged momentum density {gamma}(p) observed previously for some ground-state atoms based on the Roothaan-Hartree-Fock (RHF) wave functions of Clementi and Roetti. Highly accurate RHF wave functions of Koga et al. are used to study the existence of extrema in the momentum density {gamma}(p) of all the neutral atoms from hydrogen to xenon. Three groups of atoms are clearly identified according to the nonmonotonicity parameter {mu}, whose value is either equal to, larger, or smaller than unity. Additionally, it is found that the function p{sup -{alpha}} {gamma}(p) is (i) monotonically decreasing from the origin for {alpha}{>=}0.75, (ii) convex for {alpha}{>=}1.35, and (iii) logarithmically convex for {alpha}{>=}3.64 for all the neutral atoms with nuclear charges Z = 1-54. Finally, these monotonicity properties are applied to derive simple yet general inequalities which involve three momentum moments left angle p{sup t} right angle. These inequalities not only generalize similar inequalities reported so far but also allow us to correlate some fundamental atomic quantities, such as the electron-electron repulsion energy and the peak height of Compton profile, in a simple manner. (orig.) 40 refs.
Casey, Jennifer Ryan
Since its discovery over fifty years ago, the hydrated electron has been the subject of much interest. Hydrated electrons, which are free electrons in water, are found in fields ranging from biochemistry to radiation chemistry, so it is important that we understand the structure and dynamics of this species. Because of its high reactivity, the hydrated electron's structure has proven difficult to pin down, especially its molecular details. One-electron mixed quantum/classical molecular dynamics simulations have proven useful in helping elucidate the structure of the hydrated electron. The picture most commonly presented from these studies is one of the electron residing in a cavity, disrupting the local water structure much like an anion the size of bromide. Our group has recently proposed a completely different structure for the hydrated electron, which arose from rigorous calculations of a new electron-water potential. The picture that emerged was of an electron that does not occupy a cavity but instead draws water within itself; this non-cavity electron resides in a region of enhanced water density. The one-electron cavity and non-cavity models all predict similar experimental observables that probe the electronic structure of the hydrated electron, such as the optical absorption spectrum, which makes it difficult to determine which model most accurately describes the true structure of the hydrated electron. In this thesis, we work to calculate experimental observables for various simulated cavity and non-cavity models that are particularly sensitive to the local water structure near the electron, in an effort to distinguish the various models from each other. Two particular observables we are interested in are the resonance Raman spectrum and the temperature dependent optical absorption spectrum of the hydrated electron. We find that for both of these experiments, only the non-cavity model has qualitative agreement with experiment; the cavity models miss the
Dielectric Property Change of Ferroelectrics and Electronic Structures
Fujita, Masaki; Sekine, Rika; Sugihara, Sunao
1999-09-01
Electronic structures were investigated in relation to the relative permittivity of ferroelectrics such as the ABO3-type and A- and/or B-substituted materials, using amolecular orbital method. The A-site ions were Ba, Pb, Sr and Ca, andthe B-site ion was Zr. Calculation was performed using theDV-Xα (discrete variational Xα) method and the overlappopulation, which is related to the covalent bonding nature, was discussed together with the effective charge. As a result, the change from ferroelectric to paraelectric was found to be associated with the covalency between the A-site ion and Ti or Zr. Furthermore, the energy for π-bonding between O2p and Ti3d (or Zr4d in AZrO3) shifted toward the lower energy level by substitution of the A site with Ca to give a lower relative permittivity. Then, we studied the effect of quantitative changes of the amount (x = 0.25, 0.5, 0.75) of A-site ions in the (Ba1-x, Srx)TiO3 system on the electronic structures, and suggested that the bonding nature between O and Ti is related to the relative permittivity of the system.
Mechanical properties and electronic structures of Fe-Al intermetallic
Liu, YaHui; Chong, XiaoYu; Jiang, YeHua, E-mail: jiangyehua@kmust.edu.cn; Zhou, Rong; Feng, Jing, E-mail: jingfeng@kmust.edu.cn
2017-02-01
Using the first-principles calculations, the elastic properties, anisotropy properties, electronic structures, Debye temperature and stability of Fe-Al (Fe{sub 3}Al, FeAl, FeAl{sub 2}, Fe{sub 2}Al{sub 5} and FeAl{sub 3}) binary compounds were calculated. The formation enthalpy and cohesive energy of these Fe-Al compounds are negative, and show they are thermodynamically stable structures. Fe{sub 2}Al{sub 5} has the lowest formation enthalpy, which shows the Fe{sub 2}Al{sub 5} is the most stable of Fe-Al binary compounds. These Fe-Al compounds display disparate anisotropy due to the calculated different shape of the 3D curved surface of the Young’s modulus and anisotropic index. Fe{sub 3}Al has the biggest bulk modulus with the value 233.2 GPa. FeAl has the biggest Yong’s modulus and shear modulus with the value 296.2 GPa and 119.8 GPa, respectively. The partial density of states, total density of states and electron density distribution maps of the binary Fe-Al binary compounds are analyzed. The bonding characteristics of these Fe-Al binary compounds are mainly combination by covalent bond and metallic bonds. Meanwhile, also exist anti-bond effect. Moreover, the Debye temperatures and sound velocity of these Fe-Al compounds are explored.
Efficient Execution of Electronic Structure Calculations on SMP Clusters
Ustemirov, Nurzhan [Iowa State Univ., Ames, IA (United States)
2006-01-01
Applications augmented with adaptive capabilities are becoming common in parallel computing environments. For large-scale scientific applications, dynamic adjustments to a computationally-intensive part may lead to a large pay-off in facilitating efficient execution of the entire application while aiming at avoiding resource contention. Application-specific knowledge, often best revealed during the run-time, is required to initiate and time these adjustments. In particular, General Atomic and Molecular Electronic Structure System (GAMESS) is a program for ab initio quantum chemistry that places significant demands on the high-performance computing platforms. Certain electronic structure calculations are characterized by high consumption of a particular resource, such as CPU, main memory, or disk I/O. This may lead to resource contention among concurrent GAMESS jobs and other programs in the dynamically changing environment. Thus, it is desirable to improve GAMESS calculations by means of dynamic adaptations. In this thesis, we show how an application- or algorithm-specific knowledge may play a significant role in achieving this goal. The choice of implementation is facilitated by a module-driven middleware easily integrated with GAMESS that assesses resource consumption and invokes GAMESS adaptations to the system environment. We show that the throughput of GAMESS jobs may be improved greatly as a result of such adaptations.
