On the atomic shell structure calculation (1)
International Nuclear Information System (INIS)
Choe Sun Chol
1986-01-01
We have considered the problem of atomic shell structure calculation using operator technique. We introduce reduced matrix elements of annihilation operators according to eg. (4). The normalized basis function is denoted as || ...>. The reduced matrix elements of the pair annihilation operators are expressed throw one-electron matrix elements. Some numerical results are represented and the problem of sign assignment is discussed. (author)
Atomic Reference Data for Electronic Structure Calculations
Kotochigova, S; Shirley, E L
We have generated data for atomic electronic structure calculations, to provide a standard reference for results of specified accuracy under commonly used approximations. Results are presented here for total energies and orbital energy eigenvalues for all atoms from H to U, at microHartree accuracy in the total energy, as computed in the local-density approximation (LDA) the local-spin-density approximation (LSD); the relativistic local-density approximation (RLDA); and scalar-relativistic local-density approximation (ScRLDA).
Atomic structure calculations of Mo XV-XL
International Nuclear Information System (INIS)
Kubo, Hirotaka; Sugie, Tatsuo; Shiho, Makoto; Suzuki, Yasuo; Ishii, Keishi; Maeda, Hikosuke.
1986-06-01
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)
Efficient evaluation of atom tunneling combined with electronic structure calculations.
Ásgeirsson, Vilhjálmur; Arnaldsson, Andri; Jónsson, Hannes
2018-03-14
Methodology for finding optimal tunneling paths and evaluating tunneling rates for atomic rearrangements is described. First, an optimal JWKB tunneling path for a system with fixed energy is obtained using a line integral extension of the nudged elastic band method. Then, a calculation of the dynamics along the path is used to determine the temperature at which it corresponds to an optimal Feynman path for thermally activated tunneling (instanton) and a harmonic approximation is used to estimate the transition rate. The method is illustrated with calculations for a modified two-dimensional Müller-Brown surface but is efficient enough to be used in combination with electronic structure calculations of the energy and atomic forces in systems containing many atoms. An example is presented where tunneling is the dominant mechanism well above room temperature as an H 3 BNH 3 molecule dissociates to form H 2 . Also, a solid-state example is presented where density functional theory calculations of H atom tunneling in a Ta crystal give close agreement with experimental measurements on hydrogen diffusion over a wide range in temperature.
Calculation of atom displacement cross section for structure material
International Nuclear Information System (INIS)
Liu Ping; Xu Yiping
2015-01-01
The neutron radiation damage in material is an important consideration of the reactor design. The radiation damage of materials mainly comes from atom displacements of crystal structure materials. The reaction cross sections of charged particles, cross sections of displacements per atom (DPA) and KERMA are the basis of radiation damage calculation. In order to study the differences of DPA cross sections with different codes and different evaluated nuclear data libraries, the DPA cross sections for structure materials were calculated with UNF and NJOY codes, and the comparisons of results were given. The DPA cross sections from different evaluated nuclear data libraries were compared. And the comparison of DPA cross sections between NJOY and Monte Carlo codes was also done. The results show that the differences among these evaluated nuclear data libraries exist. (authors)
Atomic structure calculations on the CRAY X-MP
International Nuclear Information System (INIS)
Fischer, C.F.
1989-01-01
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
Self-consistent calculation of atomic structure for mixture
International Nuclear Information System (INIS)
Meng Xujun; Bai Yun; Sun Yongsheng; Zhang Jinglin; Zong Xiaoping
2000-01-01
Based on relativistic Hartree-Fock-Slater self-consistent average atomic model, atomic structure for mixture is studied by summing up component volumes in mixture. Algorithmic procedure for solving both the group of Thomas-Fermi equations and the self-consistent atomic structure is presented in detail, and, some numerical results are discussed
Atomic structure calculations using the relativistic random phase approximation
International Nuclear Information System (INIS)
Cheng, K.T.; Johnson, W.R.
1981-01-01
A brief review is given for the relativistic random phase approximation (RRPA) applied to atomic transition problems. Selected examples of RRPA calculations on discrete excitations and photoionization are given to illustrate the need of relativistic many-body theories in dealing with atomic processes where both relativity and correlation are important
Atomic structure calculations for F-like tungsten
Sunny, Aggarwal
2014-09-01
Energy levels, wavefunction compositions and lifetimes have been computed for all levels of 1s22s22p5, 1s22s2p6, 1s22s22p43s, 1s22s22p43p, and 1s22s22p43d configurations in highly charged F-like tungsten ion. The multiconfigurational Dirac—Fock method (MCDF) is adopted to generate the wavefunctions. We have also presented the transition wavelengths, oscillator strengths, transition probabilities, and line strengths for the electric dipole (E1) and magnetic quadrupole (M2) transition from the 1s22s22p5 ground configuration. We have performed parallel calculations with the flexible atomic code (FAC) for comparing the atomic data. The reliability of present data is assessed by comparison with other theoretical and experimental data available in the literature. Good agreement is found between our results and those obtained using different approaches confirm the quality of our results. Additionally, we have predicted some new atomic data for F-like W that were not available so far and may be important for plasma diagnostic analysis in fusion plasma.
Breit–Pauli atomic structure calculations for Fe XI
International Nuclear Information System (INIS)
Aggarwal, Sunny; Singh, Jagjit; Mohan, Man
2013-01-01
Energy levels, oscillator strengths, and transition probabilities are calculated for the lowest-lying 165 energy levels of Fe XI using configuration-interaction wavefunctions. The calculations include all the major correlation effects. Relativistic effects are included in the Breit–Pauli approximation by adding mass-correction, Darwin, and spin–orbit interaction terms to the non-relativistic Hamiltonian. For comparison with the calculated ab initio energy levels, we have also calculated the energy levels by using the fully relativistic multiconfiguration Dirac–Fock method. The calculated results are in close agreement with the National Institute of Standards and Technology compilation and other available results. New results are predicted for many of the levels belonging to the 3s3p 4 3d and 3s3p 3 3d 2 configurations, which are very important in astrophysics, relevant, for example, to the recent observations by the Hinode spacecraft. We expect that our extensive calculations will be useful to experimentalists in identifying the fine structure levels in their future work
A Hartree-Fock program for atomic structure calculations
International Nuclear Information System (INIS)
Mitroy, J.
1999-01-01
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
Ab initio calculations and modelling of atomic cluster structure
DEFF Research Database (Denmark)
Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.
2004-01-01
The optimized structure and electronic properties of small sodium and magnesium clusters have been investigated using it ab initio theoretical methods based on density-functional theory and post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system. A new theoretical...
Energy Technology Data Exchange (ETDEWEB)
Surdoval, Wayne A. [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Berry, David A. [National Energy Technology Lab. (NETL), Morgantown, WV (United States); Shultz, Travis R. [National Energy Technology Lab. (NETL), Morgantown, WV (United States)
2018-03-09
A set of equations are presented for calculating atomic principal spectral lines and fine-structure energy splits for single and multi-electron atoms. Calculated results are presented and compared to the National Institute of Science and Technology database demonstrating very good accuracy. The equations do not require fitted parameters. The only experimental parameter required is the Ionization energy for the electron of interest. The equations have comparable accuracy and broader applicability than the single electron Dirac equation. Three Appendices discuss the origin of the new equations and present calculated results. New insights into the special relativistic nature of the Dirac equation and its relationship to the new equations are presented.
Elantkowska, Magdalena; Ruczkowski, Jarosław; Sikorski, Andrzej; Dembczyński, Jerzy
2017-11-01
A parametric analysis of the hyperfine structure (hfs) for the even parity configurations of atomic terbium (Tb I) is presented in this work. We introduce the complete set of 4fN-core states in our high-performance computing (HPC) calculations. For calculations of the huge hyperfine structure matrix, requiring approximately 5000 hours when run on a single CPU, we propose the methods utilizing a personal computer cluster or, alternatively a cluster of Microsoft Azure virtual machines (VM). These methods give a factor 12 performance boost, enabling the calculations to complete in an acceptable time.
International Nuclear Information System (INIS)
Mizoguchi, Teruyasu
2011-01-01
In this review, following two topics are introduced: 1) experimental and theoretical electron energy loss (EEL) near edge structures (ELNES) and X-ray absorption near edge structures (XANES), and 2) atomic and electronic structure analysis of ceramic interface by combing spectroscopy, microscopy, and first principles calculation. In the ELNES/XANES calculation, it is concluded that inclusion of core-hole effect in the calculation is essential. By combining high energy resolution observation and theoretical calculation, detailed analysis of the electronic structure is achieved. In addition, overlap population (OP) diagram is used to interpret the spectrum. In the case of AlN, sharp and intense first peak of N-K edge is found to reflect narrow dispersion of the conduction band bottom. By applying ELNES and the OP diagram to Cu/Al 2 O 3 heterointerface, it is revealed that intensity of prepeak in O-K edge is inverse proportional to interface strength. The relationships between atomic structure and defect energetics at SrTiO 3 grain boundary are also investigated, and reveal that the formation behavior of Ti vacancy is sensitive to the structural distortion. In addition, by using state-of-the-art spectroscopy, microscopy, and first principles calculations, atomic scale visualization of fluorine dopant in LaFeOAs and first principles calculation of HfO 2 phase transformation are demonstrated. (author)
Directory of Open Access Journals (Sweden)
Thomas Gomez
2018-04-01
Full Text Available Atomic structure of N-electron atoms is often determined by solving the Hartree-Fock equations, which are a set of integro-differential equations. The integral part of the Hartree-Fock equations treats electron exchange, but the Hartree-Fock equations are not often treated as an integro-differential equation. The exchange term is often approximated as an inhomogeneous or an effective potential so that the Hartree-Fock equations become a set of ordinary differential equations (which can be solved using the usual shooting methods. Because the Hartree-Fock equations are an iterative-refinement method, the inhomogeneous term relies on the previous guess of the wavefunction. In addition, there are numerical complications associated with solving inhomogeneous differential equations. This work uses matrix methods to solve the Hartree-Fock equations as an integro-differential equation. It is well known that a derivative operator can be expressed as a matrix made of finite-difference coefficients; energy eigenvalues and eigenvectors can be obtained by using linear-algebra packages. The integral (exchange part of the Hartree-Fock equation can be approximated as a sum and written as a matrix. The Hartree-Fock equations can be solved as a matrix that is the sum of the differential and integral matrices. We compare calculations using this method against experiment and standard atomic structure calculations. This matrix method can also be used to solve for free-electron wavefunctions, thus improving how the atoms and free electrons interact. This technique is important for spectral line broadening in two ways: it improves the atomic structure calculations, and it improves the motion of the plasma electrons that collide with the atom.
International Nuclear Information System (INIS)
Lin, Lin; Yang, Chao; Chen, Mohan; He, Lixin
2013-01-01
We describe how to apply the recently developed pole expansion and selected inversion (PEXSI) technique to Kohn–Sham density function theory (DFT) electronic structure calculations that are based on atomic orbital discretization. We give analytic expressions for evaluating the charge density, the total energy, the Helmholtz free energy and the atomic forces (including both the Hellmann–Feynman force and the Pulay force) without using the eigenvalues and eigenvectors of the Kohn–Sham Hamiltonian. We also show how to update the chemical potential without using Kohn–Sham eigenvalues. The advantage of using PEXSI is that it has a computational complexity much lower than that associated with the matrix diagonalization procedure. We demonstrate the performance gain by comparing the timing of PEXSI with that of diagonalization on insulating and metallic nanotubes. For these quasi-1D systems, the complexity of PEXSI is linear with respect to the number of atoms. This linear scaling can be observed in our computational experiments when the number of atoms in a nanotube is larger than a few hundreds. Both the wall clock time and the memory requirement of PEXSI are modest. This even makes it possible to perform Kohn–Sham DFT calculations for 10 000-atom nanotubes with a sequential implementation of the selected inversion algorithm. We also perform an accurate geometry optimization calculation on a truncated (8, 0) boron nitride nanotube system containing 1024 atoms. Numerical results indicate that the use of PEXSI does not lead to loss of the accuracy required in a practical DFT calculation. (paper)
Atomic structure calculation of energy levels and oscillator strengths in Ti ion, 2
International Nuclear Information System (INIS)
Ishii, Keishi
1983-10-01
Energy levels and oscillator strengths are calculated for 3s-3p and 3p-3d transition arrays in Ti X, isoelectronic to Al I. The energy levels are obtained by the Slater-Condon theory of atomic structure, including explicitly the strong configuration interactions. The results are presented both in numerical tables and in diagrams. In the tables, the observed data are included for comparison, where available. The calculated weighted oscillator strengths (gf-value) are also displayed in figures, where the weighted oscillator strengths are plotted as a function of wavelength. (author)
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)
Goyal, Arun; Khatri, Indu; Aggarwal, Sunny; Singh, A.K.; Mohan, Man
2015-01-01
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. - 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
Lany, Stephan; Wolf, Herbert; Wichert, Thomas
2004-06-04
The In DX center and the DX-like configuration of the Cd host atom in CdTe are investigated using density functional theory. The simultaneous calculation of the atomic structure and the electric field gradient (EFG) allows one to correlate the theoretically predicted structure of the DX center with an experimental observable, namely, the EFG obtained from radioactive 111In/111Cd probe atoms in In doped CdTe. In this way, the experimental identification of the DX center structure is established.
Code ATOM for calculation of atomic characteristics
International Nuclear Information System (INIS)
Vainshtein, L.A.
1990-01-01
In applying atomic physics to problems of plasma diagnostics, it is necessary to determine some atomic characteristics, including energies and transition probabilities, for very many atoms and ions. Development of general codes for calculation of many types of atomic characteristics has been based on general but comparatively simple approximate methods. The program ATOM represents an attempt at effective use of such a general code. This report gives a brief description of the methods used, and the possibilities of and limitations to the code are discussed. Characteristics of the following processes can be calculated by ATOM: radiative transitions between discrete levels, radiative ionization and recombination, collisional excitation and ionization by electron impact, collisional excitation and ionization by point heavy particle (Born approximation only), dielectronic recombination, and autoionization. ATOM explores Born (for z=1) or Coulomb-Born (for z>1) approximations. In both cases exchange and normalization can be included. (N.K.)
