Relativistic calculations of atomic structure
Fricke, Burkhard
1984-01-01
A review of relativistic atomic structure calculations is given with a emphasis on the Multiconfigurational-Dirac-Fock method. Its problems and deficiencies are discussed together with the contributions which go beyond the Dirac-Fock procedure.
Atomic Structure Calculations for Neutral Oxygen
Alonizan, Norah; Qindeel, Rabia; Ben Nessib, Nabil
2016-01-01
Energy levels and oscillator strengths for neutral oxygen have been calculated using the Cowan (CW), SUPERSTRUCTURE (SS), and AUTOSTRUCTURE (AS) atomic structure codes. The results obtained with these atomic codes have been compared with MCHF calculations and experimental values from the National Institute of Standards and Technology (NIST) database.
METHODS OF CALCULATING THE ELECTRONIC AND ATOMIC STRUCTURES OF INTERFACES
Sutton, A
1985-01-01
Methods of calculating the electronic and atomic structures of interfaces are described. An introduction to pseudopotentials and LCAO methods is given. Methods of calculating the electronic structure of an interface with a given atomic structure are considered. The feasibility of total energy calculations, in which the atomic and electronic structures are calculated simultaneously, is discussed.
Atomic structure calculations of Mo XV-XL
International Nuclear Information System (INIS)
Energy levels and oscillator strengths were calculated for Mo XV - Mo XL. The computer program for atomic structure calculation, developed by Dr. Robert D. Cowan, Los Alamos National Laboratory, was used in the present work. The scaled energy parameters were empirically determined from the observed spectral data. We present wavelengths and transition probabilities of Mo XV-XL. Energy levels and spectral patterns are presented in figures that are useful for the identification of spectral lines. (author)
Ab initio calculations and modelling of atomic cluster structure
DEFF Research Database (Denmark)
Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.;
2004-01-01
The optimized structure and electronic properties of small sodium and magnesium clusters have been investigated using it ab initio theoretical methods based on density-functional theory and post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system. A new theoretical...... framework for modelling the fusion process of noble gas clusters is presented. We report the striking correspondence of the peaks in the experimentally measured abundance mass spectra with the peaks in the size-dependence of the second derivative of the binding energy per atom calculated for the chain...... of the noble gas clusters up to 150 atoms....
Atomic structure calculations using the relativistic random phase approximation
International Nuclear Information System (INIS)
A brief review is given for the relativistic random phase approximation (RRPA) applied to atomic transition problems. Selected examples of RRPA calculations on discrete excitations and photoionization are given to illustrate the need of relativistic many-body theories in dealing with atomic processes where both relativity and correlation are important
Atomic structure calculations for F-like tungsten
Sunny, Aggarwal
2014-09-01
Energy levels, wavefunction compositions and lifetimes have been computed for all levels of 1s22s22p5, 1s22s2p6, 1s22s22p43s, 1s22s22p43p, and 1s22s22p43d configurations in highly charged F-like tungsten ion. The multiconfigurational Dirac—Fock method (MCDF) is adopted to generate the wavefunctions. We have also presented the transition wavelengths, oscillator strengths, transition probabilities, and line strengths for the electric dipole (E1) and magnetic quadrupole (M2) transition from the 1s22s22p5 ground configuration. We have performed parallel calculations with the flexible atomic code (FAC) for comparing the atomic data. The reliability of present data is assessed by comparison with other theoretical and experimental data available in the literature. Good agreement is found between our results and those obtained using different approaches confirm the quality of our results. Additionally, we have predicted some new atomic data for F-like W that were not available so far and may be important for plasma diagnostic analysis in fusion plasma.
Hyun-Kyung Chung; Per Jönsson; Alexander Kramida
2013-01-01
Atomic structure and transition probabilities are fundamental physical data required in many fields of science and technology. Atomic physics codes are freely available to other community users to generate atomic data for their interest, but the quality of these data is rarely verified. This special issue addresses estimation of uncertainties in atomic structure and transition probability calculations, and discusses methods and strategies to assess and ensure the quality of theoretical atomic...
Advances in Atomic Structure Calculations%原子结构计算的进展
Institute of Scientific and Technical Information of China (English)
Charlotte Froese Fischer
2007-01-01
Correlation and relativistic effects are both needed for accurate atomic structure calculations of energy levels and their atomic properties. For transition probabilities of radiative transitions between low-lying levels of an atom or ion, accurate wave functions for the outer region of are required. For lighter atoms, relativistic effects can be included through the Breit-Pauli approximation. This paper outlines the advances in the treatment of correlation and describes the current state of Breit-Pauli calculations for complex systems.
Dzuba, V. A.; Flambaum, V. V.
A brief review of the search for variation of the fine structure constant in quasar absorption spectra is presented. Special consideration is given to the role of atomic calculations in the analysis of the observed data. A range of methods which allow to perform calculations for atoms or ions with different electron structure and which cover practically all periodic table of elements is discussed. Critical compilation of the results of the calculations as well as a review of the most recent results of the analysis are presented.
Dzuba, V A
2008-01-01
A brief review of the search for variation of the fine structure constant in quasar absorption spectra is presented. Special consideration is given to the role of atomic calculations in the analysis of the observed data. A range of methods which allow to perform calculations for atoms or ions with different electron structure and which cover practically all periodic table of elements is discussed. Critical compilation of the results of the calculations as well as a review of the most recent results of the analysis are presented.
Theoretical calculations on the atomic and electronic structure of β-SiC(110) surface
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
We present a theoretical calculation of the atomic and electronic structure of β-SiC and its non-polar (110) surface using the full potential linear augmented plane wave (FPLAPW) approach. The calculated lattice constant and bulk modulus of β-SiC crystal are in excellent agreement with experimental data. The atomic and electronic structure of β-SiC(110) surface has been calculated by employing the slab and supercell model. It is found that the surface is characterized by a top-layer bond-length-contracting rotation relaxation in which the Si-surface atom moves closer towards the substrate while the C-surface atom moves outward. This relaxation is analogous to that of Ⅲ-Ⅴ semi-conductor surface. The driving mechanism for this atomic rearrangement is that the Si atom tends to a planar sp2-like bonding situation with its three N neighbors and the N atom tends to a p3-like bonding with its three Si neighbors. Furthermore, surface relaxation induces the change from metallic to semiconducting characterization.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
Kahn, L. R.
1981-01-01
A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.
First-principles calculations atomic structure and elastic properties of Ti-Nb alloys
Timoshevskii, A N; Ivasishin, O M
2011-01-01
Elastic properties of Ti based \\beta-alloy were studied by the method of the model structure first principle calculations. Concentrational dependence of Young modulus for the binary \\beta-alloy Ti-Nb was discovered. It is shown that peculiarities visible at 15-18% concentrations can be related to the different Nb atoms distribution. Detailed comparison of the calculation results with the measurement results was done. Young modulus for the set of the ordered structures with different Nb atoms location, which simulate triple \\beta-alloys Ti-29.7%Zr-18.5%Nb and Ti-51.8%Zr-18.5%Nb have been calculated. The results of these calculations allowed us to suggest the concentration region for single-phase ternary \\beta-phase alloys possessing low values of Young's modulus.
Ansari, Reza; Ajori, Shahram; Malakpour, Sina
2016-04-01
The considerable demand for novel materials with specific properties has motivated the researchers to synthesize supramolecular nanostructures through different methods. Porous graphene is the first two-dimensional hydrocarbon synthesized quite recently. This investigation is aimed at studying the mechanical properties of atom-decorated (functionalized) porous graphene by employing density functional theory (DFT) calculation within both local density approximations (LDA) and generalized gradient approximations (GGA). The atoms are selected from period 3 of periodic table as well as Li and O atom from period 2. The results reveal that metallic atoms and noble gases are adsorbed physically on porous graphene and nonmetallic ones form chemical bonds with carbon atom in porous graphene structure. Also, it is shown that, in general, atom decoration reduces the values of mechanical properties such as Young's, bulk and shear moduli as well as Poisson's ratio, and this reduction is more considerable in the case of nonmetallic atoms (chemical adsorption), especially oxygen atoms, as compared to metallic atoms and noble gases (physical adsorption).
Per Jönsson; Hyun-Kyung Chung
2013-01-01
There exist several codes in the atomic physics community to generate atomic structure and transition probabilities freely and readily distributed to researchers outside atomic physics community, in plasma, astrophysical or nuclear physics communities. Users take these atomic physics codes to generate the necessary atomic data or modify the codes for their own applications. However, there has been very little effort to validate and verify the data sets generated by non-expert users. [...
Atomic structure calculations and identification of EUV and SXR spectral lines in Sr XXX
Goyal, Arun; Khatri, Indu; Aggarwal, Sunny; Singh, A. K.; Mohan, Man
2015-08-01
We report an extensive theoretical study of atomic data for Sr XXX in a wide range with L-shell electron excitations to the M-shell. We have calculated energy levels, wave-function compositions and lifetimes for lowest 113 fine structure levels and wavelengths of an extreme Ultraviolet (EUV) and soft X-ray (SXR) transitions. We have employed multi-configuration Dirac Fock method (MCDF) approach within the framework of Dirac-Coulomb Hamiltonian including quantum electrodynamics (QED) and Breit corrections. We have also presented the radiative data for electric and magnetic dipole (E1, M1) and quadrupole (E2, M2) transitions from the ground state. We have made comparisons with available energy levels compiled by NIST and achieve good agreement. But due to inadequate data in the literature, analogous relativistic distorted wave calculations have also been performed using flexible atomic code (FAC) to assess the reliability and accuracy of our results. Additionally, we have provided new atomic data for Sr XXX which is not published elsewhere in the literature and we believe that our results may be beneficial in fusion plasma research and astrophysical investigations and applications.
Structures of 13-atom clusters of fcc transition metals by ab initio and semiempirical calculations
Longo, R. C.; Gallego, L. J.
2006-11-01
We report the results of ab initio calculations of the structures and magnetic moments of Ni13 , Pd13 , Pt13 , Cu13 , Ag13 , and Au13 that were performed using a density-functional method that employs linear combinations of pseudoatomic orbitals as basis sets (SIESTA). Our structural results for Pt13 , Cu13 , Ag13 , and Au13 show that a buckled biplanar structure (BBP) is more stable than the icosahedral configuration, in keeping with results obtained recently by Chang and Chou [Phys. Rev. Lett. 93, 133401 (2004)] using the Vienna ab initio simulation package with a plane-wave basis. However, for Ni13 and Pd13 we found that the icosahedral structure is more stable than BBP. For all these clusters, two semiempirical methods based on spherically symmetric potentials both found the icosahedral structure to be the more stable, while the modified embedded atom model method, which uses a direction-dependent potential, found BBP to be the more stable structure. When low-energy structures found in recent ab initio studies of Pt13 , Cu13 , and Au13 other than Chang and Chou were optimized with SIESTA, those reported for Pt13 and Cu13 were found to be less stable than BBP, but the two-dimensional planar configuration reported for Au13 proved to be more stable than BBP.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
Kahn, L. R.
1982-01-01
Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.
GRASP92: a package for large-scale relativistic atomic structure calculations
Parpia, F. A.; Froese Fischer, C.; Grant, I. P.
2006-12-01
of CSFs sharing the same quantum numbers is determined using the configuration-interaction (CI) procedure that results upon varying the expansion coefficients to determine the extremum of a variational functional. Radial functions may be determined by numerically solving the multiconfiguration Dirac-Fock (MCDF) equations that result upon varying the orbital radial functions or some subset thereof so as to obtain an extremum of the variational functional. Radial wavefunctions may also be determined using a screened hydrogenic or Thomas-Fermi model, although these schemes generally provide initial estimates for MCDF self-consistent-field (SCF) calculations. Transition properties for pairs of ASFs are computed from matrix elements of multipole operators of the electromagnetic field. All matrix elements of CSFs are evaluated using the Racah algebra. Reasons for the new version: During recent studies using the general relativistic atomic structure package (GRASP92), several errors were found, some of which might have been present already in the earlier GRASP92 version (program ABJN_v1_0, Comput. Phys. Comm. 55 (1989) 425). These errors were reported and discussed by Froese Fischer, Gaigalas, and Ralchenko in a separate publication [C. Froese Fischer, G. Gaigalas, Y. Ralchenko, Comput. Phys. Comm. 175 (2006) 738-744. [7
Elmar Träbert
2014-01-01
The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem need...
Directory of Open Access Journals (Sweden)
Elmar Träbert
2014-03-01
Full Text Available The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.
International Nuclear Information System (INIS)
This report presents details of a new method to enable the computation of collision strengths for complex ions which is adapted from long established optimisation techniques previously applied to the calculation of atomic structures and oscillator strengths. The procedure involves the adjustment of Slater parameters so that they determine improved energy levels and eigenvectors. They provide a basis for collision strength calculations in ions where ab initio computations break down or result in reducible errors. This application is demonstrated through modifications of the DISTORTED WAVE collision code and SUPERSTRUCTURE atomic-structure code which interface via a transformation code JAJOM which processes their output. (author)
Calculations of effective atomic number
Energy Technology Data Exchange (ETDEWEB)
Kaliman, Z. [Department of Physics, Faculty of Arts and Sciences, Omladinska 14, Rijeka (Croatia); Orlic, N. [Department of Physics, Faculty of Arts and Sciences, Omladinska 14, Rijeka (Croatia)], E-mail: norlic@ffri.hr; Jelovica, I. [Department of Physics, Faculty of Arts and Sciences, Omladinska 14, Rijeka (Croatia)
2007-09-21
We present and discuss effective atomic number (Z{sub eff}) obtained by different methods of calculations. There is no unique relation between the computed values. This observation led us to the conclusion that any Z{sub eff} is valid only for given process. We illustrate calculations for different subshells of atom Z=72 and for M3 subshell of several other atoms.
Corsetti, Fabiano
2014-01-01
The implementation of the orbital minimization method (OMM) for solving the self-consistent Kohn-Sham (KS) problem for electronic structure calculations in a basis of non-orthogonal numerical atomic orbitals of finite-range is reported. We explore the possibilities for using the OMM as an exact cubic-scaling solver for the KS problem, and compare its performance with that of explicit diagonalization in realistic systems. We analyze the efficiency of the method depending on the choice of line search algorithm and on two free parameters, the scale of the kinetic energy preconditioning and the eigenspectrum shift. The results of several timing tests are then discussed, showing that the OMM can achieve a noticeable speedup with respect to diagonalization even for minimal basis sets for which the number of occupied eigenstates represents a significant fraction of the total basis size (>15%). We investigate the hard and soft parallel scaling of the method on multiple cores, finding a performance equal to or better ...
International Nuclear Information System (INIS)
Uranium dioxide UO2 is the standard nuclear fuel used in pressurized water reactors. During in-reactor operation, the fission of uranium atoms yields a wide variety of fission products (FP) which create numerous point defects while slowing down in the material. Point defects and FP govern in turn the evolution of the fuel physical properties under irradiation. In this study, we use electronic structure calculations in order to better understand the fuel behavior under irradiation. In particular, we investigate point defect behavior, as well as the stability of three volatile FP: iodine, krypton and xenon. In order to take into account the strong correlations of uranium 5f electrons in UO2, we use the DFT+U approximation, based on the density functional theory. This approximation, however, creates numerous metastable states which trap the system and induce discrepancies in the results reported in the literature. To solve this issue and to ensure the ground state is systematically approached as much as possible, we use a method based on electronic occupancy control of the correlated orbitals. We show that the DFT+U approximation, when used with electronic occupancy control, can describe accurately point defect and fission product behavior in UO2 and provide quantitative information regarding point defect transport properties in the oxide fuel. (author)
Comparative semi-empirical and ab initio atomic structure calculations in Yb-like tungsten W4+
International Nuclear Information System (INIS)
In this paper, we report on extensive calculations of radiative data in Yb-like tungsten ion using several independent atomic structure methods, i.e. the relativistic Hartree–Fock approach, the flexible atomic code and the multiconfiguration Dirac–Fock method. This multi-platform approach allowed us to check the consistency of our results. Advantages and shortcomings of semi-empirical and ab initio methods for atomic structure calculations in such a complex heavy ion are also discussed in detail. A new set of transition probabilities and oscillator strengths is reported for electric dipole lines together with magnetic dipole and electric quadrupole lines in this ion of interest for fusion plasma diagnostics. (paper)
Atomic and Electronic Structures of C_60+BN Nanopeapods from ab initio Pseudopotential Calculations
Trave, Andrea; Ribeiro, Filipe; Louie, Steven G.; Cohen, Marvin L.
2004-03-01
Nanopeapods are structures of nanometric size consisting of an external carbon nanotube encapsulating a chain or complex array of fullerenes. Recent calculations and experiments have proven that nanopeapods can be obtained assembling fullerenes within boron nitride nanotubes, creating novel materials of possible interest for electronic transport applications. To improve the understanding of the properties of these composite systems, as compared to empty nanotubes and carbon nanopeapods, ab-initio total energy calculations have been performed within the pseudopotential Density Functional Theory in local density approximation. Results of these calculations on the energetics and geometrical deformations involved in the encapsulation will be presented, followed by a discussion of the consequences on the electronic structures of these systems, with particular focus on aspects relevant to electronic transport phenomena. This work is supported by NFS (Grant DMR00-87088) and DOE (Contract DE-AC03-76SF00098), using computational resources at NERSC and NPACI.
Landau, Arie; Kaprálová-Žďánská, Petra Ruth; Moiseyev, Nimrod
2015-01-01
Complex eigenvalues, resonances, play an important role in large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and pre-dissociative metastable resonances are generated. However, the computation of complex resonance eigenvalues is difficult, since it requires severe modifications of standard electronic structure codes and methods. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Pad\\'{e}). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit,...
International Nuclear Information System (INIS)
The multiconfiguration Dirac-Hartree-Fock model has been employed to calculate the expectation values for the hyperfine splittings of the 5d96s22D3/2 and 5d96s22D5/2 levels of atomic gold. One-, two-, and three-body electron correlation effects involving all 79 electrons have been included in a systematic manner. The approximation employed in this study is equivalent to a complete-active-space approach. Calculated electric field gradients, together with experimental values of the electric quadrupole hyperfine-structure constants, allow us to extract a nuclear electric quadrupole moment Q(197Au)=521.5(5.0) mb.
Landau, Arie; Haritan, Idan; Kaprálová-Žd'ánská, Petra Ruth; Moiseyev, Nimrod
2016-05-19
Complex eigenvalues, resonances, play an important role in a large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and predissociative metastable resonances are generated. However, the computation of complex resonance requires modifications of standard electronic structure codes and methods, which are not always straightforward, in addition, application of complex codes requires more computational efforts. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Padé). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit, these passages to the complex plane are closed. As illustrative numerical examples we calculated the autoionization Feshbach resonances of helium, hydrogen anion, and hydrogen molecule. We show that our results are in an excellent agreement with the results obtained by other theoretical methods and with available experimental results. PMID:26677725
Gidofalvi, Gergely
2014-01-01
Molecule-optimized basis sets, based on approximate natural orbitals, are developed for accelerating the convergence of quantum calculations with strongly correlated (multi-referenced) electrons. We use a low-cost approximate solution of the anti-Hermitian contracted Schr{\\"o}dinger equation (ACSE) for the one- and two-electron reduced density matrices (RDMs) to generate an approximate set of natural orbitals for strongly correlated quantum systems. The natural-orbital basis set is truncated to generate a molecule-optimized basis set whose rank matches that of a standard correlation-consistent basis set optimized for the atoms. We show that basis-set truncation by approximate natural orbitals can be viewed as a one-electron unitary transformation of the Hamiltonian operator and suggest an extension of approximate natural-orbital truncations through two-electron unitary transformations of the Hamiltonian operator, such as those employed in the solution of the ACSE. The molecule-optimized basis set from the ACS...
dftatom: A robust and general Schrödinger and Dirac solver for atomic structure calculations
Čertík, Ondřej; Pask, John E.; Vackář, Jiří
2013-07-01
Classification: 2.1. External routines: Numpy (http://www.numpy.org/) and Cython (http://cython.org/) Nature of problem: Solution of the Schrödinger, Dirac, and Kohn-Sham equations of Density Functional Theory for isolated atoms. Solution method: Radial integrations are carried out using a combination of asymptotic forms, Runge-Kutta, and implicit Adams methods. Eigenfunctions are determined by a combination of bisection and perturbation methods. An outward Poisson integration is employed to increase accuracy in the core region. Self-consistent field equations are solved by adaptive linear mixing. Restrictions: Spherical symmetry Unusual features: Radial integrators work for general potentials and meshes. No restriction to Coulombic or self-consistent potentials; no restriction to uniform or exponential meshes. Outward Poisson integration. Fallback to bisection for robustness. Running time: For uranium, non-relativistic density functional calculation execution time is around 0.6 s for 10-6 a.u. accuracy in total energy on an Intel Core i7 1.46 GHz processor.
Bierón, Jacek; Indelicato, Paul; Jönsson, Per; Pyykkö, Pekka
2009-01-01
The multiconfiguration Dirac-Hartree-Fock (MCDHF) model has been employed to calculate the expectation values for the hyperfine splittings of the 5d96s2 2D3/2 and 5d96s2 2D5/2 levels of atomic gold. One-, two-, and three-body electron correlation effects involving all 79 electrons have been included in a systematic manner. The approximation employed in this study is equivalent to a Complete Active Space (CAS) approach. Calculated electric field gradients, together with experimental values of the electric quadrupole hyperfine structure constants, allow us to extract a nuclear electric quadrupole moment Q(197Au)=521.5(5.0) mb.
Dirac-Fock atomic electronic structure calculations using different nuclear charge distributions
Visscher, L; Dyall, KG
1997-01-01
Numerical Hartree-Fock calculations based on the Dirac-Coulomb Hamiltonian for the first 109 elements of the periodic table are presented. The results give the total electronic energy, as a function of the nuclear model that is used, for four different models of the nuclear charge distribution. The
Atomic Structure Calculations and Study of Plasma Parameters of Al-Like Ions
Directory of Open Access Journals (Sweden)
Arun Goyal
2016-07-01
Full Text Available In the present paper, the spectroscopic properties and plasma characteristics of Al-like ions are investigated in an extensive and detailed manner by adopting the GRASP2K package based on fully relativistic Multi-Configuration Dirac–Hartree–Fock (MCDHF wave-functions in the active space approximation. We have presented energy levels for Al-like ions for Valence-Valence (VV and Core-Valence (CV correlations under the scheme of active space. We have also provided radiative data for E1 transitions for Al-like ions and studied the variation of the transition wavelength and transition probability for electric dipole (E1 Extreme Ultraviolet (EUV transitions with nuclear charge. Our calculated energy levels and transition wavelengths match well with available theoretical and experimental results. The discrepancies of the GRASP2K code results with CIV3 and RMPBT (Relativistic Many Body Perturbation Theory results are also discussed. The variations of the line intensity ratio, electron density, plasma frequency and plasma skin depth with plasma temperature and nuclear charge are discussed graphically in detail for optically thin plasma in Local Thermodynamic Equilibrium (LTE. We believe that our obtained results may be beneficial for comparisons and in fusion and astrophysical plasma research.
Atomic physics: computer calculations and theoretical analysis
Drukarev, E. G.
2004-01-01
It is demonstrated, how the theoretical analysis preceding the numerical calculations helps to calculate the energy of the ground state of helium atom, and enables to avoid qualitative errors in the calculations of the characteristics of the double photoionization.
International Nuclear Information System (INIS)
This book is written to teach atom structure in very easy way. It is divided into nine chapters, which indicates what is the components of matter? when we divide matter continuously, it becomes atom, what did atom look like? particles comprised of matter is not only atom, discover of particles comprised of atom, symbol of element, various radiation, form alchemy to nuclear transmutation, shape of atom is evolving. It also has various pictures in each chapters to explain easily.
Energy Technology Data Exchange (ETDEWEB)
Lim, Suh Yeon
2006-08-15
This book is written to teach atom structure in very easy way. It is divided into nine chapters, which indicates what is the components of matter? when we divide matter continuously, it becomes atom, what did atom look like? particles comprised of matter is not only atom, discover of particles comprised of atom, symbol of element, various radiation, form alchemy to nuclear transmutation, shape of atom is evolving. It also has various pictures in each chapters to explain easily.
Bierón, Jacek; Froese Fischer, Charlotte; Indelicato, Paul; Jönsson, Per; Pyykkö, Pekka
2009-01-01
The multiconfiguration Dirac-Hartree-Fock (MCDHF) model has been employed to calculate the expectation values for the hyperfine splittings of the 5d96s2 2D3/2 and 5d96s2 2D5/2 levels of atomic gold. One-, two-, and three-body electron correlation effects involving all 79 electrons have been included in a systematic manner. The approximation employed in this study is equivalent to a Complete Active Space (CAS) approach. Calculated electric field gradients, together with experimental values of ...
Calculated Atomic Volumes of the Actinide Metals
DEFF Research Database (Denmark)
Skriver, H.; Andersen, O. K.; Johansson, B.
1979-01-01
The equilibrium atomic volume is calculated for the actinide metals. It is possible to account for the localization of the 5f electrons taking place in americium.......The equilibrium atomic volume is calculated for the actinide metals. It is possible to account for the localization of the 5f electrons taking place in americium....
Emissivity: A Program for Atomic Emissivity Calculations
Sochi, Taha
2009-01-01
In this article we report the release of a new program for calculating the emissivity of atomic transitions. The program, which can be obtained with its documentation from our website www.scienceware.net, passed various rigorous tests and was used by the author to generate theoretical data and analyze observational data. It is particularly useful for investigating atomic transition lines in astronomical context as the program is capable of generating a huge amount of theoretical data and comp...
Systematic Calculations of Total Atomic Binding Energies
International Nuclear Information System (INIS)
We have calculated total atomic binding energies of 3- to 91-electron ions of all atoms with Z=3 to 118, in the Dirac-Fock model, for applications to atomic mass determination from highly-charged ions. In this process we have determined the ground-state configuration of many ions for which it was not known. We also provide total electronic correlation including Breit correlation for iso-electronic series of beryllium, neon, magnesium and argon, using the multiconfiguration Dirac-Fock approach.
Turkington, M. D.; Ballance, C. P.; Hibbert, A.; Ramsbottom, C. A.
2016-08-01
In this work we explore the validity of employing a modified version of the nonrelativistic structure code civ3 for heavy, highly charged systems, using Na-like tungsten as a simple benchmark. Consequently, we present radiative and subsequent collisional atomic data compared with corresponding results from a fully relativistic structure and collisional model. Our motivation for this line of study is to benchmark civ3 against the relativistic grasp0 structure code. This is an important study as civ3 wave functions in nonrelativistic R -matrix calculations are computationally less expensive than their Dirac counterparts. There are very few existing data for the W LXIV ion in the literature with which we can compare except for an incomplete set of energy levels available from the NIST database. The overall accuracy of the present results is thus determined by the comparison between the civ3 and grasp0 structure codes alongside collisional atomic data computed by the R -matrix Breit-Pauli and Dirac codes. It is found that the electron-impact collision strengths and effective collision strengths computed by these differing methods are in good general agreement for the majority of the transitions considered, across a broad range of electron temperatures.
Languages for structural calculations
International Nuclear Information System (INIS)
The differences between human and computing languages are recalled. It is argued that they are to some extent structured in antagonistic ways. Languages in structural calculation, in the past, present, and future, are considered. The contribution of artificial intelligence is stressed
Calculations of electron screening in muonic atoms
International Nuclear Information System (INIS)
The electron screening in mounic atoms (O, Al, Fe, In, Ho, Au, Th) has been calculated for p3/2, d5/2 and f7/2 levels with nμ=3/2, d5/2 and f7/2 muons up to nμ=30. Screening corrections are also given for electron configurations with holes in the K and L3 shell. (orig.)
International Nuclear Information System (INIS)
The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials
Energy Technology Data Exchange (ETDEWEB)
Lee, Y.S.
1977-11-01
The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials.
Atomic structure and electron correlations
International Nuclear Information System (INIS)
Synchrotron experiments combined with theoretical calculations have already given much information on atomic structure and the effects of electron correlations, and this combination of theory and experiment is expected to yield much new information in coming years. In the calculations of photoabsorption cross sections, it is almost always necessary to include electron correlations in both initial and final states to obtain good agreement with experiment. The main theoretical approaches which include effects of electron correlations have been R-matrix theory, random phase approximation with exchange (RPAE), relativistic random phase approximation with exchange, and many-body perturbation theory
Million atom DFT calculations using coarse graining and petascale computing
Nicholson, Don; Odbadrakh, Kh.; Samolyuk, G. D.; Stoller, R. E.; Zhang, X. G.; Stocks, G. M.
2014-03-01
Researchers performing classical Molecular Dynamics (MD) on defect structures often find it necessary to use millions of atoms in their models. It would be useful to perform density functional calculations on these large configurations in order to observe electron-based properties such as local charge and spin and the Helmann-Feynman forces on the atoms. The great number of atoms usually requires that a subset be ``carved'' from the configuration and terminated in a less that satisfactory manner, e.g. free space or inappropriate periodic boundary conditions. Coarse graining based on the Locally Self-consistent Multiple Scattering method (LSMS) and petascale computing can circumvent this problem by treating the whole system but dividing the atoms into two groups. In Coarse Grained LSMS (CG-LSMS) one group of atoms has its charge and scattering determined prescriptively based on neighboring atoms while the remaining group of atoms have their charge and scattering determined according to DFT as implemented in the LSMS. The method will be demonstrated for a one-million-atom model of a displacement cascade in Fe for which 24,130 atoms are treated with full DFT and the remaining atoms are treated prescriptively. Work supported as part of Center for Defect Physics, an Energy Frontier Research Center funded by the U.S. DOE, Office of Science, Basic Energy Sciences, used Oak Ridge Leadership Computing Facility, Oak Ridge National Lab, of DOE Office of Science.
AJAC: Atomic data calculation tool in Python
Institute of Scientific and Technical Information of China (English)
Amani Tahat; Jordi Marti; Kaher Tahat; Ali Khwaldeh
2013-01-01
In this work,new features and extensions of a currently used online atomic database management system are reported.A multiplatform flexible computation package is added to the present system,to allow the calculation of various atomic radiative and collisional processes,based on simplifying the use of some existing atomic codes adopted from the literature.The interaction between users and data is facilitated by a rather extensive Python graphical user interface working online and could be installed in personal computers of different classes.In particular,this study gives an overview of the use of one model of the package models (i.e.,electron impact collisional excitation model).The accuracy of computing capability of the electron impact collisional excitation in the adopted model,which follows the distorted wave approximation approach,is enhanced by implementing the Dirac R-matrix approximation approach.The validity and utility of this approach are presented through a comparison of the current computed results with earlier available theoretical and experimental results.Finally,the source code is made available under the general public license and being distributed freely in the hope that it will be useful to a wide community of laboratory and astrophysical plasma diagnostics.
AJAC: Atomic data calculation tool in Python
International Nuclear Information System (INIS)
In this work, new features and extensions of a currently used online atomic database management system are reported. A multiplatform flexible computation package is added to the present system, to allow the calculation of various atomic radiative and collisional processes, based on simplifying the use of some existing atomic codes adopted from the literature. The interaction between users and data is facilitated by a rather extensive Python graphical user interface working online and could be installed in personal computers of different classes. In particular, this study gives an overview of the use of one model of the package models (i.e., electron impact collisional excitation model). The accuracy of computing capability of the electron impact collisional excitation in the adopted model, which follows the distorted wave approximation approach, is enhanced by implementing the Dirac R-matrix approximation approach. The validity and utility of this approach are presented through a comparison of the current computed results with earlier available theoretical and experimental results. Finally, the source code is made available under the general public license and being distributed freely in the hope that it will be useful to a wide community of laboratory and astrophysical plasma diagnostics. (interdisciplinary physics and related areas of science and technology)
BOOK REVIEW: Computational Atomic Structure
Post, Douglass E.
1998-02-01
The primary purpose of `Computational Atomic Structure' is to give a potential user of the Multi-Configuration Hartree-Fock (MCHF) Atomic Structure Package an outline of the physics and computational methods in the package, guidance on how to use the package, and information on how to interpret and use the computational results. The book is successful in all three aspects. In addition, the book provides a good overview and review of the physics of atomic structure that would be useful to the plasma physicist interested in refreshing his knowledge of atomic structure and quantum mechanics. While most of the subjects are covered in greater detail in other sources, the book is reasonably self-contained, and, in most cases, the reader can understand the basic material without recourse to other sources. The MCHF package is the standard package for computing atomic structure and wavefunctions for single or multielectron ions and atoms. It is available from a number of ftp sites. When the code was originally written in FORTRAN 77, it could only be run on large mainframes. With the advances in computer technology, the suite of codes can now be compiled and run on present day workstations and personal computers and is thus available for use by any physicist, even those with extremely modest computing resources. Sample calculations in interactive mode are included in the book to illustrate the input needed for the code, what types of results and information the code can produce, and whether the user has installed the code correctly. The user can also specify the calculational level, from simple Hartree-Fock to multiconfiguration Hartree-Fock. The MCHF method begins by finding approximate wavefunctions for the bound states of an atomic system. This involves minimizing the energy of the bound state using a variational technique. Once the wavefunctions have been determined, other atomic properties, such as the transition rates, can be determined. The book begins with an
Updated Atomic Data and Calculations for X-ray Spectroscopy
Foster, A R; Smith, R K; Brickhouse, N S
2012-01-01
We describe the latest release of AtomDB, version 2.0.2, a database of atomic data and a plasma modeling code with a focus on X-ray astronomy. This release includes several major updates to the fundamental atomic structure and process data held within AtomDB, incorporating new ionization balance data, state-selective recombination data, and updated collisional excitation data for many ions, including the iron L-shell ions from Fe$^{+16}$ to Fe$^{+23}$ and all of the hydrogen- and helium-like sequences. We also describe some of the effects that these changes have on calculated emission and diagnostic line ratios, such as changes in the temperature implied by the He-like G-ratios of up to a factor of 2.
Large-scale atomic calculations using variational methods
International Nuclear Information System (INIS)
Atomic properties, such as radiative lifetimes, hyperfine structures and isotope shift, have been studied both theoretically and experimentally. Computer programs which calculate these properties from multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) wave functions have been developed and tested. To study relativistic effects, a program which calculates hyperfine structures from multiconfiguration Dirac-Fock (MCDF) wave functions has also been written. A new method of dealing with radial non-orthogonalities in transition matrix elements has been investigated. This method allows two separate orbital sets to be used for the initial and final states, respectively. It is shown that, once the usual orthogonality restrictions have been overcome, systematic MCHF calculations are able to predict oscillator strengths in light atoms with high accuracy. In connection with recent high-power laser experiments, time-dependent calculations of the atomic response to intense laser fields have been performed. Using the frozen-core approximation, where the atom is modeled as an active electron moving in the average field of the core electrons and the nucleus, the active electron has been propagated in time under the influence of the laser field. Radiative lifetimes and hyperfine structures of excited states in sodium and silver have been experimentally determined using time-resolved laser spectroscopy. By recording the fluorescence light decay following laser excitation in the vacuum ultraviolet spectral region, the radiative lifetimes and hyperfine structures of the 7p2P states in silver have been measured. The delayed-coincidence technique has been used to make very accurate measurements of the radiative lifetimes and hyperfine structures of the lowest 2P states in sodium and silver. 77 refs, 2 figs, 14 tabs
Hylleraas-Configuration Interaction calculations on helium atom
Ruiz, Maria Belen
2012-01-01
Hylleraas-Configuration Interaction (Hy-CI) calculations on the ground 1S state of helium atom are presented using s-, p-, and d-Slater orbitals of both real and complex type. Techniques of construction of adapted configurations, optimization of the orbital exponents, structure of the wave function expansion are explored. A new method to evaluate the two-electron kinetic energy integrals occurring in the Hy-CI method is presented. The calculations show that nanohartree accuracy, about 0.0002 cm-1 is achieved.
Fisher Information and Atomic Structure
Chatzisavvas, K Ch; Panos, C P; Moustakidis, Ch C
2013-01-01
We present a comparative study of several information and statistical complexity measures in order to examine a possible correlation with certain experimental properties of atomic structure. Comparisons are also carryed out quantitatively using Pearson correlation coefficient. In particular, we show that Fisher information in momentum space is very sensitive to shell effects, and is directly associated with some of the most characteristic atomic properties, such as atomic radius, ionization energy, electronegativity, and atomic dipole polarizability. Finally we present a relation that emerges between Fisher information and the second moment of the probability distribution in momentum space i.e. an energy functional of interest in (e,2e) experiments.
Analytical relativistic self-consistent-field calculations for atoms
International Nuclear Information System (INIS)
A new second-order representation of the Dirac equation is presented. This representation which is exact for a hydrogen atom is applied to approximate analytical self-consistent-field calculations for atoms. Results are given for the rare-gas atoms from helium to radon and for lead. The results compare favorably with numerical Dirac-Hartree-Fock solutions
Convergent variational calculation of positronium-hydrogen-atom scattering lengths
Adhikari, S K; Adhikari, Sadhan K.; Mandal, Puspajit
2001-01-01
We present a convergent variational basis-set calculational scheme for elastic scattering of positronium atom by hydrogen atom in S wave. Highly correlated trial functions with appropriate symmetry are needed for achieving convergence. We report convergent results for scattering lengths in atomic units for both singlet ($=3.49\\pm 0.20$) and triplet ($=2.46\\pm 0.10$) states.
Calculation of Al-Zn diagram from central atoms model
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
A slightly modified central atoms model was proposed. The probabilities of various clusters with the central atoms and their nearest neighboring shells can be calculated neglecting the assumption of the param eter of energy in the central atoms model in proportion to the number of other atoms i (referred with the central atom). A parameter Pα is proposed in this model, which equals to reciprocal of activity coefficient of a component, therefore, the new model can be understood easily. By this model, the Al-Zn phase diagram and its thermodynamic properties were calculated, the results coincide with the experimental data.
Atomic physics processes in radial transport calculations
International Nuclear Information System (INIS)
These lectures were intended as preparation for detailed discussions of the role of atomic and molecular physics in confinement research at the 1982 NATO Advanced Study Institute. They begin with a description of the major approaches to magnetic confinement: tandem (ambipolar) mirrors with their associated auxiliary barriers, tokamaks, and stellarators. The leading alternatives, the ELMO Bumpy Torus and the reversed field pinch, are also treated. The evolution equations for particle, energy, and (where relevant) field diffusion are presented and discussed. This is the context for atomic and molecular processes relevant to confinement
Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom
Baseden, Kyle A.; Tye, Jesse W.
2014-01-01
Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…
Atomic and Electronic Structures of Zr Atomic Chains
Institute of Scientific and Technical Information of China (English)
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.
Universal bosonic tetramers of dimer-atom-atom structure
Deltuva, A
2012-01-01
Unstable four-boson states having an approximate dimer-atom-atom structure are studied using momentum-space integral equations for the four-particle transition operators. For a given Efimov trimer the universal properties of the lowest associated tetramer are determined. The impact of this tetramer on the atom-trimer and dimer-dimer collisions is analyzed. The reliability of the three-body dimer-atom-atom model is studied.
Theoretical Calculation of Absolute Radii of Atoms and Ions. Part 1. The Atomic Radii
Directory of Open Access Journals (Sweden)
Raka Biswas
2002-02-01
Full Text Available Abstract. A set of theoretical atomic radii corresponding to the principal maximum in the radial distribution function, 4ÃÂ€r2R2 for the outermost orbital has been calculated for the ground state of 103 elements of the periodic table using Slater orbitals. The set of theoretical radii are found to reproduce the periodic law and the Lother MeyerÃ¢Â€Â™s atomic volume curve and reproduce the expected vertical and horizontal trend of variation in atomic size in the periodic table. The d-block and f-block contractions are distinct in the calculated sizes. The computed sizes qualitatively correlate with the absolute size dependent properties like ionization potentials and electronegativity of elements. The radii are used to calculate a number of size dependent periodic physical properties of isolated atoms viz., the diamagnetic part of the atomic susceptibility, atomic polarizability and the chemical hardness. The calculated global hardness and atomic polarizability of a number of atoms are found to be close to the available experimental values and the profiles of the physical properties computed in terms of the theoretical atomic radii exhibit their inherent periodicity. A simple method of computing the absolute size of atoms has been explored and a large body of known material has been brought together to reveal how many different properties correlate with atomic size.
Starting SCF Calculations by Superposition of Atomic Densities
van Lenthe, J.H.; Zwaans, R.; van Dam, H.J.J.; Guest, M.F.
2006-01-01
We describe the procedure to start an SCF calculation of the general type from a sum of atomic electron densities, as implemented in GAMESS-UK. Although the procedure is well-known for closed-shell calculations and was already suggested when the Direct SCF procedure was proposed, the general procedu
Ab-initio Green's Functions Calculations of Atoms
Barbieri, C
2009-01-01
The Faddeev random phase approximation (FRPA) method is applied to calculate the ground state and ionization energies of simple atoms. First ionization energies agree with the experiment at the level of ~10 mH or less. Calculations with similar accuracy are expected to provide information required for developing the proposed quasiparticle-DFT method.
Jiang, Jun; Cheng, Yongjun; Bromley, M W J
2014-01-01
Effective oscillator strength distributions are systematically generated and tabulated for the alkali atoms, the alkaline-earth atoms, the alkaline-earth ions, the rare gases and some miscellaneous atoms. These effective distributions are used to compute the dipole, quadrupole and octupole static polarizabilities, and are then applied to the calculation of the dynamic polarizabilities at imaginary frequencies. These polarizabilities can be used to determine the long-range $C_6$, $C_8$ and $C_{10}$ atom-atom interactions for the dimers formed from any of these atoms and ions, and we present tables covering all of these combinations.
SUPERSTRUCTURE - AN ATOMIC STRUCTURE CODE
Eissner, W.
1991-01-01
We summarize the properties of the atomic structure code SUPERSTRUCTURE, which yields bound state energies in LS coupling and intermediate coupling as well as associated radiative data. Other data that can be computed include term coupling coefficients and radiative data with allowance for cascading. Results are given, mainly for members of the Be isoelectronic sequence, to demonstrate the power and range of the code. Other examples deal with "forbidden" transitions in N-like and He-like ions.
A Variational Monte Carlo Approach to Atomic Structure
Davis, Stephen L.
2007-01-01
The practicality and usefulness of variational Monte Carlo calculations to atomic structure are demonstrated. It is found to succeed in quantitatively illustrating electron shielding, effective nuclear charge, l-dependence of the orbital energies, and singlet-tripetenergy splitting and ionization energy trends in atomic structure theory.
Finite Bias Calculations to Model Interface Dipoles in Electrochemical Cells at the Atomic Scale
DEFF Research Database (Denmark)
Hansen, Martin Hangaard; Jin, Chengjun; Thygesen, Kristian Sommer;
2016-01-01
The structure of an electrochemical interface is not determined by any external electrostatic field, but rather by external chemical potentials. This paper demonstrates that the electric double layer should be understood fundamentally as an internal electric field set up by the atomic structure...... to satisfy the thermodynamic constraints imposed by the environment. This is captured by the generalized computational hydrogen electrode model, which enables us to make efficient first-principles calculations of atomic scale properties of the electrochemical interface....
Calculations of optical rotation: Influence of molecular structure
Directory of Open Access Journals (Sweden)
Yu Jia
2012-01-01
Full Text Available Ab initio Hartree-Fock (HF method and Density Functional Theory (DFT were used to calculate the optical rotation of 26 chiral compounds. The effects of theory and basis sets used for calculation, solvents influence on the geometry and values of calculated optical rotation were all discussed. The polarizable continuum model, included in the calculation, did not improve the accuracy effectively, but it was superior to γs. Optical rotation of five or sixmembered of cyclic compound has been calculated and 17 pyrrolidine or piperidine derivatives which were calculated by HF and DFT methods gave acceptable predictions. The nitrogen atom affects the calculation results dramatically, and it is necessary in the molecular structure in order to get an accurate computation result. Namely, when the nitrogen atom was substituted by oxygen atom in the ring, the calculation result deteriorated.
Investigation of atomic processes during film growth using semiempirical calculations
Leonardelli, G
2001-01-01
Growth of thin films on solid surfaces is strongly determined by the rates of the individual atomic processes and therefore depends on the energy barriers which must be surmounted during these processes. The diffusion barriers of interlayer diffusion processes are calculated in this work using embedded atom method (EAM) potentials. Great attention is paid to effects of small simulation cells preventing the atoms near the step edge from relaxing completely and thereby modifying the barriers for step descent on steps of the Pt(111) surface. Calculations in this work can also explain experimental data which show Co atoms sitting in special sites like corners and kinks when small amounts of Co are deposited on the Pt(111) surface. The results show why these sites are occupied and why configurations along A-steps are different from those on B-steps. Furthermore, calculations explain the intermixing of adlayer and substrate atoms on fcc(111) surfaces in the vicinity of rough steps occurring when these steps smoothe...
Variable atomic radii for continuum-solvent electrostatics calculation
Zhou, Baojing; Agarwal, Manish; Wong, Chung F.
2008-07-01
We have developed a method to improve the description of solute cavity defined by the interlocking-sphere model for continuum-solvent electrostatics calculations. Many models choose atomic radii from a finite set of atom types or uses an even smaller set developed by Bondi [J. Phys. Chem. 68, 441 (1964)]. The new model presented here allowed each atom to adapt its radius according to its chemical environment. This was achieved by first approximating the electron density of a molecule by a superposition of atom-centered spherical Gaussian functions. The parameters of the Gaussian functions were then determined by optimizing a function that minimized the difference between the properties from the model and those from ab initio quantum calculations. These properties included the electrostatics potential on molecular surface and the electron density within the core of each atom. The size of each atom was then determined by finding the radius at which the electron density associated with the atom fell to a prechosen value. This value was different for different chemical elements and was chosen such that the averaged radius for each chemical element in a training set of molecules matched its Bondi radius. Thus, our model utilized only a few adjustable parameters—the above density cutoff values for different chemical elements—but had the flexibility of allowing every atom to adapt its radius according to its chemical environment. This variable-radii model gave better solvation energy for 31 small neutral molecules than the Bondi radii did, especially for a quantum mechanics/Poisson-Boltzmann approach we developed earlier. The improvement was most significant for molecules with large dipole moment. Future directions for further improvement are also discussed.
New calculations of neutral atoms release in the Mercury exosphere
Borin, Patrizia; Bruno, Marco; Cremonese, Gabriele; Marzari, Francesco
Meteoroid impacts are an important source of neutral atoms in the exosphere of Mercury. Recent papers attribute to impacting particles smaller than 1 cm most of the contribution to exospheric gases. In this work we calculate the vapour and neutral atoms production rates on Mercury, as due to the impacts of micrometeoroids in the size range between 5-100 µm, that contribute for about 50% of the neutral atoms released by impacts, according to flux obtained by the new dynamical model of Borin et al. (2009). The calculations have been performed taking into account two different calibration sources for the meteoroid flux provided by Love and Brownlee (1993) (as for Borin et al., 2009) and by Grun et al. (1985). Moreover, we give different values of the vapour production rates assuming both asteroidal and cometary sources of the dust particles (Wiegert, 2009; Dermott et al., 2002). Considering three different surface composition and mass fraction of atoms in the regolith of the planet (Cremonese et al. 2005, Goettel 1988, Smith and Marconi 1995) we provide the estimate of neutral atoms production rates, as sodium, potassium, calcium and magnesium.
