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)
Atomic structure calculations on the CRAY X-MP
International Nuclear Information System (INIS)
Atomic structure calculations require both radial and angular integrations, where the latter are often based on Racah algebra. With relatively minor modifications, good performance is obtained on vector machines for radial integrations. Angular integrations, however, present the bottleneck. In this paper some recent improvements in the algorithms for angular integrations are described, as well as some multitasking experiments on the CRAY X-MP and CRAY 2. These show that the workload can easily be distributed evenly among available processors with dynamic scheduling
Multi-million atom electronic structure calculations for quantum dots
Usman, Muhammad
Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined
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
A new program for calculating matrix elements in atomic structure
International Nuclear Information System (INIS)
The solution of many problems concerning the electronic structure of atoms requires the evaluation of the matrix elements of the Hamiltonian operator, including the electrostatic interaction. These matrix elements may be expressed as weighted sums of radial integrals. The program we describe in this paper evaluates the coefficients of the Slater integrals and, if these are given, computes all the matrix elements for a given set of configurations. This program has nearly the same purposes as Hibbert's program and is also based on the Racach techniques. The main difference between this algorithm and the cited one is the method used to calculate the recoupling coefficients. While Hibbert's programs use Burke's algorithm to calculate these coefficients, in our program they are computed using the graphical techniques developed by Jucys et al. According to this method, that we describe in another paper the formulae needed to calculate the recoupling coefficients are previously derived and simplified (as a first step of the program). The use of this method may considerably reduce the running time, specially in the case of large configuration interaction matrices. (orig.)
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
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...
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.
International Nuclear Information System (INIS)
The structural, electronic and magnetic properties of free standing Au-Pd bimetallic atomic chain is studied using ab-initio method. It is found that electronic and magnetic properties of chains depend on position of atoms and number of atoms. Spin polarization factor for different atomic configuration of atomic chain is calculated predicting a half metallic behavior. It suggests a total spin polarised transport in these chains
Amani Tahat; Mahmoud Abu-Allaban; Safeia Hamasha
2011-01-01
In this study, a new atomic physics program (HTAC) is introduced and tested. It is a utility program designed to automate the computation of various atomic structure and spectral data. It is the first comprehensive code that enables performing atomic calculations based on three advanced theories: the fully relativistic configuration interactions approach, the multi-reference many body perturbation theory and the R-Matrix method. It has been designed to generate tabulated atomic data files tha...
A Hartree-Fock program for atomic structure calculations
International Nuclear Information System (INIS)
The Hartree-Fock equations for a general open shell atom are described. The matrix equations that result when the single particle orbitals are written in terms of a linear combination of analytic basis functions are derived. Attention is paid to the complexities that occur when open shells are present. The specifics of a working FORTRAN program which is available for public use are described. The program has the flexibility to handle either Slater-type orbitals or Gaussian-type orbitals. It can be obtained over the internet at http://lacebark.ntu.edu.au/j_mitroy/research/atomic.htm Copyright (1999) CSIRO Australia
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.
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.
Atomic structure calculations and identification of EUV and SXR spectral lines in Sr XXX
International Nuclear Information System (INIS)
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. - Highlights: • 113 Lowest levels for Sr XXX are calculated. • Extreme Ultraviolet (EUV) and soft-X ray (SXR) spectral lines are identified. • Wavelengths of EUV and SXR spectral lines are reported. • E1, E2, M1 and M2 transition rates, oscillator strengths and lines strengths for lowest 113 levels are presented. • Lifetimes for lowest 113 fine structure levels are provided
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
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.
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...
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)
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)
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.
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)
A robust and general Schrödinger and Dirac solver for atomic structure calculations
Czech Academy of Sciences Publication Activity Database
Čertík, O.; Pask, J.E.; Vackář, Jiří
2013-01-01
Roč. 184, č. 7 (2013), s. 1777-1791. ISSN 0010-4655 R&D Projects: GA MŠk(CZ) LC06040; GA ČR GA101/09/1630 Institutional support: RVO:68378271 Keywords : atom * electronic structure * Dirac equation * density -functional theory Subject RIV: BE - Theoretical Physics Impact factor: 2.407, year: 2013 http://www.sciencedirect.com/science/article/pii/S0010465513000714
Atomic and electronic structure of hydrogen on ZnO (1bar 100) surface: ab initio hybrid calculations
Usseinov, A. B.; Kotomin, E. A.; Zhukovskii, Yu F.; Purans, J.; Sorokin, A. V.; Akilbekov, A. T.
2013-12-01
Hydrogen atoms unavoidably incorporated into ZnO during growth of bulk samples and thin films considerably affect their electrical conductivity. The results of first principles hybrid LCAO calculations are discussed for hydrogen atoms in the bulk and on the non-polar ZnO (1bar 100) surface. The incorporation energy, the atomic relaxation, the electronic density redistribution and the electronic structure modifications are compared for the surface adsorption and bulk interstitial H positions. It is shown that hydrogen has a strong binding with the surface O ions (2.7 eV) whereas its incorporation into bulk is energetically unfavorable. Surface hydrogen atoms are very shallow donors, thus, contributing to the electronic conductivity.
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)
An accurate and efficient method is described for the evaluation of electrostatic contributions in LCAO electronic structure calculations. The charge density rho(r) is decomposed into rho/sup(1)(r), a component whose rapid variation near any nucleus reproduces that of rho(r) to a very good approximation, and a remainder density deltarho(r)equivalentrho(r)-rho/sup(1)(r), which is thereby guaranteed to be slowly varying in space. The power of the decomposition resides in the fact that rho/sup(1)(r) can be expressed exactly as a sum of one-center densities, without the use of any fit procedure. Because rho/sup(1)(r) is a sum of one-center multipolar densities, the Hartree potential is a function with a simple one-dimensional integral representation, and its matrix elements can be obtained by performing one-dimensional integrals over it. Since deltarho(r) is spatially slowly varying, the Hartree potential to which it corresponds and the matrix elements of this potential can accurately be evaluated on a relatively coarse coordinate space mesh, using fast Fourier transforms. The method is illustrated via molecular structure calculations for N2 and NH3. The calculations are accurate to a few percent when the required integrals over deltarho(r) and deltaV(r) are performed on a mesh of spacing 0.4 a.u. The N--N bond length and stretch frequency are found to equal 2.10 a.u. and 2.3 x 103 cm-1, respectively. The equilibrium N--H bond length and H--N--H angle are calculated to be 1.93 a.u. and 1050, respectively, while the NH3 inversion barrier turns out to equal 0.25 eV. These results are in good agreement with earlier calculations
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...
Calculation of the fine-structure parameters for np 5 n' f configurations of rare-gas atoms
Anisimova, G. P.; Kapel'Kina, E. L.; Semenov, R. I.
2000-12-01
In the single-configuration approximation, fine-structure parameters are calculated semiempirically in the intermediate coupling scheme for the configurations 2p 5 nf( n=4 6) of NeI, 3 p 5 nf( n=4 7) of ArI, and 4 p 54 f of KrI. With the fine-structure parameters obtained, the coefficients of expansion of the wave functions in basis functions of the LS-coupling scheme and the gyromagnetic ratios are calculated. To the authors’ knowledge, analogous data are absent in the literature. The correctness of the fine-structure parameters obtained is confirmed by values of the fine-splitting constant, which is well known for other configurations of rare-gas atoms with an almost filled p shell.
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.
International Nuclear Information System (INIS)
Present investigations deal with diagnostic X-ray qualities as applied in medical diagnostics. The track structure computer program PARTRAC simulating the coupled photon - electron transport and interactions in complex geometries has been used. Differential cross sections for electrons in gold with primary energies in the range of 100 eV to 100 keV have been derived on the basis of Seltzer model in case of ionizations and excitations with new Hartree-Fock input data. The elastic cross section data were taken from Fink et al. and Riley et al. These cross sections have been inserted into the existing track structure computer program to provide detailed simulations of electron interactions and to describe above mentioned interface effects. The tracks were simulated in a target volume of gold surrounded by water vapour to represent cell tissue and irradiated by 30 keV and 100 keV photons. The simulated geometry was chosen as in experiments using exoelectron emission. The tracks were calculated for comparison in pure water vapour under the same irradiation conditions. (author)
Atomic partial charges on CH3NH3PbI3 from first-principles electronic structure calculations
Madjet, Mohamed E.; El-Mellouhi, Fedwa; Carignano, Marcelo A.; Berdiyorov, Golibjon R.
2016-04-01
We calculated the partial charges in methylammonium (MA) lead-iodide perovskite CH3NH3PbI3 in its different crystalline phases using different first-principles electronic charge partitioning approaches, including the Bader, ChelpG, and density-derived electrostatic and chemical (DDEC) schemes. Among the three charge partitioning methods, the DDEC approach provides chemically intuitive and reliable atomic charges for this material, which consists of a mixture of transition metals, halide ions, and organic molecules. The DDEC charges are also found to be robust against the use of hybrid functionals and/or upon inclusion of spin-orbit coupling or dispersive interactions. We calculated explicitly the atomic charges with a special focus on the dipole moment of the MA molecules within the perovskite structure. The value of the dipole moment of the MA is reduced with respect to the isolated molecule due to charge redistribution involving the inorganic cage. DDEC charges and dipole moment of the organic part remain nearly unchanged upon its rotation within the octahedral cavities. Our findings will be of both fundamental and practical importance, as the accurate and consistent determination of the atomic charges is important in order to understand the average equilibrium distribution of the electrons and to help in the development of force fields for larger scale atomistic simulations to describe static, dynamic, and thermodynamic properties of the material.
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.
International Nuclear Information System (INIS)
Full text: We have briefly reported the activities in the study of atomic structure and dynamics calculations using the GRASP (General purpose Atomic Structure Program) family codes and also of some activities in NIFS. We have introduced the following items: 1. Analysis of Visible M1 Lines in Tungsten Ions, 2. Collisional-radiative model for W ions, 3. Code development for single electron capture by H nucleus from metal surface, 3. Kα radiation from low charge chlorine heated by an ion beam for plasma diagnostics, 4. Code Availability. And we have summarized the talk. The visible lights emitted from highly charged tungsten ions are of special interest; they are mainly realized by magnetic dipole transitions between the fine structure levels of ions and therefore they suffer less self-absorption by surrounding plasmas providing us with a great advantage for the diagnostics of core plasmas. We have studied the source of these visible line emissions in terms of accurate non-empirical atomic structure calculations and of population kinematics analyses. The GRASP package for multi-configuration Dirac-Fock atomic structure calculation have provided us with the transition energies that are accurate enough to discriminate the states and the charges of tungsten ions. We tried, further, to reproduce the emission spectra by modifying a population kinetics code that has been used for the analysis of boron like ion plasmas. We have assigned new visible emission lines. We have shown that the use of the GRASP family of codes is quite effective for the spectroscopy of the visible line emissions of tungsten ions and for the diagnostics of the MCF plasmas. We have extended a CR model calculation code to include the case of tungsten ions plasmas; the atomic data have been calculated using HULLAC code. We have applied the code to the analysis of W35+ to W37+ plasmas. The code is now still under development. We have now under the development of a code for single electron capture by H
Relativistic calculations for many electron atoms
International Nuclear Information System (INIS)
Many improvements have now been introduced in ab-initio methods for relativistic atomic structure calculations. After a short description of the different methods, we review the various contributions to energy levels and compare the most recent theoretical and experimental results for few electron heavy ions
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.
Atomic Structure Theory Lectures on Atomic Physics
Johnson, Walter R
2007-01-01
Atomic Structure Theory is a textbook for students with a background in quantum mechanics. The text is designed to give hands-on experience with atomic structure calculations. Material covered includes angular momentum methods, the central field Schrödinger and Dirac equations, Hartree-Fock and Dirac-Hartree-Fock equations, multiplet structure, hyperfine structure, the isotope shift, dipole and multipole transitions, basic many-body perturbation theory, configuration interaction, and correlation corrections to matrix elements. Numerical methods for solving the Schrödinger and Dirac eigenvalue problems and the (Dirac)-Hartree-Fock equations are given as well. B-spline basis sets are used to carry out sums arising in higher-order many-body calculations. Illustrative problems are provided, together with solutions. FORTRAN programs implementing the numerical methods in the text are included.
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 ...
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.
Atomic and molecular structure
International Nuclear Information System (INIS)
This book is a textbook for an introductory course of atomic physics for students of chemistry. After an introduction to the mathematical and physical foundations the quantum mechanical theory of atoms is described starting from simple examples of quantum mechanics. Then the atomic structure and the chemical bending are extensively discussed. This book is also suited for physicists who are especially interested in the atomic structure and the theory of chemical reactions. (HSI)
Electronic structure interpolation via atomic orbitals
Chen, Mohan; Guo, G-C; HE, LIXIN
2010-01-01
We present an efficient scheme for accurate electronic structure interpolations based on the systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse $k$-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals (LCAO) algorithms. We find that usually 1...
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....
Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer
2014-01-01
So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB$_2$(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle...
Calculations of atomic multiplets across the periodic table
Zhang, Qian
2014-01-01
The goal of this thesis is to develop a simulation tool for the calculation and visualization of the multiplet structure of all atoms across the periodic table. The starting point are self- consistent calculations in the spherical-potential approximation. For the resulting atomic levels we calculate the ab-initio Slater parameters that define the electron-electron repulsion term of the many-body Hamiltonian. We then construct the eigen-states of the Hamiltonian on an open shell by constructin...
Electronic structure interpolation via atomic orbitals
Energy Technology Data Exchange (ETDEWEB)
Chen Mohan; Guo, G-C; He Lixin, E-mail: helx@ustc.edu.cn [Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, 230026 (China)
2011-08-17
We present an efficient scheme for accurate electronic structure interpolation based on systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse k-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals algorithms. We find that usually 16-25 orbitals per atom can give an accuracy of about 10 meV compared to the full ab initio calculations, and the accuracy can be systematically improved by using more atomic orbitals. The scheme is easy to implement and robust, and works equally well for metallic systems and systems with complicated band structures. Furthermore, the atomic orbitals have much better transferability than Shirley's basis and Wannier functions, which is very useful for perturbation calculations.
International Nuclear Information System (INIS)
Our relativistic configuration-interaction (RCI) methodology has been extended to multireference cases, and improved to permit the construction of angular-momentum functions of arbitrary size, and to minimize the number of vectors needed with each configuration. We report RCI calculations on the fine (fs) and hyperfine (hfs) structure for the (d+s)3 J=0.5 and 1.5 levels of Zr II. The average fs error is 0.075 eV, and 17% for hfs, when compared to available experiment. These results indicate that it is possible to correctly position all levels of (d+s)n configurations in the transition-metal atoms
DEFF Research Database (Denmark)
Bork, Nicolai Christian; Eurenius, K. E. J.; Rossmeisl, Jan; Knee, C. S.; Vegge, Tejs
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......) oxygen atoms closely associated with a Ca dopant. Further, the unexpected presence of Ho hydride defects in undoped, oxygen deficient Sm2Sn2O7 is reported. Finally, the stretching frequencies and relative intensities for these and other sites are calculated. The main features of the Fourier transform...
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.
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
Theory and calculation of the atomic photoeffect
Sabbatucci, Lorenzo; Salvat, Francesc
2016-04-01
The so-called elementary theory of the atomic photoeffect is presented in a form that is suited for practical numerical calculation of subshell cross sections and angular distributions of emitted photoelectrons. Atomic states are described within the independent-electron approximation, with bound and free one-electron orbitals that are solutions of the Dirac equation with the Dirac-Hartree-Fock-Slater self-consistent potential of the ground-state configuration. Detailed derivations are given of subshell cross sections for both excitation to discrete bound levels and ionization. In the case of ionization, the cross section differential in the direction of the photoelectron is obtained for partially polarized photons, with the polarization specified by means of the Stokes parameters. The theoretical formulas have been implemented in a computer program named PHOTACS that calculates tables of excitation and ionization cross sections for any element and subshell. Numerical calculations are practicable for excitations to final states with the principal quantum number up to about 20 and for ionization by photons with energy up to about 2 MeV. Elaborate extrapolation schemes for determining the subshell cross section for excitation to bound levels with larger principal quantum numbers and for ionization by photons with higher energies are described. The effect of the finite width of atomic energy levels is accounted for by convolving the calculated subshell cross-section with a Lorentzian profile.
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
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.
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.
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
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)
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
Energy Technology Data Exchange (ETDEWEB)
Joensson, Per
1995-01-01
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 7p{sup 2}P 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.
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
International Nuclear Information System (INIS)
Atomistic electronic structure calculations are performed to study the coherent inter-dot couplings of the electronic states in a single InGaAs quantum dot molecule. The experimentally observed excitonic spectrum by Krenner et al (2005) Phys. Rev. Lett. 94 057402 is quantitatively reproduced, and the correct energy states are identified based on a previously validated atomistic tight binding model. The extended devices are represented explicitly in space with 15-million-atom structures. An excited state spectroscopy technique is applied where the externally applied electric field is swept to probe the ladder of the electronic energy levels (electron or hole) of one quantum dot through anti-crossings with the energy levels of the other quantum dot in a two-quantum-dot molecule. This technique can be used to estimate the spatial electron-hole spacing inside the quantum dot molecule as well as to reverse engineer quantum dot geometry parameters such as the quantum dot separation. Crystal-deformation-induced piezoelectric effects have been discussed in the literature as minor perturbations lifting degeneracies of the electron excited (P and D) states, thus affecting polarization alignment of wavefunction lobes for III-V heterostructures such as single InAs/GaAs quantum dots. In contrast, this work demonstrates the crucial importance of piezoelectricity to resolve the symmetries and energies of the excited states through matching the experimentally measured spectrum in an InGaAs quantum dot molecule under the influence of an electric field. Both linear and quadratic piezoelectric effects are studied for the first time for a quantum dot molecule and demonstrated to be indeed important. The net piezoelectric contribution is found to be critical in determining the correct energy spectrum, which is in contrast to recent studies reporting vanishing net piezoelectric contributions.
Structure and theoretical calculations of clay minerals
International Nuclear Information System (INIS)
Structural and spectroscopic methods are combined to determine the full structure, including hydrogen atom positions, of dickite, which is a member of the kaolin group. Using the structural information obtained, quantum chemical calculations are performed on these kaolin group minerals. Special emphasis is laid on the relationship between the experimentally derived structure and theory. Finally, the application of quantum chemical methods to study clay minerals at several levels of approximation is reviewed
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.
International Nuclear Information System (INIS)
We present the results of calculations of surface relaxations, rumplings, energetics, optical band gaps, and charge distribution for the SrZrO3 and PbZrO3 (001) and (011) surfaces using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. We consider both SrO(PbO) and ZrO2 terminations of the (001) surface and Sr(Pb), ZrO, and O terminations of the polar SrZrO3 and PbZrO3 (011) surfaces. On the (001) surfaces, we find that all upper and third layer atoms relax inward, while outward relaxations of all atoms in the second layer are found with the sole exception of the SrO-terminated SrZrO3 (001) surface second layer O atom. Between all (001) and (011) surfaces the largest relaxations, more than 15% of the bulk lattice constant, are for the Sr- and Pb-terminated SrZrO3 and PbZrO3 (011) surface upper layer Sr and Pb atoms. Our calculated surface rumpling for the SrO- and PbO-terminated SrZrO3 and PbZrO3 (001) surfaces (6.77 and 3.32% of a0) are by a factor of ten larger than the surface rumpling for the ZrO2-terminated (001) surfaces (-0.72 and 0.38% of a0, respectively). In contrast to the surface rumpling, the (001) surface energies are comparable and in the energy range from 0.93 eV/cell for the ZrO2-terminated PbZrO3 surface to 1.24 eV/cell for the ZrO2-terminated SrZrO3 surface. In contrast to the (001) surface, different terminations of the SrZrO3 and PbZrO3 (011) surfaces lead to very different surface energies ranging from 1.74 eV/cell for the Pb-terminated PbZrO3 (011) surface to 3.61 eV/cell for the ZrO-terminated SrZrO3 (011) surface. All our calculated (011) surface energies are considerably larger than the (001) surface energies. Our calculated optical band gap for the SrZrO3 bulk, 5.31 eV, is in fair agreement with the experimental value of 5.6 eV. All our calculated optical band gaps for the SrZrO3 and PbZrO3 (001) and (011) surfaces are reduced with respect to the bulk. We predict a considerable increase in the Zr-O chemical
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
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
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.
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…
International Nuclear Information System (INIS)
Windows based application has been developed for the calculation of atomic hyperfine spectrum of odd isotopes keeping in view of the needs of the atomic spectroscopists. The application can also calculate the hyperfine spectrum of another odd isotope if hyperfine structure constants of one isotope are known. Various features of the developed application are discussed. (author)
Arithmetic aspects of atomic structures
International Nuclear Information System (INIS)
The purpose of this presentation is to give an updated account of some on-going work related to the theory of large atoms in the context of large-Z asymptotics, which began over the last decade or so. The goal of that work is to produce a refined version of the Thomas-Fermi theory that accounts for observed physical features such as electronic orbitals or an atomic shell structure. This presents similarities with issues in quantum chaos. (orig.)
Multilevel domain decomposition for electronic structure calculations
International Nuclear Information System (INIS)
We introduce a new multilevel domain decomposition method (MDD) for electronic structure calculations within semi-empirical and density functional theory (DFT) frameworks. This method iterates between local fine solvers and global coarse solvers, in the spirit of domain decomposition methods. Using this approach, calculations have been successfully performed on several linear polymer chains containing up to 40,000 atoms and 200,000 atomic orbitals. Both the computational cost and the memory requirement scale linearly with the number of atoms. Additional speed-up can easily be obtained by parallelization. We show that this domain decomposition method outperforms the density matrix minimization (DMM) method for poor initial guesses. Our method provides an efficient preconditioner for DMM and other linear scaling methods, variational in nature, such as the orbital minimization (OM) procedure
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
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.
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.
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.
Calculating trajectories for atoms in near-resonant lightfields
International Nuclear Information System (INIS)
We review several methods for calculating the time development of the internal state and the external motion of atoms in near-resonant light fields, with emphasis on studying the focussing of atomic beams into microscopic and potentially nanoscopic patterns. Three different approaches are considered: two-level semiclassical, multi-level semiclassical, and the Monte Carlo wavefunction method. The two-level semiclassical technique of McClelland and Scheinfein (1991) and McClelland (1995) is extended to three dimensions, and used to calculate the trajectories of atoms and the imaging properties of a simple lens formed from a near-resonant travelling TEM01 mode laser. The model is then extended to multi-level atoms, where we calculate the density matrix for the internal state of a sample of thermal atoms in a standing wave, and show how cooling processes can be simulated. Finally, we use the Monte Carlo wavefunction method to calculate the internal state of the atom, and compare the results and required computation time to those of the multi-level semiclassical technique. (authors)
Improved density functional calculations for atoms, molecules and surfaces
International Nuclear Information System (INIS)
The non-collinear and collinear descriptions within relativistic density functional theory is described. We present results of both non-collinear and collinear calculations for atoms, diatomic molecules, and some surface simulations. We find that the accuracy of our density functional calculations for the smaller systems is comparable to good quantum chemical calculations, and thus this method provides a sound basis for larger systems where no such comparison is possible. (author)
Update on nuclear structure effects in light muonic atoms
Hernandez, Oscar Javier; Ji, Chen; Bacca, Sonia; Barnea, Nir
2016-01-01
We present calculations of the nuclear structure corrections to the Lamb shift in light muonic atoms, using state-of-the-art nuclear potentials. We outline updated results on finite nucleon size contributions.