International Nuclear Information System (INIS)
Fawcett, B.C.; Mason, H.E.
1989-02-01
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)
International Nuclear Information System (INIS)
Dorado, B.
2010-09-01
Uranium dioxide UO 2 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 UO 2 , 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 UO 2 and provide quantitative information regarding point defect transport properties in the oxide fuel. (author)
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
Theoretical Calculations of Atomic Data for Spectroscopy
Bautista, Manuel A.
2000-01-01
Several different approximations and techniques have been developed for the calculation of atomic structure, ionization, and excitation of atoms and ions. These techniques have been used to compute large amounts of spectroscopic data of various levels of accuracy. This paper presents a review of these theoretical methods to help non-experts in atomic physics to better understand the qualities and limitations of various data sources and assess how reliable are spectral models based on those data.
International Nuclear Information System (INIS)
Xie, Z.L.; Dy, K.S.; Wu, S.Y.
1997-01-01
A real-space scheme has been developed for a first-principles calculation of electronic structures and total energies of atomic clusters. The scheme is based on the combination of the tight-binding linear muffin-tin orbital (TBLMTO) method and the method of real-space Green close-quote s function. With this approach, the local electronic density of states can be conveniently determined from the real-space Green close-quote s function. Furthermore, the full electron density of a cluster can be directly calculated in real space. The scheme has been shown to be very efficient due to the incorporation of the method of real-space Green close-quote s function and Delley close-quote s method of evaluating multicenter integrals. copyright 1996 The American Physical Society
Dirac-Fock atomic electronic structure calculations using different nuclear charge distributions
Visscher, L; Dyall, KG
1997-01-01
Numerical Hartree-Fock calculations based on the Dirac-Coulomb Hamiltonian for the first 109 elements of the periodic table are presented. The results give the total electronic energy, as a function of the nuclear model that is used, for four different models of the nuclear charge distribution. The
Czech Academy of Sciences Publication Activity Database
Landau, A.; Haritan, I.; Kaprálová-Žďánská, Petra Ruth; Moiseyev, N.
2016-01-01
Roč. 120, č. 19 (2016), s. 3098-3108 ISSN 1089-5639 R&D Projects: GA MŠk(CZ) LG13029 Institutional support: RVO:68378271 Keywords : autoionizing states * coordinate calculation * scattering resonances Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 2.847, year: 2016
Many body calculations in atomic physics
International Nuclear Information System (INIS)
Kelly, H.P.
1985-01-01
The use of the many-body perturbation theory for atomic calculations are reviewed. The major emphasis is on the use of the linked-cluster many-body perturbation theory derived by Brueckner and Goldstone. Applications of many-body theory to calculations of hyperfine structure are examined. Auger rates and parity violation are discussed. Photoionization is reviewed, and the authors show how many-body perturbation theory can be applied to problems ranging from structural properties such as correlation energies and hyperfine structure to dynamical properties such as transitions induced by weak neutral currents and photoionization cross sections
International Nuclear Information System (INIS)
Choi, Sunghwan; Hong, Kwangwoo; Kim, Jaewook; Kim, Woo Youn
2015-01-01
We developed a self-consistent field program based on Kohn-Sham density functional theory using Lagrange-sinc functions as a basis set and examined its numerical accuracy for atoms and molecules through comparison with the results of Gaussian basis sets. The result of the Kohn-Sham inversion formula from the Lagrange-sinc basis set manifests that the pseudopotential method is essential for cost-effective calculations. The Lagrange-sinc basis set shows faster convergence of the kinetic and correlation energies of benzene as its size increases than the finite difference method does, though both share the same uniform grid. Using a scaling factor smaller than or equal to 0.226 bohr and pseudopotentials with nonlinear core correction, its accuracy for the atomization energies of the G2-1 set is comparable to all-electron complete basis set limits (mean absolute deviation ≤1 kcal/mol). The same basis set also shows small mean absolute deviations in the ionization energies, electron affinities, and static polarizabilities of atoms in the G2-1 set. In particular, the Lagrange-sinc basis set shows high accuracy with rapid convergence in describing density or orbital changes by an external electric field. Moreover, the Lagrange-sinc basis set can readily improve its accuracy toward a complete basis set limit by simply decreasing the scaling factor regardless of systems
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....
DEFF Research Database (Denmark)
Bork, Nicolai Christian; Eurenius, K. E. J.; Rossmeisl, Jan
2012-01-01
A combined density functional theory and Fourier transform infrared spectroscopy study of the structure and specific site preference of protons and hydrides in the pyrochlore Sm1.92Ca0.08Sn2O7-δ is presented. Two protonic sites of particular high stability are identified, both located on O(1......) 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...
Energy Technology Data Exchange (ETDEWEB)
Madjet, Mohamed E., E-mail: mmadjet@qf.org.qa; El-Mellouhi, Fedwa; Carignano, Marcelo A.; Berdiyorov, Golibjon R. [Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, P. O. Box 5825, Doha (Qatar)
2016-04-28
We calculated the partial charges in methylammonium (MA) lead-iodide perovskite CH{sub 3}NH{sub 3}PbI{sub 3} 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.
Atomic charges of sulfur in ionic liquids: experiments and calculations.
Fogarty, Richard M; Rowe, Rebecca; Matthews, Richard P; Clough, Matthew T; Ashworth, Claire R; Brandt, Agnieszka; Corbett, Paul J; Palgrave, Robert G; Smith, Emily F; Bourne, Richard A; Chamberlain, Thomas W; Thompson, Paul B J; Hunt, Patricia A; Lovelock, Kevin R J
2017-12-14
Experimental near edge X-ray absorption fine structure (NEXAFS) spectra, X-ray photoelectron (XP) spectra and Auger electron spectra are reported for sulfur in ionic liquids (ILs) with a range of chemical structures. These values provide experimental measures of the atomic charge in each IL and enable the evaluation of the suitability of NEXAFS spectroscopy and XPS for probing the relative atomic charge of sulfur. In addition, we use Auger electron spectroscopy to show that when XPS binding energies differ by less than 0.5 eV, conclusions on atomic charge should be treated with caution. Our experimental data provides a benchmark for calculations of the atomic charge of sulfur obtained using different methods. Atomic charges were computed for lone ions and ion pairs, both in the gas phase (GP) and in a solvation model (SMD), with a wide range of ion pair conformers considered. Three methods were used to compute the atomic charges: charges from the electrostatic potential using a grid based method (ChelpG), natural bond orbital (NBO) population analysis and Bader's atoms in molecules (AIM) approach. By comparing the experimental and calculated measures of the atomic charge of sulfur, we provide an order for the sulfur atoms, ranging from the most negative to the most positive atomic charge. Furthermore, we show that both ChelpG and NBO are reasonable methods for calculating the atomic charge of sulfur in ILs, based on the agreement with both the XPS and NEXAFS spectroscopy results. However, the atomic charges of sulfur derived from ChelpG are found to display significant, non-physical conformational dependence. Only small differences in individual atomic charge of sulfur were observed between lone ion (GP) and ion pair IL(SMD) model systems, indicating that ion-ion interactions do not strongly influence individual atomic charges.
Languages for structural calculations
International Nuclear Information System (INIS)
Thomas, J.B.; Chambon, M.R.
1988-01-01
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 [fr
International Nuclear Information System (INIS)
Frammelsberger, Werner; Benstetter, Guenther; Stamp, Richard; Kiely, Janice; Schweinboeck, Thomas
2005-01-01
As charge tunnelling through thin and ultra-thin silicon dioxide layers is regarded as the driving force for MOS device degradation the determination and characterisation of electrically week spots is of paramount importance for device reliability and failure analysis. Conductive atomic force microscopy (C-AFM) is able to address this issue with a spatial resolution smaller than the expected breakdown spot. For the determination of the electrically active oxide thickness in practice an easy to use model with sufficient accuracy and which is largely independent of the oxide thickness is required. In this work a simplified method is presented that meets these demands. The electrically active oxide thickness is determined by matching of C-AFM voltage-current curves and a tunnelling current model, which is based on an analytical tunnelling current approximation. The model holds for both the Fowler-Nordheim tunnelling and the direct tunnelling regime with one single tunnelling parameter set. The results show good agreement with macroscopic measurements for gate voltages larger than approximately 0.5-1 V, and with microscopic C-AFM measurements. For this reason arbitrary oxides in the DT and the FNT regime may be analysed with high lateral resolution by C-AFM, without the need of a preselection of the tunnelling regime to be addressed
Calculation of atomic integrals using commutation relations
International Nuclear Information System (INIS)
Zamastil, J.; Vinette, F.; Simanek, M.
2007-01-01
In this paper, a numerically stable method of calculating atomic integrals is suggested. The commutation relations among the components of the angular momentum and the Runge-Lenz vector are used to deduce recurrence relations for the Sturmian radial functions. The radial part of the one- and two-electron integrals is evaluated by means of these recurrence relations. The product of two radial functions is written as a linear combination of the radial functions. This enables us to write the integrals over four radial functions as a linear combination of the integrals over two radial functions. The recurrence relations for the functions are used to derive the recursion relations for the coefficients of the linear combination and for the integrals over two functions
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)
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 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
Experimental validation of calculated atomic charges in ionic liquids
Fogarty, Richard M.; Matthews, Richard P.; Ashworth, Claire R.; Brandt-Talbot, Agnieszka; Palgrave, Robert G.; Bourne, Richard A.; Vander Hoogerstraete, Tom; Hunt, Patricia A.; Lovelock, Kevin R. J.
2018-05-01
A combination of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy has been used to provide an experimental measure of nitrogen atomic charges in nine ionic liquids (ILs). These experimental results are used to validate charges calculated with three computational methods: charges from electrostatic potentials using a grid-based method (ChelpG), natural bond orbital population analysis, and the atoms in molecules approach. By combining these results with those from a previous study on sulfur, we find that ChelpG charges provide the best description of the charge distribution in ILs. However, we find that ChelpG charges can lead to significant conformational dependence and therefore advise that small differences in ChelpG charges (<0.3 e) should be interpreted with care. We use these validated charges to provide physical insight into nitrogen atomic charges for the ILs probed.
Multiconfiguration Hartree-Fock calculations for complex atoms
International Nuclear Information System (INIS)
Fischer, C.F.
1984-01-01
The Hartree-Fock method has become a standard in atomic structure theory. Simpler methods are often compared with it when accessing their reliability or worth and the notion of correlation, which intuitively may be thought of as the correction needed to account for the fact that electrons do not move independently in a central field, is defined with respect to the Hartree-Fock method rather than some other independent-particle model. In fact, in an earlier article in this series, Fricke (Progress in Atomic Spectroscopy, Part A, Plenum Press (1978)), states, ''The so-called HF method is the basis of all good atomic calculations.'' In some sense, the Hartree-Fock method is the best method. The author briefly reviews its properties here. 67 references, 2 figures
Ab initio calculation atomics ground state wave function for interactions Ion- Atom
International Nuclear Information System (INIS)
Shojaee, F.; Bolori zadeh, M. A.
2007-01-01
Ab initio calculation atomics ground state wave function for interactions Ion- Atom Atomic wave function expressed in a Slater - type basis obtained within Roothaan- Hartree - Fock for the ground state of the atoms He through B. The total energy is given for each atom.
Total energy calculations for structural phase transformations
International Nuclear Information System (INIS)
Ye, Y.Y.; Chan, C.T.; Ho, K.M.; Harmon, B.N.
1990-01-01
The structural integrity and physical properties of crystalline solids are frequently limited or enhanced by the occurrence of phase transformations. Martensitic transformations involve the collective displacement of atoms from one ordered state to another. Modern methods to determine the microscopic electronic changes as the atoms move are now accurate enough to evaluate the very small energy differences involved. Extensive first principles calculations for the prototypical martensitic transformation from body-centered cubic (bcc) to closepacked 9R structure in sodium metal are described. The minimum energy coordinate or configuration path between the bcc and 9R structures is determined as well as paths to other competing close-packed structures. The energy barriers and important anharmonic interactions are identified and general conclusions drawn. The calculational methods used to solve the Schrodinger equation include pseudopotentials, fast Fourier transforms, efficient matrix diagnonalization, and supercells with many atoms
Structural reliability of atomic power plant
International Nuclear Information System (INIS)
Klemin, A.I.; Polyakov, E.F.
1980-01-01
In 1978 the first specialized technical manual ''Technique of Calculating the Structural Reliability of an Atomic Power Plant and Its Systems in the Design Stage'' was developed. The present article contains information about the main characteristics and capabilities of the manual. The manual gives recommendations concerning the calculations of the reliability of such specific systems as the reactor control and safety system, the system of instrumentation and automatic control, and safety systems. 2 refs
Analytical relativistic self-consistent-field calculations for atoms
International Nuclear Information System (INIS)
Barthelat, J.C.; Pelissier, M.; Durand, P.
1980-01-01
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
Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom
Baseden, Kyle A.; Tye, Jesse W.
2014-01-01
Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…
Atomic structure in black hole
International Nuclear Information System (INIS)
Nagatani, Yukinori
2006-01-01
We propose that any black hole has atomic structure in its inside and has no horizon as a model of black holes. Our proposal is founded on a mean field approximation of gravity. The structure of our model consists of a (charged) singularity at the center and quantum fluctuations of fields around the singularity, namely, it is quite similar to that of atoms. Any properties of black holes, e.g. entropy, can be explained by the model. The model naturally quantizes black holes. In particular, we find the minimum black hole, whose structure is similar to that of the hydrogen atom and whose Schwarzschild radius is approximately 1.1287 times the Planck length. Our approach is conceptually similar to Bohr's model of the atomic structure, and the concept of the minimum Schwarzschild radius is similar to that of the Bohr radius. The model predicts that black holes carry baryon number, and the baryon number is rapidly violated. This baryon number violation can be used as verification of the model. (author)
Multilevel domain decomposition for electronic structure calculations
International Nuclear Information System (INIS)
Barrault, M.; Cances, E.; Hager, W.W.; Le Bris, C.
2007-01-01
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. 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
On-line system for investigation of atomic structure
International Nuclear Information System (INIS)
Amus'ya, M.Ya.; Chernysheva, L.V.