Ab initio calculation of double ionization of atoms
Energy Technology Data Exchange (ETDEWEB)
Serov, V. V., E-mail: vladislav.serov@mail.ru [Saratov State University, Department of Theoretical Physics (Russian Federation)
2013-02-15
The Solov'ev-Vinitsky method was used to perform an ab initio calculation of the triple-differential cross section for the double single-photon photoionization of helium for the case of equal emitted-electron energies. A Gaussian width {gamma} describing angular electron-electron correlations at the total electron energy E taking values in range between 0.1 and 100 eV was obtained for this cross section. The results agree with available experimental data, but they raise a doubt as to whether the well-known Wannier law {gamma} {proportional_to} E{sup 1/4} is applicable at experimentally accessible energies. The Gaussian width {gamma} was investigated as a function of the total emitted-electron energy for targets that have a strongly asymmetric configuration of the initial state-specifically, a negative atomic-hydrogen ion H{sup -} and heliumin the 1s2s{sup 1}S and 1s3s{sup 1}S excited states. It was found that this function, {gamma}(E), had a maximum at low energies. It was also shown that, at low energies, the dependence of the double-differential cross section on the angle between the emitted-electron momenta for the targets indicated above differed substantially from the Gaussian dependence, featuring maxima whose number was equal to the number of radial nodes in the initial state. This opens new possibilities for a qualitative analysis of the electron structure of targets.
Autoionizing states of atoms calculated using generalized sturmians
DEFF Research Database (Denmark)
Avery, James Emil; Avery, John Scales
2005-01-01
The generalized Sturmian method is applied to autoionizing states of atoms and ions. If the Goscinskian basis sets allow for a sufficient amount of angular correletion, the calculated energies of doubly-excited (autoionizing) states are found to agree well with the few available experimental...... energies. A large-Z approximation is discussed, and simple formulas are derived which are valid not only for autoionizing states, but for all states of an isoelectronic atomic series. Diagonalization of a small block of the interelectron repulsion matrix yields roots that can be used for a wide range of Z...
Autoionizing States of Atoms Calculated Using Generalized Sturmians
DEFF Research Database (Denmark)
Avery, James Emil; Avery, John Scales
2005-01-01
The generalized Sturmian method is applied to autoionizing states of atoms and ions. If the Goscinskian basis sets allow for a sufficient amount of angular correletion, the calculated energies of doubly-excited (autoionizing) states are found to agree well with the few available experimental...... energies. A large-Z approximation is discussed, and simple formulas are derived which are valid not only for autoionizing states, but for all states of an isoelectronic atomic series. Diagonalization of a small block of the interelectron repulsion matrix yields roots that can be used for a wide range of Z...
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.
[Atomic force field FFsol for calculation of molecular interactions of in water environment].
Pereiaslavets, L B; Finkel'shtein, A V
2010-01-01
Detailed calculations of protein interactions with explicitly considered water takes enormous computer time. The calculation becomes faster if water is considered implicitly (as a continuous media rather than as molecules); however, these calculations are much less precise, unless one uses an additional (and also volumes) computation of the solvent-accessible areas of protein atoms. The aim of our study was to obtain parameters for non-bonded atom-atom interactions for the case when water surrounding is considered implicitly and the solvent-accessible areas are not computed. Since the "in-vacuum" interactions of atoms are obtained from experimental structures of crystals and enthalpies of their sublimation, the "in-water" interactions of atoms must be corrected using solvation free energies of molecules, which can be obtained from the Henry constants. Taken 58 structures of molecular crystals and thermodynamic data on their sublimation and solubility, we obtained parameters for "in-water" attraction and repulsion of atoms typical of protein structures (H, C, N, O, S) in various covalently-bonded states, as well as parameters for electrostatic interactions. All necessary for calculations parameters of covalent interactions have been taken from the ENCAD force field, and partial charges of all atoms of separate molecules of a crystal have been obtained from quantum-mechanical calculations. The sought parameters of the "in-water" van der Waals and electrostatic interactions were optimized so as to achieve the best description of equilibrium crystal structures and their sublimation and solvation at the room temperature. With the optimized parameters, the average error in calculation of the effective cohesion energy of molecules in crystals was less than 10% both in the "in-vacuum" and "in-water" cases. PMID:20586195
Stability and structure of atomic chains on Si(111)
Battaglia, Corsin; Aebi, Philipp; Erwin, Steven C.
2008-01-01
We study the stability and structure of self-assembled atomic chains on Si(111) induced by monovalent, divalent and trivalent adsorbates, using first-principles total-energy calculations and scanning tunneling microscopy. We find that only structures containing exclusively silicon honeycomb or silicon Seiwatz chains are thermodynamically stable, while mixed configurations, with both honeycomb and Seiwatz chains, may be kinetically stable. The stability and structure of these atomic chains can...
DEFF Research Database (Denmark)
Bork, Nicolai Christian; Eurenius, K. E. J.; Rossmeisl, Jan;
2012-01-01
A combined density functional theory and Fourier transform infrared spectroscopy study of the structure and specific site preference of protons and hydrides in the pyrochlore Sm1.92Ca0.08Sn2O7-δ is presented. Two protonic sites of particular high stability are identified, both located on O(1) oxy...
Semiempirical studies of atomic structure
International Nuclear Information System (INIS)
The energy level structure, transition probabilities, and general spectroscopic properties of highly-ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser- and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large scale ab initio calculations. Large blocks of data are predictively systematized and parameterized along isoelectric, homologous, isoionic, Rydberg, and yrast series, to provide a comprehensive and reliable data base
Hyperspherical Three-Body Calculation for Exotic Atoms
International Nuclear Information System (INIS)
Ground state energies of atomic three-body systems like negatively charged hydrogen, normal helium, positively charged-lithium, beryllium, carbon, oxygen, neon and negatively charged exotic-muonium and positronium atoms have been calculated adopting hyperspherical harmonics expansion method. Calculation of matrix elements of two body interactions needed in the hyperspherical harmonics expansion method for a three body system is greatly simplified by expanding the bra-and ket-vector states in the hyperspherical harmonics (HH) basis states appropriate for the partition corresponding to the interacting pair. This involves the Raynal-Revai coefficients (RRC), which are the transformation coefficients between the HH bases corresponding to the two partitions. Use of RRC become particularly essential for the numerical solution of three-body Schroedinger equation where the two-body potentials are other than Coulomb or harmonic. However in the present work the technique is used for two electron atoms 1H-(p+e-e-), D-(d+e-e-), Mu-(μ+e-e-), 4He(4He2+e-e-), 6Li(6Li3+e-e-), 10Be( 10Be4+e-e-), 12C(12C6+e-e-), 16O(16O8+e-e-) etc. and the exotic positronium negative ion Ps-(e+e-e-) where the interactions are purely Coulomb. The relative convergence in ground state binding energy with increasing Kmax for 20Ne has been demonstrated as a representative case. The calculated energies at Kmax = 28 using RRC's have been compared with those obtained by a straight forward manner in some representative cases to demonstrate the appropriateness of the use of RRC. The extrapolated energies have also been compared with those found in the literature. The calculated binding energies agree within the computational error. (author)
Recent developments in high-spin calculations in atomic nuclei
International Nuclear Information System (INIS)
A brief introduction to the recent achievements in the high-spin domain in nuclear physics is given. Results of the calculations in highly developed rotational bands in deformed nuclei, as well as the calculations in the structure of the yrast isomers are presented. The calculations fail in two aspects: local minima in the yrast line are not confirmed experimentally, the overall slope of the yrast line in 152Dy is considerably overestimated. The calculations of the yrast line with new Woods-Saxon parameters are now in progress. The parameters are chosen to reproduce the large gap in the levels at proton number Z=64. (M.H.)
Description of an atomic structure software package
International Nuclear Information System (INIS)
The MCHF method has been shown to be effective for the study of correlation and for croblems where relativistic effects are small. It has been applied to some difficult cases where a perturber is embedded in a Rydberg series and mixing depends critically on correlation. Relativistic corrections may be included through the Breit-Pauli approximation. This approach has been used recently in a study of the Boron sequence where the fine structure splitting obtained from multiconfiguration Dirac-Hartree-Fock calculations was not in good agreement with observation and a correction process was needed. It has also been used to study forbidden transitions in the Carbon, Nitrogen, and Oxygen sequence. Thus the MCHF (or MCHF+BP) method is a versatile method for the study of atomic structure for a large class of problems. The present software package is based on this method
Semiempirical studies of atomic structure
International Nuclear Information System (INIS)
The energy level structure, transition probabilities, and general spectroscopic properties of highly ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser-and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large-scale ab initio calculations. Typical examples are the following: lifetime measurements in the neon isoelectronic sequence; multiplexed decay curve measurements of Li-like Si XII; and isoelectronic specification of intershell resonance and intercombination decay rates using measured transition probabilities and spectroscopically determined singlet-mixing amplitudes
Global nuclear-structure calculations
Energy Technology Data Exchange (ETDEWEB)
Moeller, P.; Nix, J.R.
1990-04-20
The revival of interest in nuclear ground-state octupole deformations that occurred in the 1980's was stimulated by observations in 1980 of particularly large deviations between calculated and experimental masses in the Ra region, in a global calculation of nuclear ground-state masses. By minimizing the total potential energy with respect to octupole shape degrees of freedom in addition to {epsilon}{sub 2} and {epsilon}{sub 4} used originally, a vastly improved agreement between calculated and experimental masses was obtained. To study the global behavior and interrelationships between other nuclear properties, we calculate nuclear ground-state masses, spins, pairing gaps and {Beta}-decay and half-lives and compare the results to experimental qualities. The calculations are based on the macroscopic-microscopic approach, with the microscopic contributions calculated in a folded-Yukawa single-particle potential.
Global nuclear-structure calculations
International Nuclear Information System (INIS)
The revival of interest in nuclear ground-state octupole deformations that occurred in the 1980's was stimulated by observations in 1980 of particularly large deviations between calculated and experimental masses in the Ra region, in a global calculation of nuclear ground-state masses. By minimizing the total potential energy with respect to octupole shape degrees of freedom in addition to ε2 and ε4 used originally, a vastly improved agreement between calculated and experimental masses was obtained. To study the global behavior and interrelationships between other nuclear properties, we calculate nuclear ground-state masses, spins, pairing gaps and Β-decay and half-lives and compare the results to experimental qualities. The calculations are based on the macroscopic-microscopic approach, with the microscopic contributions calculated in a folded-Yukawa single-particle potential
International Nuclear Information System (INIS)
The geometry, electronic structure and magnetic property of the hexagonal AlN (h-AlN) sheet doped by 5d atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3v and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μB for Lu, Ta and Ir; 1μB for Hf, W, Pt and Hg; 2μB for Re and Au; and 3μB for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries. (condensed matter: structural, mechanical, and thermal properties)
A New Pseudospectral Method for Calculations of Hydrogen Atom in Arbitrary External Fields
Institute of Scientific and Technical Information of China (English)
QIAO Hao-Xue; LI Bai-Wen1
2002-01-01
A new pseudospectral method was introduced to calculate wavefunctions and energy levels of hydrogen atom in arbitrary potential. Some results of hydrogen atom in uniform magnetic fields were presented, high accuracy of results was obtained with simple calculations, and our calculations show very fast convergence. It suggests a new methodfor calculations of hydrogen atom in external fields.
LOCAL ATOMIC STRUCTURE OF AMORPHOUS METALS
Egami, T.; Maed, K.; Srolovitz, D.; Vitek, V.
1980-01-01
The local parameters are introduced to describe the local atomic structure of amorphous metals. They define the structural defects which facilitate the explanation of various properties, including the volume change by annealing.
Atomic probes of surface structure and dynamics
International Nuclear Information System (INIS)
Progress for the period Sept. 15, 1992 to Sept. 14, 1993 is discussed. Semiclassical methods that will allow much faster and more accurate three-dimensional atom--surface scattering calculations, both elastic and inelastic, are being developed. The scattering of He atoms from buckyballs is being investigated as a test problem. Somewhat more detail is given on studies of He atom scattering from defective Pt surfaces. Molecular dynamics simulations of He+ and Ar+ ion sputtering of Pt surfaces are also being done. He atom scattering from Xe overlayers on metal surfaces and the thermalized dissociation of H2 on Cu(110) are being studied. (R.W.R.) 64 refs
Parallel adaptive mesh refinement for electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Kohn, S.; Weare, J.; Ong, E.; Baden, S.
1996-12-01
We have applied structured adaptive mesh refinement techniques to the solution of the LDA equations for electronic structure calculations. Local spatial refinement concentrates memory resources and numerical effort where it is most needed, near the atomic centers and in regions of rapidly varying charge density. The structured grid representation enables us to employ efficient iterative solver techniques such as conjugate gradients with multigrid preconditioning. We have parallelized our solver using an object-oriented adaptive mesh refinement framework.
The calculation of photoionization angular distribution parameter β of atomic Na
Institute of Scientific and Technical Information of China (English)
刘锦超; 蒲丰年; 刘汉奎; 郭建军; 程延松; 杨向东
1999-01-01
The differential cross sections and angular distribution parameter of the photoionization processes 2p~63s→2p~53skl of atomic Na have been calculated by using many-body perturbation theory. In the calculation, the resonant structure of the excitation process 2s→3p has been included. The electron correlation interaction was analyzed by using the effective diagram method. The summation of specific classes of these diagrams is to an infinite order. The results of calculations are compared with experimental data, which are in good agreement with the experiment.
Electronic structure of crystalline uranium nitride: LCAO DFT calculations
International Nuclear Information System (INIS)
The results of the first LCAO DFT calculations of cohesive energy, band structure and charge distribution in uranium nitride (UN) crystal are presented and discussed. The calculations are made with the uranium atom relativistic effective core potentials, including 60, 78 and 81 electrons in the core. It is demonstrated that the chemical bonding in UN crystal has a metallic-covalent nature. Three 5f-electrons are localized on the U atom and occupy the states near the Fermi level. The metallic nature of the crystal is due to the f-character of both the valence-band top and the conduction-band bottom. The covalent bonds are formed by the interaction of 7s- and 6d-states of the uranium atom with the 2p-states of the nitrogen atom. It is shown that the inclusion of 5f-electrons in the atomic core introduces small changes in the calculated cohesive energy of UN crystal and electron charge distribution. However, the inclusion of 5s-, 5p-, 5d-electrons in the valence shell allows the better agreement with the calculated and experimental cohesive-energy value. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Three-dimensional rf structure calculations
International Nuclear Information System (INIS)
The calculation of three-dimensional rf structures is rapidly approaching adolescence, after having been in its infancy for the last four years. This paper will show the kinds of calculations that are currently being performed in the frequency domain and is a companion paper to one in which time-domain calculations are described. 13 refs., 14 figs
Progress in numerical calculations of ion-atom collisions
Energy Technology Data Exchange (ETDEWEB)
Reading, J.F.; Ford, A.L.; Becker, R.L.
1983-01-01
An ion-atom collision produces a time dependent perturbation of a many fermion system. In this collision, excitation, ionization and charge transfer can occur. The driving mechanism for these processes may be thought of as the potentials seen by individual electrons at any given separation of the projectile and target nuclei. If we think of these potentials as belonging to the target (a nucleus and electrons) and the projectile (another nucleus and electrons) then as detected by an electron the potentials change because: (a) the target and projectile change position, and (b) electrons on the target and projectile change states. Most work in the past fifty years has concentrated on solving the independent particle model (IPM). Cracks are beginning to appear in this model which only allows for type (a) changes in the potential. But in a short review we shall have quite enough to do in understanding the progress made in the last decade on the IPM. This paper is divided into three parts. The first deals with how to reduce the IPM to the single electron model (SEM). The second is on a new method where charge transfer is important. The third confronts some standard models with modern calculations.
Progress in numerical calculations of ion-atom collisions
International Nuclear Information System (INIS)
An ion-atom collision produces a time dependent perturbation of a many fermion system. In this collision, excitation, ionization and charge transfer can occur. The driving mechanism for these processes may be thought of as the potentials seen by individual electrons at any given separation of the projectile and target nuclei. If we think of these potentials as belonging to the target (a nucleus and electrons) and the projectile (another nucleus and electrons) then as detected by an electron the potentials change because: (a) the target and projectile change position, and (b) electrons on the target and projectile change states. Most work in the past fifty years has concentrated on solving the independent particle model (IPM). Cracks are beginning to appear in this model which only allows for type (a) changes in the potential. But in a short review we shall have quite enough to do in understanding the progress made in the last decade on the IPM. This paper is divided into three parts. The first deals with how to reduce the IPM to the single electron model (SEM). The second is on a new method where charge transfer is important. The third confronts some standard models with modern calculations
Boukhvalov, D W; Katsnelson, M. I.; Lichtenstein, A. I.
2008-01-01
Density functional calculations of electronic structure, total energy, structural distortions, and magnetism for hydrogenated single-layer, bilayer, and multi-layer graphene are performed. It is found that hydrogen-induced magnetism can survives only at very low concentrations of hydrogen (single-atom regime) whereas hydrogen pairs with optimized structure are usually nonmagnetic. Chemisorption energy as a function of hydrogen concentration is calculated, as well as energy barriers for hydrog...
Atomic structures of 13-atom clusters by density functional theory
Chen, Hsin-Yi; Wei, Ching-Ming
2007-03-01
The 13-atom cluster structures of the alkaline metals, alkaline earth metals, boron group, 3d, 4d, and 5d transition metals in the periodic table, and Pb are investigated by density functional theory with three kinds of exchange correlation approximation: i) LDA (Local Density Approximation), ii) GGA (Generalized Gradient Approximation) [1], and iii) PBE (Perdew-Burke-Ernzerhof) [2]. The results mainly focus on five 3-D structures: icosahedral, cuboctahedral, hexagonal-closed packed, body-center cubic, decahedral, and the other two layer structures: buckled biplanar (bbp) and garrison-cap biplanar (gbp) structures. Limited by accuracy of exchange correlation approximation, two interesting results are found. The ground states of Ca13, Sr13, Ba13, Sc13, Y13, La13, Ti13, Zr13, and Hf13 are icosahedral structures. The clusters of Ir13, Pt13, Cu13, Ag13, and Au13 are more favorable for layer structures (i.e. bbp and gbp) than the other five 3-D structures. [1] J. P. Perdew et al., Phys. Rev. B 46, 6671 (1992). [2] J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).
Energy Technology Data Exchange (ETDEWEB)
Farkas, D. [Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (United States); Zhou, S.J. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Vailhe, C.; Mutasa, B.; Panova, J. [Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (United States)
1997-01-01
We performed embedded atom method calculations on surface energies and unstable stacking fault energies for a series of intermetallics for which interatomic potentials of the embedded atom type have recently been developed. These results were analyzed and applied to the prediction of relative ductility of these materials using the various current theories. Series of alloys with the B2 ordered structure were studied, and the results were compared to those in pure body-centered cubic (bcc) Fe. Ordered compounds with L1{sub 2} and L1{sub 0} structures based on the face-centered cubic (fcc) lattice were also studied. It was found that there is a correlation between the values of the antiphase boundary (APB) energies in B2 alloys and their unstackable stacking fault energies. Materials with higher APB energies tend to have higher unstable stacking fault energies, leading to an increased tendency to brittle fracture. {copyright} {ital 1997 Materials Research Society.}
Precision calculations of atoms with few valence electrons
Kozlov, M G
2003-01-01
We discuss the possibility of using pair-equations for the construction of the effective Hamiltonian $H_{\\rm eff}$ for valence electrons of an atom. The low-energy part of atomic spectrum is found by solving the eigenvalue problem for $H_{\\rm eff}$. In this way it is possible to account efficiently for the valence-valence and core-valence correlations. We tested this method on a toy model of a four-electron atom with the core $1s^2$. The spectrum obtained with $H_{\\rm eff}$ for two valence electrons is in a perfect agreement with the full configuration interaction for all four electrons.
Geminal embedding scheme for optimal atomic basis set construction in correlated calculations
Energy Technology Data Exchange (ETDEWEB)
Sorella, S., E-mail: sorella@sissa.it [International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy and INFM Democritos National Simulation Center, Trieste (Italy); Devaux, N.; Dagrada, M., E-mail: mario.dagrada@impmc.upmc.fr [Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Université Pierre et Marie Curie, Case 115, 4 Place Jussieu, 75252 Paris Cedex 05 (France); Mazzola, G., E-mail: gmazzola@phys.ethz.ch [Theoretische Physik, ETH Zurich, 8093 Zurich (Switzerland); Casula, M., E-mail: michele.casula@impmc.upmc.fr [CNRS and Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Université Pierre et Marie Curie, Case 115, 4 Place Jussieu, 75252 Paris Cedex 05 (France)
2015-12-28
We introduce an efficient method to construct optimal and system adaptive basis sets for use in electronic structure and quantum Monte Carlo calculations. The method is based on an embedding scheme in which a reference atom is singled out from its environment, while the entire system (atom and environment) is described by a Slater determinant or its antisymmetrized geminal power (AGP) extension. The embedding procedure described here allows for the systematic and consistent contraction of the primitive basis set into geminal embedded orbitals (GEOs), with a dramatic reduction of the number of variational parameters necessary to represent the many-body wave function, for a chosen target accuracy. Within the variational Monte Carlo method, the Slater or AGP part is determined by a variational minimization of the energy of the whole system in presence of a flexible and accurate Jastrow factor, representing most of the dynamical electronic correlation. The resulting GEO basis set opens the way for a fully controlled optimization of many-body wave functions in electronic structure calculation of bulk materials, namely, containing a large number of electrons and atoms. We present applications on the water molecule, the volume collapse transition in cerium, and the high-pressure liquid hydrogen.
Atomic Structure and Properties of Extended Defects in Silicon
Energy Technology Data Exchange (ETDEWEB)
Buczko, R.; Chisholm, M.F.; Kaplan, T.; Maiti, A.; Mostoller, M.; Pantelides, S.T.; Pennycook, S.J.
1998-10-15
The Z-contrast technique represents a new approach to high-resolution electron microscopy allowing for the first time incoherent imaging of materials on the atomic scale. The key advantages of the technique, an intrinsically higher resolution limit and directly interpretable, compositionally sensitive imaging, allow a new level of insight into the atomic configurations of extended defects in silicon. This experimental technique has been combined with theoretical calculations (a combination of first principles, tight binding, and classical methods) to extend this level of insight by obtaining the energetic and electronic structure of the defects.
Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework.
Berger, Daniel; Logsdail, Andrew J; Oberhofer, Harald; Farrow, Matthew R; Catlow, C Richard A; Sherwood, Paul; Sokol, Alexey A; Blum, Volker; Reuter, Karsten
2014-07-14
We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capability by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO2(110).
Boucard, Stéphane
1998-01-01
In this work we present the calculations of transition energies inlithiumlike and in exotics atoms : 1) With the use of new ions beamsource, it is now possible to produce highly charged ions. We thushave studied li-like ions hyperfine structure to obtain information onrelativistic many-body corrections and the magnetic sector of strongfield QED. In heavy ions these are of the order of a few percent ofthe total transition energy. We also evaluated the Bohr-Weisskopfcorrection, which depends on...
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...
Institute of Scientific and Technical Information of China (English)
林圣路; 张秋菊; 赵珂; 宋晓红; 张延惠
2002-01-01
By using the region-splitting consistent and iterative method, we calculate the recurrence spectra of lithium atoms in parallel strong external electric and magnetic fields, and obtain the novel resonance structure in the photoabsorption spectrum above the ionization threshold with a constant scaled electric field at F ＝ 0.036, and a scaled energy at e ＝ 0.58 and e = 0.006, respectively. The results are compared with those of hydrogen obtained by using standard closed orbit theory. It is demonstrated that the core-scattered effects exhibited in combination recurrence play a great role.
Atomic and electronic structure of exfoliated black phosphorus
Energy Technology Data Exchange (ETDEWEB)
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.
Atomic and electronic structure of exfoliated black phosphorus
International Nuclear Information System (INIS)
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 PO3 or H3PO3 during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time
Charge-correlation effects in calculations of atomic short-range order in metallic alloys
Energy Technology Data Exchange (ETDEWEB)
Pinski, F.J. [Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221 (United States); Staunton, J.B. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Johnson, D.D. [Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801 (United States)
1998-06-01
The {open_quotes}local{close_quotes} chemical environment that surrounds an atom directly influences its electronic charge density. These atomic charge correlations play an important role in describing the Coulomb and total energies for random substitutional alloys. Although the electronic structure may be well represented by a single-site theory, such as the coherent potential approximation, the electrostatic energy is not as well represented when these charge correlations are ignored. For metals, including the average effect from the charge correlation coming from only the nearest-neighbor shell has been shown to be sufficient to determine accurately the energy of formation. In this paper, we incorporate such charge correlations into the concentration-wave approach for calculating the atomic short-range order in random (substitutional) alloys. We present changes within the formalism, and apply the resulting equations to equiatomic nickel platinum. By including these effects, we obtain significantly better agreement with experimental data. In fact, particular to NiPt, a consequence of the charge correlation is a screening which cancels much of the electrostatic contribution to the energy and thus to the atomic short-range order, resulting in agreement with a picture originally outlined using only {open_quotes}band-energy{close_quotes} contributions. {copyright} {ital 1998} {ital The American Physical Society}
PAMOP: Petascale Atomic, Molecular and Optical Collision Calculations
McLaughlin, Brendan M.; Ballance, Connor P.; Pindzola, Michael S.; Müller, Alfred
2015-01-01
Petaflop architectures are currently being utilized efficiently to perform large scale computations in Atomic, Molecular and Optical Collisions. We solve the Schr\\"odinger or Dirac equation for the appropriate collision problem using the R-matrix or R-matrix with pseudo-states approach. We briefly outline the parallel methodology used and implemented for the current suite of Breit-Pauli and DARC codes. In this report, various examples are shown from our theoretical results compared with exper...
Nuclear structure calculations for astrophysical applications
International Nuclear Information System (INIS)
Here we present calculated results on such diverse properties as nuclear energy levels, ground-state masses and shapes, β-decay properties and fission-barrier heights. Our approach to these calculations is to use a unified theoretical framework within which the above properties can all be studied. The results are obtained in the macroscopic-microscopic approach in which a microscopic nuclear-structure single-particle model with extensions is combined with a macroscopic model, such as the liquid drop model. In this model the total potential energy of the nucleus may be calculated as a function of shape. The maxima and minima in this function correspond to such features as the ground state, fission saddle points and shape-isomeric states. Various transition rate matrix elements are determined from wave-functions calculated in the single-particle model with pairing and other relevant residual interactions taken into account
Atomic Structure of Ultrathin Gold Nanowires.
Yu, Yi; Cui, Fan; Sun, Jianwei; Yang, Peidong
2016-05-11
Understanding of the atomic structure and stability of nanowires (NWs) is critical for their applications in nanotechnology, especially when the diameter of NWs reduces to ultrathin scale (1-2 nm). Here, using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), we report a detailed atomic structure study of the ultrathin Au NWs, which are synthesized using a silane-mediated approach. The NWs contain large amounts of generalized stacking fault defects. These defects evolve upon sustained electron exposure, and simultaneously the NWs undergo necking and breaking. Quantitative strain analysis reveals the key role of strain in the breakdown process. Besides, ligand-like morphology is observed at the surface of the NWs, indicating the possibility of using AC-HRTEM for surface ligand imaging. Moreover, the coalescence dynamic of ultrathin Au NWs is demonstrated by in situ observations. This work provides a comprehensive understanding of the structure of ultrathin metal NWs at atomic-scale and could have important implications for their applications. PMID:27071038
Study on the electronic structure of nickel hydroxide by quantum chemical DV-Xα calculation
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The electronic structures of atom clusters Ni7O12H122+and Ni7O12H-9 of β-Ni(OH)2 were calculated by quantum chemical DV-Xα method.By analyzing the state densities,orbital populations,net charges and electric charge density differences of the selected clusters,it was indicated that β-Ni(OH)2 was not typical ionic crystal,and the bonds between Ni and O atoms had obvious covalent characteristics.The bonds between H atom and other atoms in the crystal structure were weaker,which ensured that H atoms can easily deintercalate and intercalate into β-Ni(OH)2-The structure of β-Ni(OH)2 was not changed by moderate de-intercalation of H atoms.However,with the excessive de-intercalation of H atoms,the structure of β-Ni(OH)2 changed and the electrochemical active properties were reduced.
Large-scale quantum transport calculations for electronic devices with over ten thousand atoms
Lu, Wenchang; Lu, Yan; Xiao, Zhongcan; Hodak, Miro; Briggs, Emil; Bernholc, Jerry
The non-equilibrium Green's function method (NEGF) has been implemented in our massively parallel DFT software, the real space multigrid (RMG) code suite. Our implementation employs multi-level parallelization strategies and fully utilizes both multi-core CPUs and GPU accelerators. Since the cost of the calculations increases dramatically with the number of orbitals, an optimal basis set is crucial for including a large number of atoms in the ``active device'' part of the simulations. In our implementation, the localized orbitals are separately optimized for each principal layer of the device region, in order to obtain an accurate and optimal basis set. As a large example, we calculated the transmission characteristics of a Si nanowire p-n junction. The nanowire is along (110) direction in order to minimize the number dangling bonds that are saturated by H atoms. Its diameter is 3 nm. The length of 24 nm is necessary because of the long-range screening length in Si. Our calculations clearly show the I-V characteristics of a diode, i.e., the current increases exponentially with forward bias and is near zero with backward bias. Other examples will also be presented, including three-terminal transistors and large sensor structures.
Calculation of the elastic collision properties of Na and Li atoms at ultracold temperature
Institute of Scientific and Technical Information of China (English)
Zhang Ji-Cai; Zhang Ying; Du Bing-Ge; Sun Jin-Feng
2009-01-01
This paper firstly reports a theoretical study of elastic scattering properties in a mixture of 23Na and 7Li atoms at cold and ultracold temperatures in detail.Based on the new constructed accurate singlet X1∑+g and the triplet a3∑+u states interatomic potentials for 23Na7Li mixture,it calculates the scattering lengths and the effective ranges by three computational methods,and obtains good agreements.Using the mass scaling method,it also calculates 23Na6Li scattering lengths and s-wave and total elastic cross sections,whose rich resonance structures were found and interpreted in terms of quasibound diatomic levels trapped behind a centrifugal barrier.
PAMOP: Petascale Atomic, Molecular and Optical Collision Calculations
McLaughlin, Brendan M; Pindzola, Michael S; Müller, Alfred
2015-01-01
Petaflop architectures are currently being utilized efficiently to perform large scale computations in Atomic, Molecular and Optical Collisions. We solve the Schr\\"odinger or Dirac equation for the appropriate collision problem using the R-matrix or R-matrix with pseudo-states approach. We briefly outline the parallel methodology used and implemented for the current suite of Breit-Pauli and DARC codes. In this report, various examples are shown from our theoretical results compared with experimental results obtained from Synchrotron Radiation facilities where the Cray architecture at HLRS is playing an integral part in our computational projects.
Extracting chemical information from plane wave calculations by a 3D 'fuzzy atoms' analysis
Bakó, I.; Stirling, A.; Seitsonen, A. P.; Mayer, I.
2013-03-01
Bond order and valence indices have been calculated by the method of the three-dimensional 'fuzzy atoms' analysis, using the numerical molecular orbitals obtained from plane wave DFT calculations, i.e., without introducing any external atom-centered functions. Weight functions of both Hirshfeld and Becke types have been applied. The results are rather close to the similar 'fuzzy atoms' ones obtained by using atom-centered basis sets and agree well with the chemical expectations, stressing the power of the genuine chemical concepts.
Lattice location of dopant atoms: An -body model calculation
Indian Academy of Sciences (India)
N K Deepak
2010-03-01
The channelling and scattering yields of 1 MeV -particles in the $\\langle 1 0 0 \\rangle$, $\\langle 1 1 0 \\rangle and $\\langle 1 1 1 \\rangle$ directions of silicon implanted with bismuth and ytterbium have been simulated using -body model. The close encounter yield from dopant atoms in silicon is determined from the flux density, using the Bontemps and Fontenille method. All previous works reported in literature so far have been done with computer programmes using a statistical analytical expression or by a binary collision model or a continuum model. These results at the best gave only the transverse displacement of the lattice site from the concerned channelling direction. Here we applied the superior -body model to study the yield from bismuth in silicon. The finding that bismuth atom occupies a position close to the silicon substitutional site is new. The transverse displacement of the suggested lattice site from the channelling direction is consistent with the experimental results. The above model is also applied to determine the location of ytterbium in silicon. The present values show good agreement with the experimental results.
Kodera, M.; Higuchi, K.; Narita, A; Higuchi, M
2008-01-01
We present a density-functional scheme for calculating the orbital-dependent exchange-correlation potential using the virial theorem as a sum rule. In order to check the validity of this scheme, atomic-structure calculations only with the exchange potential are performed. The accuracy of this scheme is shown to be comparable to that of the optimized effective potential (OEP) method, while the computational workload is extremely reduced compared to the OEP method.
Directory of Open Access Journals (Sweden)
Yingfeng Li
2013-05-01
Full Text Available The ways in which carbon atoms coalesce over the steps on copper (111 surface are ascertained by density functional theory (DFT calculations in the context of chemical vapor deposition (CVD growth of graphene. Two strategies, (1 by putting carbon atoms on and under the steps separately and (2 by importing additional carbon atoms between the ones separated by the steps, have been attempted to investigate if an over-step coalescence of carbon atoms could take place. Based on analyses about the optimized configurations and adsorption energies of carbon atoms nearby the steps, as well as the energy evolution curve of the system throughout the geometry optimizations process, we determined the main way in which graphene grows over the steps continuously: the carbon atoms, adsorbed additionally on the locations between the already existing ones which are separated by the steps, link them (these carbon atoms separated by the steps together. The direct over-step coalescence of the carbon atoms separated by the steps is very difficult, although the energy barrier preventing their coalescence can be weakened by importing carbon atoms on and under the steps gradually. Our results imply potential applications in directing the fabrication of graphene with particular structure by controlling the surface topography of copper substrate.
Calculation of electron scattering on atoms and ions
Energy Technology Data Exchange (ETDEWEB)
Bray, I.
1995-02-01
This paper reviews the applications of the convergent close-coupling (CCC) method to electron scattering on light atoms and ions. Particular emphasis is given to those areas where other theories have difficulty, e g. total ionization cross sections and the associated spin asymmetries. It begins with the simplest application to the Temkin-Poet model problem of electron-hydrogen scattering, which is used to validate the CCC approach. Subsequently, results are given for electron impact ionization of various initial states of the targets H(1s,2s), He(1{sup 1}S,2{sup 3.1}S), He{sup +}(1s), Li(2s), O{sup 5+}(2s) and Na(3s). 50 refs., 10 figs.
Variational calculation of electron elastic scattering by atomic helium
Chernek, P. J.
1982-12-01
The elastic-scattering of electrons from atomic helium in the ground state is investigated. It is shown that for low energy incident electrons the scattering problem reduced to solving an ordinary integro-differential equation for the scattering wave-function. A method is discussed to obtain approximate solutions to the integro-differential equation by variational principles. The extremum condition of the variational method is formulated into a general N x N matrix equation which reduces to a 2 x 2 eigen-value matrix problem for the phase-shift of the scattering electron. An algorithm is presented to obtain the collisional cross-section for elastic scattering as a function of incident electron energy.
The variational method in the atomic structure calcularion
International Nuclear Information System (INIS)
The importance and limitations of variational methods on the atomic structure calculations is set into relevance. Comparisons are made to the Perturbation Theory. Ilustrating it, the method is applied to the H-, H+ and H+2 simple atomic structure systems, and the results are analysed with basis on the study of the associated essential eigenvalue spectrum. Hydrogenic functions (where the screening constants are replaced by variational parameters) are combined to construct the wave function with proper symmetry for each one of the systems. This shows the existence of a bound state for H-, but no conclusions can be made for the others, where it may or may not be necessary to use more flexible wave functions, i.e., with greater number of terms and parameters. (author)
Atomic density functions: atomic physics calculations analyzed with methods from quantum chemistry
Borgoo, Alex; Geerlings, P
2011-01-01
This contribution reviews a selection of findings on atomic density functions and discusses ways for reading chemical information from them. First an expression for the density function for atoms in the multi-configuration Hartree--Fock scheme is established. The spherical harmonic content of the density function and ways to restore the spherical symmetry in a general open-shell case are treated. The evaluation of the density function is illustrated in a few examples. In the second part of the paper, atomic density functions are analyzed using quantum similarity measures. The comparison of atomic density functions is shown to be useful to obtain physical and chemical information. Finally, concepts from information theory are introduced and adopted for the comparison of density functions. In particular, based on the Kullback--Leibler form, a functional is constructed that reveals the periodicity in Mendeleev's table. Finally a quantum similarity measure is constructed, based on the integrand of the Kullback--L...
Directory of Open Access Journals (Sweden)
Raiker Witter
2015-01-01
Full Text Available Polarization of atoms plays a substantial role in molecular interactions. Class I and II force fields mostly calculate with fixed atomic charges which can cause inadequate descriptions for highly charged molecules, for example, ion channels or metalloproteins. Changes in charge distributions can be included into molecular mechanics calculations by various methods. Here, we present a very fast computational quantum mechanical method, the Bond Polarization Theory (BPT. Atomic charges are obtained via a charge calculation method that depend on the 3D structure of the system in a similar way as atomic charges of ab initio calculations. Different methods of population analysis and charge calculation methods and their dependence on the basis set were investigated. A refined parameterization yielded excellent correlation of R=0.9967. The method was implemented in the force field COSMOS-NMR and applied to the histidine-tryptophan-complex of the transmembrane domain of the M2 protein channel of influenza A virus. Our calculations show that moderate changes of side chain torsion angle χ1 and small variations of χ2 of Trp-41 are necessary to switch from the inactivated into the activated state; and a rough two-side jump model of His-37 is supported for proton gating in accordance with a flipping mechanism.
Atomic Structure of Benzene Which Accounts for Resonance Energy
Heyrovska, Raji
2008-01-01
Benzene is a hexagonal molecule of six carbon atoms, each of which is bound to six hydrogen atoms. The equality of all six CC bond lengths, despite the alternating double and single bonds, and the surplus (resonance) energy, led to the suggestion of two resonanting structures. Here, the new atomic structure shows that the bond length equality is due to three carbon atoms with double bond radii bound to three other carbon atoms with resonance bond radii (as in graphene). Consequently, there ar...
Quasiparticle GW calculations within the GPAW electronic structure code
DEFF Research Database (Denmark)
Hüser, Falco
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...... is considered, which can be regarded as the lowest level of the GW approximation. This thesis documents the implementation of the G0W0 approximation in GPAW. It serves two purposes: First, it can be read as a manual by anyone who is interested in doing GW calculations with GPAW. All features and requirements...
Aggarwal, Kanti M.
2015-11-01
Recently, Goyal et al. [1] reported energies and lifetimes (τ) for the lowest 113 levels of the 2s22p5, 2s2p6, 2s22p43ℓ, 2s2p53ℓ and 2p63ℓ configurations of F-like Sr XXX. For the calculations they adopted the multi-configuration Dirac-Fock (MCDF) and the flexible atomic code (FAC). Additionally, they also listed radiative rates (A- values), oscillator strengths (f- values) and line strengths (S- values) for four types of transitions, namely electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1) and magnetic quadrupole (M2), but only from the ground to the higher excited levels. However, there are two clear anomalies in their reported data. Firstly, the f-values listed from FAC in their Tables 3-6 are larger than from MCDF by a factor of two, for all transitions. This is because they have blindly listed the output from FAC without realising that, unlike MCDF, FAC lists ωf where ω is the statistical weight, and happens to be exactly 2 in the present case. Secondly, their lifetime for level 2 (2s22p51/2 o 2P) is incorrect. This is because the dominant contributing transition for this level is 1-2 M1 for which A=3.25×106 s-1, listed (correctly) in their Table 5, and this leads to τ=3.08×10-7 s, and not 1.54×10-7 s, as listed in their Table 1.
Seldam, C.A. ten; Groot, S.R. de
1952-01-01
From Jensen's and Gombás' modification of the statistical Thomas-Fermi atom model, a theory for compressed atoms is developed by changing the boundary conditions. Internal kinetic energy and polarizability of argon are calculated as functions of pressure. At 1000 atm. an internal kinetic energy of a
Calculating the Finite-Speed-of-Light Effect in Atom Gravimeters with General Relativity
Tan, Yu-Jie
2016-01-01
This work mainly presents a relativistic analytical calculating method for the finite speed-of-light effect in atom gravimeters, which can simplify the deriva- tion and give a more complete expression for the associated correction.
Effects of NMR spectral resolution on protein structure calculation.
Directory of Open Access Journals (Sweden)
Suhas Tikole
Full Text Available Adequate digital resolution and signal sensitivity are two critical factors for protein structure determinations by solution NMR spectroscopy. The prime objective for obtaining high digital resolution is to resolve peak overlap, especially in NOESY spectra with thousands of signals where the signal analysis needs to be performed on a large scale. Achieving maximum digital resolution is usually limited by the practically available measurement time. We developed a method utilizing non-uniform sampling for balancing digital resolution and signal sensitivity, and performed a large-scale analysis of the effect of the digital resolution on the accuracy of the resulting protein structures. Structure calculations were performed as a function of digital resolution for about 400 proteins with molecular sizes ranging between 5 and 33 kDa. The structural accuracy was assessed by atomic coordinate RMSD values from the reference structures of the proteins. In addition, we monitored also the number of assigned NOESY cross peaks, the average signal sensitivity, and the chemical shift spectral overlap. We show that high resolution is equally important for proteins of every molecular size. The chemical shift spectral overlap depends strongly on the corresponding spectral digital resolution. Thus, knowing the extent of overlap can be a predictor of the resulting structural accuracy. Our results show that for every molecular size a minimal digital resolution, corresponding to the natural linewidth, needs to be achieved for obtaining the highest accuracy possible for the given protein size using state-of-the-art automated NOESY assignment and structure calculation methods.
Direct observation of a long-lived single-atom catalyst chiseling atomic structures in graphene.
Wang, Wei Li; Santos, Elton J G; Jiang, Bin; Cubuk, Ekin Dogus; Ophus, Colin; Centeno, Alba; Pesquera, Amaia; Zurutuza, Amaia; Ciston, Jim; Westervelt, Robert; Kaxiras, Efthimios
2014-02-12
Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.
Radziute, Laima; Jonsson, Per; Biero, Jacek
2013-01-01
The multiconfiguration Dirac-Hartree-Fock (MCDHF) method has been employed to calculate atomic electric dipole moments (EDM) of 225^Ra, 199^Hg, and 171^Yb. For the calculations of the matrix elements we extended the relativistic atomic structure package GRASP2K. The extension includes programs to evaluate matrix elements of (P, T)-odd e-N tensor-pseudotensor and pseudoscalar-scalar interactions, the atomic electric dipole interaction, the nuclear Schiff moment, and the interaction of the electron electric dipole moment with nuclear magnetic moments. The interelectronic interactions were accounted for through valence and core-valence electron correlation effects. The electron shell relaxation was included with separately optimised wave functions of opposite parities.
Shevlin, S A
2001-01-01
transport properties of the line are also calculated. Finally we find which of the two models of the (4x1)-Si(111)-ln reconstruction is thermodynamically favoured in a supercell geometry. We use ab initio plane wave techniques in the Local-Density-Approximation, and calculate and compare the electronic structure of the two models with respect to the characteristic energies for electron dispersion along and across the chain structures. We also consider the effects of electronic structure on the in-plane transport properties of the indium lines. The structural and electronic properties of several candidate atomic scale wires are analysed. Three candidates are studied: the trans-polyacetylene molecule, the silicon line on the (001) face of cubic silicon carbide (the (nx2) series of reconstructions) and the indium chain on the (111) face of silicon carbide (the (4x1) reconstruction). We use the polyacetylene molecule as a test-bed for the techniques that we use to calculate transport properties in an empirically ...
Lattice QCD Calculation of Nucleon Structure
Energy Technology Data Exchange (ETDEWEB)
Liu, Keh-Fei [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy; Draper, Terrence [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy
2016-08-30
It is emphasized in the 2015 NSAC Long Range Plan [1] that "understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large scale computer simulation. We started out by calculating the nucleon form factors ₋ electromagnetic [2], axial-vector [3], π NN [4], and scalar [5] form factors, the quark spin contribution [6] to the proton spin, the strangeness magnetic moment [7], the quark orbital angular momentum [8], the quark momentum fraction [9], and the quark and glue decomposition of the proton momentum and angular momentum [10]. These first round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations [11, 12]. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors [13], charm and strange quark masses, the charmonium spectrum and the D_{s} meson decay constant fD_{s} [14], the
Lattice QCD Calculation of Nucleon Structure
Energy Technology Data Exchange (ETDEWEB)
Liu, Keh-Fei; Draper, Terrence
2016-08-30
It is emphasized in the 2015 NSAC Long Range Plan [1] that \\understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out rst-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large scale computer simulation. We started out by calculating the nucleon form factors { electromagnetic [2], axial-vector [3], NN [4], and scalar [5] form factors, the quark spin contribution [6] to the proton spin, the strangeness magnetic moment [7], the quark orbital angular momentum [8], the quark momentum fraction [9], and the quark and glue decomposition of the proton momentum and angular momentum [10]. These rst round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical e ects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge con gurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations [11, 12]. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at 300 MeV and obtained the strange form factors [13], charm and strange quark masses, the charmonium spectrum and the Ds meson decay constant fDs [14], the strangeness and charmness [15], the
Studying Atomic Structures by Aberration-Corrected Transmission Electron Microscopy
Urban, Knut W.
2008-07-01
Seventy-five years after its invention, transmission electron microscopy has taken a great step forward with the introduction of aberration-corrected electron optics. An entirely new generation of instruments enables studies in condensed-matter physics and materials science to be performed at atomic-scale resolution. These new possibilities are meeting the growing demand of nanosciences and nanotechnology for the atomic-scale characterization of materials, nanosynthesized products and devices, and the validation of expected functions. Equipped with electron-energy filters and electron-energy loss spectrometers, the new instruments allow studies not only of structure but also of elemental composition and chemical bonding. The energy resolution is about 100 milli electron volts, and the accuracy of spatial measurements has reached a few picometers. However, understanding the results is generally not straightforward and only possible with extensive quantum-mechanical computer calculations.
Calculated Structural Phase-Transitions in the Alkaline-Earth Metals
DEFF Research Database (Denmark)
Skriver, Hans Lomholt
1982-01-01
The local-density approximation and the linear muffin-tin orbital method have been used within the atomic-sphere approximation to calculate structural energy differences for all the alkaline earth metals at zero temperature. At ordinary pressure the calculations predict the crystal structure sequ...... sequence hcp→fcc→bcc as a function of atomic number. As a function of pressure they predict the structure sequence fcc→bcc→hcp. The structural transitions and the onset of superconductivity under pressure are correlated with the d occupation number....
Evolution of atomic structure during nanoparticle formation
Directory of Open Access Journals (Sweden)
Christoffer Tyrsted
2014-05-01
Full Text Available Understanding the mechanism of nanoparticle formation during synthesis is a key prerequisite for the rational design and engineering of desirable materials properties, yet remains elusive due to the difficulty of studying structures at the nanoscale under real conditions. Here, the first comprehensive structural description of the formation of a nanoparticle, yttria-stabilized zirconia (YSZ, all the way from its ionic constituents in solution to the final crystal, is presented. The transformation is a complicated multi-step sequence of atomic reorganizations as the material follows the reaction pathway towards the equilibrium product. Prior to nanoparticle nucleation, reagents reorganize into polymeric species whose structure is incompatible with the final product. Instead of direct nucleation of clusters into the final product lattice, a highly disordered intermediate precipitate forms with a local bonding environment similar to the product yet lacking the correct topology. During maturation, bond reforming occurs by nucleation and growth of distinct domains within the amorphous intermediary. The present study moves beyond kinetic modeling by providing detailed real-time structural insight, and it is demonstrated that YSZ nanoparticle formation and growth is a more complex chemical process than accounted for in conventional models. This level of mechanistic understanding of the nanoparticle formation is the first step towards more rational control over nanoparticle synthesis through control of both solution precursors and reaction intermediaries.