Mechanical properties and electronic structures of Fe-Al intermetallic
Liu, YaHui; Chong, XiaoYu; Jiang, YeHua; Zhou, Rong; Feng, Jing
2017-02-01
Using the first-principles calculations, the elastic properties, anisotropy properties, electronic structures, Debye temperature and stability of Fe-Al (Fe3Al, FeAl, FeAl2, Fe2Al5 and FeAl3) binary compounds were calculated. The formation enthalpy and cohesive energy of these Fe-Al compounds are negative, and show they are thermodynamically stable structures. Fe2Al5 has the lowest formation enthalpy, which shows the Fe2Al5 is the most stable of Fe-Al binary compounds. These Fe-Al compounds display disparate anisotropy due to the calculated different shape of the 3D curved surface of the Young's modulus and anisotropic index. Fe3Al has the biggest bulk modulus with the value 233.2 GPa. FeAl has the biggest Yong's modulus and shear modulus with the value 296.2 GPa and 119.8 GPa, respectively. The partial density of states, total density of states and electron density distribution maps of the binary Fe-Al binary compounds are analyzed. The bonding characteristics of these Fe-Al binary compounds are mainly combination by covalent bond and metallic bonds. Meanwhile, also exist anti-bond effect. Moreover, the Debye temperatures and sound velocity of these Fe-Al compounds are explored.
Structural and electronic properties of Diisopropylammonium bromide molecular ferroelectric crystal
Alsaad, A.; Qattan, I. A.; Ahmad, A. A.; Al-Aqtash, N.; Sabirianov, R. F.
2015-10-01
We report the results of ab-initio calculations based on Generalized Gradient Approximation (GGA) and hybrid functional (HSE06) of electronic band structure, density of states and partial density of states to get a deep insight into structural and electronic properties of P21 ferroelectric phase of Diisopropylammonium Bromide molecular crystal (DIPAB). We found that the optical band gap of the polar phase of DIPAB is ∼ 5 eV confirming it as a good dielectric. Examination of the density of states and partial density of states reveal that the valence band maximum is mainly composed of bromine 4p orbitals and the conduction band minimum is dominated by carbon 2p, carbon 2s, and nitrogen 2s orbitals. A unique aspect of P21 ferroelectric phase is the permanent dipole within the material. We found that P21 DIPAB has a spontaneous polarization of 22.64 consistent with recent findings which make it good candidate for the creation of ferroelectric tunneling junctions (FTJs) which have the potential to be used as memory devices.
Structural and electronic implications for carrier injection into organic semiconductors
Castellani, Mauro [Universitaet Potsdam, Institut fuer Physik und Astronomie, Potsdam-Golm (Germany); Salzmann, Ingo; Yu, Shuwen; Koch, Norbert [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Berlin (Germany); Bugnon, Philippe [Ecole Polytechnique Federale de Lausanne (Switzerland). Institut des Materiaux; Oehzelt, Martin [Johannes Kepler Universitaet Linz (Austria). Institut fuer Experimentalphysik
2009-10-15
We report on the structural and electronic interface formation between ITO (indium-tin-oxide) and prototypical organic small molecular semiconductors, i.e., CuPc (copper phthalocyanine) and {alpha}-NPD (N,N'-di(naphtalen-1-yl)-N,N'-diphenyl-benzidine). In particular, the effects of in situ oxygen plasma pretreatment of the ITO surface on interface properties are examined in detail: Organic layer-thickness dependent Kelvin probe measurements revealed a good alignment of the ITO work function and the highest occupied electronic level of the organic material in all samples. In contrast, the electrical properties of hole-only and bipolar organic diodes depend strongly on the treatment of ITO prior to organic deposition. This dependence is more pronounced for diodes made of polycrystalline CuPc than for those of amorphous {alpha}-NPD layers. X-ray diffraction and atomic force microscopic (AFM) investigations of CuPc nucleation and growth evidenced a more pronounced texture of the polycrystalline film structure on the ITO substrate that was oxygen plasma treated prior to organic layer deposition. These findings suggest that the anisotropic electrical properties of CuPc crystallites, and their orientation with respect to the substrate, strongly affect the charge carrier injection and transport properties at the anode interface. (orig.)
Structural enzymology using X-ray free electron lasers.
Kupitz, Christopher; Olmos, Jose L; Holl, Mark; Tremblay, Lee; Pande, Kanupriya; Pandey, Suraj; Oberthür, Dominik; Hunter, Mark; Liang, Mengning; Aquila, Andrew; Tenboer, Jason; Calvey, George; Katz, Andrea; Chen, Yujie; Wiedorn, Max O; Knoska, Juraj; Meents, Alke; Majriani, Valerio; Norwood, Tyler; Poudyal, Ishwor; Grant, Thomas; Miller, Mitchell D; Xu, Weijun; Tolstikova, Aleksandra; Morgan, Andrew; Metz, Markus; Martin-Garcia, Jose M; Zook, James D; Roy-Chowdhury, Shatabdi; Coe, Jesse; Nagaratnam, Nirupa; Meza, Domingo; Fromme, Raimund; Basu, Shibom; Frank, Matthias; White, Thomas; Barty, Anton; Bajt, Sasa; Yefanov, Oleksandr; Chapman, Henry N; Zatsepin, Nadia; Nelson, Garrett; Weierstall, Uwe; Spence, John; Schwander, Peter; Pollack, Lois; Fromme, Petra; Ourmazd, Abbas; Phillips, George N; Schmidt, Marius
2017-07-01
Mix-and-inject serial crystallography (MISC) is a technique designed to image enzyme catalyzed reactions in which small protein crystals are mixed with a substrate just prior to being probed by an X-ray pulse. This approach offers several advantages over flow cell studies. It provides (i) room temperature structures at near atomic resolution, (ii) time resolution ranging from microseconds to seconds, and (iii) convenient reaction initiation. It outruns radiation damage by using femtosecond X-ray pulses allowing damage and chemistry to be separated. Here, we demonstrate that MISC is feasible at an X-ray free electron laser by studying the reaction of M. tuberculosis ß-lactamase microcrystals with ceftriaxone antibiotic solution. Electron density maps of the apo-ß-lactamase and of the ceftriaxone bound form were obtained at 2.8 Å and 2.4 Å resolution, respectively. These results pave the way to study cyclic and non-cyclic reactions and represent a new field of time-resolved structural dynamics for numerous substrate-triggered biological reactions.