1983-01-01
A description of the on-line ATOM system is presented that enables to investigate the structure of atomic electron shells and their interactions with different scattering particles-electrons, positronse photons, mesons - with the use of computerized numerical solutions. The problem is stated along with mathematical description of atomic properties including theoretical and numerical models for each investigated physical process. The ATOM system structure is considered. The Hartree-Fock method is used to determine the wave functions of the ground and excited atomic states. The programs are written in the ALGOL langauge. Different atomic characteristics were possible to be calculated for the first time with an accuracy exceeding an experimental one
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.
Calculations of nucleon structure functions
International Nuclear Information System (INIS)
Signal, A.I.
1990-01-01
We present a method of calculating deep inelastic nucleon structure functions using bag model wavefunctions. Our method uses the Peierls - Yoccoz projection to form translation invariant bag states. We obtain the correct support for the structure functions and satisfy the positivity requirements for quark and anti-quark distribution functions. (orig.)
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
Calculating trajectories for atoms in near-resonant lightfields
International Nuclear Information System (INIS)
Scholten, R.E.; O' Kane, T.J.; Mackin, T.R.; Hunt, T.A.; Farrell, P.M.
1999-01-01
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 TEM 01 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)
Evolution in time of an N-atom system. II. Calculation of the eigenstates
International Nuclear Information System (INIS)
Rudolph, Terry; Yavin, Itay; Freedhoff, Helen
2004-01-01
We calculate the energy eigenvalues and eigenstates corresponding to coherent single and multiple excitations of a number of different arrays of N identical two-level atoms (TLA's) or qubits, including polygons, 'diamond' structures, polygon multilayers, icosahedra, and dodecahedra. We assume only that the coupling occurs via an exchange interaction which depends on the separation between the atoms. We include the interactions between all pairs of atoms, and our results are valid for arbitrary separations relative to the radiation wavelength
Improved density functional calculations for atoms, molecules and surfaces
International Nuclear Information System (INIS)
Fricke, B.; Anton, J.; Fritzsche, S.; Sarpe-Tudoran, C.
2005-01-01
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)
Current Capability of Atomic Structure Theory
International Nuclear Information System (INIS)
Kim, Yong Ki
1993-01-01
Current capability of atomic structure theory is reviewed, and advantages, disadvantages and major features of popular atomic structure codes described. Comparisons between theoretical and experimental data on transition energies and lifetimes of excited levels are presented to illustrate the current capability of atomic structure codes.
Update on nuclear structure effects in light muonic atoms
Energy Technology Data Exchange (ETDEWEB)
Hernandez, Oscar Javier, E-mail: javierh@triumf.ca; Dinur, Nir Nevo; Ji, Chen; Bacca, Sonia [TRIUMF (Canada); Barnea, Nir [The Hebrew University, Racah Institute of Physics (Israel)
2016-12-15
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.
Automated atomic absorption spectrophotometer, utilizing a programmable desk calculator
International Nuclear Information System (INIS)
Futrell, T.L.; Morrow, R.W.
1977-01-01
A commercial, double-beam atomic absorption spectrophotometer has been interfaced with a sample changer and a Hewlett-Packard 9810A calculator to yield a completely automated analysis system. The interface electronics can be easily constructed and should be adaptable to any double-beam atomic absorption instrument. The calculator is easily programmed and can be used for general laboratory purposes when not operating the instrument. The automated system has been shown to perform very satisfactorily when operated unattended to analyze a large number of samples. Performance statistics agree well with a manually operated instrument
Atomic probes of surface structure and dynamics
International Nuclear Information System (INIS)
Heller, E.J.; Jonsson, H.
1992-01-01
The following were studied: New semiclassical method for scattering calculations, He atom scattering from defective Pt surfaces, He atom scattering from Xe overlayers, thermal dissociation of H 2 on Cu(110), spin flip scattering of atoms from surfaces, and Car-Parrinello simulations of surface processes
International Nuclear Information System (INIS)
Chun-Mei, Tang; Wei-Hua, Zhu; Kai-Ming, Deng
2010-01-01
This paper uses the generalised gradient approximation based on density functional theory to analyse the geometric structure and properties of the 3d transition metal atom doped endohedral fullerene M@C 20 F 20 (M = Sc–Ni). The geometric optimization shows that the cage centre is the most stable position for M, forming the structure named as M@C 20 F 20 -4. The inclusion energy, zero-point energy, and energy gap calculations tell us that N@C 20 F 20 -4 should be thermodynamically and kinetically stablest. M@C 20 F 20 -4 (M = Sc–Co) possesses high magnetic moments varied from 1 to 6 μ B , while Ni@C 20 F 20 -4 is nonmagnetic. The Ni–C bond in Ni@C 20 F 20 -4 contains both the covalent and ionic characters
Schwinger variational calculation of ionization of hydrogen atoms for ...
Indian Academy of Sciences (India)
Schwinger variational calculation of ionization of hydrogen atoms for large momentum transfers. K CHAKRABARTI. Department of Mathematics, Scottish Church College, 1 & 3 Urquhart Square,. Kolkata 700 006, India. MS received 7 July 2001; revised 10 October 2001. Abstract. Schwinger variational principle is used here ...
Report on atomic structure research 1961-1990
International Nuclear Information System (INIS)
Fawcett, B.C.
1990-07-01
This report documents the atomic-structure research carried out during the period 1961-90. The contributions are in two main areas. The first comprises original line classifications of spectra of highly ionized atoms including identifications of a major proportion of newly observed lines in the solar far ultraviolet and soft X-ray spectrum. The second consists of theoretical calculations of atomic data such as oscillator strengths, wavelengths, energy levels and their composition. These were calculated with advanced atomic-structure codes and cover most solar abundant ions. A new method was applied to collision calculations. Research in this field, presently conducted at Rutherford Appleton Laboratory (RAL), was initiated in the United Kingdom Atomic Energy Authority (UKAEA) at Harwell in 1960. It continued under the UKAEA at Culham Laboratory in 1962 and until 1986 when staff were taken over by Science and Engineering Research Council (SERC) and later transferred to RAL in 1981. (author)
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.
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
Energy Technology Data Exchange (ETDEWEB)
Borschevsky, A. [School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel and Centre for Theoretical Chemistry and Physics, The New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand); Yakobi, H.; Eliav, E.; Kaldor, U. [School of Chemistry, Tel Aviv University, 69978 Tel Aviv (Israel)
2015-01-22
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{sup −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.
High-accuracy coupled cluster calculations of atomic properties
International Nuclear Information System (INIS)
Borschevsky, A.; Yakobi, H.; Eliav, E.; Kaldor, U.
2015-01-01
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
Electronic structure calculations of calcium silicate hydrates
International Nuclear Information System (INIS)
Sterne, P.A.; Meike, A.
1995-11-01
Many phases in the calcium-silicate-hydrate system can develop in cement exposed over long periods of time to temperatures above 25 C. As a consequence, chemical reactions involving these phases can affect the relative humidity and water chemistry of a radioactive waste repository that contains significant amounts of cement. In order to predict and simulate these chemical reactions, the authors are developing an internally consistent database of crystalline Ca-Si-hydrate structures. The results of first principles electronic structure calculations on two such phases, wollastonite (CaSiO 3 ) and xonotlite (Ca 6 Si 6 O 17 (OH) 2 ), are reported here. The calculated ground state properties are in very good agreement with experiment, providing equilibrium lattice parameters within about 1--1.4% of the experimentally reported values. The roles of the different types of oxygen atoms, which are fundamental to understanding the energetics of crystalline Ca-Si-hydrates are briefly discussed in terms of their electronic state densities. The good agreement with experiment for the lattice parameters and the consistency of the electronic density of states features for the two structures demonstrate the applicability of these electronic structure methods in calculating the fundamental properties of these phases
Efficient calculation of atomic rate coefficients in dense plasmas
Aslanyan, Valentin; Tallents, Greg J.
2017-03-01
Modelling electron statistics in a cold, dense plasma by the Fermi-Dirac distribution leads to complications in the calculations of atomic rate coefficients. The Pauli exclusion principle slows down the rate of collisions as electrons must find unoccupied quantum states and adds a further computational cost. Methods to calculate these coefficients by direct numerical integration with a high degree of parallelism are presented. This degree of optimization allows the effects of degeneracy to be incorporated into a time-dependent collisional-radiative model. Example results from such a model are presented.
Semiempirical studies of atomic structure
International Nuclear Information System (INIS)
Curtis, L.J.
1992-01-01
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
Electronic structure of atoms: atomic spectroscopy information system
International Nuclear Information System (INIS)
Kazakov, V V; Kazakov, V G; Kovalev, V S; Meshkov, O I; Yatsenko, A S
2017-01-01
The article presents a Russian atomic spectroscopy, information system electronic structure of atoms (IS ESA) (http://grotrian.nsu.ru), and describes its main features and options to support research and training. The database contains over 234 000 records, great attention paid to experimental data and uniform filling of the database for all atomic numbers Z, including classified levels and transitions of rare earth and transuranic elements and their ions. Original means of visualization of scientific data in the form of spectrograms and Grotrian diagrams have been proposed. Presentation of spectral data in the form of interactive color charts facilitates understanding and analysis of properties of atomic systems. The use of the spectral data of the IS ESA together with its functionality is effective for solving various scientific problems and training of specialists. (paper)
Electronic structure of atoms: atomic spectroscopy information system
Kazakov, V. V.; Kazakov, V. G.; Kovalev, V. S.; Meshkov, O. I.; Yatsenko, A. S.
2017-10-01
The article presents a Russian atomic spectroscopy, information system electronic structure of atoms (IS ESA) (http://grotrian.nsu.ru), and describes its main features and options to support research and training. The database contains over 234 000 records, great attention paid to experimental data and uniform filling of the database for all atomic numbers Z, including classified levels and transitions of rare earth and transuranic elements and their ions. Original means of visualization of scientific data in the form of spectrograms and Grotrian diagrams have been proposed. Presentation of spectral data in the form of interactive color charts facilitates understanding and analysis of properties of atomic systems. The use of the spectral data of the IS ESA together with its functionality is effective for solving various scientific problems and training of specialists.
Kinetic-energy density functional: Atoms and shell structure
International Nuclear Information System (INIS)
Garcia-Gonzalez, P.; Alvarellos, J.E.; Chacon, E.
1996-01-01
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)
Heller, E.J.; Jonsson, H.
1992-01-01
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 H 2 on Cu(110) are being studied. (R.W.R.) 64 refs
Self-consistent-field calculations of atoms and ions using a modified local-density approximation
International Nuclear Information System (INIS)
Liberman, D.A.; Albritton, J.R.; Wilson, B.G.; Alley, W.E.
1994-01-01
Local-density-approximation calculations of atomic structure are useful for the description of atoms and ions in plasmas. The large number of different atomic configurations that exist in typical plasmas leads one to consider the expression of total energies in terms of a Taylor series in the orbital occupation numbers. Two schemes for computing the second derivative Taylor-series coefficients are given; the second, and better one, uses the linear response method developed by Zangwill and Soven [Phys. Rev. A 21, 1561 (1980)] for the calculation of optical response in atoms. A defect in the local-density approximation causes some second derivatives involving Rydberg orbitals to be infinite. This is corrected by using a modified local-density approximation that had previously been proposed [Phys. Rev. B 2, 244 (1970)
Atomic structure of highly-charged ions. Final report
International Nuclear Information System (INIS)
Livingston, A. Eugene
2002-01-01
Atomic properties of multiply charged ions have been investigated using excitation of energetic heavy ion beams. Spectroscopy of excited atomic transitions has been applied from the visible to the extreme ultraviolet wavelength regions to provide accurate atomic structure and transition rate data in selected highly ionized atoms. High-resolution position-sensitive photon detection has been introduced for measurements in the ultraviolet region. The detailed structures of Rydberg states in highly charged beryllium-like ions have been measured as a test of long-range electron-ion interactions. The measurements are supported by multiconfiguration Dirac-Fock calculations and by many-body perturbation theory. The high-angular-momentum Rydberg transitions may be used to establish reference wavelengths and improve the accuracy of ionization energies in highly charged systems. Precision wavelength measurements in highly charged few-electron ions have been performed to test the most accurate relativistic atomic structure calculations for prominent low-lying excited states. Lifetime measurements for allowed and forbidden transitions in highly charged few-electron ions have been made to test theoretical transition matrix elements for simple atomic systems. Precision lifetime measurements in laser-excited alkali atoms have been initiated to establish the accuracy of relativistic atomic many-body theory in many-electron systems
Density functional calculations for atoms, molecules and clusters
International Nuclear Information System (INIS)
Gunnarsson, O.; Jones, R.O.
1980-01-01
The density functional formalism provides a framework for including exchange and correlation effects in the calculation of ground state properties of many-electron systems. The reduction of the problem to the solution of single-particle equations leads to important numerical advantages over other ab initio methods of incorporating correlation effects. The essential features of the scheme are outlined and results obtained for atomic and molecular systems are surveyed. The local spin density (LSD) approximation gives generally good results for systems where the bonding involves s and p electrons, but results are less satisfactory for d-bonded systems. Non-local modifications to the LSD approximation have been tested on atomic systems yielding much improved total energies. (Auth.)
DEFF Research Database (Denmark)
Avery, John Scales; Avery, James Emil; Aquilanti, Vincenzo
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_\
Electronic structure of fractionally nuclear charged atoms
International Nuclear Information System (INIS)
Pavao, Antonio C.; Bastos, Cristiano C.; Ferreira, Joacy V.