Relativistic calculations of quasi-one-electron atoms and ions using Laguerre and Slater spinors
Jiang, Jun; Cheng, Yongjun; Bromley, Michael W J
2016-01-01
A relativistic description of the structure of heavy alkali atoms and alkali-like ions using S-spinors and L-spinors has been developed. The core wavefunction is defined by a Dirac-Fock calculation using an S-spinors basis. The S-spinor basis is then supplemented by a large set of L-spinors for the calculation of the valence wavefunction in a frozen-core model. The numerical stability of the L-spinor approach is demonstrated by computing the energies and decay rates of several low-lying hydrogen eigenstates, along with the polarizabilities of a $Z=60$ hydrogenic ion. The approach is then applied to calculate the dynamic polarizabilities of the $5s$, $4d$ and $5p$ states of Sr$^+$. The magic wavelengths at which the Stark shifts between different pairs of transitions are zero are computed. Determination of the magic wavelengths for the $5s \\to 4d_{\\frac32}$ and $5s \\to 4d_{\\frac52}$ transitions near $417$~nm (near the wavelength for the $5s \\to 5p_j$ transitions) would allow a determination of the oscillator s...
Structurally uniform and atomically precise carbon nanostructures
Segawa, Yasutomo; Ito, Hideto; Itami, Kenichiro
2016-01-01
Nanometre-sized carbon materials consisting of benzene units oriented in unique geometric patterns, hereafter named nanocarbons, conduct electricity, absorb and emit light, and exhibit interesting magnetic properties. Spherical fullerene C60, cylindrical carbon nanotubes and sheet-like graphene are representative forms of nanocarbons, and theoretical simulations have predicted several exotic 3D nanocarbon structures. At present, synthetic routes to nanocarbons mainly lead to mixtures of molecules with a range of different structures and properties, which cannot be easily separated or refined into pure forms. Some researchers believe that it is impossible to synthesize these materials in a precise manner. Obtaining ‘pure’ nanocarbons is a great challenge in the field of nanocarbon science, and the construction of structurally uniform nanocarbons, ideally as single molecules, is crucial for the development of functional materials in nanotechnology, electronics, optics and biomedical applications. This Review highlights the organic chemistry approach — more specifically, bottom-up construction with atomic precision — that is currently the most promising strategy towards this end.
Kevorkyants, Ruslan; Wang, Xiqiao; Close, David M; Pavanello, Michele
2013-11-14
We present an application of the linear scaling frozen density embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfcc's) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems range from an isolated guanine to a 15,000 atom QM/MM cluster where the QM region is comprised of 36 protonated guanine cations, 36 chlorine anions, and 42 water molecules. Our calculations show that the embedding effects of the surrounding crystal cannot be reproduced by small model systems nor by a pure QM/MM procedure. Instead, a large QM region is needed to fully capture the complicated nature of the embedding effects in this system. The unprecedented system size for a relativistic all-electron isotropic hfcc calculation can be approached in this work because the local nature of the electronic structure of the organic crystals considered is fully captured by the FDE approach.
Inner Space: The Structure of the Atom
Energy Technology Data Exchange (ETDEWEB)
Glasstone, Samuel
1972-01-01
The atom is now regarded as the smallest possible particle of an element that retains the identity of that element. The atoms of an element determine the characteristics of that particular element. One of the purposes of this booklet is to explain how the atoms of various elements differ from one another.
The calculation of satellite line structures in highly stripped plasmas
Energy Technology Data Exchange (ETDEWEB)
Abdallah, J. Jr.; Kilcrease, D.P. [Los Alamos National Lab., NM (United States); Faenov, A.Ya.; Pikuz, T.A. [Multicharged Ion Spectra Data Center, Moscow (Russian Federation)
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Recently developed high-resolution x-ray spectrographs have made it possible to measure satellite structures from various plasma sources with great detail. These lines are weak optically thin lines caused by the decay of dielectronic states and generally accompany the resonance lines of H-like and He-like ions. The Los Alamos atomic physics and kinetics codes provide a unique capability for calculating the position and intensities of such lines. These programs have been used to interpret such highly resolved spectral measurements from pulsed power devices and laser produced plasmas. Some of these experiments were performed at the LANL Bright Source and Trident laser facilities. The satellite structures are compared with calculations to diagnose temperatures and densities. The effect of non-thermal electron distributions of electrons on calculated spectra was also considered. Collaborations with Russian scientists have added tremendous value to this research die to their vast experience in x-ray spectroscopy.
The calculation of satellite line structures in highly stripped plasmas
International Nuclear Information System (INIS)
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Recently developed high-resolution x-ray spectrographs have made it possible to measure satellite structures from various plasma sources with great detail. These lines are weak optically thin lines caused by the decay of dielectronic states and generally accompany the resonance lines of H-like and He-like ions. The Los Alamos atomic physics and kinetics codes provide a unique capability for calculating the position and intensities of such lines. These programs have been used to interpret such highly resolved spectral measurements from pulsed power devices and laser produced plasmas. Some of these experiments were performed at the LANL Bright Source and Trident laser facilities. The satellite structures are compared with calculations to diagnose temperatures and densities. The effect of non-thermal electron distributions of electrons on calculated spectra was also considered. Collaborations with Russian scientists have added tremendous value to this research die to their vast experience in x-ray spectroscopy
Structural Features of Boron-Doped Si(113) Surfaces Simulated by ab initio Calculations
Institute of Scientific and Technical Information of China (English)
LIAO Long-Zhong; LIU Zheng-Hui; ZHANG Zhao-Hui
2008-01-01
Based on ab initio calculations, boron-doped Si(113) surfaces have been simulated and atomic structures of the surfaces have been proposed. It has been determined that surface features of empty and filled states that are separately localized at pentamers and adatoms indicates a low surface density of B atoms, while it is attributed to heavy doping of B atoms at the second layer that pentamers and adatoms are both present in an image of scanning tunnelling microscopy. B doping at the second layer should be balanced by adsorbed B or Si atoms beside the adatoms and inserted B interstitials below the adatoms.
Calculating merit increases: a structured approach.
Seithel, W W; Emans, J S
1983-01-01
Determining the amount of salary increase appropriate for each employee poses a major dilemma for many human resources managers and/or compensation managers (not to mention the employee's supervisor). This task requires complying with the company's compensation philosophy, meeting market competition, and rewarding employees fairly and equitably. Authors William W. Seithel, vice president, personnel of the Midwest Stock Exchange, Inc., and Jeff S. Emans, director, employee compensation of the Kemper Group, describe a method for pinpointing a salary rate increase that is not only structured enough to move people through the salary range in accordance with a reward philosophy, but precise enough to provide a basis for projecting costs and flexible enough to meet the needs of various performance levels. The method entails the use of a structured matrix that spells out the target percentage raises for various levels of performance. By using both the matrix-which is constructed to meet the individual company's needs-and a guide chart provided by the authors, it is possible to calculate a specific percentage increase for each employee. The manager who uses this system will find that the matrix is a mechanism for control as well as a means for projecting costs. PMID:10262948
Non-perturbative calculations for the multiphoton ionization of hydrogen and lithium atoms
International Nuclear Information System (INIS)
Multiphoton ionization rates for the Hydrogen atom are calculated by direct solution of the time-dependent Schrodinger equation for several intensities at a photon energy of 5.0 eV (KrF laser). Ionization rates for linear polarized light are extracted front the time evolution of the ground state on a 2d cylindrical coordinate lattice, while rates for circular polarized light are extracted from calculations on a 3d Cartesian coordinate lattice. Multiphoton ionization rates for the Lithium atom are calculated in the frozen-core TDHF approximation for a variety of intensities and photon frequencies. The time-dependent equation for the valence HF orbital is solved on a 2d cylindrical coordinate lattice using both fixed and variable grid spacings. The non-perturbative results for both atoms are in sharp contrast to perturbation theory predictions
Understanding the proton radius puzzle: Nuclear structure effects in light muonic atoms
Ji, Chen; Dinur, Nir Nevo; Bacca, Sonia; Barnea, Nir
2015-01-01
We present calculations of nuclear structure effects to the Lamb shift in light muonic atoms. We adopt a modern ab-initio approach by combining state-of-the-art nuclear potentials with the hyperspherical harmonics method. Our calculations are instrumental to the determination of nuclear charge radii in the Lamb shift measurements, which will shed light on the proton radius puzzle.
Atomic Structure of Benzene Which Accounts for Resonance Energy
Heyrovska, Raji
2008-01-01
Benzene is a hexagonal molecule of six carbon atoms, each of which is bound to six hydrogen atoms. The equality of all six CC bond lengths, despite the alternating double and single bonds, and the surplus (resonance) energy, led to the suggestion of two resonanting structures. Here, the new atomic structure shows that the bond length equality is due to three carbon atoms with double bond radii bound to three other carbon atoms with resonance bond radii (as in graphene). Consequently, there are two kinds of CH bonds of slightly different lengths. The bond energies account for the resonance energy.
Calculation of the ionization differential effective cross sections in fast ion-atom collisions
Kaminskij, A K
2002-01-01
The method of the calculations of the ionization effective cross sections d sigma/d OMEGA differential in the incident ion scattering angle is described in fast collisions of light ions and atoms. The calculated values of angular distributions of the ions Al, Mg (for the different values of charge and energy of ions) after their collisions with the Ne, Mg atoms being ionized are reported. The dependence of such angular distributions on the incident ion charge and energy and the initial state of ejected electron is investigated
Coupled-cluster calculations of properties of Boron atom as a monovalent system
Gharibnejad, H
2015-01-01
We present relativistic coupled-cluster (CC) calculations of energies, magnetic-dipole hyperfine constants, and electric-dipole transition amplitudes for low-lying states of atomic boron. The trivalent boron atom is computationally treated as a monovalent system. We explore performance of the CC method at various approximations. Our most complete treatment involves singles, doubles and the leading valence triples. The calculations are done using several approximations in the coupled-cluster (CC) method. The results are within 0.2-0.4% of the energy benchmarks. The hyperfine constants are reproduced with 1-2% accuracy.
Calculation of phonon spectrum for noble metals by modified analytic embedded atom method (MAEAM)
Institute of Scientific and Technical Information of China (English)
Zhang Xiao-Jun; Zhang Jian-Min; Xu Ke-Wei
2006-01-01
In the harmonic approximation, the atomic force constants are derived and the phonon dispersion curves along four major symmetry directions [00ζ], [0ζζ], [ζζζ] and [0ζ1] (or △, ∑, A and Z in group-theory notation) are calculated for four noble metals Cu, Ag, Au and Pt by combining the modified analytic embedded atom method (MAEAM) with the theory of lattice dynamics. A good agreement between calculations and measurements, especially for lower frequencies,shows that the MAEAM provides a reasonable description of lattice dynamics in noble metals.
Computer Simulation of Atoms Nuclei Structure Using Information Coefficients of Proportionality
Labushev, Mikhail M
2012-01-01
The latest research of the proportionality of atomic weights of chemical elements made it possible to obtain 3 x 3 matrices for the calculation of information coefficients of proportionality Ip that can be used for 3D modeling of the structure of atom nucleus. The results of computer simulation show high potential of nucleus structure research for the characterization of their chemical and physical properties.
Understanding the structure of the first atomic contact in gold.
Sabater, Carlos; Caturla, María José; Palacios, Juan José; Untiedt, Carlos
2013-01-01
: We have studied experimentally jump-to-contact (JC) and jump-out-of-contact (JOC) phenomena in gold electrodes. JC can be observed at first contact when two metals approach each other, while JOC occurs in the last contact before breaking. When the indentation depth between the electrodes is limited to a certain value of conductance, a highly reproducible behaviour in the evolution of the conductance can be obtained for hundreds of cycles of formation and rupture. Molecular dynamics simulations of this process show how the two metallic electrodes are shaped into tips of a well-defined crystallographic structure formed through a mechanical annealing mechanism. We report a detailed analysis of the atomic configurations obtained before contact and rupture of these stable structures and obtained their conductance using first-principles quantum transport calculations. These results help us understand the values of conductance obtained experimentally in the JC and JOC phenomena and improve our understanding of atomic-sized contacts and the evolution of their structural characteristics. PMID:23718316
Energy losses of fast heavy multiply charged structural ions in collisions with complex atoms
Matveev, V. I.; Sidorov, D. B.
2007-07-01
A nonperturbatve theory of energy losses of fast heavy multiply charged structural ions in collisions with neutral complex atoms is elaborated with allowance for simultaneous excitations of ionic and atomic electron shells. Formulas for the effective deceleration that are similar to the well-known Bethe-Bloch formulas are derived. By way of example, the energy lost by partially stripped U q+ ions (10 ≤ q ≤ 70) colliding with argon atoms and also the energy lost by Au, Pb, and Bi ions colliding with various targets are calculated. The results of calculation are compared with experimental data.
Cipolla, Laura; Ferrari, Lia A.
2016-01-01
A hands-on approach to introduce the chemical elements and the atomic structure to elementary/middle school students is described. The proposed classroom activity presents Bohr models of atoms using common and inexpensive materials, such as nested plastic balls, colored modeling clay, and small-sized pasta (or small plastic beads).
Magnetism, microstructure and First Principles calculations of atomized and annealed Ni{sub 3}Al
Energy Technology Data Exchange (ETDEWEB)
García-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Crespo, P.; Hernando, A. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Marín, P.; Velasco, V. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Ynduráin, F. [Dpto. de Física de la Materia Condensada, UAM, Cantoblanco, 28049 Madrid (Spain)
2014-12-05
Highlights: • The microstructure and order of as-atomized Ni{sub 3}Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni{sub 3}Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni{sub 3}Al, L1{sub 2}, phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position.
Teo, Boon K.; Li, Wai-Kee
2011-01-01
This article is divided into two parts. In the first part, the atomic unit (au) system is introduced and the scales of time, space (length), and speed, as well as those of mass and energy, in the atomic world are discussed. In the second part, the utility of atomic units in quantum mechanical and spectroscopic calculations is illustrated with…
Post, D; Clark, R E H; Putvinskaya, N
1995-01-01
Reduction of the peak heat loads on the plasma facing components is essential for the success of the next generation of high fusion power tokamaks such as the International Thermonuclear Experimental Reactor (ITER) 1 . Many present concepts for accomplishing this involve the use of atomic processes to transfer the heat from the plasma to the main chamber and divertor chamber walls and much of the experimental and theoretical physics research in the fusion program is directed toward this issue. The results of these experiments and calculations are the result of a complex interplay of many processes. In order to identify the key features of these experiments and calculations and the relative role of the primary atomic processes, simple quasi-analytic models and the latest atomic physics rate coefficients and cross sections have been used to assess the relative roles of central radiation losses through bremsstrahlung, impurity radiation losses from the plasma edge, charge exchange and hydrogen radiation losses f...
Evaluation and Comparison of the Configuration Interaction Calculations for Complex Atoms
Directory of Open Access Journals (Sweden)
Charlotte Froese Fischer
2014-03-01
Full Text Available Configuration interaction (CI methods are the method of choice for the determination of wave functions for complex atomic systems from which a variety of atomic properties may be computed. When applied to highly ionized atoms, where few, if any, energy levels from observed wavelengths are available, the question arises as to how a calculation may be evaluated. Many different codes are available for such calculations. Agreement between the results from different codes in itself is not a check on accuracy, but may be due to a similarity in the computational procedures. This paper reviews basic theory, which, when applied in a systematic manner, can be the basis for the evaluation of accuracy. Results will be illustrated in the study of 4s24p5 (odd and 4s24p44d (even levels in W39+ and the transitions between them.
Calculation of parity and time invariance violation in the radium atom
Dzuba, V A; Ginges, J S M
1999-01-01
Parity (P) and time (T) invariance violating effects in the Ra atom are strongly enhanced due to close states of opposite parity, the large nuclear charge Z and the collective nature of P,T-odd nuclear moments. We have performed calculations of the atomic electric dipole moments (EDM) produced by the electron EDM and the nuclear magnetic quadrupole and Schiff moments. We have also calculated the effects of parity non-conservation produced by the nuclear anapole moment and the weak charge. Our results show that as a rule the values of these effects are much larger than those considered so far in other atoms (enhancement is up to 10^5 times).
Boll, Torben
2012-10-01
In this article the Cu-Au binding energy in Cu3Au is determined by comparing experimental atom probe tomography (APT) results to simulations. The resulting bonding energy is supported by density functional theory calculations. The APT simulations are based on the Müller-Schottky equation, which is modified to include different atomic neighborhoods and their characteristic bonds. The local environment is considered up to the fifth next nearest neighbors. To compare the experimental with simulated APT data, the AtomVicinity algorithm, which provides statistical information about the positions of the neighboring atoms, is applied. The quality of this information is influenced by the field evaporation behavior of the different species, which is connected to the bonding energies. © Microscopy Society of America 2012.
International Nuclear Information System (INIS)
C and N atoms are the most frequent foreign interstitial atoms (FIAs), and often incorporated into the surface layers of steels to enhance their properties by thermochemical treatments. Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Nb and Mo are the most common alloying elements in steels, also can be called foreign substitutional atoms (FSAs). The FIA and FSA interactions play an important role in the diffusion of C and N atoms, and the microstructures and mechanical properties of surface modified layers. Ab initio calculations based on the density functional theory are carried out to investigate FIA interactions with FSA in ferromagnetic bcc iron. The FIA–FSA interactions are analyzed systematically from five aspects, including interaction energies, density of states (DOS), bond populations, electron density difference maps and local magnetic moments
The effective atomic numbers of some biomolecules calculated by two methods: A comparative study
DEFF Research Database (Denmark)
Manohara, S.R.; Hanagodimath, S.M.; Gerward, Leif
2009-01-01
The effective atomic numbers Z(eff) of some fatty acids and amino acids have been calculated by two numerical methods, a direct method and an interpolation method, in the energy range of 1 keV-20 MeV. The notion of Z(eff) is given a new meaning by using a modern database of photon interaction cross...
CALCULATED PROPERTIES OF TWO-DIMENSIONAL SPIN-POLARIZED ATOMIC HYDROGEN
Lantto, L.; Nieminen, R.
1980-01-01
Optimal HNC-Jastrow calculations have been carried out for gaseous spin-polarized hydrogen in two space dimensions. Accurate values for the ground state energy, radial distribution function, average exchange energy and momentum distribution are obtained at low atomic densities.
A full CI treatment of Ne atom - A benchmark calculation performed on the NAS CRAY 2
Bauschlicher, C. W., Jr.; Langhoff, S. R.; Partridge, H.; Taylor, P. R.
1986-01-01
Full CI calculations are performed for Ne atom using Gaussian basis sets of up to triple-zeta plus double polarization quality. The total valence correlation energy through double, triple, quadruple and octuple excitations is compared for eight different basis sets. These results are expected to be an important benchmark for calibrating methods for estimating the importance of higher excitations.
The stability and electronic structure of Fe atoms embedded in zigzag graphene nanoribbons
International Nuclear Information System (INIS)
The stability and electronic properties of the Fe atoms embedded in divacancy defects in graphene nanoribbons (GNR) with zigzag-shaped edges have been studied by first-principles calculations. When Fe is positioned in the middle of the ribbon, it has little effect on the edge C atoms, which reserves the flat edges of graphene nanoribbons. On the other hand, when Fe atom is near the edge, structural distortion takes place resulting in tilted-edge structure with low energies. This indicates that the Fe atoms prefer to occupy divacancy sites near the edges. This is also in consistent with the analyses of electronic structures. Meanwhile, our results reveal that embedding Fe atom in the graphene nanoribbons is an effective method to make the GNR possessing metallic properties.
Chain-Branching Control of the Atomic Structure of Alkanethiol-Based Gold–Sulfur Interfaces
DEFF Research Database (Denmark)
Wang, Yun; Chi, Qijin; Zhang, Jingdong;
2011-01-01
Density functional theory structure calculations at 0 K and simulations at 300 K of observed high-resolution in situ scanning tunneling microscopy (STM) images reveal three different atomic-interface structures for the self-assembled monolayers (SAMs) of three isomeric butanethiols on Au(111): di...
Atomic structure of (111) twist grain boundaries in f.c.c. metals
Hosson, J.Th.M. De; Vitek, V.
1990-01-01
In this paper we have studied the atomic structures of (111) twist boundaries and investigated the applicability of the structural unit model which has previously been established for tilt boundaries and (001) twist boundaries. The calculations were carried out using two different descriptions of in
STARK STRUCTURE OF THE RYDBERG STATES OF ALKALINE-EARTH ATOMS
Institute of Scientific and Technical Information of China (English)
郅妙婵; 戴长建; 李士本
2001-01-01
The Stark effects of the Rydberg states in the alkaline-earth atoms are studied theoretically. Using a method similar to the treatment of alkali atoms, the properties of the Stark states of Mg, Ca, Sr and Ba atoms in the regions far away from the perturbers are investigated. The Stark maps for Mg (n=16, M=0), Ca (n=10, M=0), Sr (n=12,M=0) and Ba (n=13, |M|=0,1) are presented. Topics such as the general methods of calculation, the treatment of fine structure, and the structure of level anti-crossings are discussed. The comparison between the theoretical and experimental Stark maps is satisfactory.
Embedded atom study of dislocation core structure in Fe
Energy Technology Data Exchange (ETDEWEB)
Farkas, D.; Rodriguez, P.L. (Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Materials Science and Engineering Centro Atomico Bariloche (Argentina))
1994-04-01
The relaxed atomistic structure of dislocation cores in body centered cubic metals was investigated many years ago, using pair potentials. These studies are now classic and have been the basis for understanding mechanical behavior of these materials. They constitute the classic example of the importance of non-elastic core effect for the dislocations responsible for deformation, as described in several reviews written on the subject. Volume-dependent interatomic potentials were introduced in 1984. Despite the importance of the results obtained with pair potentials, no calculation of dislocation cores in pure bcc metals using volume-dependent interatomic potentials has yet been performed. The purpose of the present investigation is to compute the structures of 1/2[111] screw dislocation cores Fe. The objective is to compare these results with the structures obtained with pair potentials. The computation of Peierls stresses with pair potentials usually gives an overestimate of the actual Peierls stress. In the present work, they also use an improved boundary condition technique for the simulation of the dislocation cores can give more accurate Peierls stresses using manageable atomic block sizes. They also use a more recent graphical method for the representation of the core structures to obtain the information on the core structures and their relationship to the various crystallographic planes in the material and to analyze the shape of core in relation with the possible glide planes of the dislocation.
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.
Spectral fine structure of the atomic ground states based on full relativistic theory
Institute of Scientific and Technical Information of China (English)
Zhenghe Zhu; Yongjian Tang
2011-01-01
@@ We focus on the full relativistic quantum mechanical calculations from boron to fluorine atoms with electronic configuration of 1s22s22pn (n = 1, 2, 3, 4, and 5), where 1s22s2 is the closed shell and 2pn is the open shell. Their active electrons in the open shell occupy all the six spinors as far as possible.Therefore, we suggest a new rule called "maximum probability" for the full symmetry group relativistic theory. Furthermore, the spectral fine structure of the atomic ground states based on the full relativistic theory and their intervals of L-S splitting are all reasonable. It is impossible to calculate the L-S splitting through non-relativistic quantum mechanics. The relativistic effect of atomic mass is increased significantly by about 12 folds from boron atom to fluorine atom.%We focus on the full relativistic quantum mechanical calculations from boron to fluorine atoms with electronic configuration of 1s22s22pn (n = 1, 2, 3, 4, and 5), where 1s22s2 is the closed shell and 2pn is the open shell. Their active electrons in the open shell occupy all the six spinors as far as possible.Therefore, we suggest a new rule called "maximum probability" for the full symmetry group relativistic theory. Furthermore, the spectral fine structure of the atomic ground states based on the full relativistic theory and their intervals of L-S splitting are all reasonable. It is impossible to calculate the L-S splitting through non-relativistic quantum mechanics. The relativistic effect of atomic mass is increased significantly by about 12 folds from boron atom to fluorine atom.
Fluid-structure interaction calculations using a linear perturbation method
International Nuclear Information System (INIS)
Aim of the work is to present and validate FSI (Fluid-Structure Interaction) calculations by using a linear perturbation method and commercial Computational Fluid Dynamics (CFD) and structural analysis codes. Star-CD is used for CFD calculations and ABAQUS for structural analysis. The external MpCCI code is used for coupling the CFD and structural analysis codes
Sharma, Pragati; Roy, Sudip; Karimi-Varzaneh, Hossein Ali
2016-02-25
Microsecond atomic-scale molecular dynamics simulation has been employed to calculate the glass-transition temperature (Tg) of cis- and trans-1,4-polybutadiene (PB) and 1,4-polyisoprene (PI). Both all-atomistic and united-atom models have been simulated using force fields, already available in literature. The accuracy of these decade old force fields has been tested by comparing calculated glass-transition temperatures to the corresponding experimental values. Tg depicts the phase transition in elastomers and substantially affects various physical properties of polymers, and hence the reproducibility of Tg becomes very crucial from a thermodynamic point of view. Such validation using Tg also evaluates the ability of these force fields to be used for advanced materials like rubber nanocomposites, where Tg is greatly affected by the presence of fillers. We have calculated Tg for a total of eight systems, featuring all-atom and united-atom models of cis- and trans-PI and -PB, which are the major constituents of natural and synthetic rubber. Tuning and refinement of the force fields has also been done using quantum-chemical calculations to obtain desirable density and Tg. Thus, a set of properly validated force fields, capable of reproducing various macroscopic properties of rubber, has been provided. A novel polymer equilibration protocol, involving potential energy convergence as the equilibration criterion, has been proposed. We demonstrate that not only macroscopic polymer properties like density, thermal expansion coefficient, and Tg but also local structural characteristics like end-to-end distance (R) and radius of gyration (Rg) and mechanical properties like bulk modulus have also been equilibrated using our strategy. Complete decay of end-to-end vector autocorrelation function with time also supports proper equilibration using our strategy. PMID:26836395
Energy Technology Data Exchange (ETDEWEB)
Piñera, Ibrahin, E-mail: ipinera@ceaden.edu.cu [Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, CEADEN, 30 St. 502, Playa 11300, Havana (Cuba); Cruz, Carlos M.; Leyva, Antonio; Abreu, Yamiel; Cabal, Ana E. [Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, CEADEN, 30 St. 502, Playa 11300, Havana (Cuba); Espen, Piet Van; Remortel, Nick Van [University of Antwerp, CGB, Groenenborgerlaan 171, 2020 Antwerpen (Belgium)
2014-11-15
Highlights: • We present a calculation procedure for dpa cross section in solids under irradiation. • Improvement about 10–90% for the gamma irradiation induced dpa cross section. • Improvement about 5–50% for the electron irradiation induced dpa cross section. • More precise results (20–70%) for thin samples irradiated with electrons. - Abstract: Several authors had estimated the displacements per atom cross sections under different approximations and models, including most of the main gamma- and electron-material interaction processes. These previous works used numerical approximation formulas which are applicable for limited energy ranges. We proposed the Monte Carlo assisted Classical Method (MCCM), which relates the established theories about atom displacements to the electron and positron secondary fluence distributions calculated from the Monte Carlo simulation. In this study the MCCM procedure is adapted in order to estimate the displacements per atom cross sections for gamma and electron irradiation. The results obtained through this procedure are compared with previous theoretical calculations. An improvement in about 10–90% for the gamma irradiation induced dpa cross section is observed in our results on regard to the previous evaluations for the studied incident energies. On the other hand, the dpa cross section values produced by irradiation with electrons are improved by our calculations in about 5–50% when compared with the theoretical approximations. When thin samples are irradiated with electrons, more precise results are obtained through the MCCM (in about 20–70%) with respect to the previous studies.
Atomic displacements in ferroelectric trigonal and orthorhombic boracite structures
Dowty, Eric; Clark, J.R.
1972-01-01
New crystal-structure refinements of Pca21 boracite, Mg3ClB7O13, and R??{lunate}c ericaite, Fe2.4Mg0.6ClB7O13, show that some boron and oxygen atoms are involved in the 'ferro' transitions as well as the metal and halogen atoms. The atomic displacements associated with the polarity changes are as large as 0.6A??. ?? 1972.
Electronic Structure of Helium Atom in a Quantum Dot
Jayanta, K. Saha; Bhattacharyya, S.; T. K., Mukherjee
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
Determination of diffusion coefficients of oxygen atoms in ZrO2 using first-principles calculations
International Nuclear Information System (INIS)
Density functional theory and nudged elastic band calculations were performed in order to determine the diffusion coefficient for oxygen from monoclinic ZrO2. The calculated values for monoclinic ZrO2 at 1000 K and 1500 K were 5.88 × 10-16 cm2s-1 and 2.91 × 10-11 cm2s-1, respectively, and agreed with previously determined experimental values. In addition, the results of the nudged elastic band calculations suggest that interstitial oxygen sites exist between stable oxygen sites, and if oxygen atoms occupy these sites, stable structures with values for the lattice angle β of greater than 80.53° may be obtained. (author)
Institute of Scientific and Technical Information of China (English)
XIAO Hai; LI Jun
2008-01-01
Benchmark calculations on the molar atomization enthalpy, geometry, and vibrational frequencies of uranium hexafluoride (UF6) have been performed by using relativistic density functional theory (DFT) with various levels of relativistic effects, different types of basis sets, and exchange-correlation functionals. Scalar relativistic effects are shown to be critical for the structural properties. The spin-orbit coupling effects are important for the calculated energies, but are much less important for other calculated ground-state properties of closed-shell UF6. We conclude through systematic investigations that ZORA- and RECP-based relativistic DFT methods are both appropriate for incorporating relativistic effects. Comparisons of different types of basis sets (Slater, Gaussian, and plane-wave types) and various levels of theoretical approximation of the exchange-correlation functionals were also made.
Quantum-mechanical calculations of cross sections for electron collisions with atoms and molecules
Bartschat, Klaus; Zatsarinny, Oleg
2016-01-01
An overview of quantum-mechanical methods to generate cross-section data for electron collisions with atoms and molecules is presented. Particular emphasis is placed on the time-independent close-coupling approach, since it is particularly suitable for low-energy collisions and also allows for systematic improvements as well as uncertainty estimates. The basic ideas are illustrated with examples for electron collisions with argon atoms and methane. For many atomic systems, such as e-Ar collisions, highly reliable cross sections can now be computed with quantified uncertainties. On the other hand, while electron collision calculations with molecules do provide key input data for plasma models, the methods and computer codes presently used require further development to make these inputs robust.
Semiclassical Calculation of Recurrence Spectra of Rydberg Hydrogen Atom Near a Metal Surface
Institute of Scientific and Technical Information of China (English)
WANG De-Hua
2009-01-01
Using closed orbit theory, we give a clear physical picture description of the Rydberg hydrogen atom near a metal surface and calculate the Fourier transformed recurrence spectra of this system at different scaled energies below ionization threshold.The results show that with the increase of the scaled energy, the number of the closed orbit increases greatly.Some of the orbits are created by the bifurcation of the perpendicular orbit.This case is quite similar to the Rydberg atom in an electric field.When the scaled energy increases furthermore, chaotic orbits appear.This study provides a different perspective on the dynamical behavior of the Rydberg atom near a metal surface.
Institute of Scientific and Technical Information of China (English)
Wang De-Hua; Lin Sheng-Lu
2004-01-01
Closed orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. By developing the closed orbit theory from two degrees of freedom to three non-separable degrees of freedom, we calculated the recurrence spectra of He Rydberg atom in perpendicular electric and magnetic fields. The closed orbits in the corresponding classical system have also been obtained. Fourier transformed spectra of He atoms have allowed direct comparison between the resonance peaks and the scaled action values of closed orbits, whereas the nonhydrogenic resonance can be explained in terms of the new orbits created by the core scattering. The semiclassical result is in good agreement with the quantum spectra, which suggests that our method is correct.
Structures of 38-atom gold-platinum nanoalloy clusters
Energy Technology Data Exchange (ETDEWEB)
Ong, Yee Pin; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technology, Multimedia University, Melaka Campus, 75450 Melaka (Malaysia)
2015-04-24
Bimetallic nanoclusters, such as gold-platinum nanoclusters, are nanomaterials promising wide range of applications. We perform a numerical study of 38-atom gold-platinum nanoalloy clusters, Au{sub n}Pt{sub 38−n} (0 ≤ n ≤ 38), to elucidate the geometrical structures of these clusters. The lowest-energy structures of these bimetallic nanoclusters at the semi-empirical level are obtained via a global-minimum search algorithm known as parallel tempering multi-canonical basin hopping plus genetic algorithm (PTMBHGA), in which empirical Gupta many-body potential is used to describe the inter-atomic interactions among the constituent atoms. The structures of gold-platinum nanoalloy clusters are predicted to be core-shell segregated nanoclusters. Gold atoms are observed to preferentially occupy the surface of the clusters, while platinum atoms tend to occupy the core due to the slightly smaller atomic radius of platinum as compared to gold’s. The evolution of the geometrical structure of 38-atom Au-Pt clusters displays striking similarity with that of 38-atom Au-Cu nanoalloy clusters as reported in the literature.
Presentation of Atomic Structure in Turkish General Chemistry Textbooks
Niaz, Mansoor; Costu, Bayram
2009-01-01
Research in science education has recognized the importance of teaching atomic structure within a history and philosophy of science perspective. The objective of this study is to evaluate general chemistry textbooks published in Turkey based on the eight criteria developed in previous research. Criteria used referred to the atomic models of…
An universal algorithm of calculating terms of atomic many-body perturbation theory
Dzuba, V A
2007-01-01
An algorithm, based on numerical description of the terms of many-body perturbation theory (Goldstone diagrams), is presented. The algorithm assumes a basis set of orthogonal single-electron orbitals supplied by the user. These orbitals are the eigenstates of the Dirac operator in the spherically-symmetric case. Apart from this the algorithm is practically free from any limitations and can be used for calculating of wide range of atomic properties in any order of the perturbation theory and with any external field applied to the atom. The use of the algorithm is illustrated by calculating of the second and third order correlation corrections to the ground state energies of sodium, copper and gallium.
Neutron and gamma ray calculation for Hiroshima-type atomic bomb
Energy Technology Data Exchange (ETDEWEB)
Hoshi, Masaharu; Endo, Satoru; Takada, Jun [Hiroshima Univ. (Japan). Research Inst. for Radiation Biology and Medicine; Iwatani, Kazuo; Oka, Takamitsu; Shizuma, Kiyoshi; Fujita, Shoichiro; Hasai, Hiromi
1998-03-01
We looked at the radiation dose of Hiroshima and Nagasaki atomic bomb again in 1986. We gave it the name of ``Dosimetry System 1986`` (DS86). We and other groups have measured the expose dose since 1986. Now, the difference between data of {sup 152}Eu and the calculation result on the basis of DS86 was found. To investigate the reason, we carried out the calculations of neutron transport and neutron absorption gamma ray for Hiroshima atomic bomb by MCNP3A and MCNP4A code. The problems caused by fast neutron {sup 32}P from sulfur in insulator of pole. To correct the difference, we investigated many models and found agreement of all data within 1 km. (S.Y.)
Calculation of the fine structure of the level in Rydberg state of lithium
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The level shift and level formula of lithium atom in Rydberg states are achieved by means of the calculation of polarization of the atomic core (including the contribution of dipole moment, quadrupole moment and octupole moment);meanwhile, the effect of relativity theory, the orbital angular momentum L and the spin angular momentum S coupling (LS coupling), and high order correction of the effective potential are considered. The some fine structures (N=5～12,L=4～9,J=L±1/2) and the corresponding level intervals in Rydberg states can be calculated by the above-mentioned level formula and compared with correlated experimental data.
Block Tridiagonal Matrices in Electronic Structure Calculations
DEFF Research Database (Denmark)
Petersen, Dan Erik
is developed and compared to standard Gaussian elimination, where it is shown to be qualitatively quicker for the task of determining the block tridiagonal portion of the Green’s function matrix. The Sweep algorithm is then parallelized via a straightforward approach in order to enable moderate speedup...... and memory distribution. The well known block cyclic reduction algorithm first developed by Gene Golub is then presented and analyzed for further expanding our parallel options, and finally a new hybrid method that combines block cyclic reduction and a form of Schur complement calculation is introduced...... in the Landauer–Büttiker ballistic transport regime. These calculations concentrate on determining the so– called Green’s function matrix, or portions thereof, which is the inverse of a block tridiagonal general complex matrix. To this end, a sequential algorithm based on Gaussian elimination named Sweeps...
The Calculations of Oscillator Strengths and Transition Probabilities for Atomic Fluorine
ÇELİK, Gültekin; KILIÇ, H. Şükür; Akin, Erhan
2006-01-01
Oscillator strengths for transitions between individual lines belonging to some doublet and quartet terms, and multiplet transition probabilities of atomic fluorine have been calculated using weakest bound electron potential model theory (WBEPMT). In the determination of relevant parameters, we employed numerical non-relativistic Hartree-Fock (NRHF) wave functions for expectation values of radii and the necessary energy values have been taken from experimental energy data in the liter...
International Nuclear Information System (INIS)
We have analyzed differential cross sections (DCSs) for the elastic scattering of electrons by neutral atoms that have been derived from two commonly used atomic potentials: the Thomas-Fermi-Dirac (TFD) potential and the Dirac-Hartree-Fock (DHF) potential. DCSs from the latter potential are believed to be more accurate. We compared DCSs for six atoms (H, Al, Ni, Ag, Au, and Cm) at four energies (100, 500, 1000, and 10 000 eV) from two databases issued by the National Institute of Standards and Technology in which DCSs had been obtained from the TFD and DHF potentials. While the DCSs from the two potentials had similar shapes and magnitudes, there can be pronounced deviations (up to 70%) for small scattering angles for Al, Ag, Au, and Cm. In addition, there were differences of up to 400% at scattering angles for which there were deep minima in the DCSs; at other angles, the differences were typically less than 20%. The DCS differences decreased with increasing electron energy. DCSs calculated from the two potentials were compared with measured DCSs for six atoms (He, Ne, Ar, Kr, Xe, and Hg) at energies between 50 eV and 3 keV. For Ar, the atom for which experimental data are available over the largest energy range there is good agreement between the measured DCSs and those calculated from the TFD and DHF potentials at 2 and 3 keV, but the experimental DCSs agree better with the DCSs from the DHF potential at lower energies. A similar trend is found for the other atoms. At energies less than about 1 keV, there are increasing differences between the measured DCSs and the DCSs calculated from the DHF potential. These differences were attributed to the neglect of absorption and polarizability effects in the calculations. We compare transport cross sections for H, Al, Ni, Ag, Au, and Cm obtained from the DCSs for each potential. For energies between 200 eV and 1 keV, the largest differences are about 20% (for H, Au, and Cm); at higher energies, the differences are
Calculation of moments of structure functions
International Nuclear Information System (INIS)
The progress on the lattice computation of low moments of both the unpolarised and polarised nucleon structure functions is reviewed with particular emphasis on continuum and chiral extrapolations and comparison between quenched and unquenched fermions. (orig.)
International Nuclear Information System (INIS)
Analyses of the resonant multiphoton ionization of atoms require knowledge of ac Stark energy shifts and of multiphoton, bound-to-bound state, transition amplitudes. In this paper, we consider the three-photon photoionization of hydrogen atoms at frequencies that are at and surrounding the two-photon 1s to 2s resonance. AC energy shift sums of both the 1s and 2s states are calculated as a function of the laser frequency along with two-photon 1s → 2s resonant transition amplitude sums. These quantities are calculated using an extended version of a method, which has often been employed in a variety of ways, of calculating these sums by expressing them in terms of solutions to a variety of differential equations that are derived from the different sums being evaluated. We demonstrate how exact solutions are obtained to these differential equations, which lead to exact evaluations of the corresponding sums. A variety of different cases are analysed, some involving analytic continuation, some involving real number analysis and some involving complex number analysis. A dc Stark sum calculation of the 2s state is carried out to illustrate the case where analytic continuation, pole isolation and pole subtraction are required and where the calculation can be carried out analytically; the 2s state, ac Stark shift sum calculations involve a case where no analytic continuation is required, but where the solution to the differential equation produces complex numbers owing to the finite photoionization lifetime of the 2s state. Results from these calculations are then used to calculate three-photon ionization probabilities of relevance to an analysis of the multiphoton ionization data published by Kyrala and Nichols (1991 Phys. Rev. A 44, R1450)
Atomic structures and oxygen dynamics of CeO2 grain boundaries
Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi
2016-02-01
Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells.
Institute of Scientific and Technical Information of China (English)
杨忠志; 沈尔忠
1996-01-01
On the basis of a more precise expression of the atomic effective electronegativity deduced from the density functional theory and electronegativity equalization principle, a new scheme for calculating the group electronegativity and the atomic charges in a group is proposed and programed, and various parameters of electronegativity and hardness are given for some common atoms. Through calculation, analysis and comparison of more than one hundred groups, it is shown that the results from this scheme are reasonable and may be extended.
Atomic fine structure in a space of constant curvature
Energy Technology Data Exchange (ETDEWEB)
Bessis, N.; Bessis, G.; Shamseddine, R. (Lyon-1 Univ., 69 - Villeurbanne (France))
1982-10-01
As a contribution to a tentative formulation of atomic physics in a curved space, the determination of atomic fine structure energies in a space of constant curvature is investigated. Starting from the Dirac equation in a curved space-time, the analogue of the Pauli equation in a general coordinate system is derived. The theoretical curvature induced shifts and splittings of the fine structure energy levels are put in evidence and examined for the particular case of the hydrogenic n=2 levels.
Interfacial Atomic Structure of Twisted Few-Layer Graphene
Ryo Ishikawa; Nathan R. Lugg; Kazutoshi Inoue; Hidetaka Sawada; Takashi Taniguchi; Naoya Shibata; Yuichi Ikuhara
2016-01-01
A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterize...
Atomic fine structure in a space of constant curvature
International Nuclear Information System (INIS)
As a contribution to a tentative formulation of atomic physics in a curved space, the determination of atomic fine structure energies in a space of constant curvature is investigated. Starting from the Dirac equation in a curved space-time, the analogue of the Pauli equation in a general coordinate system is derived. The theoretical curvature induced shifts and splittings of the fine structure energy levels are put in evidence and examined for the particular case of the hydrogenic n=2 levels. (author)
Mechanical deformation of atomic-scale metallic contacts: Structure and mechanisms
DEFF Research Database (Denmark)
Sørensen, Mads Reinholdt; Brandbyge, Mads; Jacobsen, Karsten Wedel
1998-01-01
We have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain using molecular dynamics and effective medium theory potentials. The evolution of the structure of the contacts and the underlying deformation mechanisms are described along with the calculated ele...
Structure function calculations for Ostwald Ripening processes
Hassan, Razi A.
1990-01-01
A program for computing the structure function for configurations involved in Ostwald Ripening was written. The basic algorithms are derived from a mathematical analysis of a two-dimensional model system developed by Bortz, et. al. (1974). While it is expected that the values form the computer simulations will reflect Ostwald Ripening, at this point the program is still being tested. Some preliminary runs seem to justify the expectations.
The structural and electronic properties of amorphous HgCdTe from first-principles calculations
International Nuclear Information System (INIS)
Amorphous mercury cadmium telluride (a-MCT) model structures, with x being 0.125 and 0.25, are obtained from first-principles calculations. We generate initial structures by computation alchemy method. It is found that most atoms in the network of amorphous structures tend to be fourfold and form tetrahedral structures, implying that the chemical ordered continuous random network with some coordination defects is the ideal structure for a-MCT. The electronic structure is also concerned. The gap is found to be 0.30 and 0.26 eV for a-Hg0.875Cd0.125Te and a-Hg0.75Cd0.25Te model structures, independent of the composition. By comparing with the properties of crystalline MCT with the same composition, we observe a blue-shift of energy band gap. The localization of tail states and its atomic origin are also discussed. (paper)
Relativistic calculations of double $K$-shell photoionization for neutral medium-$Z$ atoms
Yerokhin, V A; Fritzsche, S
2014-01-01
Fully relativistic calculations are presented for the double $K$-shell photoionization cross section for several neutral medium-$Z$ atoms, from magnesium ($Z = 10$) up to silver ($Z = 47$). The calculations take into account all multipoles of the absorbed photon as well as the retardation of the electron-electron interaction. The approach is based on the partial-wave representation of the Dirac continuum states and uses the Green-function technique to represent the full Dirac spectrum of intermediate states. The method is strictly gauge invariant, which is used as an independent cross check of the computational procedure. The calculated ratios of the double-to-single $K$-shell ionization cross sections are compared with the experimental data and with previous computations.
International Nuclear Information System (INIS)
Isotopic selectivity calculations are carried out for minor calcium isotopes against the major isotope 40Ca for the single-resonance two-step and double-resonance three-step photoionization schemes with narrow-band lasers by using spectral simulation (SS) and modified spectrum (MS) approaches. The results of these calculations are compared with the density matrix (DM) results reported in the literature. It is noted that the values of isotopic selectivity from the SS approach do not agree with those from the DM approach whereas the MS approach, considering hole burning in the Doppler-broadened atomic spectrum, predicts selectivity values which are in good agreement with the DM results. It is argued that one can adequately use the simple MS approach rather than the complex DM approach for the calculation of isotopic selectivity of multi-step photoionization with single-frequency lasers. (author)
Investigation of the diffusion of atomic fission products in UC by density functional calculations
Energy Technology Data Exchange (ETDEWEB)
Bévillon, Émile, E-mail: emile.bevillon@yahoo.fr [IRSN, SEMIC, DPAM, LETR, Centre de Cadarache, 13115 Saint Paul Lez Durance (France); Ducher, Roland; Barrachin, Marc; Dubourg, Roland [IRSN, SEMIC, DPAM, LETR, Centre de Cadarache, 13115 Saint Paul Lez Durance (France)
2013-03-15
Activation energies of U and C atoms self-diffusion in UC, as well as activation energies of hetero-diffusion of fission products (FPs) are investigated by first-principles calculations. According to a previous study which showed a likely U site occupation was favoured for all the FPs, their diffusion is restricted to the uranium sublattice of UC in the present study. In this framework, long-range displacements are only possible through a concerted mechanism with a surrounding uranium vacancy. Using the apparent formation energies of the uranium vacancy defect calculated in our previous study and the classical approach used in UO{sub 2} by Andersson et al., the activation energies of the main fission products in the various stoichiometric domains have been calculated. The results are compared to those obtained with the five frequency model applied to two representative fission products, Xe and Zr. Interestingly, despite strong differences of formalism, both models provided similar activation energies.
Investigation of the diffusion of atomic fission products in UC by density functional calculations
Bévillon, Émile; Ducher, Roland; Barrachin, Marc; Dubourg, Roland
2013-03-01
Activation energies of U and C atoms self-diffusion in UC, as well as activation energies of hetero-diffusion of fission products (FPs) are investigated by first-principles calculations. According to a previous study which showed a likely U site occupation was favoured for all the FPs, their diffusion is restricted to the uranium sublattice of UC in the present study. In this framework, long-range displacements are only possible through a concerted mechanism with a surrounding uranium vacancy. Using the apparent formation energies of the uranium vacancy defect calculated in our previous study and the classical approach used in UO2 by Andersson et al., the activation energies of the main fission products in the various stoichiometric domains have been calculated. The results are compared to those obtained with the five frequency model applied to two representative fission products, Xe and Zr. Interestingly, despite strong differences of formalism, both models provided similar activation energies.