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.
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.
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...
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...
High-accuracy coupled cluster calculations of atomic properties
International Nuclear Information System (INIS)
The four-component Fock-space coupled cluster and intermediate Hamiltonian methods are implemented to evaluate atomic properties. The latter include the spectra of nobelium and lawrencium (elements 102 and 103) in the range 20000-30000 cm−1, the polarizabilities of elements 112-114 and 118, required for estimating their adsorption enthalpies on surfaces used to separate them in accelerators, and the nuclear quadrupole moments of some heavy atoms. The calculations on superheavy elements are supported by the very good agreement with experiment obtained for the lighter homologues
[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
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
Theoretical Calculation of Absolute Radii of Atoms and Ions. Part 1. The Atomic Radii
Raka Biswas; Dulal C. Ghosh
2002-01-01
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...
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
DFT calculations on atom-specific electronic properties of G/SiC(0001)
Kajihara, M.; Suzuki, T.; Shahed, S. M. F.; Komeda, T.; Minamitani, E.; Watanabe, S.
2016-05-01
We investigate the atom-specific interfacial electronic properties of the epitaxial graphene on Si-terminated SiC substrate using density functional theory (DFT) calculation with van der Waals interaction correction, focusing on the dependency of the local electronic state on the chemical environment. The band structure projected on the respective atomic orbitals of the carbon atoms in the buffer layer and uppermost Si atoms demonstrates that the dangling bonds of these atoms form band structures around the Fermi level. The contribution of each atom to the dangling bond states strongly depends on the chemical environment, i.e., the presence/absence of the interlayer Si-C covalent bond. This difference also affects the atom-specific local density of states of the top-layer graphene through its interaction with the substrate/buffer layer. We demonstrate that the bias voltage dependency of the scanning tunneling spectroscopy (STS) mapping image clearly reflects the presence of the dangling bonds of the buffer layer carbon or uppermost Si atom in the substrate, which would enable the detection of the buried dangling bond with an atomic spatial resolution via STS.
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
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.)
DEFF Research Database (Denmark)
Avery, John Scales; Avery, James Emil; Aquilanti, Vincenzo; Caligiana, Andrea
2004-01-01
The generalized Sturmian method for atomic and molecular electronic structure calculations is a direct configuration interaction method in which the configurations are chosen to be isoenergetic solutions of an approximate N-electron Schrödinger equation with a weighted potential, $\\beta_\
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)
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.
Kinetic-energy density functional: Atoms and shell structure
International Nuclear Information System (INIS)
We present a nonlocal kinetic-energy functional which includes an anisotropic average of the density through a symmetrization procedure. This functional allows a better description of the nonlocal effects of the electron system. The main consequence of the symmetrization is the appearance of a clear shell structure in the atomic density profiles, obtained after the minimization of the total energy. Although previous results with some of the nonlocal kinetic functionals have given incipient structures for heavy atoms, only our functional shows a clear shell structure for most of the atoms. The atomic total energies have a good agreement with the exact calculations. Discussion of the chemical potential and the first ionization potential in atoms is included. The functional is also extended to spin-polarized systems. copyright 1996 The American Physical Society
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
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.
Ab Initio factorized LCAO calculation of the electronic structure of α-SiO2
International Nuclear Information System (INIS)
The authors report on the results of calculations of the electronic structure of α-quartz that were made using first principles, factorized linear combination of atomic orbitals method. Results were obtained for the primitive 9-atom, and orthorhombic 18- and 72-atom unit cells. Application of this method to the calculation of the electronic structure of the neutral oxygen vacancy in α-quartz is discussed and results obtained using a 72-atom unit cell are given
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.
Introduction to Atomic Structure: Demonstrations and Labs.
Ciparick, Joseph D.
1988-01-01
Demonstrates a variety of electrical phenomena to help explain atomic structure. Topics include: establishing electrical properties, electrochemistry, and electrostatic charges. Recommends demonstration equipment needed and an explanation of each. (MVL)
Electronic structure of crystalline uranium nitride: LCAO DFT calculations
International Nuclear Information System (INIS)
The results of electronic structure calculations performed for the first time for crystalline uranium nitride and using a LCAO basis are discussed. For calculations we used the density functional method with the PW91 exchange correlation potential and a variety of relativistic core potentials for the uranium atom. The calculated atomization energy of the crystal agrees well with the experimental data and with the results of calculations with the plane wave basis. It is shown that a chemical bond in crystalline uranium nitride is a metal covalent bond. The metal component of the bond is due to the 5f electrons localized on the uranium atom and having energies near the Fermi level and the bottom of the conduction band. The covalent component of the chemical bond results from an overlap between the uranium 6d and 7s valence orbitals and the nitrogen 2p atomic orbitals. Inclusion of the 5f electrons in the core of the uranium atom introduces relatively minor changes in the calculated binding energy and electron density distribution
DEFF Research Database (Denmark)
Falkenberg, G.; Bunk, O.; Johnson, R.L.; Rodrigues, J.A.; Takeuchi, N.
2002-01-01
Using scanning-tunneling microscopy (STM) and first-principles total-energy calculations, we have determined the atomic geometry of the superstructures formed by the adsorption of up to 0.5 monolayer of indium on Ge(001) and annealing at temperatures above 200 degreesC. A strong interaction between...... indium adatoms and the germanium substrate atoms leads to the formation of two different In-Ge subunits on the Ge(001) surface. In the subsaturation regime separate (nx4) subunits are observed where n can be either 3 or 4 and the STM images resemble those of the Si(001)-(3x4)-In and -Al reconstructions......, Appl. Surf. Sci. 123/124, 104 (1998) for In on Si(001). For the (4x4) subunit, we propose a model that includes the main features of the (3x4) subunit together with additional mixed Ge-In dimers. The atomic positions were optimized using ab initio total-energy calculations. The calculated local...
Calculation of electron-impace excitation and ionization of atoms
International Nuclear Information System (INIS)
Over the last few years it has been the author's goal to develop a open-quotes completeclose quotes electron-atom scattering theory. For a given projectile energy such a theory would be able to correctly predict the major scattering processes. These include elastic, excitation, and ionization cross sections. The convergent close-coupling (CCC) approach is a candidate for such a theory. Hamiltonians in an orthogonal Laguerre basis. The usage of this basis ensures that open-quotes completenessclose quotes is approached as N is increased. The CCC method may be thought of as a more systematic implementation of pseudostate methods. Whereas the success of the close-coupling approach to the calculation of excitation cross sections has been demonstrated for many decades it has rarely been applied to the calculation of ionization processes. By demonstrating the ability to obtain accurate ionization cross sections simultaneously with excitation processes the CCC method appears to have fulfilled these goals. In the talk a general outline of the CCC method will be given and its recent applications to the measurements of electron-impact ionization and excitation of the ground state of helium discussed
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
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.)
Final disposal room structural response calculations
International Nuclear Information System (INIS)
Finite element calculations have been performed to determine the structural response of waste-filled disposal rooms at the WIPP for a period of 10,000 years after emplacement of the waste. The calculations were performed to generate the porosity surface data for the final set of compliance calculations. The most recent reference data for the stratigraphy, waste characterization, gas generation potential, and nonlinear material response have been brought together for this final set of calculations
International Nuclear Information System (INIS)
The equilibrium lattice parameters, formation energy, and diffusion behavior of hydrogen atoms in vanadium hydrides with and without Ti substitution were calculated by ab initio calculations and quantum correction by zero point energy was achieved using phonon vibration calculations. The calculated formation energies indicated that Ti substitution induces instability in the vanadium hydrides and electron density calculations showed that hydrogen has strong electrochemical affinity with Ti. The diffusion behavior was examined by the nudged elastic band (NEB) method to investigate the transition states of the hydrides. It revealed that Ti substitution is shown to reduce the diffusion coefficient and this effect was decreased with increasing temperature. The results of this study are expected to provide useful guidelines for understanding hydrogen absorption and desorption properties of hydrogen storage materials. - Highlights: • Ti substitution expands any crystal structure of vanadium metal or hydride. • H atoms are repulsed by Ti atoms despite their high electrochemical affinity. • Strong electrochemical bonding between Ti and H lowers the formation energy. • Ti substitution reduces hydrogen diffusion by over 90% at room temperature
Energy Technology Data Exchange (ETDEWEB)
Kim, Jiwoong, E-mail: jwk@kigam.re.kr; Yoo, Jeong-Hyun, E-mail: yjh0010@naver.com; Cho, Sung-Wook, E-mail: cho@kigam.re.kr
2014-12-15
The equilibrium lattice parameters, formation energy, and diffusion behavior of hydrogen atoms in vanadium hydrides with and without Ti substitution were calculated by ab initio calculations and quantum correction by zero point energy was achieved using phonon vibration calculations. The calculated formation energies indicated that Ti substitution induces instability in the vanadium hydrides and electron density calculations showed that hydrogen has strong electrochemical affinity with Ti. The diffusion behavior was examined by the nudged elastic band (NEB) method to investigate the transition states of the hydrides. It revealed that Ti substitution is shown to reduce the diffusion coefficient and this effect was decreased with increasing temperature. The results of this study are expected to provide useful guidelines for understanding hydrogen absorption and desorption properties of hydrogen storage materials. - Highlights: • Ti substitution expands any crystal structure of vanadium metal or hydride. • H atoms are repulsed by Ti atoms despite their high electrochemical affinity. • Strong electrochemical bonding between Ti and H lowers the formation energy. • Ti substitution reduces hydrogen diffusion by over 90% at room temperature.
2007-01-01
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...
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...
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
Monte Carlo algorithm for calculating moments of atomic transition arrays
International Nuclear Information System (INIS)
A new method for calculating moments of atomic transition arrays is described. It is based on the collective vector method described in earlier publications. In this new approach a single collective state vector is generated from a single parent state vector encompassing the entire parent basis. The amplitudes of the basis vectors comprising the parent state vector are randomized. Thus it is representative of the entire parent manifold. We show that a statistical estimate of the transition moments of the array is given by a suitable combination of moments of the matrix element of the E1 (electric dipole) operator between the representative parent state vector and the collective state vector derived from it. Although the detailed characteristics of the dispersion in these statistical results are determined by the detailed characteristics of the Hamiltonian and the model space, we find that overall the dispersion decreases inversely as the square root of the dimension of the model space. This is in keeping with results obtained earlier for the Hamiltonian moments of nuclear systems and means, speaking broadly, the larger the problem the more accurate the method
Atomic vapor spectroscopy in integrated photonic structures
Ritter, Ralf; Pernice, Wolfram; Kübler, Harald; Pfau, Tilman; Löw, Robert
2015-01-01
We investigate an integrated optical chip immersed in atomic vapor providing several waveguide geometries for spectroscopy applications. The narrow-band transmission through a silicon nitride waveguide and interferometer is altered when the guided light is coupled to a vapor of rubidium atoms via the evanescent tail of the waveguide mode. We use grating couplers to couple between the waveguide mode and the radiating wave, which allow for addressing arbitrary coupling positions on the chip surface. The evanescent atom-light interaction can be numerically simulated and shows excellent agreement with our experimental data. This work demonstrates a next step towards miniaturization and integration of alkali atom spectroscopy and provides a platform for further fundamental studies of complex waveguide structures.
Atomic vapor spectroscopy in integrated photonic structures
Energy Technology Data Exchange (ETDEWEB)
Ritter, Ralf; Kübler, Harald; Pfau, Tilman; Löw, Robert, E-mail: r.loew@physik.uni-stuttgart.de [5. Physikalisches Institut and Center for Integrated Quantum Science and Technology, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany); Gruhler, Nico; Pernice, Wolfram [Institute of Nanotechnology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen (Germany)
2015-07-27
We investigate an integrated optical chip immersed in atomic vapor providing several waveguide geometries for spectroscopy applications. The narrow-band transmission through a silicon nitride waveguide and interferometer is altered when the guided light is coupled to a vapor of rubidium atoms via the evanescent tail of the waveguide mode. We use grating couplers to couple between the waveguide mode and the radiating wave, which allow for addressing arbitrary coupling positions on the chip surface. The evanescent atom-light interaction can be numerically simulated and shows excellent agreement with our experimental data. This work demonstrates a next step towards miniaturization and integration of alkali atom spectroscopy and provides a platform for further fundamental studies of complex waveguide structures.
Study of the embedded atom method of atomistic calculations for metals and alloys
International Nuclear Information System (INIS)
Two projects were completed in the past year. The stability of a series of binary alloys was calculated using the embedded-atom method (EAM) with an analytic form for two-body potentials derived previously. Both disordered alloys and intermetallic compounds with the L10 and L12 structures were studied. The calculated heats of solution of alloys of Cu, Ag, Au, Ni, and Pt were satisfactory, while results for alloys containing Pd were too high. Atomistic calculations using the EAM were also carried out for point defects in hcp metals. By comparison with results in the literature, it was found that many body effects from the EAM significantly alter predicted physical properties of hcp metals. For example, the EAM calculations yield anisotropic vacancy diffusion with greater vacancy mobility in the basal plane, and imply that diffusion will start at a lower fraction of the melting temperature
International Nuclear Information System (INIS)
The binding energy of an interstitial hydrogen atom at various lattice sites around the a0/2[111] screw dislocation core in BCC iron has been determined using the first-principles calculation. The calculation was based on the core structure of a screw dislocation with symmetric displacement field, which was obtained using the large-scale supercell containing 231 atoms and 1 x 1 x 4 k-point samplings. The binding or trapping energy of a hydrogen atom at both the t-site (tetrahedral site) and o-site (octahedral site) near a core is found to be approximately 0.2 eV. (author)
International Nuclear Information System (INIS)
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 C6, C8 and C10 atom–atom interactions for the dimers formed from any of these atoms and ions, and we present tables covering all of these combinations
Energy Technology Data Exchange (ETDEWEB)
Jiang, Jun, E-mail: phyjiang@yeah.net [Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); School of Engineering, Charles Darwin University, Darwin, Northern Territory, 0909 (Australia); Mitroy, J. [School of Engineering, Charles Darwin University, Darwin, Northern Territory, 0909 (Australia); Cheng, Yongjun, E-mail: cyj83mail@gmail.com [School of Engineering, Charles Darwin University, Darwin, Northern Territory, 0909 (Australia); Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Harbin 150080 (China); Bromley, M.W.J., E-mail: brom@physics.uq.edu.au [School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4075 (Australia)
2015-01-15
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{sub 6}, C{sub 8} and C{sub 10} atom–atom interactions for the dimers formed from any of these atoms and ions, and we present tables covering all of these combinations.
Electronic Structure and Molecular Dynamics Calculations for KBH4
Papaconstantopoulos, Dimitrios; Shabaev, Andrew; Hoang, Khang; Mehl, Michael; Kioussis, Nicholas
2012-02-01
In the search for hydrogen storage materials, alkali borohydrides MBH4 (M=Li, Na, K) are especially interesting because of their light weight and the high number of hydrogen atoms per metal atom. Electronic structure calculations can give insights into the properties of these complex hydrides and provide understanding of the structural properties and of the bonding of hydrogen. We have performed first-principles density-functional theory (DFT) and tight-binding (TB) calculations for KBH4 in both the high temperature (HT) and low temperature (LT) phases to understand its electronic and structural properties. Our DFT calculations were carried out using the VASP code. The results were then used as a database to develop a tight-binding Hamiltonian using the NRL-TB method. This approach allowed for computationally efficient calculations of phonon frequencies and elastic constants using the static module of the NRL-TB, and also using the molecular dynamics module to calculate mean-square displacements and formation energies of hydrogen vacancies.
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.
Calculation of tolerances in accelerating structures
International Nuclear Information System (INIS)
A method is suggested for calculating tolerances for similar elements of an accelerating-focusing channel of a charged particle linac the particle dynamics in which is described by linear or non-linear equations. Tolerances for each drift tube of the accelerating structure with modified variable-phase focusing are determined with respect to tolerances for the output parameters of an accelerated beam at preset lengths of drift tubes. The tolerances obtained in supposition of equal effects, equal tolerances and those accounting for the cost of fabrication and assembling of the elements of the structure are compared. The algorithm suggested can also be used for calculating tolerances in structures with hard focusing
Geminal embedding scheme for optimal atomic basis set construction in correlated calculations
International Nuclear Information System (INIS)
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
Geminal embedding scheme for optimal atomic basis set construction in correlated calculations.
Sorella, S; Devaux, N; Dagrada, M; Mazzola, G; Casula, M
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. PMID:26723656
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.
First principles calculation of current-induced forces in atomic gold contacts
Brandbyge, Mads; Stokbro, Kurt; Taylor, Jeremy; Mozos, Jose-Luis; Ordejon, Pablo
2002-03-01
We have recently developed an first principles method [1] for calculating the electronic structure, electronic transport, and forces acting on the atoms, for atomic scale systems connected to semi-infinite electrodes and with an applied voltage bias. Our method is based on the density functional theory (DFT) as implemented in the well tested SIESTA program [2]. We fully deal with the atomistic structure of the whole system, treating both the contact and the electrodes on the same footing. The effect of the finite bias (including selfconsistency and the solution of the electrostatic problem) is taken into account using nonequilibrium Green's functions. In this talk we show results for the forces acting on the contact atoms due to the nonequilibrium situation in the electronic subsystem, i.e. in the presence of an electronic current. We concentrate on one atom wide gold contacts/wires connected to bulk gold electrodes. References [1] Our implementation is called TranSIESTA and is described in M. Brandbyge, J. Taylor, K. Stokbro, J-L. Mozos, and P. Ordejon, cond-mat/0110650 [2] D. Sanchez-Portal, P. Ordejon, E. Artacho and J. Soler, Int. J. Quantum Chem. 65, 453 (1997).
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...
Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework
International Nuclear Information System (INIS)
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...
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
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.
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2011-01-01
First-principles FLAPW-GGA band structure calculations were employed to examine the structural, electronic properties and the chemical bonding picture for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be viewed as "intermediate" systems between two main isostructural groups of superconducting and semiconducting 1111 phases. The Th 5f states participate actively in the formation of valence bands ...
Elongation method for electronic structure calculations of random DNA sequences.
Orimoto, Yuuichi; Liu, Kai; Aoki, Yuriko
2015-10-30
We applied ab initio order-N elongation (ELG) method to calculate electronic structures of various deoxyribonucleic acid (DNA) models. We aim to test potential application of the method for building a database of DNA electronic structures. The ELG method mimics polymerization reactions on a computer and meets the requirements for linear scaling computational efficiency and high accuracy, even for huge systems. As a benchmark test, we applied the method for calculations of various types of random sequenced A- and B-type DNA models with and without counterions. In each case, the ELG method maintained high accuracy with small errors in energy on the order of 10(-8) hartree/atom compared with conventional calculations. We demonstrate that the ELG method can provide valuable information such as stabilization energies and local densities of states for each DNA sequence. In addition, we discuss the "restarting" feature of the ELG method for constructing a database that exhaustively covers DNA species. PMID:26337429
Hylleraas-Configuration Interaction calculations on the 1 ^1S ground state of helium atom
Ruiz, Maria Belen
2012-01-01
Hylleraas-Configuration Interaction (Hy-CI) calculations on the ground $1^1$S state of helium atom are presented using s-, p-, d-, and f-Slater orbitals of both real and complex form. Techniques of construction of adapted configurations, optimization of the orbital exponents and 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 has been tested here and compared with other methods. The non-rel...
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 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
Calculation of a shadow cone formed by scattering of an ion beam from an atom
International Nuclear Information System (INIS)
The shadow cone formed by the scattering of ions from an atom was calculated using Moliere potential. Calculated radii of the shadow cone by replacing the Thomas-Fermi radius, a sub(TF), with 0.85 a sub(TF) show a good agreement with an experiment for 1 keV helium ions on a titanium atom. (author)
International Nuclear Information System (INIS)
Calculations of hyperfine interaction strength and life-times of states in highly ionized atoms, using the GRASP atomic structure package, are reported. The calculations aim at providing calibration for Recoil-in-Vacuum nuclear excited state g-factor measurements. The method is outlined and results compared with experiment. Inclusion of decay of higher electronic states is discussed.
Block Tridiagonal Matrices in Electronic Structure Calculations
DEFF Research Database (Denmark)
Petersen, Dan Erik
This thesis focuses on some of the numerical aspects of the treatment of the electronic structure problem, in particular that of determining the ground state electronic density for the non–equilibrium Green’s function formulation of two–probe systems and the calculation of transmission in the Lan...
Cobalamins uncovered by modern electronic structure calculations
DEFF Research Database (Denmark)
Kepp, Kasper Planeta; Ryde, Ulf
electronic-structure calculations, in particular density functional methods, the understanding of the molecular mechanism of cobalamins has changed dramatically, going from a dominating view of trans-steric strain effects to a much more complex view involving an arsenal of catalytic strategies. Among these...
Multilevel domain decomposition for electronic structure calculations
Barrault, M; Hager, W W; Le Bris, C
2005-01-01
We introduce a new multilevel domain decomposition method (MDD) for electronic structure calculations within semi-empirical and Density Functional Theory (DFT) frameworks. This method iterates between local fine solvers and global coarse solvers, in the spirit of domain decomposition methods.
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}
Multigrid Methods in Electronic Structure Calculations
Briggs, E L; Bernholc, J
1996-01-01
We describe a set of techniques for performing large scale ab initio calculations using multigrid accelerations and a real-space grid as a basis. The multigrid methods provide effective convergence acceleration and preconditioning on all length scales, thereby permitting efficient calculations for ill-conditioned systems with long length scales or high energy cut-offs. We discuss specific implementations of multigrid and real-space algorithms for electronic structure calculations, including an efficient multigrid-accelerated solver for Kohn-Sham equations, compact yet accurate discretization schemes for the Kohn-Sham and Poisson equations, optimized pseudo\\-potentials for real-space calculations, efficacious computation of ionic forces, and a complex-wavefunction implementation for arbitrary sampling of the Brillioun zone. A particular strength of a real-space multigrid approach is its ready adaptability to massively parallel computer architectures, and we present an implementation for the Cray-T3D with essen...
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
Electronic Structure of Silicon Nanowires Matrix from Ab Initio Calculations.
Monastyrskii, Liubomyr S; Boyko, Yaroslav V; Sokolovskii, Bogdan S; Potashnyk, Vasylyna Ya
2016-12-01
An investigation of the model of porous silicon in the form of periodic set of silicon nanowires has been carried out. The electronic energy structure was studied using a first-principle band method-the method of pseudopotentials (ultrasoft potentials in the basis of plane waves) and linearized mode of the method of combined pseudopotentials. Due to the use of hybrid exchange-correlation potentials (B3LYP), the quantitative agreement of the calculated value of band gap in the bulk material with experimental data is achieved. The obtained results show that passivation of dangling bonds with hydrogen atoms leads to substantial transformation of electronic energy structure. At complete passivation of the dangling silicon bonds by hydrogen atoms, the band gap value takes the magnitude which substantially exceeds that for bulk silicon. The incomplete passivation gives rise to opposite effect when the band gap value decreases down the semimetallic range. PMID:26768147
Dynamic response of some atoms: Many-body calculations
Directory of Open Access Journals (Sweden)
Tančić Aleksandar R.