2008-01-01
Different properties of quark chemistry are studied by performing accurate ab initio Hartree- Fock calculations on fractionally nuclear charged atoms. Ground and first excited states of sodium atoms with quarks attached to the nucleus are obtained using CI calculations. It is suggested that the sodium 2 P -> 2 S electronic transition can be used as a guide in searching for unconfined quarks. Also, the variation of the binding electronic energy with nuclear charge in the isoelectronic series of fractionally nuclear charged atoms A ±2/3 and A ±1/3 (A = H, Li, Na, P and Ca) is analyzed. The present calculations suggest that unconfined colored particles have large appetite for heavy nuclei and that quark-antiquark pairs could be stabilized in presence of the atomic matter. (author)
Electronic structure of super heavy atoms revisited
International Nuclear Information System (INIS)
Gitman, D M; Levin, A D; Tyutin, I V; Voronov, B L
2013-01-01
The electronic structure of an atom with Z ⩽ Z c = 137 can be described by the Dirac equation with the Coulomb field of a point charge Ze. It was believed that the Dirac equation with Z > Z c poses difficulties because the formula for the lower energy level of the Dirac Hamiltonian formally gives imaginary eigenvalues. But a strict mathematical consideration shows that difficulties with the electronic spectrum for Z > Z c do not arise if the Dirac Hamiltonian is correctly defined as a self-adjoint operator. In this paper, we briefly summarize the main physical results of that consideration in a form suitable for physicists with some additional new details and numerical calculations of the electronic spectra. (comment)
Recent developments in high-spin calculations in atomic nuclei
International Nuclear Information System (INIS)
Szymanski, Z.
1980-01-01
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 152 Dy 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.)
International Nuclear Information System (INIS)
Zhang Zhao-Fu; Zhou Tie-Ge; Zhao Hai-Yang; Wei Xiang-Lei
2014-01-01
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: C 3v and D 3h . The symmetry will deviate from exact C 3v and D 3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μ B for Lu, Ta and Ir; 1μ B for Hf, W, Pt and Hg; 2μ B for Re and Au; and 3μ B 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)
Time-dependence and averaging techniques in atomic photoionization calculations
International Nuclear Information System (INIS)
Scheibner, K.F.
1984-01-01
Two distinct problems in the development and application of averaging techniques to photoionization calculations are considered. The first part of the thesis is concerned with the specific problem of near-resonant three-photon ionization in hydrogen, a process for which no cross section exists. Effects of the inclusion of the laser pulse characteristics (both temporal and spatial) on the dynamics of the ionization probability and of the metastable state probability are examined. It is found, for example, that the ionization probability can decrease with increasing field intensity. The temporal profile of the laser pulse is found to affect the dynamics very little, whereas the spatial character of the pulse can affect the results drastically. In the second part of the thesis techniques are developed for calculating averaged cross sections directly without first calculating a detailed cross section. Techniques are developed whereby the detailed cross section never has to be calculated as an intermediate step, but rather, the averaged cross section is calculated directly. A variation of the moment technique and a new method based on the stabilization technique are applied successfully to atomic hydrogen and helium
Global nuclear-structure calculations
International Nuclear Information System (INIS)
Moeller, P.; Nix, J.R.
1990-01-01
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 ε 2 and ε 4 used originally, a vastly improved agreement between calculated and experimental masses was obtained. To study the global behavior and interrelationships between other nuclear properties, we calculate nuclear ground-state masses, spins, pairing gaps and 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
The cellular approach to band structure calculations
International Nuclear Information System (INIS)
Verwoerd, W.S.
1982-01-01
A short introduction to the cellular approach in band structure calculations is given. The linear cellular approach and its potantial applicability in surface structure calculations is given some consideration in particular
Relativistic Collisions of Structured Atomic Particles
Voitkiv, Alexander
2008-01-01
The book reviews the progress achieved over the last decade in the study of collisions between an ion and an atom in which both the atomic particles carry electrons and can undergo transitions between their internal states -- including continua. It presents the detailed considerations of different theoretical approaches, that can be used to describe collisions of structured atomic particles for the very broad interval of impact energies ranging from 0.5--1 MeV/u till extreme relativistic energies where the collision velocity very closely approaches the speed of light.
Relativistic calculations of screening parameters and atomic radii of neutral atoms
Guerra, M.; Amaro, P.; Santos, J. P.; Indelicato, P.
2017-09-01
Calculations of the effective nuclear charge for elements with 1 ≤ Z ≤ 118 have been performed in a Dirac-Fock approach including all relativistic effects as well as contributions from quantum electrodynamics. Maximum charge density for every subshell of every element in the periodic table was also computed in the same framework as well as atomic radii based on the total charge density. Results were compared with the extensively cited works of Clementi et al., obtained in the 1960s with Roothan's self-consistent-field method.
Techniques of nuclear structure calculations
International Nuclear Information System (INIS)
Dyson, R.D.
1967-04-01
The quasiparticle method for identical particles interacting through pairing forces has been extended by others for use with systems of neutrons and protons. The method is to project isospin from separately considered neutron and proton quasiparticle wavefunctions. This is discussed in detail, and it seems that the projection may not be important. Therefore unprojected quasiparticle wavefunctions are tried with some success as a basis of states in which to diagonalize a realistic nuclear Hamiltonian. Brief unrelated calculations on nuclei of mass 19 and the SU(3) classification of states in the p-f shell are also presented. (author)
Atomic process calculations in hot dense plasmas using average atom models
International Nuclear Information System (INIS)
Velarde, G.; Aragones, J.M.; Gamez, L.; Honrubia, J.J.; Martinez-Val, J.M.; Minguez, E.; Ocana, J.L.; Perlado, J.M.; Serrano, J.F.
1987-01-01
During the past years, an important effort has been devoted in the authors Institute to develop the NORCLA code, which in the first version was characterized by the following features: one-dimensional lagrangian mesh; equilibrium between radiation, ion and electron species; local alpha energy deposition; neutron transport by the discrete ordinates method and analytical equation of state, opacities and conductivities. In the successive versions of NORCLA, EOS and electron conductivities were modified by the pressure ionization and degeneracy corrections; a module was also developed for computing the energy deposition of the incident ion beams coupled to the energy equation, and a code to calculate the alpha particle transport and energy deposition. Recently, a 3T version of the NORCLA code, with tabular EOS, opacities and conductivities, laser ray tracing and suprathermal electrons transport has been produced. In this article, the atomic physic models developed to determine more accurate the atomic data, such as EOS and opacities are explained, giving a brief description and a comparison of them. As a result of this development, a DENIM Atomic Data Library is being generated, taking some data and procedures from the SESAME Library. This library is presented, including a comparison of the opacity data for aluminium and iron at different densities and temperatures. Conclusions about this work are presented, and the ongoing developments summarized
Classical calculation of the total ionization energy of helium-like atoms
International Nuclear Information System (INIS)
Karastoyanov, A.
1990-01-01
Quantum mechanics rejects the classical modelling of microworld. One of the reasons is that the Bohr's rules can not be applied for many-electron atoms and molecules. But the many-body problem in classical mechanics has no analytical solution even for 3 particles. Numerical solutions should be used. The quantum Bohr's rule expressing the moment of momentum conservation for two particles is invalid in more complicated cases. Yet Bohr reached some success for helium-like atoms. The Bohr's formula concerning helim-like atoms is deduced again in this paper and its practical reliability is analyzed with contemporary data. The binding energy of the system is obtained in the simple form E=(Z-1/4) 2 α 2 mc 2 , where Z is the atomic number, α - the fine structure constant, M - the electron mass and c - the light speed in vacuum. The calculated values are compared with experimental data on the total ionization energy of the helium-like atoms from 2 He 4 to 29 Cu 64 . The error decreases quickly with the increasing of atomic mass, reaching zero for Cu. This indicated that the main source of error is the nucleus motion. The role of other possible causes is analyzed and proves negligible. (author). 1 tab, 4 refs
Fast numerical calculations of ion-atom collisions
International Nuclear Information System (INIS)
Reading, J.F.; Ford, A.L.; Becker, R.L.
1979-01-01
When an ion impinges on an atom, the cross sections for electronic transitions can be described in the independent electron model by functions of single electron amplitudes. A single centered expansion of the time-dependent wave function of an electron about the heavier nucleus, with charge Z/sub N/, is shown to be moderately successful in explaining the dependence of K-shell hole production on the charge, Z/sub p/, of the projectile. However, capture of electrons by the projectile is important for a complete understanding and can be incorporated, in principle, in the single-center approach by evaluation of a transition matrix element involving a final state on the projectile. This is not an easy theoretical problem even in an asymmetric (Z/sub p/ much less than Z/sub N/) collision, because long times are involved which aggravate the inadequacies of a coupled-state calculation where the continuum is replaced by a discrete set of pseudostates. Nevertheless a method was devised which allows convergence in the truncated expansion of Hilbert states. Comparisons are made to experiment. Future developments are discussed
The atomic structure of transition metal clusters
International Nuclear Information System (INIS)
Riley, S.J.
1995-01-01
Chemical reactions are used to probe the atomic (geometrical) structure of isolated clusters of transition metal atoms. The number of adsorbate molecules that saturate a cluster, and/or the binding energy of molecules to cluster surfaces, are determined as a function of cluster size. Systematics in these properties often make it possible to propose geometrical structures consistent with the experimental observations. We will describe how studies of the reactions of cobalt and nickel clusters with ammonia, water, and nitrogen provide important and otherwise unavailable structural information. Specifically, small (less than 20 atoms) clusters of cobalt and nickel atoms adopt entirely different structures, the former having packing characteristic of the bulk and the latter having pentagonal symmetry. These observations provide important input for model potentials that attempt to describe the local properties of transition metals. In particular, they point out the importance of a proper treatment of d-orbital binding in these systems, since cobalt and nickel differ so little in their d-orbital occupancy
Relativistic atomic structure: past, present and future
International Nuclear Information System (INIS)
Grant, I P
2010-01-01
Developments in a relativistic atomic structure have been driven by a combination of advances in experimental methods, in the theory of quantum electrodynamics, in numerical algorithms, computer hardware and software. Today's programs are still in many respects 'legacy codes' containing many features going back nearly half a century. It is time for a rethink.
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.
International Nuclear Information System (INIS)
Jiang, Jun; Mitroy, J.; Cheng, Yongjun; Bromley, M.W.J.
2015-01-01
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
Final disposal room structural response calculations
International Nuclear Information System (INIS)
Stone, C.M.
1997-08-01
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
Structure sensitivity in CO oxidation by a single Au atom supported on ceria
Song, W.; Hensen, E.J.M.
2013-01-01
The mechanism of CO oxidation by a CeO2(110)-supported gold atom has been investigated by DFT calculations. A novel stable surface structure has been identified in which one surface O atom of ceria migrates toward the isolated Au atom, resulting in a surface Au–O species that can react with CO.
Study of the embedded atom method of atomistic calculations for metals and alloys
International Nuclear Information System (INIS)
Johnson, R.A.
1990-10-01
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 L1 0 and L1 2 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
Atomic parity nonconservation: Electroweak parameters and nuclear structure
International Nuclear Information System (INIS)
Pollock, S.J.; Fortson, E.N.; Wilets, L.
1992-01-01
There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic-structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the standard model at the level of one-loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and nonrelativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear-structure effects may preclude using Pb isotope ratios to test the standard model at better than a 1% level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei
Geminal embedding scheme for optimal atomic basis set construction in correlated calculations
Energy Technology Data Exchange (ETDEWEB)
Sorella, S., E-mail: sorella@sissa.it [International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy and INFM Democritos National Simulation Center, Trieste (Italy); Devaux, N.; Dagrada, M., E-mail: mario.dagrada@impmc.upmc.fr [Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Université Pierre et Marie Curie, Case 115, 4 Place Jussieu, 75252 Paris Cedex 05 (France); Mazzola, G., E-mail: gmazzola@phys.ethz.ch [Theoretische Physik, ETH Zurich, 8093 Zurich (Switzerland); Casula, M., E-mail: michele.casula@impmc.upmc.fr [CNRS and Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Université Pierre et Marie Curie, Case 115, 4 Place Jussieu, 75252 Paris Cedex 05 (France)
2015-12-28
We introduce an efficient method to construct optimal and system adaptive basis sets for use in electronic structure and quantum Monte Carlo calculations. The method is based on an embedding scheme in which a reference atom is singled out from its environment, while the entire system (atom and environment) is described by a Slater determinant or its antisymmetrized geminal power (AGP) extension. The embedding procedure described here allows for the systematic and consistent contraction of the primitive basis set into geminal embedded orbitals (GEOs), with a dramatic reduction of the number of variational parameters necessary to represent the many-body wave function, for a chosen target accuracy. Within the variational Monte Carlo method, the Slater or AGP part is determined by a variational minimization of the energy of the whole system in presence of a flexible and accurate Jastrow factor, representing most of the dynamical electronic correlation. The resulting GEO basis set opens the way for a fully controlled optimization of many-body wave functions in electronic structure calculation of bulk materials, namely, containing a large number of electrons and atoms. We present applications on the water molecule, the volume collapse transition in cerium, and the high-pressure liquid hydrogen.
Atomic and electronic structure of exfoliated black phosphorus
International Nuclear Information System (INIS)
Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre; Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J.
2015-01-01
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 3 or H 3 PO 3 during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time
Atomic and electronic structure of exfoliated black phosphorus
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.
An Atomic Data and Analysis Structure
International Nuclear Information System (INIS)
Summers, Hugh P.
2000-01-01
The Atomic Data and Analysis Structure (ADAS) Project is a shared activity of a world-wide consortium of fusion and astrophysical laboratories directed at developing and maintaining a common approach to analysing and modelling the radiating properties of plasmas. The origin and objectives of ADAS and the organization of its codes and data collections outlined. Current special projects in the ADAS Project work-plans are listed and an illustration given of ADAS at work. (author)
Automated protein structure calculation from NMR data
International Nuclear Information System (INIS)
Williamson, Mike P.; Craven, C. Jeremy
2009-01-01
Current software is almost at the stage to permit completely automatic structure determination of small proteins of <15 kDa, from NMR spectra to structure validation with minimal user interaction. This goal is welcome, as it makes structure calculation more objective and therefore more easily validated, without any loss in the quality of the structures generated. Moreover, it releases expert spectroscopists to carry out research that cannot be automated. It should not take much further effort to extend automation to ca 20 kDa. However, there are technological barriers to further automation, of which the biggest are identified as: routines for peak picking; adoption and sharing of a common framework for structure calculation, including the assembly of an automated and trusted package for structure validation; and sample preparation, particularly for larger proteins. These barriers should be the main target for development of methodology for protein structure determination, particularly by structural genomics consortia
Broyden's method in nuclear structure calculations
International Nuclear Information System (INIS)
Baran, Andrzej; Bulgac, Aurel; Forbes, Michael McNeil; Hagen, Gaute; Nazarewicz, Witold; Schunck, Nicolas; Stoitsov, Mario V.