Understanding the proton radius puzzle: Nuclear structure effects in light muonic atoms
Directory of Open Access Journals (Sweden)
Ji Chen
2016-01-01
Full Text Available We present calculations of nuclear structure effects to the Lamb shift in light muonic atoms. We adopt a modern ab-initio approach by combining state-of-the-art nuclear potentials with the hyperspherical harmonics method. Our calculations are instrumental to the determination of nuclear charge radii in the Lamb shift measurements, which will shed light on the proton radius puzzle.
MUTA calculations of a laser-produced Mg hollow atom spectrum
International Nuclear Information System (INIS)
A study is made of the spectra produced from a short-wavelength long-pulse (nanosecond) laser incident on a Mg plasma. A very complex experimental spectrum is analyzed in detail by comparison with large-scale atomic kinetics calculations using the recently developed mixed-UTA (MUTA) model. We find that the experimental spectrum appears to contain lines from many inner-shell transitions from ions ranging from neutral Mg to Li-like Mg. Lines from transitions such as 1s-3l, 1s-4l, and from hollow atoms (where in this context hollow atoms refer to ions with an empty 1s shell) are observed. The inclusion of very small fractions of hot electrons is demonstrated to make significant differences to the spectra. Although it is found that the calculations do not match perfectly the experimental spectra, reasonable agreement between the experiment and the theory can be obtained if temperature and density gradients are assumed present in the experimental conditions
International Nuclear Information System (INIS)
The paper gives a brief survey of the fifth three-dimensional dynamic Atomic Energy Research benchmark calculation results received with the code DYN3D/ATHLET at NRI Rez. This benchmark was defined at the seventh Atomic Energy Research Symposium (Hoernitz near Zittau, 1997). Its initiating event is a symmetrical break of the main steam header at the end of the first fuel cycle and hot shutdown conditions with one stuck out control rod group. The calculations were performed with the externally coupled codes ATHLET Mod.1.1 Cycle C and DYN3DH1.1/M3. The standard WWER-440/213 input deck of ATHLET code was adopted for benchmark purposes and for coupling with the code DYN3D. The first part of paper contains a brief characteristics of NPP input deck and reactor core model. The second part shows the time dependencies of important global and local parameters. In comparison with the results published at the eighth Atomic Energy Research Symposium (Bystrice nad Pernstejnem, 1998), the results published in this paper are based on improved ATHLET descriptions of control and safety systems. (Author)
DEFF Research Database (Denmark)
Johnsen, Kristinn; Yngvason, Jakob
1996-01-01
We report on a numerical study of the density matrix functional introduced by Lieb, Solovej, and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes exactly the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge Z and...... obtained by other methods. For iron at B=1012 G the ground-state energy differs by less than 2% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative...... the electron number N tend to infinity with N/Z fixed, and the magnetic field B tends to infinity in such a way that B/Z4/3→∞. We have calculated electronic density profiles and ground-state energies for values of the parameters that prevail on neutron star surfaces and compared them with results...
Rotational Spectrum and Carbon Atom Structure of Dihydroartemisinic Acid
Evangelisti, Luca; Seifert, Nathan A.; Spada, Lorenzo; Pate, Brooks
2016-06-01
Dihydroartemisinic acid (DHAA, C15H24O2, five chiral centers) is a precursor in proposed low-cost synthetic routes to the antimalarial drug artemisinin. In one reaction process being considered in pharmaceutical production, DHAA is formed from an enantiopure sample of artemisinic acid through hydrogenation of the alkene. This reaction needs to properly set the stereochemistry of the asymmetric carbon for the synthesis to produce artemisinin. A recrystallization process can purify the diastereomer mixture of the hydrogenation reaction if the unwanted epimer is produced in less than 10% abundance. There is a need in the process analytical chemistry to rapidly (less than 1 min) measure the diastereomer excess and current solutions, such a HPLC, lack the needed measurement speed. The rotational spectrum of DHAA has been measured at 300:1 signal-to-noise ratio in a chirped-pulsed Fourier transform microwave spectrometer operating from 2-8 GHz using simple heating of the compound. The 13C isotope analysis provides a carbon atom structure that confirms the diastereomer. This structure is in excellent agreement with quantum chemistry calculations at the B2PLYPD3/ 6-311++G** level of theory. The DHAA spectrum is expected to be fully resolved from the unwanted diastereomer raising the potential for fast diastereomer excess measurement by rotational spectroscopy in the pharmaceutical production process.
Ab initio calculations of electronic structure of anatase TiO2
Institute of Scientific and Technical Information of China (English)
Chen Qiang; Cao Hong-Hong
2004-01-01
This paper presents the results of the self-consistent calculations on the electronic structure of anatase phase of TiO2. The calculations were performed using the full potential-linearized augmented plane wave method (FP-LAPW)in the framework of the density functional theory (DFT) with the generalized gradient approximation (GGA). The fully optimized structure, obtained by minimizing the total energy and atomic forces, is in good agreement with experiment.We also calculated the band structure and the density of states. In particular, the calculated band structure prefers an indirect transition between wlence and conduction bands of anatase TiO2, which may be helpful for clarifying the ambiguity in other theoretical works.
Institute of Scientific and Technical Information of China (English)
WANGDe-Hua; DINGShi-Liang
2003-01-01
Closed-orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. Using the dosed-orblt theory and classical perturbation theory, we calculate the scaled recurrence spectra of Lithium atom in magnetic field plus a weak perpendicular electric field. The results show when the crossed electric field is added, the recurrence spectra are weakened greatly. As the scaled electric field f increases, the peaks of the recurrence spectra lose strength. Some recurrences are very sensitive and fall off rapidly as f increases, others persist till much higher f. As the electric field is stronger, some of the peaks revive. This phenomenon, caused by the interference among the electron waves that return to the nucleus, can be computed from the azimuthal dependence of the classical closed orbits.
Institute of Scientific and Technical Information of China (English)
WANG De-Hua; DING Shi-Liang
2003-01-01
Closed-orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. Using the closed-orbit theory and classical perturbation theory, we calculate the scaled recurrence spectra of Lithium atom in magnetic field plus a weak perpendicular electric field. The results show when the crossed electric field is added, the recurrence spectra are weakened greatly. As the scaled electric field f increases, the peaks of the recurrence spectra lose strength. Some recurrences are very sensitive and fall off rapidly as f increases; others persist till much higher f . As the electric field is stronger, some of the peaks revive. This phenomenon, caused by the interference among the electron waves that return to the nucleus, can be computed from the azimuthal dependence of the classical closed orbits.
Ling, Tao; Yan, Dong-Yang; Jiao, Yan; Wang, Hui; Zheng, Yao; Zheng, Xueli; Mao, Jing; Du, Xi-Wen; Hu, Zhenpeng; Jaroniec, Mietek; Qiao, Shi-Zhang
2016-01-01
Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts. PMID:27650485
A novel Gaussian-Sinc mixed basis set for electronic structure calculations
Jerke, Jonathan L.; Lee, Young; Tymczak, C. J.
2015-08-01
A Gaussian-Sinc basis set methodology is presented for the calculation of the electronic structure of atoms and molecules at the Hartree-Fock level of theory. This methodology has several advantages over previous methods. The all-electron electronic structure in a Gaussian-Sinc mixed basis spans both the "localized" and "delocalized" regions. A basis set for each region is combined to make a new basis methodology—a lattice of orthonormal sinc functions is used to represent the "delocalized" regions and the atom-centered Gaussian functions are used to represent the "localized" regions to any desired accuracy. For this mixed basis, all the Coulomb integrals are definable and can be computed in a dimensional separated methodology. Additionally, the Sinc basis is translationally invariant, which allows for the Coulomb singularity to be placed anywhere including on lattice sites. Finally, boundary conditions are always satisfied with this basis. To demonstrate the utility of this method, we calculated the ground state Hartree-Fock energies for atoms up to neon, the diatomic systems H2, O2, and N2, and the multi-atom system benzene. Together, it is shown that the Gaussian-Sinc mixed basis set is a flexible and accurate method for solving the electronic structure of atomic and molecular species.
Energy Technology Data Exchange (ETDEWEB)
Margulis, Vl.A. [Department of Physics, N.P. Ogarev Mordovian State University, Saransk 430000 (Russian Federation)]. E-mail: 612033@inbox.ru; Muryumin, E.E. [Department of Chemistry, N.P. Ogarev Mordovian State University, Saransk 430000 (Russian Federation)
2007-03-01
We report a model calculation of the chemisorption energies {delta}E{sub ads} of single fluorine atoms on the outer surface of zigzag single-walled carbon nanotubes (Z-SWCNTs) (p,0) with p ranging from 11 to 21. A simplified model based on an effective-mass theory is adopted to describe the electronic structure of the nanotubes. Chemisorption is treated within the Anderson-Newns approach, which takes account of Coulomb interaction between adsorbate electrons. Considering adsorption of an adatom directly on top of a surface carbon atom, we find that in the case of a fluorine atom bonded to the sidewall of the nanotubes, the absolute values of {delta}E{sub ads} are in the range 4.3-5.5eV for Z-SWCNTs with typical diameters of 0.86-1.66nm, larger {delta}E{sub ads} values being associated with semiconducting tubes. For the latter ones, {delta}E{sub ads} decreases rather significantly as the radius R of the tubes increases, tending towards the ''infinite'' radius graphene case, whereas for metallic tubes {delta}E{sub ads} slightly increases with increasing R. The localized acceptor states induced by a fluorine atom in the band gap of the semiconducting tubes are found to be responsible for such difference in the behaviour of {delta}E{sub ads} for the two above-mentioned types of tubes. The results obtained shed light on the possible mechanism of the atomic fluorine adsorption-induced hole-doping of the semiconducting tubes, which might significantly affect the transport properties of these tubes.
Ab-initio calculations of electronic structure and optical properties of TiAl alloy
Energy Technology Data Exchange (ETDEWEB)
Hussain, Altaf [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63120 (Pakistan); Sikandar Hayat, Sardar, E-mail: sikandariub@yahoo.co [Department of Physics, Hazara University, Mansehra 21300 (Pakistan); Choudhry, M.A. [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63120 (Pakistan)
2011-05-01
The electronic structures and optical properties of TiAl intermetallic alloy system are studied by the first-principle orthogonalized linear combination of atomic orbitals method. Results on the band structure, total and partial density of states, localization index, effective atomic charges, and optical conductivity are presented and discussed in detail. Total density of states spectra reveal that (near the Fermi level) the majority of the contribution is from Ti-3d states. The effective charge calculations show an average charge transfer of 0.52 electrons from Ti to Al in primitive cell calculations of TiAl alloy. On the other hand, calculations using supercell approach reveal an average charge transfer of 0.48 electrons from Ti to Al. The localization index calculations, of primitive cell as well as of supercell, show the presence of relatively localized states even above the Fermi level for this alloy. The calculated optical conductivity spectra of TiAl alloy are rich in structures, showing the highest peak at 5.73 eV for supercell calculations. Calculations of the imaginary part of the linear dielectric function show a prominent peak at 5.71 eV and a plateau in the range 1.1-3.5 eV.
Rittenhouse, Robert C.
2015-01-01
The "atoms first" philosophy, adopted by a growing number of General Chemistry textbook authors, places greater emphasis on atomic structure as a key to a deeper understanding of the field of chemistry. A pivotal concept needed to understand the behavior of atoms is the restriction of an atom's energy to specific allowed values. However,…
Unraveling the atomic structure of ultrafine iron clusters
Wang, Hongtao
2012-12-18
Unraveling the atomic structures of ultrafine iron clusters is critical to understanding their size-dependent catalytic effects and electronic properties. Here, we describe the stable close-packed structure of ultrafine Fe clusters for the first time, thanks to the superior properties of graphene, including the monolayer thickness, chemical inertness, mechanical strength, electrical and thermal conductivity. These clusters prefer to take regular planar shapes with morphology changes by local atomic shuffling, as suggested by the early hypothesis of solid-solid transformation. Our observations differ from observations from earlier experimental study and theoretical model, such as icosahedron, decahedron or cuboctahedron. No interaction was observed between Fe atoms or clusters and pristine graphene. However, preferential carving, as observed by other research groups, can be realized only when Fe clusters are embedded in graphene. The techniques introduced here will be of use in investigations of other clusters or even single atoms or molecules.
Connolly Surface on an Atomic Structure via Voronoi Diagram of Atoms
Institute of Scientific and Technical Information of China (English)
Joonghyun Ryu; Rhohun Park; Deok-Soo Kim
2006-01-01
One of the most important geometric structures of a protein is the Connolly surface of protein since a Connolly surface plays an important role in protein folding, docking, interactions between proteins, amongst other things. This paper presents an algorithm for precisely and efficiently computing the Connolly surface of a protein using a proposed geometric construct called β-shape based on the Voronoi diagram of atoms in the protein. Given the Voronoi diagram of atoms based on the Euclidean distance from the atom surfaces, the proposed algorithm first computes a β-shape with an appropriate probe. Then, the Connolly surface is computed by employing the blending operation on the atomic complex of the protein by the given probe.
Calculation of the surface energy of fcc metals with modified embedded-atom method
Institute of Scientific and Technical Information of China (English)
Zhang Jian-Min; Ma Fei; Xu Ke-Wei
2004-01-01
The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, Al, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, Al, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy.
Fluctuations of spacetime and hyperfine structure of the hydrogen atom
Energy Technology Data Exchange (ETDEWEB)
Goeklue, Ertan [ZARM-Universitaet Bremen (Germany); Rivas, Juan Israel; Camacho, Abel [Universidad Autonoma Metropolitana-Iztapalapa, Mexico (Mexico)
2012-07-01
We consider the consequences of the presence of metric fluctuations upon the properties of a hydrogen atom. Particularly, we introduce these metric fluctuations in the corresponding effective Schroedinger equation and deduce the modifications that they entail upon the hyperfine structure related to a hydrogen atom. We will find the change that these effects imply for the ground state energy of the system and obtain a bound for its size comparing our theoretical predictions against the experimental uncertainty reported in the literature.
A fully relativistic approach for calculating atomic data for highly charged ions
Energy Technology Data Exchange (ETDEWEB)
Zhang, Hong Lin [Los Alamos National Laboratory; Fontes, Christopher J [Los Alamos National Laboratory; Sampson, Douglas H [PENNSYLVANIA STATE UNIV
2009-01-01
We present a review of our fully relativistic approach to calculating atomic data for highly charged ions, highlighting a research effort that spans twenty years. Detailed discussions of both theoretical and numerical techniques are provided. Our basic approach is expected to provide accurate results for ions that range from approximately half ionized to fully stripped. Options for improving the accuracy and range of validity of this approach are also discussed. In developing numerical methods for calculating data within this framework, considerable emphasis is placed on techniques that are robust and efficient. A variety of fundamental processes are considered including: photoexcitation, electron-impact excitation, electron-impact ionization, autoionization, electron capture, photoionization and photorecombination. Resonance contributions to a variety of these processes are also considered, including discussions of autoionization, electron capture and dielectronic recombination. Ample numerical examples are provided in order to illustrate the approach and to demonstrate its usefulness in providing data for large-scale plasma modeling.
Energy Technology Data Exchange (ETDEWEB)
Bross, David H.; Parmar, Payal; Peterson, Kirk A., E-mail: kipeters@wsu.edu [Department of Chemistry, Washington State University, Pullman, Washington 99164-4630 (United States)
2015-11-14
The first 6 ionization potentials (IPs) of the uranium atom have been calculated using multireference configuration interaction (MRCI+Q) with extrapolations to the complete basis set limit using new all-electron correlation consistent basis sets. The latter was carried out with the third-order Douglas-Kroll-Hess Hamiltonian. Correlation down through the 5s5p5d electrons has been taken into account, as well as contributions to the IPs due to the Lamb shift. Spin-orbit coupling contributions calculated at the 4-component Kramers restricted configuration interaction level, as well as the Gaunt term computed at the Dirac-Hartree-Fock level, were added to the best scalar relativistic results. The final ionization potentials are expected to be accurate to at least 5 kcal/mol (0.2 eV) and thus more reliable than the current experimental values of IP{sub 3} through IP{sub 6}.
Learning Approach on the Ground State Energy Calculation of Helium Atom
Shah, Syed Naseem Hussain
2010-07-01
This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function. The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.
New version: GRASP2K relativistic atomic structure package
Jönsson, P.; Gaigalas, G.; Bieroń, J.; Fischer, C. Froese; Grant, I. P.
2013-09-01
, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 730252 No. of bytes in distributed program, including test data, etc.: 14808872 Distribution format: tar.gz Programming language: Fortran. Computer: Intel Xeon, 2.66 GHz. Operating system: Suse, Ubuntu, and Debian Linux 64-bit. RAM: 500 MB or more Classification: 2.1. Catalogue identifier of previous version: ADZL_v1_0 Journal reference of previous version: Comput. Phys. Comm. 177 (2007) 597 Does the new version supersede the previous version?: Yes Nature of problem: Prediction of atomic properties — atomic energy levels, oscillator strengths, radiative decay rates, hyperfine structure parameters, Landé gJ-factors, and specific mass shift parameters — using a multiconfiguration Dirac-Hartree-Fock approach. Solution method: The computational method is the same as in the previous GRASP2K [1] version except that for v3 codes the njgraf library module [2] for recoupling has been replaced by librang [3,4]. Reasons for new version: New angular libraries with improved performance are available. Also methodology for transforming from jj- to LSJ-coupling has been developed. Summary of revisions: New angular libraries where the coefficients of fractional parentage have been extended to j=9/2, making calculations feasible for the lanthanides and actinides. Inclusion of a new program jj2lsj, which reports the percentage composition of the wave function in LSJ. Transition programs have been modified to produce a file of transition data with one record for each transition in the same format as Atsp2K [C. Froese Fischer, G. Tachiev, G. Gaigalas and M.R. Godefroid, Comput. Phys. Commun. 176 (2007) 559], which identifies each atomic state by the total energy and a label for the CSF with the largest expansion coefficient in LSJ intermediate coupling. Updated to 64-bit architecture. A
Roberts, B M; Flambaum, V V; Pospelov, M; Stadnik, Y V
2016-01-01
We revisit the WIMP-type dark matter scattering on electrons that results in atomic ionization, and can manifest itself in a variety of existing direct-detection experiments. Unlike the WIMP-nucleon scattering, where current experiments probe typical interaction strengths much smaller than the Fermi constant, the scattering on electrons requires a much stronger interaction to be detectable, which in turn requires new light force carriers. We account for such new forces explicitly, by introducing a mediator particle with scalar or vector couplings to dark matter and to electrons. We then perform state of the art numerical calculations of atomic ionization relevant to the existing experiments. Our goals are to consistently take into account the atomic physics aspect of the problem (e.g., the relativistic effects, which can be quite significant), and to scan the parameter space: the dark matter mass, the mediator mass, and the effective coupling strength, to see if there is any part of the parameter space that c...
Roberts, B. M.; Dzuba, V. A.; Flambaum, V. V.; Pospelov, M.; Stadnik, Y. V.
2016-06-01
We revisit the WIMP-type dark matter scattering on electrons that results in atomic ionization and can manifest itself in a variety of existing direct-detection experiments. Unlike the WIMP-nucleon scattering, where current experiments probe typical interaction strengths much smaller than the Fermi constant, the scattering on electrons requires a much stronger interaction to be detectable, which in turn requires new light force carriers. We account for such new forces explicitly, by introducing a mediator particle with scalar or vector couplings to dark matter and to electrons. We then perform state-of-the-art numerical calculations of atomic ionization relevant to the existing experiments. Our goals are to consistently take into account the atomic physics aspect of the problem (e.g., the relativistic effects, which can be quite significant) and to scan the parameter space—the dark matter mass, the mediator mass, and the effective coupling strength—to see if there is any part of the parameter space that could potentially explain the DAMA modulation signal. While we find that the modulation fraction of all events with energy deposition above 2 keV in NaI can be quite significant, reaching ˜50 %, the relevant parts of the parameter space are excluded by the XENON10 and XENON100 experiments.
Atomic structure of intracellular amorphous calcium phosphate deposits.
Betts, F; Blumenthal, N C; Posner, A S; Becker, G L; Lehninger, A L
1975-06-01
The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed.
Infrared image recognition based on structure sparse and atomic sparse parallel
Wu, Yalu; Li, Ruilong; Xu, Yi; Wang, Liping
2015-12-01
Use the redundancy of the super complete dictionary can capture the structural features of the image effectively, can achieving the effective representation of the image. However, the commonly used atomic sparse representation without regard the structure of the dictionary and the unrelated non-zero-term in the process of the computation, though structure sparse consider the structure feature of dictionary, the majority coefficients of the blocks maybe are non-zero, it may affect the identification efficiency. For the disadvantages of these two sparse expressions, a weighted parallel atomic sparse and sparse structure is proposed, and the recognition efficiency is improved by the adaptive computation of the optimal weights. The atomic sparse expression and structure sparse expression are respectively, and the optimal weights are calculated by the adaptive method. Methods are as follows: training by using the less part of the identification sample, the recognition rate is calculated by the increase of the certain step size and t the constraint between weight. The recognition rate as the Z axis, two weight values respectively as X, Y axis, the resulting points can be connected in a straight line in the 3 dimensional coordinate system, by solving the highest recognition rate, the optimal weights can be obtained. Through simulation experiments can be known, the optimal weights based on adaptive method are better in the recognition rate, weights obtained by adaptive computation of a few samples, suitable for parallel recognition calculation, can effectively improve the recognition rate of infrared images.
Calculation of inelastic helium atom scattering from H2/ NaCl(001)
DEFF Research Database (Denmark)
Bruch, L.W.; Hansen, Flemming Yssing; Traeger, F.
2011-01-01
The one-phonon inelastic low energy helium atom scattering theory is adapted to cases where the target monolayer is a p(1 × 1) commensurate square lattice. Experimental data for para-H2/NaCl(001) are re-analyzed and the relative intensities of energy loss peaks in the range 6 to 9 meV are determi......The one-phonon inelastic low energy helium atom scattering theory is adapted to cases where the target monolayer is a p(1 × 1) commensurate square lattice. Experimental data for para-H2/NaCl(001) are re-analyzed and the relative intensities of energy loss peaks in the range 6 to 9 me...... in the wave-packet-scattering calculation and a long series of Fourier amplitudes to represent the helium-target potential energy surface. A modified series is constructed in which a truncated Fourier expansion of the potential is constrained to give the exact value of the potential at some key points...... and which mimics the potential with fewer Fourier amplitudes. The shear horizontal phonon mode is again accessed by the helium scattering for small misalignment of the scattering plane relative to symmetry axes of the monolayer. For 1 misalignment, the calculated intensity of the longitudinal acoustic...
The grasp2K relativistic atomic structure package
Jönsson, P.; He, X.; Froese Fischer, C.; Grant, I. P.
2007-10-01
This paper describes grasp2K, a general-purpose relativistic atomic structure package. It is a modification and extension of the GRASP92 package by [F.A. Parpia, C. Froese Fischer, I.P. Grant, Comput. Phys. Comm. 94 (1996) 249]. For the sake of continuity, two versions are included. Version 1 retains the GRASP92 formats for wave functions and expansion coefficients, but no longer requires preprocessing and more default options have been introduced. Modifications have eliminated some errors, improved the stability, and simplified interactive use. The transition code has been extended to cases where the initial and final states have different orbital sets. Several utility programs have been added. Whereas Version 1 constructs a single interaction matrix for all the J's and parities, Version 2 treats each J and parity as a separate matrix. This block structure results in a reduction of memory use and considerably shorter eigenvectors. Additional tools have been developed for this format. The CPU intensive parts of Version 2 have been parallelized using MPI. The package includes a "make" facility that relies on environment variables. These make it easier to port the application to different platforms. The present version supports the 32-bit Linux and ibmSP environments where the former is compatible with many Unix systems. Descriptions of the features and the program/data flow of the package will be given in some detail in this report. Program summaryProgram title: grasp2K Catalogue identifier: ADZL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADZL_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 213 524 No. of bytes in distributed program, including test data, etc.: 1 328 588 Distribution format: tar.gz Programming language: Fortran and C Computer: Intel
Hao, Yajiang; Inhester, Ludger; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin
2015-07-01
We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging. PMID:26798806
Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity
Hao, Yajiang; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin
2015-01-01
We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging.
Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity
Directory of Open Access Journals (Sweden)
Yajiang Hao
2015-07-01
Full Text Available We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging.
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.
Atomic structure of grain boundaries in iron modeled using the atomic density function
Kapikranian, O.; Zapolsky, H; Domain, Ch.; Patte, R.; Pareige, C.; Radiguet, B.; Pareige, P.
2013-01-01
A model based on the continuous atomic density function (ADF) approach is applied to predict the atomic structure of grain boundaries (GBs) in iron. Symmetrical [100] and [110] tilt GBs in bcc iron are modeled with the ADF method and relaxed afterwards in molecular dynamics (MD) simulations. The shape of the GB energy curve obtained in the ADF model reproduces well the peculiarities of the angles of 70.53 deg. [$\\Sigma$ 3(112)] and 129.52 deg. [$\\Sigma$ 11(332)] for [110] tilt GBs. The result...
Theoretical atomic physics code development I: CATS: Cowan Atomic Structure Code
International Nuclear Information System (INIS)
An adaptation of R.D. Cowan's Atomic Structure program, CATS, has been developed as part of the Theoretical Atomic Physics (TAPS) code development effort at Los Alamos. CATS has been designed to be easy to run and to produce data files that can interface with other programs easily. The CATS produced data files currently include wave functions, energy levels, oscillator strengths, plane-wave-Born electron-ion collision strengths, photoionization cross sections, and a variety of other quantities. This paper describes the use of CATS. 10 refs
Bo, Xu; Huan-Sheng, Lu; Bo, Liu; Gang, Liu; Mu-Sheng, Wu; Chuying, Ouyang
2016-06-01
The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory. Silicane is staler against the metal adatoms than silicene. Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene. Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed. However, the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate. Combining the adsorption energy with the diffusion energy barriers, it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage. In order to avoid forming a metal cluster, we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane. Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials. Project supported by the Natural Science Foundation of Jiangxi Province, China (Grant Nos. 20152ACB21014, 20151BAB202006, and 20142BAB212002) and the Fund from the Jiangxi Provincial Educational Committee, China (Grant No. GJJ14254). Bo Xu is also supported by the Oversea Returned Project from the Ministry of Education, China.
Energy Technology Data Exchange (ETDEWEB)
Campbellova, Anna; Klapetek, Petr [Czech Metrology Institute, OkruznI 31, 638 00, Brno (Czech Republic); Ondracek, Martin; JelInek, Pavel [Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 162 00 Prague (Czech Republic); Pou, Pablo; Perez, Ruben, E-mail: jelinekp@fzu.cz [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, 28049 Madrid (Spain)
2011-07-22
A Si adatom on a Si(111)-(7 x 7) reconstructed surface is a typical atomic feature that can rather easily be imaged by a non-contact atomic force microscope (nc-AFM) and can be thus used to test the atomic resolution of the microscope. Based on our first principles density functional theory (DFT) calculations, we demonstrate that the structure of the termination of the AFM tip plays a decisive role in determining the appearance of the adatom image. We show how the AFM image changes depending on the tip-surface distance and the composition of the atomic apex at the end of the tip. We also demonstrate that contaminated tips may give rise to image patterns displaying so-called 'sub-atomic' features even in the attractive force regime.
Rodríguez, Juan I; Ayers, Paul W; Götz, Andreas W; Castillo-Alvarado, F L
2009-07-14
A new approach for computing the atom-in-molecule [quantum theory of atoms in molecule (QTAIM)] energies in Kohn-Sham density-functional theory is presented and tested by computing QTAIM energies for a set of representative molecules. In the new approach, the contribution for the correlation-kinetic energy (T(c)) is computed using the density-functional theory virial relation. Based on our calculations, it is shown that the conventional approach where atomic energies are computed using only the noninteracting part of the kinetic energy might be in error by hundreds of kJ/mol. PMID:19603962
Rodríguez, Juan I; Ayers, Paul W; Götz, Andreas W; Castillo-Alvarado, F L
2009-07-14
A new approach for computing the atom-in-molecule [quantum theory of atoms in molecule (QTAIM)] energies in Kohn-Sham density-functional theory is presented and tested by computing QTAIM energies for a set of representative molecules. In the new approach, the contribution for the correlation-kinetic energy (T(c)) is computed using the density-functional theory virial relation. Based on our calculations, it is shown that the conventional approach where atomic energies are computed using only the noninteracting part of the kinetic energy might be in error by hundreds of kJ/mol.
11. 208 82Pb, 232 90 Th, 256 100 Fm nucleus internal structure and Parameter calculation
Directory of Open Access Journals (Sweden)
Huang Zhenqiang and Huang Yuxiang
2013-10-01
Full Text Available Pass in front of the internal structure of the nucleus, chapter 7 ~ 10 nuclear force, magnetic forming principle and parameters of calculation, we not only have "assembly" the basis of atomic nuclei, and predictable "assembly" nucleus must abide by the principle of a couple of items. At the same time also will to book model, theory of thorough and the strict proof of simulatio
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.
2015-05-01
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm-1 based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ≥ 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models.
Results of calculations of isotope-selective laser excitation of long-lived levels of zinc atoms
International Nuclear Information System (INIS)
On the basis of mathematical model of laser isotope-selective excitation of long-lived atoms numerical calculations were conducted for zinc atoms. These atoms are characterized by small shifts between lines of different isotopes (600700 MHz), while the method are particularly effective in the case of big shifts. In spite of that due to relative simplicity of the method in comparison with AVLIS it is used for zinc isotope separation. The method is effective in the case of excitation of atom long-lived level. In this case in the interval between radiation impulses at the account of chemical reaction with some molecules atoms in this state could be removed. Calculation results show efficiency of burning out of those isotopes, which lines are nearest to radiation line
Abdalmoneam, Marwa Hefny
Relativistic Configuration Interaction (RCI) method has been used to investigate atomic properties of the singly ionized transition metals including Nickel (Ni II), Vanadium (V II), and Tungsten (W II). The methodology of RCI computations was also improved. Specifically, the method to shift the energy diagonal matrix of the reference configurations was modified which facilitated including the effects of many electronic configurations that used to be difficult to be included in the energy matrix and speeded-up the final calculations of the bound and continuum energy spectrum. RCI results were obtained for three different cases: i. Atomic moments and polarizabilities of Ni II; ii. Hyperfine structure constants of V II; iii. Lifetime, Lande g-values, and Oscillator strength of W II. Four atomic quantities of Ni II were calculated; scalar dipole polarizability, off-diagonal electric dipole polarizability, non-adiabatic scalar dipole polarizability, and quadrupole polarizability of Ni II. These quantities appear as effective parameters in an effective potential model. These quantities are computed for the first time. The two hyperfine structure (HFS) constants ; magnetic dipole interaction constant, A, and the electric quadrupole interaction constant, B, have been calculated for the V II 3d4, 3d3 4s, and 3d 2 4s2 J=1 to 5 even parity states . Analysis of the results shows the sum of HFS A of nearby energy levels to be conserved. The Lande g-value and the vector composition percentages for all the wavefunctions of those configurations have also been calculated. RCI results are in good agreement with most of the available experimental data. Lifetimes of 175 decay branches in W II have been calculated. Also, Lande g-values have been calculated for all measured W II odd parity levels J=1/2-11/2. The RCI oscillator strengths and branching fraction values of the lowest 10 energy levels for each odd parity J are presented. The calculated results are only in semi
Workshop on foundations of the relativistic theory of atomic structure
Energy Technology Data Exchange (ETDEWEB)
None
1981-03-01
The conference is an attempt to gather state-of-the-art information to understand the theory of relativistic atomic structure beyond the framework of the original Dirac theory. Abstracts of twenty articles from the conference were prepared separately for the data base. (GHT)
Pattern recognition approach to quantify the atomic structure of graphene
DEFF Research Database (Denmark)
Kling, Jens; Vestergaard, Jacob Schack; Dahl, Anders Bjorholm;
2014-01-01
We report a pattern recognition approach to detect the atomic structure in high-resolution transmission electron microscopy images of graphene. The approach provides quantitative information such as carbon-carbon bond lengths and bond length variations on a global and local scale alike. © 2014...
Ab initio calculations of the electronic structure and bonding characteristics of LaB6
Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.
2005-12-01
Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.
The atomic structure and the properties of Ununbium (z=112) and Mercury (Z=80)
Institute of Scientific and Technical Information of China (English)
LI; JiGuang
2007-01-01
A super heavy element Uub (Z = 112) has been studied theoretically in conjunction with rela-tivistic effects and the effects of electron correlations. The atomic structure and the oscillator strengths of low-lying levels have been calculated, and the ground states have also been determined for the singly and doubly charged ions. The influence of relativity and correlation effects to the atomic properties of such a super heavy element has been investigated in detail. The results have been compared with the properties of an element Hg. Two energy levels at wave numbers 64470 and 94392 are suggested to be of good candidates for experimental observations.……
Nanoscale Structuring of Surfaces by Using Atomic Layer Deposition.
Sobel, Nicolas; Hess, Christian
2015-12-01
Controlled structuring of surfaces is interesting for a wide variety of areas, including microelectronic device fabrication, optical devices, bio(sensing), (electro-, photo)catalysis, batteries, solar cells, fuel cells, and sorption. A unique feature of atomic layer deposition (ALD) is the possibility to form conformal uniform coatings on arbitrarily shaped materials with controlled atomic-scale thickness. In this Minireview, we discuss the potential of ALD for the nanoscale structuring of surfaces, highlighting its versatile application to structuring both planar substrates and powder materials. Recent progress in the application of ALD to porous substrates has even made the nanoscale structuring of high-surface-area materials now feasible, thereby enabling novel applications, such as those in the fields of catalysis and alternative energy.
Gurin, V.; Shpotyuk, O.; Boyko, V
2015-01-01
Small clusters of the As/Sb-S/Se system that is of importance for simulation of elementary structure units of chalcogenide glasses are calculated using DFT technique. Different structures of As2Xn- and Sb2Xn- (X=S,Se) with proper hydrogen termination are compared by the total electronic energy values. The most stable As-X structures are of corner-sharing (CS) type (i.e. the elementary AsX3-pyramids linked via one X atom, and in the case of Sb-X family a new asymmetrical Sb2Se3 cluster appears...
Insights inot the atomic many-particle dynamics of scattering processes by ab-initio calculations
International Nuclear Information System (INIS)
The present thesis gives a theoretical contribution to the understanding of the many-particle dynamics in inelastic ion-atom collisions. Many-electron dynamics in ion-helium collisions and proton-sodium collisions was theoretically studied. The description is based on the semiclassical approximation with the straight orbit for the projectile motion. The ion-atom collision problem is by this reduced to a time-dependent many-electron problem and in the non-relativistic approximation described by the time-dependent Schroedinger equation. The solution of the many-electron problem pursues in the framework of the time-dependent density functional theory. The time-dependent Schroedinger equation for the interacting many-electron problem is transformed to the system of the time-dependent Kohn-Sham equations and solved by the two-center-basis generator method. The unknown time-dependent exchange-correlation one-particle potential forces different approximation int he time-dependent Kohn-Shan scheme. In this thesis the model of the independent electrons was applied as basis model, in which the electron-electron correlation is consistently neglected in all parts and in all steps. Differential cross sections for different one- and two-electron processes were calculated in the so-called eikonal approximation for the collisional systems p-He, He2+-He, and Arq+-He (q=15-18)
International Nuclear Information System (INIS)
Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient, effective atomic, numbers (Zeff), effective electron densities (Ne) and photon interaction cross section (σa) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory. (authors)
Damla, N; Baltas, H; Celik, A; Kiris, E; Cevik, U
2012-07-01
Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient (μ/ρ), effective atomic, numbers (Z(eff)), effective electron densities (N(e)) and photon interaction cross section (σ(a)) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory. PMID:22128356
A computer code for calculations in the algebraic collective model of the atomic nucleus
Welsh, T A
2016-01-01
A Maple code is presented for algebraic collective model (ACM) calculations. The ACM is an algebraic version of the Bohr model of the atomic nucleus, in which all required matrix elements are derived by exploiting the model's SU(1,1) x SO(5) dynamical group. This, in particular, obviates the use of coefficients of fractional parentage. This paper reviews the mathematical formulation of the ACM, and serves as a manual for the code. The code makes use of expressions for matrix elements derived elsewhere and newly derived matrix elements of the operators [pi x q x pi]_0 and [pi x pi]_{LM}, where q_M are the model's quadrupole moments, and pi_N are corresponding conjugate momenta (-2>=M,N<=2). The code also provides ready access to SO(3)-reduced SO(5) Clebsch-Gordan coefficients through data files provided with the code.
International Nuclear Information System (INIS)
New methods for the accurate quantum mechanical treatment of inelastic atom-molecule collisions and electron scattering are considered. The advantages of expanding the system wave function in adiabatic basis functions are emphasized. For a model collinear He-H2 system, the advantages of using vibrationally adiabatic basis functions in close coupling calculations of vibrationally elastic and inelastic transition probabilities are shown. For this system the detailed dynamics of multiquantum transitions is also considered, and the significance of various reactance matrix elements is probed. The close coupling method with conventional, l-dominant, and rotationally and orbitally adiabatic basis functions is applied to rotationally inelastic electron-molecule scattering in the laboratory frame. Electron-N2 scattering is treated in the rigid rotator approximation at total energy E = 30 eV and total angular momentum J = 5. The l-dominant bases afford a useful approximation, but dramatically more accurate results can be obtained with even smaller adiabatic bases. The accuracy and efficiency of close coupling calculations using conventional, l-dominant, adiabatic, and adiabatic l-dominant bases in rotationally inelastic atom-molecule scattering are compared. He-HF is treated in the rigid-rotator approximation at E = 0.05 and 0.017 eV for J = 4, 12, and 20. The effect of various reactance matrix elements on the partial cross sections is shown. S-, p-, and d-wave inelastic e-H scattering is treated in the 1s-2s close coupling approximation. The effects of electron exchange can be successfully approximated by replacing the nonlocal exchange potentials with approximate energy-dependent local potentials
The development of high-resolution spectroscopic methods and their use in atomic structure studies
International Nuclear Information System (INIS)
This thesis discusses work performed during the last nine years in the field of atomic spectroscopy. Several high-resolution techniques, ranging from quantum beats, level crossings, rf-laser double resonances to nonlinear field atom interactions, have been employed. In particular, these methods have been adopted and developed to deal with fast accelerated atomic or ionic beams, allowing studies of problems in atomic-structure theory. Fine- and hyperfine-structure determinations in the He I and Li I isoelectronic sequences, in 51V I, and in 235U I, II have permitted a detailed comparison with ab initio calculations, demonstrating the change in problems when going towards heavier elements or higher ionization stage. The last part of the thesis is concerned with the fundamental question of obtaining very high optical resolution in the interaction between a fast accelerated atom or ion beam and a laser field, this problem being the core in the continuing development of atomic spectroscopy necessary to challenge the more precise and sophisticated theories advanced. (Auth.)
The shells of atomic structure in metallic glasses
Pan, S. P.; Feng, S. D.; Qiao, J. W.; Dong, B. S.; Qin, J. Y.
2016-02-01
We proposed a scheme to describe the spatial correlation between two atoms in metallic glasses. Pair distribution function in a model iron was fully decomposed into several shells and can be presented as the spread of nearest neighbor correlation via distance. Moreover, angle distribution function can also be decomposed into groups. We demonstrate that there is close correlation between pair distribution function and angle distribution function for metallic glasses. We think that our results are very helpful understanding the atomic structure of metallic glasses.
Bekenstein, J D
2003-01-01
Calculation of the Dirac hydrogen atom spectrum in the framework of dynamical fine structure constant (alpha) variability discloses a small departure in the laboratory from Sommerfeld's formula for the fine structure shifts, possibly measurable today. And for a distant object in the universe, the wavelength shift of a spectral line specifically ascribable to cosmological alpha variation is found to depend differently on the quantum numbers than in the conventional view. This last result clashes with the conventional wisdom that an atom's spectrum can change with cosmological time only through evolution of the alpha parameter in the energy eigenvalue formula, and thus impacts on the Webb group's analysis of fine structure intervals in quasar absorption lines (which has been claimed to disclose cosmological alpha evolution). In particular, analyzing together a mix of quasar absorption lines from different fine structure multiplets can bias estimates of cosmological alpha variability.
Volcano structure in atomic resolution core-loss images
Energy Technology Data Exchange (ETDEWEB)
D' Alfonso, A.J.; Findlay, S.D. [School of Physics, University of Melbourne, Victoria, 3010 (Australia); Oxley, M.P. [Materials Science and Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 (United States); Allen, L.J. [School of Physics, University of Melbourne, Victoria, 3010 (Australia)], E-mail: lja@physics.unimelb.edu.au
2008-06-15
A feature commonly present in simulations of atomic resolution electron energy loss spectroscopy images in the scanning transmission electron microscope is the volcano or donut structure. In the past this has been understood in terms of a geometrical perspective using a dipole approximation. It is shown that the dipole approximation for core-loss spectroscopy begins to break down as the probe forming aperture semi-angle increases, necessitating the inclusion of higher order terms for a quantitative understanding of volcano formation. Using such simulations we further investigate the mechanisms behind the formation of such structures in the single atom case and extend this to the case of crystals. The cubic SrTiO{sub 3} crystal is used as a test case to show the effects of nonlocality, probe channelling and absorption in producing the volcano structure in crystal images.
Atomic spectroscopy introduction to the theory of hyperfine structure
Andreev, Anatoli V
2006-01-01
Atomic Spectroscopy provides a comprehensive discussion on the general approach to the theory of atomic spectra, based on the use of the Lagrangian canonical formalism. This approach is developed and applied to explain the hydrogenic hyperfine structure associated with the nucleus motion, its finite mass, and spin. The non-relativistic or relativistic, spin or spin-free particle approximations can be used as a starting point of general approach. The special attention is paid to the theory of Lamb shift formation. The formulae for hydrogenic spectrum including the account of Lamb shift are written in simple analytical form. The book is of interest to specialists, graduate and postgraduate students, who are involved into the experimental and theoretical research in the field of modern atomic spectroscopy.
Results of the fifth three-dimensional dynamic atomic energy research benchmark problem calculation
International Nuclear Information System (INIS)
The pare gives a brief survey of the fifth three-dimensional dynamic atomic energy research benchmark calculation results received with the code DYN3D/ATHLET at NRI Rez. This benchmark was defined at the seventh AER Symposium. Its initiating event is a symmetrical break of the main steam header at the end of the first fuel cycle and hot shutdown conditions with one stuck out control rot group. The calculations were performed with the externally coupled codes ATHLET Mod.1.1 Cycle C and DYN3DH1.1/M3. The Kasseta library was used for the generation of reactor core neutronic parameters. The standard WWER-440/213 input deck of ATHLET code was adopted for benchmark purposes and for coupling with the code DYN3D. The first part of paper contains a brief characteristics of NPP input deck and reactor core model. The second part shows the time dependencies of important global, fuel assembly and loops parameters.(Author)
Atomic structure of non-stoichiometric transition metal carbides
International Nuclear Information System (INIS)
Different kinds of experimental studies of the atomic arrangement in non-stoichiometric transition metal carbides are proposed: the ordering of carbon vacancies and the atomic static displacements are the main subjects studied. Powder neutron diffraction on TiCsub(1-x) allowed us to determine the order-disorder transition critical temperature -Tsub(c) approximately 7700C- in the TiCsub(0.52-0.67) range, and to analyze at 300 K the crystal structure of long-range ordered samples. A neutron diffuse scattering quantitative study at 300 K of short-range order in TiCsub(0.76), TiCsub(0.79) and NbCsub(0.73) single crystals is presented: as in Ti2Csub(1+x) and Nb6C5 superstructures, vacancies avoid to be on each side of a metal atom. Besides, the mean-square carbon atom displacements from their sites are small, whereas metal atoms move radially about 0.03 A away from vacancies. These results are in qualitative agreement with EXAFS measurements at titanium-K edge of TiCsub(1-x). An interpretation of ordering in term of short-range interaction pair potentials between vacancies is proposed
Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations
Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; Wang, Cai-Zhuang; Ho, Kai-Ming
2015-06-01
The structures and magnetic properties of Co-Zr-B alloys near the composition of Co5Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the "Co11Zr2" polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the "interruption" sites. First-principles calculations showed that the magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co5Zr phase and larger than that of the low-temperature Co5.25Zr phase. Our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.
Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; Wang, Cai-Zhuang, E-mail: wangcz@ameslab.gov; Ho, Kai-Ming, E-mail: kmh@ameslab.gov [Ames Laboratory, U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)
2015-06-28
The structures and magnetic properties of Co-Zr-B alloys near the composition of Co{sub 5}Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the “Co{sub 11}Zr{sub 2}” polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the “interruption” sites. First-principles calculations showed that the magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co{sub 5}Zr phase and larger than that of the low-temperature Co{sub 5.25}Zr phase. Our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.
Stable atomic structure of NiTi austenite
Energy Technology Data Exchange (ETDEWEB)
Zarkevich, Nikolai A [Ames Laboratory; Johnson, Duane D [Ames Laboratory
2014-08-01
Nitinol (NiTi), the most widely used shape-memory alloy, exhibits an austenite phase that has yet to be identified. The usually assumed austenitic structure is cubic B2, which has imaginary phonon modes, hence it is unstable. We suggest a stable austenitic structure that “on average” has B2 symmetry (observed by x-ray and neutron diffraction), but it exhibits finite atomic displacements from the ideal B2 sites. The proposed structure has a phonon spectrum that agrees with that from neutron scattering, has diffraction spectra in agreement with x-ray diffraction, and has an energy relative to the ground state that agrees with calorimetry data.
Real Space Approach to Electronic-Structure Calculations
Tsuchida, E; Tsuchida, Eiji; Tsukada, Masaru
1994-01-01
We have applied the Finite Element Method to the self-consistent electronic structure calculations of molecules and solids for the first time. In this approach all the calculations are performed in "real space" and the use of non-uniform mesh is made possible, thus enabling us to deal with localized systems with ease. To illustrate the utility of this method, we perform an all-electron calculation of hydrogen molecule in a supercell with LDA approximation. Our method is also applicable to mesoscopic systems.
Interfacial Atomic Structure of Twisted Few-Layer Graphene.
Ishikawa, Ryo; Lugg, Nathan R; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi
2016-01-01
A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene. PMID:26888259
Atomic Structure Control of Silica Thin Films on Pt(111)
Crampton, Andrew S
2015-05-27
Metal oxide thin films grown on metal single crystals are commonly used to model heterogeneous catalyst supports. The structure and properties of thin silicon dioxide films grown on metal single crystals have only recently been thoroughly characterized and their spectral properties well established. We report the successful growth of a three- dimensional, vitreous silicon dioxide thin film on the Pt(111) surface and reproduce the closed bilayer structure previously reported. The confirmation of the three dimensional nature of the film is unequivocally shown by the infrared absorption band at 1252 cm−1. Temperature programmed desorption was used to show that this three-dimensional thin film covers the Pt(111) surface to such an extent that its application as a catalyst support for clusters/nanoparticles is possible. The growth of a three-dimensional film was seen to be directly correlated with the amount of oxygen present on the surface after the silicon evaporation process. This excess of oxygen is tentatively attributed to atomic oxygen being generated in the evaporator. The identification of atomic oxygen as a necessary building block for the formation of a three-dimensional thin film opens up new possibilities for thin film growth on metal supports, whereby simply changing the type of oxygen enables thin films with different atomic structures to be synthesized. This is a novel approach to tune the synthesis parameters of thin films to grow a specific structure and expands the options for modeling common amorphous silica supports under ultra high vacuum conditions.