2005-01-01
Full Text Available The frequency-dependent polarizability in the Hartree-Fock (HF approximation has been corrected for true correlation effects by means of many-body theory. The polarizability has been computed in the Random Phase Approximation with Exchange (RPAE for He, Ar Xe, Kr, Li, Ca through the second (and some higher order in the correlation potential. With this polarizability as input we obtained the values of some atomic interaction constants.
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...
Generalized atomic displacements in crystallographie structure analysis
International Nuclear Information System (INIS)
An attempt is made to summarize both theoretical and experimental aspects of generalized atomic displacement parameters (ADP's) in crystalline matter. Generalized displacement parameters are used to describe the weakening of Bragg intensities via the anharmonic (static or thermal) Debye-Waller factor (DWF) and its real-space counterpart, the generalized atomic probability density function (p.d.f.). The lattice dynamical base of the harmonic and anharmonic thermal DWF is discussed. It is pointed out that the static DWF frequently contains higher-order terms. The mathematical case for an experimental determination of generalized ADP's is given. The most popular current formulations (one-particle potential and statistical approaches) are reviewed and their individual limitations are discussed. Likewise the demands put on the quality and extent of experimental data are assessed. Some aids to the interpretation of generalized ADP's established by crystallographic least-squares procedures are given and a Monte-Carlo method for the calculation of errors in p.d.f. maps is presented. Finally, some prospects for future work are outlined and a more frequent comparison of theoretical calculations and experimental determinations of generalized ADP's is advocated. (orig.)
Calculating atomic and molecular properties using variational Monte Carlo methods
International Nuclear Information System (INIS)
The authors compute a number of properties for the 1 1S, 21S, and 23S states of helium as well as the ground states of H2 and H/+3 using Variational Monte Carlo. These are in good agreement with previous calculations (where available). Electric-response constants for the ground states of helium, H2 and H+3 are computed as derivatives of the total energy. The method used to calculate these quantities is discussed in detail
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.
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.......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...
Fock space relativistic coupled-Cluster calculations of Two-Valence Atoms
Mani, B. K.; Angom, D.
2010-01-01
We have developed an all particle Fock-space relativistic coupled-cluster method for two-valence atomic systems. We then describe a scheme to employ the coupled-cluster wave function to calculate atomic properties. Based on these developments we calculate the excitation energies, magnetic hyperfine constants and electric dipole matrix elements of Sr, Ba and Yb. Further more, we calculate the electric quadrupole HFS constants and the electric dipole matrix elements of Sr$^+$, Ba$^+$ and Yb$^+$...
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.
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)
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.
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.
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...
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.
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...
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.
Calculation of electron scattering on atoms and ions
International Nuclear Information System (INIS)
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(11S,23.1S), He+(1s), Li(2s), O5+(2s) and Na(3s). 50 refs., 10 figs
Learning from numerical calculations of ion-atom collisions
International Nuclear Information System (INIS)
Violent collision of two independent many-particle systems, victims, are discussed in the atomic sphere. The asymmetric region where the charge of the projectile Z/sub p/ is less than the target nuclear charge Z/sub n/ is now well understood though interesting details still need to be worked out. Negatively charged projectiles offer a new illustration of Fadeev re-arrangement collisions. Multi-electron coherence effects illustrate the richness of the field but a symmetric (Z/sub p/ approx. Z/sub n/) collision treatment is needed. A new one and a half center expansion method promises a solution to this problem. Future areas of interest are discussed
Prediction of hexagonal Ta2O5 structure by first-principles calculations
International Nuclear Information System (INIS)
The undetermined crystal structure of hexagonal Ta2O5 is predicted by the first-principles ultrasoft pseudopotential calculations. Among the several hypothetical structures, the structure which is energetically favorable and consistent with the available experimental data is determined by minimizing the total energy with respect to the volume, the c/a ratio, and the atomic configurations. The predicted structure has the space group of P6/mmm with two formula units in the unit cell. The calculated lattice constants, a=7.191 Angstrom and c=3.831 Angstrom, are in good agreement with the x-ray-diffraction measurement if a is assumed to be twice as large as the measured value due to the extinction rule. The coordination number of O atom to Ta atom is 8 for one Ta atom and 6 for the other three Ta atoms. copyright 1997 The American Physical Society
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.
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.
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...
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.
International Nuclear Information System (INIS)
Protein structure determination using Nuclear Magnetic Resonance (NMR) requires the use of molecular dynamics programs that incorporate both NMR experimental and implicit atomic data. Atomic parameters for each amino acid type are encoded in libraries used by structure calculation programs such as DYANA and AMBER. However, only a few non-standard amino acid library sets are included in these programs or the molecular visualization program MOLMOL. Our laboratory is calculating the phosphorylated and non-phosphorylated states of peptides and proteins using NMR methods. To calculate chemically correct structures, we have extended the available molecular libraries for these programs to include the modified amino acids phosphoserine, phosphothreonine, and phosphotyrosine
Ballance, Connor
2013-05-01
Over the last couple of decades, a number of advanced non-perturbative approaches such as the R-matrix, TDCC and CCC methods have made great strides in terms of improved target representation and investigating fundamental 2-4 electron problems. However, for the electron-impact excitation of near-neutral species or complicated open-shell atomic systems we are forced to make certain compromises in terms of the atomic structure and/or the number of channels included in close-coupling expansion of the subsequent scattering calculation. The availability of modern supercomputing architectures with hundreds of thousands of cores, and the emergence new opportunities through GPU usauge offers one possibility to address some of these issues. To effectively harness this computational power will require significant revision of the existing code structures. I shall discuss some effective strategies within a non-relativistic and relativistic R-matrix framework using the examples detailed below. The goal is to extend existing R-matrix methods from 1-2 thousand close coupled channels to 10,000 channels. With the construction of the ITER experiment in Cadarache, which will have Tungsten plasma-facing components, there is an urgent diagnostic need for the collisional rates for the near-neutral ion stages. In particular, spectroscopic diagnostics of impurity influx require accurate electron-impact excitation and ionisation as well as a good target representation. There have been only a few non-perturbative collisional calculations for this system, and the open-f shell ion stages provide a daunting challenge even for perturbative approaches. I shall present non-perturbative results for for the excitation and ionisation of W3+ and illustrate how these fundamental calculations can be integrated into a meaningful diagnostic for the ITER device. We acknowledge support from DoE fusion.
Analytical calculations of scattering lengths in atomic physics
International Nuclear Information System (INIS)
We describe a method for evaluating analytical long-range contributions to scattering lengths for some potentials used in atomic physics. We assume that an interaction potential between colliding particles consists of two parts. The form of a short-range component, vanishing beyond some distance from the origin (a core radius), need not be given. Instead, we assume that a set of short-range scattering lengths due to that part of the interaction is known. A long-range tail of the potential is chosen to be an inverse power potential, a superposition of two inverse power potentials with suitably chosen exponents or the Lent potential. For these three classes of long-range interactions a radial Schrodinger equation at zero energy may be solved analytically with solutions expressed in terms of the Bessel, Whittaker and Legendre functions, respectively. We utilize this fact and derive exact analytical formulae for the scattering lengths. The expressions depend on the short-range scattering lengths, the core radius and parameters characterizing the long-range part of the interaction. Cases when the long-range potential (or its part) may be treated as a perturbation are also discussed and formulae for scattering lengths linear in strengths of the perturbing potentials are given. It is shown that for some combination of the orbital angular momentum quantum number and an exponent of the leading term of the potential the derived formulae, exact or approximate, take very simple forms and contain only polynomial and trigonometric functions. The expressions obtained in this paper are applicable to scattering of charged particles by neutral targets and to collisions between neutrals. The results are illustrated by accelerating convergence of scattering lengths computed for e--Xe and Cs-Cs systems. (author)
International Nuclear Information System (INIS)
Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)
Hydrogen atom position in hydrated iodide anion from x-ray absorption near edge structure
International Nuclear Information System (INIS)
Hydrogen atom position in the hydrated iodide anion complex is determined from X-ray Absorption Near Edge Structure (XANES) of an aqueous iodide solution at both the K- and L-edges. The spectra are compared with the theoretical ones calculated by using the FEFF method for several model geometries having hydrogen atoms at different positions. Satisfactory agreements are obtained from models with an almost linear alignment of iodine-hydrogen-oxygen atoms, indicating the capability of the XANES analysis when it is combined with the multiple scattering calculations as a method to detect the positions of hydrogen atoms in the first coordination sphere. (author)
Relativistic ab initio calculations for ion-atom collisions
International Nuclear Information System (INIS)
Within the independent particle model we solve the time---dependent single-particle equation using ab initio SCF-DIRAC-FOCK-SLATER wavefunctions as a basis. To reinstate the many-particle aspect of the collision system we use the inclusive probability formalism to answer experimental questions. As an example we show an application to the case of S15+ on Ar where experimental data on the K-K charge transfer are available for a wide range of impact energies from 4.7 to 90 MeV. Our molecular adiabatic calculations and the evaluation using the inclusive probability formalism show good results in the low energy range from 4.7 to 16 MeV impact energy
Isogeometric analysis in electronic structure calculations
Czech Academy of Sciences Publication Activity Database
Cimrman, R.; Novák, M.; Kolman, Radek; Tůma, Miroslav; Vackář, Jiří
Ostrava: Ústav geoniky AV ČR, 2014 - (Blaheta, R.; Starý, J.; Sysalová, D.). s. 49-49 ISBN 978-80-86407-47-0. [Modelling 2014. 02.06.2014-06.06.2014, Rožnov pod Radhoštěm] R&D Projects: GA ČR(CZ) GAP101/12/2315; GA ČR(CZ) GAP108/11/0853 Institutional support: RVO:61388998 ; RVO:68378271 ; RVO:67985807 Keywords : isogeometric analysis * electronic structure calculations * density functional theory Subject RIV: JJ - Other Materials
Study on structures and electronic properties of NaxV (x = 1-12) atomic clusters
International Nuclear Information System (INIS)
Superatoms, novel entities being studied extensively in recent years, can be stabilized by mixing with transition metal atoms. The aim of this paper is to present some recent theoretical results on the application of quantum calculations for examining the atomic clusters NaxV (x = 1-12) made from the mixing of Nax superatoms with vanadium transition metal atom. Optimized structures of NaxV, NaxV+ and NaxV- are determined by using the TPSSTPSS/DZVP DFT calculations. Characteristics of optimized structures, as point group symmetry, chemical hardness (η), absolute electronegativity (χ), electrophilicity index (ω), fragmentation energy (Ef), secondary energy (∆2E), are calculated. The obtained results point out that among different structures of an atomic cluster, the more negative total energy the more stable structure and the Na8V cluster is the most stable in NaxV (x = 1-12) clusters. (author)
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.
Absence of a stable atomic structure in fluorinated graphene.
Boukhvalov, Danil W
2016-05-21
Based on the results of first-principles calculations we demonstrate that significant distortion of graphene sheets caused by adsorption of fluorine atoms leads to the formation of metastable patterns for which the next step of fluorination is considerably less energetically favorable. Existence of these stable patterns oriented along the armchair direction makes possible the synthesis of various CFx structures. The combination of strong distortion of the nonfluorinated graphene sheet with the doping caused by the polar nature of C-F bonds reduces the energy cost of migration and the energy of migration barriers, making possible the migration of fluorine atoms on the graphene surface as well as transformation of the shapes of fluorinated areas. The decreasing energy cost of migration with increasing fluorine content also leads to increasing numbers of single fluorine adatoms, which could be the source of magnetic moments. PMID:27116897
Electron Affinity Calculations for Atoms: Sensitive Probe of Many-Body Effects
Felfli, Z.; Msezane, A. Z.
2016-05-01
Electron-electron correlations and core-polarization interactions are crucial for the existence and stability of most negative ions. Therefore, they can be used as a sensitive probe of many-body effects in the calculation of the electron affinities (EAs) of atoms. The importance of relativistic effects in the calculation of the EAs of atoms has recently been assessed to be insignificant up to Z of 85. Here we use the complex angular momentum (CAM) methodology wherein is embedded fully the electron-electron correlations, to investigate core-polarization interactions in low-energy electron elastic scattering from the atoms In, Sn, Eu, Au and At through the calculation of their EAs. For the core-polarization interaction we use the 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 CAM 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 correlations and core polarization interactions (both major many-body effects) are accounted for adequately the importance of relativity on the calculation of the EAs of atoms can be assessed. Even for the high Z (85) At atom relativistic effects are estimated to contribute a maximum of 3.6% to its EA calculation.
Unfolding method for first-principles LCAO electronic structure calculations
Lee, Chi-Cheng; Yamada-Takamura, Yukiko; Ozaki, Taisuke
2013-08-01
Unfolding the band structure of a supercell to a normal cell enables us to investigate how symmetry breakers such as surfaces and impurities perturb the band structure of the normal cell. We generalize the unfolding method, originally developed based on Wannier functions, to the linear combination of atomic orbitals (LCAO) method, and present a general formula to calculate the unfolded spectral weight. The LCAO basis set is ideal for the unfolding method because the basis functions allocated to each atomic species are invariant regardless of the existence of surface and impurity. The unfolded spectral weight is well defined by the property of the LCAO basis functions. In exchange for the property, the non-orthogonality of the LCAO basis functions has to be taken into account. We show how the non-orthogonality can be properly incorporated in the general formula. As an illustration of the method, we calculate the dispersive quantized spectral weight of a ZrB2 slab and show strong spectral broadening in the out-of-plane direction, demonstrating the usefulness of the unfolding method.
Unfolding method for first-principles LCAO electronic structure calculations
International Nuclear Information System (INIS)
Unfolding the band structure of a supercell to a normal cell enables us to investigate how symmetry breakers such as surfaces and impurities perturb the band structure of the normal cell. We generalize the unfolding method, originally developed based on Wannier functions, to the linear combination of atomic orbitals (LCAO) method, and present a general formula to calculate the unfolded spectral weight. The LCAO basis set is ideal for the unfolding method because the basis functions allocated to each atomic species are invariant regardless of the existence of surface and impurity. The unfolded spectral weight is well defined by the property of the LCAO basis functions. In exchange for the property, the non-orthogonality of the LCAO basis functions has to be taken into account. We show how the non-orthogonality can be properly incorporated in the general formula. As an illustration of the method, we calculate the dispersive quantized spectral weight of a ZrB2 slab and show strong spectral broadening in the out-of-plane direction, demonstrating the usefulness of the unfolding method. (paper)
Structure and properties of atomic nanoclusters
Alonso, Julio A
2011-01-01
Atomic clusters are aggregates of atoms containing a few to several thousand atoms. Due to the small size of these pieces of matter, the properties of atomic clusters in general are different from those of the corresponding material in the macroscopic bulk phase. This monograph presents the main developments of atomic clusters and the current status of the field. The book treats different types of clusters with very different properties: clusters in which the atoms or molecules are tied by weak van der Waals interactions, metallic clusters, clusters of ionic materials, and network clusters mad
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.
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.
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.
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...
Atomic and electronic structure of divacancies in carbon nanotubes
Berber, Savas; Oshiyama, Atsushi
2008-04-01
We present atomic and electronic structure of divacancies in carbon nanotubes, which is calculated using the density functional theory. Divacancies in carbon nanotubes self-heal by spontaneous reconstructions, which consist of concerted bond formations. Divacancy formation energies EDV , which strongly depend on the divacancy orientation with respect to the tube axis, are in the range of 2.8 4.3 eV for favorable orientations in the nanotubes of 4 9Å diameter, making divacancies more probable than monovacancies in carbon nanotubes. Defect related states lead to a higher density of states around the Fermi level. Semiconducting nanotubes develop midgap levels that may adversely affect the functionality of carbon nanotube based devices. Our spin polarized density functional calculations show that the exchange splitting of defect-related bands in nonsemiconducting defective nanotubes leads to net spin polarizations of ρ↑-ρ↓≤0.5μB per divacancy for some divacancy orientations.
Kevorkyants, Ruslan; Close, David M; Pavanello, Michele
2013-01-01
We present an application of the linear scaling Frozen Density Embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfccs) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems considered 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 neither 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 hfccs 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.
Parquet theory in nuclear structure calculations
International Nuclear Information System (INIS)
The thesis concerns a numerical implementation of the Parquet summation of diagrams within Green's functions theory applied to calculations of nuclear systems. The main motivation has been to investigate whether it is possible to develop this approach to a level comparable in accuracy and reliability to other ab initio nuclear structure methods. The Green's functions approach is theoretically well-established in many-body theory, but to our knowledge, no actual application to nuclear systems has been previously published. It has a number of desirable properties, foremost the gently scaling with system size compared to direct diagonalization and the closeness to experimentally accessible quantities. The main drawback is the numerical instabilities due to the pole structure of the one-particle propagator, leading to convergence difficulties. This issue is one of the main focal points of the work presented in this thesis, and strategies to improve the convergence properties are described and investigated. We have applied the method both to a simple model which can be solved by exact diagonalization and to the more realistic 4He system. The results shows that our implementation is close to the exact solution in the simple model as long as the interaction strengths are small. As the number of particles increases, convergence is increasingly hard to obtain. In the 4He case, we obtain results in the vicinity of the results from comparable approaches. The numerical in-stabilities in the current implementation still prevents the desired accuracy and stability necessary to achieve the current benchmark standards. (Author)
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
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.
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.
Study of the atomic rare gas behaviour by ab initio calculations
International Nuclear Information System (INIS)
The atomic behaviour of helium and krypton in uranium dioxide has been studied using an ab initio simulation technique. Incorporation energies and solution energies of these two rare gases have been calculated. Krypton atoms are found to be insoluble in this nuclear fuel whatever the trap considered and their presence in the lattice induces swelling when they are located in interstitial sites or in oxygen vacancies. Due to its small atomic size, the predicted helium behaviour is very different. Indeed, helium is found to be soluble in stoichiometric and hyper-stoichiometric uranium dioxide in the presence of uranium vacancies or divacancies constituted by one uranium and one oxygen vacancy. Moreover helium atoms induce a lattice parameter contraction except in interstitial sites where a slight expansion is calculated. (author)
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.
Atomic and magnetic structure of manganites
International Nuclear Information System (INIS)
Complete text of publication follows. Perovskite manganites A1-xA'xMnO3 (A=La, Pr, ..., A' = Ca, Sr,...) have become a hot problem for neutron scattering during last three years. A long story of their neutron diffraction studies, started by a classical work of Wollan and Koehler [1] on La1-xCaxMnO3 and continued by a detailed investigation of Pr1-xCaxMnO3 by Jirak et al. [2], finalised with a burst-like interest in the middle of ninetieths which was provoked by rediscovering of CMR-effect in these compounds. In last three years numerous studies have been performed in all neutron scattering centres, which helped physicists to understand the main features of CMR materials. The most important of them are the strong correlation between transport properties and changes in atomic (charge/orbital ordering) and magnetic (FM/AFM ordering) structure and their dependence on the doping level, the mean A-site canon radius and its variance, as well as cation off-stoichiometry in the compound. Neutron scattering helped also to understand the important role of a local disorder and unusually strong electron-phonon coupling for the properties of manganites. (author) [1] E.O. Wollan and W.C. Koehler, Phys. Rev. 100 (1995) 545. [2] Z. Jirak, S. Krupicka, Z. Simsa, M. Dlouha and S. Vratislav, J. Magn. Magn. Mater. 53 (1985) 153
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.
Analytic methods for the calculation of the electronic structure of solids
International Nuclear Information System (INIS)
Andersen's atomic-sphere approximation has been utilized with approximations based upon linear-combination of atomic orbitals (LCAO) theory to obtain approximate energy-band parameters for solids. Simple analytic expressions for the bandwidth and position of the band center have been derived that require only free-atom wave functions evaluated at the Wigner-Seitz atomic-sphere radius. For convenience, the method has been named the atomic surface method (ASM). The following simple analytic expressions for the band parameters have been derived from the ASM: (i) The bandwidth is equal to the product of h2/m, the gradient of the electron density at the atomic-sphere radius, and the surface area of the sphere; (ii) the average band energy is shifted from the atomic-term-value energy by an amount given by the product of the bandwidth, electron density at the atomic-sphere radius, and atomic-sphere volume. The theory has been applied without adjustable parameters to the transition metals and f-shell metals with use of tabulated Hartree-Fock wave functions and is in reasonable agreement with full band-structure calculations. The same analysis is applied to atomic core states under compression and is also in reasonable agreement with complete band-structure calculations. The 2s and 2p states of Na and Al have been calculated to the point where they merge with the conduction band as free-electron states. These bandwidths and shifts are also written in terms of the atomic term values by using the asymptotic form of the radial wave function. Finally, the LCAO energy bands of Ni are calculated with use of the ASM parameters
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
Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model
International Nuclear Information System (INIS)
We develop a 16-band atomic bond-orbital model (16ABOM) to compute the spin splitting induced by bulk inversion asymmetry in zincblende materials. This model is derived from the linear combination of atomic-orbital (LCAO) scheme such that the characteristics of the real atomic orbitals can be preserved to calculate the spin splitting. The Hamiltonian of 16ABOM is based on a similarity transformation performed on the nearest-neighbor LCAO Hamiltonian with a second-order Taylor expansion over k-vector at the Γ point. The spin-splitting energies in bulk zincblende semiconductors, GaAs and InSb, are calculated, and the results agree with the LCAO and first-principles calculations. However, we find that the spin-orbit coupling between bonding and antibonding p-like states, evaluated by the 16ABOM, dominates the spin splitting of the lowest conduction bands in the zincblende materials.
Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model
Kao, Hsiu-Fen; Lo, Ikai; Chiang, Jih-Chen; Chen, Chun-Nan; Wang, Wan-Tsang; Hsu, Yu-Chi; Ren, Chung-Yuan; Lee, Meng-En; Wu, Chieh-Lung; Gau, Ming-Hong
2012-10-01
We develop a 16-band atomic bond-orbital model (16ABOM) to compute the spin splitting induced by bulk inversion asymmetry in zincblende materials. This model is derived from the linear combination of atomic-orbital (LCAO) scheme such that the characteristics of the real atomic orbitals can be preserved to calculate the spin splitting. The Hamiltonian of 16ABOM is based on a similarity transformation performed on the nearest-neighbor LCAO Hamiltonian with a second-order Taylor expansion over \\vec{k} at the Γ point. The spin-splitting energies in bulk zincblende semiconductors, GaAs and InSb, are calculated, and the results agree with the LCAO and first-principles calculations. However, we find that the spin-orbit coupling between bonding and antibonding p-like states, evaluated by the 16ABOM, dominates the spin splitting of the lowest conduction bands in the zincblende materials.