Organic/metal interfaces. Electronic and structural properties
Duhm, Steffen
2008-07-17
This work addresses several important topics of the field of organic electronics. The focus lies on organic/metal interfaces, which exist in all organic electronic devices. Physical properties of such interfaces are crucial for device performance. Four main topics have been covered: (i) the impact of molecular orientation on the energy levels, (ii) energy level tuning with strong electron acceptors, (iii) the role of thermodynamic equilibrium at organic/ organic homo-interfaces and (iv) the correlation of interfacial electronic structure and bonding distance. To address these issues a broad experimental approach was necessary: mainly ultraviolet photoelectron spectroscopy was used, supported by X-ray photoelectron spectroscopy, metastable atom electron spectroscopy, X-ray diffraction and X-ray standing waves, to examine vacuum sublimed thin films of conjugated organic molecules (COMs) in ultrahigh vacuum. (i) A novel approach is presented to explain the phenomenon that the ionization energy in molecular assemblies is orientation dependent. It is demonstrated that this is due to a macroscopic impact of intramolecular dipoles on the ionization energy in molecular assemblies. Furthermore, the correlation of molecular orientation and conformation has been studied in detail for COMs on various substrates. (ii) A new approach was developed to tune hole injection barriers ({delta}{sub h}) at organic/metal interfaces by adsorbing a (sub-) monolayer of an organic electron acceptor on the metal electrode. Charge transfer from the metal to the acceptor leads to a chemisorbed layer, which reduces {delta}{sub h} to the COM overlayer. This concept was tested with three acceptors and a lowering of {delta}{sub h} of up to 1.2 eV could be observed. (iii) A transition from vacuum-level alignment to molecular level pinning at the homo-interface between a lying monolayer and standing multilayers of a COM was observed, which depended on the amount of a pre-deposited acceptor. The
Kervalishvili, N A
2015-01-01
The results of experimental investigations of the ejection of electrons from gas-discharge nonneutral electron plasma at interaction of vortex structures have been given. The periodical approach of vortex structures causes the ejection of electrons both from the vortex structures themselves and from the adjacent regions of electron sheath to the end cathodes of discharge device. The ejection takes place in the form of short and long pulses following each other. The nature of these pulses and the dynamics of interaction of vortex structures at their approach were studied.
Scanning Probe Evaluation of Electronic, Mechanical and Structural Material Properties
Virwani, Kumar
2011-03-01
We present atomic force microscopy (AFM) studies of a range of properties from three different classes of materials: mixed ionic electronic conductors, low-k dielectrics, and polymer-coated magnetic nanoparticles. (1) Mixed ionic electronic conductors are being investigated as novel diodes to drive phase-change memory elements. Their current-voltage characteristics are measured with direct-current and pulsed-mode conductive AFM (C-AFM). The challenges to reliability of the C-AFM method include the electrical integrity of the probe, the sample and the contacts, and the minimization of path capacitance. The role of C-AFM in the optimization of these electro-active materials will be presented. (2) Low dielectric constant (low-k) materials are used in microprocessors as interlayer insulators, a role directly affected by their mechanical performance. The mechanical properties of nanoporous silicate low-k thin films are investigated in a comparative study of nanomechanics measured by AFM and by traditional nanoindentation. Both methods are still undergoing refinement as reliable analytical tools for determining nanomechanical properties. We will focus on AFM, the faster of the two methods, and its developmental challenges of probe shape, cantilever force constant, machine compliance and calibration standards. (3) Magnetic nanoparticles are being explored for their use in patterned media for magnetic storage. Current methods for visualizing the core-shell structure of polymer-coated magnetic nanoparticles include dye-staining the polymer shell to provide contrast in transmission electron microscopy. AFM-based fast force-volume measurements provide direct visualization of the hard metal oxide core within the soft polymer shell based on structural property differences. In particular, the monitoring of adhesion and deformation between the AFM tip and the nanoparticle, particle-by-particle, provides a reliable qualitative tool to visualize core-shell contrast without the use
Structural and electronic properties of SnO{sub 2}
Akgul, Funda Aksoy, E-mail: fundaaksoy01@gmail.com [Physics Department, Nigde University, 51240 Nigde (Turkey); Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Gumus, Cebrail, E-mail: cgumus@cu.edu.tr [Physics Department, Cukurova University, 01330 Adana (Turkey); Er, Ali O. [Department of Chemistry, University of California, Irvine, CA 92612 (United States); Farha, Ashraf H. [Electrical and Computer Engineering, Old Dominion University, Norfolk, VA 23529 (United States); Physics Department, Ain Shams University, Cairo 11566 (Egypt); Akgul, Guvenc [Bor Vocational School, Nigde University, 51700 Nigde (Turkey); Ufuktepe, Yuksel [Physics Department, Cukurova University, 01330 Adana (Turkey); Liu, Zhi [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
2013-12-05
Highlights: •Structural and electronic properties of SnO{sub 2} films were determined. •Oxidation states of the SnO{sub 2} thin films were confirmed by XPS analysis. •Chemical component is non-stoichiometric and ratio of oxygen to tin was 1.85. -- Abstract: Highly transparent polycrystalline thin film of SnO{sub 2} (tin dioxide) was deposited using a simple and low cost spray pyrolysis method. The film was prepared from an aqueous solution of tin tetrachloride (stannic chloride) onto glass substrates at 400 °C. A range of diagnostic techniques including X-ray diffraction (XRD), UV–visible absorption, atomic force microscopy (AFM), scanning electron microscopy (SEM), and synchrotron-based X-ray photoelectron spectroscopy (XPS) were used to investigate structural, optical, and electronic properties of the resulting film. Deposited film was found to be polycrystalline. A mixture of SnO and SnO{sub 2} phases was observed. The average crystallite size of ∼21.3 nm for SnO{sub 2} was calculated by Rietveld method using XRD data. The oxidation states of the SnO{sub 2} thin film were confirmed by the shape analysis of corresponding XPS O 1s, Sn 3d, and Sn 4d peaks using the decomposition procedure. The analysis of the XPS core level peaks showed that the chemical component is non-stoichiometric and the ratio of oxygen to tin (O/Sn) is 1.85 which is slightly under stoichiometry.
Godunov, I. A.; Bataev, V. A.; Maslov, D. V.; Yakovlev, N. N.
2016-12-01
The structure of conformational non-rigid molecules in the excited electronic states are investigated by joint theoretical and experimental methods. The theoretical part of work consist of two stages. In first stage the ab initio quantum-chemical calculations are carried out using high level methods. In second stage the vibrational problems of the various dimensions are solved by variational method for vibrations of large amplitude. In experimental part of work the vibronic spectra are investigated: gas-phase absorption and also, fluorescence excitation spectra of jet-cooled molecules. Some examples are considered.