Institute of Scientific and Technical Information of China (English)
刘洪毓
2007-01-01
Atoms(原子)are all around us.They are something like the bricks (砖块)of which everything is made. The size of an atom is very,very small.In just one grain of salt are held millions of atoms. Atoms are very important.The way one object acts depends on what
Institute of Scientific and Technical Information of China (English)
王金照; 陈民; 过增元
2002-01-01
Pair distribution functions and constant-volume heat capacities of liquid copper, silver and nickel have been calculated by molecular dynamics simulations with four different versions of the embedded-atom method (EAM) model, namely, the versions of Johnson, Mei, Cai and Pohlong. The simulated structural properties with the four potential models show reasonable agreement with experiments and have little difference with each other, while the calculated heat capacities with the different EAM versions show remarkable discrepancies. Detailed analyses of the energy of the liquid metallic system show that, to predict successfully the heat capacity, an EAM model should match the state equation first proposed by Rose.
Energy Technology Data Exchange (ETDEWEB)
Kwon, Nam Ic [Hankuk University of foreign studies, Seoul (Korea)
2000-03-01
The source of anomalous broad linewidth of 3{sup 3}P{sub 1},{sub 2},{sub 3}-3{sup 3}D{sub 2},{sub 3},4(3s') transition was explained. The broad optogalvanic spectrum was consisted of two gaussian peaks of different linewidths, and they are separated by 250 MHz. The Narrow peak, which has linewidth of room temperature, is from oxygen atoms already separated, and the shifted broad peak, which has linewidth corresponding to a temperature of 9000 K, is from weakly bound molecular ions. Obtained hyperfine spectrum of fluorine atom at the expected frequency, was too weak to analyze hyperfine structure constants. Microwave discharge might be necessary for higher density of excited state. 16 refs., 11 figs. (Author)
Felfli, Z
2015-01-01
Core-polarization interactions are investigated in low-energy electron elastic scattering from the atoms In,Sn,Eu,Au and At through the calculation of their electron affinities. The complex angular momentum method wherein is embedded the vital electron-electron correlations is used. The core-polarization effects are studied through the well investigated rational function approximation of the Thomas-Fermi potential,which can be analytically continued into the complex plane. The EAs are extracted from the large resonance peaks in the calculated low-energy electron atom scattering total cross sections and compared with those from measurements and sophisticated theoretical methods. It is concluded that when the electron-electron correlation effects and core polarization interactions are accounted for adequately the importance of relativity on the calculation of the electron affinities of atoms can be assessed. For At, relativistic effects are estimated to contribute a maximum of about 3.6 percent to its (non-rela...
Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition
Mauguiere, Frederic A L; Collins, Peter R C; Kramer, Zeb C.; Carpenter, Barry K.; Ezra, Gregory S.; Farantos, Stavros; Wiggins, Stephen R
2015-01-01
We re-examine the prototypical roaming reaction—hydrogen atom roaming in formaldehyde decomposition—from a phase space perspective. Specifically, we address the question “why do trajectories roam, rather than dissociate through the radical channel?” We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs,...
Institute of Scientific and Technical Information of China (English)
白玉林; 周晓林; 陈向荣; 芶清泉
2003-01-01
Local density approximation within the framework of the density functional theory is applied to calculate the scanning tunnelling microscopy(STM)images of Ar atoms adsorbed on a graphite sheet(Ar/graphite system).It is found that the optimal site of adsorbed Ar atom is at the top of the centre of the carbon hexagon and its equilibrium distance from the graphite surface is about 3.20A.We demonstrate that it is the hybridization of the C 2 p electronic states with the Ar 3 p and 4 s electronic states,which renders Ar atoms visible in the STM experiment.
Shen, Lin; Yang, Weitao
2016-04-12
We developed a new multiresolution method that spans three levels of resolution with quantum mechanical, atomistic molecular mechanical, and coarse-grained models. The resolution-adapted all-atom and coarse-grained water model, in which an all-atom structural description of the entire system is maintained during the simulations, is combined with the ab initio quantum mechanics and molecular mechanics method. We apply this model to calculate the redox potentials of the aqueous ruthenium and iron complexes by using the fractional number of electrons approach and thermodynamic integration simulations. The redox potentials are recovered in excellent accordance with the experimental data. The speed-up of the hybrid all-atom and coarse-grained water model renders it computationally more attractive. The accuracy depends on the hybrid all-atom and coarse-grained water model used in the combined quantum mechanical and molecular mechanical method. We have used another multiresolution model, in which an atomic-level layer of water molecules around redox center is solvated in supramolecular coarse-grained waters for the redox potential calculations. Compared with the experimental data, this alternative multilayer model leads to less accurate results when used with the coarse-grained polarizable MARTINI water or big multipole water model for the coarse-grained layer.
Cavities and atomic packing in protein structures and interfaces.
Directory of Open Access Journals (Sweden)
Shrihari Sonavane
2008-09-01
Full Text Available A comparative analysis of cavities enclosed in a tertiary structure of proteins and interfaces formed by the interaction of two protein subunits in obligate and non-obligate categories (represented by homodimeric molecules and heterocomplexes, respectively is presented. The total volume of cavities increases with the size of the protein (or the interface, though the exact relationship may vary in different cases. Likewise, for individual cavities also there is quantitative dependence of the volume on the number of atoms (or residues lining the cavity. The larger cavities tend to be less spherical, solvated, and the interfaces are enriched in these. On average 15 A(3 of cavity volume is found to accommodate single water, with another 40-45 A(3 needed for each additional solvent molecule. Polar atoms/residues have a higher propensity to line solvated cavities. Relative to the frequency of occurrence in the whole structure (or interface, residues in beta-strands are found more often lining the cavities, and those in turn and loop the least. Any depression in one chain not complemented by a protrusion in the other results in a cavity in the protein-protein interface. Through the use of the Voronoi volume, the packing of residues involved in protein-protein interaction has been compared to that in the protein interior. For a comparable number of atoms the interface has about twice the number of cavities relative to the tertiary structure.
International Nuclear Information System (INIS)
The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
The atomic structure of liquid Fe–C alloys
Energy Technology Data Exchange (ETDEWEB)
Pan, Shaopeng, E-mail: shaopengpan@gmail.com [College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Feng, Shidong [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Qiao, Junwei [College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Dong, Bangshao [Advanced Technology & Materials Co., Ltd., China Iron & Steel Research Institute Group, Beijing 100081 (China); Qin, Jingyu, E-mail: qinjy@sdu.edu.cn [Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061 (China)
2015-11-05
The structures of liquid Fe–C alloys in the Fe-rich end were investigated by ab initio molecular dynamics simulations. The trend of intensity of chemical short range order around Fe and C atoms changes at the eutectic composition, indicating the close correlation between liquid structure and phase diagram. The tri-capped trigonal prism (Voronoi index <0,3,6,0>) and mono-capped square archimedean antiprism (Voronoi index <0,4,4,0>) around C atoms have the largest frequency fractions and the longest lifetimes among all the polyhedra. Moreover, they tend to connect with each other to form network structure. The maximum intensity of network structure is located at the 20% C composition, which might be the reason why alloys near eutectic composition have great glass-forming ability. - Highlights: • A new parameter is proposed to describe chemical short range order. • Close correlation between structure and phase diagram is found in Fe–C system. • Close correlation between structure and glass forming ability is also found.
Calculation of surface acoustic waves in a multilayered piezoelectric structure
Institute of Scientific and Technical Information of China (English)
Zhang Zuwei; Wen Zhiyu; Hu Jing
2013-01-01
The propagation properties of the surface acoustic waves (SAWs) in a ZnO-SiO2-Si multilayered piezoelectric structure are calculated by using the recursive asymptotic method.The phase velocities and the electromechanical coupling coefficients for the Rayleigh wave and the Love wave in the different ZnO-SiO2-Si structures are calculated and analyzed.The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate.In order to prove the calculated results,a Love mode SAW device based on the ZnO-SiO2-Si multilayered structure is fabricated by micromachining,and its frequency responses are detected.The experimental results are found to be mainly consistent with the calculated ones,except for the slightly larger velocities induced by the residual stresses produced in the fabrication process of the films.The deviation of the experimental results from the calculated ones is reduced by thermal annealing.
Program package for semi-empirical analysis of the fine- and hyperfine structure of complex atoms
International Nuclear Information System (INIS)
The experimental work combined with semi-empirical calculations is a very efficient tool for the investigations of the fine- and hyperfine structure of the complex atoms. We present a set of programs for the analysis of the fine- and hyperfine structure. The input data for the calculations are: the fine structure energy levels, the gJ-factors and the hyperfine structure (hfs) A and B constants of experimentally observed levels. The programs are used for the analysis of electron systems containing any number of configurations up to four open shells. In the energy matrix generated, all kinds of electrostatic, magnetic and correlated electrostatic and magnetic interaction, up to second order perturbation theory, were included. As a result, we obtain predicted energy values for all the levels of the system considered, their exact spectroscopic description and also gJ-factors and hfs A and B constants
The crystal structure of samarosporin I at atomic resolution.
Gessmann, Renate; Axford, Danny; Evans, Gwyndaf; Brückner, Hans; Petratos, Kyriacos
2012-11-01
The atomic resolution structures of samarosporin I have been determined at 100 and 293 K. This is the first crystal structure of a natural 15-residue peptaibol. The amino acid sequence in samarosporin I is identical to emerimicin IV and stilbellin I. Samarosporin is a peptide antibiotic produced by the ascomycetous fungus Samarospora rostrup and belongs to peptaibol subfamily 2. The structures at both temperatures are very similar to each other adopting mainly a 3₁₀-helical and a minor fraction of α-helical conformation. The helices are significantly bent and packed in an antiparallel fashion in the centered monoclinic lattice leaving among them an approximately 10-Å channel extending along the crystallographic twofold axis. Only two ordered water molecules per peptide molecule were located in the channel. Comparisons have been carried out with crystal structures of subfamily 2 16-residue peptaibols antiamoebin and cephaibols. The repercussion of the structural analysis of samarosporin on membrane function is discussed.
Atom exchange between aqueous Fe(II) and structural Fe in clay minerals.
Neumann, Anke; Wu, Lingling; Li, Weiqiang; Beard, Brian L; Johnson, Clark M; Rosso, Kevin M; Frierdich, Andrew J; Scherer, Michelle M
2015-03-01
Due to their stability toward reductive dissolution, Fe-bearing clay minerals are viewed as a renewable source of Fe redox activity in diverse environments. Recent findings of interfacial electron transfer between aqueous Fe(II) and structural Fe in clay minerals and electron conduction in octahedral sheets of nontronite, however, raise the question whether Fe interaction with clay minerals is more dynamic than previously thought. Here, we use an enriched isotope tracer approach to simultaneously trace Fe atom movement from the aqueous phase to the solid ((57)Fe) and from the solid into the aqueous phase ((56)Fe). Over 6 months, we observed a significant decrease in aqueous (57)Fe isotope fraction, with a fast initial decrease which slowed after 3 days and stabilized after about 50 days. For the aqueous (56)Fe isotope fraction, we observed a similar but opposite trend, indicating that Fe atom movement had occurred in both directions: from the aqueous phase into the solid and from the solid into aqueous phase. We calculated that 5-20% of structural Fe in clay minerals NAu-1, NAu-2, and SWa-1 exchanged with aqueous Fe(II), which significantly exceeds the Fe atom layer exposed directly to solution. Calculations based on electron-hopping rates in nontronite suggest that the bulk conduction mechanism previously demonstrated for hematite1 and suggested as an explanation for the significant Fe atom exchange observed in goethite2 may be a plausible mechanism for Fe atom exchange in Fe-bearing clay minerals. Our finding of 5-20% Fe atom exchange in clay minerals indicates that we need to rethink how Fe mobility affects the macroscopic properties of Fe-bearing phyllosilicates and its role in Fe biogeochemical cycling, as well as its use in a variety of engineered applications, such as landfill liners and nuclear repositories.
Theoretical Calculation of Absolute Radii of Atoms and Ions. Part 2. The Ionic Radii
Directory of Open Access Journals (Sweden)
Raka Biswas
2003-05-01
Full Text Available Abstract: The theoretical method of determination of absolute atomic size, discussed in Int. J. Mol. Sci. 2002, 3, 87-113, is exploited to calculate absolute radii of the ions whose experimental radii are published by Shanon. The computed radii are found to reproduce the expected periodic variation of size in periods and in groups and nicely reproduce the d-block and f-block contractions in the respective series. It is pointed out that experimental radii of d and f block transition metal ions make erroneous and misleading representation of the size behaviour of the respective series. A detailed comparative study of the crystal radii vis-ÃƒÂ -vis the theoretical radii is reported. A rationale of the double hump curve of the experimental radii of 3 d-block transition metal ions is put forward in terms of the crystal field theory and Jahn-Teller distortion. The theoretical radii are exploited to calculate the diamagnetic susceptibility, polarizability and chemical hardness of the ions and compared with available experimental data. The fact of good agreement between the experimental and computed global hardness of ions and correct demonstration of d-block and f-block contraction by the computed radii are used as benchmark to test the validity of the values of the computed theoretical radii of the ions as their representative sizes. It is concluded that the theoretically computed radii of ions are visualizable size representation of ions and can be used as their absolute radii at the respective oxidation states.
Energy Technology Data Exchange (ETDEWEB)
Kaganovich, I. D., Shnidman, Ariel, Mebane, Harrison, Davidson, R.C.
2008-10-10
Evaluation of ion-atom charge-changing cross sections is needed for many accelerator applications. A classical trajectory Monte Carlo (CTMC) simulation has been used to calculate ionization and charge exchange cross sections. For benchmarking purposes, an extensive study has been performed for the simple case of hydrogen and helium targets in collisions with various ions. Despite the fact that the simulation only accounts for classical mechanics, the calculations are comparable to experimental results for projectile velocities in the region corresponding to the vicinity of the maximum cross section. Shortcomings of the CTMC method for multielectron target atoms are discussed.
International Nuclear Information System (INIS)
Evaluation of ion-atom charge-changing cross sections is needed for many accelerator applications. A classical trajectory Monte Carlo (CTMC) simulation has been used to calculate ionization and charge exchange cross sections. For benchmarking purposes, an extensive study has been performed for the simple case of hydrogen and helium targets in collisions with various ions. Despite the fact that the simulation only accounts for classical mechanics, the calculations are comparable to experimental results for projectile velocities in the region corresponding to the vicinity of the maximum cross section. Shortcomings of the CTMC method for multielectron target atoms are discussed
Inverse boundary element calculations based on structural modes
DEFF Research Database (Denmark)
Juhl, Peter Møller
2007-01-01
The inverse problem of calculating the flexural velocity of a radiating structure of a general shape from measurements in the field is often solved by combining a Boundary Element Method with the Singular Value Decomposition and a regularization technique. In their standard form these methods sol...
Calculation of structurally related properties of bulk and surface Si
International Nuclear Information System (INIS)
The self-consistent pseudopotential method is applied to study the bulk and surface structurally related properties of Si. Equilibrium configurations are determined by minimizing the total energy of the system; the calculated bulk properties and the surface relaxation of Si are found to be in good agreement with experiment. The surface energy and the surface reconstruction of Si are briefly discussed
Calculation of forces arising from impacting projectiles upon yielding structures
International Nuclear Information System (INIS)
Calculations concerning the impact of airplanes upon nuclear power plant buildings usually imply that the building [QUOTE]acts' as a rigid target. This assumption is justified for considerations concerning the structural integrity of the building being hit. However, for investigating induced vibrations of components within the structure, this approach might-in general-be too conservative. It is expected, that yielding of the structure during impact reduces the peak values of the loads and changes the temporal behaviour of the load function which is obtained for a rigid target. To calculate the changes of the load function which are due to deformations of the structure, Riera's method is extended for the case of a yielding target. The calculations are performed with a one-dimensional model for the projectile. The presented model calculations seem to verify that the motion of the target does not have much influence on the impact force for projectiles similar to the model projectile, provided the displacement of the yielding target is small in comparison with the path covered by the free-flying projectile during a time which is equivalent to the total time of impact. (Auth.)
Electronic structure of the heavy fermion superconductor Ce2PdIn8: Experiment and calculations
International Nuclear Information System (INIS)
The electronic structure of a heavy-fermion superconductor Ce2PdIn8 was investigated by means of X-ray photoelectron spectroscopy (XPS) and ab initio density functional band structure calculations. The Ce 3d core-level XPS spectra point to stable trivalent configuration of Ce atoms that is also reproduced in the band structure calculations within the generalized gradient approximation GGA+U approach. Analysis of the 3d9f2 weight in the 3d XPS spectra within the Gunnarsson-Schönhammer model suggests that the onsite hybridization energy between Ce 4f and the conduction band states, Δfs, is ∼120 meV, which is about 30 meV larger than Δfs in isostructural Ce2TIn8 compounds with T = Co, Rh, and Ir. Taking into account a Coulomb repulsion U on both the Ce 4f and Pd 4d states in electronic band structure calculations, a satisfactory agreement was found between the calculated density of states (DOS) and the measured valence band XPS spectra. - Highlights: • XPS data validated strong electronic correlations in superconducting Ce2PdIn8. • DFT calculations reproduced XPS spectra measured for Ce2PdIn8. • Crucial role of Pd d electrons in the HF behavior of Ce2PdIn8 was established
Calculation of forces arising from impacting projectiles upon yielding structures
International Nuclear Information System (INIS)
Calculations concerning the impact of airplanes upon nuclear power plant buildings usually imply that the building 'acts' as a rigid target. This assumption is justified for considerations concerning the structural integrity of the building being hit. However, for investigating induced vibrations of components within the structure, this approach might -in general- be too conservative. It is expected, that yielding of the structure during impact reduces the peak values of the loads and changes the temporal behavior of the load function which is obtained for a rigid target. To calculate the changes of the load function which are due to deformations of the structure, Riera's method is extended for the case of a yielding target. In view of the applications of the calculations to the impact of airplanes upon buildings which are constructed to withstand loads of this kind without serious damage and without large deformations, it is possible to simplify the calculations to some extent. That is, the investigations need not take into account in detail the behavior of the target during impact. The calculations are performed with a one-dimensional model for the projectile. The direction of impact is perpendicular to the target surface; direction of impact and projectile axis coincide. The calculations were performed for several initial velocities of the projectiles simulating a fast flying military airplane. Variations of the peak values of the load functions as compared to corresponding values for a rigid target do not exceed about 10%. The overall temporal behavior of the load curves turns out to be not very sensitive to the yielding of the target, though, in some cases displacements in time of the peak positions within a single load curve do arise
Atomic structures of peptide self-assembly mimics
Makabe, Koki; McElheny, Dan; Tereshko, Valentia; Hilyard, Aaron; Gawlak, Grzegorz; Yan, Shude; Koide, Akiko; Koide, Shohei
2006-01-01
Although the β-rich self-assemblies are a major structural class for polypeptides and the focus of intense research, little is known about their atomic structures and dynamics due to their insoluble and noncrystalline nature. We developed a protein engineering strategy that captures a self-assembly segment in a water-soluble molecule. A predefined number of self-assembling peptide units are linked, and the β-sheet ends are capped to prevent aggregation, which yields a mono-dispersed soluble p...
All-atom molecular dynamics calculation study of entire poliovirus empty capsids in solution
Energy Technology Data Exchange (ETDEWEB)
Andoh, Y.; Yoshii, N.; Yamada, A.; Kojima, H.; Mizutani, K.; Okazaki, S., E-mail: okazaki@apchem.nagoya-u.ac.jp [Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Fujimoto, K. [Department of Pharmacy, College of Pharmaceutical Sciences, Ritsumeikan University, Nojihigashi, Kusatsu, Shiga 525-8577 (Japan); Nakagawa, A. [Institute for Protein Research, Osaka University, Yamadaoka, Suita, Osaka 565-0871 (Japan); Nomoto, A. [Institute of Microbial Chemistry, Kamiosaki, Shinagawa-ku, Tokyo 141-0021 (Japan)
2014-10-28
Small viruses that belong, for example, to the Picornaviridae, such as poliovirus and foot-and-mouth disease virus, consist simply of capsid proteins and a single-stranded RNA (ssRNA) genome. The capsids are quite stable in solution to protect the genome from the environment. Here, based on long-time and large-scale 6.5 × 10{sup 6} all-atom molecular dynamics calculations for the Mahoney strain of poliovirus, we show microscopic properties of the viral capsids at a molecular level. First, we found equilibrium rapid exchange of water molecules across the capsid. The exchange rate is so high that all water molecules inside the capsid (about 200 000) can leave the capsid and be replaced by water molecules from the outside in about 25 μs. This explains the capsid's tolerance to high pressures and deactivation by exsiccation. In contrast, the capsid did not exchange ions, at least within the present simulation time of 200 ns. This implies that the capsid can function, in principle, as a semipermeable membrane. We also found that, similar to the xylem of trees, the pressure of the solution inside the capsid without the genome was negative. This is caused by coulombic interaction of the solution inside the capsid with the capsid excess charges. The negative pressure may be compensated by positive osmotic pressure by the solution-soluble ssRNA and the counter ions introduced into it.
All-atom molecular dynamics calculation study of entire poliovirus empty capsids in solution
International Nuclear Information System (INIS)
Small viruses that belong, for example, to the Picornaviridae, such as poliovirus and foot-and-mouth disease virus, consist simply of capsid proteins and a single-stranded RNA (ssRNA) genome. The capsids are quite stable in solution to protect the genome from the environment. Here, based on long-time and large-scale 6.5 × 106 all-atom molecular dynamics calculations for the Mahoney strain of poliovirus, we show microscopic properties of the viral capsids at a molecular level. First, we found equilibrium rapid exchange of water molecules across the capsid. The exchange rate is so high that all water molecules inside the capsid (about 200 000) can leave the capsid and be replaced by water molecules from the outside in about 25 μs. This explains the capsid's tolerance to high pressures and deactivation by exsiccation. In contrast, the capsid did not exchange ions, at least within the present simulation time of 200 ns. This implies that the capsid can function, in principle, as a semipermeable membrane. We also found that, similar to the xylem of trees, the pressure of the solution inside the capsid without the genome was negative. This is caused by coulombic interaction of the solution inside the capsid with the capsid excess charges. The negative pressure may be compensated by positive osmotic pressure by the solution-soluble ssRNA and the counter ions introduced into it
A computer code for calculations in the algebraic collective model of the atomic nucleus
Welsh, T. A.; Rowe, D. J.
2016-03-01
A Maple code is presented for algebraic collective model (ACM) calculations. The ACM is an algebraic version of the Bohr model of the atomic nucleus, in which all required matrix elements are derived by exploiting the model's SU(1 , 1) × SO(5) dynamical group. This paper reviews the mathematical formulation of the ACM, and serves as a manual for the code. The code enables a wide range of model Hamiltonians to be analysed. This range includes essentially all Hamiltonians that are rational functions of the model's quadrupole moments qˆM and are at most quadratic in the corresponding conjugate momenta πˆN (- 2 ≤ M , N ≤ 2). The code makes use of expressions for matrix elements derived elsewhere and newly derived matrix elements of the operators [ π ˆ ⊗ q ˆ ⊗ π ˆ ] 0 and [ π ˆ ⊗ π ˆ ] LM. The code is made efficient by use of an analytical expression for the needed SO(5)-reduced matrix elements, and use of SO(5) ⊃ SO(3) Clebsch-Gordan coefficients obtained from precomputed data files provided with the code.
Chiral nucleon-nucleon forces in nuclear structure calculations
Directory of Open Access Journals (Sweden)
Coraggio L.
2016-01-01
Full Text Available Realistic nuclear potentials, derived within chiral perturbation theory, are a major breakthrough in modern nuclear structure theory, since they provide a direct link between nuclear physics and its underlying theory, namely the QCD. As a matter of fact, chiral potentials are tailored on the low-energy regime of nuclear structure physics, and chiral perturbation theory provides on the same footing two-nucleon forces as well as many-body ones. This feature fits well with modern advances in ab-initio methods and realistic shell-model. Here, we will review recent nuclear structure calculations, based on realistic chiral potentials, for both finite nuclei and infinite nuclear matter.
Chiral nucleon-nucleon forces in nuclear structure calculations
Coraggio, L; Holt, J W; Itaco, N; Machleidt, R; Marcucci, L E; Sammarruca, F
2016-01-01
Realistic nuclear potentials, derived within chiral perturbation theory, are a major breakthrough in modern nuclear structure theory, since they provide a direct link between nuclear physics and its underlying theory, namely the QCD. As a matter of fact, chiral potentials are tailored on the low-energy regime of nuclear structure physics, and chiral perturbation theory provides on the same footing two-nucleon forces as well as many-body ones. This feature fits well with modern advances in ab-initio methods and realistic shell-model. Here, we will review recent nuclear structure calculations, based on realistic chiral potentials, for both finite nuclei and infinite nuclear matter.
Institute of Scientific and Technical Information of China (English)
POPEL; P; S; KONSTANTINOVA; N; Yu
2010-01-01
The method of crucible rotating oscillation damping was employed to measure the kinematic viscosity of aluminum melt,and the curve of viscosity v versus temperature T from 935 to 1383 K was obtained.Besides,based on the calculation model of the evolution behavior of atomic clusters in liquid structure,the curve of atomic clusters size d versus temperature was obtained,and the calculated results are in good agreement with the experimental values.By analyzing experimental data,it was found that both the viscosity and the size of atomic clusters of aluminum melt are monodrome functions of temperature,and the relation between v(T) and d(T) is a linear function,i.e.,v = v 0 + K·d(T).This relation indirectly verifies the calculation model of the structural information of metal melt,which is of great significance for studying the relation between melt microstructure and macro-physical properties.
Stability and Strength of Atomically Thin Borophene from First Principles Calculations
Peng, Bo; Shao, Hezhu; Ning, Zeyu; Xu, Yuanfeng; Lu, Hongliang; Zhang, David Wei; Zhu, Heyuan
2016-01-01
A new two-dimensional (2D) material, borophene (2D boron sheet), has been grown successfully recently on single crystal Ag substrates by two parallel experiments [Mannix \\textit{et al., Science}, 2015, \\textbf{350}, 1513] [Feng \\textit{et al., Nature Chemistry}, 2016, \\textbf{advance online publication}]. Three main structures have been proposed ($\\beta_{12}$, $\\chi_3$ and striped borophene). However, the stability of three structures is still in debate. Using first principles calculations, we examine the dynamical, thermodynamical and mechanical stability of $\\beta_{12}$, $\\chi_3$ and striped borophene. Free-standing $\\beta_{12}$ and $\\chi_3$ borophene is dynamically, thermodynamically, and mechanically stable, while striped borophene is dynamically and thermodynamically unstable due to high stiffness along $a$ direction. The origin of high stiffness and high instability in striped borophene along $a$ direction can both be attributed to strong directional bonding. This work provides a benchmark for examining...
Structural and Magnetic Evolution of Bimetallic MnAu Clusters Driven by Asymmetric Atomic Migration
Energy Technology Data Exchange (ETDEWEB)
Wei, Xiaohui; Zhou, Rulong; Lefebvre, Williams; He, Kai; Le Roy, Damien; Skomski, Ralph; Li, Xingzhong; Shield, Jeffrey E; Kramer, Matthew J; Chen, Shuang; Zeng, Xiao Cheng; Sellmyer, David J
2014-03-12
The nanoscale structural, compositional, and magnetic properties are examined for annealed MnAu nanoclusters. The MnAu clusters order into the L10 structure, and monotonic size-dependences develop for the composition and lattice parameters, which are well reproduced by our density functional theory calculations. Simultaneously, Mn diffusion forms 5 Å nanoshells on larger clusters inducing significant magnetization in an otherwise antiferromagnetic system. The differing atomic mobilities yield new cluster nanostructures that can be employed generally to create novel physical properties.
Atomic Clocks and Variations of the FIne Structure Constant
Prestage, John D.; Tjoelker, Robert L.; Maleki, Lute
1995-01-01
We describe a new test for possible variations of the fine structure constant alpha by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg(+) clocks have a different dependence on alpha via relativistic contributions of order (Z-alpha)(sup 2). Recent H-maser vs Hg(+) clock comparison data improve laboratory limits on a time variation by 100-fold to give dot-alpha less than or equal to 3.7 x 10(exp -14)/yr. Future laser cooled clocks (Be(+), Rb, Cs, Hg(+), etc.), when compared, will yield the most sensitive of all tests for dot-alpha/alpha.
Structures of cefradine dihydrate and cefaclor dihydrate from DFT-D calculations
DEFF Research Database (Denmark)
van de Streek, Jacco; Rantanen, Jukka; Bond, Andrew D
2013-01-01
The crystal structure of cefradine dihydrate, C16H19N3O4S·2H2O, is considered in the pharmaceutical sciences to be the epitome of an isolated-site hydrate. The structure from single-crystal X-ray data was described in 1976, but atomic coordinates were not published. The atomic coordinates...... from comparison with cefaclor dihydrate, C15H14ClN3O4S·2H2O, which is isomorphous and for which more complete single-crystal data are available. H-atom positions have not previously been published for either compound. The DFT-D calculations confirm that both cefradine and cefaclor are present...... are determined here by combining the information available from the published single-crystal data with a dispersion-corrected density functional theory (DFT-D) method that has been validated to reproduce molecular crystal structures very accurately. Additional proof for the correctness of the structure comes...
Directory of Open Access Journals (Sweden)
Odru P.
2006-11-01
Full Text Available Cet article présente une méthode de calcul des structures composites fibres-résine appliquée aux cas des tubes minces. Outre l'établissement des relations contraintes - déformations généralisées des tubes à partir des caractéristiques des matériaux de base et de leur orientation, on pose les relations permettant de calculer leur comportement et leur dimensionnement sous des charges axisymétriques combinées de traction, pression et flexion. Une méthode simplifiée applicable au cas des composites microfissurés est aussi présentée. On montre ensuite, à travers quelques exemples concrets d'applications, les propriétés intéressantes ou inhabituelles que le matériau permet de conférer aux structures. This article presents a method of calculation of composite structures applied to thin-walled tubes. Starting from the characteristics and orientation of the basic materials, the generalized stress-strain equations of the tubes are determined ; then the relationship allowing the calculation of their design and behavior under combined axisymmetrical loads of tension, pressure and bending are established. A simplified method applicable to microcracked composite materials is also described. Several complete examples of applications illustrate the interesting or unusual properties that this material can impart to structures
Semiclassical calculation of ionisation rate for Rydberg helium atoms in an electric field
Institute of Scientific and Technical Information of China (English)
Wang De-Hua
2011-01-01
The ionisation of Rydberg helium atoms in an electric field above the classical ionisation threshold has been examined using the semiclassical method, with particular emphasis on discussing the influence of the core scattering on the escape dynamics of electrons. The results show that the Rydberg helium atoms ionise by emitting a train of electron pulses. Unlike the case of the ionisation of Rydberg hydrogen atom in parallel electric and magnetic fields,where the pulses of the electron are caused by the external magnetic field, the pulse trains for Rydberg helium atoms are created through core scattering. Each peak in the ionisation rate corresponds to the contribution of one core-scattered combination trajectory. This fact further illustrates that the ionic core scattering leads to the chaotic property of the Rydberg helium atom in external fields. Our studies provide a simple explanation for the escape dynamics in the ionisation of nonhydrogenic atoms in external fields.
Atomic Structure of Au−Pd Bimetallic Alloyed Nanoparticles
Ding, Yong
2010-09-08
Using a two-step seed-mediated growth method, we synthesized bimetallic nanoparticles (NPs) having a gold octahedron core and a palladium epitaxial shell with controlled Pd-shell thickness. The mismatch-release mechanism between the Au core and Pd shell of the NPs was systematically investigated by high-resolution transmission electron microscopy. In the NPs coated with a single atomic layer of Pd, the strain between the surface Pd layer and the Au core is released by Shockley partial dislocations (SPDs) accompanied by the formation of stacking faults. For NPs coated with more Pd (>2 nm), the stacking faults still exist, but no SPDs are found. This may be due to the diffusion of Au atoms into the Pd shell layers to eliminate the SPDs. At the same time, a long-range ordered L11 AuPd alloy phase has been identified in the interface area, supporting the assumption of the diffusion of Au into Pd to release the interface mismatch. With increasing numbers of Pd shell layers, the shape of the Au-Pd NP changes, step by step, from truncated-octahedral to cubic. After the bimetallic NPs were annealed at 523 K for 10 min, the SPDs at the surface of the NPs coated with a single atomic layer of Pd disappeared due to diffusion of the Au atoms into the surface layer, while the stacking faults and the L11 Au-Pd alloyed structure remained. When the annealing temperature was increased to 800 K, electron diffraction patterns and diffraction contrast images revealed that the NPs became a uniform Au-Pd alloy, and most of the stacking faults disappeared as a result of the annealing. Even so, some clues still support the existence of the L11 phase, which suggests that the L11 phase is a stable, long-range ordered structure in Au-Pd bimetallic NPs. © 2010 American Chemical Society.
Serov, Vladislav V; Sergeeva, Tatiana A; Vinitsky, Sergue I
2012-01-01
A review of some recently developed methods of calculating multiple differential cross-sections of photoionization and electron impactionization of atoms and molecules having two active electrons is presented. The methods imply original approaches to calculating three-particle Coulomb wave functions. The external complex scaling method and the formalism of the Schroedinger equation with a source in the right-hand side are considered. Efficiency of the time-dependent approaches to the scattering problem, such as the paraxial approximation and the time-dependent scaling, is demonstrated. An original numerical method elaborated by the authors for solving the 6D Schroedinger equation for an atom with two active electrons, based on the Chang-Fano transformation and the discrete variable representation, is formulated. Basing on numerical simulations, the threshold behavior of angular distributions of two-electron photoionization of the negative hydrogen ion and helium atom, and multiple differential cross-sections ...
Minimal parameter implicit solvent model for ab initio electronic structure calculations
Dziedzic, Jacek; Skylaris, Chris-Kriton; Mostofi, Arash A; Payne, Mike C
2011-01-01
We present an implicit solvent model for ab initio electronic structure calculations which is fully self-consistent and is based on direct solution of the nonhomogeneous Poisson equation. The solute cavity is naturally defined in terms of an isosurface of the electronic density according to the formula of Fattebert and Gygi (J. Comp. Chem. 23, 6 (2002)). While this model depends on only two parameters, we demonstrate that by using appropriate boundary conditions and dispersion-repulsion contributions, solvation energies obtained for an extensive test set including neutral and charged molecules show dramatic improvement compared to existing models. Our approach is implemented in, but not restricted to, a linear-scaling density functional theory (DFT) framework, opening the path for self-consistent implicit solvent DFT calculations on systems of unprecedented size, which we demonstrate with calculations on a 2615-atom protein-ligand complex.
Pfennig, Brian W.; Schaefer, Amy K.
2011-01-01
A general chemistry laboratory experiment is described that introduces students to instrumental analysis using gas chromatography-mass spectrometry (GC-MS), while simultaneously reinforcing the concepts of mass percent and the calculation of atomic mass. Working in small groups, students use the GC to separate and quantify the percent composition…
Quantum chemical calculations on structure of Mo8 O4-26
Institute of Scientific and Technical Information of China (English)
吴争平; 尹周澜; 陈启元; 张平民
2002-01-01
Two possible structures of Mo8O4-26 were optimized using the Polak-Ribiere method of Molecular Mechanics Optimization and the termination condition is RMS (Root-mean-square) gradient of 0.42kJ/mol. Based on the calculations of the molecular dynamics, Lengevin dynamics and Monte Carlo dynamics simulation, the structure models of Mo8O4-26 with the lowest energy were acquired respectively according to the energy of the systems calculated using the ZIDO/1 and PM3 methods. The total energy, energies of some frontier molecular orbitals and atomic charges of Mo8O4-26 were computed at the HF/3-21G and HF/STO-3G levels. The calculation results show that the contortion of the structure with eight MoO6 is smaller than that of the structure with six MoO6 and two MoO4. The total energies of the two structures are nearly equal because the contortion of the structure with six MoO6 and two MoO4 would make the exclusion force decreased.
Atomic-resolution structures of prion AGAAAAGA amyloid fibrils
Zhang, Jiapu
2011-01-01
To the best of the author's knowledge, there is little structural data available on the AGAAAAGA palindrome in the hydrophobic region (113-120) of prion proteins due to the unstable, noncrystalline and insoluble nature of the amyloid fibril, although many experimental studies have shown that this region has amyloid fibril forming properties and plays an important role in prion diseases. In view of this, the present study is devoted to address this problem from computational approaches such as local optimization steepest descent, conjugate gradient, discrete gradient and Newton methods, global optimization simulated annealing and genetic algorithms, canonical dual optimization theory, and structural bioinformatics. The optimal atomic-resolution structures of prion AGAAAAGA amyloid fibils reported in this Chapter have a value to the scientific community in its drive to find treatments for prion diseases or at least be useful for the goals of medicinal chemistry.
Calculation of complex band structure for low symmetry lattices
Srivastava, Manoj; Zhang, Xiaoguang; Cheng, Hai-Ping
2009-03-01
Complex band structure calculation is an integral part of a first-principles plane-wave based quantum transport method. [1] The direction of decay for the complex wave vectors is also the transport direction. The existing algorithm [1] has the limitation that it only allows the transport direction along a lattice vector perpendicular to the basal plane formed by two other lattice vectors, e.g., the c-axis of a tetragonal lattice. We generalize this algorithm to nonorthogonal lattices with transport direction not aligned with any lattice vector. We show that this generalization leads to changes in the boundary conditions and the Schrodinger's equation projected to the transport direction. We present, as an example, the calculation of the complex band structure of fcc Cu along a direction perpendicular to the (111) basal plane. [1] Hyoung Joon Choi and Jisoon Ihm, Phys. Rev. B 59, 2267 (1999).
Heyrovska, Raji
2007-01-01
The interpretation by the author in recent years of bond lengths as sums of the relevant atomic or ionic radii has been extended here to the bonds in the skeletal structures of adenine, guanine, thymine, cytosine, uracil, ribose, deoxyribose and phosphoric acid. On examining the bond length data in the literature, it has been found that the averages of the bond lengths are close to the sums of the corresponding atomic covalent radii of carbon, nitrogen, oxygen, hydrogen and phosphorus. Thus, the conventional molecular structures have been resolved here, for the first time, into probable atomic structures.
Refinement of Atomic Structures Against cryo-EM Maps.
Murshudov, G N
2016-01-01
This review describes some of the methods for atomic structure refinement (fitting) against medium/high-resolution single-particle cryo-EM reconstructed maps. Some of the tools developed for macromolecular X-ray crystal structure analysis, especially those encapsulating prior chemical and structural information can be transferred directly for fitting into cryo-EM maps. However, despite the similarities, there are significant differences between data produced by these two techniques; therefore, different likelihood functions linking the data and model must be used in cryo-EM and crystallographic refinement. Although tools described in this review are mostly designed for medium/high-resolution maps, if maps have sufficiently good quality, then these tools can also be used at moderately low resolution, as shown in one example. In addition, the use of several popular crystallographic methods is strongly discouraged in cryo-EM refinement, such as 2Fo-Fc maps, solvent flattening, and feature-enhanced maps (FEMs) for visualization and model (re)building. Two problems in the cryo-EM field are overclaiming resolution and severe map oversharpening. Both of these should be avoided; if data of higher resolution than the signal are used, then overfitting of model parameters into the noise is unavoidable, and if maps are oversharpened, then at least parts of the maps might become very noisy and ultimately uninterpretable. Both of these may result in suboptimal and even misleading atomic models. PMID:27572731
AMO Database in KAERI and Atomic Structure Studies
Rhee, Yongjoo; Park, H. M.; Kwon, D. H.
2005-05-01
Atomic spectroscopy studies carried out at the Laboratory for Quantum Optics in Korea Atomic Energy Research Institute are introduced together with the AMO (Atomic, Molecular, and Optical) database established based upon those studies.
NUMERICAL CALCULATIONS IN GEOMECHANICS APPLICABLE TO LINEAR STRUCTURES
Vlasov Aleksandr Nikolaevich; Volkov-Bogorodskiy Dmitriy Borisovich; Znamenskiy Vladimir Valerianovich; Mnushkin Mikhail Grigorevich
2012-01-01
The article covers the problem of applicability of finite-element and engineering methods to the development of a model of interaction between pipeline structures and the environment in the complex conditions with a view to the simulation and projection of exogenous geological processes, trustworthy assessment of their impacts on the pipeline, and the testing of varied calculation methodologies. Pipelining in the areas that have a severe continental climate and permafrost soils is accompanied...
Directory of Open Access Journals (Sweden)
S. J Hashemifar
2015-01-01
Full Text Available In this paper, the structural, magnetic, and electronic properties of two- to nine-atom copper and silver clusters and their alloys with one palladium atom are investigated by using full-potential all-electron density functional computations. After calculating minimized energy of several structural isomers of every nanocluster, it is argued that the small size nanoclusters (up to size of 6, prefer planar structures, while by increasing size a 2D-3D structural transformation is observed. The structural transformation of pure and copper-palladium clusters occurs in the size of seven and that of silver-palladium cluster in happens at the size of six. The calculated second difference and dissociation energies confirm that the two- and eight- atom pure clusters and three- and seven- atom alloyed clusters are magic clusters. The electronic and magnetic properties of stable isomers are calculated and considered after applying many body based GW correction.
Energy Technology Data Exchange (ETDEWEB)
Hegde, Ganesh, E-mail: ganesh.h@ssi.samsung.com; Bowen, R. Chris [Advanced Logic Lab, Samsung Semiconductor Inc., Austin, TX 78754 (United States)
2015-10-15
The accuracy of a single s-orbital representation of Cu towards enabling multi-thousand atom ab initio calculations of electronic structure is evaluated in this work. If an electrostatic compensation charge of 0.3 electron per atom is used in this basis representation, the electronic transmission in bulk and nanocrystalline Cu can be made to compare accurately to that obtained with a Double Zeta Polarized basis set. The use of this representation is analogous to the use of single band effective mass representation for semiconductor electronic structure. With a basis of just one s-orbital per Cu atom, the representation is extremely computationally efficient and can be used to provide much needed ab initio insight into electronic transport in nanocrystalline Cu interconnects at realistic dimensions of several thousand atoms.
Are the program packages for molecular structure calculations really black boxes?
Directory of Open Access Journals (Sweden)
ANA MRAKOVIC
2007-12-01
Full Text Available In this communication it is shown that the widely held opinion that compact program packages for quantum–mechanical calculations of molecular structure can safely be used as black boxes is completely wrong. In order to illustrate this, the results of computations of equilibrium bond lengths, vibrational frequencies and dissociation energies for all homonuclear diatomic molecules involving the atoms from the first two rows of the Periodic Table, performed using the Gaussian program package are presented. It is demonstrated that the sensible use of the program requires a solid knowledge of quantum chemistry.
The effect of molecular dynamics sampling on the calculated observable gas-phase structures.
Tikhonov, Denis S; Otlyotov, Arseniy A; Rybkin, Vladimir V
2016-07-21
In this study, we compare the performance of various ab initio molecular dynamics (MD) sampling methods for the calculation of the observable vibrationally-averaged gas-phase structures of benzene, naphthalene and anthracene molecules. Nose-Hoover (NH), canonical and quantum generalized-Langevin-equation (GLE) thermostats as well as the a posteriori quantum correction to the classical trajectories have been tested and compared to the accurate path-integral molecular dynamics (PIMD), static anharmonic vibrational calculations as well as to the experimental gas electron diffraction data. Classical sampling methods neglecting quantum effects (NH and canonical GLE thermostats) dramatically underestimate vibrational amplitudes for the bonded atom pairs, both C-H and C-C, the resulting radial distribution functions exhibit nonphysically narrow peaks. This deficiency is almost completely removed by taking the quantum effects on the nuclei into account. The quantum GLE thermostat and a posteriori correction to the canonical GLE and NH thermostatted trajectories capture most vibrational quantum effects and closely reproduce computationally expensive PIMD and experimental radial distribution functions. These methods are both computationally feasible and accurate and are therefore recommended for calculations of the observable gas-phase structures. A good performance of the quantum GLE thermostat for the gas-phase calculations is encouraging since its parameters have been originally fitted for the condensed-phase calculations. Very accurate molecular structures can be predicted by combining the equilibrium geometry obtained at a high level of electronic structure theory with vibrational amplitudes and corrections calculated using MD driven by a lower level of electronic structure theory. PMID:27331660
Long-range correlation energy calculated from coupled atomic response functions
Ambrosetti, Alberto; DiStasio, Robert A; Tkatchenko, Alexandre
2013-01-01
An accurate determination of the electron correlation energy is essential for describing the structure, stability, and function in a wide variety of systems, ranging from gas-phase molecular assemblies to condensed matter and organic/inorganic interfaces. Even small errors in the correlation energy can have a large impact on the description of chemical and physical properties in the systems of interest. In this context, the development of efficient approaches for the accurate calculation of the long-range correlation energy (and hence dispersion) is the main challenge. In the last years a number of methods have been developed to augment density functional approximations via dispersion energy corrections, but most of these approaches ignore the intrinsic many-body nature of correlation effects, leading to inconsistent and sometimes even qualitatively incorrect predictions. Here we build upon the recent many-body dispersion (MBD) framework, which is intimately linked to the random-phase approximation for the co...
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Calculations have been made for single-walled zigzag(n,0) carbon nanotubes containing substitutional boron impurity atoms using ab initio density functional theory.It is found that the formation energies of these nanotubes depend on the tube diameter,as do the electronic properties,and show periodic fea-ture that results from their different π bonding structures compared to those of perfect zigzag carbon nanotubes.When more boron atoms are incorporated into a single-walled zigzag carbon nanotube,the substitutional boron atoms tend to come together to form structure of BC3 nanodomains,and B-doped tubes have striking acceptor states above the top of the valence bands.For the structure of BC3,there are two kinds of configurations with different electronic structures.
Atomic Resolution Structure of Monomorphic Aβ42 Amyloid Fibrils.