A new approach to the structure of the lightest atoms
International Nuclear Information System (INIS)
Full text: Negative ions of the lightest nuclei are often produced in ion sources of modern linear accelerators. Apart from that H- machines are currently used for producing radiopharmaceuticals. The structure of H- atom is missing in many textbooks on quantum mechanics. The H- atom is one of the simplest three-body (or four-body) systems and it is tempting to use the variation method, which leads to the classical formula for the ground state energy of Helium-like atoms: Eo(Z)= -27.2(Z-5/16)2. However, variation methods with 3, 6, and 11 parameters were used in the case of H-. Using the formula, one takes into account the screening of the atomic charge by one electron from the point of view of the other. Nevertheless, the trial function used in classical calculations exhibits the same probability of finding two electrons at the same point as e.g. in two points, where the nucleus in midway between them. This is the reason why one is tempted to modify the classical trial function by the factor s(Z) (r1-r2), in the hope to avoid the necessity of introducing so many variation parameters. In eq.(2) we introduced s(Z) for the new variation parameter and r1 and r2 are position vectors of the two electrons. The expression (2) is zero, when the two electrons coincide. The optimal value of s(1) turns out to be s(1)=0.03037 for Z=1, while for heavier helium-like atoms the optimal s(Z) will be negative. In the case of Z=10, the parameter s(10) reaches almost its asymptotic value Sasmp= -0.0541. The expression for the ground state energy of Helium-like atoms Eo,s(Z) is now, of course, more complicated than eq.(1). In the case of H- we obtain Eo,s(1)=-12.82762 eV, the value slightly smaller than the binding energy of the neutral Hydrogen atom, EH=-13.5985 eV. Since Eo,s(1) is not directly accessible in experiment, we have to start up with the reactions like: H2 + e→H-+H or H2 + e→ H-+H+e. They provide us in fact with the binding energy of H- in the molecule H2, which turns
Atomic and electronic structures of montmorillonite in soft rock
International Nuclear Information System (INIS)
Montmorillonite is a kind of clay mineral which often causes large deformation in soft-rock tunnel engineering and thus brings about safety problems in practice. To deal with these engineering safety problems, the physical and chemical properties of montmorillonite should be studied from basic viewpoints. We study the atomic and electronic structures of montmorillonite by using density-functional theory within the local-density approximation (LDA). The results of calculation show that Al–O bond lengths are longer than Si–O bond lengths. It is found that both the valence band maximum (VBM) and the conduction band minimum (CBM) of montmorillonite are at point Γ, and the calculated direct band gap of montmorillonite is 5.35 eV. We show that the chemical bonding between cations and oxygen anions in montmorillonite is mainly ionic, accompanied as well by a minor covalent component. It is pointed out that the VBM and CBM of montmorillonite consist of oxygen 2p and cation s states, respectively. Our calculated results help to understand the chemical and physical properties of montmorillonite, and are expected to be a guide for solving the problem of large deformation of soft-rock tunnels. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
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.
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...... constant and equal to the mean atomic number of the material. Wherever possible, the calculated values of Z(eff) are compared with experimental data....
Band Structure Calculation of MnxCoyFe3-x-yO4
Rosenson, A.; Tailhades, Ph.
1997-01-01
Electronic band structure of MnxCoyFe3-x-yO4 has been calculated in high symmetrical points and lines of the first Brillouin zone within the scope one-electron quasirelativistic pseudopotential approach. Atomic potential form-factors have been calculated in accordance with modified LCAO method. Dependence of energy gap Eg=Eg(x,y) against Mn, Co and Fe concentrations is calculated and presented.
Theoretical development of atomic structure: Past, present and future
International Nuclear Information System (INIS)
Theoretical development of atomic structure is briefly discussed. The role of correlation, relativity, quantum electrodynamic (QED), finite nuclear size (FNS) and parity nonconservation (PNC) in high precision theoretical investigation of properties of atomic and ionic systems is demonstrated. At present, we do not have a comprehensive and practical atomic structure theory which accounts all these physical effects on an equal footing. Suggestions are made for future directions. (author). 108 refs, 5 figs, 9 tabs
The generalized sturmian method for calculating spectra of atoms and ions
DEFF Research Database (Denmark)
Avery, James Emil; Avery, John Scales
2003-01-01
The properties of generalized Sturmian basis sets are reviewed, and functions of this type are used to perform direct configuration interaction calculations on the spectra of atoms and ions. Singlet excited states calculated in this way show good agreement with experimentally measured spectra. When...... Slater–Condon rules must be used. This aspect of the problem is discussed in detail. Finally spectra are calculated in the presence of a strong external electric field. In addition to the expected Stark effect, the calculated spectra exhibit anomalous states. These are shown to be states where one of the...
Determination of atomic cluster structure with cluster fusion algorithm
DEFF Research Database (Denmark)
Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter
We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters.......We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters....
International Nuclear Information System (INIS)
Full text: To understand the plasma-wall interaction on divertor plates, we investigate the interaction of hydrogen atoms and carbon materials used in the high heat flux components by the use of the following simulations. Monte-Carlo (MC) method based on binary collision approximation can calculate the sputtering process of hydrogen atoms on the carbon material quickly. Classical molecular dynamics (MD) method employs multi-body potential models and can treat realistic structures of crystal and molecule. The ab-initio method can calculate electron energy in quantum mechanics, which is regarded as realistic potential for atoms. In the present paper, the interaction of the hydrogen and the carbon material is investigated using the multi-scale (MC, MD and ab-initio) methods. The bombardment of hydrogen atoms onto the carbon material is simulated by the ACAT-code of the MC method, which cannot represent the structure of crystal, and the MD method using modified reactive empirical bond order (REBO) potential, which treats single crystal graphite and amorphous carbon. Consequently, we clarify that the sputtering yield and the reflection rate calculated by the ACAT-code agree with those on the amorphous carbon calculated by the MD. Moreover, there are many kinds of REBO potential for the MD. Adsorption, reflection and penetration rates between a hydrogen atom and a graphene surface are calculated by the MD simulations using the two kinds of potential model. For the incident energy of less than 1 eV, the MD simulation using the modified REBO potential, which is based on Brenner's REBO potential in 2002, shows that reflection is dominant, while the most popular Brenner's REBO potential in 1990 shows that adsorption is dominant. This reflection of the low energy injection is caused by a small potential barrier for the hydrogen atom in the modified REBO potential. The small potential barrier is confirmed by the ab-initio calculations, which are hybrid DFT (B3LYP/cc-pVDZ), ab
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.
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.
Calculations with the quasirelativistic local-spin-density-functional theory for high-Z atoms
International Nuclear Information System (INIS)
The generalized-exchange local-spin-density-functional theory (LSD-GX) with relativistic corrections of the mass velocity and Darwin terms has been used to calculate statistical total energies for the neutral atoms, the positive ions, and the negative ions for high-Z elements. The effect of the correlation and relaxation correction on the statistical total energy is discussed. Comparing the calculated results for the ionization potentials and electron affinities for the atoms (atomic number Z from 37 to 56 and 72 to 80) with experiment, shows that for the atoms rubidium to barium both the LSD-GX and the quasirelativistic LSD-GX, with self-interaction correction, Gopinathan, Whitehead, and Bogdanovic's Fermi-hole parameters [Phys. Rev. A 14, 1 (1976)], and Vosko, Wilk, and Nusair's correlation correction [Can. J. Phys. 58, 1200 (1980)], are very good methods for calculating ionization potentials and electron affinities. For the atoms hafnium to mercury the relativistic effect has to be considered
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.
Using Density Functional Theory (DFT) for the Calculation of Atomization Energies
Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)
1995-01-01
The calculation of atomization energies using density functional theory (DFT), using the B3LYP hybrid functional, is reported. The sensitivity of the atomization energy to basis set is studied and compared with the coupled cluster singles and doubles approach with a perturbational estimate of the triples (CCSD(T)). Merging the B3LYP results with the G2(MP2) approach is also considered. It is found that replacing the geometry optimization and calculation of the zero-point energy by the analogous quantities computed using the B3LYP approach reduces the maximum error in the G2(MP2) approach. In addition to the 55 G2 atomization energies, some results for transition metal containing systems will also be presented.
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...
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).
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.
Atomic-absorption programmes for the Hewlett Packard H.P. 97S programmable calculator
International Nuclear Information System (INIS)
This report outlines the limitations of the atomic-absorption (AA) programmes supplied with the Hewlett Packard H.P.97S programmable calculator, and proposes ways in which these limitations can be overcome. Three new programmes, for AA on-line analysis, off-line analysis and an automatic system, are described
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.
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.
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
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.
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.
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
Large Scale Electronic Structure Calculations using Quantum Chemistry Methods
Scuseria, Gustavo E.
1998-03-01
This talk will address our recent efforts in developing fast, linear scaling electronic structure methods for large scale applications. Of special importance is our fast multipole method( M. C. Strain, G. E. Scuseria, and M. J. Frisch, Science 271), 51 (1996). (FMM) for achieving linear scaling for the quantum Coulomb problem (GvFMM), the traditional bottleneck in quantum chemistry calculations based on Gaussian orbitals. Fast quadratures(R. E. Stratmann, G. E. Scuseria, and M. J. Frisch, Chem. Phys. Lett. 257), 213 (1996). combined with methods that avoid the Hamiltonian diagonalization( J. M. Millam and G. E. Scuseria, J. Chem. Phys. 106), 5569 (1997) have resulted in density functional theory (DFT) programs that can be applied to systems containing many hundreds of atoms and ---depending on computational resources or level of theory-- to many thousands of atoms.( A. D. Daniels, J. M. Millam and G. E. Scuseria, J. Chem. Phys. 107), 425 (1997). Three solutions for the diagonalization bottleneck will be analyzed and compared: a conjugate gradient density matrix search (CGDMS), a Hamiltonian polynomial expansion of the density matrix, and a pseudo-diagonalization method. Besides DFT, our near-field exchange method( J. C. Burant, G. E. Scuseria, and M. J. Frisch, J. Chem. Phys. 105), 8969 (1996). for linear scaling Hartree-Fock calculations will be discussed. Based on these improved capabilities, we have also developed programs to obtain vibrational frequencies (via analytic energy second derivatives) and excitation energies (through time-dependent DFT) of large molecules like porphyn or C_70. Our GvFMM has been extended to periodic systems( K. N. Kudin and G. E. Scuseria, Chem. Phys. Lett., in press.) and progress towards a Gaussian-based DFT and HF program for polymers and solids will be reported. Last, we will discuss our progress on a Laplace-transformed \\cal O(N^2) second-order pertubation theory (MP2) method.
Mikajlo, E A; Ford, M J
2003-01-01
This paper presents an experimental measurement of the electronic structure of Na sub 2 O in the solid phase using electron momentum spectroscopy and compares the results with ab initio calculations performed within the linear combination of atomic orbitals (LCAO) approximation. While Hartree-Fock (HF) can reproduce elastic properties we find it overestimates splitting of the oxygen valence bands by around 30% and the width of the O 2p band by a factor of 2. Our experimental values are 15.85 +- 0.2 and 0.6 +- 0.2 eV for these two quantities, respectively. Density functional methods are significantly better, with the hybrid functional PBE0 predicting the oxygen bandgap to within the experimental error. PBE0 also gives the best estimate of the Na core level energies. In contrast, HF performs best for the splitting between the oxygen and sodium bands. Our experimental values of 32.85 +- 0.2 and 27.45 +- 0.2 eV for the Na 2p-Na 2s and O 2p-Na 2p splittings agree well with previous measurements. Distribution of el...
Theoretical calculations of electron-impact and radiative processes in atoms
International Nuclear Information System (INIS)
Electron-impact and radiative processes in atoms are investigated with particular attention paid to the effects of electron correlations. Using the optical potential method, the cross section for the elastic scattering of electrons by the neutral argon atom is calculated from 0 to 300 eV. Corrections to the Hartree--Fock cross section are obtained from a many-particle perturbation expansion. The effects of electron correlations are found to be quite significant at low energy. The optical potential results are compared with a polarized orbital calculation, the Born approximation and experiment. The 2s and 2p excitation cross sections for electron scattering on hydrogen are calculated by two similar methods. The distorted wave method is applied and the effect of calculating the outgoing scattered electron in the potential of the initial or final state is investigated. The imaginary part of the optical potential is also calculated in lowest order by the use of many-body diagrams. The subshell photoionization cross sections in argon are calculated using the acceleration, length and velocity forms of the dipole operator. First order electron correlation corrections to the Hartree--Fock approximation are obtained through the use of many-body perturbation theory. Also investigated is the two photon ionization cross section for the neutral argon atom. A double perturbation expansion in the Coulomb correlations and the atom-radiation field interaction is made. Contributions from intermediate states are obtained by direct summation over Hartree--Fock bound and continuum single particle states. The effects of electron correlations and photon radiative corrections are investigated
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
Accelerating structure optimization and tolerance calculation
International Nuclear Information System (INIS)
The problem of optimizing the dynamics of a charged particle beam with high volumetric charge density in an accelerating structure with space-homogeneous quadrupole focusing (SHQF) is considered. The mathematical model of interacting particle dynamics is based on equations for beam envelopes. The optimization criterion (functional) is selected from the terms of obtaining a structure with an assigned length, beam energy at the accelerator outlet and the maximum particle capture for acceleration mode. A method for determining tolerance for the structure parameters based on optimization algorithm is proposed for the structure with SHQF. 4 refs.; 2 figs
Wagner, Philipp; Ewels, Christopher P.; Suarez-Martinez, Irene; Guiot, Vincent; Cox, Stephen F. J.; Lord, James S.; Briddon, Patrick R.
2011-01-01
We examine the behaviour of hydrogen ions, atoms and molecules in alpha-boron using density functional calculations. Hydrogen behaves as a negative-U centre, with positive H ions preferring to sit off-center on inter-layer bonds and negative H ions sitting preferably at in-plane sites between three B12 icosahedra. Hydrogen atoms inside B12 icosahedral cages are unstable, drifting off-center and leaving the cage with only a 0.09 eV barrier. While H0 is extremely mobile (diffusion barrier 0.25 ...
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
Single structured light beam as an atomic cloud splitter
International Nuclear Information System (INIS)
We propose a scheme to split a cloud of cold noninteracting neutral atoms based on their dipole interaction with a single structured light beam which exhibits parabolic cylindrical symmetry. Using semiclassical numerical simulations, we establish a direct relationship between the general properties of the light beam and the relevant geometric and kinematic properties acquired by the atomic cloud as it passes through the beam.
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…
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.
Structures of 38-atom gold-platinum nanoalloy clusters
International Nuclear Information System (INIS)
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, AunPt38−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
Electronic structure calculations on defects and impurities in semiconductors
International Nuclear Information System (INIS)
Self-consistent tight-binding methods are developed and used to investigate a number of defects in silicon and in four different lll-V compound semiconductors, GaP, GaAs, GaSb, and InP. The wave functions of defect states are calculated with the use of the 'largest weight method'. The hyperfine interaction parameters are in turn derived from the calculated wave functions of gap states. Substitutional phosphorus-vacancy (V-P), interstitial hydrogen-vacancy (V-H), and substitutional phosphorus-interstitial hydrogen-vacancy (V-H-P) complexes in silicon are studied in detail. We demonstrate that in the V-H and V-H-P complexes the electrical activity of the silicon dangling bonds are well passivated by phosphorus atoms at substitutional position through Coulomb attractions and by hydrogen atoms at bonding positions through strong orbital interactions, and all the remaining electrical activity in these complexes can be accounted for by those silicon dangling bonds which have neither been attached by hydrogen atoms nor replaced by phosphorus dangling bonds. In the V-P complexes, the phosphorus-dangling-bond states are found to interact with the silicon-dangling-bond states and, therefore, significant contributions from phosphorus dangling bonds to the electrically active gap states of these complexes are found. Detailed investigations on neutral and charged vacancies and divacancies in GaP, GaAs, GaSb, and InP are carried out. We find that with the Fermi level at an energy around the midpoint of the fundamental band gap, an isolated cation and an isolated anion vacancy in each of the four compound semiconductors have opposite charge states and may thus attract each other. We demonstrate that a divacancy in these compounds can have many charge states, and can introduce many energy levels into the fundamental band gap, revealing the complex nature of the defect. A simple one-electron molecular-orbital model accounting for the basic feature of the electronic structure of a
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.
International Nuclear Information System (INIS)
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
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.
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)
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.)
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.
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.
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.
The atomic structure of Pt on Si(1 1 1) studied by scanning tunneling microscopy
International Nuclear Information System (INIS)
Highlights: • Two kinds of ordered reconstruction surface were prepared on Pt/Si(1 1 1) surface. • The atomic structures were observed and verified by STM. • Calculation results confirmed the bonding energy between Si and Pt atoms. - Abstract: Two kinds of ordered reconstruction surface (√3 × √3) R30° and (√7 × √7) R19.1°, are prepared by depositing different amounts of Pt on Si(1 1 1). The atomic structure and electronic properties are studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Then two models are built to explain the results. And the calculated results using density functional theory based first principle calculation show that the distance between Pt and Si atoms in (√7 × √7) R19.1° structure is smaller than that in (√3 × √3) R30° structure, which can increase the bonding energy between Pt and Si atoms
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...
Crystal structure solution from experimentally determined atomic pair distribution functions
Juhas, Pavol; Granlund, Luke; Gujarathi, Saurabh R.; Duxbury, Phillip M.; Billinge, Simon J. L.
2010-01-01
The paper describes an extension of the Liga algorithm for structure solution from atomic pair distribution function (PDF), to handle periodic crystal structures with multiple elements in the unit cell. The procedure is performed in 2 separate steps - at first the Liga algorithm is used to find unit cell sites consistent with pair distances extracted from the experimental PDF. In the second step the assignment of atom species over cell sites is solved by minimizing the overlap of their empiri...
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.
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)
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.)
Neutron and gamma ray calculation for Hiroshima-type atomic bomb
International Nuclear Information System (INIS)
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 152Eu 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 32P 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.)
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...
Calculation of triple differential cross sections in electron scattering on atomic hydrogen
International Nuclear Information System (INIS)
Calculations of the triple differential cross sections for electrons scattering on the ground state of atomic hydrogen at incident energies of 54.4 and 150 eV is presented. The Convergent Close-Coupling (CCC) method is used. For this target the method is essentially without approximation. The total wave function was expanded in an ever increasing Laguerre basis until convergence has been obtained. A generally good agreement with experiment was found, but some quantitative discrepancies remain. 15 refs., 2 figs
Energy Technology Data Exchange (ETDEWEB)
Maeta, Takahiro [Graduate School of System Engineering, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197 (Japan); GlobalWafers Japan Co., Ltd., Higashikou, Seirou-machi, Kitakanbara-gun, Niigata 957-0197 (Japan); Sueoka, Koji [Department of Communication Engineering, Okayama Prefectural University, 111 Kuboki, Soja, Okayama 719-1197 (Japan)
2014-08-21
Ge-based substrates are being developed for applications in advanced nano-electronic devices because of their higher intrinsic carrier mobility than Si. The stability and diffusion mechanism of impurity atoms in Ge are not well known in contrast to those of Si. Systematic studies of the stable sites of 2nd to 6th row element impurity atoms in Ge crystal were undertaken with density functional theory (DFT) and compared with those in Si crystal. It was found that most of the impurity atoms in Ge were stable at substitutional sites, while transition metals in Si were stable at interstitial sites and the other impurity atoms in Si were stable at substitutional sites. Furthermore, DFT calculations were carried out to clarify the mechanism responsible for the diffusion of impurity atoms in Ge crystals. The diffusion mechanism for 3d transition metals in Ge was found to be an interstitial-substitutional diffusion mechanism, while in Si this was an interstitial diffusion mechanism. The diffusion barriers in the proposed diffusion mechanisms in Ge and Si were quantitatively verified by comparing them to the experimental values in the literature.
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
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)
Structure determination in 55-atom Li-Na and Na-K nanoalloys.
Aguado, Andrés; López, José M
2010-09-01
The structure of 55-atom Li-Na and Na-K nanoalloys is determined through combined empirical potential (EP) and density functional theory (DFT) calculations. The potential energy surface generated by the EP model is extensively sampled by using the basin hopping technique, and a wide diversity of structural motifs is reoptimized at the DFT level. A composition comparison technique is applied at the DFT level in order to make a final refinement of the global minimum structures. For dilute concentrations of one of the alkali atoms, the structure of the pure metal cluster, namely, a perfect Mackay icosahedron, remains stable, with the minority component atoms entering the host cluster as substitutional impurities. At intermediate concentrations, the nanoalloys adopt instead a core-shell polyicosahedral (p-Ih) packing, where the element with smaller atomic size and larger cohesive energy segregates to the cluster core. The p-Ih structures show a marked prolate deformation, in agreement with the predictions of jelliumlike models. The electronic preference for a prolate cluster shape, which is frustrated in the 55-atom pure clusters due to the icosahedral geometrical shell closing, is therefore realized only in the 55-atom nanoalloys. An analysis of the electronic densities of states suggests that photoelectron spectroscopy would be a sufficiently sensitive technique to assess the structures of nanoalloys with fixed size and varying compositions. PMID:20831313
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)
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.
Max Auwaerter Price lecture: building and probing atomic structures
International Nuclear Information System (INIS)
Full text: The control of the geometric, electronic, and magnetic properties of atomic-scale nanostructures is a prerequisite for the understanding and fabrication of new materials and devices. Two routes lead towards this goal: Atomic manipulation of single atoms and molecules by scanning probe microscopy, or patterning using self-assembly. Atomic manipulation has been performed since almost 20 years, but it has been difficult to answer the simple question: how much force does it take to manipulate atoms and molecules on surfaces? To address this question, we used a combined atomic force and scanning tunneling microscope to simultaneously measure the force and the current between an adsorbate and a tip during atomic manipulation. We found that the force it takes to move an atom depends crucially on the binding between adsorbate and surface. Our results indicate that for moving metal atoms on metal surfaces, the lateral force component plays the dominant role. Measuring the forces during manipulation yielded the full potential energy landscape of the tip-sample interaction. Surprisingly, the potential energy barriers are comparable to diffusion barriers, which are obtained in the absence of a probe tip. Furthermore, we used the scanning tunneling microscope to assemble magnetic structures on a thin insulator. We found, that the spin of the atom is influenced by the magnetocrystalline anisotropy of the supporting surface which lifts the spin degeneracy of the ground state and enables the identification of individual atoms. The ground state of atoms with half-integer spin remains always degenerated at zero field due to Kramers theorem. We found that if these states differ by an orbital momentum of m = ±1 the localized spin is screened by the surrounding conducting electrons of the non-magnetic host and form a many-electron spin-singlet at sufficiently low temperature. (author)
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.
Unfolding method for the first-principles LCAO electronic structure calculations
Lee, Chi-Cheng; Yamada-Takamura, Yukiko; Ozaki, Taisuke
2012-01-01
Unfolding the band structure of a supercell to a normal cell enables us to investigate how symmetry breakers such as surfaces and impurities perturb the band structure of the normal cell. We generalize the unfolding method, originally developed based on Wannier functions, to the linear combination of atomic orbitals (LCAO) method, and present a general formula to calculate the unfolded spectral weight. The LCAO basis set is ideal for the unfolding method because of the invariance that basis f...
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)
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.