Manganites in Perovskite Superlattices: Structural and Electronic Properties
Jilili, Jiwuer
2016-07-13
Perovskite oxides have the general chemical formula ABO3, where A is a rare-earth or alkali-metal cation and B is a transition metal cation. Perovskite oxides can be formed with a variety of constituent elements and exhibit a wide range of properties ranging from insulators, metals to even superconductors. With the development of growth and characterization techniques, more information on their physical and chemical properties has been revealed, which diversified their technological applications. Perovskite manganites are widely investigated compounds due to the discovery of the colossal magnetoresistance effect in 1994. They have a broad range of structural, electronic, magnetic properties and potential device applications in sensors and spintronics. There is not only the technological importance but also the need to understand the fundamental mechanisms of the unusual magnetic and transport properties that drive enormous attention. Manganites combined with other perovskite oxides are gaining interest due to novel properties especially at the interface, such as interfacial ferromagnetism, exchange bias, interfacial conductivity. Doped manganites exhibit diverse electrical properties as compared to the parent compounds. For instance, hole doped La0.7Sr0.3MnO3 is a ferromagnetic metal, whereas LaMnO3 is an antiferromagnetic insulator. Since manganites are strongly correlated systems, heterojunctions composed of manganites and other perovskite oxides are sunject to complex coupling of the spin, orbit, charge, and lattice degrees of freedom and exhibit unique electronic, magnetic, and transport properties. Electronic reconstructions, O defects, doping, intersite disorder, magnetic proximity, magnetic exchange, and polar catastrophe are some effects to explain these interfacial phenomena. In our work we use first-principles calculations to study the structural, electronic, and magnetic properties of manganite based superlattices. Firstly, we investigate the electronic
Insight into the antiferromagnetic structure manipulated by electronic reconstruction
Cui, B.; Li, F.; Song, C.; Peng, J. J.; Saleem, M. S.; Gu, Y. D.; Li, S. N.; Wang, K. L.; Pan, F.
2016-10-01
Antiferromagnetic (AFM) materials, with robust rigidity to magnetic field perturbations and ultrafast spin dynamics, show great advantages in information storage and have developed into a fast-emerging field of AFM spintronics. However, a direct characterization of spin alignments in AFM films has been challenging, and their manipulation by lattice distortion and magnetic proximity is inevitably accompanied by "ferromagnetic" features within the AFM matrix. Here we resolve the G -type AFM structure of SrCo O2.5 and find that the interfacial AFM structure could be modulated intrinsically from in plane to out of plane with a canted angle of 60∘ by the charge transfer and orbital reconstruction in SrCo O2.5/L a2 /3S r1 /3Mn O3 heterostructures both experimentally and theoretically. Such an interfacial AFM reconfiguration caused by electronic reconstruction does not cause the ferromagnetic feature and changes the magnetization switching process of L a2 /3S r1 /3Mn O3 from in plane to perpendicular to the plane, in turn. Our study not only reveals the coupling between charge, orbital, and AFM structure, but also provides a unique approach to manipulating AFM structure.
Electronic and Magnetic Structure of Octahedral Molecular Sieves
Morey-Oppenheim, Aimee M.
The major part of this research consists of magnetic and electronic studies of metal doped cryptomelane-type manganese oxide octahedral molecular sieves (KOMS-2). The second part of this study involves the magnetic characterization of cobalt doped MCM-41 before and after use in the synthesis of single walled carbon nanotubes. Manganese oxides have been used widely as bulk materials in catalysis, chemical sensors, and batteries due to the wide range of possible stable oxidation states. The catalytic function of manganese oxides is further tuned by doping the material with numerous transition metals. It is of particular interest the oxidation states of Mn present after doping. New titrations to determine the oxidation state of Mn were investigated. To further examine the structure of KOMS-2, the magnetic contribution of dopant metals was also examined. The KOMS-2 structure having both diamagnetic and paramagnetic metal ions substitutions was studied. MCM-41 with the incorporation of cobalt into the structure was analyzed for its magnetic properties. The material undergoes significant structural change during the synthesis of single walled carbon nanotubes. It was the focus of this portion of the research to do a complete magnetic profile of both the before and after reaction material.
HOMOTOPY SOLUTION OF THE INVERSE GENERALIZED EIGENVALUE PROBLEMS IN STRUCTURAL DYNAMICS
李书; 王波; 胡继忠
2004-01-01
The structural dynamics problems, such as structural design, parameter identification and model correction, are considered as a kind of the inverse generalized eigenvalue problems mathematically. The inverse eigenvalue problems are nonlinear. In general, they could be transformed into nonlinear equations to solve. The structural dynamics inverse problems were treated as quasi multiplicative inverse eigenalue problems which were solved by homotopy method for nonlinear equations. This method had no requirements for initial value essentially because of the homotopy path to solution. Numerical examples were presented to illustrate the homotopy method.