Colvin, Michael T; Silvers, Robert; Ni, Qing Zhe; Can, Thach V; Sergeyev, Ivan; Rosay, Melanie; Donovan, Kevin J; Michael, Brian; Wall, Joseph; Linse, Sara; Griffin, Robert G
2016-08-01
Amyloid-β (Aβ) is a 39-42 residue protein produced by the cleavage of the amyloid precursor protein (APP), which subsequently aggregates to form cross-β amyloid fibrils that are a hallmark of Alzheimer's disease (AD). The most prominent forms of Aβ are Aβ1-40 and Aβ1-42, which differ by two amino acids (I and A) at the C-terminus. However, Aβ42 is more neurotoxic and essential to the etiology of AD. Here, we present an atomic resolution structure of a monomorphic form of AβM01-42 amyloid fibrils derived from over 500 (13)C-(13)C, (13)C-(15)N distance and backbone angle structural constraints obtained from high field magic angle spinning NMR spectra. The structure (PDB ID: 5KK3 ) shows that the fibril core consists of a dimer of Aβ42 molecules, each containing four β-strands in a S-shaped amyloid fold, and arranged in a manner that generates two hydrophobic cores that are capped at the end of the chain by a salt bridge. The outer surface of the monomers presents hydrophilic side chains to the solvent. The interface between the monomers of the dimer shows clear contacts between M35 of one molecule and L17 and Q15 of the second. Intermolecular (13)C-(15)N constraints demonstrate that the amyloid fibrils are parallel in register. The RMSD of the backbone structure (Q15-A42) is 0.71 ± 0.12 Å and of all heavy atoms is 1.07 ± 0.08 Å. The structure provides a point of departure for the design of drugs that bind to the fibril surface and therefore interfere with secondary nucleation and for other therapeutic approaches to mitigate Aβ42 aggregation. PMID:27355699
Understanding atomic-resolved STM images on TiO{sub 2}(110)-(1 x 1) surface by DFT calculations
Energy Technology Data Exchange (ETDEWEB)
Sanchez-Sanchez, C; Gonzalez, C; Mendez, J; De Andres, P L; MartIn-Gago, J A; Lopez, M F [Instituto Ciencia de Materiales de Madrid (CSIC), C/Sor Juana Ines de la Cruz 3, 28049-Madrid (Spain); Jelinek, P, E-mail: mflopez@icmm.csic.es [Institute of Physics, Czech Academy of Sciences, Cukrovarnicka 10, 162 53-Prague (Czech Republic)
2010-10-08
We present a combination of experimental STM images and DFT calculations to understand the atomic scale contrast of features found in high-resolution STM images. Simulating different plausible structural models for the tip, we have been able to reproduce various characteristics previously reported in experimental images on TiO{sub 2}(110)-(1 x 1) under controlled UHV conditions. Our results allow us to determine the influence of different chemical and morphological tip terminations on the atomic-resolution STM images of the TiO{sub 2}(110)-(1 x 1) surface. The commonest images have been properly explained using standard models for a W tip, either clean or with a single O atom located at the apex. Furthermore, a double transfer of oxygen atoms can account for different types of bizarre atomic-resolution features occasionally seen, and not conclusively interpreted before. Importantly, we discuss how typical point-defects are imaged on this surface by different tips, namely bridging O vacancies and adsorbed OH groups.
New crystal structure prediction of fully hydrogenated borophene by first principles calculations
Wang, Zhi-Qiang; Wang, Hui-Qiong; Feng, Yuan Ping; Zheng, Jin-Cheng
2016-01-01
We have studied the structure stability, band structures and mechanical properties of fully hydrogenated borophene (borophane) with different configurations by first principles calculations. Comparing with the Chair-like borophane (C-boropane) that has been reported in literature, we obtained four new conformers with much lower total-energy. The most stable one, Washboard-like borophane (W-borophane), has energy difference about 113.41 meV/atom lower than C-borophane. In W-borophane, B atoms are staggered by zigzag mode along the a direction, and staggered by up and down wrinkle mode along the b direction. Furthermore, we examined the dynamical stability of borophane conformers by calculating phonon dispersions. For the five conformers, no imaginary frequencies along the high-symmetry directions of the Brillouin zone were found, indicating that the five conformers are all dynamically stable. In addition, the band structures of the five conformers all show a Dirac cone along {\\Gamma}-Y or {\\Gamma}-X direction....
Morphology and atomic-scale structure of single-layer WS2 nanoclusters.
Füchtbauer, Henrik G; Tuxen, Anders K; Moses, Poul G; Topsøe, Henrik; Besenbacher, Flemming; Lauritsen, Jeppe V
2013-10-14
Two-dimensional sheets of transition metal (Mo and W) sulfides are attracting strong attention due to the unique electronic and optical properties associated with the material in its single-layer form. The single-layer MoS2 and WS2 are already in widespread commercial use in catalytic applications as both hydrotreating and hydrocracking catalysts. Consequently, characterization of the morphology and atomic structure of such particles is of utmost importance for the understanding of the catalytic active phase. However, in comparison with the related MoS2 system only little is known about the fundamental properties of single-layer WS2 (tungstenite). Here, we use an interplay of atom-resolved Scanning Tunneling Microscopy (STM) studies of Au(111)-supported WS2 nanoparticles and calculated edge structures using Density Functional Theory (DFT) to reveal the equilibrium morphology and prevalent edge structures of single-layer WS2. The STM results reveal that the single layer S-W-S sheets adopt a triangular equilibrium shape under the sulfiding conditions of the synthesis, with fully sulfided edges. The predominant edge structures are determined to be the (101[combining macron]0) W-edge, but for the smallest nanoclusters also the (1[combining macron]010) S-edges become important. DFT calculations are used to construct phase diagrams of the WS2 edges, and describe their sulfur and hydrogen coordination under different conditions, and in this way shed light on the catalytic role of WS2 edges.
The atomic and electronic structure of dislocations in Ga based nitride semiconductors
BELABBAS, Imad; Ruterana, Pierre; Chen, Jun; NOUET, Gérard
2006-01-01
Abstract The atomic and electronic properties of dislocations in III-N semiconductor layers, especially GaN are presented. The atomic structure of the edge threading dislocation is now well established with three different cores (8 or full core, 5/7 or open core and 4 atom ring). The use of atomistic simulations has confirmed these atomic structures and has given a good understanding of the electronic structure of the screw dislocation. Partial dislocations which are mostly confin...
International Nuclear Information System (INIS)
Born partial wave integrals are considered for electron-neutral atom collisions. It is shown that for relatively general atomic wave functions these may be evaluated analytically. These form the Born reactance matrix Rsub(B) and can be used to calculate the collision strengths in the approximations Ωsup(I), Ωsup(II). It is shown how to modify Ωsup(I) to take some account of exchange using the simple Ochkur approximation. A result is presented for the coupling coefficients that occur in Seaton's multiplication theorem for spherical Bessel functions. (author)
Ternary atom site location in L12-structured intermetallic compounds
International Nuclear Information System (INIS)
Ternary sublattice site occupancy in two L12-structured intermetallic compounds were evaluated by a transmission electron microscope technique called ALCHEMI, or atom site location by channeling enhanced microanalysis, and by x-ray diffractometry, through measuring the relative integrated intensity of fundamental and superlattice x-ray diffraction peaks. The x-ray diffractometry showed that in nickel-rich Ni3Al+Hf hafnium was found to occupy preferentially the aluminum sublattice, and in a multiphase alloy an L12-structured phase with the composition Al74.2Ti19Ni6.8 nickel atoms showed a strong preference for the titanium sublattice. The ALCHEMI data broadly agreed with the x-ray results for Ni3Al but gave completely the opposite result, i.e., a preference of nickel for the titanium sublattice, for Al3Ti. The methods of ALCHEMI and x-ray diffractometry are compared, and it is concluded that ALCHEMI data may be easily convoluted by peak overlap and delocalization effects
Atomic structure of amorphous shear bands in boron carbide.
Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W
2013-01-01
Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.
Simultaneous calculation of aircraft design loads and structural member sizes
Giles, G. L.; Mccullers, L. A.
1975-01-01
A design process which accounts for the interaction between aerodynamic loads and changes in member sizes during sizing of aircraft structures is described. A simultaneous iteration procedure is used wherein both design loads and member sizes are updated during each cycle yielding converged, compatible loads and member sizes. A description is also given of a system of programs which incorporates this process using lifting surface theory to calculate aerodynamic pressure distributions, using a finite-element method for structural analysis, and using a fully stressed design technique to size structural members. This system is tailored to perform the entire process with computational efficiency in a single computer run so that it can be used effectively during preliminary design. Selected results, considering maneuver, taxi, and fatigue design conditions, are presented to illustrate convergence characteristics of this iterative procedure.
Schwinger variational calculation of ionization of hydrogen atoms for large momentum transfers
Indian Academy of Sciences (India)
K Chakrabarti
2002-03-01
Schwinger variational principle is used here to study large momentum transfer cases of electron and positron impact ionization of atomic hydrogen from the ground state at intermediate and moderately high energies. The results appear somewhat better compared to other theories.
Exact calculation of quantum mechanics for inelastic atom-molecule scattering
International Nuclear Information System (INIS)
The time-dependent quantum mechanical method applied to inelastic atom-molecule scattering is presented and examined in interaction picture. The method is not only extremely accurate but also more efficient than the CC method
Wang, Hui; Li, Xu; Gao, Liang; Zhai, Jiao; Liu, Ru; Gao, Xueyun; Wang, Dongqi; Zhao, Lina
2016-06-01
Peptide coated gold nanoclusters (AuNCs) have a precise molecular formula and atomic structure, which are critical for their unique applications in targeting specific proteins either for protein analysis or drug design. To date, a study of the crystal structure of peptide coated AuNCs is absent primarily due to the difficulty of obtaining their crystalline phases in an experiment. Here we study a typical peptide coated AuNC (Au24Peptide8, Peptide = H2N-CCYKKKKQAGDV-COOH, Anal. Chem., 2015, 87, 2546) to figure out its atomic structure and electronic structure using a theoretical method for the first time. In this work, we identify the explicit configuration of the essential structure of Au24Peptide8, Au24(Cys-Cys)8, using density functional theory (DFT) computations and optical spectroscopic experiments, where Cys denotes cysteine without H bonded to S. As the first multidentate ligand binding AuNC, Au24(Cys-Cys)8 is characterized as a distorted Au13 core with Oh symmetry covered by two Au(Cys-Cys) and three Au3(Cys-Cys)2 staple motifs in its atomic structure. The most stable configuration of Au24(Cys-Cys)8 is confirmed by comparing its UV-vis absorption spectrum from time-dependent density-functional theory (TDDFT) calculations with optical absorption measurements, and these results are consistent with each other. Furthermore, we carry out frontier molecular orbital (FMO) calculations to elucidate that the electronic structure of Au24(Cys-Cys)8 is different from that of Au24(SR)20 as they have a different Au/S ratio, where SR represents alkylthiolate. Importantly, the different ligand coatings, Cys-Cys and SR, in Au24(Cys-Cys)8 and Au24(SR)20 cause the different Au/S ratios in the coated Au24. The reason is that the Au/S ratio is crucial in determining the size of the Au core of the ligand protected AuNC, and the size of the Au core corresponds to a specific electronic structure. By the adjustment of ligand coatings from alkylthiolate to peptide, the Au/S ratio
Ying, Chun; Zhao, Erjun; Lin, Lin; Hou, Qingyu
2014-10-01
The structural determination, thermodynamic, mechanical, dynamic and electronic properties of 4d transitional metal diborides MB2 (M = Y-Ag) are systematically investigated by first-principles within the density functional theory (DFT). For each diboride, five structures are considered, i.e. AlB2-, ReB2-, OsB2-, MoB2- and WB2-type structures. The calculated lattice parameters are in good agreement with the previously theoretical and experimental studies. The formation enthalpy increases from YB2 to AgB2 in AlB2-type structure (similar to MoB2- and WB2-type). While the formation enthalpy decreases from YB2 to MoB2, reached minimum value to TcB2, and then increases gradually in ReB2-type structure (similar to OsB2-type), which is consistent with the results of the calculated density of states. The structural stability of these materials relates mainly on electronegative of metals, boron structure and bond characters. Among the considered structures, TcB2-ReB2 (TcB2-ReB2 represents TcB2 in ReB2-type structure, the same hereinafter) has the largest shear modulus (248 GPa), and is the hardest compound. The number of electrons transferred from metals to boron atoms and the calculated densities of states (DOS) indicate that each diboride is a complex mixture of metallic, ionic and covalent characteristics. Trends are discussed.
Improved reliability, accuracy and quality in automated NMR structure calculation with ARIA
Energy Technology Data Exchange (ETDEWEB)
Mareuil, Fabien [Institut Pasteur, Cellule d' Informatique pour la Biologie (France); Malliavin, Thérèse E.; Nilges, Michael; Bardiaux, Benjamin, E-mail: bardiaux@pasteur.fr [Institut Pasteur, Unité de Bioinformatique Structurale, CNRS UMR 3528 (France)
2015-08-15
In biological NMR, assignment of NOE cross-peaks and calculation of atomic conformations are critical steps in the determination of reliable high-resolution structures. ARIA is an automated approach that performs NOE assignment and structure calculation in a concomitant manner in an iterative procedure. The log-harmonic shape for distance restraint potential and the Bayesian weighting of distance restraints, recently introduced in ARIA, were shown to significantly improve the quality and the accuracy of determined structures. In this paper, we propose two modifications of the ARIA protocol: (1) the softening of the force field together with adapted hydrogen radii, which is meaningful in the context of the log-harmonic potential with Bayesian weighting, (2) a procedure that automatically adjusts the violation tolerance used in the selection of active restraints, based on the fitting of the structure to the input data sets. The new ARIA protocols were fine-tuned on a set of eight protein targets from the CASD–NMR initiative. As a result, the convergence problems previously observed for some targets was resolved and the obtained structures exhibited better quality. In addition, the new ARIA protocols were applied for the structure calculation of ten new CASD–NMR targets in a blind fashion, i.e. without knowing the actual solution. Even though optimisation of parameters and pre-filtering of unrefined NOE peak lists were necessary for half of the targets, ARIA consistently and reliably determined very precise and highly accurate structures for all cases. In the context of integrative structural biology, an increasing number of experimental methods are used that produce distance data for the determination of 3D structures of macromolecules, stressing the importance of methods that successfully make use of ambiguous and noisy distance data.
Energy Technology Data Exchange (ETDEWEB)
Yuan, H. K.; Chen, H., E-mail: chenh@swu.edu.cn; Tian, C. L.; Kuang, A. L.; Wang, J. Z. [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China)
2014-04-21
Gadolinium-oxide clusters in various sizes and stoichiometries have been systematically studied by employing the density functional theory with the generalized gradient approximation. The clusters in bulk stoichiometry are relatively more stable and their binding energies increase with the increasing size. Stoichiometric (Gd{sub 2}O{sub 3}){sub n} clusters of n = 1–3 prefer cage-like structures, whereas the clusters of n = 4–30 prefer compact structures layered by wedge-like units and exhibit a rough feature toward the bulk-like arrangement with small disorders of atomic positions. The polyhedral-cages analogous to carbon-fullerenes are stable isomers yet not the minimum energy configurations. Their stabilities can be improved by embedding one oxygen atom or a suitable cage to form core-shell configurations. The mostly favored antiferromagnetic couplings between adjacent Gd atoms are nearly degenerated in energy with their ferromagnetic couplings, resulting in super-paramagnetic characters of gadolinium-oxide clusters. The Ruderman-Kittel-Kasuya-Yosida (RKKY)-type mechanism together with the superexchange-type mechanism plays cooperation role for the magnetic interactions in clusters. We present, as a function of n, calculated binding energies, ionization potential, electron affinity, and electronic dipole moment.
Tailoring atomic structure to control the electronic transport in zigzag graphene nanoribbon
Energy Technology Data Exchange (ETDEWEB)
Zeng, Hui [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Zhao, Jun, E-mail: zhaojun@yangtzeu.edu.cn [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Wei, Jianwei [College of Optoelectronic Information, Chongqing University of Technology, Chongqing 400054 (China); Zeng, Xianliang [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Xu, Yang [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou, Zhejiang 310027 (China)
2012-10-01
We have performed ab initio density functional theory calculation to study the electronic transport properties of the tailored zigzag-edged graphene nanoribbon (ZGNR) with particular electronic transport channels. Our results demonstrated that tailoring the atomic structure had significantly influenced the electronic transport of the defective nanostructures, and could lead to the metal-semiconducting transition when sufficient atoms are tailored. The asymmetric I–V characteristics as a result of symmetry breaking have been exhibited, which indicates the route to utilize GNR as a basic component for novel nanoelectronics. -- Highlights: ► M–S transition induced by tailoring nanostructure. ► Asymmetric I–V curve due to symmetry breaking. ► Controllable electron transport by designing nanofiguration.
Atomic structures of Zr-based metallic glasses
Institute of Scientific and Technical Information of China (English)
2008-01-01
The atomic structures of Zr-Ni and Zr-Ti-Al-Cu-Ni metallic glasses were investigated by using classical molecular dynamic (MD),reverse Monte Carlo (RMC),ab initio MD (AIMD) simulations and high resolution transmission electron microscopy (HRTEM) techniques. We focused on the short-range order (SRO) and medium-range order (MRO) in the glassy structure. It is shown that there are icosahedral,FCC-and BCC-type SROs in the Zr-based metallic glasses. A structural model,characterized by imperfect ordered packing (IOP),was proposed based on the MD simulation and confirmed by the HRTEM observation. Furthermore,the evolution from IOP to nanocrystal during the crystallization of metallic glasses was also ex-plored. It is found that the growth from IOP to nanocrystal proceeds through three distinct stages: the formation of quasi-ordered structure with one-dimensional (1D) periodicity,then 2D periodicity,and finally the formation of 3D nanocrystals. It is also noted that these three growth steps are crosslinked.
Atomic structures of Zr-based metallic glasses
Institute of Scientific and Technical Information of China (English)
HUI XiDong; LIU Xiongdun; GAO Rui; HOU HuaiYu; FANG HuaZhi; LIU ZiKui; CHEN GuoLiang
2008-01-01
The atomic structures of Zr-Ni and Zr-Ti-Al-Cu-Ni metallic glasses were investigated by using classical molecular dynamic (MD), reverse Monte Carlo (RMC), ab initio MD (AIMD) simulations and high resolution transmission electron microscopy (HRTEM) techniques. We focused on the short-range order (SRO) and medium-range order (MRO) in the glassy structure. It is shown that there are icosahedral, FCC- and BCC-type SROs in the Zr-based metallic glasses. A structural model, characterized by imperfect ordered packing (IOP), was proposed based on the MD simulation and confirmed by the HRTEM observation. Furthermore, the evolution from lOP to nanocrystal during the crystallization of metallic glasses was also ex-plored. It is found that the growth from IOP to nanocrystal proceeds through three distinct stages: the formation of quasi-ordered structure with one-dimensional (1 D) periodicity, then 2D periodicity, and finally the formation of 3D nanocrystals. It is also noted that these three growth steps are crosslinked.
The Structure of Light Nuclei and Its Effect on Precise Atomic Measurements
Friar, J. L.
2002-01-01
My talk will consist of three parts: (a) what every atomic physicist needs to know about the physics of light nuclei [and no more]; (b) what nuclear physicists can do for atomic physics; (c) what atomic physicists can do for nuclear physics. A brief qualitative overview of the nuclear force and calculational techniques for light nuclei will be presented, with an emphasis on debunking myths and on recent progress in the field. Nuclear quantities that affect precise atomic measurements will be ...
The Structure of Light Nuclei and Its Effect on Precise Atomic Measurements
Friar, J. L.
2002-01-01
This review consists of three parts: (a) what every atomic physicist needs to know about the physics of light nuclei; (b) what nuclear physicists can do for atomic physics; (c) what atomic physicists can do for nuclear physics. A brief qualitative overview of the nuclear force and calculational techniques for light nuclei will be presented, with an emphasis on debunking myths and on recent progress in the field. Nuclear quantities that affect precise atomic measurements will be discussed, tog...
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The stacking fault energies of five fcc metals (Cu, Ag, Au, Ni and Al) with various quantivalences have been calculated by embedded-atom method (EAM). It indicated that the stacking fault energy is mainly determined by the metallic bond-energy and the lattice constant. Thus, monovalent fcc metals should have different stacking fault energies, contrary to Attree's conclusion. The interaction energy between stacking faults one {111} layer apart in a fcc metal is found to be 1/40-1/250 of its self-energy, while it becomes zero when the two stacking faults are two layers apart. The twin energy is just half of the energy of intrinsic stacking fault energy without the consideration of lattice relax-ation and the energy of a single intrinsic stacking fault is almost the same as that of extrinsic stacking fault, which are consistent with the results from the calculation of Lennard-Jones force between atoms, but differ from Attree's result.
Kinkhabwala, A; Sako, M; Gu, M F; Kahn, S M; Paerels, F B S
2003-01-01
We present a detailed model of the discrete X-ray spectroscopic features expected from steady-state, low-density photoionized plasmas. We apply the Flexible Atomic Code (FAC) to calculate all of the necessary atomic data for the full range of ions relevant for the X-ray regime. These calculations have been incorporated into a simple model of a cone of ions irradiated by a point source located at its tip (now available as the XSPEC model PHOTOION). For each ionic species in the cone, photoionization is balanced by recombination and ensuing radiative cascades, and photoexcitation of resonance transitions is balanced by radiative decay. This simple model is useful for diagnosing X-ray emission mechanisms, determining photoionization/photoexcitation/recombination rates, fitting temperatures and ionic emission measures, and probing geometrical properties (covering factor/column densities/radial filling factor/velocity distributions) of absorbing/reemitting regions in photoionized plasmas. Such plasmas have already...
Atomic structure of the adsorption of transition metals on silicon surfaces
Energy Technology Data Exchange (ETDEWEB)
Cocoletzi, G.H. [IF-BUAP, 72000 Puebla (Mexico); Takeuchi, N. [CCMC-UNAM, Ensenada, BCN (Mexico)
2007-07-01
Full text: Solid state devices are useful for their high sensitivity in a small volume. Applications of such devices as dose materials include semi-conducting dose-rate, and dose-reading measuring devices. Transition metals (TM) have electronic and atomic properties similar to those of rare earth elements when they are adsorbed on silicon surfaces. The interfaces of transition metals silicides with Si (111) have very small lattice mismatches, sharp interfaces, and low Schottky barrier, making them ideal in electronic devices, such as infrared detectors and rectifying contacts. In this work we shall describe our first principles total energy calculations to investigate structural properties of bulk ScSi and YSi, the two dimensional arrangement of ScSi{sub 2} and YSi{sub 2} on the Si(111) surface, and the growth of a few layers of ScSi{sub 1.7} and YSi{sub 1.7} on the Si(111) surface. Our calculated bulk structural parameters are in excellent agreement with experimental values. It will be shown that one monolayer of a TM on Si( l l 1) yields a two dimensional phase with (lxl) periodicity consisting of a layer of TM atoms on T4 sites and a Si bilayer on top. This double layer of Si atoms is very close to ideal Si(111)-(1x1) surface, but rotated 180 with respect to the rest of the crystal. More layers of TM silicide epitaxially grown on Si(l 11) result in a hexagonal structure similar to bulk ScSi2 and YSi2: graphite-like Si planes (with vacancies) intercalated with TM planes, and forming a ({radical}3x{radical}3) arrangement with a ScSi{sub 1.7} and YSi{sub 1.7} stoichiometry. The top Si layer does not contain vacancies and it does not present a graphite-like structure, but forms a bilayer arrangement as in bulk Si. (Author)
The Atomic scale structure of liquid metal-electrolyte interfaces.
Murphy, B M; Festersen, S; Magnussen, O M
2016-08-01
Electrochemical interfaces between immiscible liquids have lately received renewed interest, both for gaining fundamental insight as well as for applications in nanomaterial synthesis. In this feature article we demonstrate that the atomic scale structure of these previously inaccessible interfaces nowadays can be explored by in situ synchrotron based X-ray scattering techniques. Exemplary studies of a prototypical electrochemical system - a liquid mercury electrode in pure NaCl solution - reveal that the liquid metal is terminated by a well-defined atomic layer. This layering decays on length scales of 0.5 nm into the Hg bulk and displays a potential and temperature dependent behaviour that can be explained by electrocapillary effects and contributions of the electronic charge distribution on the electrode. In similar studies of nanomaterial growth, performed for the electrochemical deposition of PbFBr, a complex nucleation and growth behaviour is found, involving a crystalline precursor layer prior to the 3D crystal growth. Operando X-ray scattering measurements provide detailed data on the processes of nanoscale film formation. PMID:27301317
The Atomic scale structure of liquid metal-electrolyte interfaces
Murphy, B. M.; Festersen, S.; Magnussen, O. M.
2016-07-01
Electrochemical interfaces between immiscible liquids have lately received renewed interest, both for gaining fundamental insight as well as for applications in nanomaterial synthesis. In this feature article we demonstrate that the atomic scale structure of these previously inaccessible interfaces nowadays can be explored by in situ synchrotron based X-ray scattering techniques. Exemplary studies of a prototypical electrochemical system - a liquid mercury electrode in pure NaCl solution - reveal that the liquid metal is terminated by a well-defined atomic layer. This layering decays on length scales of 0.5 nm into the Hg bulk and displays a potential and temperature dependent behaviour that can be explained by electrocapillary effects and contributions of the electronic charge distribution on the electrode. In similar studies of nanomaterial growth, performed for the electrochemical deposition of PbFBr, a complex nucleation and growth behaviour is found, involving a crystalline precursor layer prior to the 3D crystal growth. Operando X-ray scattering measurements provide detailed data on the processes of nanoscale film formation.
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.
An Extensive Database of Electronic Structure Calculations between Transition Metals
Sayed, Shereef; Papaconstantopoulos, Dimitrios
Density Functional Theory and its derived application methods, such as the Augmented Plane Wave (APW) method, have shown great success in predicting the fundamental properties of materials. In this work, we apply the APW method to explore the properties of diatomic pairs of transition metals in the CsCl structure, for all possible combinations. A total of 435 compounds have been studied. The predicted Density of States, and Band Structures are presented, along with predicted electron-phonon coupling and Stoner Criterion, in order to identify potential new superconducting or ferromagnetic materials. This work is performed to demonstrate the concept of ``high-throughput'' calculations at the crossing-point of ``Big Data'' and materials science. Us Dept of Energy.
Calculation of bipolar injection and recombination in MNOS structure
Energy Technology Data Exchange (ETDEWEB)
Gadiyak, G.V.; Obrekht, M.S.; Sinitsa, S.P.
1986-07-01
The authors calculate the process of polarization of MNOS structure under conditions of bipolar injection and recombination and calculate the basic features of the behavior of the current and the trapped charge in the process of polarization. The authors also propose that the electrons and holes tunnel directly into the conduction band of the nitride so that the tunneling is determined by the quasiclassical probability of sub-barrier transmission. Comparison with experimental data shows that the calculation describes only the exponential dependence of the time up to breakdown on the applied electric field. Quantitative agreement requires substantial lowering of the magnitude of the hole current flowing through the triangular barrier. On the basis of the model of the Si/sub 3/N/sub 4/-Al contact studied, this cannot be achieved because of the magnitude of the Si/sub 3/N/sub 4/-Al is probably more complicated, possibly because of the formation of intermediate AlN and Al/sub 2/O/sub 3/ phases.
Bencs, László; Laczai, Nikoletta; Ajtony, Zsolt
2015-07-01
A combination of former convective-diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass - m0) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m0 values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm3 min- 1) of the internal sheath gas during atomization. The theoretical and experimental ratios of m0(mini-flow)-to-m0(stop-flow) were closely similar for each study analyte. Likewise, the calculated m0 data gave a fairly good agreement with the corresponding experimental m0 values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology.
Wang, Hui; Li, Xu; Gao, Liang; Zhai, Jiao; Liu, Ru; Gao, Xueyun; Wang, Dongqi; Zhao, Lina
2016-06-01
Peptide coated gold nanoclusters (AuNCs) have a precise molecular formula and atomic structure, which are critical for their unique applications in targeting specific proteins either for protein analysis or drug design. To date, a study of the crystal structure of peptide coated AuNCs is absent primarily due to the difficulty of obtaining their crystalline phases in an experiment. Here we study a typical peptide coated AuNC (Au24Peptide8, Peptide = H2N-CCYKKKKQAGDV-COOH, Anal. Chem., 2015, 87, 2546) to figure out its atomic structure and electronic structure using a theoretical method for the first time. In this work, we identify the explicit configuration of the essential structure of Au24Peptide8, Au24(Cys-Cys)8, using density functional theory (DFT) computations and optical spectroscopic experiments, where Cys denotes cysteine without H bonded to S. As the first multidentate ligand binding AuNC, Au24(Cys-Cys)8 is characterized as a distorted Au13 core with Oh symmetry covered by two Au(Cys-Cys) and three Au3(Cys-Cys)2 staple motifs in its atomic structure. The most stable configuration of Au24(Cys-Cys)8 is confirmed by comparing its UV-vis absorption spectrum from time-dependent density-functional theory (TDDFT) calculations with optical absorption measurements, and these results are consistent with each other. Furthermore, we carry out frontier molecular orbital (FMO) calculations to elucidate that the electronic structure of Au24(Cys-Cys)8 is different from that of Au24(SR)20 as they have a different Au/S ratio, where SR represents alkylthiolate. Importantly, the different ligand coatings, Cys-Cys and SR, in Au24(Cys-Cys)8 and Au24(SR)20 cause the different Au/S ratios in the coated Au24. The reason is that the Au/S ratio is crucial in determining the size of the Au core of the ligand protected AuNC, and the size of the Au core corresponds to a specific electronic structure. By the adjustment of ligand coatings from alkylthiolate to peptide, the Au/S ratio
Calculating the energy of electron in H-atom using modified SUSY physics
Directory of Open Access Journals (Sweden)
U. V. S. Seshavatharam
2015-02-01
Full Text Available In this paper considering the authors previously proposed SUSY concept - ‘fermion and boson mass ratio is close to 2.26’ and considering the electroweak neutral boson, an attempt is made to understand the total energy of revolving electron in the Hydrogen atom. Thus in this paper authors succeeded in extending the basic applications of SUSY and Electroweak theory to atomic level. With further research and analysis, the hidden secrets of electroweak unification can be understood very easily.
You, Pei-Lin
2008-01-01
Using special capacitors our experiments discovered that the electric susceptibility Xe of K, Rb or Cs vapor varies in direct proportion to their density N, and inversely proportional to the absolute temperature T as polar molecules. Their capacitance(C) at different voltage (V) was measured. The C-V curve shows that the saturation polarization of K, Rb or Cs vapor has be observed when the field E more than ten to fiveth power V/m. The measurements show that the ground state K, Rb or Cs atom is polar atom with a large permanent electric dipole moment (EDM) of the order of eao (ao is Bohr radius) as excited state of hydrogen atom. But we can not calculate the EDM of an atom using Boltzmann constant. Because of the mechanism of polar atoms by which orientation polarization arises completely differs from polar molecules. The orientation polarization of polar molecule, such as HCl or H2O etc, is a molecule as a whole turned toward the direction of an external field. Unlike polar molecules, the orientation polariz...
Energy Technology Data Exchange (ETDEWEB)
Miyasita, Mitiyasu, E-mail: miyasita.mitiyasu@gmail.com [Graduate School of Science and Engineering, Shinshu University, Ueda 386-8567 (Japan); Higuchi, Katsuhiko [Graduate School of Advanced Science of Matter, Hiroshima University, Higashi-Hiroshima 739-8527 (Japan); Higuchi, Masahiko [Department of Physics, Faculty of Science, Shinshu University, Matsumoto 390-8621 (Japan)
2012-07-15
We present an alternative scheme for calculating the unrestricted Hartree-Fock (HF) equation. The scheme is based on the variational method utilizing the sophisticated basis functions that include no adjustable parameters. The validity of the present scheme is confirmed by actual calculations of the boron and neon atoms. The total energy of the present scheme is lower than that of the conventional restrictive HF equation, but higher than that of the CI method. Also, the resultant wave function satisfies the electron-nucleus cusp condition.
Thies, B.; Sepp, W.-D.; Fricke, B.
1989-07-01
The time dependence of a heavy-ion-atom collision system is solved via a set of coupled channel equations using energy eigen-values and matrix elements from a self-consistent field relativistic molecular many-electron Dirac-Fock-Slater calculation. Within this independent particle model we give a full many-particle interpretation by performing a small number of single-particle calculations. First results for the P( b) curves for the Ne K-hole excitation for the systems F 8+-Ne and F 6+-Ne as examples are discussed.
International Nuclear Information System (INIS)
The improved adiabatic representation is used in calculations of elastic and hyperfine-transition cross sections for symmetric collisions of pμ, dμ, and tμ with bare p, d, and t nuclei and with H, D, and T atoms, respectively. The cross sections for dμ+d and tμ+t are in excellent agreement with other recent determinations, while those for pμ+p are about 30% larger at low energies. The electronic screening is calculated nonperturbatively and found to be about 30% smaller in magnitude than the previously calculated value at large internuclear distances, and to deviate considerably from the asymptotic form in the molecular region. The resulting screened elastic cross sections are up to 60% smaller than those obtained using the old screening potential. The reactance matrices, needed for calculations of molecular-target effects, are given in tables
International Nuclear Information System (INIS)
A pseudopotential model for calculation of atomic processes under interaction with hard x-ray photons is applied to calculation of Krypton photoionization cross sections by photons with energy in the 20–25 keV range. These cross sections, as well as the mean charge of the resulting ions calculated using the Monte Carlo simulation scheme, are in good agreement with the other theoretical calculations and with the experiment. The obtained results open the doors for new techniques in the design of gas-monitor detectors to control the intensity, coordinates and energy of x-ray free-electron laser (XFEL) beams in the hard x-ray photon energy range. First, Monte Carlo simulations of a scintillation detector application for gas-monitors have been performed. (letter)
Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition.
Mauguière, Frédéric A L; Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Farantos, Stavros C; Wiggins, Stephen
2015-10-15
We re-examine the prototypical roaming reaction--hydrogen atom roaming in formaldehyde decomposition--from a phase space perspective. Specifically, we address the question "why do trajectories roam, rather than dissociate through the radical channel?" We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs, we show that in the roaming region, there is an unstable periodic orbit whose stable and unstable manifolds define a conduit that both encompasses all roaming trajectories exiting the formaldehyde well and shepherds them toward the H2···CO well. PMID:26499774
First-principles calculations of BC{sub 4}N nanostructures: stability and electronic structure
Energy Technology Data Exchange (ETDEWEB)
Freitas, A.; Azevedo, S. [Universidade Federal da Paraiba, CCEN, Departamento de Fisica, Joao Pessoa, PB (Brazil); Machado, M. [Universidade Federal de Pelotas, Departamento de Fisica, Pelotas, RS (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitoria da Conquista, Vitoria da Conquista, BA (Brazil)
2012-07-15
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC{sub 4}N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 A, or cut and bent to form nanocones, with 60 and 120 disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B-N and C-C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D {sup 2} law. The results show that the 60 disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. (orig.)
DEFF Research Database (Denmark)
Ruud, Kenneth; Helgaker, Trygve; Kobayashi, Rika;
1994-01-01
to corresponding individual gauges for localized orbitals (IGLO) results. The London results show better basis set convergence than IGLO, especially for heavier atoms. It is shown that the choice of active space is crucial for determination of accurate nuclear shielding constants. © 1994 American Institute...
Energy Technology Data Exchange (ETDEWEB)
Davis, Barry M.; McCaffrey, John G., E-mail: john.mccaffrey@nuim.ie [Department of Chemistry, Maynooth University, National University of Ireland—Maynooth, County Kildare (Ireland)
2016-01-28
Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y{sup 1}P←a{sup 1}S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm{sup −1}). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr{sub 2} while this transition is quenched in Ba{sub 2}. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba{sub 2} indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.
Ren, Xiao-Yan; Niu, Chun-Yao; Chen, Wei-Guang; Tang, Ming-Sheng; Cho, Jun-Hyung
2016-07-21
Exploring the properties of noble metal atoms and nano- or subnano-clusters on the semiconductor surface is of great importance in many surface catalytic reactions, self-assembly processes, crystal growth, and thin film epitaxy. Here, the energetics and kinetic properties of a single Cu atom and previously reported Cu magic clusters on the Si(111)-(7 × 7) surface are re-examined by the state-of-the-art first-principles calculations based on density functional theory. First of all, the diffusion path and high diffusion rate of a Cu atom on the Si(111)-(7 × 7) surface are identified by mapping out the total potential energy surface of the Cu atom as a function of its positions on the surface, supporting previous experimental hypothesis that the apparent triangular light spots observed by scanning tunneling microscopy (STM) are resulted from a single Cu atom frequently hopping among adjacent adsorption sites. Furthermore, our findings confirm that in the low coverage of 0.15 monolayer (ML) the previously proposed hexagonal ring-like Cu6 cluster configuration assigned to the STM pattern is considerably unstable. Importantly, the most stable Cu6/Si(111) complex also possesses a distinct simulated STM pattern with the experimentally observed ones. Instead, an energetically preferred solid-centered Cu7 structure exhibits a reasonable agreement between the simulated STM patterns and the experimental images. Therefore, the present findings convincingly rule out the tentative six-atom model and provide new insights into the understanding of the well-defined Cu nanocluster arrays on the Si(111)-(7 × 7) surface. PMID:27341196
Fabrication and atomic structure of size-selected, layered MoS2 clusters for catalysis.
Cuddy, Martin J; Arkill, Kenton P; Wang, Zhi Wei; Komsa, Hannu-Pekka; Krasheninnikov, Arkady V; Palmer, Richard E
2014-11-01
Well defined MoS2 nanoparticles having a layered structure and abundant edges would be of considerable interest for applications including photocatalysis. We report the atomic structure of MoS2 size-selected clusters with mass in a range all the way from 50 to ∼2000 MoS2 units. The clusters were prepared by magnetron sputtering and gas condensation prior to size selection and soft landing on carbon supports. Aberration-corrected scanning transmission electron microscopy (STEM) in high-angle annular dark-field (HAADF) mode reveals a layered structure and Mo-Mo spacing similar to the bulk material. The mean number of layers in these lamellar clusters increases from one to three with increasing mass, consistent with density functional theory calculations of the balance between edge energies and interlayer binding. PMID:25226541
Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface.
Sun, Ce; Paulauskas, Tadas; Sen, Fatih G; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K Y; Klie, Robert F; Kim, Moon J
2016-01-01
Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1-10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis. PMID:27255415
Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface
Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.
2016-06-01
Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.
Energy Technology Data Exchange (ETDEWEB)
Belianinov, Alex, E-mail: belianinova@ornl.gov; Ganesh, Panchapakesan; Lin, Wenzhi; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V. [Oak Ridge National Laboratory, Institute for Functional Imaging of Materials, Center for Nanophase Material Science, Oak Ridge, Tennessee 37922 (United States); Sales, Brian C.; Sefat, Athena S. [Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, Tennessee 37922 (United States)
2014-12-01
Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe{sub 0.55}Se{sub 0.45} (T{sub c} = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe{sub 1−x}Se{sub x} structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.
Dopant distributions in n-MOSFET structure observed by atom probe tomography.
Inoue, K; Yano, F; Nishida, A; Takamizawa, H; Tsunomura, T; Nagai, Y; Hasegawa, M
2009-11-01
The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted. PMID:19775815
Dopant distributions in n-MOSFET structure observed by atom probe tomography
Energy Technology Data Exchange (ETDEWEB)
Inoue, K., E-mail: koji.inoue@hs3.ecs.kyoto-u.ac.jp [The Oarai Center, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yano, F.; Nishida, A. [MIRAI-Selete, Tsukuba, Ibaraki 305-8569 (Japan); Takamizawa, H. [The Oarai Center, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Tsunomura, T. [MIRAI-Selete, Tsukuba, Ibaraki 305-8569 (Japan); Nagai, Y. [The Oarai Center, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Hasegawa, M. [Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577 (Japan); Cyclotron and Radioisotope Center, Tohoku University, Sendai 980-8578 (Japan)
2009-11-15
The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted.
Heyrovska, Raji
2008-01-01
It has been shown recently that chemical bond lengths, in general, like those in the components of nucleic acids, caffeine related compounds, all essential amino acids, methane, benzene, graphene and fullerene are sums of the radii of adjacent atoms constituting the bond. Earlier, the crystal ionic distances in all alkali halides and lengths of many partially ionic bonds were also accounted for by the additivity of ionic as well as covalent radii. Here, the atomic structures of riboflavin and its reduced form are presented based on the additivity of the same set of atomic radii as for other biological molecules.
Siretanu, Igor; van den Ende, Dirk; Mugele, Frieder
2016-04-01
Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all materials investigated, namely gibbsite, kaolinite, illite, and Na-montmorillonite of both natural and synthetic origin. Next to regions of perfect crystallinity, we routinely observe extended regions of various types of defects on the surfaces, including vacancies of one or few atoms, vacancy islands, atomic steps, apparently disordered regions, as well as strongly adsorbed seemingly organic and inorganic species. While their exact nature is frequently difficult to identify, our observations clearly highlight the ubiquity of such defects and their relevance for the overall physical and chemical properties of clay nanoparticle-water interfaces.Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed
2012-08-20
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Heyrovska, Raji
2008-01-01
It has been shown recently that chemical bond lengths, in general, like those in the components of nucleic acids, caffeine related compounds, all essential amino acids, methane, benzene, graphene and fullerene are sums of the radii of adjacent atoms constituting the bond. Earlier, the crystal ionic distances in all alkali halides and lengths of many partially ionic bonds were also accounted for by the additivity of ionic as well as covalent radii. Here, the atomic structures of riboflavin and...
Heyrovska, Raji
2007-01-01
The interpretation by the author in recent years of bond lengths as sums of the relevant atomic or ionic radii has been extended here to the bonds in the skeletal structures of adenine, guanine, thymine, cytosine, uracil, ribose, deoxyribose and phosphoric acid. On examining the bond length data in the literature, it has been found that the averages of the bond lengths are close to the sums of the corresponding atomic covalent radii of carbon, nitrogen, oxygen, hydrogen and phosphorus. Thus, ...
Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces
McBriarty, Martin E.
Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.
Galvan, D H
2003-01-01
To get insight into the electronic properties of PrFe4P12 skutterudite, band electronic structure calculations, Total and Projected Density of States, Crystal Orbital Overlap Population and Mulliken Population Analysis were performed. The energy bands yield a semi metallic behavior with a direct gap (at gamma) of 0.02 eV. Total and Projected Density of States provided information of the contribution from each orbital of each atom to the total Density of States. Moreover, the bonding strength between some atoms within the unit cell was obtained. Mulliken Population analysis suggests ionic behavior for this compound.
Relativistic calculations of the non-resonant two-photon ionization of neutral atoms
Hofbrucker, Jiri; Fritzsche, Stephan
2016-01-01
The non-resonant two-photon one-electron ionization of neutral atoms is studied theoretically in the framework of relativistic second-order perturbation theory and independent particle approximation. In particular, the importance of relativistic and screening effects in the total two-photon ionization cross section is investigated. Detailed computations have been carried out for the K-shell ionization of neutral Ne, Ge, Xe, and U atoms. The relativistic effects significantly decrease the total cross section, for the case of U, for example, they reduce the total cross section by a factor of two. Moreover, we have found that the account for the screening effects of the remaining electrons leads to occurrence of an unexpected minimum in the total cross section at the total photon energies equal to the ionization threshold, for the case of Ne, for example, the cross section drops there by a factor of three.
QED shift calculations in relativistic many-electron atoms and ions
Tupitsyn, I I; Safronova, M S; Shabaev, V M; Dzuba, V A
2016-01-01
We incorporated quantum electrodynamics (QED) corrections into the broadly-applicable high-precision relativistic method that combines configuration interaction (CI) and linearized coupled-cluster approaches. With the addition of the QED, this CI+all-order method allows one to accurately predict properties of heavy ions of particular interest to the design of precision atomic clocks and tests of fundamental physics. To evaluate the accuracy of the QED contributions and test various QED models, we incorporated four different one-electron QED potentials. We demonstrated that all of them give consistent and reliable results. For the strongly bound electrons (i.e. inner electrons of heavy atoms, or valence electrons in highly-charged ions), the nonlocal potentials are more accurate, than the local one. Results are presented for cases of particular experimental interest.
International Nuclear Information System (INIS)
A combination of former convective–diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass — m0) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m0 values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm3 min−1) of the internal sheath gas during atomization. The theoretical and experimental ratios of m0(mini-flow)-to-m0(stop-flow) were closely similar for each study analyte. Likewise, the calculated m0 data gave a fairly good agreement with the corresponding experimental m0 values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology. - Highlights: • A calculation scheme for convective–diffusive vapor loss in GFAAS is described. • Residence time (τ) formulas were compared for sensitivity (m0) in a THGA furnace. • Effects of the sample/platform dimension and dosing hole on τ were assessed. • Theoretical m0 of 18 analytes were calculated for stopped & mini furnace gas flows. • Experimental
Energy Technology Data Exchange (ETDEWEB)
Bencs, László, E-mail: bencs.laszlo@wigner.mta.hu [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Laczai, Nikoletta [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Ajtony, Zsolt [Institute of Food Science, University of West Hungary, H-9200 Mosonmagyaróvár, Lucsony utca 15–17 (Hungary)
2015-07-01
A combination of former convective–diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass — m{sub 0}) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m{sub 0} values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm{sup 3} min{sup −1}) of the internal sheath gas during atomization. The theoretical and experimental ratios of m{sub 0}(mini-flow)-to-m{sub 0}(stop-flow) were closely similar for each study analyte. Likewise, the calculated m{sub 0} data gave a fairly good agreement with the corresponding experimental m{sub 0} values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology. - Highlights: • A calculation scheme for convective–diffusive vapor loss in GFAAS is described. • Residence time (τ) formulas were compared for sensitivity (m{sub 0}) in a THGA furnace. • Effects of the sample/platform dimension and dosing hole on τ were assessed. • Theoretical m{sub 0} of 18 analytes were
Ab initio random structure search for 13-atom clusters of fcc elements.
Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M
2013-03-27
The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd13 and Au13, we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au13, which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons.
k.p Parameters with Accuracy Control from Preexistent First-Principles Band Structure Calculations
Sipahi, Guilherme; Bastos, Carlos M. O.; Sabino, Fernando P.; Faria Junior, Paulo E.; de Campos, Tiago; da Silva, Juarez L. F.
The k.p method is a successful approach to obtain band structure, optical and transport properties of semiconductors. It overtakes the ab initio methods in confined systems due to its low computational cost since it is a continuum method that does not require all the atoms' orbital information. From an effective one-electron Hamiltonian, the k.p matrix representation can be calculated using perturbation theory and the parameters identified by symmetry arguments. The parameters determination, however, needs a complementary approach. In this paper, we developed a general method to extract the k.p parameters from preexistent band structures of bulk materials that is not limited by the crystal symmetry or by the model. To demonstrate our approach, we applied it to zinc blende GaAs band structure calculated by hybrid density functional theory within the Heyd-Scuseria-Ernzerhof functional (DFT-HSE), for the usual 8 ×8 k.p Hamiltonian. Our parameters reproduced the DFT-HSE band structure with great accuracy up to 20% of the first Brillouin zone (FBZ). Furthermore, for fitting regions ranging from 7-20% of FBZ, the parameters lie inside the range of values reported by the most reliable studies in the literature. The authors acknowledge financial support from the Brazilian agencies CNPq (Grant #246549/2012-2) and FAPESP (Grants #2011/19333-4, #2012/05618-0 and #2013/23393-8).
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...
Molecular Structure, Theoretical Calculation and Thermodynamic Properties of Tebuconazole
Institute of Scientific and Technical Information of China (English)
MA Haixia; SONG Jirong; HUANG Ting; LU Xingqiang; XU Kangzhen; SUN Xiaohong
2009-01-01
Single crystals of 5-(4-chlorophenyl)-2,2-dimethyl-3-(1,2,4-triazol-1-ylmethyl)-pentom-3-ol (tebuconazole) were obtained in toluene. The single-crystal X-ray diffraction studies showed that it crystallized in the monoclinic system, with space group P2(1)/c and crystal parameters of a= 1.1645(1) nm, b= 1.6768(2) nm, c= 1.7478(2) nm,β=92.055(2)°, Dc= 1.199 g/cm3, Z=4 and F(000)= 1312. Density functional theory (DFT) B3LYP was employed to optimize the structure and calculate the frequencies of tebuconazole. The calculated geometrical parameters are close to the corresponding experimental ones. The specific heat capacity of the title compound was determined with continuous Cp mode of a mircocalorimeter. In the determining temperature range from 283 to 353 K, the special heat capacity of the title compound presents good linear relation with temperature. Using the determined relation-ship of Cp with temperature T, thermodynamic functions (enthalpy, entropy and Gibbs free energy) of the title compound between 283 and 353 K, relative to the standard temperature 298.15 K, were derived through thermody-namic relationship.