Synthesis and atomic structure determination of Al8V5 gamma-brass
International Nuclear Information System (INIS)
Many structurally complex compounds like quasicrystals and their approximants are known to be stabilized at a particular electron per atom ratio e/a, regardless of constituent elements involved. This has been often referred to as the Hume-Rothery electron concentration rule. We consider the understanding of the Hume-Rothery stabilization mechanism to be best deepened by performing both ab initio LMTO-ASA and FLAPW band calculations for the complex compound whose atomic structure is experimentally determined. Admittedly, however, a computing time increases rapidly beyond practical level with increasing the number of atoms in a unit cell. Among various candidates, we chose a series of gamma-brasses containing 52 atoms in a unit cell by taking a full advantage of the facts that it exists in as many as 24 binary alloy systems and that its unit cell is just in size to be handled even in more time-consuming FLAPW method. We have so far studied the stability mechanism of Cu5Zn8 and Cu9Al4, both being regarded as its prototype, and TM2Zn11 gamma-brasses containing late transition elements TM=Fe, Co, Ni and Pd. In the present work, we chose the gamma-brass consisting of early transition metal element V and trivalent element Al. An almost single phase Al8V5 gamma-brass was ultimately synthesized by overcoming metallurgical difficulties encountered. Its atomic structure was determined by using the Brandon model as a starting structure in the Rietveld structure analysis for powdered diffraction spectra taken at the beam line BL02B2 of 8 GeV synchrotron radiation facility, SPring-8, Japan. The atomic structure suitable for band calculations was then proposed by eliminating quenched-in chemical disorder, i.e., partial mixing of Al and V atoms at given sites with minimum sacrifice. (author)
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...
International Nuclear Information System (INIS)
In this paper, we report the discovery of the diamond pyramid structures in the electroless copper deposits on both epoxy and stainless steel substrates. The surface morphology of the structure was characterized with scanning electron microscope (SEM). According to the morphological feature of the structure, an atom model was brought forward in order to describe the possible mechanism of forming such structure. Molecular dynamics (MD) simulations were then carried out to investigate the growing process of the diamond pyramid structure. The final structures of the simulation were compared with the SEM images and the atomic model. The radial distribution function of the final structures of the simulation was compared with that calculated from the X-ray diffraction pattern of the electroless copper deposit sample
Wu, X.; Sha, W.
2008-12-01
In this paper, we report the discovery of the diamond pyramid structures in the electroless copper deposits on both epoxy and stainless steel substrates. The surface morphology of the structure was characterized with scanning electron microscope (SEM). According to the morphological feature of the structure, an atom model was brought forward in order to describe the possible mechanism of forming such structure. Molecular dynamics (MD) simulations were then carried out to investigate the growing process of the diamond pyramid structure. The final structures of the simulation were compared with the SEM images and the atomic model. The radial distribution function of the final structures of the simulation was compared with that calculated from the X-ray diffraction pattern of the electroless copper deposit sample.
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.
Direct experimental determination of the atomic structure at internal interfaces
Energy Technology Data Exchange (ETDEWEB)
Browning, N.D. [Oak Ridge National Lab., TN (United States)]|[Illinois Univ., Chicago, IL (United States); Pennycook, S.J. [Oak Ridge National Lab., TN (United States)
1995-07-01
A crucial first step in understanding the effect that internal interfaces have on the properties of materials is the ability to determine the atomic structure at the interface. As interfaces can contain atomic disorder, dislocations, segregated impurities and interphases, sensitivity to all of these features is essential for complete experimental characterization. By combining Z-contrast imaging and electron energy loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope (STEM), the ability to probe the structure, bonding and composition at interfaces with the necessary atomic resolution has been obtained. Experimental conditions can be controlled to provide, simultaneously, both incoherent imaging and spectroscopy. This enables interface structures observed in the image to be interpreted intuitively and the bonding in a specified atomic column to be probed directly by EELS. The bonding and structure information can then be correlated using bond-valence sum analysis to produce structural models. This technique is demonstrated for 25{degrees}, 36{degrees} and 67{degrees} symmetric and 45{degrees} and 25{degrees} asymmetric [001] tilt grain boundaries in SrTiO{sub 3} The structures of both types of boundary were found to contain partially occupied columns in the boundary plane. From these experimental results, a series of structural units were identified which could be combined, using continuity of gain boundary structure principles, to construct all [001] tilt boundaries in SrTiO{sub 3}. Using these models, the ability of this technique to address the issues of vacancies and dopant segregation at grain boundaries in electroceramics is discussed.
Atomic quantum systems in optical micro-structures
International Nuclear Information System (INIS)
Full text: We combine state-of-the-art technology in micro-optics with the quantum optical techniques of laser cooling, laser trapping, and quantum control to open a new gateway for quantum information processing and matter wave optics with atomic systems. We use micro-fabricated optical systems to create light fields that allow us to trap and guide neutral atoms as a result of the optical dipole force experienced by the atoms. The realization of arrays of laser traps that can serve as registers for atomic quantum bits and as integrated waveguide structures for atom optics and atom interferometry has been achieved. This approach opens the possibility to scale, parallelize, and miniaturize systems for quantum information processing and atom optics. Currently we investigate the production of quantum-degenerate systems in pure optical trapping geometries and the coherent manipulation (1-qubit rotations, Ramsey-oscillations, spin-echo experiments) of internal qubit states for atoms trapped in arrays of dipole traps (author)
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.
A novel Gaussian-Sinc mixed basis set for electronic structure calculations
International Nuclear Information System (INIS)
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
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,…
Structural characteristics and quantum chemistry calculation of Si-doped boron carbides
International Nuclear Information System (INIS)
Structural characteristics, chemical bonds and thermoelectric properties of Si-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation Xα method. The calculations show that Si atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Si to substitute B or C atom in the centers of chain or in the icosahedra. A representative structural unit containing a Si atom is [C-B-Si]ε+-[B11C]ε-, while the structural unit without Si is [C-B-B(C)]δ'-[B11C]δ+, and the coexistence of these two different structural units makes the electrical conductivity increases. As the covalent bond of Si-B or Si-C is weaker than that of B-B or B-C, the thermal conductivity decreases when Si is added into boron carbides. With the electrical conductivity increases and the thermal conductivity decreases, Si doping has significant effect on thermoelectric properties of boron carbides
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.
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.
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.
The fifth Atomic Energy Research dynamic benchmark calculation with HEXTRAN-SMABRE
International Nuclear Information System (INIS)
The fifth Atomic Energy Research dynamic benchmark is the first Atomic Energy Research benchmark for coupling of the thermohydraulic codes and three-dimensional reactor dynamic core models. In VTT HEXTRAN 2.7 is used for the core dynamics and SMABRE 4.6 as a thermohydraulic model for the primary and secondary loops. The plant model for SMABRE is based mainly on two input models. the Loviisa model and standard WWER-440/213 plant model. The primary circuit includes six separate loops, totally 505 nodes and 652 junctions. The reactor pressure vessel is divided into six parallel channels. In HEXTRAN calculation 176 symmetry is used in the core. In the sequence of main steam header break at the hot standby state, the liquid temperature is decreased symmetrically in the core inlet which leads to return to power. In the benchmark, no isolations of the steam generators are assumed and the maximum core power is about 38 % of the nominal power at four minutes after the break opening in the HEXTRAN-SMABRE calculation. Due to boric acid in the high pressure safety injection water, the power finally starts to decrease. The break flow is pure steam in the HEXTRAN-SMABRE calculation during the whole transient even in the swell levels in the steam generators are very high due to flashing. Because of sudden peaks in the preliminary results of the steam generator heat transfer, the SMABRE drift-flux model was modified. The new model is a simplified version of the EPRI correlation based on test data. The modified correlation behaves smoothly. In the calculations nuclear data is based on the ENDF/B-IV library and it has been evaluated with the CASMO-HEX code. The importance of the nuclear data was illustrated by repeating the benchmark calculation with using three different data sets. Optimal extensive data valid from hot to cold conditions were not available for all types of fuel enrichments needed in this benchmark.(Author)
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
Electronic structure of helium atom in a quantum dot
Saha, Jayanta K; Mukherjee, T K
2015-01-01
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] configuration 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 representing the quantum dot. It has been explicitly demonstrated that electronic structure properties become a sensitive function of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within 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 wi...
Atomic structures and electronic properties of phosphorene grain boundaries
Guo, Yu; Zhou, Si; Zhang, Junfeng; Bai, Yizhen; Zhao, Jijun
2016-06-01
Grain boundary (GB) is one main type of defects in two-dimensional (2D) crystals, and has significant impact on the physical properties of 2D materials. Phosphorene, a recently synthesized 2D semiconductor, possesses a puckered honeycomb lattice and outstanding electronic properties. It is very interesting to know the possible GBs present in this novel material, and how their properties differ from those in the other 2D materials. Based on first-principles calculations, we explore the atomic structure, thermodynamic stability, and electronic properties of phosphorene GBs. A total of 19 GBs are predicted and found to be energetically stable with formation energies much lower than those in graphene. These GBs do not severely affect the electronic properties of phosphorene: the band gap of perfect phosphorene is preserved, and the electron mobilities are only moderately reduced in these defective systems. Our theoretical results provide vital guidance for experimental tailoring the electronic properties of phosphorene as well as the device applications using phosphorene materials.
Calculated electronic and magnetic structure of screw dislocations in alpha iron
Energy Technology Data Exchange (ETDEWEB)
Odbadrakh, K.; Rusanu, A.; Stocks, G. Malcolm; Samolyuk, G. D.; Eisenbach, M.; Wang, Yang; Nicholson, D. M.
2011-01-01
Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated local moments using the locally self-consistent multiple scattering (LSMS) method for a supercell containing a screw-dislocation quadrupole. Finite size effects are found to be significant indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations points to a need to study individual dislocations from first principles just as they appear amid surrounding atoms in large-scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in subvolumes of large atomic configurations generated in the course of classical molecular dynamics simulation of dislocationdynamics is discussed.
Calculated electronic and magnetic structure of screw dislocations in alpha iron
Energy Technology Data Exchange (ETDEWEB)
Odbadrakh, Khorgolkhuu [ORNL; Rusanu, Aurelian [ORNL; Stocks, George Malcolm [ORNL; Samolyuk, German D [ORNL; Eisenbach, Markus [ORNL; Wang, Yang Nmn [ORNL; Nicholson, Don M [ORNL
2011-01-01
Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated local moments using the locally self-consistent multiple scattering (LSMS) method for a supercell containing a screw-dislocation quadrupole. Finite size effects are found to be significant indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations points to a need to study individual dislocations from first principles just as they appear amid surrounding atoms in large-scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in subvolumes of large atomic configurations generated in the course of classical molecular dynamics simulation of dislocation dynamics is discussed. VC2011 American Institute of Physics. [doi:10.1063/1.3562217
Density functional calculation of the structural and electronic properties of germanium quantum dots
International Nuclear Information System (INIS)
We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation
Monte Carlo calculation of the Born-Oppenheimer potential between two helium atoms
International Nuclear Information System (INIS)
Fully correlated Hylleraas-type electronic wave functions and a biased-selection Monte Carlo method have been used to find a rigorous upper bound to the Born-Oppenheimer potential between two helium atoms. The potential agrees with the experimental results of Burgmans, Farrar, and Lee (BFL) to within 1.4 Monte Carlo standard deviations for all nuclear separation distances calculated (4.5--15.0a/sub B/). At the potential minimum of 5.6a/sub B/ this bound (-7.10 +- 0.30 Ry) is slightly below the BFL value of -6.70 Ry
Monte Carlo calculation of the Born-Oppenheimer potential between two helium atoms
Energy Technology Data Exchange (ETDEWEB)
Lowther, R.E.; Coldwell, R.L.
1980-07-01
Fully correlated Hylleraas-type electronic wave functions and a biased-selection Monte Carlo method have been used to find a rigorous upper bound to the Born-Oppenheimer potential between two helium atoms. The potential agrees with the experimental results of Burgmans, Farrar, and Lee (BFL) to within 1.4 Monte Carlo standard deviations for all nuclear separation distances calculated (4.5--15.0a/sub B/). At the potential minimum of 5.6a/sub B/ this bound (-7.10 +- 0.30 Ry) is slightly below the BFL value of -6.70 Ry.
First-principle calculation of GaAs electronic structure by doping with Mn and P
International Nuclear Information System (INIS)
The geometry structure of Mn, P doped 64-atom supercell of GaAs (Ga1-xMnxAs1-yPy) was optimized and studied by the self-consistent full-potential linearized augmented plane wave method (FPLAPW) based on the density functional theory (DFT). Cell parameters of both doped and undoped were calculated theoretically. Band structure, binding energies, partial density of states, mulliken charges, and electron density different of doped GaAs crystals were calculated and analyzed in detail. The results revealed that the both doped compounds are true half-metallic ferromagnets and the near distance doped one is a stable ground state.
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
International Nuclear Information System (INIS)
The methods that are actively used for electronic structure calculations of low-lying states of heavy- and superheavy-element compounds are briefly described. The advantages and disadvantages of the Dirac-Coulomb-Breit Hamiltonian, Huzinaga-type potential, shape-consistent Relativistic Effective Core Potential (RECP), and Generalized RECP are discussed. The nonvariational technique of the electron-structure restoration in atomic cores after the RECP calculation of a molecule is presented. The features of the approaches accounting for electron correlation, the configuration interaction and coupled cluster methods, are also described. The results of calculations on E113, E114, U, and other heavy-atom systems are presented
Calculated Electronic and Magnetic Structure of Screw Dislocations in Alpha Iron
Energy Technology Data Exchange (ETDEWEB)
Odbadrakh, Khorgolkhuu [ORNL; Rusanu, Aurelian [ORNL; Stocks, George Malcolm [ORNL; Samolyuk, German D [ORNL; Eisenbach, Markus [ORNL; Wang, Yang [Pittsburgh Supercomputing Center; Nicholson, Don M [ORNL
2011-01-01
Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated the local moments using the Locally Self-consistent Multiple Scattering (LSMS) method for an 1848 atom supercell containing a screw- dislocation quadrupole. The atomic positions were determined by relaxation with an embedded atom force field. Finite size effects are found to be significant for this small cell size indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations point to a need to study individual dislocations from first principles just as they appear amidst surrounding atoms in large scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in sub-volumes of large atomic configurations generated in the course of classical MD simulation of dislocation dynamics is discussed.
International Nuclear Information System (INIS)
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 IP3 through IP6
Learning Approach on the Ground State Energy Calculation of Helium Atom
International Nuclear Information System (INIS)
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.
Inner-shell correlations and Sturm expansions in coupled perturbation calculations of atomic systems
Energy Technology Data Exchange (ETDEWEB)
Sherstyuk, A.I.; Solov`eva, G.S. [Vavilov State Optical Institute, St. Petersburg (Russian Federation)
1995-04-01
It is shown that virtual Hartree-Fock orbitals in Sturm-type expansions can be used to calculate the response of atomic systems to an external field within the framework of the coupled perturbation theory with allowance for correlation effects. The corrected electron-electron interaction in a system with field-distorted orbitals is considered by adding a nonlocal potential to a one-electron Hartree-Fock operator within each group of equivalent elections. The remaining correlation effects are calculated by solving a system of equations for corrections to the radial functions. The system is solved iteratively, with each subsequent iteration corresponding to a correction of an increasingly higher order in the electron--electron interaction. The explicit expression derived for the polarizability contains one-and two-particle radial integrals of the Sturm functions.
Inner-shell correlations and Sturm expansions in coupled perturbation calculations of atomic systems
International Nuclear Information System (INIS)
It is shown that virtual Hartree-Fock orbitals in Sturm-type expansions can be used to calculate the response of atomic systems to an external field within the framework of the coupled perturbation theory with allowance for correlation effects. The corrected electron-electron interaction in a system with field-distorted orbitals is considered by adding a nonlocal potential to a one-electron Hartree-Fock operator within each group of equivalent elections. The remaining correlation effects are calculated by solving a system of equations for corrections to the radial functions. The system is solved iteratively, with each subsequent iteration corresponding to a correction of an increasingly higher order in the electron--electron interaction. The explicit expression derived for the polarizability contains one-and two-particle radial integrals of the Sturm functions
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.
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...
Calculation of Ion Charge State Distributions After Inner-Shell Ionization in Xe Atom
International Nuclear Information System (INIS)
The vacancy cascades following initial inner-shell vacancies in single and multi-ionized atoms often lead to highly charged residual ions. The inner-shell vacancy produced by ionization processes may decay by either a radiative or non-radiative transition. In addition to the vacancy filling processes, there is an electron shake off process due to the change of core potential of the atom. In the calculation of vacancy cascades, the radiative (x-ray) and non-radiative (Auger and Coster-Kronig) branching ratios give valuable information on the de-excitation dynamics of an atom with inner-shell vacancy. The production of multi-charged ions yield by the Auger cascades following inner shell ionization of an atom has been studied both experimentally and theoretically. Multi-charged Xe ions following de-excitation of K-, L1-, L2,3-, M1-, M2,3- and M4,5 subshell vacancies are calculated using Monte-Carlo algorithm to simulate the vacancy cascade development. Fluorescence yield (radiative) and Auger, Coster- Kronig yield (non- radiative) are evaluated. The decay of K hole state through radiative transitions is found to be more probable than non-radiative transitions in the first step of de-excitation. On the other hand, the decay of L, M vacancies through non-radiative transitions are more probable. The K shell ionization in Xe atom mainly yields Xe7+, Xe8+, Xe9+ and Xe10+ ions, and the charged X8+ ions are the highest. The main product from the L1- shell ionization is found to be Xe8+, Xe9+ ions, while the charged Xe8+ ions predominate at L2,3 hole states. The charged Xe6+, Xe7+ and Xe8+ ions mainly yield from 3s1/2 and 3p1/2,3/2 ionization, while Xe in 3d3/2,5/2 hole states mainly turns into Xe4+ and Xe5+ ions. The present results are found to agree well with the experimental data.
Calculation of Ion Charge State Distributions After Inner-Shell Ionization in Xe Atom
International Nuclear Information System (INIS)
The vacancy cascades following initial inner-shell vacancies in single and multi-ionized atoms often lead to highly charged residual ions. The inner-shell vacancy produced by ionization processes may decay by either a radiative or non-radiative transition. In addition to the vacancy filling processes, there is an electron shake off process due to the change of core potential of the atom. In the calculation of vacancy cascades, the radiative (x-ray) and non-radiative (Auger and Coster-Kronig) branching ratios give valuable information on the de-excitation dynamics of an atom with inner-shell vacancy. The production of multi-charged ions yield by the Auger cascades following inner shell ionization of an atom has been studied both experimentally and theoretically. Multi-charged Xe ions following de-excitation of K, L1, L2,3, M1, M2,3 and M4,5 subshell vacancies are calculated using Monte-Carlo algorithm to simulate the vacancy cascade development. Fluorescence yield (radiative) and Auger, Coster- Kronig yield (non- radiative) are evaluated. The decay of K hole state through radiative transitions is found to be more probable than non-radiative transitions in the first step of de-excitation. On the other hand, the decay of L, M vacancies through non-radiative transitions are more probable. The K shell ionization in Xe atom mainly yields Xe7+, Xe8+, Xe9+ and Xe10+ ions, and the charged X8+ ions are the highest. The main product from the L1 shell ionization is found to be Xe8+, Xe9+ ions, while the charged Xe8+ ions predominate at L2,3 hole states. The charged Xe6+, Xe7+ and Xe8+ ions mainly yield from 3s1/2 and 3p1/2,3/2 ionization, while Xe in 3d3/2,5/2 hole states mainly turns into Xe4+ and Xe5+ ions. The present results are found to agree well with the experimental data. (author)
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.
Effects of Contact Atomic Structure on Electronic Transport in Molecular Junction
International Nuclear Information System (INIS)
Based on nonequilibrium Green's function and first-principles calculations, we investigate the change in molecular conductance caused by different adsorption sites with the presence of additional Au atom around the metal-molecule contact in the system that benzene sandwiched between two Au(111) leads. The motivation is the variable situations that may arise in break junction experiments. Numerical results show that the enhancement of conductance induced by the presence of additional Au is dependent on the adsorption sites of anchoring atom. When molecule is located on top site with the presence of additional Au atoms, it can increase molecular conductance remarkably and present negative differential resistance under applied bias which cannot be found in bridge and hollow sites. Furthermore, the effects of different distance between additional Au and sulfur atoms in these three adsorption sites are also discussed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
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
A knowledge-based structure-discriminating function that requires only main-chain atom coordinates
Directory of Open Access Journals (Sweden)
Itoh Nobuya
2008-10-01
Full Text Available Abstract Background The use of knowledge-based potential function is a powerful method for protein structure evaluation. A variety of formulations that evaluate single or multiple structural features of proteins have been developed and studied. The performance of functions is often evaluated by discrimination ability using decoy structures of target proteins. A function that can evaluate coarse-grained structures is advantageous from many aspects, such as relatively easy generation and manipulation of model structures; however, the reduction of structural representation is often accompanied by degradation of the structure discrimination performance. Results We developed a knowledge-based pseudo-energy calculating function for protein structure discrimination. The function (Discriminating Function using Main-chain Atom Coordinates, DFMAC consists of six pseudo-energy calculation components that deal with different structural features. Only the main-chain atom coordinates of N, Cα, and C atoms for the respective amino acid residues are required as input data for structure evaluation. The 231 target structures in 12 different types of decoy sets were separated into 154 and 77 targets, and function training and the subsequent performance test were performed using the respective target sets. Fifty-nine (76.6% native and 68 (88.3% near-native (α RMSD targets in the test set were successfully identified. The average Cα RMSD of the test set resulted in 1.174 with the tuned parameters. The major part of the discrimination performance was supported by the orientation-dependent component. Conclusion Despite the reduced representation of input structures, DFMAC showed considerable structure discrimination ability. The function can be applied to the identification of near-native structures in structure prediction experiments.
Structure and transport properties of atomic chains and molecules
DEFF Research Database (Denmark)
Strange, Mikkel
2008-01-01
as the Siesta basis is enlarged. Overall, we find that a double zeta polarized atomic basis is generally sufficient, and in some cases necessary, to ensure quantitative agreement with the plane-wave calculation. In a detailed DFT study of the carbon monoxide molecule between Pt electrodes, a particularly stable...... with the experimental findings [5]. The observed conductance properties of Metal/CO are shown to be determined by the local d-band at the Metal apex atoms. For carbon nanotubes it is shown that the conductance may be controlled by site selective adsorption of molecules. A model to explain this behavior is verified...... by direct visualization of Kohn-Sham eigenchannel states. The possibility of non-carbon based nanotubes is also discussed. Both calculations of the strain energy of infinite PtO2 nanotubes that this material could be a candidate for non-carbon based nanotubes, as was recently suggested [6]....