2008-01-01
Broyden's method, widely used in quantum chemistry electronic-structure calculations for the numerical solution of nonlinear equations in many variables, is applied in the context of the nuclear many-body problem. Examples include the unitary gas problem, the nuclear density functional theory with Skyrme functionals, and the nuclear coupled-cluster theory. The stability of the method, its ease of use, and its rapid convergence rates make Broyden's method a tool of choice for large-scale nuclear structure calculations
Atomic structure of a decagonal Al-Pd-Mn phase
Mihalkovič, Marek; Roth, Johannes; Trebin, Hans-Rainer
2017-12-01
We present a detailed structure solution for the 16 -Å decagonal quasicrystal in the Al-Pd-Mn system by means of cluster decoration and ab initio energy minimization. It is based on structure models of the ɛ and other approximant phases. The ɛ phases can be represented as subsets of a hexagon-boat-star (HBS) tiling. The decagonal phase comprises further HBS tiles. We have constructed several fictitious HBS approximants and optimized their structures individually. All tiles are decorated by two types of atomic clusters: the pseudo-Mackay icosahedron (PMI) and the large bicapped pentagonal prism (LBPP). It turns out that, whereas the PMI clusters can be kept essentially unchanged, the LBPP clusters must be adjusted in occupancy with Al atoms depending on their positions in the various tiles. In this way we obtain cluster decorations for all tiles of the decagonal quasicrystal. The calculations were confirmed by evaluation of an effective tile Hamiltonian.
Antiprotonic Radioactive Atom for Nuclear Structure Studies
International Nuclear Information System (INIS)
Wada, M.; Yamazaki, Y.
2005-01-01
A future experiment to synthesize antiprotonic radioactive nuclear ions is proposed for nuclear structure studies. Antiprotonic radioactive nuclear atom can be synthesized in a nested Penning trap where a cloud of antiprotons is prestored and slow radioactive nuclear ions are bunch-injected into the trap. By observing of the ratio of π+ and π- produced in the annihilation process, we can deduce the different abundance of protons and neutrons at the surface of the nuclei. The proposed method would provide a unique probe for investigating the nuclear structure of unstable nuclei
Diamond surface: atomic and electronic structure
International Nuclear Information System (INIS)
Pate, B.B.
1984-01-01
Experimental studies of the diamond surface (with primary emphasis on the (111) surface) are presented. Aspects of the diamond surface which are addressed include (1) the electronic structure, (2) the atomic structure, and (3) the effect of termination of the lattice by foreign atoms. Limited studies of graphite are discussed for comparison with the diamond results. Experimental results from valence band and core level photoemission spectroscopy (PES), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and carbon 1s near edge x-ray absorption fine structure (NEXAFS) spectroscopy (both the total electron yield (TEY) and Auger electron yield (AEY) techniques) are used to study and characterize both the clean and hydrogenated surface. In addition, the interaction of hydrogen with the diamond surface is examined using results from vibrational high resolution low energy electron loss spectroscopy (in collaboration with Waclawski, Pierce, Swanson, and Celotta at the National Bureau of Standards) and photon stimulated ion desorption (PSID) yield at photon energies near the carbon k-edge (hv greater than or equal to 280 eV). Both EELS and PSID verify that the mechanically polished 1 x 1 surface is hydrogen terminated and also that the reconstructed surface is hydrogen free. The (111) 2 x 2/2 x 1 reconstructed surface is obtained from the hydrogenated (111) 1 x 1:H surface by annealing to approx. = 1000 0 C. We observe occupied intrinsic surface states and a surface chemical shift (0.95 +- 0.1 eV) to lower binding energy of the carbon 1s level on the hydrogen-free reconstructed surface. Atomic hydrogen is found to be reactive with the reconstructed surface, while molecular hydrogen is relatively inert. Exposure of the reconstructed surface to atomic hydrogen results in chemisorption of hydrogen and removal of the intrinsic surface state emission in and near the band gap region
Theoretical calculation of saturated absorption for multilevel atoms
International Nuclear Information System (INIS)
O'Kane, T.J.; Scholten, R.E.; Farrell, P.M.
1998-01-01
We present the first theoretical saturated absorption spectra for general multi-level atoms, using a model based on extensions of the optical Bloch equations, and using Monte Carlo averaging of the absorption of individual atoms with random trajectories through a standing wave. We are for the first time able to accurately predict the merging of hyperfine and cross-over resonances due to intensity dependent phenomena such as power broadening. Results for 20-level sodium and 24-level rubidium models are presented and compared to experiment, demonstrating excellent agreement
International Nuclear Information System (INIS)
Gao Xiang; Cheng Cheng; Li Jiaming
2011-01-01
Scientific research fields for future energies such as inertial confinement fusion researches and astrophysics studies especially with satellite observatories advance into stages of precision physics. The relevant atomic data are not only enormous but also of accuracy according to requirements, especially for both energy levels and the collision data. The fine structure of high excited states of atoms and ions can be measured by precision spectroscopy. Such precision measurements can provide not only knowledge about detailed dynamics of electron-ion interactions but also a bench mark examination of the accuracy of electron-ion collision data, especially incorporating theoretical computations. We illustrate that by using theoretical calculation methods which can treat the bound states and the adjacent continua on equal footing. The precision spectroscopic measurements of excited fine structures can be served as stringent tests of electron-ion collision data. (authors)
International Nuclear Information System (INIS)
Rossi, F.N.
1986-10-01
The adiabatic potential lines are first obtained through the use of a pseudo-potential, depending on the electronic orbital moment. A perturbative method is then used to generate the potential surfaces, according to the potential lines. A quantum calculation in the thermal energy domain is realized, for the cross-sections concerning the structure transitions of the Rubidium, induced by the collision with hydrogen or deuterium molecules. This allowed the interpretation of the experimentally observed isotopic effect [fr
Gonzalez Lazo, Eduardo; Cruz Inclán, Carlos M.; Rodríguez Rodríguez, Arturo; Guzmán Martínez, Fernando; Abreu Alfonso, Yamiel; Piñera Hernández, Ibrahin; Leyva Fabelo, Antonio
2017-09-01
A primary approach for evaluating the influence of point defects like vacancies on atom displacement threshold energies values Td in BaTiO3 is attempted. For this purpose Molecular Dynamics Methods, MD, were applied based on previous Td calculations on an ideal tetragonal crystalline structure. It is an important issue in achieving more realistic simulations of radiation damage effects in BaTiO3 ceramic materials. It also involves irradiated samples under severe radiation damage effects due to high fluency expositions. In addition to the above mentioned atom displacement events supported by a single primary knock-on atom, PKA, a new mechanism was introduced. It corresponds to the simultaneous excitation of two close primary knock-on atoms in BaTiO3, which might take place under a high flux irradiation. Therefore, two different BaTiO3 Td MD calculation trials were accomplished. Firstly, single PKA excitations in a defective BaTiO3 tetragonal crystalline structure, consisting in a 2×2×2 BaTiO3 perovskite like super cell, were considered. It contains vacancies on Ba and O atomic positions under the requirements of electrical charge balance. Alternatively, double PKA excitations in a perfect BaTiO3 tetragonal unit cell were also simulated. On this basis, the corresponding primary knock-on atom (PKA) defect formation probability functions were calculated at principal crystal directions, and compared with the previous one we calculated and reported at an ideal BaTiO3 tetrahedral crystal structure. As a general result, a diminution of Td values arises in present calculations in comparison with those calculated for single PKA excitation in an ideal BaTiO3 crystal structure.
International Nuclear Information System (INIS)
Ehvarestov, R.A.; Panin, A.I.; Bandura, A.V.
2008-01-01
Account of relativistic effects on the properties of uranium hexafluoride is testified. Detailed comparison of single electron energies spectrum revealed in nonrelativistic (by Hartree-Fock method), relativistic (by Dirac-Fock method), and scalar-relativistic (using relativistic potential of atomic uranium frame) has been conducted. Optimization procedures of atomic basis in LCAO calculations of molecules and crystals permissive taking into account distortion of atomic orbitals when chemical bonding are discussed, and optimization effect of atomic basis on the results of scalar-relativistic calculations of UF 6 molecule properties is analyzed. Calculations of electronic structure and properties of UO 2 crystal having relativistic and nonrelativistic pseudopotentials have been realized [ru
Accurate methods for calculating atomic processes in high temperature plasmas
International Nuclear Information System (INIS)
Keady, J.J.; Abdallah, J.A. Jr.; Clark, R.E.H.
1992-01-01
A technique for computing monochromatic X-ray absorption is described and compared to experimental data. Calculations of power loss from carbon plasmas with comprehensive new datasets confirm that the direct inclusion of metastable states can noticeably decrease the calculated power loss
VIBRATIONAL RAMAN OPTICAL-ACTIVITY CALCULATIONS USING LONDON ATOMIC ORBITALS
DEFF Research Database (Denmark)
Helgaker, T.; Ruud, K.; Bak, Keld L.
1994-01-01
Ab initio calculations of Raman differential intensities are presented at the self-consistent field (SCF) level of theory. The electric dipole-electric dipole, electric dipole-magnetic dipole and electric dipole-electric quadrupole polarizability tensors are calculated at the frequency of the inc...
Virial-statistic method for calculation of atom and molecule energies
International Nuclear Information System (INIS)
Borisov, Yu.A.
1977-01-01
A virial-statistical method has been applied to the calculation of the atomization energies of the following molecules: Mo(CO) 6 , Cr(CO) 6 , Fe(CO) 5 , MnH(CO) 5 , CoH(CO) 4 , Ni(CO) 4 . The principles of this method are briefly presented. Calculation results are given for the individual contributions to the atomization energies together with the calculated and experimental atomization energies (D). For the Mo(CO) 6 complex Dsub(calc) = 1759 and Dsub(exp) = 1763 kcal/mole. Calculated and experimental combination heat values for carbonyl complexes are presented. These values are shown to be adequately consistent [ru
The variational method in the atomic structure calcularion
International Nuclear Information System (INIS)
Tomimura, A.
1970-01-01
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) [pt
Energy Technology Data Exchange (ETDEWEB)
Kohn, S.; Weare, J.; Ong, E.; Baden, S.
1997-05-01
We have applied structured adaptive mesh refinement techniques to the solution of the LDA equations for electronic structure calculations. Local spatial refinement concentrates memory resources and numerical effort where it is most needed, near the atomic centers and in regions of rapidly varying charge density. The structured grid representation enables us to employ efficient iterative solver techniques such as conjugate gradient with FAC multigrid preconditioning. We have parallelized our solver using an object- oriented adaptive mesh refinement framework.
Benchmark calculation programme concerning typical LMFBR structures
International Nuclear Information System (INIS)
Donea, J.; Ferrari, G.; Grossetie, J.C.; Terzaghi, A.
1982-01-01
This programme, which is part of a comprehensive activity aimed at resolving difficulties encountered in using design procedures based on ASME Code Case N-47, should allow to get confidence in computer codes which are supposed to provide a realistic prediction of the LMFBR component behaviour. The calculations started on static analysis of typical structures made of non linear materials stressed by cyclic loads. The fluid structure interaction analysis is also being considered. Reasons and details of the different benchmark calculations are described, results obtained are commented and future computational exercise indicated
International Nuclear Information System (INIS)
Fuchs, Alain; Villani, Cedric; Guthleben, Denis; Leduc, Michele; Brenner, Anastasios; Pouthas, Joel; Perrin, Jean
2014-01-01
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)
Local atomic structure of α-Pu
International Nuclear Information System (INIS)
Espinosa, F. J.; Villella, P.; Lashley, J. C.; Conradson, S. D.; Cox, L. E.; Martinez, R.; Martinez, B.; Morales, L.; Terry, J.; Pereyra, R. A.
2001-01-01
The local atomic structure of α-Pu was investigated using x-ray absorption fine structure (XAFS) spectroscopy. XAFS spectra were obtained for a zone-refined α-Pu and the results were compared to 32-year-old and Ce-doped (0.34 at.%) samples. X-ray diffraction (XRD) patterns were also measured for the zone-refined and 32-year-old materials. The extent of the Bragg peaks showed that amorphization of the 32-year-old sample had not occurred despite the prolonged exposure to self-radiation. Analogous to metastable δ-Pu alloys, the local atomic structure around Pu for the zone-refined material shows the possible presence of noncrystallographic Pu-Pu distances. Conversely, the Ce and the 32-year-old sample show no evidence for such noncrystallographic distances. Disorder in the Pu local environment was found to be impurity dependent. The Ce-doped sample presented a larger Pu-Pu nearest neighbor disorder than the aged sample, although the total amount of Am, U, and He impurities was actually higher in the aged sample. The local environment around U and Ce impurities is consistent with these elements being in substitutional lattice sites. In addition, U and Ce do not introduce significant lattice distortion to their nearest neighbors. This is consistent with disorder being more related to the perturbation of the coupling between the electronic and crystal structure, or the Peierls--Jahn-Teller distortion that generates the monoclinic α-Pu structure, and less to strain fields produced in the vicinity of the impurities
International Nuclear Information System (INIS)
Glushkov, A.V.
1994-01-01
Based on the method of effective potential involving the new polarization interaction potential calculated from polarization diagrams of the perturbation theory in the Thomas-Fermi approximation, the main parameters of the interatomic potentials (equilibrium distances, potential well depth) are evaluated for a system consisting of an alkali atom in the ground and excited states and of a mercury atom. The results of calculations of quasi-molecular terms for the A-Hg system, where A = Na, Cs, Fr, are reported, some of which are obtained for the first time. A comparison is made with available experimental and theoretical data. 29 refs., 2 figs., 1 tab
Nuclear structure calculations for astrophysical applications
International Nuclear Information System (INIS)
Moeller, P.; Kratz, K.L.
1992-01-01
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
International Nuclear Information System (INIS)
Grudzevich, O.D.; Zelenetskij, A.V.; Pashchenko, A.B.