Electronic structure of LaTe and CeTe
Chainani, A., E-mail: chainania@gmail.com [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan); Department of Physics, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan); Oura, M. [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan); Matsunami, M. [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Ochiai, A.; Takahashi, T. [Department of Physics, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan); Tanaka, Y. [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan); Graduate School of Material Science, University of Hyogo, 3-2-1 Kouto, Hyogo 678-1297 (Japan); Tamasaku, K.; Kohmura, Y.; Ishikawa, T. [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan)
2016-04-15
Highlights: • Hard X-ray and soft X-ray photoelectron spectroscopy of LaTe and CeTe. • Evidence for Kondo screening in antiferromagnetic(T{sub N} = 2.2 K) compound CeTe. • Suppressed Kondo resonance in CeTe compared to typical Kondo materials. - Abstract: We report a comparative study of the electronic structure of the compounds LaTe and CeTe, both of which crystallize in the rock salt structure. LaTe is a paramagnetic metal while CeTe is known to exhibit anomalous Kondo-like transport behaviour and undergoes a transition to a complex magnetically ordered state at low temperature (T{sub N} = 2.2 K). We carry out hard X-ray photoelectron spectroscopy (HAXPES) of the core-levels and valence band of LaTe and CeTe at T = 20 K, in order to characterize their intrinsic electronic structure, and to address the role of Kondo effect on the electronic structure of CeTe. The bulk sensitive core level HAXPES spectra show evidence of screened features in the La 3d and Ce 3d states mixed with plasmon features. From a careful analysis of the Te, La and Ce derived core levels, we separate out the respective origins of the satellites and show that CeTe indeed exhibits definitive but weak f{sup 0} and f{sup 2} satellites due to Kondo screening, in addition to the main f{sup 1} peak. The comparison of the valence band spectra of CeTe obtained using HAXPES and soft X-ray PES clearly identifies the Ce 4f derived features. Resonant photoelectron spectrosocopy across the Ce 3d − 4f threshold confirms the Ce 4f{sup 1} final state at the Fermi level, corresponding to the tail of the Kondo resonance feature which occurs above the Fermi level, while the Ce 4f{sup 0} final state feature is observed at a binding energy of 2.4 eV. The 4f{sup 0} and 4f{sup 1} final states show giant resonances compared to the off-resonant spectra. However, in contrast to typical Kondo systems, the tail of the Ce 4f{sup 1} Kondo resonance at the Fermi level is relatively suppressed compared to the Ce 4f
Atomistic modeling of electronic structure and transport in disordered nanostructures
Kharche, Neerav
As the Si-CMOS technology approaches the end of the International Technology Roadmap for Semiconductors (ITRS), the semiconductor industry faces a formidable challenge to continue the transistor scaling according to Moore's law. To continue the scaling of classical devices, alternative channel materials such as SiGe, carbon nanotubes, nanowires, and III-V based materials are being investigated along with novel 3D device geometries. Researchers are also investigating radically new quantum computing devices, which are expected to perform calculations faster than the existing classical Si-CMOS based structures. Atomic scale disorders such as interface roughness, alloy randomness, non-uniform strain, and dopant fluctuations are routinely present in the experimental realization of such devices. These disorders now play an increasingly important role in determining the electronic structure and transport properties as device sizes enter the nanometer regime. This work employs the atomistic tight-binding technique, which is ideally suited for modeling systems with local disorders on an atomic scale. High-precision multi-million atom electronic structure calculations of (111) Si surface quantum wells and (100) SiGe/Si/SiGe heterostructure quantum wells are performed to investigate the modulation of valley splitting induced by atomic scale disorders. The calculations presented here resolve the existing discrepancies between theoretically predicted and experimentally measured valley splitting, which is an important design parameter in quantum computing devices. Supercell calculations and the zone-unfolding method are used to compute the bandstructures of inhomogeneous nanowires made of AlGaAs and SiGe and their connection with the transmission coefficients computed using non-equilibrium Green's function method is established. A unified picture of alloy nanowires emerges, in which the nanodevice (transmission) and nanomaterials (bandstructure) viewpoints complement each other
A multi objective geometric programming approach for electronic product pricing problem
Mohsen Fathollah Bayati
2011-07-01
Full Text Available Nowadays electronic commerce plays an important role in many business activities, operations, and transaction processing. The recent advances on e-businesses have created tremendous opportunities to increase profitability. This paper presents a multi-objective marketing planning model which simultaneously determines efficient marketing expenditure, service cost and product's selling price in two competitive markets. To solve the proposed model, we discuss a multi-objective geometric programming (GP approach based on compromise programming method. Since our proposed model is a signomial GP and global optimality is not guaranteed for the problem, we transform the model to posynomial form. Finally, the solution procedure is illustrated via a numerical example and a sensitivity analysis is presented.
Calculation of electron spectra and some problems in the thermodynamics of graphene layers
Alisultanov, Z. Z., E-mail: zaur0102@gmail.com [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)
2016-02-15
The expressions for the energy spectra of monolayer, bilayer, and multilayer graphene, as well as epitaxial graphene, are derived using the quantum Green’s functions method. Analytic expressions are obtained for the densities of states of these systems. It is shown that a bandgap can appear the spectrum of an epitaxial graphene bilayer. A number of problems in the thermodynamics of electrons in free and epitaxial graphene layers are considered as applications. Analytic expressions are obtained for the chemical potential and heat capacity in the limiting cases of low and high temperatures. Quantum oscillations of heat capacity in graphene are analyzed taking into account the Coulomb interaction. The Berry phase of epitaxial graphene is investigated.
The EGS4 Code System: Solution of Gamma-ray and Electron Transport Problems
Nelson, W. R.; Namito, Yoshihito
1990-03-01
In this paper we present an overview of the EGS4 Code System -- a general purpose package for the Monte Carlo simulation of the transport of electrons and photons. During the last 10-15 years EGS has been widely used to design accelerators and detectors for high-energy physics. More recently the code has been found to be of tremendous use in medical radiation physics and dosimetry. The problem-solving capabilities of EGS4 will be demonstrated by means of a variety of practical examples. To facilitate this review, we will take advantage of a new add-on package, called SHOWGRAF, to display particle trajectories in complicated geometries. These are shown as 2-D laser pictures in the written paper and as photographic slides of a 3-D high-resolution color monitor during the oral presentation. 11 refs., 15 figs.
Pennycook, S.J.; Nellist, P.D. [Oak Ridge National Lab., TN (United States); Browning, N.D. [Illinois Univ., Chicago, IL (United States). Dept. of Physics
1996-08-01
The bulk properties of a large range of materials are controlled by the atomic structure and chemistry of grain boundaries, but how this occurs, at the fundamental atomic level, remains poorly understood. This is due largely to the many degrees of freedom associated with grain boundaries - five geometrical degrees of freedom along with a myriad of possibilities involving impurity segregation. Based on Z- contrast electron microscopy, a method have been developed for determining grain boundary atomic structure and chemistry directly from experimental data. The method utilizes the incoherent nature of the Z-contrast image; as there is no phase problem associated with an incoherent image, it represents a compositionally sensitive structure image which may be directly inverted to give atomic column positions. This method extracts the column locations to an accuracy of {+-}0.2 {Angstrom}, while preserving the intensity information. The procedure has been applied to SrTiO{sub 3} and YBCO.
Kovalenko, V. I.; Tuktamysheva, R. A.; Khamatgalimov, A. R.
2014-01-01
The electronic structures of the pristine fullerene molecules have been shown for the first time to be is the most important factor affecting the distribution of addends in the addition reactions of perfluoroalkyl radicals RF to C84 fullerene, and most likely positions of addends on the fullerene core are hexagons with delocalized π-bonds.
Data Structures: Sequence Problems, Range Queries, and Fault Tolerance
Jørgensen, Allan Grønlund
for a range of sequence analysis problems that have risen from applications in pattern matching, bioinformatics, and data mining. On a high level, each problem is dened by a function and some constraints and the job at hand is to locate subsequences that score high with this function and are not invalidated...... a certain function on the elements in a given query subsequence. There are many types of functions that has been considered in connection with input from dierent sources. The input could be ip-data sorted by ip-address, real estate prices sorted by zip code, advertising cost sorted by time etc. We consider...
[Problems of formal organizational structure of industrial health care complexes].
Włodarczyk, C
1978-01-01
The author formulates the thesis that the description of organizational structure of industrial health care complex calls for isolation of the following aspects:--structure of territorial links--systemof organizational units and divisions--organization of basic functions--structure of management--structure of supervision of middle and lowe-level personnel--composition of health care complex council--system of accessibility ranges. Each of the above aspects has been considered on the basis of operative rules of law, using organizational analysis methods.