Formation and atomic structure of tetrahedral carbon onion produced by electron-beam irradiation
International Nuclear Information System (INIS)
Full text: Various fullerene structures has been designed and produced after the discovery of C60. These fullerene materials are good candidates as nanoscale devises such as single-electron devices, nano-diode, nano-transistor, nano-ball bearing and insulator lubricant. The onion structures, which generally consist of some quasi-spherical fullerene group, are also discovered and studied in detail. The tetrahedral carbon onions had been calculated to be unstable compared to the spherical onions due to the rigidity. The purpose of the present work is to produce new carbon onion by high-energy electron-irradiation on amorphous carbon at 1250 kV, and to investigate atomic structures and stability of the new carbon onion cluster by high-resolution electron microscopy (HREM) and molecular orbital/mechanics calculations. To confirm the structure model from HREM data, HREM image simulation were carried out. The tetrahedral carbon onion was successfully produced by high-energy electron-irradiation. A HREM image of tetrahedral carbon onion would consist of pentagonal and hexagonal rings. The HREM result indicates that new fullerene structures formed into the carbon onion. Molecular mechanics calculations (MM2), semi-empirical molecular orbital calculations (PM3), and density functional theory (DFT) were used to get structure optimization about first and second internal shell. The energy levels and density of states were also calculated by the first principles method (DV-Xα). The smallest tetrahedral onion in the HREM image agreed well with the proposed structure model of C84atC276. Each vertex consists of a hexagonal ring, and three pentagonal rings exist around the vertex along the edge. In summary, the tetrahedral carbon cluster was produced by energy transfer of electron-irradiation, and the new atomic structure model of tetrahedral carbon onion was proposed. The electronic structures were also calculated theoretically. Copyright (2002) Australian Society for Electron
An approach to first principles electronic structure calculation by symbolic-numeric computation
Kikuchi, Akihito
2013-01-01
This article is an introduction to a new approach to first principles electronic structure calculation. The starting point is the Hartree-Fock-Roothaan equation, in which molecular integrals are approximated by polynomials by way of Taylor expansion with respect to atomic coordinates and other variables. It leads to a set of polynomial equations whose solutions are eigenstate, which is designated as algebraic molecular orbital equation. Symbolic computation, especially, Gr\\"obner bases theory, enables us to rewrite the polynomial equations into more trimmed and tractable forms with identical roots, from which we can unravel the relationship between physical parameters (wave function, atomic coordinates, and others) and numerically evaluate them one by one in order. Furthermore, this method is a unified way to solve the electronic structure calculation, the optimization of physical parameters, and the inverse problem as a forward problem.
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...
Workshop on foundations of the relativistic theory of atomic structure
International Nuclear Information System (INIS)
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
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. PMID:26538495
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.
Are the program packages for molecular structure calculations really black boxes?
ANA MRAKOVIC; MILICA DRVENDZIJA; ALEKSANDRA SAMOLOV; MILENA PETKOVIC; MILJENKO PERIC
2007-01-01
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...
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
Atomic-scale structure of disordered Ga1-xInxP alloys
International Nuclear Information System (INIS)
Extended x-ray-absorption fine-structure experiments have previously demonstrated that for each composition x, the sample average of all nearest-neighbor A-C distances in an A1-xBxC semiconductor alloy is closer to the values in the pure (x→0) AC compound than to the composition-weighted (virtual) lattice average. Such experiments do not reveal, however, the distribution of atomic positions in an alloy, so the principle displacement directions and the degrees of correlation among such atomic displacements remain unknown. Here we calculate both structural and thermodynamic properties of Ga1-xInxP alloys using an explicit occupation- and position-dependent energy functional. The latter is taken as a modified valence force field, carefully fit to structural energies determined by first-principles local-density calculations. Configurational and vibrational degrees of freedom are then treated via the continuous-space Monte Carlo approach. We find good agreement between the calculated and measured mixing enthalpy of the random alloy, nearest-neighbor bond lengths, and temperature-composition phase diagram. In addition, we predict yet unmeasured quantities such as (a) distributions, fluctuations, and moments of first- and second-neighbor bond lengths as well as bond angles, (b) radial distribution functions, (c) the dependence of short-range order on temperature, and (d) the effect of temperature on atomic displacements. Our calculations provide a detailed picture of how atoms are arranged in substitutionally random but positionally relaxed alloys, and offer an explanation for the effects of site correlations, static atomic relaxations, and dynamic vibrations on the phase-diagram and displacement maps. (Abstract Truncated)
Campbell, Erin Roberts
The process of chemical education should facilitate students' construction of meaningful conceptual structures about the concepts and processes of chemistry. It is evident, however, that students at all levels possess concepts that are inconsistent with currently accepted scientific views. The purpose of this study was to examine undergraduate chemistry students' conceptions of atomic structure, chemical bonding and molecular structure. A diagnostic instrument to evaluate students' conceptions of atomic and molecular structure was developed by the researcher. The instrument incorporated multiple-choice items and reasoned explanations based upon relevant literature and a categorical summarization of student responses (Treagust, 1988, 1995). A covalent bonding and molecular structure diagnostic instrument developed by Peterson and Treagust (1989) was also employed. The ex post facto portion of the study examined the conceptual understanding of undergraduate chemistry students using descriptive statistics to summarize the results obtained from the diagnostic instruments. In addition to the descriptive portion of the study, a total score for each student was calculated based on the combination of correct and incorrect choices made for each item. A comparison of scores obtained on the diagnostic instruments by the upper and lower classes of undergraduate students was made using a t-Test. This study also examined an axiomatic assumption that an understanding of atomic structure is important in understanding bonding and molecular structure. A Pearson Correlation Coefficient, ṟ, was calculated to provide a measure of the strength of this association. Additionally, this study gathered information regarding expectations of undergraduate chemistry students' understanding held by the chemical community. Two questionnaires were developed with items based upon the propositional knowledge statements used in the development of the diagnostic instruments. Subgroups of items from
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.……
Atomic structure of Ag(111) saturated with chlorine: Formation of Ag3Cl7 clusters
Andryushechkin, B. V.; Cherkez, V. V.; Gladchenko, E. V.; Zhidomirov, G. M.; Kierren, B.; Fagot-Revurat, Y.; Malterre, D.; Eltsov, K. N.
2011-08-01
The structure of saturated chlorine layer on Ag(111) has been studied with low temperature scanning tunneling microscopy and density functional theory. For the first time atomic-resolution STM images of saturated chlorine coverage have been obtained. STM images demonstrate coexistence of the domain with (3 × 3)-like reconstruction and numerous bright objects identified as Ag3Cl7 clusters. According to our model supported by DFT calculations, clusters are formed on the boundaries between the adjacent (3×3) antiphase domains. These boundaries have a characteristic triangular shape and are formed by six chlorine atoms chemisorbed on the triangular silver island with local periodicity (1 × 1).
International Nuclear Information System (INIS)
Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 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 FeTe1−xSex 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
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.
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...
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
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.)
Scanning probe microscopy of oxide surfaces: atomic structure and properties
International Nuclear Information System (INIS)
The intersection of two fields, oxide surface science and scanning probe microscopy (SPM), has yielded considerable insight on atomic processes at surfaces. Oxide surfaces, especially those containing transition metals, offer a rich variety of structures and localized physical phenomena that are exploited in a wide range of applications. Nonlinear optics, superconductivity, ferroelectricity and chemical catalytic activity are but a few. Furthermore, the challenges and solutions associated with the chemistry of these surfaces and particularly the solutions to these problems have led to important understanding of tip-surface interactions that can inform SPM studies of all materials. Here, the development of understanding of the model systems TiO2 and SrTiO3 are considered in detail, to demonstrate the role of nonstoichiometry in surface structure evolution and the approach to interpreting structure at the atomic level. Then a combination of scanning tunneling microscopy, noncontact atomic force microscopy and theory are applied to a variety of oxide systems including Al2O3, NiO, ferroelectric BaTiO3, tungstates and molybdates. Recently developed sophisticated probes of local properties include spin-polarized tunneling, Fourier mapping of charge density waves, band gap mapping of superconductors and ultra fast imaging of atomic diffusion. The impact of these studies on our understanding of the behavior of oxides and of tip-surface interactions is summarized
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
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
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.
Influence of the plasma environment on atomic structure using an ion-sphere model
International Nuclear Information System (INIS)
Plasma environment effects on atomic structure are analyzed using various atomic structure codes. To monitor the effect of high free-electron density or low temperatures, Fermi-Dirac and Maxwell-Boltzmann statistics are compared. After a discussion of the implementation of the Fermi-Dirac approach within the ion-sphere model, several applications are considered. In order to check the consistency of the modifications brought here to extant codes, calculations have been performed using the Los Alamos Cowan Atomic Structure (cats) code in its Hartree-Fock or Hartree-Fock-Slater form and the parametric potential Flexible Atomic Code (fac). The ground-state energy shifts due to the plasma effects for the six most ionized aluminum ions have been calculated using the fac and cats codes and fairly agree. For the intercombination resonance line in Fe22+, the plasma effect within the uniform electron gas model results in a positive shift that agrees with the MCDF value of B. Saha et al
Optomechanical self-structuring in cold atomic gases
Labeyrie, Guillaume; Gomes, Pedro M; Oppo, Gian-Luca; Firth, William J; Robb, Gordon R M; Arnold, Aidan S; Kaiser, Robin; Ackemann, Thorsten
2013-01-01
The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.
Structural properties of lithium atom under weakly coupled plasma environment
Dutta, S.; Saha, J. K.; Chandra, R.; Mukherjee, T. K.
2016-04-01
The Rayleigh-Ritz variational technique with a Hylleraas basis set is being tested for the first time to estimate the structural modifications of a lithium atom embedded in a weakly coupled plasma environment. The Debye-Huckel potential is used to mimic the weakly coupled plasma environment. The wave functions for both the helium-like lithium ion and the lithium atom are expanded in the explicitly correlated Hylleraas type basis set which fully takes care of the electron-electron correlation effect. Due to the continuum lowering under plasma environment, the ionization potential of the system gradually decreases leading to the destabilization of the atom. The excited states destabilize at a lower value of the plasma density. The estimated ionization potential agrees fairly well with the few available theoretical estimates. The variation of one and two particle moments, dielectric susceptibility and magnetic shielding constant, with respect to plasma density is also been discussed in detail.
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.
Convergence of CI single center calculations of positron-atom interactions
Mitroy, J
2006-01-01
The Configuration Interaction (CI) method using orbitals centered on the nucleus has recently been applied to calculate the interactions of positrons interacting with atoms. Computational investigations of the convergence properties of binding energy, phase shift and annihilation rate with respect to the maximum angular momentum of the orbital basis for the e^+Cu and PsH bound states, and the e^+-H scattering system were completed. The annihilation rates converge very slowly with angular momentum, and moreover the convergence with radial basis dimension appears to be slower for high angular momentum. A number of methods of completing the partial wave sum are compared, an approach based on a Delta X_J = a/(J + 1/2)^n + b/(J + 1/2)^(n+1) form (with n = 4 for phase shift (or energy) and n = 2 for the annihilation rate) seems to be preferred on considerations of utility and underlying physical justification.
Convergence of configuration-interaction single-center calculations of positron-atom interactions
International Nuclear Information System (INIS)
The configuration interaction (CI) method using orbitals centered on the nucleus has recently been applied to calculate the interactions of positrons interacting with atoms. Computational investigations of the convergence properties of binding energy, phase shift, and annihilation rate with respect to the maximum angular momentum of the orbital basis for the e+Cu and PsH bound states, and the e+-H scattering system were completed. The annihilation rates converge very slowly with angular momentum, and moreover the convergence with radial basis dimension appears to be slower for high angular momentum. A number of methods of completing the partial wave sum are compared; an approach based on a ΔXJ=a(J+(1/2))-n+b(J+(1/2))-(n+1) form [with n=4 for phase shift (or energy) and n=2 for the annihilation rate] seems to be preferred on considerations of utility and underlying physical justification
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
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
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
International Nuclear Information System (INIS)
Effect of hydrogen atoms on the mobility of a screw dislocation in BCC iron has been evaluated using the first-principles calculation. The stable position of a hydrogen atom is found to be near the screw dislocation core and inside the core respectively when the dislocation is at the easy-core or hard-core configuration in BCC iron. The intrinsically unstable hard-core configuration of the screw dislocation is stabilized when a hydrogen atom is trapped inside the core. On the basis of this first-principles result, an elastic string model of a dislocation is developed to predict the kink motion in the presence of a hydrogen atom. It is found that a double-kink formation is facilitated when a hydrogen atom is located near a dislocation line, however, a kink motion is retarded when a hydrogen atom is behind the kink. (author)
Chuluunbaatar, O; Vinitsky, S I
2002-01-01
The uncoupled correlated variational function of the helium atom ground state declared earlier is examined in calculations of differential cross sections of fast electron impact single and double binary ionization processes. An optimal one-parametric set of orthogonal basic functions is generated to provide the considerable coincidence with the experiment and calculations with the alternative multiparametric trial wave functions.
International Nuclear Information System (INIS)
One calculated four certain modifications of SrZrO3 crystal of various symmetry: a cubic one, a tetragonal one and two orthorhombic ones, by the density functional technique in the basis of linear combination of atomic orbitals. One carried out comparison analysis of electron properties of the investigated crystals based on the calculated band structures and distribution densities of electron states (the complete ones and atomic state designed ones). The calculation base relative stability of different modifications correlates adequately with the experimental data on phase transitions in SrZrO3 crystal: less symmetric low-temperature modifications are more stable ones
Large-dimension configuration-interaction calculations of positron binding to the group-II atoms
International Nuclear Information System (INIS)
The configuration-interaction (CI) method is applied to the calculation of the structures of a number of positron binding systems, including e+Be, e+Mg, e+Ca, and e+Sr. These calculations were carried out in orbital spaces containing about 200 electron and 200 positron orbitals up to l=12. Despite the very large dimensions, the binding energy and annihilation rate converge slowly with l, and the final values do contain an appreciable correction obtained by extrapolating the calculation to the l→∞ limit. The binding energies were 0.00317 hartree for e+Be, 0.0170 hartree for e+Mg, 0.0189 hartree for e+Ca, and 0.0131 hartree for e+Sr
Calculation of wakefields in 2D rectangular structures
International Nuclear Information System (INIS)
We consider the calculation of electromagnetic fields generated by an electron bunch passing through a vacuum chamber structure that, in general, consists of an entry pipe, followed by some kind of transition or cavity, and ending in an exit pipe. We limit our study to structures having rectangular cross-section, where the height can vary as function of longitudinal coordinate but the width and side walls remain fixed. For such structures, we derive a Fourier representation of the wake potentials through one-dimensional functions. A new numerical approach for calculating the wakes in such structures is proposed and implemented in the computer code ECHO(2D). The computation resource requirements for this approach are moderate and comparable to those for finding the wakes in 2D rotationally symmetric structures. Numerical examples obtained with the new numerical code are presented.
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.
Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations
International Nuclear Information System (INIS)
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.
Calculation of Free-Atom Fractions in Hydrocarbon-Fueled Rocket Engine Plume
Verma, Satyajit
2006-01-01
Free atom fractions (Beta) of nine elements are calculated in the exhaust plume of CH4- oxygen and RP-1-oxygen fueled rocket engines using free energy minimization method. The Chemical Equilibrium and Applications (CEA) computer program developed by the Glenn Research Center, NASA is used for this purpose. Data on variation of Beta in both fuels as a function of temperature (1600 K - 3100 K) and oxygen to fuel ratios (1.75 to 2.25 by weight) is presented in both tabular and graphical forms. Recommendation is made for the Beta value for a tenth element, Palladium. The CEA computer code was also run to compare with experimentally determined Beta values reported in literature for some of these elements. A reasonable agreement, within a factor of three, between the calculated and reported values is observed. Values reported in this work will be used as a first approximation for pilot rocket engine testing studies at the Stennis Space Center for at least six elements Al, Ca, Cr, Cu, Fe and Ni - until experimental values are generated. The current estimates will be improved when more complete thermodynamic data on the remaining four elements Ag, Co, Mn and Pd are added to the database. A critique of the CEA code is also included.
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)
Term structure of 4d-electron configurations and calculated spectrum in Sn-isonuclear sequence
International Nuclear Information System (INIS)
Theoretical calculations of term structure are carried out for the ground configurations 4dw, of atomic ions in the Sn isonuclear sequence. Atomic computations are performed to give a detailed account of the transitions in Sn+6 to Sn+13 ions. The spectrum is calculated for the most important excited configurations 4p5 4dn+1, 4dn-1 4f1, and 4dn-1 5p1 with respect to the ground configuration 4dn, with n=8-1, respectively. The importance of 4p-4d, 4d-4f, and 4d-5p transitions is stressed, as well as the need for the configuration-interaction CI treatment of the Δn=0 transitions. In the region of importance for extreme ultraviolet (EUV) lithography around 13.4nm, the strongest lines were expected to be 4dn-4p5 4dn+1 and 4dn-4dn-1 4f1
Atomic scale structure investigations of epitaxial Fe/Cr multilayers
International Nuclear Information System (INIS)
Fe/Cr multilayers were deposited by molecular beam epitaxy on the MgO(1 0 0) substrate. Structural properties of the samples were analyzed by low energy electron diffraction, high resolution transmission electron microscopy (HRTEM), as well as by X-ray reflectivity, conversion electron Mössbauer spectroscopy (CEMS) and Auger electron spectroscopy. Investigations revealed multilayered system built of well-ordered Fe and Cr thin films with (1 0 0) orientation. A high geometrical perfection of the system, i.e. planar form of interfaces and reproducible thickness of layers, was also proven. Fe/Cr interface roughness was determined to be 2–3 atomic layers. CEMS studies allowed to analyze at atomic scale the structure of buried Fe/Cr interfaces, as well as to distinguish origin of interface roughness. Roughnesses resulting from interface corrugations and from the Fe–Cr interdiffusion at interfaces were observed. Fe/Cr multilayers showed strong antiferromagnetic coupling of Fe layers.
Study of atomic structure of polycrystalline vanadium molybdate
International Nuclear Information System (INIS)
Atomic structure of polycrystalline V0.95Mo0.97O5 (V4+/V5+=0.6) was investigated by the methods of X-ray diffraction analysis, electron microdiffraction and high resolution electron microscopy. Lattice parameters: a=6.3340, b=4.0463, c=3.7255 A, α=90.0, β=107.3, γ=90.5 deg, sp.gr. P1, Z=1. Mo and V atoms substitute statistically each other in two independent octahedral positions: (0.4 Mo + 0.6 V4+) and (0.6 Mo + 0.4 V5+). The compound is refferred to V2O5 structural type
Dielectric band structure of crystals: General properties, and calculations for silicon
International Nuclear Information System (INIS)
We shift the dielectric band structure method, orginially proposed by Baldereschi and Tosatti for the description of microscopic electronic screening in crystals. Some general properties are examined first, including the requirements of causality and stability. The specific test case of silicon is then considered. Dielectric bands are calculated, according to several different prescriptions for the construction of the dielectric matrix. It is shown that the results allow a very direct appraisal of the screening properties of the system, as well as of the quality of the dielectric model adopted. The electronic charge displacement induced by γsub(25') and X3 phonon-like displacements of the atoms is also calculated and compared with the results of existent full self-consistent calculations. Conclusions are drawn on the relative accuracies of the dielectric band structures. (author)
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.
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,...
Structural and chemical characterization of complex nanomaterials at atomic resolution
Sanchez, Sergio I.
Catalytic and energetic nanomaterials are analyzed chemically and structurally in atomistic detail. Examination of the prototypical industrial catalyst Pt catalysts supported on gamma-Al2O3 using X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) revealed non-bulk-like behavior. Anomalous, temperature-dependent structural dynamics were characterized in the form of negative thermal expansion (NTE) and abnormal levels of disorder. To examine a less complex system, electrocatalytically-active, core-shell nanostructures assembled from Pt and Pd were synthesized and subsequently examined using spherical aberration-corrected STEM (Cs-STEM) and high-energy X-ray diffraction (XRD). Atomically resolved micrographs provide significant insight into the differences in crystallinity and metal-atom bonding between Pt and Pd. The apparent structural dichotomy between Pt and Pd was extended to studying the differences in nanostructure between other third row fcc transition metals (3M -- Ir, Pt, and Au) and their second row counterparts (2M -- Rh, Pd, and Ag). With the use of Cs-STEM and atomic pair distribution function (PDF) measurements it was determined that the Au, Pt and Ir nanocrystals were more crystalline than their Ag, Pd and Rh analogues and that the 3M series was capable of imparting its crystal structure onto the atoms from the 2M series. Lastly, we looked at highly-reactive Al crystals and their successive passivation by secondary transition metals (Cu, Ni, Ag, Pd, Au and Pt). Rather than affording a uniform, monolayer coverage, C s-STEM, XRD and energy dispersive X-ray spectroscopy revealed unalloyed, particulate deposits of the secondary metal on the Al.
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)
Atomic-scale observation of dynamical fluctuation and three-dimensional structure of gold clusters
Energy Technology Data Exchange (ETDEWEB)
Li, Junjie [Engineering Research Center for Nanophotonics and Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, North Zhongshan Road 3663, Shanghai 200062 (China); Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Yin, Deqiang [School of Manufacturing Science and Engineering, Sichuan University, Chengdu 610064 (China); Chen, Chunlin; Lin, Liyang; Wang, Zhongchang, E-mail: zcwang@wpi-aimr.tohoku.ac.jp [Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Li, Qiang [School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093 (China); Sun, Rong [Institute of Engineering Innovation, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Huang, Sumei, E-mail: smhuang@phy.ecnu.edu.cn [Engineering Research Center for Nanophotonics and Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, North Zhongshan Road 3663, Shanghai 200062 (China)
2015-02-28
Unravelling three-dimensional structures and dynamical fluctuation of metal nanoclusters is critical to understanding reaction process and the origin of catalytic activity in many heterogeneous catalytic systems. We obtain three-dimensional structures of ultra-small Au clusters by combining aberration-corrected scanning transmission electron microscopy, density functional theory calculations, and imaging simulations. The configurations of unique Au clusters are revealed at the atomic scale and the corresponding electronic states are given. The sequential observations reveal a transition of ultra-small Au clusters with about 25 atoms from a near-square to an elongated structure. We also find a transition from two dimensions to three dimensions for the Au clusters. The obtained three-dimensional geometry and associated electronic states help to clarify atomistic mechanism of shape- and number-dependent catalytic activities of Au clusters.
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.
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.
Dynamic calculation of structures in seismic zones. 2. ed.
International Nuclear Information System (INIS)
The aims of this book are both didactic and practical. It is therefore addressed to both experienced engineers and students. Some general information about earthquakes and their occurrence is first given. The problem of a simple oscillator is presented. In this way, the reader is provided with an insight into undestanding the dynamic phenomena taking place and is introduced to the concept of response spectra and to an intuitive comprehension of the behavior of structures during earthquakes. The next chapter is devoted to the cases most frequently encountered with multiple oscillator structures. Theoretical studies are based on the usual modal decomposition method. The various practical methods of calculation employed are then examined, emphasis being given to the various different stages involved and to which of them is the best suited for a particular type of structure. Advise is given on how to select the model whose behavior best describes the real structure, both manual and computer methods of calculation being envisaged
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
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
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.
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)
Masso, Majid
2012-01-01
Delaunay tessellation of the atomic coordinates for a crystallographic protein structure yields an aggregate of non-overlapping and space-filling irregular tetrahedral simplices. The vertices of each simplex objectively identify a quadruplet of nearest neighbor atoms in the protein. Here we apply Delaunay tessellation to 1417 high-resolution structures of single chains that share low sequence identity, for the purpose of determining the relative frequencies of occurrence for all possible nearest neighbor atomic quadruplet types. Alternative distributions are explored by varying two fundamental parameters: atomic alphabet selection and cutoff length for admissible simplex edges. The distributions are then converted to four-body potential functions by implementing the inverted Boltzmann principle, which requires calculating the distribution of the reference state. Two alternative definitions for the reference state are presented, which introduces a third parameter, and we derive and compare an array of such potential functions. These knowledge-based statistical potentials based on higher-order interactions complement and generalize the more commonly encountered atom-pair potentials, for which a number of approaches are described in the literature. PMID:23367374
International Nuclear Information System (INIS)
The interaction of an interstitial hydrogen atom with a screw dislocation in BCC iron has been determined using the first principles calculation. The calculation was carried out for a pair of screw dislocations using the large-scale supercell containing 231 atoms and 1 x 1 x 4 k-point samplings. It is found that a hydrogen atom at an octahedral site near the screw dislocation attracts the dislocation core under the applied shear stress condition. However, the resultant stress-strain relation in the presence of a hydrogen atom is found to be almost the same with that of no hydrogen case. This indicates clearly that a significant enhancement of dislocation mobility, previously reported in Al, is not observed in BCC iron. (author)
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...