1986-01-01
The last version of the KOP program for calculating cross sections of neutron and charged particle interaction with atomic nuclei within the scope of the optical model is described. The structure and program organization, library of total parameters of the optical potential, program identificators and peculiarities of its operation, input of source data and output of calculational results for printing are described in detail. The KOP program is described in Fortran- and adapted for EC-1033 computer
Learning from numerical calculations of ion-atom collisions
International Nuclear Information System (INIS)
Reading, J.F.; Ford, A.L.; Martir, M.; Becker, R.L.
1981-01-01
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
Learning from numerical calculations of ion-atom collisions
International Nuclear Information System (INIS)
Reading, J.F.; Ford, A.L.; Martir, M.
1982-01-01
Violent collisions of two independent many-particle systems, victims, are discussed in the atomic sphere. The asymmetric region where the charge of the projectile Zsub(p) is less than the target nuclear charge Zsub(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 (Zsub(p) approx. equal to Zsub(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. (orig.)
Calculating evolutionary dynamics in structured populations.
Directory of Open Access Journals (Sweden)
Charles G Nathanson
2009-12-01
Full Text Available Evolution is shaping the world around us. At the core of every evolutionary process is a population of reproducing individuals. The outcome of an evolutionary process depends on population structure. Here we provide a general formula for calculating evolutionary dynamics in a wide class of structured populations. This class includes the recently introduced "games in phenotype space" and "evolutionary set theory." There can be local interactions for determining the relative fitness of individuals, but we require global updating, which means all individuals compete uniformly for reproduction. We study the competition of two strategies in the context of an evolutionary game and determine which strategy is favored in the limit of weak selection. We derive an intuitive formula for the structure coefficient, sigma, and provide a method for efficient numerical calculation.
Implementation of highly parallel and large scale GW calculations within the OpenAtom software
Ismail-Beigi, Sohrab
The need to describe electronic excitations with better accuracy than provided by band structures produced by Density Functional Theory (DFT) has been a long-term enterprise for the computational condensed matter and materials theory communities. In some cases, appropriate theoretical frameworks have existed for some time but have been difficult to apply widely due to computational cost. For example, the GW approximation incorporates a great deal of important non-local and dynamical electronic interaction effects but has been too computationally expensive for routine use in large materials simulations. OpenAtom is an open source massively parallel ab initiodensity functional software package based on plane waves and pseudopotentials (http://charm.cs.uiuc.edu/OpenAtom/) that takes advantage of the Charm + + parallel framework. At present, it is developed via a three-way collaboration, funded by an NSF SI2-SSI grant (ACI-1339804), between Yale (Ismail-Beigi), IBM T. J. Watson (Glenn Martyna) and the University of Illinois at Urbana Champaign (Laxmikant Kale). We will describe the project and our current approach towards implementing large scale GW calculations with OpenAtom. Potential applications of large scale parallel GW software for problems involving electronic excitations in semiconductor and/or metal oxide systems will be also be pointed out.
Atomic structures and compositions of internal interfaces
Energy Technology Data Exchange (ETDEWEB)
Seidman, D.N. (Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering); Merkle, K.L. (Argonne National Lab., IL (United States))
1992-03-01
This research program addresses fundamental questions concerning the relationships between atomic structures and chemical compositions of metal/ceramic heterophase interfaces. The chemical composition profile across a Cu/MgO {l brace}111{r brace}-type heterophase interface, produced by the internal oxidation of a Cu(Mg) single phase alloy, is measured via atom-probe field-ion microscopy with a spatial resolution of 0.121 nm; this resolution is equal to the interplanar space of the {l brace}222{r brace} MgO planes. In particular, we demonstrate for the first time that the bonding across a Cu/MgO {l brace}111{r brace}-type heterophase interface, along a <111> direction common to both the Cu matrix and an MgO precipitate, has the sequence Cu{vert bar}O{vert bar}Mg{hor ellipsis} and not Cu{vert bar}Mg{vert bar}O{hor ellipsis}; this result is achieved without any deconvolution of the experimental data. Before determining this chemical sequence it was established, via high resolution electron microscopy, that the morphology of an MgO precipitate in a Cu matrix is an octahedron faceted on {l brace}111{r brace} planes with a cube-on-cube relationship between a precipitate and the matrix. First results are also presented for the Ni/Cr{sub 2}O{sub 4} interface; for this system selected area atom probe microscopy was used to analyze this interface; Cr{sub 2}O{sub 4} precipitates are located in a field-ion microscope tip and a precipitate is brought into the tip region via a highly controlled electropolishing technique.
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 structure investigation of ionized krypton
International Nuclear Information System (INIS)
Kotze, P.B.
1981-12-01
The experimental lifetimes of ionized Krypton are discussed. Theoretical, the Coulomb approximation proves to be a reliable tool for the performance of calculations in Krypton II, where in general good agreement between experimental and theoretical lifetimes is reached, but its vulnerability is exposed in the case of Krypton III, where only results concerning levels with a 4p 3 ( 4 S 0 ) parent core can be obtained. Although the single configuration Hartree-Fock approximation turns out to be an adequate way of obtaining wave functions of excited states in Krypton III, cancellation effects resulting from configuration-interaction mixing, make the calculated transition probabilities in Krypton II less reliable. Previous work on configuration-interaction effects in the spectrum of Krypton II (El 76a, El 76b) reveals that good agreement between experimental and theoretical results can be obtained. A systematic theoretical analysis based on the multi-configurarion Hartree-Fock approximation to account for configuration-interaction effects should contribute a great deal to the existing knowledge of the energy spectra of ionized atoms
Calculation of the number of atoms displaced during the irradiation of monolayer graphene
International Nuclear Information System (INIS)
Daniel Codorniu Pujals; Yuri Aguilera Corrales; Francesco Baldassarre
2011-01-01
The irradiation of monolayer graphene, combined with chemical functionalization, could be an effective method for modifying its electronic structure and for achieving specific physical properties adjusted to different applications. A difficulty arising during planning and studying the irradiation in this system is that many of the models of interaction of the radiation with the substance cannot be applied to the two-dimensional structure of graphene. In particular, the mathematical expressions available to calculate the number of atoms displaced during the bombardment with particles can be applied only to 3D isotropic solids. In the present work, an alternative analytic expression is presented for the irradiation of graphene with heavy ions or with protons and other light charged particles. The expression was obtained on the basis of the classic theory of dispersion, using a Coulomb potential for the light charged particles and one of Inverse Square for heavy ions. For medium values of the energy of the incident particle a decreasing dependence of the number of displaced atoms with energy is obtained. This behavior, related with the two-dimensional structure of the target, had been observed in other authors' works using computational simulation. (author)
A simple algorithm for calculating the scattering angle in atomic collisions
International Nuclear Information System (INIS)
Belchior, J.C.; Braga, J.P.
1996-01-01
A geometric approach to calculate the classical atomic scattering angle is presented. The trajectory of the particle is divided into several straight-lines and changing in direction from one sector to the other is used to calculate the scattering angle. In this model, calculation of the scattering angle does not involve either the direct evaluation of integrals nor classical turning points. (author)
Directory of Open Access Journals (Sweden)
Raiker Witter
2015-01-01
Full Text Available Polarization of atoms plays a substantial role in molecular interactions. Class I and II force fields mostly calculate with fixed atomic charges which can cause inadequate descriptions for highly charged molecules, for example, ion channels or metalloproteins. Changes in charge distributions can be included into molecular mechanics calculations by various methods. Here, we present a very fast computational quantum mechanical method, the Bond Polarization Theory (BPT. Atomic charges are obtained via a charge calculation method that depend on the 3D structure of the system in a similar way as atomic charges of ab initio calculations. Different methods of population analysis and charge calculation methods and their dependence on the basis set were investigated. A refined parameterization yielded excellent correlation of R=0.9967. The method was implemented in the force field COSMOS-NMR and applied to the histidine-tryptophan-complex of the transmembrane domain of the M2 protein channel of influenza A virus. Our calculations show that moderate changes of side chain torsion angle χ1 and small variations of χ2 of Trp-41 are necessary to switch from the inactivated into the activated state; and a rough two-side jump model of His-37 is supported for proton gating in accordance with a flipping mechanism.
Directory of Open Access Journals (Sweden)
Koji Ogata
2018-02-01
Full Text Available The octanol–water partition coefficient (logPow is an important index for measuring solubility, membrane permeability, and bioavailability in the drug discovery field. In this paper, the logPow values of 58 compounds were predicted by alchemical free energy calculation using molecular dynamics simulation. In free energy calculations, the atomic charges of the compounds are always fixed. However, they must be recalculated for each solvent. Therefore, three different sets of atomic charges were tested using quantum chemical calculations, taking into account vacuum, octanol, and water environments. The calculated atomic charges in the different environments do not necessarily influence the correlation between calculated and experimentally measured ∆Gwater values. The largest correlation coefficient values of the solvation free energy in water and octanol were 0.93 and 0.90, respectively. On the other hand, the correlation coefficient of logPow values calculated from free energies, the largest of which was 0.92, was sensitive to the combination of the solvation free energies calculated from the calculated atomic charges. These results reveal that the solvent assumed in the atomic charge calculation is an important factor determining the accuracy of predicted logPow values.
Equilibrium structure and atomic vibrations of Nin clusters
Borisova, Svetlana D.; Rusina, Galina G.
2017-12-01
The equilibrium bond lengths and binding energy, second differences in energy and vibrational frequencies of free clusters Nin (2 ≤ n ≤ 20) were calculated with the use of the interaction potential obtained in the tight-binding approximation (TBA). The results show that the minimum vibration frequency plays a significant role in the evaluation of the dynamic stability of the clusters. A nonmonotonic dependence of the minimum vibration frequency of clusters on their size and the extreme values for the number of atoms in a cluster n = 4, 6, 13, and 19 are demonstrated. This result agrees with the theoretical and experimental data on stable structures of small metallic clusters.
Atomic structures of Cd Te and Cd Se (110) surfaces
International Nuclear Information System (INIS)
Watari, K.; Ferraz, A.C.
1996-01-01
Results are reported based on the self-consistent density-functional theory, within the local-density approximation using ab-initio pseudopotentials of clean Cd Te and Cd Se (110) surfaces. We analyzed the trends for the equilibrium atomic structures, and the variations of the bond angles at the II-VI (110). The calculations are sensitive to the ionicity of the materials and the results are in agreement with the arguments which predict that the relaxed zinc-blend (110) surfaces should depend on ionicity. (author). 17 refs., 1 figs., 3 tabs
Multiconfiguration Dirac-Fock method for atomic structure
International Nuclear Information System (INIS)
Sasaki, Ken
1982-02-01
The multiconfiguration Dirac-Fock method for calculating the atomic structure is reviewed in some detail. Being more comprehensive than the ones introduced in Desclaux's paper, the mathematical formulae derived in this review are more helpful to trace the thread of ideas and understand the algorithm in Desclaux's computer program which embodied the method. A detailed analysis is made on the restrictions on how the program is used, that is, on the fact that it does not apply to the problem where the configuration mixing occurs via the one-electron Hamiltonian. Finally, in conclusion, a way to overcome the difficulty is suggested. (author)
Seldam, C.A. ten; Groot, S.R. de
1952-01-01
From Jensen's and Gombás' modification of the statistical Thomas-Fermi atom model, a theory for compressed atoms is developed by changing the boundary conditions. Internal kinetic energy and polarizability of argon are calculated as functions of pressure. At 1000 atm. an internal kinetic energy of
Boll, Torben; Zhu, Zhiyong; Al-Kassab, Talaat; Schwingenschlö gl, Udo
2012-01-01
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
Calculation of the photoionization cross section of the 4d10 subshell of the La atom
International Nuclear Information System (INIS)
Amusia, M.Ya.; Sheftel, S.I.
1976-01-01
The photoionization cross section of 4d 10 subshell of La atom is calculated. The cross section curve near its threshold is strongly modified by rearrangement of outer shells in the process of photoionization. (Auth.)
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.
Influence of the atomic structure on the quantum state of sputtered Ir atoms
International Nuclear Information System (INIS)
Bastiaansen, J.; Philipsen, V.; Lievens, P.; Silverans, R.E.; Vandeweert, E.
2004-01-01
The probability of the ejection of a neutral atom in a specific quantum state after keV-ion beam sputtering is often interpreted in terms of the interaction between the atomic states of the escaping atom and the electronic states of the solid. In this work, we examined this interplay in the sputtering of iridium as this element has--unlike the elements employed in previous investigations--a complex atomic structure due to strong configuration interactions. Double-resonant two-photon laser ionization is used to probe the sputtered Ir atoms yielding information about the probability for an ejected atom to populate a specific atomic state and its escape velocity. The qualitative features of the corresponding population partition and state-selective velocity distributions show the influence of the excitation energy and the electronic structure of the different atomic states. A comparison is made between the experimental data and predictions from the resonant electron transfer description
Self-consistent electronic-structure calculations for interface geometries
International Nuclear Information System (INIS)
Sowa, E.C.; Gonis, A.; MacLaren, J.M.; Zhang, X.G.
1992-01-01
This paper describes a technique for computing self-consistent electronic structures and total energies of planar defects, such as interfaces, which are embedded in an otherwise perfect crystal. As in the Layer Korringa-Kohn-Rostoker approach, the solid is treated as a set of coupled layers of atoms, using Bloch's theorem to take advantage of the two-dimensional periodicity of the individual layers. The layers are coupled using the techniques of the Real-Space Multiple-Scattering Theory, avoiding artificial slab or supercell boundary conditions. A total-energy calculation on a Cu crystal, which has been split apart at a (111) plane, is used to illustrate the method
Diagnosing Students’ conception on atomic structure using open ended questions
Fitriza, Z.; Gazali, F.
2018-05-01
This study aims to diagnose students’ conception on atomic structure concepts using open ended questions. For this reason, a 7 items of assay test was administered to 135 senior high school students from different schools in West Sumatera. The data were collected using a an open ended test which is covering the concept used in the topic Atomic Structure. The open ended test of students’ conceptual was developed to identify the alternative conceptions that student might have regarding the concepts in Atomic Structure, to measure the level of students’ conceptions, and the way of students’ thinking concerning the concepts. The results showed that students find difficulties about some concepts of Atomic structure such as atom, atomic model, electron configuration, period and group.The result of this study illuminated the concepts to be underlined in developing teaching and learning approach concerning the topic of Atomic Structure.