Electronic structure of ruthenium-doped iron chalcogenides
Winiarski, M. J.; Samsel-Czekała, M.; Ciechan, A.
2014-12-01
The structural and electronic properties of hypothetical RuxFe1-xSe and RuxFe1-xTe systems have been investigated from first principles within the density functional theory (DFT). Reasonable values of lattice parameters and chalcogen atomic positions in the tetragonal unit cell of iron chalcogenides have been obtained with the use of norm-conserving pseudopotentials. The well known discrepancies between experimental data and DFT-calculated results for structural parameters of iron chalcogenides are related to the semicore atomic states which were frozen in the used here approach. Such an approach yields valid results of the electronic structures of the investigated compounds. The Ru-based chalcogenides exhibit the same topology of the Fermi surface (FS) as that of FeSe, differing only in subtle FS nesting features. Our calculations predict that the ground states of RuSe and RuTe are nonmagnetic, whereas those of the solid solutions RuxFe1-xSe and RuxFe1-xTe become the single- and double-stripe antiferromagnetic, respectively. However, the calculated stabilization energy values are comparable for each system. The phase transitions between these magnetic arrangements may be induced by slight changes of the chalcogen atom positions and the lattice parameters a in the unit cell of iron selenides and tellurides. Since the superconductivity in iron chalcogenides is believed to be mediated by the spin fluctuations in single-stripe magnetic phase, the RuxFe1-xSe and RuxFe1-xTe systems are good candidates for new superconducting iron-based materials.
V. See
2013-04-01
Full Text Available Under sufficiently high electric field gradients, electron behaviour within exactly perpendicular shocks is unstable to the so-called trajectory instability. We extend previous work paying special attention to short-scale, high-amplitude structures as observed within the electric field profile. Via test particle simulations, we show that such structures can cause the electron distribution to heat in a manner that violates conservation of the first adiabatic invariant. This is the case even if the overall shock width is larger than the upstream electron gyroradius. The spatial distance over which these structures occur therefore constitutes a new scale length relevant to the shock heating problem. Furthermore, we find that the spatial location of the short-scale structure is important in determining the total effect of non-adiabatic behaviour – a result that has not been previously noted.
Quantum Monte Carlo for electronic structure: Recent developments and applications
Rodriquez, Maria Milagos Soto [Lawrence Berkeley Lab. and Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
1995-04-01
Quantum Monte Carlo (QMC) methods have been found to give excellent results when applied to chemical systems. The main goal of the present work is to use QMC to perform electronic structure calculations. In QMC, a Monte Carlo simulation is used to solve the Schroedinger equation, taking advantage of its analogy to a classical diffusion process with branching. In the present work the author focuses on how to extend the usefulness of QMC to more meaningful molecular systems. This study is aimed at questions concerning polyatomic and large atomic number systems. The accuracy of the solution obtained is determined by the accuracy of the trial wave function`s nodal structure. Efforts in the group have given great emphasis to finding optimized wave functions for the QMC calculations. Little work had been done by systematically looking at a family of systems to see how the best wave functions evolve with system size. In this work the author presents a study of trial wave functions for C, CH, C_{2}H and C_{2}H_{2}. The goal is to study how to build wave functions for larger systems by accumulating knowledge from the wave functions of its fragments as well as gaining some knowledge on the usefulness of multi-reference wave functions. In a MC calculation of a heavy atom, for reasonable time steps most moves for core electrons are rejected. For this reason true equilibration is rarely achieved. A method proposed by Batrouni and Reynolds modifies the way the simulation is performed without altering the final steady-state solution. It introduces an acceleration matrix chosen so that all coordinates (i.e., of core and valence electrons) propagate at comparable speeds. A study of the results obtained using their proposed matrix suggests that it may not be the optimum choice. In this work the author has found that the desired mixing of coordinates between core and valence electrons is not achieved when using this matrix. A bibliography of 175 references is
Relativistic equation-of-motion coupled-cluster method for the electron attachment problem
Pathak, Himadri; Nayak, Malaya K; Vaval, Nayana; Pal, Sourav
2016-01-01
The article considers the successful implementation of relativistic equation-of-motion coupled clus- ter method for the electron attachment problem (EA-EOMCC) at the level of single- and double- excitation approximation. The Dirac-Coulomb Hamiltonian is used to generate the single particle orbitals and two-body matrix elements. The implemented relativistic EA-EOMCC method is em- ployed to calculate ionization potential values of alkali metal atoms (Li, Na, K, Rb, Cs, Fr) and the vertical electron affinity values of LiX (X=H, F, Cl, Br), NaY (Y=H, F, Cl) starting from their closed-shell configuration. We have taken C 2 as an example to understand what should be the na- ture of the basis and cut off in the orbital energies that can be used for the correlation calculations without loosing a considerable amount of accuracy in the computed values. Both four-component and X2C calculations are done for all the opted systems to understand the effect of relativity in our calculations as well as to justify the fact tha...
On some fundamental properties of structural topology optimization problems
Stolpe, Mathias
2010-01-01
convergence properties of penalization approaches based on material interpolation models. Furthermore, we illustrate that the optimal solutions to the considered problems in general are not symmetric even if the design domain, the external loads, and the boundary conditions are symmetric around an axis...
Structural analysis of complex ecological economic optimal control problems
Kiseleva, T.
2011-01-01
This thesis demonstrates the importance and effectiveness of methods of bifurcation theory applied to studying non-convex optimal control problems. It opens up a new methodological approach to investigation of parameterized economic models. While standard analytical methods are not efficient and
Algorithmic and structural aspects of graph partitioning and related problems
Zhang, Xiaoyan
2014-01-01
Graph partitioning problems enjoy many practical applications as well as algorithmic and theoretical challenges. This motivates the topics of this thesis that is composed of two parts. The first part of the thesis consists of Chapters 2 to 4. In this part, we present results on the complexity and in
The solution of location problems with certain existing facility structures
Juel, Henrik; Love, Robert F.
1983-01-01
It is known that in the Euclidean distance case, the optimal minisum location of a new facility in relation to four existing facilities is at the intersection of the two lines joining two pairs of the facilities. The authors extend this concept to minisum problems having any even number of existi...
The solution of location problems with certain existing facility structures
Juel, Henrik; Love, Robert F.
1983-01-01
It is known that in the Euclidean distance case, the optimal minisum location of a new facility in relation to four existing facilities is at the intersection of the two lines joining two pairs of the facilities. The authors extend this concept to minisum problems having any even number of existing...... facilities and characterized by generalized distance norms...