Adaptations in Electronic Structure Calculations in Heterogeneous Environments
Energy Technology Data Exchange (ETDEWEB)
Talamudupula, Sai [Iowa State Univ., Ames, IA (United States)
2011-01-01
Modern quantum chemistry deals with electronic structure calculations of unprecedented complexity and accuracy. They demand full power of high-performance computing and must be in tune with the given architecture for superior e ciency. To make such applications resourceaware, it is desirable to enable their static and dynamic adaptations using some external software (middleware), which may monitor both system availability and application needs, rather than mix science with system-related calls inside the application. The present work investigates scienti c application interlinking with middleware based on the example of the computational chemistry package GAMESS and middleware NICAN. The existing synchronous model is limited by the possible delays due to the middleware processing time under the sustainable runtime system conditions. Proposed asynchronous and hybrid models aim at overcoming this limitation. When linked with NICAN, the fragment molecular orbital (FMO) method is capable of adapting statically and dynamically its fragment scheduling policy based on the computing platform conditions. Signi cant execution time and throughput gains have been obtained due to such static adaptations when the compute nodes have very di erent core counts. Dynamic adaptations are based on the main memory availability at run time. NICAN prompts FMO to postpone scheduling certain fragments, if there is not enough memory for their immediate execution. Hence, FMO may be able to complete the calculations whereas without such adaptations it aborts.
A near atomic structure of the active human apoptosome
Cheng, Tat Cheung; Hong, Chuan; Akey, Ildikó V; Yuan, Shujun; Akey, Christopher W
2016-01-01
In response to cell death signals, an active apoptosome is assembled from Apaf-1 and procaspase-9 (pc-9). Here we report a near atomic structure of the active human apoptosome determined by cryo-electron microscopy. The resulting model gives insights into cytochrome c binding, nucleotide exchange and conformational changes that drive assembly. During activation an acentric disk is formed on the central hub of the apoptosome. This disk contains four Apaf-1/pc-9 CARD pairs arranged in a shallow spiral with the fourth pc-9 CARD at lower occupancy. On average, Apaf-1 CARDs recruit 3 to 5 pc-9 molecules to the apoptosome and one catalytic domain may be parked on the hub, when an odd number of zymogens are bound. This suggests a stoichiometry of one or at most, two pc-9 dimers per active apoptosome. Thus, our structure provides a molecular framework to understand the role of the apoptosome in programmed cell death and disease. DOI: http://dx.doi.org/10.7554/eLife.17755.001
New crystal structure and physical properties of TcB from first-principles calculations
Zhang, Gang-Tai; Bai, Ting-Ting; Yan, Hai-Yan; Zhao, Ya-Ru
2015-10-01
By combining first-principles calculations with the particle swarm optimization algorithm, we predicted a hexagonal structure for TcB, which is energetically more favorable than the previously reported WC-type and Cmcm structures. The new phase is mechanically and dynamically stable, as confirmed by its phonon and elastic constants calculations. The calculated mechanical properties show that it is an ultra-incompressible and hard material. Meanwhile, the elastic anisotropy is investigated by the shear anisotropic factors and ratio of the directional bulk modulus. Density of states analysis reveals that the strong covalent bonding between Tc and B atoms plays a leading role in forming a hard material. Additionally, the compressibility, bulk modulus, Debye temperature, Grüneisen parameter, specific heat, and thermal expansion coefficient of TcB are also successfully obtained by using the quasi-harmonic Debye model. Project supported by the Science Foundation of Baoji University of Arts and Sciences of China (Grant No. ZK11061) and the Natural Science Foundation of the Education Committee of Shaanxi Province, China (Grant Nos. 2013JK0637, 2013JK0638, and 2014JK1044).
QED Based Calculation of the Fine Structure Constant
Energy Technology Data Exchange (ETDEWEB)
Lestone, John Paul [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-10-13
Quantum electrodynamics is complex and its associated mathematics can appear overwhelming for those not trained in this field. Here, semi-classical approaches are used to obtain a more intuitive feel for what causes electrostatics, and the anomalous magnetic moment of the electron. These intuitive arguments lead to a possible answer to the question of the nature of charge. Virtual photons, with a reduced wavelength of λ, are assumed to interact with isolated electrons with a cross section of πλ^{2}. This interaction is assumed to generate time-reversed virtual photons that are capable of seeking out and interacting with other electrons. This exchange of virtual photons between particles is assumed to generate and define the strength of electromagnetism. With the inclusion of near-field effects the model presented here gives a fine structure constant of ~1/137 and an anomalous magnetic moment of the electron of ~0.00116. These calculations support the possibility that near-field corrections are the key to understanding the numerical value of the dimensionless fine structure constant.
Nuclear structure of light thallium isotopes as deduced from laser spectroscopy on a fast atom beam
International Nuclear Information System (INIS)
After optimizing the system by experiments on /sup 201,203,205/Tl, the neutron-deficient isotopes 189-193Tl have been studied using the collinear fast atom beam laser spectroscopy system at UNISOR on-line to the Holifield Heavy Ion Research Facility. A sensitive system for the measurements was developed since the light isotopes were available in mass-separated beams of only 7 x 104 to 4 x 105 atoms per second. By laser excitation of the 535 nm atomic transitions of atoms in the beam, the 6s27s 2S/sub 1/2/ and 6s26s 2P/sub 3/2/ hyperfine structures were measured, as were the isotope shifts of the 535 nm transitions. From these, the magnetic dipole moments, spectroscopic quadrupole moments and isotopic changes in mean-square charge radius were deduced. The magnetic dipole moments are consistent with previous data. The /sup 190,192/Tl isotopes show a considerable difference in quadrupole deformations as well as an anomalous isotope shift with respect to 194Tl. A large isomer shift in 193Tl is observed implying a larger deformation in the 9/2- isomer than in the 1/2+ ground state. The /sup 189,191,193/Tl isomers show increasing deformation away from stability. A deformed shell model calculation indicates that this increase in deformation can account for the dropping of the 9/2- band in these isotopes while an increase in neutron pairing correlations, having opposite and compensating effects on the rotational moment of inertia, maintains the 9/2- strong-coupled band structure. 105 refs., 27 figs
First principles calculations of the structure and elastic constants of α, β and γ uranium
International Nuclear Information System (INIS)
This study analyzes structural and elastic properties of five uranium crystal structures: the face centered orthorhombic A20 (α phase), the tetragonal D8b (β phase), body centered tetragonal (bct), body centered cubic (γ phase) and face centered cubic structures. Calculations are performed within the density functional theory framework employing the Projector Augmented Wave method and the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE–GGA) of the exchange correlation. The elastic constants are used to compute polycrystalline elastic moduli, Poisson’s ratio and the Debye temperature for all five structures. The α and γ phase properties are compared with theoretical and experimental results. The complex tetragonal 30 atom beta phase is examined in detail. Representation of the β phase by a bct structure is examined; we find that the structure of the β phase is significantly different from the bct phase but exhibits similar elastic properties. This is the first comprehensive investigation into the elastic constants of uranium utilizing the PBE–GGA
Pawlak, Remy; Klinovaja, Jelena; Meier, Tobias; Kawai, Shigeki; Glatzel, Thilo; Loss, Daniel; Meyer, Ernst
2015-01-01
Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localization of MBSs is a key feature and crucial for their future implementation as qubits. Here, we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunneling microscopy (STM) and atomic force microscopy (AFM). We demonstrate that the Fe chains are mono-atomic, structured in a linear fashion, and exhibit zero-bias conductance peaks at their ends which we interprete as signature for a Majorana bound state. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localized at the chain ends (below 25 nm), with two localization lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum computing devices.
International Nuclear Information System (INIS)
Reduction of the peak heat loads on the plasma facing components is essential for the success of the next generation of high fusion power tokamaks such as the International Thermonuclear Experimental Reactor (ITER) [Rebut et al., Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, in press)]. Many present concepts for accomplishing this involve the use of atomic processes to transfer the heat from the plasma to the main chamber and divertor chamber walls and much of the experimental and theoretical physics research in the fusion program is directed toward this issue. The results of these experiments and calculations depend upon a complex interplay of many processes. In order to identify the key features of these experiments and calculations and the relative role of the primary atomic processes, simple quasianalytic models and the latest atomic physics rate coefficients and cross sections have been used to assess the relative roles of central radiation losses through bremsstrahlung, impurity radiation losses from the plasma edge, charge exchange and hydrogen radiation losses from the scrape-off layer, and divertor plasma and impurity radiation losses from the divertor plasma. This analysis indicates that bremsstrahlung from the plasma center and impurity radiation from the plasma edge and divertor plasma can each play a significant role in reducing the power to the divertor plates, and identifies many of the factors which determine the relative role of each process. For instance, for radiation losses in the divertor to be large enough to radiate the power in the divertor for high power experiments, a neutral fraction of 10-3 to 10-2 and an impurity recycling rate of neτrecycle of ∼1016 s m-3 will be required in the divertor
Voronoi analysis of the short-range atomic structure in iron and iron-carbon melts
Sobolev, Andrey; Mirzoev, Alexander
2015-08-01
In this work, we simulated the atomic structure of liquid iron and iron-carbon alloys by means of ab initio molecular dynamics. Voronoi analysis was used to highlight changes in the close environments of Fe atoms as carbon concentration in the melt increases. We have found, that even high concentrations of carbon do not affect short-range atomic order of iron atoms — it remains effectively the same as in pure iron melts.
NUMERICAL CALCULATIONS IN GEOMECHANICS APPLICABLE TO LINEAR STRUCTURES
Directory of Open Access Journals (Sweden)
Vlasov Aleksandr Nikolaevich
2012-10-01
Full Text Available The article covers the problem of applicability of finite-element and engineering methods to the development of a model of interaction between pipeline structures and the environment in the complex conditions with a view to the simulation and projection of exogenous geological processes, trustworthy assessment of their impacts on the pipeline, and the testing of varied calculation methodologies. Pipelining in the areas that have a severe continental climate and permafrost soils is accompanied by cryogenic and exogenous processes and developments. It may also involve the development of karst and/or thermokarst. The adverse effect of the natural environment is intensified by the anthropogenic impact produced onto the natural state of the area, causing destruction of forests and other vegetation, changing the ratio of soils in the course of the site planning, changing the conditions that impact the surface and underground waters, and causing the thawing of the bedding in the course of the energy carrier pumping, etc. The aforementioned consequences are not covered by effective regulatory documents. The latter constitute general and incomplete recommendations in this respect. The appropriate mathematical description of physical processes in complex heterogeneous environments is a separate task to be addressed. The failure to consider the above consequences has repeatedly caused both minor damages (denudation of the pipeline, insulation stripping and substantial accidents; the rectification of their consequences was utterly expensive. Pipelining produces a thermal impact on the environment; it may alter the mechanical properties of soils and de-frost the clay. The stress of the pipeline is one of the principal factors that determines its strength and safety. The pipeline stress exposure caused by loads and impacts (self-weight, internal pressure, etc. may be calculated in advance, and the accuracy of these calculations is sufficient for practical
Atomic structure of "vitreous" interfacial films in sialon
Thorel, A.; Laval, J; Broussaud, Daniel
1988-01-01
Atomic resolution imaging of siliceous interfacial films in a sialon has been achieved using transmission electron microscopy at 1000 KV. Although such films have always been reputed as vitreous, we show that they are at least partially crystallized. An atomic model is proposed and simulated. The stability of these films is discussed when special crystallographic relationships exist between the two adjacent grains.
A curved line search algorithm for atomic structure relaxation
Chen, Zhanghui; Wang, Linwang; Li, Jingbo; Li, Shushen
2015-01-01
Ab initio atomic relaxations often take large numbers of steps and long times to converge. An atomic relaxation method based on on-the-flight force learning and a corresponding new curved line minimization algorithm is presented to dramatically accelerate this process. Results for metal clusters demonstrate the significant speedup of this method compared with conventional conjugate-gradient method.
Grimme, Stefan; Brandenburg, Jan Gerit; Bannwarth, Christoph; Hansen, Andreas
2015-08-01
and reach that of triple-zeta AO basis set second-order perturbation theory (MP2/TZ) level at a tiny fraction of computational effort. Periodic calculations conducted for molecular crystals to test structures (including cell volumes) and sublimation enthalpies indicate very good accuracy competitive to computationally more involved plane-wave based calculations. PBEh-3c can be applied routinely to several hundreds of atoms on a single processor and it is suggested as a robust "high-speed" computational tool in theoretical chemistry and physics.
Energy Technology Data Exchange (ETDEWEB)
Grimme, Stefan, E-mail: grimme@thch.uni-bonn.de; Brandenburg, Jan Gerit; Bannwarth, Christoph; Hansen, Andreas [Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraße 4, 53115 Bonn (Germany)
2015-08-07
methods and reach that of triple-zeta AO basis set second-order perturbation theory (MP2/TZ) level at a tiny fraction of computational effort. Periodic calculations conducted for molecular crystals to test structures (including cell volumes) and sublimation enthalpies indicate very good accuracy competitive to computationally more involved plane-wave based calculations. PBEh-3c can be applied routinely to several hundreds of atoms on a single processor and it is suggested as a robust “high-speed” computational tool in theoretical chemistry and physics.
Institute of Scientific and Technical Information of China (English)
XIE Wen-Fang
2006-01-01
@@ Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of the confined helium atom in a spherical parabolic well. We find that the energies of a spherical parabolic well are in good agreement with those of an impenetrable spherical box for the larger confined potential radius. However, the energy values of a spherical parabolic well are much lower than those of an impenetrable spherical box for small values of re. We also find that the confinement may cause accidental degeneracies between levels with different low-excited states and the inversion of the energy values.
Lee, Chaohong; Duan, Yiwu; Liu, Wing-Ki; Yuan, Jian-Min; Shi, Lei; Zhu, Xiwen; Gao, Kelin
2001-01-01
Based upon our previous works (Eur.Phys.J.D 6, 319(1999); Chin.Phys.Lett. 18, 236(2001)), we develop a classical approach to calculate the high-order harmonic generation of the laser driven atoms and molecules. The Coulomb singularities in the system have been removed by a regularization procedure. Action-angle variables have been used to generate the initial microcanonical distribution which satisfies the inversion symmetry of the system. The numerical simulation show, within a proper laser ...
Consensus structure elucidation combining GC/EI-MS, structure generation, and calculated properties.
Schymanski, Emma L; Gallampois, Christine M J; Krauss, Martin; Meringer, Markus; Neumann, Steffen; Schulze, Tobias; Wolf, Sebastian; Brack, Werner
2012-04-01
This article explores consensus structure elucidation on the basis of GC/EI-MS, structure generation, and calculated properties for unknown compounds. Candidate structures were generated using the molecular formula and substructure information obtained from GC/EI-MS spectra. Calculated properties were then used to score candidates according to a consensus approach, rather than filtering or exclusion. Two mass spectral match calculations (MOLGEN-MS and MetFrag), retention behavior (Lee retention index/boiling point correlation, NIST Kovat's retention index), octanol-water partitioning behavior (log K(ow)), and finally steric energy calculations were used to select candidates. A simple consensus scoring function was developed and tested on two unknown spectra detected in a mutagenic subfraction of a water sample from the Elbe River using GC/EI-MS. The top candidates proposed using the consensus scoring technique were purchased and confirmed analytically using GC/EI-MS and LC/MS/MS. Although the compounds identified were not responsible for the sample mutagenicity, the structure-generation-based identification for GC/EI-MS using calculated properties and consensus scoring was demonstrated to be applicable to real-world unknowns and suggests that the development of a similar strategy for multidimensional high-resolution MS could improve the outcomes of environmental and metabolomics studies. PMID:22414024
Energy Technology Data Exchange (ETDEWEB)
Shamim, Md; Harbola, Manoj K, E-mail: sami@iitk.ac.i, E-mail: mkh@iitk.ac.i [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)
2010-11-14
Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.
Refinement of the protein backbone angle {psi} in NMR structure calculations
Energy Technology Data Exchange (ETDEWEB)
Sprangers, R.; Bottomley, M.J.; Linge, J.P.; Schultz, J.; Nilges, M.; Sattler, M. [European Molecular Biology Laboratory (Germany)
2000-01-15
Cross-correlated relaxation rates involving the C{sup {alpha}}-H{sup {alpha}} dipolar interaction and the carbonyl (C') chemical shift anisotropy (CSA) have been measured using two complementary 3D experiments. We show that the protein backbone angle {psi} can be directly refined against such cross-correlated relaxation rates ({gamma}{sup H{alpha}}{sup C{alpha}}{sup ,C'}) and the three-bond H/D isotope effect on the C{sup {alpha}} chemical shifts ({sup 3}{delta}C{sup {alpha}}{sub (ND)}). By simultaneously using both experimental parameters as restraints during NMR structure calculations, a unique value for the backbone angle {psi} is defined. We have applied the new refinement method to the {alpha}-Spectrin SH3 domain (a {beta}-sheet protein) and to the Sgs1p HRDC domain (an {alpha}-helical protein) and show that the quality of the NMR structures is substantially improved, judging from the atomic coordinate precision and the Ramachandran map. In addition, the {psi}-refined NMR structures of the SH3 domain deviate less from the 1.8 A crystal structure, suggesting an improved accuracy. The proposed refinement method can be used to significantly improve the quality of NMR structures and will be applicable to larger proteins.
Energy Technology Data Exchange (ETDEWEB)
Nascimento, Josenaide P. do; Santos, Lourivaldo S.; Carmo, Maria Carolina L. do; Brasil, Davi S.B.; Alves, Claudio N., E-mail: nahum@ufpa.b [Universidade Federal do Para (UFPA), Belem, PA (Brazil). Inst. de Ciencias Exatas e Naturais; Santos, Regina Helena A.; Tozzo, Erica; Ferreira, Janaina G. [Universidade de Sao Paulo (IQSC/USP), Sao Carlos, SP (Brazil). Inst. de Quimica
2010-07-01
The synthesis and X-ray crystal diffraction structure of two analogues of neolignans, 2-(4-chlorophenyl)-1-phenylethanone (20) and 2-[(4-chlorophenyl)thio]-1-(3,4-dimethoxyphenyl) propan-1-one (12) is described. The compound 12 presents activity against intracellular Leishmania donovani and Leishmania amazonensis amastigotes that cause cutaneous and visceral leishmaniasis. In addition, the density functional theory (DFT) with the B3LYP hybrid functional was employed to calculate a set of molecular descriptors for nineteen synthetic analogues of neolignans with antileishmanial activities. Afterwards, the stepwise discriminant analysis was performed to investigate possible relationship between the molecular descriptors and biological activities. Through this analysis the compounds were classified into two groups active and inactive according to their degree of biological activities, and the more important properties were charges on some key atoms, electronic affinity and ClogP. (author)
Atomic structure of machined semiconducting chips: An x-ray absorption spectroscopy study
Energy Technology Data Exchange (ETDEWEB)
Paesler, M.; Sayers, D.
1988-12-01
X-ray absorption spectroscopy (XAS) has been used to examine the atomic structure of chips of germanium that were produced by single point diamond machining. It is demonstrated that although the local (nearest neighbor) atomic structure is experimentally quite similar to that of single crystal specimens information from more distant atoms indicates the presence of considerable stress. An outline of the technique is given and the strength of XAS in studying the machining process is demonstrated.
Quasilattice-conserved optimization of the atomic structure of decagonal Al-Co-Ni quasicrystals
Li, Xiao-Tian; Yang, Xiao-Bao; Zhao, Yu-Jun
2014-01-01
The detailed atomic structure of quasicrystals has been an open question for decades. Here, we present a quasilattice-conserved optimization method (quasiOPT), with particular quasiperiodic boundary conditions. As the atomic coordinates described by basic cells and quasilattices, we are able to maintain the self-similarity characteristics of qusicrystals with the atomic structure of the boundary region updated timely following the relaxing region. Exemplified with the study of decagonal Al-Co...
An approach to first principles electronic structure calculation by symbolic-numeric computation
Directory of Open Access Journals (Sweden)
Akihito Kikuchi
2013-04-01
Full Text Available There is a wide variety of electronic structure calculation cooperating with symbolic computation. The main purpose of the latter is to play an auxiliary role (but not without importance to the former. In the field of quantum physics [1-9], researchers sometimes have to handle complicated mathematical expressions, whose derivation seems almost beyond human power. Thus one resorts to the intensive use of computers, namely, symbolic computation [10-16]. Examples of this can be seen in various topics: atomic energy levels, molecular dynamics, molecular energy and spectra, collision and scattering, lattice spin models and so on [16]. How to obtain molecular integrals analytically or how to manipulate complex formulas in many body interactions, is one such problem. In the former, when one uses special atomic basis for a specific purpose, to express the integrals by the combination of already known analytic functions, may sometimes be very difficult. In the latter, one must rearrange a number of creation and annihilation operators in a suitable order and calculate the analytical expectation value. It is usual that a quantitative and massive computation follows a symbolic one; for the convenience of the numerical computation, it is necessary to reduce a complicated analytic expression into a tractable and computable form. This is the main motive for the introduction of the symbolic computation as a forerunner of the numerical one and their collaboration has won considerable successes. The present work should be classified as one such trial. Meanwhile, the use of symbolic computation in the present work is not limited to indirect and auxiliary part to the numerical computation. The present work can be applicable to a direct and quantitative estimation of the electronic structure, skipping conventional computational methods.
Directory of Open Access Journals (Sweden)
Alberto Milani
2015-02-01
Full Text Available Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanced technological applications due to the different coordination of carbon atoms and to the possibility of π-conjugation. In this context, atomic-scale wires comprised of sp-hybridized carbon atoms represent ideal 1D systems to potentially downscale devices to the atomic level. Carbon-atom wires (CAWs can be arranged in two possible structures: a sequence of double bonds (cumulenes, resulting in a 1D metal, or an alternating sequence of single–triple bonds (polyynes, expected to show semiconducting properties. The electronic and optical properties of CAWs can be finely tuned by controlling the wire length (i.e., the number of carbon atoms and the type of termination (e.g., atom, molecular group or nanostructure. Although linear, sp-hybridized carbon systems are still considered elusive and unstable materials, a number of nanostructures consisting of sp-carbon wires have been produced and characterized to date. In this short review, we present the main CAW synthesis techniques and stabilization strategies and we discuss the current status of the understanding of their structural, electronic and vibrational properties with particular attention to how these properties are related to one another. We focus on the use of vibrational spectroscopy to provide information on the structural and electronic properties of the system (e.g., determination of wire length. Moreover, by employing Raman spectroscopy and surface enhanced Raman scattering in combination with the support of first principles calculations, we show that a detailed understanding of the charge transfer between CAWs and metal nanoparticles may open the possibility to tune the electronic structure from alternating to equalized bonds.
Institute of Scientific and Technical Information of China (English)
何刚; 戎咏华; 徐祖耀
2000-01-01
The stacking fault energies of five fcc metals (Cu, Ag, Au, Ni and Al) with various quan-tivalences have been calculated by embedded-atom method (EAM). It indicated that the stacking fault energy is mainly determined by the metallic bond-energy and the lattice constant. Thus, monovalent fcc metals should have different stacking fault energies, contrary to Attree’s conclusion. The interaction energy between stacking faults one I 111 I layer apart in a fcc metal is found to be 1/40-1/250 of its self-energy, while it becomes zero when the two stacking faults are two layers apart. The twin energy is just half of the energy of intrinsic stacking fault energy without the consideration of lattice relaxation and the energy of a single intrinsic stacking fault is almost the same as that of extrinsic stacking fault, which are consistent with the results from the calculation of Lennard-Jones force between atoms, but differ from Attree’s result.
Chougale, Yashwant; Nath, Rejish
2016-07-01
We obtain ab initio the Hubbard parameters for Rydberg-dressed atoms in a one-dimensional (1D) sinusoidal optical lattice on the basis of maximally-localized Wannier states. Finite range, soft-core interatomic interactions become the trait of Rydberg admixed atoms, which can be extended over many neighboring lattice sites. In contrast to dipolar gases, where the interactions follow an inverse cubic law, the key feature of Rydberg-dressed interactions is the possibility of making neighboring couplings to the same magnitude as that of the onsite ones. The maximally-localized Wannier functions (MLWFs) are typically calculated via a spread-minimization procedure (Marzari N and Vanderbilt D 1997 Phys. Rev. B 56 12847) and are always found to be real functions apart from a trivial global phase when an isolated set of Bloch bands are considered. For an isolated single Bloch band, the above procedure reduces to a simple quasi-momentum-dependent unitary phase transformation. Here, instead of minimizing the spread, we employ a diagonal phase transformation which eliminates the imaginary part of the Wannier functions. The resulting Wannier states are found to be maximally localized and in exact agreement with those obtained via a spread-minimization procedure. Using these findings, we calculate the Hubbard couplings from the Rydberg admixed interactions, including dominant density-assisted tunneling (DAT) coefficients. Finally, we provide realistic lattice parameters for the state-of-the-art experimental Rydberg-dressed rubidium setup.
Orbital-Free Density Functional Theory for Molecular Structure Calculations
Institute of Scientific and Technical Information of China (English)
Huajie Chen; Aihui Zhou
2008-01-01
We give here an overview of the orbital-free density functional theory that is used for modeling atoms and molecules. We review typical approximations to the kinetic energy, exchange-correlation corrections to the kinetic and Hartree energies, and constructions of the pseudopotentials. We discuss numerical discretizations for the orbital-free methods and include several numerical results for illustrations.
Atomic shell structure from the Single-Exponential Decay Detector
International Nuclear Information System (INIS)
The density of atomic systems is analysed via the Single-Exponential Decay Detector (SEDD). SEDD is a scalar field designed to explore mathematical, rather than physical, properties of electron density. Nevertheless, it has been shown that SEDD can serve as a descriptor of bonding patterns in molecules as well as an indicator of atomic shells [P. de Silva, J. Korchowiec, and T. A. Wesolowski, ChemPhysChem 13, 3462 (2012)]. In this work, a more detailed analysis of atomic shells is done for atoms in the Li–Xe series. Shell populations based on SEDD agree with the Aufbau principle even better than those obtained from the Electron Localization Function, which is a popular indicator of electron localization. A link between SEDD and the local wave vector is given, which provides a physical interpretation of SEDD
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Based on the theory of micro-inhomogeneity of liquid metal,a calculation model is established for the quantitative description of the structural information of metal melts.Only by thermophysical property parameters and basic structural parameters of solid metal,can this model produce the main information of melt structure,including the relative concentration of active atoms,size of atomic clusters and number of short-range order atoms.Based on this model,the main structural information of Al and Ni melts in the not high range above the liquidus is calculated,with results in good agreement with experimental values.Besides,analyzed is the influence of superheating temperature and atomic number on the melt structural information of the first (IA) and second main group (IIA) elements.With temperature increasing,melt structural information regularly changes for both IA and IIA elements.With the atomic number increasing,melt structural information of IA elements changes regularly,for the crystal structures of the IA elements are all of bcc lattice type.However,no notable regular change of melt structural information for IIA elements has been found,mainly because the lattice type of IIA elements is of hcp-fcc-bcc transition.The present work presents an effective way for better understanding metal melt structure and for forecasting the change of the physical property of metal melts.
Systematic model calculations of the hyperfine structure in light and heavy ions
Tomaselli, M; Nörtershäuser, W; Ewald, G; Sánchez, R; Fritzsche, S; Karshenboim, S G
2003-01-01
Systematic model calculations are performed for the magnetization distributions and the hyperfine structure (HFS) of light and heavy ions with a mass close to A ~ 6 208 235 to test the interplay of nuclear and atomic structure. A high-precision measurement of lithium-isotope shifts (IS) for suitable transition, combined with an accurate theoretical evaluation of the mass-shift contribution in the respective transition, can be used to determine the root-mean-square (rms) nuclear-charge radius of Li isotopes, particularly of the halo nucleus /sup 11/Li. An experiment of this type is currently underway at GSI in Darmstadt and ISOLDE at CERN. However, the field-shift contributions between the different isotopes can be evaluated using the results obtained for the charge radii, thus casting, with knowledge of the ratio of the HFS constants to the magnetic moments, new light on the IS theory. For heavy charged ions the calculated n- body magnetization distributions reproduce the HFS of hydrogen-like ions well if QED...
Energy Technology Data Exchange (ETDEWEB)
Chuluunbaatar, O [Joint Institute for Nuclear Research, Dubna, Moscow Region 141980 (Russian Federation); Gusev, A A [Joint Institute for Nuclear Research, Dubna, Moscow Region 141980 (Russian Federation); Derbov, V L [Saratov State University (Russian Federation); Kaschiev, M S [Institute of Mathematics and Informatics, BAS, Sofia (Bulgaria); Melnikov, L A [Saratov State University (Russian Federation); Serov, V V [Saratov State University (Russian Federation); Vinitsky, S I [Joint Institute for Nuclear Research, Dubna, Moscow Region 141980 (Russian Federation)
2007-09-21
A new efficient method for calculating the photoionization of a hydrogen atom in a strong magnetic field is developed based on the Kantorovich approach to the parametric boundary problems in spherical coordinates using the orthogonal basis set of angular oblate spheroidal functions. The progress as compared with our previous paper (Dimova M G, Kaschiev M S and Vinitsky S I 2005 J. Phys. B: At. Mol. Opt. Phys. 38 2337-52) consists of the development of the Kantorovich method for calculating the wavefunctions of a continuous spectrum, including the quasi-stationary states imbedded in the continuum. Resonance transmission and total reflection effects for scattering processes of electrons on protons in a homogenous magnetic field are manifested. The photoionization cross sections found for the ground and excited states are in good agreement with the calculations by other authors and demonstrate correct threshold behavior. The estimates using the calculated photoionization cross section show that due to the quasi-stationary states the laser-stimulated recombination may be enhanced by choosing the optimal laser frequency.
Energy Technology Data Exchange (ETDEWEB)
Clade, P
2005-10-15
From a measurement of the recoil velocity of an atom absorbing a photon, it is possible to deduce a determination of the ratio h/m between the Planck constant and the mass of the atoms and then to deduce a value of the fine structure constant alpha. To do this measurement, we use the technique of Bloch oscillations, which allows us to transfer a large number of recoils to atoms. A velocity sensor, based on velocity selective Raman transition, enables us to measure the momentum transferred to the atoms. A measurement with a statistical uncertainty of 4.4 10{sup -9}, in conjunction with a careful study of systematic effects (5 10{sup -9}), has led us to a determination of alpha with an uncertainty of 6.7 10{sup -9}: {alpha}{sup -1}(Rb) = 137.03599878 (91). This uncertainty is similar to the uncertainty of the best determinations of alpha based on atom interferometry. (author)
Analysis of Nanometer Structure for Chromium Atoms in Gauss Standing Laser Wave
Institute of Scientific and Technical Information of China (English)
ZHANG Wen-Tao; ZHU Bao-Hua; XIONG Xian-Ming
2010-01-01
@@ The equation of motion of two-level chromium atoms in Gauss standing laser wave is discussed and the distribution of chromium atoms is given under different transverse velocity conditions.The results show that the focusing position of atoms will be affected by the transverse velocity of atoms.Based on the four-order Runge-Kutta method,the locus of chromium atoms in Gauss standing laser wave is simulated.The three-dimensional characteristics of nanometer structures are stimulated under perfect and emanative conditions.
Smallest Nanoelectronic with Atomic Devices with Precise Structures
Yamada, Toshishige
2000-01-01
Since its invention in 1948, the transistor has revolutionized our everyday life - transistor radios and TV's appeared in the early 1960s, personal computers came into widespread use in the mid-1980s, and cellular phones, laptops, and palm-sized organizers dominated the 1990s. The electronics revolution is based upon transistor miniaturization; smaller transistors are faster, and denser circuitry has more functionality. Transistors in current generation chips are 0.25 micron or 250 nanometers in size, and the electronics industry has completed development of 0.18 micron transistors which will enter production within the next few years. Industry researchers are now working to reduce transistor size down to 0.13 micron - a thousandth of the width of a human hair. However, studies indicate that the miniaturization of silicon transistors will soon reach its limit. For further progress in microelectronics, scientists have turned to nanotechnology to advance the science. Rather than continuing to miniaturize transistors to a point where they become unreliable, nanotechnology offers the new approach of building devices on the atomic scale [see sidebar]. One vision for the next generation of miniature electronics is atomic chain electronics, where devices are composed of atoms aligned on top of a substrate surface in a regular pattern. The Atomic Chain Electronics Project (ACEP) - part of the Semiconductor Device Modeling and Nanotechnology group, Integrated Product Team at the NAS Facility has been developing the theory of understanding atomic chain devices, and the author's patent for atomic chain electronics is now pending.
Collective vector method for calculation of E1 moments in atomic transition arrays
International Nuclear Information System (INIS)
The CV (collective vector) method for calculating E1 moments for a transition array is described and applied in two cases, herein denoted Z26A and Z26B, pertaining to two different configurations of iron VI. The basic idea of the method is to create a CV from each of the parent (''initial state'') state-vectors of the transition array by application of the E1 operator. The moments of each of these CV's, referred to the parent energy, are then the rigorous moments for that parent, requiring no state decomposition of the manifold of daughter state-vectors. Since, in cases of practical interest, the daughter manifold can be orders of magnitude larger in size than the parent manifold, this makes possible the calculation of many moments higher than the second in situations hitherto unattainable via standard methods. The combination of the moments of all the parents, with proper statistical weighting, then yields the transition array moments from which the transition strength distribution can be derived by various procedures. We describe two of these procedures: (1) The well-known GC (Gram-Charlier) expansion in terms of Hermite polynomials, (2) The Lanczos algorithm or Stieltjes imaging method, also called herein the delta expansion. Application is made in the cases of Z26A (50 lines) and Z26B (5523 lines) and the relative merits and shortcomings of the two procedures are discussed. 10 refs., 15 figs., 2 tabs
Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun
2016-07-01
We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen‑ (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen‑ clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen‑/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters.
Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun
2016-01-01
We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen− (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen− clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen−/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters. PMID:27439955
Calculation of harmonic radiation and nuclear coupling arising from atoms in strong laser fields
International Nuclear Information System (INIS)
A numerical, time-dependent quantum mechanical model is used to describe the interaction of an isolated ion with an intense applied laser field, including both electron and nuclear degrees of freedom. Calculated results are presented. We find that the model ion radiates in low odd harmonics of the laser frequency, in qualitative agreement with experimental observations. In addition, it radiates strongly in the x-ray region, at frequencies comparable with the electron Rydberg frequency. Such radiation should be possible to observe in future experiments. If it exists, it could provide a basis for a reasonably coherent x-ray source. We find that the probability of induced nuclear excitation is small for higher electric multipoles, although observable probabilities are obtained under appropriate circumstances for L = 1. 2 refs., 12 figs
Density functional calculations on 13-atom Pd12M (M=Sc-Ni) bimetallic clusters
Institute of Scientific and Technical Information of China (English)
Tang Chun-Mei; Chen Sheng-Wei; Zhu Wei-Hua; Tao Cheng-Jun; Zhang Ai-Mei; Gong Jiang-Feng; Zou Hua; Liu Ming-Yi; Zhu Feng
2012-01-01
The geometric structures,electronic and magnetic properties of the 3d transition metal doped clusters Pd12M (M =Sc Ni) are studied using the semi-core pseudopots density functional theory.The groundstate geometric structure of the Pd12M cluster is probably of pseudoicosahedron.The Ih-Pd12M cluster has the most thermodynamic stability in five different symmetric isomers.The energy gap shows that Pd12M cluster is partly metallic.Both the absolutely predominant metal bond and very weak covalent bond might exist in the Pd12M cluster.The magnetic moment of Pd12M varies from 0 to 5 μB' implying that it has a potential application in new nanomaterials with tunable magnetic properties.
Atomic structure of the Σ = 2 twist carbide grain boundary in WC-Co alloys
Lay, Sabine; Missiaen, Jean-Michel
2013-04-01
The Σ = 2 twist carbide grain boundary with a (10 ? 0) habit plane was investigated by high resolution transmission electron microscopy in a WC-Co alloy. The atomic structure at the boundary was determined by comparing experimental images and simulations. It corresponds to the boundary model with the lowest energy according to atomistic calculations. Periodic monolayer interfacial steps, compensating for the parametric misfit at the boundary were studied. The displacement field around the defects was simulated and corresponds to a dislocation with a mixed character and a Burgers vectors equal to 1/6⟨ ? 2 ? 3⟩ lying in the boundary plane. Another step with a larger height and connected to a stacking fault was analyzed. It likely arises from the interaction of a matrix dislocation with the boundary. The observations suggest that the migration of Σ = 2 grain boundaries can be induced by the glide of the monolayer steps along the grain boundary.
A DFT study of atomic structure and adhesion at the Fe(BCC)/Fe3O4 interfaces
Forti, M. D.; Alonso, P. R.; Gargano, P. H.; Balbuena, P. B.; Rubiolo, G. H.
2016-05-01
The adhesion at Fe/Fe3O4 interface is one of the critical pieces of information that is often lacking upon designing the protective magnetite layer on the inner surfaces of carbon steel piping or upon modeling the scale removal mechanism for optimization of industrial descaling of the wire or strip surface of carbon steel after hot rolling process. In this context, we have performed ab initio DFT calculations to determine the atomic structure, work of separation (γ), and bonding character of the Fe(001)/Fe3O4(001) interface. Three candidate interface geometries were considered, including Fe and FeO2 terminations of the oxide. The minimization of the forces resulted in substantial changes to the atomic structure of the metal and oxide layer at both side of the interface, and also of the subsurface layer of the oxide in the case of Fe-terminated oxide slab. Moreover, the relaxation of the geometry in one of the two considered Fe-terminated oxide interface leads to completely unstable interface structures. By applying several methods of analysis, we have thoroughly characterized the electronic structure and have determined that the dominant bonding mechanism is the metallic-ionic interaction between the iron atoms of both metal and oxide slabs. Our calculations predict γ ≈ 1.42 J/m2 regardless of the interfacial stoichiometry.
Structural properties of Al and TiAl3 metallic glasses — An embedded atom method study
Tahiri, M.; Trady, S.; Hasnaoui, A.; Mazroui, M.; Saadouni, K.; Sbiaai, K.
2016-06-01
In this paper, we investigated the structural properties of metallic glasses (MGs). We emphasized our study on monatomic Al and binary TiAl3 systems. The calculations are performed by using the molecular dynamics (MD) simulation based on semi-empirical many-body potentials derived from the embedded atom method. The structure is analyzed using the radial distribution function (RDF), the common neighbor analysis (CNA) and the coordination numbers (CNs). Our results demonstrated that it is possible to form MGs in both systems upon fast cooling from the liquid state. This is confirmed by the fact that the system energy and/or volume during the cooling stage decrease continuously with a slight change and by atomic scale analysis using the RDF, CNA and CN analyzing techniques. Furthermore, this specific study shows that under the same conditions, the icosahedral structures appeared in TiAl3 are more abundant than in pure Al. Implications of these findings are discussed.
International Nuclear Information System (INIS)
An algorithm, CYLIB, is presented for converting molecular topology descriptions from the PDB Chemical Component Dictionary into CYANA residue library entries. The CYANA structure calculation algorithm uses torsion angle molecular dynamics for the efficient computation of three-dimensional structures from NMR-derived restraints. For this, the molecules have to be represented in torsion angle space with rotations around covalent single bonds as the only degrees of freedom. The molecule must be given a tree structure of torsion angles connecting rigid units composed of one or several atoms with fixed relative positions. Setting up CYANA residue library entries therefore involves, besides straightforward format conversion, the non-trivial step of defining a suitable tree structure of torsion angles, and to re-order the atoms in a way that is compatible with this tree structure. This can be done manually for small numbers of ligands but the process is time-consuming and error-prone. An automated method is necessary in order to handle the large number of different potential ligand molecules to be studied in drug design projects. Here, we present an algorithm for this purpose, and show that CYANA structure calculations can be performed with almost all small molecule ligands and non-standard amino acid residues in the PDB Chemical Component Dictionary
Energy Technology Data Exchange (ETDEWEB)
Yilmaz, Emel Maden; Güntert, Peter, E-mail: guentert@em.uni-frankfurt.de [Goethe University Frankfurt am Main, Center for Biomolecular Magnetic Resonance, Institute of Biophysical Chemistry (Germany)
2015-09-15
An algorithm, CYLIB, is presented for converting molecular topology descriptions from the PDB Chemical Component Dictionary into CYANA residue library entries. The CYANA structure calculation algorithm uses torsion angle molecular dynamics for the efficient computation of three-dimensional structures from NMR-derived restraints. For this, the molecules have to be represented in torsion angle space with rotations around covalent single bonds as the only degrees of freedom. The molecule must be given a tree structure of torsion angles connecting rigid units composed of one or several atoms with fixed relative positions. Setting up CYANA residue library entries therefore involves, besides straightforward format conversion, the non-trivial step of defining a suitable tree structure of torsion angles, and to re-order the atoms in a way that is compatible with this tree structure. This can be done manually for small numbers of ligands but the process is time-consuming and error-prone. An automated method is necessary in order to handle the large number of different potential ligand molecules to be studied in drug design projects. Here, we present an algorithm for this purpose, and show that CYANA structure calculations can be performed with almost all small molecule ligands and non-standard amino acid residues in the PDB Chemical Component Dictionary.
Amano, Ken-ich
2013-01-01
Recent frequency-modulated atomic force microscopy (FM-AFM) can measure three-dimensional force distribution between a probe and a sample surface in liquid. The force distribution is, in the present circumstances, assumed to be solvation structure on the sample surface, because the force distribution and solvation structure have somewhat similar shape. However, the force distribution is exactly not the solvation structure. If we would like to obtain the solvation structure by using the liquid AFM, a method for transforming the force distribution into the solvation structure is necessary. Therefore, in this letter, we present the transforming method in a brief style. We call this method as a solution for an inverse problem, because the solvation structure is obtained at first and the force distribution is obtained next in general calculation processes. The method is formulated (mainly) by statistical mechanics of liquid.
Johnston, Karen; Verho, Tuukka; Puska, Martti J
2010-01-01
Several dissociated and two non-dissociated adsorption structures of the phenol molecule on the Si(001)-(2 \\times 1) surface are studied using density functional theory with various exchange and correlation functionals. The relaxed structures and adsorption energies are obtained and it is found that the dissociated structures are energetically more favourable than the non-dissociated structures. However, the ground state energies alone do not determine which structure is obtained experimentally. To elucidate the situation core level shift spectra for Si 2p and C 1s states are simulated and compared with experimentally measured spectra. Several transition barriers were calculated in order to determine which adsorption structures are kinetically accessible. Based on these results we conclude that the molecule undergoes the dissociation of two hydrogen atoms on adsorption.
Femtosecond structural dynamics on the atomic length scale
Energy Technology Data Exchange (ETDEWEB)
Zhang, Dongfang
2014-03-15
This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm{sup 2}) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO{sub 2} and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been
Structure and transport properties of atomic chains and molecules
DEFF Research Database (Denmark)
Strange, Mikkel
2008-01-01
of atomically thin, suspended chains containing silver and oxygen atoms in an alternating sequence has been studied. The conductances of the chains exhibit weak even-odd oscillations around an anomalously low value of 0.1G0 (G0 = 2e2/h) in agreement with experiments [1] in the long chain limit. These unusual...... conductance properties are explained in terms of a resonating-chain model, which takes the reflection probability and phase-shift of a single bulk-chain interface as the only input. The stability of silver-oxygen chains was studied with a thermodynamic model. This model has been developed in this work...... plane-wave code Dacapo [2] in combination with maximally localized Wannier functions and the norm-conserving pseudopotential code Siesta [3]which applies an atomic orbital basis set. For the systems studied we find that the Siesta transmission functions converge toward the plane-wave result...
Ding, Yi; Wang, Yanli
2016-08-17
Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics. PMID:27491896
Ding, Yi; Wang, Yanli
2016-08-17
Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics.
Pan, Yong; Guan, Weiming
2016-09-01
MoS3 has attracted considerable attention as potential hydrogen storage material due to the interaction between the hydrogen and unsaturated sulfur atoms. However, its structure and physical properties are unknown. By means of first-principles approach and Inorganic crystal structure Database (ISCD), we systematically investigated the structure, relevant physical and thermodynamic properties of MoS3. Phonon dispersion, electronic structure, band structure and heat capacity are calculated in detail. We predicted the orthorhombic B2ab (SrS3-type) and tetragonal P-421m (BaS3-type) structures of MoS3, which prefers to form the SrS3-type (Space group: B2ab, No.41) structure at the ground state. High pressure results in structural transition from SrS3-type structure to BaS3-type structure. This sulfide exhibits a degree of metallic behavior. The calculated heat capacity of MoS3 with SrS3-type structure is about of 39 J/(mol·K).
Energy Technology Data Exchange (ETDEWEB)
Ilyasov, V.V., E-mail: viily@mail.ru; Pham, Khang D., E-mail: dinhkhang307@gmail.com; Holodova, O.M.; Ershov, I.V., E-mail: thijd@mail.ru
2015-10-01
We have performed ab initio simulation of oxygen atom adsorption on TiC(0 0 1) laser-reconstructed surface. Relaxed atomic structures of the O/Ti{sub x}C{sub y}(0 0 1) surface observed upon thermal impact have been studied. DFT calculations of their thermodynamic, electronic, and elastic properties have been carried out. For the first time we have established the bond length and adsorption energy for various reconstructions of the O/Ti{sub x}C{sub y}(0 0 1) surface atomic structure. We have examined the effects of the oxygen adatom upon the band and electron spectra of the O/TiC(0 0 1) surface in its various reconstructions. For the first time we have established a correlation between the energy level of flat bands (−5.4 eV and −5.8 eV) responsible for the doublet of singular peaks of partial densities of oxygen 2p electrons, and the adsorption energy of oxygen atom in non-stoichiometric O/TiC{sub y}(0 0 1) systems. Effective charges of titanium and carbon atoms surrounding the oxygen adatom in various reconstructions have been identified. We have established charge transfer from titanium atom to oxygen and carbon atoms determined by the reconstruction of local atomic and electron structures which correlate with atomic electronegativity values and chemisorption processes. Potential mechanisms for laser nanostructuring of titanium carbide surface have been suggested.
Songjun, Hou; Sunchao, Huang; Zhi, Zeng
2015-01-01
First principles calculations were performed to study the structural, elastic, and bonding properties of hcp ZrxTi1-x binary alloy. The special quasi- random structure (SQS) method is employed to mimic the random hcp ZrxTi1-x alloy. It is found that Bulk modulus, B, Young's modulus, E, and shear modulus, G, exhibit decreasing trends as increasing the amount of Zr. A ductile behavior ZrxTi1-x is predicted in the whole composition range. In terms of Mulliken charge analisis, we found that the element Ti behaves much more electronegative than Zr in hcp ZrxTi1-x alloy, and the charge transfer of an atom is approximately linear to the amount of other element atom surrounding it.