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
Enumeration of structure-sensitive graphical subsets: Calculations
Marrifield, R. E.; Simmons, H. E.
1981-01-01
Numerical calculations are presented, for all connected graphs on six and fewer vertices, of the numbers of independent sets, connected sets, point and line covers, externally stable sets, kernels, and irredundant sets. With the exception of the number of kernels, the numbers of such sets are all highly structure-sensitive quantities.
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.)
Quasiparticle GW calculations within the GPAW electronic structure code
DEFF Research Database (Denmark)
Hüser, Falco
The GPAW electronic structure code, developed at the physics department at the Technical University of Denmark, is used today by researchers all over the world to model the structural, electronic, optical and chemical properties of materials. They address fundamental questions in material science...... 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...... respect to the system one wants to investigate by choosing a certain functional or by tuning parameters. A succesful alternative is the so-called GW approximation. It is mathematically precise and gives a physically well-founded description of the complicated electron interactions in terms of screening...
Structures of cefradine dihydrate and cefaclor dihydrate from DFT-D calculations
DEFF Research Database (Denmark)
van de Streek, Jacco; Rantanen, Jukka; Bond, Andrew D
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...... 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 in the...... zwitterionic form in the two dihydrate structures. A potential ambiguity concerning the orientation of the cyclohexadienyl ring in cefradine dihydrate is also clarified, and on the basis of the calculated energies it is shown that disorder should not be expected at room temperature. The DFT-D methods can be...
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
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
Vibrational and structural study of onopordopicrin based on the FTIR spectrum and DFT calculations.
Chain, Fernando E; Romano, Elida; Leyton, Patricio; Paipa, Carolina; Catalán, César A N; Fortuna, Mario; Brandán, Silvia Antonia
2015-11-01
In the present work, the structural and vibrational properties of the sesquiterpene lactone onopordopicrin (OP) were studied by using infrared spectroscopy and density functional theory (DFT) calculations together with the 6-31G(∗) basis set. The harmonic vibrational wavenumbers for the optimized geometry were calculated at the same level of theory. The complete assignment of the observed bands in the infrared spectrum was performed by combining the DFT calculations with Pulay's scaled quantum mechanical force field (SQMFF) methodology. The comparison between the theoretical and experimental infrared spectrum demonstrated good agreement. Then, the results were used to predict the Raman spectrum. Additionally, the structural properties of OP, such as atomic charges, bond orders, molecular electrostatic potentials, characteristics of electronic delocalization and topological properties of the electronic charge density were evaluated by natural bond orbital (NBO), atoms in molecules (AIM) and frontier orbitals studies. The calculated energy band gap and the chemical potential (μ), electronegativity (χ), global hardness (η), global softness (S) and global electrophilicity index (ω) descriptors predicted for OP low reactivity, higher stability and lower electrophilicity index as compared with the sesquiterpene lactone cnicin containing similar rings. PMID:26057092
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...
Sun, Dongqiang; Wang, Yongxin; Lu, Yanli; Chen, Zheng; Rao, Qinglei
2016-06-01
First-principles calculations was used to explore the influence of atom termination and stacking sequence on the interface strength and stability between θ‧(Al2Cu) precipitate and Al matrix along experimentally observed orientations, (001)θ‧/(001)Al and (010)θ‧/(010)Al interfaces. Six interfacial structures were modeled, and work of adhesion, bonding characters, number of valence electrons and thermal stability had been studied. Calculated results revealed that the Cu-terminated interface has larger work of adhesion than Al-terminated interface, and hollow site stacking sequence, with stronger bonding, is superior to top site stacking sequence, adhesion strength for coherent (001)θ‧/(001)Al interface is better than that for semi-coherent (010)θ‧/(010)Al interface. These differences are attributed to the bonding feature and number of valence electrons. Among the six interface models, the Cu-terminated (001)θ‧/(001)Al interface with hollow site stacking has the largest work of adhesion and the smallest interface energy, indicating that it has the best mechanical and thermodynamic properties.
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.
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. PMID:26930454
de Jong, Maarten; Qi, Liang; Olmsted, David L.; van de Walle, Axel; Asta, Mark
2016-03-01
A method is described for calculating the energetics of planar defects in alloys based on the special-quasirandom-structure (SQS) approach. We examine the accuracy of the approach employing atomistic calculations based on a classical embedded-atom-method (EAM) interatomic potential for hexagonal close packed (hcp) alloys, for which benchmark results can be obtained by direct configurational averaging. The results of these calculations demonstrate that the SQS-based approach can be employed to derive the concentration dependence of the energies of twin boundaries, unstable stacking faults, and surfaces to within an accuracy of approximately 10%. The SQS considered in this study contain up to 72 atoms and hence are small enough to be considered in first-principles density-functional-theory (DFT) based calculations. The application of the SQS-based approach in direct DFT-based calculations is demonstrated in a study of the concentration dependence of interfacial energies for {11 2 ¯1 } twins in hcp Ti-Al alloys.
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.
Local atomic arrangements and electronic structure of Zr-Ni-Al bulk metallic glass
International Nuclear Information System (INIS)
Internal energy of a bulk metallic glass (BMG) was investigated by making full use of its relevant crystals. The local atomic arrangements commonly existing both in the BMG and the relevant crystals were identified using experimentally determined radial distribution functions. The electronic structure of the relevant crystals was investigated by discrete variational X alpha (DVXα) cluster calculations and high-resolution photoemission spectroscopy. The present analysis on the electronic structure revealed that the simultaneous formations of characteristic cluster levels and a pseudogap at the Fermi level effectively reduce the internal energy to stabilize BMGs
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.
Atomic layer deposition in porous structures: 3D photonic crystals
International Nuclear Information System (INIS)
This paper reports recent results from studies of atomic layer deposition for the infiltration of three-dimensional photonic crystals. Infiltration of ZnS:Mn and TiO2 are reported for SiO2-based opal templates. It has been demonstrated that high filling fractions can be achieved and that the infiltrated material can be of high crystalline quality as assessed by photoluminescence measurements. The highly conformal and uniform coatings obtained in these studies are shown to contribute significantly to the photonic band gap properties. These investigations show the advantages of atomic layer deposition (ALD) as a flexible and practical pathway for attaining high performance photonic crystal structures and optical microcavities
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.
Spatial multimode structure of atom-generated squeezed light
Zhang, Mi; Lanning, R. Nicholas; Xiao, Zhihao; Dowling, Jonathan P.; Novikova, Irina; Mikhailov, Eugeniy E.
2016-01-01
We investigated the spatial distribution of quantum fluctuations in a squeezed vacuum field, generated via polarization self-rotation (PSR) interaction of an ensemble of Rb atoms and a strong near-resonant linearly polarized laser field. We found that the noise suppression is greatly effected by the transverse profile of a spatial mask, placed in both the squeezed field and the local oscillator, as well as its position along the focused beam near the focal point. These observations indicate the spatial multimode structure of the squeezed vacuum field. We have developed a theoretical model that describes the generation of higher-order Laguerre-Gauss modes as a result of PSR light-atom interaction. The prediction of this model is in a good qualitative agreement with the experimental measurements.
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
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.
International Nuclear Information System (INIS)
The fuel used for the research reactors of Japan Atomic Energy Research Institute (JAERI) is presently highly enriched uranium of 93%. However, the U.S. government (the supplier of fuel) is claiming to utilize low or medium enriched uranium from the viewpoint of resistivity to nuclear proliferation, and the availability of highly enriched uranium is becoming hard owing to the required procedure. This report is described on the results of nuclear calculation which is the basis of fuel design in the countermeasures to the reduction of enrichment. The basic conception in the reduction of enrichment is three-fold: to lower the latent potential of nuclear proliferation as far as possible, to hold the present reactor performance as far as possible, and to limit the reduction in the range which is not accompanied by the modification of reactor core construction and cooling system. This time, the increase of the density and thickness of fuel plates and the effect of enrichment change to 45% on reactivity and neutron flux were investigated. The fuel of UAl sub(x) - Al system was assumed, which was produced by powder metallurgical method. The results of investigations on JRR-2 and JMTR reactors revealed that 45% enriched fuel does not affect the performances much. However, deterioration of the performances is not neglegible if further reduction is needed. In future, the influence of the burn-up effect of fuel on the life of reactor cores must be investigated. (Wakatsuki, Y.)
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
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.
Statistical learning for alloy design from electronic structure calculations
Broderick, Scott R.
The objective of this thesis is to explore how statistical learning methods can contribute to the interpretation and efficacy of electronic structure calculations. This study develops new applications of statistical learning and data mining methods to both semi-empirical and density functional theory (DFT) calculations. Each of these classes of electronic structure calculations serves as templates for different data driven discovery strategies for materials science applications. In our study of semi-empirical methods, we take advantage of the ability of data mining methods to quantitatively assess high dimensional parameterization schemes. The impact of this work includes the development of accelerated computational schemes for developing reduced order models. Another application is the use of these informatics based techniques to serve as a means for estimating parameters when data for such calculations are not available. Using density of states (DOS) spectra derived from DFT calculations we have demonstrated the classification power of singular value decomposition methods to accurately develop structural and stoichiometric classifications of compounds. Building on this work we have extended this analytical strategy to apply the predictive capacity of informatics methods to develop a new and far more robust modeling approach for DOS spectra, addressing an issue that has gone relatively unchallenged over two decades. By exploring a diverse array of materials systems (metals, ceramics, different crystal structures) this work has laid the foundations for expanding the linkages between statistical learning and statistical thermodynamics. The results of this work provide exciting new opportunities in computational based design of materials that have not been explored before.
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
Microscopic calculations of nuclear structure and nuclear correlations
International Nuclear Information System (INIS)
A major goal in nuclear physics is to understand how nuclear structure comes about from the underlying interactions between nucleons. This requires modelling nuclei as collections of strongly interacting particles. Using realistic nucleon-nucleon potentials, supplemented with consistent three-nucleon potentials and two-body electroweak current operators, variational Monte Carlo methods are used to calculate nuclear ground-state properties, such as the binding energy, electromagnetic form factors, and momentum distributions. Other properties such as excited states and low-energy reactions are also calculable with these methods
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...
International Nuclear Information System (INIS)
We investigate the initial and secondary oxidation products on the Si(111)-(7 × 7) surface at room-temperature using atomic force microscopy (AFM) and density functional theory calculations. At the initial oxidation stages, we find that there are two types of bright spots in AFM images. One of them is identified as a Si adatom with one O atom inserted into one of the backbonds, while the other is ascribed to a Si adatom with two inserted O atoms. We observe that the latter one turns into the secondary oxidation product by a further coming O2 molecule, which appears as a more protruded bright spot. The atomic configuration of this product is identified as Si adatom whose top and all three backbonds make bonds with O atoms. The appearances of initial and secondary oxidation products are imaged as bright and dark sites by scanning tunneling microscopy, respectively. It is revealed that AFM gives us the topographic information close to the real atomic corrugation of adsorbed structures on the semiconductor surfaces
The structure determination of Al20Cu2Mn3 by near atomic resolution chemical mapping
International Nuclear Information System (INIS)
Highlights: • The structure of Al20Cu2Mn3 with a space group of Bbmm is completely determined. • The actual formula of Al20Cu2Mn3 is Al31Cu3Mn5. • Al20Cu2Mn3 is formed by a parallel tessellation of hexagon subunits. • Al20Cu2Mn3 is prone to twinning by an alternate tessellation of hexagon subunits. • The Al20Cu2Mn3 is coherent with α-Al along its longitudinal axis. - Abstract: Al20Cu2Mn3 phase is one kind of common dispersoids in aluminum alloys; however, the atomic arrangement of Al20Cu2Mn3 has not yet been clearly identified. Combining the atomic resolution high angle annular dark field and chemical composition quantitative results, three structure models of Al20Cu2Mn3 were derived basing on the isostructural Mn11Ni4Al60. The formation enthalpies and total energy were calculated using the first-principles approach. The structure of the Al20Cu2Mn3 phase with the minimal energy was identified, giving a fully relaxed structure with lattice parameters of a = 23.98 Å, b = 12.54 Å, c = 7.66 Å, which belongs to a space group of Bbmm. The determined structure is in excellent agreement with the near atomic resolution chemical mapping results
Whitford, Paul C.; Jeffrey K Noel; Gosavi, Shachi; Schug, Alexander; Sanbonmatsu, Kevin Y.; Onuchic, José N.
2009-01-01
Protein dynamics take place on many time and length scales. Coarse-grained structure-based (Gō) models utilize the funneled energy landscape theory of protein folding to provide an understanding of both long time and long length scale dynamics. All-atom empirical forcefields with explicit solvent can elucidate our understanding of short time dynamics with high energetic and structural resolution. Thus, structure-based models with atomic details included can be used to bridge our understanding...
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.
Atomic structure of Re-Si amorphous alloys
International Nuclear Information System (INIS)
The atomic structure of Re100-xSix (x=0, 4, 11, 20, 31, 47, 54, 70, 82, 88, 100) amorphous alloys (AA) was studied by X-ray diffraction. In as-quenched alloys two amorphous phase were observed: the AI-phase-10-90 at.% Si and AII-phase-45-100 at.% Si, especially that in the composition range 45-90 at.% Si is the coexistence of two phase AI and AII. A comparison of the short range order parameters of the AA and those of the corresponding crystalline compounds has been done. The short-range order of AI-phase and coordination polyhedrons of Re5Si3, ReSi2 compounds is similar. Contrary to the Gaskell's model for metal-metalloid AA (trigonal prismatic structural unit) it seems to be tetragonal antiprism. The structure of AII-phase is the same as a-Si. (orig.)
Suleiman, Mohammed S. H.; Joubert, Daniel P.
2015-11-01
In the present work, the atomic and the electronic structures of Au3N, AuN and AuN2 are investigated using first-principles density-functional theory (DFT). We studied cohesive energy vs. volume data for a wide range of possible structures of these nitrides. Obtained data were fitted to a Birch-Murnaghan third-order equation of state (EOS) so as to identify the most likely candidates for the true crystal structure in this subset of the infinite parameter space, and to determine their equilibrium structural parameters. The analysis of the electronic properties was achieved by the calculations of the band structure and the total and partial density of states (DOS). Some possible pressure-induced structural phase transitions have been pointed out. Further, we carried out GW0 calculations within the random-phase approximation (RPA) to the dielectric tensor to investigate the optical spectra of the experimentally suggested modification: Au3N(D09). Obtained results are compared with experiment and with some available previous calculations.
Wang, Junmei; Cieplak, Piotr; Li, Jie; Hou, Tingjun; Luo, Ray; Duan, Yong
2011-03-31
In this work, four types of polarizable models have been developed for calculating interactions between atomic charges and induced point dipoles. These include the Applequist, Thole linear, Thole exponential model, and the Thole Tinker-like. The polarizability models have been optimized to reproduce the experimental static molecular polarizabilities obtained from the molecular refraction measurements on a set of 420 molecules reported by Bosque and Sales. We grouped the models into five sets depending on the interaction types, that is, whether the interactions of two atoms that form the bond, bond angle, and dihedral angle are turned off or scaled down. When 1-2 (bonded) and 1-3 (separated by two bonds) interactions are turned off, 1-4 (separated by three bonds) interactions are scaled down, or both, all models including the Applequist model achieved similar performance: the average percentage error (APE) ranges from 1.15 to 1.23%, and the average unsigned error (AUE) ranges from 0.143 to 0.158 Å(3). When the short-range 1-2, 1-3, and full 1-4 terms are taken into account (set D models), the APE ranges from 1.30 to 1.58% for the three Thole models, whereas the Applequist model (DA) has a significantly larger APE (3.82%). The AUE ranges from 0.166 to 0.196 Å(3) for the three Thole models, compared with 0.446 Å(3) for the Applequist model. Further assessment using the 70-molecule van Duijnen and Swart data set clearly showed that the developed models are both accurate and highly transferable and are in fact have smaller errors than the models developed using this particular data set (set E models). The fact that A, B, and C model sets are notably more accurate than both D and E model sets strongly suggests that the inclusion of 1-2 and 1-3 interactions reduces the transferability and accuracy. PMID:21391553
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.
Atomic structures of icosahedral phases of type F and dislocations
International Nuclear Information System (INIS)
The object of this thesis is the study of atomic structures of icosahedral phases of type F and their dislocations. In this study, we have first built a prototypical structure that describes the already known F type icosahedral phases. In order to check it we synthesized some of the new compositions predicted by this model. This synthesis led to the discovery of two new quasi-periodical phases of the stoichiometry Al66,08Cu21,35Mn8,29Fe4,28. One of these phases is icosahedral (metastable) of type F and the other one is decagonal (stable). A F-IQC phase is present on these compounds that have a different composition with respect to the ones already studied for the system (Al,Pd,Fe). Globally, these experimental results on new icosahedral phases allowed to prove the viability of the model: on the three samples of new composition, two of them have shown the existence of icosahedral phases of type F and the third one has given a decagonal phase, in relation of canonical orientation with the icosahedral metastable phase (10-fold axis parallel with 5-fold axis). Using this reliable model, we have been able to introduce dislocations. We could thus provide the geometry of dislocations (outside the dislocation core) at atomic scale for F-IQC phases. On this structure we have also identified the distributions of phasons and given some elements of answer for the global dislocations moves. (author)
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
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).
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.
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.
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...
Thick-Restart Lanczos Method for Electronic Structure Calculations
International Nuclear Information System (INIS)
This paper describes two recent innovations related to the classic Lanczos method for eigenvalue problems, namely the thick-restart technique and dynamic restarting schemes. Combining these two new techniques we are able to implement an efficient eigenvalue problem solver. This paper will demonstrate its effectiveness on one particular class of problems for which this method is well suited: linear eigenvalue problems generated from non-self-consistent electronic structure calculations
International Nuclear Information System (INIS)
The Density-Functional method, with Linear Combination of Atomic Orbitals, has been applied to eight crystals; the lattice equilibrium parameters, and the lattice formation energies have been calculated at the Hartree-Fock level (HF), at the hybrid Hartree-Fock Density-Functional level (DFT/HF), and at the Kohn-Sham Density-Functional level (DFT). The band structures and the electronic charge distributions calculated at the DFT and HF levels are compared
International Nuclear Information System (INIS)
We have developed a theoretical model of ion-atom collisions based on the time-dependent density-functional theory. We solve the time-dependent Kohn-Sham equation for electrons employing the real-space and real-time method, while the ion dynamics are described in classical mechanics by the Ehrenfest method. Taking advantage of the real-space grid method, we introduce the 'coordinate space translation' technique to allow one to focus on a certain space of interest. Benchmark calculations are given for collisions between proton and argon over a wide range of impact energy. Electron transfer total cross sections showed a fairly good agreement with available experimental data. -- Highlights: → We have developed a theoretical model of ion-atom collisions based on TDDFT. → The coordinate space translation technique was introduced into present calculation. → Charge transfer cross sections showed a good agreement with available experimental data.
Pore pressure calculation of the UO2 high burnup structure
International Nuclear Information System (INIS)
Highlights: • Pore pressure is calculated based on local burnup, density and porosity. • Ronchi's equations of state are used instead of van der Waals’ equation. • Pore pressure increases as HBS transformation begins and then stays constant. • A best approximated parameter used for pore pressure calculation is recommended. -- Abstract: UO2 high burnup structure has an important impact on fuel behavior, especially in case of reactivity initiated accident (RIA). Pore relaxation enhances local fuel swelling and puts additional load to the fuel cladding, which makes fuel more susceptible to pellet–cladding mechanical interaction induced failure. Therefore, pore pressure calculation becomes vital when evaluating the fuel failure. In this paper pore pressure is calculated as a function of pellet radial local burnup based on the basic characteristics of HBS using Ronchi's correlation. The results indicate that pore pressure will approach a stable value as HBS is developing. A best approximated C value of 55 N/m is recommended for pore pressure calculation
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.
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…
International Nuclear Information System (INIS)
The results of semiclassical calculations on one-, two-, three-, and four-photon absorption in truncated models of the hydrogen atom are presented. The temporal behavior near ''resonance'' is confirmed to be Rabi-like, with a transition probability given by P (t) = ]γ2/[(ω0/N + delta - ω)2 + γ2
International Nuclear Information System (INIS)
Highlights: • Determination of effective atomic and effective electron number is very important. • The Direct-Zeff software calculates effective atomic and effective electron number. • The Direct-Zeff software calculates for total and partial photon interactions. • Calculations of The Direct-Zeff are in good agreement with experimental results. - Abstract: Determination of the mass attenuation coefficient, μ/ρ, the effective atomic number, Zeff, and the effective electron number, Neff, is very important in the fields of nuclear diagnostics, radiation protection, nuclear medicine and radiation dosimetry. In this work, the Direct-Zeff software was developed for the computation of the mass attenuation coefficient, the effective atomic number and the effective electron number per unit mass in the energy range 1 keV–100 GeV. The values of the Zeff, Neff and μ/ρ can be determined for total photon interaction with and without coherent interaction as well as partial photon interactions such as coherent scattering, incoherent scattering, photoelectric absorption and pair production by using the Direct-Zeff software. The accuracy of the Direct-Zeff software has been demonstrated by comparing the calculated data and the experimental values for the various materials. The Direct-Zeff software can be freely obtained by contacting with the authors
Salvat, Francesc; Jablonski, Aleksander; Powell, Cedric J.
2005-01-01
The FORTRAN 77 code system ELSEPA for the calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules is presented. These codes perform relativistic (Dirac) partial-wave calculations for scattering by a local central interaction potential V(r). For atoms and ions, the static-field approximation is adopted, with the potential set equal to the electrostatic interaction energy between the projectile and the target, plus an approximate local exchange interaction when the projectile is an electron. For projectiles with kinetic energies up to 10 keV, the potential may optionally include a semiempirical correlation-polarization potential to describe the effect of the target charge polarizability. Also, for projectiles with energies less than 1 MeV, an imaginary absorptive potential can be introduced to account for the depletion of the projectile wave function caused by open inelastic channels. Molecular cross sections are calculated by means of a single-scattering independent-atom approximation in which the electron density of a bound atom is approximated by that of the free neutral atom. Elastic scattering by individual atoms in solids is described by means of a muffin-tin model potential. Partial-wave calculations are feasible on modest personal computers for energies up to about 5 MeV. The ELSEPA code also implements approximate factorization methods that allow the fast calculation of elastic cross sections for much higher energies. The interaction model adopted in the calculations is defined by the user by combining the different options offered by the code. The nuclear charge distribution can be selected among four analytical models (point nucleus, uniformly charged sphere, Fermi's distribution and Helm's uniform-uniform distribution). The atomic electron density is handled in numerical form. The distribution package includes data files with electronic densities of neutral atoms of the elements hydrogen to lawrencium ( Z=1
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.