Benchmark Calculations for Electron Collisions with Complex Atoms
International Nuclear Information System (INIS)
Zatsarinny, Oleg; Bartschat, Klaus
2014-01-01
The B-spline R-matrix (BSR) approach [1,2] is based on the non-perturbative close-coupling method. As such it is, in principle, based on an exact expansion of the solution of the time-independent Schrödinger equation, as an infinite sum/integral of N-electron target states coupled to the wave function of the scattering projectile. The N-electron target states, again, can in principle be calculated with almost arbitrary accuracy using sufficiently large configuration-interaction expansions and the correct interaction hamiltonian. In practice, of course, the infinite expansions have to be cut off in some way and the exact hamiltonian may not be available. In the collision part of the BSR method, the integral over the ionization continuum and the infinite sum over high-lying Rydberg states are replaced by a finite sum over square-integrable pseudo-states. Also, a number of inner shells are treated as (partially) inert, i.e., a minimum number of electrons are required in those subshells.
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...... the generalized Sturmian method is applied to atoms, the configurations are constructed from hydrogenlike atomic orbitals with an effective charge which is characteristic of the configuration. Thus, orthonormality between the orbitals of different configurations cannot be assumed, and the generalized Slater...
DEFF Research Database (Denmark)
Ruud, Kenneth; Helgaker, Trygve; Kobayashi, Rika
1994-01-01
to corresponding individual gauges for localized orbitals (IGLO) results. The London results show better basis set convergence than IGLO, especially for heavier atoms. It is shown that the choice of active space is crucial for determination of accurate nuclear shielding constants.......Nuclear shielding calculations are presented for multiconfigurational self-consistent field wave functions using London atomic orbitals (gauge invariant atomic orbitals). Calculations of nuclear shieldings for eight molecules (H2O, H2S, CH4, N2, CO, HF, F2, and SO2) are presented and compared...
Atomic and electronic structures of divacancy in graphene nanoribbons
Energy Technology Data Exchange (ETDEWEB)
Zhao Jun [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Zeng Hui, E-mail: zenghui@yangtzeu.edu.cn [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Wei Jianwei [School of Mathematics and Physics, Chongqing University of Technology, Chongqing 400054 (China)
2012-01-15
First principles calculations have been performed to investigate the electronic structures and transport properties of defective graphene nanoribbons (GNRs) in the presence of pentagon-octagon-pentagon (5-8-5) defects. Electronic band structure results reveal that 5-8-5 defects in the defective zigzag graphene nanoribbon (ZGNR) is unfavorable for electronic transport. However, such defects in the defective armchair graphene nanoribbon (AGNR) give rise to smaller band gap than that in the pristine AGNR, and eventually results in semiconductor to metal-like transition. The distinct roles of 5-8-5 defects in two kinds of edged-GNR are attributed to the different coupling between {pi}{sup Low-Asterisk} and {pi} subbands influenced by the defects. Our findings indicate the possibility of a new route to improve the electronic transport properties of graphene nanoribbons via tailoring the atomic structures by ion irradiation.
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.
Modulated structure calculated for superconducting hydrogen sulfide
Energy Technology Data Exchange (ETDEWEB)
Majumdar, Arnab; Tse, John S.; Yao, Yansun [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK (Canada)
2017-09-11
Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calculations revealed a modulated structure with high proton mobility which exhibits a diffraction pattern matching well with experiment. The structure consists of a sublattice of rectangular meandering SH{sup -} chains and molecular-like H{sub 3}S{sup +} stacked alternately in tetragonal and cubic slabs forming a long-period modulation. The novel structure offers a new perspective on the possible origin of the superconductivity at very high temperatures in which the conducting electrons in the SH chains are perturbed by the fluxional motions of the H{sub 3}S resulting in strong electron-phonon coupling. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)
Local atomic structure inheritance in Ag50Sn50 melt
International Nuclear Information System (INIS)
Bai, Yanwen; Bian, Xiufang; Qin, Jingyu; Hu, Lina; Yang, Jianfei; Zhang, Kai; Zhao, Xiaolin; Yang, Chuncheng; Zhang, Shuo; Huang, Yuying
2014-01-01
Local structure inheritance signatures were observed during the alloying process of the Ag 50 Sn 50 melt, using high-temperature X-ray diffraction and ab initio molecular dynamics simulations. The coordination number N m around Ag atom is similar in the alloy and in pure Ag melts (N m ∼ 10), while, during the alloying process, the local structure around Sn atoms rearranges. Sn-Sn covalent bonds were substituted by Ag-Sn chemical bonds, and the total coordination number around Sn increases by about 70% as compared with those in the pure Sn melt. Changes in the electronic structure of the alloy have been studied by Ag and Sn K-edge X-ray absorption spectroscopy, as well as by calculations of the partial density of states. We propose that a leading mechanism for local structure inheritance in Ag 50 Sn 50 is due to s-p dehybridization of Sn and to the interplay between Sn-s and Ag-d electrons
The atomic and electronic structure of amorphous silicon nitride
International Nuclear Information System (INIS)
Alvarez, F.; Valladares, A.A.
2002-01-01
Using a novel approach to the ab initio generation of random networks we constructed two nearly stoichiometric samples of amorphous silicon nitride with the same content x= 1.29. The two 64-atom periodically-continued cubic diamond-like cells contain 28 silicons and 36 nitrogens randomly substituted, and were amorphized with a 6 f s time step by heating them to just below their melting temperature with a Harris-functional based, molecular dynamics code in the LDA approximation. The averaged total radial distribution function (RDF) obtained is compared with some existing Tersoff-like potential simulations and with experiment; ours agree with experiment. All the partial radial features are calculated and the composition of the second peak also agrees with experiment. The electronic structure is calculated and the optical gaps obtained using both a HOMO-LUMO approach and the Tauc-like procedure developed recently that gives reasonable gaps. (Author)
An Efficient Method for Electron-Atom Scattering Using Ab-initio Calculations
Energy Technology Data Exchange (ETDEWEB)
Xu, Yuan; Yang, Yonggang; Xiao, Liantuan; Jia, Suotang [Shanxi University, Taiyuan (China)
2017-02-15
We present an efficient method based on ab-initio calculations to investigate electron-atom scatterings. Those calculations profit from methods implemented in standard quantum chemistry programs. The new approach is applied to electron-helium scattering. The results are compared with experimental and other theoretical references to demonstrate the efficiency of our method.
Cobalamins uncovered by modern electronic structure calculations
DEFF Research Database (Denmark)
Kepp, Kasper Planeta; Ryde, Ulf
2009-01-01
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 are cis-steric distortions, electrostatic stabilization of radical products, the realization that nucleotide units can serve as polar handles, and the careful design of the active sites, with polar residues in the radical enzymes and non-polar residues in the transferases. Together, these strategies...
Lattice QCD Calculation of Nucleon Structure
International Nuclear Information System (INIS)
Liu, Keh-Fei; Draper, Terrence
2016-01-01
It is emphasized in the 2015 NSAC Long Range Plan that 'understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics.' Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large-scale computer simulation. We started out by calculating the nucleon form factors -- electromagnetic, axial-vector, ?NN, and scalar form factors, the quark spin contribution to the proton spin, the strangeness magnetic moment, the quark orbital angular momentum, the quark momentum fraction, and the quark and glue decomposition of the proton momentum and angular momentum. The first round of calculations were done with Wilson fermions in the 'quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors, charm and strange quark masses, the charmonium spectrum and the D_s meson decay constant f_D__s, the strangeness and charmness, the meson mass decomposition and the strange quark spin from the
Lattice QCD Calculation of Nucleon Structure
Energy Technology Data Exchange (ETDEWEB)
Liu, Keh-Fei [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy; Draper, Terrence [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy
2016-08-30
It is emphasized in the 2015 NSAC Long Range Plan that "understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large-scale computer simulation. We started out by calculating the nucleon form factors -- electromagnetic, axial-vector, πNN, and scalar form factors, the quark spin contribution to the proton spin, the strangeness magnetic moment, the quark orbital angular momentum, the quark momentum fraction, and the quark and glue decomposition of the proton momentum and angular momentum. The first round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors, charm and strange quark masses, the charmonium spectrum and the D_{s} meson decay constant f_{Ds}, the strangeness and charmness, the meson mass
Molecular structures from density functional calculations with simulated annealing
International Nuclear Information System (INIS)
Jones, R.O.
1991-01-01
The geometrical structure of any aggregate of atoms is one of its basic properties and, in principle, straightforward to predict. One chooses a structure, determines the total energy E of the system of electrons and ions, and repeats the calculation for all possible geometries. The ground state structure is that with the lowest energy. A quantum mechanical calculation of the exact wave function Ψ would lead to the total energy, but this is practicable only in very small molecules. Furthermore, the number of local minima in the energy surface increases dramatically with increasing molecular size. While traditional ab initio methods have had many impressive successes, the difficulties have meant that they have focused on systems with relatively few local minima, or have used experiments or experience to limit the range of geometries studied. On the other hand, calculations for much larger molecules and extended systems are often forced to use simplifying assumptions about the interatomic forces that limit their predictive capability. The approach described here avoids both of these extremes: Total energies of predictive value are calculated without using semi-empirical force laws, and the problem of multiple minima in the energy surface is addressed. The density functional formalism, with a local density approximation for the exchange-correlation energy, allows one to calculate the total energy for a given geometry in an efficient, if approximate, manner. Calculations for heavier elements are not significantly more difficult than for those in the first row and provide an ideal way to study bonding trends. When coupled with finite-temperature molecular dynamics, this formalism can avoid many of the energetically unfavorable minima in the energy surface. We show here that the method leads to surprising and exciting results. (orig.)
Cipolla, Laura; Ferrari, Lia A.
2016-01-01
A hands-on approach to introduce the chemical elements and the atomic structure to elementary/middle school students is described. The proposed classroom activity presents Bohr models of atoms using common and inexpensive materials, such as nested plastic balls, colored modeling clay, and small-sized pasta (or small plastic beads).
Energy Technology Data Exchange (ETDEWEB)
Kroes, Geert-Jan, E-mail: g.j.kroes@chem.leidenuniv.nl; Pavanello, Michele [Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands); Blanco-Rey, María [Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20080 Donostia-San Sebastián (Spain); Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Alducin, Maite [Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales, Centro Mixto CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Auerbach, Daniel J. [Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands); Max Planck Institute for Biophysical Chemistry, Göttingen (Germany); Institute for Physical Chemistry, Georg-August University of Göttingen, Göttingen (Germany)
2014-08-07
Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction (“EF”) model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated “post” (“p”) the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy
Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J
2014-08-07
Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the
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.
Ab Initio Calculations of the Electronic Structures and Biological Functions of Protein Molecules
Zheng, Haoping
2003-04-01
The self-consistent cluster-embedding (SCCE) calculation method reduces the computational effort from M3 to about M1 (M is the number of atoms in the system) with unchanged calculation precision. So the ab initio, all-electron calculation of the electronic structure and biological function of protein molecule becomes a reality, which will promote new proteomics considerably. The calculated results of two real protein molecules, the trypsin inhibitor from the seeds of squash Cucurbita maxima (CMTI-I, 436 atoms) and the Ascaris trypsin inhibitor (912 atoms, two three-dimensional structures), are presented. The reactive sites of the inhibitors are determined and explained. The precision of structure determination of inhibitors are tested theoretically.
Theoretical development of atomic structure: Past, present and future
International Nuclear Information System (INIS)
Tiwary, S.N.
1994-11-01
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
Calculation on uranium carbon oxygen system molecular structure by DFT
International Nuclear Information System (INIS)
Zhang Guangfeng; Wang Xiaolin; Zou Lexi; Sun Ying; Xue Weidong; Zhu Zhenghe; Wang Hongyan
2001-01-01
The authors study on the possible molecular structures U-C-O, U-O-C, C-U-O (angular structure C a nd linear structure C ∞υ ) of carbon monoxide interacting on uranium metal surface by Density functional theory (DFT). The uranium atom is used RECP (Relativistic Effective Core Potential) and contracted valence basis sets (6s5p2d4f)/[3s3p2d2f], and for carbon and oxygen atoms all are 6-311G basis sets. The author presents the results of energy optimum which shows that triple and quintuple state are more stable. The authors get the electronic state, geometry structure, energy, harmonic frequency, mechanical property, etc. of these twelve triple and quintuple state relative stable structures. The normal vibrational analytical figure of angular structure (C s ) and linear structure (C ∞υ ) is given at the same time. It is indicated that angular structure has lower energy than linear structure, moreover the angular structure of U-C-O( 3 A ) has the lowest energy. The bond strength between uranium atom and carbon monoxide is weak and between uranium atom and oxygen atom is slightly stronger than between uranium atom and carbon atom which the authors can know by superposition population and bond energy analysis among atoms
International Nuclear Information System (INIS)
Utsumi, Takayuki; Sasaki, Akira
2000-02-01
The procedures of grasp92 code to calculate accurate (relative error nearly equal 10 -7 ) eigenvalue for the ground sate of helium atom of the Dirac-Coulomb Hamiltonian are presented. The grasp92 code, based on the multi-configuration Dirac-Fock method, is widely used to calculate the atomic properties. However, the main part of the accurate calculations, extended optimal level calculation (EOL), suffer frequently numerical instabilities due to the lack of the confident procedures. The purpose of this report is to illustrate the guideline for stable EOL calculations by calculating the most fundamental atomic system, i.e. the ground sate of helium atom ls 2 1 S 2 . This procedure could be extended for the high-precise eigenfunction calculation of more complex atomic systems, for example highly ionized atoms and high-Z atoms. (author)
Nuclear structure effects on calculated fast neutron reaction cross sections
International Nuclear Information System (INIS)
Avrigeanu, V.