Hydrogen trapping in δ-Pu: insights from electronic structure calculations
International Nuclear Information System (INIS)
Density functional theory calculations have been performed to provide details of the structural and charge-transfer details related to the solid solution of hydrogen in (δ)-plutonium. We follow the Flanagan model that outlines the process by which hydrogen interacts with a metal to produce hydride phases, via a sequence of surface, interstitial and defect-bound (trapped) states. Due to the complexities of the electronic structure in plutonium solid-state systems, we take the pragmatic approach of adopting the ‘special quasirandom structure’ to disperse the atomic magnetic moments. We find that this approach produces sound structural and thermodynamic properties in agreement with the available experimental data. In δ-Pu, hydrogen has an exothermic binding energy to all of the states relevant in the Flanagan model, and, furthermore, is anionic in all these states. The charge transfer is maximized (i.e. most negative for hydrogen) in the hydride phase. The pathway from surface to hydride is sequentially exothermic, in the order surface < interstitial < grain boundary < vacancy < hydride (hydride being the most exothermic state). Thus, we find that there is no intermediate state that involves an endothermic increase in energy, consistent with the general experimental observations that the hydriding reaction in plutonium metal can proceed with zero apparent activation barrier. (paper)
Energy Technology Data Exchange (ETDEWEB)
Werwiński, M. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań (Poland); Szajek, A. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław (Poland); Ślebarski, A. [Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław (Poland); Kaczorowski, D., E-mail: D.Kaczorowski@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P. O. Box 1410, 50-950 Wrocław (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław (Poland)
2015-10-25
The electronic structure of a heavy-fermion superconductor Ce{sub 2}PdIn{sub 8} was investigated by means of X-ray photoelectron spectroscopy (XPS) and ab initio density functional band structure calculations. The Ce 3d core-level XPS spectra point to stable trivalent configuration of Ce atoms that is also reproduced in the band structure calculations within the generalized gradient approximation GGA+U approach. Analysis of the 3d{sup 9}f{sup 2} weight in the 3d XPS spectra within the Gunnarsson-Schönhammer model suggests that the onsite hybridization energy between Ce 4f and the conduction band states, Δ{sub fs}, is ∼120 meV, which is about 30 meV larger than Δ{sub fs} in isostructural Ce{sub 2}TIn{sub 8} compounds with T = Co, Rh, and Ir. Taking into account a Coulomb repulsion U on both the Ce 4f and Pd 4d states in electronic band structure calculations, a satisfactory agreement was found between the calculated density of states (DOS) and the measured valence band XPS spectra. - Highlights: • XPS data validated strong electronic correlations in superconducting Ce{sub 2}PdIn{sub 8}. • DFT calculations reproduced XPS spectra measured for Ce{sub 2}PdIn{sub 8}. • Crucial role of Pd d electrons in the HF behavior of Ce{sub 2}PdIn{sub 8} was established.
Institute of Scientific and Technical Information of China (English)
杨忠志; 沈尔忠
1995-01-01
On the basis of electronegativity expressed in density functional theory and electronegativity equalization principle, a new scheme for calculating the atomic charges in a molecule has been proposed and designed, which gives a new scale of the atomic electronegativity and hardness in a certain molecular environment and takes the harmonic mean electronegativity as a reference value of the molecular electronegativity so that the multiple-regression and nonuniform parameters in the original method are avoided. This approach can be easily and widely applied to the calculation of atomic charges for a big molecule and quite good results of atomic charges in some illustrated molecules are obtained as compared with those from the ab initio STO-3G SCF calculations.
Valla, Maxence; Rossini, Aaron J; Caillot, Maxime; Chizallet, Céline; Raybaud, Pascal; Digne, Mathieu; Chaumonnot, Alexandra; Lesage, Anne; Emsley, Lyndon; van Bokhoven, Jeroen A; Copéret, Christophe
2015-08-26
Despite the widespread use of amorphous aluminosilicates (ASA) in various industrial catalysts, the nature of the interface between silica and alumina and the atomic structure of the catalytically active sites are still subject to debate. Here, by the use of dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) and density functional theory (DFT) calculations, we show that on silica and alumina surfaces, molecular aluminum and silicon precursors are, respectively, preferentially grafted on sites that enable the formation of Al(IV) and Si(IV) interfacial sites. We also link the genesis of Brønsted acidity to the surface coverage of aluminum and silicon on silica and alumina, respectively. PMID:26244620
Atomic structure of threading dislocations in AlN thin films
Energy Technology Data Exchange (ETDEWEB)
Tokumoto, Yuki, E-mail: y.tokumoto@imr.tohoku.ac.j [Institute for Materials Research, Tohoku University, 2-1-2, Katahira, Aoba-ku, Sendai 980-8577 (Japan); Shibata, Naoya [Institute of Engineering Innovation, School of Engineering, University of Tokyo, 2-11-16, Yayoi, Bunkyo, Tokyo 113-8656 (Japan); PRESTO, JST, 4-1-8, Honcho, Kawaguchi, Saitama 332-0012 (Japan); Mizoguhci, Teruyasu [Institute of Engineering Innovation, School of Engineering, University of Tokyo, 2-11-16, Yayoi, Bunkyo, Tokyo 113-8656 (Japan); Yamamoto, Takahisa [Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8651 (Japan); Ikuhara, Yuichi [Institute of Engineering Innovation, School of Engineering, University of Tokyo, 2-11-16, Yayoi, Bunkyo, Tokyo 113-8656 (Japan); WPI Advanced Institute for Materials Research, Tohoku University, 2-1-2, Katahira, Aoba-ku, Sendai 980-8577 (Japan)
2009-12-15
The core structure of threading dislocations in AlN films was investigated by atomic-resolution scanning transmission electron microscopy. The threading dislocations in the AlN films were found to be mostly edge-type perfect dislocations. It was directly revealed that the edge dislocation core has the 8-atom ring structure which is an energetically favorable structure predicted by previous theoretical studies.
Chain-branching control of the atomic structure of alkanethiol-based gold-sulfur interfaces.
Wang, Yun; Chi, Qijin; Zhang, Jingdong; Hush, Noel S; Reimers, Jeffrey R; Ulstrup, Jens
2011-09-28
Density functional theory structure calculations at 0 K and simulations at 300 K of observed high-resolution in situ scanning tunneling microscopy (STM) images reveal three different atomic-interface structures for the self-assembled monolayers (SAMs) of three isomeric butanethiols on Au(111): direct binding to the Au(111) surface without pitting, binding to adatoms above a regular surface with extensive pitting, and binding to adatoms with local surface vacancies and some pitting. Thermal motions are shown to produce some observed STM features, with a very tight energy balance controlling the observed structures. Variation of the degree of substitution on the α carbon is found to significantly change the relative energies for interaction of the different types of adatom structures with the surface, while the nature of the surface cell, controlled primarily by inter-adsorbate steric interactions, controls substrate reorganization energies and adsorbate distortion energies. Most significantly, by manipulating these features, chemical control of the adsorbate can produce stable interfaces with surface pitting eliminated, providing new perspectives for technological applications of SAMs.
Lee, C; Liu, W K; Yuan Jian Min; Shi, L; Zhu, X; Gao, K; Lee, Chaohong; Duan, Yiwu; Liu, Wing-Ki; Yuan, Jian-Min; Shi, Lei; Zhu, Xiwen; Gao, Kelin
2001-01-01
Based upon our previous works (Eur.Phys.J.D 6, 319(1999); Chin.Phys.Lett. 18, 236(2001)), we develop a classical approach to calculate the high-order harmonic generation of the laser driven atoms and molecules. The Coulomb singularities in the system have been removed by a regularization procedure. Action-angle variables have been used to generate the initial microcanonical distribution which satisfies the inversion symmetry of the system. The numerical simulation show, within a proper laser intensity, a harmonic plateau with only odd harmonics appears. At higher intensities, the spectra become noisier because of the existence of chaos. With further increase in laser intensity, ionization takes place, and the high-order harmonics disappear. Thus chaos introduces noise in the spectra, and ionization suppresses the harmonic generation, with the onset of the ionization follows the onset of chaos.
Electronic structures of halogen-doped Cu2O based on DFT calculations
Zhao, Zong-Yan; Yi, Juan; Zhou, Da-Cheng
2014-01-01
In order to construct p—n homojunction of Cu2O-based thin film solar cells that may increase its conversion efficiency, to synthesize n-type Cu2O with high conductivity is extremely crucial, and considered as a challenge in the near future. The doping effects of halogen on electronic structure of Cu2O have been investigated by density function theory calculations in the present work. Halogen dopants form donor levels below the bottom of conduction band through gaining or losing electrons, suggesting that halogen doping could make Cu2O have n-type conductivity. The lattice distortion, the impurity formation energy, the position, and the band width of donor level of Cu2O1-xHx (H = F, Cl, Br, I) increase with the halogen atomic number. Based on the calculated results, chlorine doping is an effective n-type dopant for Cu2O, owing to the lower impurity formation energy and suitable donor level.
Electronic structure and optical properties of B/P-doped amorphous Si calculated by first-principles
International Nuclear Information System (INIS)
Highlights: • Short-range order in a-Si lead to the similar electronic structure and optical properties with c-Si. • Long-range disorder of a-Si lead to the different electronic structure and optical properties. • Localized states predominately determine the optical properties in visible-light region of a-Si. • B/P-doping have no obvious effects for the electronic structure and optical properties of a-Si. - Abstract: In order to understand the electronic structures, optical properties, and explain the experimental observations of B/P-doped amorphous Si, the relevant micro-structure and properties have been calculated by simulated annealing and DFT+U methods. Based on the calculated results, the short-range order features of micro-structure in amorphous Si lead to the similar electronic structure and optical properties with crystalline Si, owing to the short-range order reflects the nature of atomic chemical bonding and plays a major role in the decision of fundamental characteristics of amorphous Si. What is important, the long-range disorder features of micro-structure lead to the different electronic structure and optical properties of amorphous Si, in compared with crystalline Si. Especially, the localized states caused by structural defects predominately determined the optical properties in visible-light region. The findings in the present work could well explain the experimental observations in literatures, and are helpful for the development of amorphous Si based functional materials
Heyrovska, Raji
2008-01-01
Recently, the bond lengths of the molecular components of nucleic acids and of caffeine and related molecules were shown to be sums of the appropriate covalent radii of the adjacent atoms. Thus, each atom was shown to have its specific contribution to the bond length. This enabled establishing their atomic structures for the first time. In this work, the known bond lengths for amino acids and the peptide bond are similarly shown to be sums of the atomic covalent radii. Based on this result, the atomic structures of glycine, alanine and serine and their tripeptide have been presented.
Tan, J; Wang, G; Liu, Z Y; Bednarčík, J; Gao, Y L; Zhai, Q J; Mattern, N; Eckert, J
2014-01-01
A model Zr41.25Ti13.75Ni10Cu12.5Be22.5 (at.%) bulk metallic glass (BMG) is selected to explore the structural evolution on the atomic scale with decreasing temperature down to cryogenic level using high energy X-ray synchrotron radiation. We discover a close correlation between the atomic structure evolution and the strength of the BMG and find out that the activation energy increment of the concordantly atomic shifting at lower temperature is the main factor influencing the strength. Our results might provide a fundamental understanding of the atomic-scale structure evolution and may bridge the gap between the atomic-scale physics and the macro-scale fracture strength for BMGs. PMID:24469299
A Calculation Model for Corrosion Cracking in RC Structures
Institute of Scientific and Technical Information of China (English)
Xu Gang; Wei Jun; Zhang Keqiang; Zhou Xiwu
2007-01-01
A novel calculation model is proposed aiming at the problem of concrete cover cracking induced by reinforcement corrosion. In this article, the relationship between the corrosion depth of the bar and the thickness of the rust layer is established. By deducing the radial displacement expression of concrete, the formula for corrosion depth and corrosion pressure before cracking is proposed. The crack depth of cover in accordance with the maximum corrosion pressure is deduced; furthermore, the corrosion depth and corrosion pressure at the cracking time are obtained. Finally, the theoretical model is validated by several experiments, and the calculated values agree well with the experiment results.
The fine structure of niobium condensates deposited from ion-atomic fluxes in helium atmosphere
International Nuclear Information System (INIS)
Helium gas influence on the structural characteristics of niobium coatings deposited by low-energy metallic Nb ion-stoic fluxes in He atmosphere is investigated. It is shown that He implantation in Nb films during condensation is accompanied with the decreasing of the mean size of condensate grains. At the same time, He atoms modify no physical processes of the fine structure formation. Using thermodesorption spectroscopy we have determined that He atoms mainly belong to vacancy/vacancy-solute complexes in Nb coatings. Our conclusion is that such complexes play a dominant role in formation of the fine structure of vacuum coatings deposited from ion-atomic fluxes
Boundary Collisions of Slow Atoms with Two-dimensional Hexagonal Structure
Directory of Open Access Journals (Sweden)
A.S. Dolgov
2014-11-01
Full Text Available It is shown that location of target atoms, specified by the structure geometry, define the distribution of impact parameters and energy transfer which strongly differs from the distribution of random location of targets. Considering model of solid spheres, energy spectrum of reflected atoms and probability of single or multiple collisions with the structure are found. Increase in the energy efficiency with respect to the disordered structure is established. Possibility and conditions of realizations of collisions with the second layer atoms omitting first ones are demonstrated.
Realizing high magnetic moments in fcc Fe nanoparticles through atomic structure stretch.
Baker, S H; Roy, M; Thornton, S C; Binns, C
2012-05-01
We describe the realization of a high moment state in fcc Fe nanoparticles through a controlled change in their atomic structure. Embedding Fe nanoparticles in a Cu(1-x)Au(x) matrix causes their atomic structure to switch from bcc to fcc. Extended x-ray absorption fine structure (EXAFS) measurements show that the structure in both the matrix and the Fe nanoparticles expands as the amount of Au in the matrix is increased, with the data indicating a tetragonal stretch in the Fe nanoparticles. The samples were prepared directly from the gas phase by co-deposition, using a gas aggregation source and MBE-type sources respectively for the nanoparticle and matrix materials. The structure change in the Fe nanoparticles is accompanied by a sharp increase in atomic magnetic moment, ultimately to values of ~2.5 ± 0.3 μ(B)/atom .
DEFF Research Database (Denmark)
Long, A.; Rydberg, Patrik
2013-01-01
To enhance the discrimination rate for methods applying structural alerts and biotransformation rules in the prediction of toxicity and drug metabolism we have developed a set of novel fragment based atomic descriptors. These atomic descriptors encode the properties of the fragments separating an...
Niaz, Mansoor; Aguilera, Damarys; Maza, Arelys; Liendo, Gustavo
2002-01-01
Reports on a study aimed at facilitating freshman general chemistry students' understanding of atomic structure based on the work of Thomson, Rutherford, and Bohr. Hypothesizes that classroom discussions based on arguments/counterarguments of the heuristic principles on which these scientists based their atomic models can facilitate students'…
Identifying Atomic Structure as a Threshold Concept: Student Mental Models and Troublesomeness
Park, Eun Jung; Light, Gregory
2009-01-01
Atomic theory or the nature of matter is a principal concept in science and science education. This has, however, been complicated by the difficulty students have in learning the concept and the subsequent construction of many alternative models. To understand better the conceptual barriers to learning atomic structure, this study explores the…
Microscopic Nuclear Structure and Reaction Calculations in the FMD Approach
Neff, T.; Feldmeier, H.; Langanke, K.
We present here a first application of the Fermionic Molecular Dynamics (FMD) approach to low-energy nuclear reactions, namely the $^3$He($\\alpha$,$\\gamma$)$^7$Be radiative capture reaction. We divide the Hilbert space into an external region where the system is described as $^3$He and $^4$He clusters interacting only via the Coulomb interaction and an internal region where the nuclear interaction will polarize the clusters. Polarized configurations are obtained by a variation after parity and angular momentum projection procedure with respect to the parameters of all single particle states. A constraint on the radius of the intrinsic many-body state is employed to obtain polarized clusters at desired distances. The boundary conditions for bound and scattering states are implemented using the Bloch operator. The FMD calculations reproduce the correct energy for the centroid of the $3/2^-$ and $1/2^-$ bound states in $^7$Be. The charge radius of the ground state is in good agreement with recent experimental results. The FMD calculations also describe well the experimental phase shift data in the $1/2^+$, $3/2^+$ and $5/2^+$ channels that are important for the capture reaction at low energies. Using the bound and scattering many-body wave functions we calculate the radiative capture cross section. The calculated $S$ factor agrees very well, both in absolute normalization and energy dependence, with the recent experimental data from the Weizmann, LUNA, Seattle and ERNA experiments.
Calculation of hybrid joints used in modern aerospace structures
Directory of Open Access Journals (Sweden)
Marcel STERE
2011-12-01
Full Text Available The state – of - the art of aeronautical structures show that parts are manufactured and subsequently assembled with the use of fasteners and/ or bonding. Adhesive bonding is a key technology to low weight, high fatigue resistance, robustness and an attractive design for cost structures.The paper results resolve significant problems for two groups of end-users:1 for the aerospace design office: a robust procedure for the design of the hybrid joint structural components;2 for the aeronautical repair centres: a useful procedure for structural design and analysis with significant cost savings.
Spek, Anthony L
2015-01-01
The completion of a crystal structure determination is often hampered by the presence of embedded solvent molecules or ions that are seriously disordered. Their contribution to the calculated structure factors in the least-squares refinement of a crystal structure has to be included in some way. Traditionally, an atomistic solvent disorder model is attempted. Such an approach is generally to be preferred, but it does not always lead to a satisfactory result and may even be impossible in cases where channels in the structure are filled with continuous electron density. This paper documents the SQUEEZE method as an alternative means of addressing the solvent disorder issue. It conveniently interfaces with the 2014 version of the least-squares refinement program SHELXL [Sheldrick (2015). Acta Cryst. C71. In the press] and other refinement programs that accept externally provided fixed contributions to the calculated structure factors. The PLATON SQUEEZE tool calculates the solvent contribution to the structure factors by back-Fourier transformation of the electron density found in the solvent-accessible region of a phase-optimized difference electron-density map. The actual least-squares structure refinement is delegated to, for example, SHELXL. The current versions of PLATON SQUEEZE and SHELXL now address several of the unnecessary complications with the earlier implementation of the SQUEEZE procedure that were a necessity because least-squares refinement with the now superseded SHELXL97 program did not allow for the input of fixed externally provided contributions to the structure-factor calculation. It is no longer necessary to subtract the solvent contribution temporarily from the observed intensities to be able to use SHELXL for the least-squares refinement, since that program now accepts the solvent contribution from an external file (.fab file) if the ABIN instruction is used. In addition, many twinned structures containing disordered solvents are now also
New density-independent interactions for nuclear structure calculations
International Nuclear Information System (INIS)
We present a new two-body finite-range and momentum-dependent but density-independent effective interaction, which can be interpreted as a regularized zero-range force. We show that no three-body or density-dependent terms are needed for a correct description of saturation properties in infinite matter, that is, on the level of low-energy density functional, the physical three-body effects can be efficiently absorbed in effective two-body terms. The new interaction gives a satisfying equation of state of nuclear matter and opens up extremely interesting perspectives for the mean-field and beyond-mean-field descriptions of atomic nuclei. (authors)
Wetsel, Grover C., Jr.
1978-01-01
Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)
Low viscosity and high attenuation in MgSiO3 post-perovskite inferred from atomic-scale calculations
Goryaeva, Alexandra M.; Carrez, Philippe; Cordier, Patrick
2016-10-01
This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO3 post-perovskite (Mg-ppv) at 120 GPa. We propose an approach based on a one-dimensional line tension model in conjunction with atomic-scale calculations. In this model, the key parameters, namely, the line tension and the Peierls barrier, are obtained from density functional theory calculations. We find a Peierls stress σp = 2.1 GPa and a line tension Γ = 9.2 eV/Å, which lead to a kink-pair enthalpy (under zero stress) of 2.69 eV. These values confirm that this slip system bears a very low lattice friction because it vanishes for temperatures above approximately 500 K under mantle conditions. In the Earth’s mantle, high-pressure Mg-ppv silicate is thus expected to become as ductile as ferropericlase. These results confirm the hypothesis of a weak layer in the D″ layer where Mg-ppv is present. Easy glide along [100](010) suggests strong preferred orientations with (010) planes aligned. Highly mobile [100] dislocations are also likely to respond to stresses related to seismic waves, leading to energy dissipation and strong attenuation.
Sarkadi, L
2015-01-01
The three-body dynamics of the ionization of the atomic hydrogen by 30 keV antiproton impact has been investigated by calculation of fully differential cross sections (FDCS) using the classical trajectory Monte Carlo (CTMC) method. The results of the calculations are compared with the predictions of quantum mechanical descriptions: The semi-classical time-dependent close-coupling theory, the fully quantal, time-independent close-coupling theory, and the continuum-distorted-wave-eikonal-initial-state model. In the analysis particular emphasis was put on the role of the nucleus-nucleus (NN) interaction played in the ionization process. For low-energy electron ejection CTMC predicts a large NN interaction effect on FDCS, in agreement with the quantum mechanical descriptions. By examining individual particle trajectories it was found that the relative motion between the electron and the nuclei is coupled very weakly with that between the nuclei, consequently the two motions can be treated independently. A simple ...
International Nuclear Information System (INIS)
The relationship between the mean isotropic e.s.d. anti σ(A)o of any element type A in a crystal structure and the R factor and atomic constitution of that structure is explored for 124 905 element-type occurrences calculated from 33 955 entries in the Cambridge Structural Database. On the basis of the work of Cruickshank [Acta Cryst. (1960), 13, 774-777], it is shown that anti σ(A)p values can be estimated by equations of the form anti σ(A)p = KRN1/2c/ZA where Nc is taken as ΣZ2i/Z2C, the Zi are atomic numbers and the summation is over all atoms in the asymmetric unit. Values of K were obtained by regression techniques using the anti σ(A)o as basis. The constant Knc for noncentrosymmetric structures is found to be larger than Kc for centrosymmetric structures by a factor of ∼21/2, as predicted by Cruickshank (1960). Two predictive equations are generated, one for first-row elements and the second for elements with ZA > 10. The relationship between the different constants K that arise in these two situations is linked to shape differentials in scattering-factor (fi) curves for light and heavy atoms. It is found that predictive equations in which the Zi are selectively replaced by fi at a constant sinθ/λ of 0.30 A-1 generate closely similar values of K for the light-atom and heavy-atom subsets. The overall analysis indicates that atomic e.s.d.'s may be seriously underestimated in the more precise structure determinations, that e.s.d.'s for the heaviest atoms may be less reliable than those for lighter atoms and that e.s.d.'s in noncentrosymmetric structures may be less accurate than those in centrosymmetric structures. (orig.)
Directory of Open Access Journals (Sweden)
Liangliang Gou
2015-11-01
Full Text Available The study of crystal structures in shape memory alloys is of fundamental importance for understanding the shape memory effect. In order to investigate the mechanism of how Cu content affects martensite crystal structures of TiNiCu alloys, the present research examines the atomic displacement of Ti50Ni50−xCux (x = 0, 5, 12.5, 15, 18.75, 20, 25 shape memory alloys using density functional theory (DFT. By the introduction of Cu atoms into TiNi martensite crystal to replace Ni, the displacements of Ti and Ni/Cu atoms along the x-axis are obvious, but they are minimal along the y- and z-axes. It is found that along the x-axis, the two Ti atoms in the unit cell move in opposite directions, and the same occurred with the two Ni/Cu atoms. With increasing Cu content, the distance between the two Ni/Cu atoms increases while the Ti atoms draw closer along the x-axis, leading to a rotation of the (100 plane, which is responsible for the decrease in the monoclinic angle. It is also found that the displacements of both Ti atoms and Ni/Cu atoms along the x-axis are progressive, which results in a gradual change of monoclinic angle and a transition to B19 martensite crystal structure.
Electronic structure calculations on lithium battery electrolyte salts.
Johansson, Patrik
2007-03-28
New lithium salts for non-aqueous liquid, gel and polymeric electrolytes are crucial due to the limiting role of the electrolyte in modern lithium batteries. The solvation of any lithium salt to form an electrolyte solution ultimately depends on the strength of the cation-solvent vs. the cation-anion interaction. Here, the latter is probed via HF, B3LYP and G3 theory gas-phase calculations for the dissociation reaction: LiX Li(+) + X(-). Furthermore, a continuum solvation method (C-PCM) has been applied to mimic solvent effects. Anion volumes were also calculated to facilitate a discussion on ion conductivities and cation transport numbers. Judging from the present results, synthesis efforts should target heterocyclic anions with a size of ca. 150 A(3) molecule(-1) to render new highly dissociative lithium salts that result in electrolytes with high cation transport numbers. PMID:17356757
Combined automated NOE assignment and structure calculation with CYANA
Energy Technology Data Exchange (ETDEWEB)
Güntert, Peter, E-mail: guentert@em.uni-frankfurt.de; Buchner, Lena [Goethe University Frankfurt am Main, Center for Biomolecular Magnetic Resonance, Institute of Biophysical Chemistry (Germany)
2015-08-15
The automated assignment of NOESY cross peaks has become a fundamental technique for NMR protein structure analysis. A widely used algorithm for this purpose is implemented in the program CYANA. It has been used for a large number of structure determinations of proteins in solution but was so far not described in full detail. In this paper we present a complete description of the CYANA implementation of automated NOESY assignment, which differs extensively from its predecessor CANDID by the use of a consistent probabilistic treatment, and we discuss its performance in the second round of the critical assessment of structure determination by NMR.
Cosmic ray physics in calculations of cosmological structure formation
Ensslin, Torsten A.; Pfrommer, Christoph; Springel, Volker; Jubelgas, Martin
2006-01-01
Cosmic rays (CRs) play a decisive role within our own Galaxy. They provide partial pressure support against gravity, they trace past energetic events such as supernovae, and they reveal the underlying structure of the baryonic matter distribution through their interactions. To study the impact of CRs on galaxy and cosmic structure formation and evolution, we develop an approximative framework for treating dynamical and radiative effects of CRs in cosmological simulations. Our guiding principl...
Structure-Property Relationships in Atomic-Scale Junctions: Histograms and Beyond.
Hybertsen, Mark S; Venkataraman, Latha
2016-03-15
are pulled apart has given complementary information such as the stiffness and rupture force of the molecule-metal link bond. Overall, while the BJ technique does not produce a single molecule circuit for practical applications, it has proved remarkably versatile for fundamental studies. Measured data and analysis have been combined with atomic-scale theory and calculations, typically performed for representative junction structures, to provide fundamental physical understanding of structure-function relationships. This Account integrates across an extensive series of our specific nanoscale junction studies which were carried out with the STM- and AFM-BJ techniques and supported by theoretical analysis and density functional theory based calculations, with emphasis on the physical characteristics of the measurement process and the rich data sets that emerge. Several examples illustrate the impact of measured trends based on the most probable values for key characteristics (obtained from ensembles of order 1000-10 000 individual junctions) to build a solid picture of conductance phenomena as well as attributes of the link bond chemistry. The key forward-looking question posed here is the extent to which the full data sets represented by the individual trajectories can be analyzed to address structure-function questions at the level of individual junctions. Initial progress toward physical modeling of conductance of individual junctions indicates trends consistent with physical junction structures. Analysis of junction mechanics reveals a scaling procedure that collapses existing data onto a universal force-extension curve. This research directed to understanding the distribution of structures and physical characteristics addresses fundamental questions concerning the interplay between chemical control and stochastically driven diversity. PMID:26938931
Zhang, Wei; Chen, Qing-Yun; Zeng, Zhao-Yi; Cai, Ling-Cang
2015-10-01
We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound (Na8Si46) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus, Young’s modulus, Debye temperature, sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46. Project supported by National Natural Science Foundation of China (Grant Nos. 11347134 and 11304254) and the Doctor Foundation of Southwest University of Science and Technology, China (Grant No. 13zx7125).
Institute of Scientific and Technical Information of China (English)
张伟; 陈青云; 曾召益; 蔡灵仓
2015-01-01
We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon–clathrate compound (Na8Si46) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus ,Young’s modulus, Debye temperature, sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46.
Banerjee, Amartya S; Hu, Wei; Yang, Chao; Pask, John E
2016-01-01
The Discontinuous Galerkin (DG) electronic structure method employs an adaptive local basis set to solve the equations of density functional theory in a discontinuous Galerkin framework. The methodology is implemented in the Discontinuous Galerkin Density Functional Theory (DGDFT) code for large-scale parallel electronic structure calculations. In DGDFT, the basis is generated on-the-fly to capture the local material physics, and can systematically attain chemical accuracy with only a few tens of degrees of freedom per atom. Hence, DGDFT combines the key advantage of planewave basis sets in terms of systematic improvability with that of localized basis sets in reducing basis size. A central issue for large-scale calculations, however, is the computation of the electron density from the discretized Hamiltonian in an efficient and scalable manner. We show in this work how Chebyshev polynomial filtered subspace iteration (CheFSI) can be used to address this issue and push the envelope in large-scale materials si...
Wang, Zhiqiang; Chen, Jianchao; Li, Linwei; Zhou, Zhixu; Geng, Yiding; Sun, Tiemin
2015-10-01
In this study, the experimental and theoretical studies on the structure of β-artemether are presented. The optimized molecular structure, Mulliken atomic charges, vibrational spectra (IR, Raman and vibrational circular dichroism), and molecular electrostatic potential have been calculated by density functional theory (DFT) using B3LYP method with the 6-311++G (2d, p) basis set. Reliable vibrational assignments for Artemether have been made on the basis of potential energy distribution (PED). The vibrational circular dichroism (VCD) has been explored by ab initio calculations, and then was used to compare with the experimental VCD. The consistence between them confirmed the absolute configuration of Artemether. In addition, HOMO-LUMO of the title compound as well as thermo-dynamical parameters has illustrated the stability of β-artemether.
Semiempirical Studies of Atomic Structure. Final Report for July 1, 2000 - June 30, 2003
Energy Technology Data Exchange (ETDEWEB)
Curtis, L. J.
2004-05-01
This project has developed a comprehensive and reliable base of accurate atomic structure data for complex many-electron systems. This has been achieved through the use of sensitive data-based parametric systematizations, precise experimental measurements, and supporting theoretical computations. The atomic properties studies involved primary data (wavelengths, frequency intervals, lifetimes, relative intensities, production rates, etc.) and derived structural parameters (energy levels, ionization potentials, line strengths, electric polarizabilities, branching fractions, excitation functions, etc).
Semiempirical Studies of Atomic Structure. Final Report for July 1, 2000 - June 30, 2003
International Nuclear Information System (INIS)
This project has developed a comprehensive and reliable base of accurate atomic structure data for complex many-electron systems. This has been achieved through the use of sensitive data-based parametric systematizations, precise experimental measurements, and supporting theoretical computations. The atomic properties studies involved primary data (wavelengths, frequency intervals, lifetimes, relative intensities, production rates, etc.) and derived structural parameters (energy levels, ionization potentials, line strengths, electric polarizabilities, branching fractions, excitation functions, etc)
Valence electron structure of the（ZrTi）B2 solid solutions calculated by the three models
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The Zr-rich(Zr0.8Ti0.2)B2 and the Ti-rich(Ti0.8Zr0.2)B2 solid solutions are formed when TiB2 and ZrB2 are hot-pressed.To forecast the properties of the two solid solutions,their valence electron structure was analyzed based on the empirical electron theory(EET) of solids and molecules.We used three different models,the average atom model,the average cell model and the real cell model,and compared with the calculation results from the three models.In the real cell model,the lattice constants of the solid solu-tions were supposed to be changed or unchanged.The results showed that different models could only result in slight change in the hybridization levels of the metal atoms in the two solid solutions and little difference between the calculation values.However,they can not change the variant trend of the va-lence electron structure nor the properties of the solid solutions.Thus,the three models and the methods are appropriate and the calculation results are reasonable and consistent.
Microstructural Characterization of Hierarchical Structured Surfaces by Atomic Force Microscopy
Ponomareva, A. A.; Moshnikov, V. A.; Suchaneck, G.
2013-12-01
In this work, we evaluate the hierarchical surface topography of reactively sputtered nanocrystalline Pb(Zr,Ti)O3 and TiO2 thin films as well as plasma-treated antireflective PET films by means of determining the fractal dimension and power spectral density (PSD) of surface topography recorded by atomic force microscopy (AFM). Local fractal dimension was obtained using the triangulation method. The PSDs of all samples were fitted to the k-correlation model (also called ABC model) valid for a self-affine surface topography. Fractal analysis of AFM images was shown to be an appropriate and easy to use tool for the characterization of hierarchical nanostructures.
Atomic-scale nanowires: physical and electronic structure
International Nuclear Information System (INIS)
The technology to build and study nanowires with sizes ranging from individual atoms to tens of nanometres has been developing rapidly over the last few years. We survey the motivation behind these developments, and summarize the basics behind quantized conduction. Several of the different experimental techniques and materials systems used in the creation of nanowires are examined, and the range of theoretical methods developed both for examining open systems (especially their conduction properties) and for modelling large systems are considered. We present various noteworthy example results from the field, before concluding with a look at future directions. (topical review)
Molecular-Field Calculation of the Magnetic Structure in Erbium
DEFF Research Database (Denmark)
Jensen, J.
1976-01-01
A molecular-field calculation of the magnetic configurations in Er is found to reproduce the neutron diffraction results of the three different magnetic phases and to give a reasonable fit to the magnetization data at 4.2K. The two-ion coupling is considered to be described by the inter......-planar coupling parameters deduced from the dispersion of the spin waves in the low temperature conical phases. The four (effective) crystal-field parameters are determined by the fit to the experimental data. Projecting the magnetic moments present in the intermediate phase of Er (18-52.4K) to a common origin...
Tan, J.; Wang, G.; Z. Y. LIU; Bednarčík, J.; Gao, Yan; Zhai, Q. J.; Mattern, N.; Eckert, J.
2014-01-01
A model Zr41.25Ti13.75Ni10Cu12.5Be22.5 (at.%) bulk metallic glass (BMG) is selected to explore the structural evolution on the atomic scale with decreasing temperature down to cryogenic level using high energy X-ray synchrotron radiation. We discover a close correlation between the atomic structure evolution and the strength of the BMG and find out that the activation energy increment of the concordantly atomic shifting at lower temperature is the main factor influencing the strength. Our res...
Sun, Minglei; Hao, Yitong; Ren, Qingqiang; Zhao, Yiming; Du, Yanhui; Tang, Wencheng
2016-09-01
Using density functional theory computations, we systematically investigated the structural, electronic and magnetic properties of Al, Si, As and Sb doped blue phosphorene. The electronic properties of blue phosphorene can be effectively turned by substitutional doping. Especially, Al and Sb lead to an indirect-to-direct-gap transition. The interaction between the impurity and P atoms should be responsible for the transition. In addition, blue phosphorene can exhibit dilute magnetic semiconductor property with doping of Si impurity. The magnetic moment in Si-substituted blue phosphorene predominantly originates from the hybridization of Si-s pz and P-pz orbitals. These results provide many useful applications of blue phosphorene in electronics, optoelectronics and spintronics.
Song, Yun; Cao, Yu; Wang, Jing; Zhou, Yong-Ning; Fang, Fang; Li, Yuesheng; Gao, Shang-Peng; Gu, Qin-Fen; Hu, Linfeng; Sun, Dalin
2016-08-24
As a novel class of soft matter, two-dimensional (2D) atomic nanosheet-like crystals have attracted much attention for energy storage devices due to the fact that nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. Herein, atomically thin γ-FeOOH nanosheets with a thickness of ∼1.5 nm are synthesized in a high yield, and the band and electronic structures of the γ-FeOOH nanosheet are revealed using density-functional theory calculations for the first time. The rationally designed γ-FeOOH@rGO composites with a heterostacking structure are used as an anode material for lithium-ion batteries (LIBs). A high reversible capacity over 850 mAh g(-1) after 100 cycles at 200 mA g(-1) is obtained with excellent rate capability. The remarkable performance is attributed to the ultrathin nature of γ-FeOOH nanosheets and 2D heterostacking structure, which provide the minimized Li(+) diffusion length and buffer zone for volume change. Further investigation on the Li storage electrochemical mechanism of γ-FeOOH@rGO indicates that the charge-discharge processes include both conversion reaction and capacitive behavior. This synergistic effect of conversion reaction and capacitive behavior originating from 2D heterostacking structure casts new light on the development of high-energy anode materials. PMID:27471909
Institute of Scientific and Technical Information of China (English)
Ryota NAKANISHI; Koji SUEOKA; Seiji SHIBA; Makoto HINO; Koji MURAKAMI; Ken MURAOKA
2009-01-01
A study the with first principles calculation of the interfaces of the Ni layer or Cu layer on the Fe(100) surface formed with metal plating was performed. Ni or Cu atoms were shown to adopt the corresponding position to the bcc structure of the Fe(100) substrate. Other calculations showed that the interfaces of Ni (5 atomic layers)/Fe(100) (5 layers) or Cu (5 atomic layers)/Fe(100) (5 layers) had square lattices. The orientation relationship of Ni/Fe(100) interface corresponds to fcc-Ni(100)//bcc-Fe(100), Ni[011]//Fe[010], and Similar results were obtained for Cu/Fe(100) interfaces. This structure was supported by TEM analysis of plated Ni layer on Fe(100) surfaces. The adhesion strength of the Ni/Fe(100) interface evaluated by first principles calculation was higher than that of the Cu/Fe(100) interface. The experimental results of Hull cell iron plated with Ni or Cu supported the results of the calculation. These results indicate that the first principles calculation, which deals with the ideal interface at the atomic scale, has the potential to evaluate the adhesion strength of metallic material interfaces.
Atomic Resolution Imaging of Nanoscale Structural Ordering in a Complex Metal Oxide Catalyst
Zhu, Yihan
2012-08-28
The determination of the atomic structure of a functional material is crucial to understanding its "structure-to-property" relationship (e.g., the active sites in a catalyst), which is however challenging if the structure possesses complex inhomogeneities. Here, we report an atomic structure study of an important MoVTeO complex metal oxide catalyst that is potentially useful for the industrially relevant propane-based BP/SOHIO process. We combined aberration-corrected scanning transmission electron microscopy with synchrotron powder X-ray crystallography to explore the structure at both nanoscopic and macroscopic scales. At the nanoscopic scale, this material exhibits structural and compositional order within nanosized "domains", while the domains show disordered distribution at the macroscopic scale. We proposed that the intradomain compositional ordering and the interdomain electric dipolar interaction synergistically induce the displacement of Te atoms in the Mo-V-O channels, which determines the geometry of the multifunctional metal oxo-active sites.
Role of anion doping on electronic structure and magnetism of GdN by first principles calculations
Zhang, Xuejing
2014-01-01
We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.
Farhadi, Saeed; Mahmoudi, Farzaneh; Simpson, Jim
2016-03-01
A new nano-structured Mn(II) coordination polymer [Mn(HL)(dca)(Cl)]n(1), [HL= Pyridine-2-carbaldehyde semicarbazone, dca= dicyanamide] has been synthesized by a sonochemical method and has been characterized by scanning electron microscopy, X-ray powder diffraction elemental analysis and IR spectroscopy. Single crystals of compound 1 was synthesized by slow evaporation method and was structurally characterised by single crystal X-ray diffraction. The single crystal structure shows one dimensional zig-zag chains with end-to-end dicyanamide-bridged ligand. A distorted octahedral geometry around the Mn2+centers was achieved by NNO atoms from HL, two nitrogen atoms of dicyanamide and one chlorine atom. Also for more details, the structure of 1, has been optimized by density functional theory (DFT calculations).
International Nuclear Information System (INIS)
This book is an introduction to modern physics for undergraduate students of physics or students of related fields. After an introduction to the wave-particle dualism the structure of atoms is considered with regards to atomic models. Then the foundations of quantum mechanics are introduced with regards to their application to atomic structure calculations. Thereafter the chemical bond and the molecular structure are discussed. Then classical and quantum statistical mechanics are introduced. Thereafter the crystal binding, the crystal structure, and the specific heat of solids are considered. Finally the band theory of solids is briefly introduced. Every chapter contains exercise problems. (HSI)
Local atomic and electronic structure of boron chemical doping in monolayer graphene.
Zhao, Liuyan; Levendorf, Mark; Goncher, Scott; Schiros, Theanne; Pálová, Lucia; Zabet-Khosousi, Amir; Rim, Kwang Taeg; Gutiérrez, Christopher; Nordlund, Dennis; Jaye, Cherno; Hybertsen, Mark; Reichman, David; Flynn, George W; Park, Jiwoong; Pasupathy, Abhay N
2013-10-01
We use scanning tunneling microscopy and X-ray spectroscopy to characterize the atomic and electronic structure of boron-doped and nitrogen-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice primarily in the graphitic form and contributes ~0.5 carriers into the graphene sheet per dopant. Density functional theory calculations indicate that boron dopants interact strongly with the underlying copper substrate while nitrogen dopants do not. The local bonding differences between graphitic boron and nitrogen dopants lead to large scale differences in dopant distribution. The distribution of dopants is observed to be completely random in the case of boron, while nitrogen displays strong sublattice clustering. Structurally, nitrogen-doped graphene is relatively defect-free while boron-doped graphene films show a large number of Stone-Wales defects. These defects create local electronic resonances and cause electronic scattering, but do not electronically dope the graphene film. PMID:24032458
Resonance structure in elastic scattering of electrons from atomic hydrogen
Energy Technology Data Exchange (ETDEWEB)
Warner, C.D.; King, G.C.; Hammond, P.; Slevin, J.
1986-10-28
High-energy-resolution spectra of electrons scattered elastically from atomic hydrogen have been obtained for incident electron energies of 9.2-10.4 eV and at angles of 33/sup 0/, 54/sup 0/, 70/sup 0/ and 90/sup 0/. The energy spread of the incident electron beam is estimated to be typically 25 meV FWHM. In addition to the /sup 1/S and /sup 3/P resonances which have been reported in earlier studies, a /sup 1/D resonance can be clearly seen and there is some evidence of a resonance state at a higher energy, probably corresponding to a /sup 1/S resonance state. The energies and resonance widths of all these features have been determined.
Resonance structure in elastic scattering of electrons from atomic hydrogen
International Nuclear Information System (INIS)
High-energy-resolution spectra of electrons scattered elastically from atomic hydrogen have been obtained for incident electron energies of 9.2-10.4 eV and at angles of 330, 540, 700 and 900. The energy spread of the incident electron beam is estimated to be typically 25 meV FWHM. In addition to the 1S and 3P resonances which have been reported in earlier studies, a 1D resonance can be clearly seen and there is some evidence of a resonance state at a higher energy, probably corresponding to a 1S resonance state. The energies and resonance widths of all these features have been determined. (author)
Atomic Models of Strong Solids Interfaces Viewed as Composite Structures
Staffell, I.; Shang, J. L.; Kendall, K.
2014-02-01
This paper looks back through the 1960s to the invention of carbon fibres and the theories of Strong Solids. In particular it focuses on the fracture mechanics paradox of strong composites containing weak interfaces. From Griffith theory, it is clear that three parameters must be considered in producing a high strength composite:- minimising defects; maximising the elastic modulus; and raising the fracture energy along the crack path. The interface then introduces two further factors:- elastic modulus mismatch causing crack stopping; and debonding along a brittle interface due to low interface fracture energy. Consequently, an understanding of the fracture energy of a composite interface is needed. Using an interface model based on atomic interaction forces, it is shown that a single layer of contaminant atoms between the matrix and the reinforcement can reduce the interface fracture energy by an order of magnitude, giving a large delamination effect. The paper also looks to a future in which cars will be made largely from composite materials. Radical improvements in automobile design are necessary because the number of cars worldwide is predicted to double. This paper predicts gains in fuel economy by suggesting a new theory of automobile fuel consumption using an adaptation of Coulomb's friction law. It is demonstrated both by experiment and by theoretical argument that the energy dissipated in standard vehicle tests depends only on weight. Consequently, moving from metal to fibre construction can give a factor 2 improved fuel economy performance, roughly the same as moving from a petrol combustion drive to hydrogen fuel cell propulsion. Using both options together can give a factor 4 improvement, as demonstrated by testing a composite car using the ECE15 protocol.
International Nuclear Information System (INIS)
Evaluation of ion-atom charge-changing cross-sections is needed for many accelerator applications. A Classical Trajectory Monte Carlo (CTMC) simulation has been used to calculate ionization and charge-exchange cross-sections. For benchmarking purposes, an extensive study has been performed for the simple case of hydrogen and helium targets in collisions with various ions. Despite the fact that the simulation only accounts for classical mechanics, the calculations are comparable to experimental results for projectile velocities in the region corresponding to the vicinity of the maximum cross-section. The shortcomings of the CTMC method for multielectron target atoms are discussed.
Comparison of measured and calculated temperatures for a Mach 8 hypersonic wing test structure
Quinn, R. D.; Fields, R. A.
1986-01-01
Structural temperatures were measured on a hypersonic wing test structure during a heating test that simulated a Mach 8 thermal environment. Measured data are compared to design calculations and temperature predictions obtained from a finite-difference thermal analysis.
Mancera, L; Takeuchi, N
2003-01-01
We have studied the structural and electronic properties of YN in rock salt (sodium chloride), caesium chloride, zinc blende and wurtzite structures using first-principles total energy calculations. Rock salt is the calculated ground state structure with a = 4.93 A, B sub 0 = 157 GPa. The experimental lattice constant is a = 4.877 A. There is an additional local minimum in the wurtzite structure with total energy 0.28 eV/unit cell higher. At high pressure (approx 138 GPa), our calculations predict a phase transformation from a NaCl to a CsCl structure.
Microscopic Nuclear Structure and Reaction Calculations in the FMD Approach
Neff, Thomas; Langanke, Karlheinz
2010-01-01
We present here a first application of the Fermionic Molecular Dynamics (FMD) approach to low-energy nuclear reactions, namely the $^3$He($\\alpha$,$\\gamma$)$^7$Be radiative capture reaction. We divide the Hilbert space into an external region where the system is described as $^3$He and $^4$He clusters interacting only via the Coulomb interaction and an internal region where the nuclear interaction will polarize the clusters. Polarized configurations are obtained by a variation after parity and angular momentum projection procedure with respect to the parameters of all single particle states. A constraint on the radius of the intrinsic many-body state is employed to obtain polarized clusters at desired distances. The boundary conditions for bound and scattering states are implemented using the Bloch operator. The FMD calculations reproduce the correct energy for the centroid of the $3/2^-$ and $1/2^-$ bound states in $^7$Be. The charge radius of the ground state is in good agreement with recent experimental re...
Calculation and Analysis of Internal Force in Arch Structure of Frozen Soil
Institute of Scientific and Technical Information of China (English)
YUE Feng-tian; ZHANG Yong; SHI Rong-jian
2005-01-01
Aimed at the frozen soil arch reinforcement form of upside shed used for the shield machine launching in tunneling the internal force of the structure was calculated with the aid of the structural mechanics theory. Considering the space characteristics of the structure,this calculating method is suitable for practical engineering.Moreover,the behavior of the freezing arch reinforcement structure was analyzed combined with an engineering case.
Variation of 3s photoionization resonance structures in a serial atomic number species Ar, K, and Ca
International Nuclear Information System (INIS)
Subvalence 3s-shell photoionization resonances of Ca were measured with monochromatized synchrotron radiation and photoion time-of-flight spectroscopy method. Charge resolved photoion yield spectra were obtained. Broad peak structures were found in the Ca+ spectrum and shallow window structures were found in the Ca2+ spectrum. We performed MCDF calculations to assign the resonance structures. The 3s-shell photoionization of Ar and K were also measured for comparison. A systematic increase was observed in Fano-Beutler parameter and in the resonance width along with the increase of atomic number from Z=18(Ar) to 20(Ca). We discuss also the spectral structures that could be of the 3p double-shake-up satellites, which are observed in the 3s photoionization region. (author)