Order and disorder in quaternary atomic laminates from first-principles calculations.
Dahlqvist, Martin; Rosen, Johanna
2015-12-21
We report on the phase stability of chemically ordered and disordered quaternary MAX phases - TiMAlC, TiM2AlC2, MTi2AlC2, and Ti2M2AlC3 where M = Zr, Hf (group IV), M = V, Nb, Ta (group V), and M = Cr, Mo, W (group VI). At 0 K, layered chemically ordered structures are predicted to be stable for M from groups V and VI. By taking into account the configurational entropy, an order-disorder temperature Tdisorder can be estimated. TiM2AlC2 (M = Cr, Mo, W) and Ti2M2AlC3 (M = Mo, W) are found with Tdisorder > 1773 K and are hence predicted to be ordered at the typical bulk synthesis temperature of 1773 K. Other ordered phases, even though metastable at elevated temperatures, may be synthesized by non-equilibrium methods such as thin film growth. Furthermore, phases predicted not to be stable in any form at 0 K can be stabilized at higher temperatures in a disordered form, being the case for group IV, for MTi2AlC2 (M = V, Cr, Mo), and for Ti2M2AlC3 (M = V, Ta). The stability of the layered ordered structures with M from group VI can primarily be explained by Ti breaking the energetically unfavorable stacking of M and C where M is surrounded by C in a face-centered cubic configuration, and by M having a larger electronegativity than Al resulting in a fewer electrons available for populating antibonding Al-Al orbitals. The results show that these chemically ordered quaternary MAX phases allow for new elemental combinations in MAX phases, which can be used to add new properties to this family of atomic laminates and in turn prospects for tuning these properties. PMID:26565395
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.
International Nuclear Information System (INIS)
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
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.
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
{2p_\\pi}-{2p_\\sigma} crossing in heavy symmetric ion-atom collisions: I. Level structure
Morovi´c, Tihomir; Sepp, Wolf-Dieter; Fricke, Burkhard
1982-01-01
Ab initio self-consistent DFS calculations are performed for five different symmetric atomic systems from Ar-Ar to Pb-Pb. The level structure for the {2p_\\pi}-{2p_\\sigma} crossing as function of the united atomic charge Z_u is studied and interpreted. Manybody effects, spin-orbit splitting, direct relativistic effects as well as indirect relativistic effects are differently important for different Z_u. For the I-I system a comparison with other calculations is given.
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. PMID:24052052
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...
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...
Hyperfine structure near infrared spectrum of atomic iodine
International Nuclear Information System (INIS)
The hyperfine structure of spectral lines of neutral iodine (II) in the wavenumber region from 11 300 cm−1 to 13 000 cm−1 was studied using optical heterodyne concentration modulation absorption spectroscopy with a tunable single-mode cw Ti:Sapphire laser. The iodine atoms were produced and excited by a discharge operated in a mixture of helium and iodine vapor. A total of 89 lines were observed and the hyperfine structure of 45 of these lines was studied. For 40 lines, the hyperfine structure was not previously known. The magnetic dipole and the electric quadrupole hyperfine structure constants of 18 even and 28 odd levels were extracted. The constants of one even level and of 16 odd levels are presented for the first time. - Highlights: • Absorption spectrum of neutral iodine (II) between 11 300 cm−1 and 13 000 cm−1. • The hyperfine structures of II are resolved for 45 lines. • Magnetic dipole and the electric quadrupole constants are obtained. • Constants of some levels are newly reported
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.
Atomic structures of a liquid-phase bonded metal/nitride heterointerface
Kumamoto, Akihito; Shibata, Naoya; Nayuki, Kei-Ichiro; Tohei, Tetsuya; Terasaki, Nobuyuki; Nagatomo, Yoshiyuki; Nagase, Toshiyuki; Akiyama, Kazuhiro; Kuromitsu, Yoshirou; Ikuhara, Yuichi
2016-03-01
Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices.
Atomic structures of a liquid-phase bonded metal/nitride heterointerface.
Kumamoto, Akihito; Shibata, Naoya; Nayuki, Kei-Ichiro; Tohei, Tetsuya; Terasaki, Nobuyuki; Nagatomo, Yoshiyuki; Nagase, Toshiyuki; Akiyama, Kazuhiro; Kuromitsu, Yoshirou; Ikuhara, Yuichi
2016-01-01
Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices. PMID:26961157
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.
International Nuclear Information System (INIS)
The interfacial atomic structure and misfits of Ω precipitates formed in the face-centered cubic Al in the Al–Cu–Mg–Ag alloy have been determined by combining scanning transmission electron microscopy (STEM) Z-contrast imaging with chemical analysis and ab initio density functional theory (DFT) calculations. Precipitates of several thicknesses formed after heat treatment at 250 °C, starting from 0 to 2 unit cells of Ω phase, were examined by STEM in four different projections. The results show that a remarkably stable double-layered interface is formed at all observed thicknesses, which separates the Ω phase from the Al matrix. The outermost interfacial layer next to Al is composed of Ag atoms in a hexagonal structure and Mg or Cu atoms below the center of the hexagon. Structural models constructed based on the experimental data were relaxed using DFT-based molecular dynamics calculations. The results show that interfacial Mg atoms, together with Ag atoms, greatly stabilize the interface structure and consequently the Ω phase on the Al {1 1 1} habit planes. Comparison between the measured and calculated precipitate misfit along the thickness direction suggests that atomic substitutions of light atoms, Al and Mg, at the interface mediate the misfit strain and free energy, which is further supported by experimental evidence obtained from STEM. Thus, we have identified here: (i) the driving force for the Ag and Mg segregation in the formation of the Ω phase; (ii) the precipitation sequence characterized by a stable interfacial double-layer; and (iii) an interfacial substitution mechanism for misfit accommodation
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)
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.
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 structure and electronic states of extended defects in silicon
International Nuclear Information System (INIS)
Defects in silicon like dislocations, grain boundaries, silicide precipitates, etc. are spatially extended and associated with a large number of electronic states in the band gap. Our knowledge on the relation between atomic structure and electronic states of these extended defects presently starts to grow by applying high-resolution electron microscopy (HRTEM) and deep level transient spectroscopy (DLTS) in combination with numerical simulations. While by means of HRTEM details of structure can be studied, DLTS has been shown to allow for a classification of extended defect states into bandlike and localized. Moreover, this method opens the perspective to distinguish between trap-like and recombination-like electrical activity. In this paper, we emphasize the particular role of nickel and copper silicide precipitates, since in their cases structural features could be successfully related to specific DLTS line characteristics. Rapid quenching from high diffusion temperatures prevents decoration of platelet-shaped NiSi2 and Cu3Si precipitates with other impurities. This allows to study their intrinsic electrical activity. Comparison of experimental results with numerical simulations enables identification of structural units originating electrical activity and yields first evaluations of extended defect parameters. Accordingly, e.g., in the case of as-quenched NiSi2 it is the dislocation bounding the platelet that provides a one-dimensional distribution of deep electronic states
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.
Mechanical and structural characterization of atomic layer deposition-based ZnO films
International Nuclear Information System (INIS)
Zinc oxide thin films were deposited by atomic layer deposition (ALD). The structural and mechanical properties of the thin films were investigated by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and nanoindentation. Diethyl zinc was used as the chemical precursor for zinc and water vapor was used as the oxidation agent. The samples were deposited at 150 °C and at a pressure of 2.1 × 10−1 Torr in the ALD reactor. A growth rate of 2 Å per cycle was calculated in the ALD process window. The Nano Indenter XP was used in conjunction with the continuous stiffness method in depth control mode in order to measure and to analyze the mechanical properties of hardness and modulus of ALD ZnO thin film samples. For comparison, we benchmarked the mechanical properties of single crystal bulk ZnO samples against those of our ALD ZnO thin films
Mechanical and structural characterization of atomic layer deposition-based ZnO films
Tapily, K.; Gu, D.; Baumgart, H.; Namkoong, G.; Stegall, D.; Elmustafa, A. A.
2011-11-01
Zinc oxide thin films were deposited by atomic layer deposition (ALD). The structural and mechanical properties of the thin films were investigated by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and nanoindentation. Diethyl zinc was used as the chemical precursor for zinc and water vapor was used as the oxidation agent. The samples were deposited at 150 °C and at a pressure of 2.1 × 10-1 Torr in the ALD reactor. A growth rate of 2 Å per cycle was calculated in the ALD process window. The Nano Indenter XP was used in conjunction with the continuous stiffness method in depth control mode in order to measure and to analyze the mechanical properties of hardness and modulus of ALD ZnO thin film samples. For comparison, we benchmarked the mechanical properties of single crystal bulk ZnO samples against those of our ALD ZnO thin films.
Energy Technology Data Exchange (ETDEWEB)
Babilas, Rafał, E-mail: rafal.babilas@polsl.pl
2015-09-15
The atomic structure of Fe{sub 70}Nb{sub 10}B{sub 20} alloy in “as-cast” state and after annealing was investigated using high-energy X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and high resolution transmission electron microscopy (HRTEM). The HRTEM observations allowed to indicate some medium-range order (MRO) regions about 2 nm in size and formation of some kinds of short-range order (SRO) structures represented by atomic clusters with diameter ca. 0.5 nm. The Reverse Monte Carlo (RMC) method basing on the results of XRD measurements was used in modeling the atomic structure of Fe-based alloy. The structural model was described by peak values of partial pair correlation functions and coordination numbers determined by Mössbauer spectroscopy investigations. The three-dimensional configuration box of atoms was obtained from the RMC simulation and the representative Fe-centered clusters were taken from the calculated structure. According to the Gonser et al. approach, the measured spectra of alloy studied were decomposed into 5 subspectra representing average Fe–Fe coordination numbers. Basing on the results of disaccommodation of magnetic permeability, which is sensitive to the short order of the random packing of atoms, it was stated that an occurrence of free volume is not detected after nanocrystallization process. - Highlights: • Atomic cluster model of amorphous structure was proposed for studied glassy alloy. • Short range order (ca. 0.5 nm) regions interpreted as clusters were identified by HREM. • Clusters correspond to coordination numbers (N = 4,6,8,9) calculated by using Gonser approach. • Medium-range order (ca. 2 nm) could be referred to few atomic clusters. • SRO regions are able to grow up as nuclei of crystalline bcc Fe and iron borides. • Crystalline particles have spherical morphology with an average diameter of 20 nm.
International Nuclear Information System (INIS)
The atomic structure of Fe70Nb10B20 alloy in “as-cast” state and after annealing was investigated using high-energy X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and high resolution transmission electron microscopy (HRTEM). The HRTEM observations allowed to indicate some medium-range order (MRO) regions about 2 nm in size and formation of some kinds of short-range order (SRO) structures represented by atomic clusters with diameter ca. 0.5 nm. The Reverse Monte Carlo (RMC) method basing on the results of XRD measurements was used in modeling the atomic structure of Fe-based alloy. The structural model was described by peak values of partial pair correlation functions and coordination numbers determined by Mössbauer spectroscopy investigations. The three-dimensional configuration box of atoms was obtained from the RMC simulation and the representative Fe-centered clusters were taken from the calculated structure. According to the Gonser et al. approach, the measured spectra of alloy studied were decomposed into 5 subspectra representing average Fe–Fe coordination numbers. Basing on the results of disaccommodation of magnetic permeability, which is sensitive to the short order of the random packing of atoms, it was stated that an occurrence of free volume is not detected after nanocrystallization process. - Highlights: • Atomic cluster model of amorphous structure was proposed for studied glassy alloy. • Short range order (ca. 0.5 nm) regions interpreted as clusters were identified by HREM. • Clusters correspond to coordination numbers (N = 4,6,8,9) calculated by using Gonser approach. • Medium-range order (ca. 2 nm) could be referred to few atomic clusters. • SRO regions are able to grow up as nuclei of crystalline bcc Fe and iron borides. • Crystalline particles have spherical morphology with an average diameter of 20 nm
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
Hyperfine-structure calculations of excited levels in neutral scandium
International Nuclear Information System (INIS)
The multi-configuration Dirac-Fock model is used to evaluate the magnetic dipole hyperfine interaction constants of the 3d4s('1D)4p 2Do3/2,5/2, 3d4s(3D)4p 4Fo9/2, 3d4s(1D)4p 2Fo5/2,-7/2 and 3d2(1D)4s 2D3/2,5/2 levels of atomic scandium. The wavefunctions are obtained with the active space expansion method, where configuration state functions of a specific parity and J value are generated by substitutions from the reference configurations to an active set of orbitals. The active set is then increased in a systematic way, allowing the convergence of the expectation values to be monitored. The calculated magnetic dipole hyperfine interaction constants are compared with experimentally determined values. On the grounds of the level of agreement between experiment and theory, we confirm three of the hypothetical A-values, previously deduced from high-resolution Fourier transform spectroscopy. (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.
Atomic and electronic structures of a-SiC:H from tight-binding molecular dynamics
Ivashchenko, V I; Shevchenko, V I; Ivashchenko, L A; Rusakov, G V
2003-01-01
The atomic and electronic properties of amorphous unhydrogenated (a-SiC) and hydrogenated (a-SiC:H) silicon carbides are studied using an sp sup 3 s sup * tight-binding force model with molecular dynamics simulations. The parameters of a repulsive pairwise potential are determined from ab initio pseudopotential calculations. Both carbides are generated from dilute vapours condensed from high temperature, with post-annealing at low temperature for a-SiC:H. A plausible model for the inter-atomic correlations and electronic states in a-SiC:H is suggested. According to this model, the formation of the amorphous network is weakly sensitive to the presence of hydrogen. Hydrogen passivates effectively only the weak bonds of threefold-coordinated atoms. Chemical ordering is very much affected by the cooling rate and the structure of the high-temperature vapour. The as-computed characteristics are in rather good agreement with the results for a-SiC and a-Si:H from ab initio calculations.
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.
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.
Automating the parallel processing of fluid and structural dynamics calculations
Arpasi, Dale J.; Cole, Gary L.
1987-01-01
The NASA Lewis Research Center is actively involved in the development of expert system technology to assist users in applying parallel processing to computational fluid and structural dynamic analysis. The goal of this effort is to eliminate the necessity for the physical scientist to become a computer scientist in order to effectively use the computer as a research tool. Programming and operating software utilities have previously been developed to solve systems of ordinary nonlinear differential equations on parallel scalar processors. Current efforts are aimed at extending these capabilties to systems of partial differential equations, that describe the complex behavior of fluids and structures within aerospace propulsion systems. This paper presents some important considerations in the redesign, in particular, the need for algorithms and software utilities that can automatically identify data flow patterns in the application program and partition and allocate calculations to the parallel processors. A library-oriented multiprocessing concept for integrating the hardware and software functions is described.
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
Capelli, Silvia C; Hans-Beat Bürgi; Birger Dittrich; Simon Grabowsky; Dylan Jayatilaka
2014-01-01
Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-made ab initio quantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements,...
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...
The International Atomic Energy Agency: Structure, organs, and practice
International Nuclear Information System (INIS)
As a special organization of the UN system the International Atomic Energy Agency (IAEA) bears world-wide responsibility for the promotion of peaceful uses of nuclear power as well as for the control of preventing its misuse for non-peaceful purposes. Based on this fundamental objective of the IAEA a survey of structure, organs and practice of the Agency is given. Particularly, those special programmes are detailed which are of importance to the use of nuclear power for energy generation, and those contributions of the IAEA are concerned which it has to make as the international control authority to prevent the proliferation of nuclear weapons. In conclusions, the future activities of the IAEA and the cooperation of the GDR with the IAEA are dealt with. (author)
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
Electronic structure of alkali metal hydrides on data of cluster calculations by LCAO MO SCF CNDO
International Nuclear Information System (INIS)
The results of quantum-chemical study in where by M = Li, Na, K, Rb and Cs, are presented. The calculation expresses the expected electron density distributions in hydrides on the hydrogen and metal atoms as well as the energy characteristics: M-H, M-M and compounds binding energies. The latter ones qualitatively correlate with the binding energies of LiH-CsH compounds. The calculated values for the Fermi energy and the width of the forbidden zone at the Fermi level make it possible to suppose that the ideally formed lithium hydride crystal will be characterized by the highest electrical resistance. It is established that quantum-chemical characteristics of the MH hydrides structure change nonmonotonously by transfer from Li to Cs
Structure of Self-Assembled Mn Atom Chains on Si(001).
Villarreal, R; Longobardi, M; Köster, S A; Kirkham, Ch J; Bowler, D; Renner, Ch
2015-12-18
Mn has been found to self-assemble into atomic chains running perpendicular to the surface dimer reconstruction on Si(001). They differ from other atomic chains by a striking asymmetric appearance in filled state scanning tunneling microscopy (STM) images. This has prompted complicated structural models involving up to three Mn atoms per chain unit. Combining STM, atomic force microscopy, and density functional theory we find that a simple necklacelike chain of single Mn atoms reproduces all their prominent features, including their asymmetry not captured by current models. The upshot is a remarkably simpler structure for modeling the electronic and magnetic properties of Mn atom chains on Si(001). PMID:26722930
Monte Carlo calculation of the collision density of superthermal produced H atoms in thermal H2 gas
Panarese, A
2011-01-01
We propose a simple and reliable method to study the collision density of H atoms following their production by chemical mechanisms. The problem is relevant to PDR's, shocks, photospheres, atmospheric entry problems. We show that the thermalization of H atoms can be conveniently studied by a simple method and set the basis for further investigations. Besides our aims are also to review the theoretical basis, the limitation of simpler approaches and address the analogue problems in neutronics. The method adopted is Monte Carlo method including the thermal distri- bution of background molecules. The transport cross section is determined by the inversion of transport data. Plots of the collisions density of H atoms in H2 gas are calculated and discussed also in the context of simple theories. The application of the results to astrophysical problems is outlined.
International Nuclear Information System (INIS)
Density functional theory (DFT) is the most widely used ab initio method in material simulations. It accounts for 75% of the NERSC allocation time in the material science category. The DFT can be used to calculate the electronic structure, the charge density, the total energy and the atomic forces of a material system. With the advance of the HPC power and new algorithms, DFT can now be used to study thousand atom systems in some limited ways (e.g, a single selfconsistent calculation without atomic relaxation). But there are many problems which either requires much larger systems (e.g, >100,000 atoms), or many total energy calculation steps (e.g. for molecular dynamics or atomic relaxations). Examples include: grain boundary, dislocation energies and atomic structures, impurity transport and clustering in semiconductors, nanostructure growth, electronic structures of nanostructures and their internal electric fields. Due to the O(N3) scaling of the conventional DFT algorithms (as implemented in codes like Qbox, Paratec, Petots), these problems are beyond the reach even for petascale computers. As the proposed petascale computers might have millions of processors, new computational paradigms and algorithms are needed to solve the above large scale problems. In particular, O(N) scaling algorithms with parallelization capability up to millions of processors are needed. For a large material science problem, a natural approach to achieve this goal is by divide-and-conquer method: to spatially divide the system into many small pieces, and solve each piece by a small local group of processors. This solves the O(N) scaling and the parallelization problem at the same time. However, the challenge of this approach is for how to divide the system into small pieces and how to patch them up without the trace of the spatial division. Here, we present a linear scaling 3 dimensional fragment (LS3DF) method which uses a novel division-patching scheme that cancels out the artificial
Brachytherapy structural shielding calculations using Monte Carlo generated, monoenergetic data
International Nuclear Information System (INIS)
: The data of this work allow for the accurate calculation of structural shielding thickness, taking into account the spectral variation with shield thickness, and broad beam conditions, in a realistic geometry. The simplicity of calculations also obviates the need for the use of crude transmission data estimates such as the half and tenth value layer indices. Although this study was primarily designed for brachytherapy, results might also be useful for radiology and nuclear medicine facility design, provided broad beam conditions apply
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
Chemical structure imaging of a single molecule by atomic force microscopy at room temperature
Iwata, Kota; Yamazaki, Shiro; Mutombo, Pingo; Hapala, Prokop; Ondráček, Martin; Jelínek, Pavel; Sugimoto, Yoshiaki
2015-07-01
Atomic force microscopy is capable of resolving the chemical structure of a single molecule on a surface. In previous research, such high resolution has only been obtained at low temperatures. Here we demonstrate that the chemical structure of a single molecule can be clearly revealed even at room temperature. 3,4,9,10-perylene tetracarboxylic dianhydride, which is strongly adsorbed onto a corner-hole site of a Si(111)-(7 × 7) surface in a bridge-like configuration is used for demonstration. Force spectroscopy combined with first-principle calculations clarifies that chemical structures can be resolved independent of tip reactivity. We show that the submolecular contrast over a central part of the molecule is achieved in the repulsive regime due to differences in the attractive van der Waals interaction and the Pauli repulsive interaction between different sites of the molecule.
Zhang, Chuanzhao; Kuang, Xiaoyu; Jin, Yuanyuan; Lu, Cheng; Zhou, Dawei; Li, Peifang; Bao, Gang; Hermann, Andreas
2015-12-01
We present results of an unbiased structure search for stable ruthenium silicide compounds with various stoichiometries, using a recently developed technique that combines particle swarm optimization algorithms with first-principles calculations. Two experimentally observed structures of ruthenium silicides, RuSi (space group P2(1)3) and Ru2Si3 (space group Pbcn), are successfully reproduced under ambient pressure conditions. In addition, a stable RuSi2 compound with β-FeSi2 structure type (space group Cmca) was found. The calculations of the formation enthalpy, elastic constants, and phonon dispersions demonstrate the Cmca-RuSi2 compound is energetically, mechanically, and dynamically stable. The analysis of electronic band structures and densities of state reveals that the Cmca-RuSi2 phase is a semiconductor with a direct band gap of 0.480 eV and is stabilized by strong covalent bonding between Ru and neighboring Si atoms. On the basis of the Mulliken overlap population analysis, the Vickers hardness of the Cmca structure RuSi2 is estimated to be 28.0 GPa, indicating its ultra-incompressible nature. PMID:26576622
International Nuclear Information System (INIS)
A scheme of calculation of the electronic structure of a solid state surface and chemisorbed molecules is discussed. The method of the Green's function and MO LCAO approximation are used which permits to perform calculations, taking into account the whole crystal but not its fragment only, with the accuracy adopted by quantum chemistry. Results of model calculations are presented: chemisorption of hydrogen-like atom on the (100) face of the one-band crystal model and dispersion curves for the density of states of nickel (100) face. (Auth.)
Electronic Structure of KFe2Se2 from First-Principles Calculations
International Nuclear Information System (INIS)
Electronic structures and magnetic properties for iron-selenide KFe2Se2 are studied by first-principles calculations. The ground state is collinear antiferromagnetic with calculated 2.26μB magnetic moment on Fe atoms; and the J1 and J2 coupling strengths are calculated to be 0.038eV and 0.029eV. The states around EF are dominated by the Fe 3d orbitals which hybridize noticeably to the Se 4p orbitals. While the band structure of KFe2Se2 is similar to a heavily electron-doped BaFe2AS2 or FeSe system, the Fermi surface of KFe2Se2 is much closer to the FeSe system since the electron sheets around M are symmetric with respect to x—y exchange. These features, as well as the absence of Fermi surface nesting, suggest that the parent KFe2Se2 could be regarded as an electron doped FeSe system with possible local moment magnetism. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
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
2016-01-01
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.
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)