McEvoy, Dustin; Gandhi, Tejal K; Turchin, Alexander; Wright, Adam
2017-07-28
Quality improvement professionals often choose between patient-specific interventions, like clinical decision support (CDS), and population-based interventions, like registries or care management. In this paper, we explore the synergy of these two strategies, targeting the problem of procedure documentation for patients with a history of splenectomy. We developed a population health documentation (PHD) intervention and a CDS intervention to improve splenectomy documentation within our electronic health record. Rates of splenectomy documentation were collected before and after the implementation of both interventions to assess their impact on the rate of procedure documentation. Both the PHD and CDS interventions led to statistically significant (pleading to a larger number of incremental procedure documentations, in batches, and the CDS intervention augmenting procedure documentation on an ongoing basis. Our results suggest that population health and CDS strategies complement each other and, where possible, should be used in conjunction. PHD and CDS strategies may best be used in conjunction to create a symbiotic relationship in which current problem and procedure documentation gaps are closed using PHD strategies, while new gaps are prevented through ongoing CDS interventions. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.
Pressure effects on crystal and electronic structure of bismuth tellurohalides
Rusinov, I. P.; Menshchikova, T. V.; Sklyadneva, I. Yu; Heid, R.; Bohnen, K.-P.; Chulkov, E. V.
2016-11-01
We study the possibility of pressure-induced transitions from a normal semiconductor to a topological insulator (TI) in bismuth tellurohalides using density functional theory and tight-binding method. In BiTeI this transition is realized through the formation of an intermediate phase, a Weyl semimetal, that leads to modification of surface state dispersions. In the topologically trivial phase, the surface states exhibit a Bychkov-Rashba type dispersion. The Weyl semimetal phase exists in a narrow pressure interval of 0.2 GPa. After the Weyl semimetal-TI transition occurs, the surface electronic structure is characterized by gapless states with linear dispersion. The peculiarities of the surface states modification under pressure depend on the band-bending effect. We have also calculated the frequencies of Raman active modes for BiTeI in the proposed high-pressure crystal phases in order to compare them with available experimental data. Unlike BiTeI, in BiTeBr and BiTeCl the topological phase transition does not occur. In BiTeBr, the crystal structure changes with pressure but the phase remains a trivial one. However, the transition appears to be possible if the low-pressure crystal structure is retained. In BiTeCl under pressure, the topological phase does not appear up to 18 GPa due to a relatively large band gap width in this compound.
Structure, electronic properties, and aggregation behavior of hydroxylated carbon nanotubes
López-Oyama, A. B.; Silva-Molina, R. A.; Ruíz-García, J.; Guirado-López, R. A., E-mail: guirado@ifisica.uaslp.mx [Instituto de Física “Manuel Sandoval Vallarta,” Universidad Autónoma de San Luis Potosí, Álvaro Obregón 64, 78000 San Luis Potosí, San Luis Potosí (Mexico); Gámez-Corrales, R. [Departamento de Física, Universidad de Sonora, Apartado Postal 5-088, 83190, Hermosillo, Sonora (Mexico)
2014-11-07
We present a combined experimental and theoretical study to analyze the structure, electronic properties, and aggregation behavior of hydroxylated multiwalled carbon nanotubes (OH–MWCNT). Our MWCNTs have average diameters of ∼2 nm, lengths of approximately 100–300 nm, and a hydroxyl surface coverage θ∼0.1. When deposited on the air/water interface the OH–MWCNTs are partially soluble and the floating units interact and link with each other forming extended foam-like carbon networks. Surface pressure-area isotherms of the nanotube films are performed using the Langmuir balance method at different equilibration times. The films are transferred into a mica substrate and atomic force microscopy images show that the foam like structure is preserved and reveals fine details of their microstructure. Density functional theory calculations performed on model hydroxylated carbon nanotubes show that low energy atomic configurations are found when the OH groups form molecular islands on the nanotube's surface. This patchy behavior for the OH species is expected to produce nanotubes having reduced wettabilities, in line with experimental observations. OH doping yields nanotubes having small HOMO–LUMO energy gaps and generates a nanotube → OH direction for the charge transfer leading to the existence of more hole carriers in the structures. Our synthesized OH–MWCNTs might have promising applications.
Surface topology and electronic structure of layered strontium ruthenates
Bienert, Robert; Klinke, Melanie; Waelsch, Michael; Mietke, Sebastian; Matzdorf, Rene [Experimentalphysik II, Universitaet Kassel (Germany); Peng, Jin; Mao, Zhiqiang [Department of Physics, Tulane University, New Orleans (United States)
2012-07-01
In complex materials the interplay of properties like crystal structure, electronic structure and magnetism results in very interesting physical phenomena. The Ruddlesden-Popper series of layered Strontium Ruthenates Sr{sub n+1}Ru{sub n}O{sub 3n+1} describes one class of these materials. The double and triple layer systems behave like a Fermi liquid up to the transition temperature of 15 K and 24 K, respectively. In both compounds the local density of states (LDOS) shows a peak within the dip-like feature around the Fermi energy E{sub F}. Using low-temperature (LT) STM and STS we studied the temperature dependence of the LDOS in the range from 4.7 to 35 K. By increasing the temperature the peak within the dip in the LDOS at E{sub F} is only affected by thermal broadening. The surface unit cell of the Strontium Ruthenates exhibits a c(2 x 2) super structure, which is stable from 4.7 K up to room temperature as shown by our atomically resolved LT STM images and room temperature LEED experiments.
Bismuth zinc vanadate, BiZn2VO6 : new crystal structure type and electronic structure.
Nunes, Sayonara Eliziario; Wang, Chun-Hai; So, Karwei; Evans, John S. O.; Evans, Ivana Radosavljevic
2015-01-01
We report a combined experimental and computational study of the crystal structure and electronic properties of bismuth zinc vanadate, BiZn2VO6, known for its visible light photocatalytic activity. The crystal structure has been solved from laboratory powder X-ray diffraction data using the repeated minimisations from random starting values method. BiZn2VO6 adopts a new structure type, based on the following building blocks: corner- and edge-sharing ZnO4 tetrahedra, ZnO6 octahedra and VO4 tet...
Structural Features That Stabilize ZnO Clusters: An Electronic Structure Approach
Csaba E. Szakacs
2013-05-01
Full Text Available We show that a simple approach to building small computationally inexpensive clusters offers insights on specific structural motifs that stabilize the electronic structure of ZnO. All-electron calculations on ZniOi needle (i = 6, 9, 12, 15, and 18 and plate (i = 9 and 18 clusters within the density functional theory (DFT formalism show a higher stability for ZnO needles that increases with length. Puckering of the rings to achieve a more wurtzite-like structure destabilizes the needles, although this destabilization is reduced by going to infinite needles (calculated using periodic boundary conditions. Calculations of density of states (DOS curves and band gaps for finite clusters and infinite needles highlight opportunities for band-gap tuning through kinetic control of nanocrystal growth.
Reference Map Technique for Incompressible Fluid-Structure Interaction Problems
Rycroft, Chris; Wu, Chen-Hung; Yu, Yue; Kamrin, Ken
2016-11-01
We present a fully Eulerian approach to simulate soft structures immersed in an incompressible fluid. The flow is simulated on a fixed grid using a second order projection method to solve the incompressible Navier-Stokes equations, and the fluid-structure interfaces are modeled using the level set method. By introducing a reference map variable to model finite-deformation constitutive relations in the structure on the same grid as the fluid, the interfacial coupling is highly simplified. This fully Eulerian approach provides a computationally efficient alternative to moving mesh approaches. Example simulations featuring many-body contacts and flexible swimmers will be presented.
Electronic structure of nanocrystalline and polycrystalline hydrogen storage materials
Smardz, L. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17 Street, 60-179 Poznan (Poland); Jurczyk, M.; Smardz, K.; Nowak, M.; Makowiecka, M.; Okonska, I. [Institute of Materials Science and Engineering, Poznan University of Technology, M. Sklodowska-Curie 5 Sq., 60-965 Poznan (Poland)
2008-02-15
To optimise the choice of the compounds for a selected application, a better understanding of the role of each alloy constituent on the electronic properties of the material is crucial. In this work, we study experimentally the electronic properties of nanocrystalline and polycrystalline (Mg{sub 1-x}M{sub x}){sub 2}Ni, (Mg{sub 1-x}M{sub x}){sub 2}Cu, La(Ni{sub 1-x}M{sub x}){sub 5}, and Ti(Ni{sub 1-x}M'{sub x}) (M = Mn, Al; M' = Fe, Mg, Zr) alloys. The nanocrystalline and polycrystalline samples were prepared by mechanical alloying (MA) followed by annealing and arc melting method, respectively. All X-ray photoelectron spectroscopy (XPS) spectra were measured immediately after cleaning of the sample surface in a vacuum of 8 x 10{sup -11} mbar. Furthermore, we have measured XPS spectra of in situ prepared nanocrystalline and polycrystalline LaNi{sub 5}, TiNi, and Mg{sub 2}Ni thin films and compared with those obtained for ex situ prepared bulk materials. The substitution of Mg in Mg{sub 2}Ni and Mg{sub 2}Cu, Ni in LaNi{sub 5} and TiNi by transition metals leads to significant modifications of the shape and width of the valence band of the nanocrystalline as well as polycrystalline samples. Especially, the valence bands of the MA nanocrystalline alloys are considerably broader compared to those measured for the polycrystalline samples. Results also showed that the strong modifications of the electronic structure of the nanocrystalline alloys could significantly influence on their hydrogenation properties. (author)
Kinetic structure of the electron diffusion region in antiparallel magnetic reconnection.
Ng, J; Egedal, J; Le, A; Daughton, W; Chen, L-J
2011-02-11
Strong electron pressure anisotropy has been observed upstream of electron diffusion regions during reconnection in Earth's magnetotail and kinetic simulations. For collisionless antiparallel reconnection, we find that the anisotropy drives the electron current in the electron diffusion region, and that this current is insensitive to the reconnection electric field. Reconstruction of the electron distribution function within this region at enhanced resolutions reveals its highly structured nature and the mechanism by which the pressure anisotropy sets the structure of the region.
Electronic structure characterization and bandgap engineeringofsolar hydrogen materials
Guo, Jinghua
2007-11-01
Bandgap, band edge positions as well as the overall band structure of semiconductors are of crucial importance in photoelectrochemical and photocatalytic applications. The energy position of the band edge level can be controlled by the electronegativity of the dopants, the pH of the solution (flatband potential variation of 60 mV per pH unit), as well as by quantum confinement effects. Accordingly, band edges and bandgap can be tailored to achieve specific electronic, optical or photocatalytic properties. Synchrotron radiation with photon energy at or below 1 keV is giving new insight into such areas as condensed matter physics and extreme ultraviolet optics technology. In the soft x-ray region, the question tends to be, what are the electrons doing as they migrated between the atoms. In this paper, I will present a number of soft x-ray spectroscopic study of nanostructured 3d metal compounds Fe{sub 2}O{sub 3} and ZnO.
Electronic Structure and Maximum Energy Product of MnBi
Jihoon Park
2014-08-01
Full Text Available We have performed first-principles calculations to obtain magnetic moment, magnetocrystalline anisotropy energy (MAE, i.e., the magnetic crystalline anisotropy constant (K, and the Curie temperature (Tc of low temperature phase (LTP MnBi and also estimated the maximum energy product (BHmax at elevated temperatures. The full-potential linearized augmented plane wave (FPLAPW method, based on density functional theory (DFT within the local spin density approximation (LSDA, was used to calculate the electronic structure of LPM MnBi. The Tc was calculated by the mean field theory. The calculated magnetic moment, MAE, and Tc are 3.63 μB/f.u. (formula unit (79 emu/g or 714 emu/cm3, −0.163 meV/u.c. (or K = −0.275 × 106 J/m3 and 711 K, respectively. The (BHmax at the elevated temperatures was estimated by combining experimental coercivity (Hci and the temperature dependence of magnetization (Ms(T. The (BHmax is 17.7 MGOe at 300 K, which is in good agreement with the experimental result for directionally-solidified LTP MnBi (17 MGOe. In addition, a study of electron density maps and the lattice constant c/a ratio dependence of the magnetic moment suggested that doping of a third element into interstitial sites of LTP MnBi can increase the Ms.
Electronic Structure of Helium Atom in a Quantum Dot
Saha, Jayanta K.; Bhattacharyya, S.; Mukherjee, T. K.
2016-03-01
Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) (n = 1-6) states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns (n = 2-5) and 2pnp (n = 2-5) configurations of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential due to the quantum dot. It has been explicitly demonstrated that the electronic structural properties become sensitive functions of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within a quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the width of the quantum cavity is also discussed here. TKM Gratefully Acknowledges Financial Support under Grant No. 37(3)/14/27/2014-BRNS from the Department of Atomic Energy, BRNS, Government of India. SB Acknowledges Financial Support under Grant No. PSW-160/14-15(ERO) from University Grants Commission, Government of India