1992-01-01
The importance of accurate low-lying level schemes for reaction cross section calculation and need for microscopically calculated levels are proved with reference to fast neutron induced reactions in the A = 50 atomic mass range. The uses of the discrete levels both for normalization of phenomenological level density approaches and within Hauser-Feshbach calculations are discussed in this respect. (Author)
Semi-empirical calculations on the structure of the uronium ion
Harkema, Sybolt
1972-01-01
Semi-empirical calculations (CNDO/2) on the structure of the uronium ion are presented. Assuming a planar ion with fixed bond lengths, the bond angles involving the heavy atoms can be calculated with fair accuracy. Changes in bond length and angles, which occur upon protonation of the urea molecule,
Niels Bohr and the Atomic Structure
Indian Academy of Sciences (India)
IAS Admin
principle with the restriction that no more than two electrons occupy a given ... displacement laws. Early in his ... The only difference between them is their atomic weight. F Soddy ... validity, Bohr took his theory to Rutherford. Unfortunately,.
Determination of atomic cluster structure with cluster fusion algorithm
DEFF Research Database (Denmark)
Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.
2005-01-01
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....
Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model
International Nuclear Information System (INIS)
Kao, Hsiu-Fen; Lo, Ikai; Chiang, Jih-Chen; Wang, Wan-Tsang; Hsu, Yu-Chi; Wu, Chieh-Lung; Gau, Ming-Hong; Chen, Chun-Nan; Ren, Chung-Yuan; Lee, Meng-En
2012-01-01
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 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.
Unraveling the atomic structure of ultrafine iron clusters
Wang, Hongtao; Li, Kun; Yao, Yingbang; Wang, Qingxiao; Cheng, Yingchun; Schwingenschlö gl, Udo; Zhang, Xixiang; Yang, Wei
2012-01-01
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
DEFF Research Database (Denmark)
Christensen, N. Egede; Feuerbacher, B.
1974-01-01
is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi...... of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.......The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure...
Atomic structure of self-organizing iridium induced nanowires on Ge(001)
Energy Technology Data Exchange (ETDEWEB)
Kabanov, N.S., E-mail: n.kabanov@utwente.nl [Faculty of Physics, Moscow State University, 119991 (Russian Federation); Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P. O. Box 217, Enschede 7500 AE (Netherlands); Heimbuch, R.; Zandvliet, H.J.W. [Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P. O. Box 217, Enschede 7500 AE (Netherlands); Saletsky, A.M.; Klavsyuk, A.L. [Faculty of Physics, Moscow State University, 119991 (Russian Federation)
2017-05-15
Highlights: • Ir/Ge(001) structure has been studied with DFT calculations and scanning tunneling microscopy. • Ir/Ge(001) nanowires are composed of Ge atoms and Ir atoms are located in subsurface positions. • The regions in the vicinity of the nanowires are very dynamic, even at temperatures as low as 77 K. - Abstract: The atomic structure of self-organizing iridium (Ir) induced nanowires on Ge(001) is studied by density functional theory (DFT) calculations and variable-temperature scanning tunneling microscopy. The Ir induced nanowires are aligned in a direction perpendicular to the Ge(001) substrate dimer rows, have a width of two atoms and are completely kink-less. Density functional theory calculations show that the Ir atoms prefer to dive into the Ge(001) substrate and push up the neighboring Ge substrate atoms. The nanowires are composed of Ge atoms and not Ir atoms as previously assumed. The regions in the vicinity of the nanowires are very dynamic, even at temperatures as low as 77 K. Time-resolved scanning tunneling microscopy measurements reveal that this dynamics is caused by buckled Ge substrate dimers that flip back and forth between their two buckled configurations.
Angular momentum branching ratios for electron-induced ionization: Atomic and model calculations
International Nuclear Information System (INIS)
Mehl, M.J.; Einstein, T.L.
1987-01-01
We present calculations of the matrix elements for electron-induced ionization of core electrons of atoms. We use both self-consistent atomic potentials for accuracy and model potentials to gain physical insight. We pay particular attention to the angular momentum distribution of the two final-state electrons, especially when one of them lies near what would be the Fermi energy in a solid (i.e., as in an absorption fine-structure experiment). For nodeless core wave functions, in the dominant channel both final-state electrons have angular momentum one greater than that of the initial core state. For sufficiently deeply bound states, this first approximate selection rule holds until the incident electron energy exceeds the ionization threshold by at least 500 eV, i.e., over the experimentally relevant range. It is also possible to determine the angular momentum distribution of the final-state electron. The EXAFS-like electron tends to have angular momentum one greater than that of the initial core state, even in some cases where the first approximate selection rule does not hold. (EXAFS is extended x-ray-absorption fine structure.) The strongest trend is that the dipole component in a partial-wave expansion of the Coulomb interaction dominates the matrix element. In these studies, careful treatment of not just the core state but also the unbound states is crucial; we show that the conventional orthogonalized plane-wave approximation is inadequate, giving incorrect ordering of the channels. For model potentials with an adjustable screening length, low-lying bound resonances are found to play an important role
Calculating Relativistic Transition Matrix Elements for Hydrogenic Atoms Using Monte Carlo Methods
Alexander, Steven; Coldwell, R. L.
2015-03-01
The nonrelativistic transition matrix elements for hydrogen atoms can be computed exactly and these expressions are given in a number of classic textbooks. The relativistic counterparts of these equations can also be computed exactly but these expressions have been described in only a few places in the literature. In part, this is because the relativistic equations lack the elegant simplicity of the nonrelativistic equations. In this poster I will describe how variational Monte Carlo methods can be used to calculate the energy and properties of relativistic hydrogen atoms and how the wavefunctions for these systems can be used to calculate transition matrix elements.
Calculation of the fifth atomic energy research dynamic benchmark with APROS
International Nuclear Information System (INIS)
Puska Eija Karita; Kontio Harii
1998-01-01
The band-out presents the model used for calculation of the fifth atomic energy research dynamic benchmark with APROS code. In the calculation of the fifth atomic energy research dynamic benchmark the three-dimensional neutronics model of APROS was used. The core was divided axially into 20 nodes according to the specifications of the benchmark and each six identical fuel assemblies were placed into one one-dimensional thermal hydraulic channel. The five-equation thermal hydraulic model was used in the benchmark. The plant process and automation was described with a generic WWER-440 plant model created by IVO Power Engineering Ltd. - Finland. (Author)
Calculation of Bremsstrahlung radiation of electrons on atoms in wide energy range of photons
Romanikhin, V P
2002-01-01
The complete spectra of the Bremsstrahlung radiation on the krypton atoms within the range of the photon energies of 10-25000 eV and lanthanum near the potential of the 4d-shell ionization is carried out. The atoms summarized polarizability is calculated on the basis of the simple semiclassical approximation of the local electron density and experimental data on the photoabsorption. The comparison with the calculational results is carried out through the method of distorted partial waves (PDWA) for Kr and with the experimental data on La
Ben-Nun, M; Mills, J D; Hinde, R J; Winstead, C L; Boatz, J A; Gallup, G A; Langhoff, P W
2009-07-02
Recent progress is reported in development of ab initio computational methods for the electronic structures of molecules employing the many-electron eigenstates of constituent atoms in spectral-product forms. The approach provides a universal atomic-product description of the electronic structure of matter as an alternative to more commonly employed valence-bond- or molecular-orbital-based representations. The Hamiltonian matrix in this representation is seen to comprise a sum over atomic energies and a pairwise sum over Coulombic interaction terms that depend only on the separations of the individual atomic pairs. Overall electron antisymmetry can be enforced by unitary transformation when appropriate, rather than as a possibly encumbering or unnecessary global constraint. The matrix representative of the antisymmetrizer in the spectral-product basis, which is equivalent to the metric matrix of the corresponding explicitly antisymmetric basis, provides the required transformation to antisymmetric or linearly independent states after Hamiltonian evaluation. Particular attention is focused in the present report on properties of the metric matrix and on the atomic-product compositions of molecular eigenstates as described in the spectral-product representations. Illustrative calculations are reported for simple but prototypically important diatomic (H(2), CH) and triatomic (H(3), CH(2)) molecules employing algorithms and computer codes devised recently for this purpose. This particular implementation of the approach combines Slater-orbital-based one- and two-electron integral evaluations, valence-bond constructions of standard tableau functions and matrices, and transformations to atomic eigenstate-product representations. The calculated metric matrices and corresponding potential energy surfaces obtained in this way elucidate a number of aspects of the spectral-product development, including the nature of closure in the representation, the general redundancy or
Parquet theory in nuclear structure calculations
International Nuclear Information System (INIS)
Bergli, Elise
2010-01-01
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 4 He 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 4 He 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)
Teo, Boon K.; Li, Wai-Kee
2011-01-01
This article is divided into two parts. In the first part, the atomic unit (au) system is introduced and the scales of time, space (length), and speed, as well as those of mass and energy, in the atomic world are discussed. In the second part, the utility of atomic units in quantum mechanical and spectroscopic calculations is illustrated with…
International Nuclear Information System (INIS)
Ito, A.; Kenmotsu, T.; Kikuhara, Y.; Inai, K.; Ohya, K.; Wang, Y.; Irle, S.; Morokuma, K.; Nakamura, H.
2009-01-01
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
Magnetism, microstructure and First Principles calculations of atomized and annealed Ni3Al
International Nuclear Information System (INIS)
García-Escorial, A.; Crespo, P.; Hernando, A.; Lieblich, M.; Marín, P.; Velasco, V.; Ynduráin, F.
2014-01-01
Highlights: • The microstructure and order of as-atomized Ni 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 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 3 Al, L1 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
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.
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.
Calculations with the quasirelativistic local-spin-density-functional theory for high-Z atoms
International Nuclear Information System (INIS)
Guo, Y.; Whitehead, M.A.
1988-01-01
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
Calculation of atom ranges in solids for quasi-small-angle scattering
International Nuclear Information System (INIS)
Pustovit, A.N.
2004-01-01
A formula for quasi-small-angle scattering of atomic particle and power law interaction potential have been used for the calculation of the differential cross-section, elastic stopping cross-section and a mean projected range in a solid. It is found that the limit energy transfer in the collisions depends on the screening of the power law interaction potentials. The calculated mean ranges in matter are compared with experimental data [ru
International Nuclear Information System (INIS)
Castro, Eduardo A.
2002-01-01
An improved simplified method of atom equivalents is applied to the calculation of enthalpies of formation of several alkyl radicals. Some statistical mechanics and thermodynamic corrections are added to compare theoretical values with available experimental data. The estimation is quite satisfactory and the average error is similar to current experimental uncertainties, thus providing a direct and simple procedure for this sort of calculation when experimental results are unavailable or/and as an independent check when experimental data are in doubt. (Author) [es
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.
You, Y.; Yan, M. F.
2013-05-01
C and N atoms are the most frequent foreign interstitial atoms (FIAs), and often incorporated into the surface layers of steels to enhance their properties by thermochemical treatments. Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Nb and Mo are the most common alloying elements in steels, also can be called foreign substitutional atoms (FSAs). The FIA and FSA interactions play an important role in the diffusion of C and N atoms, and the microstructures and mechanical properties of surface modified layers. Ab initio calculations based on the density functional theory are carried out to investigate FIA interactions with FSA in ferromagnetic bcc iron. The FIA-FSA interactions are analyzed systematically from five aspects, including interaction energies, density of states (DOS), bond populations, electron density difference maps and local magnetic moments.
The calculation of surface free energy based on embedded atom method for solid nickel
International Nuclear Information System (INIS)
Luo Wenhua; Hu Wangyu; Su Kalin; Liu Fusheng
2013-01-01
Highlights: ► A new solution for accurate prediction of surface free energy based on embedded atom method was proposed. ► The temperature dependent anisotropic surface energy of solid nickel was obtained. ► In isotropic environment, the approach does not change most predictions of bulk material properties. - Abstract: Accurate prediction of surface free energy of crystalline metals is a challenging task. The theory calculations based on embedded atom method potentials often underestimate surface free energy of metals. With an analytical charge density correction to the argument of the embedding energy of embedded atom method, an approach to improve the prediction for surface free energy is presented. This approach is applied to calculate the temperature dependent anisotropic surface energy of bulk nickel and surface energies of nickel nanoparticles, and the obtained results are in good agreement with available experimental data.
International Nuclear Information System (INIS)
Yu, Rong Mei; Zan, Li Rong; Jiao, Li Guang; Ho, Yew Kam
2017-01-01
Spatially confined atoms have been extensively investigated to model atomic systems in extreme pressures. For the simplest hydrogen-like atoms and isotropic harmonic oscillators, numerous physical quantities have been established with very high accuracy. However, the expectation value of which is of practical importance in many applications has significant discrepancies among calculations by different methods. In this work we employed the basis expansion method with cut-off Slater-type orbitals to investigate these two confined systems. Accurate values for several low-lying bound states were obtained by carefully examining the convergence with respect to the size of basis. A scaling law for was derived and it is used to verify the accuracy of numerical results. Comparison with other calculations show that the present results establish benchmark values for this quantity, which may be useful in future studies. (author)
International Nuclear Information System (INIS)
Dimakis, Nicholas; Valdez, Danielle; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade; Vargas, Sarah; Saenz, Justin
2017-01-01
Highlights: • Li, K, Na, and Ca graphene interaction is primarily ionic, whereas small covalent interactions also co-exist in these cases. • Van der Waals interactions are revealed by comparing adatom-graphene geometries between 1.4% and 3% adatom coverages and using Grimme corrections. • The Li, K, Na graphene interactions are accurately described by both PBE0 and PBE functionals. For Ca/graphene, the PBE0 functional should not be used. • For Li, K, and Na adsorbed on graphene, adatom-graphene interaction weakens as the adatom coverages increases. • The Ca-graphene interaction strength, which is stronger at high coverages, is opposite to increases in the Ca–4s orbital population. - Abstract: The adsorption of the alkali Li, K, and Na and the alkaline Ca on graphene is studied using periodic density functional theory (DFT) under various adatom coverages. The charge transfers between the adatom and the graphene sheet and the almost unchanged densities-of-states spectra in the energy region near and below the Fermi level support an ionic bond pattern between the adatom and the graphene atoms. However, the presence of small orbital overlap between the metal and the nearest graphene atom is indicative of small covalent bonding. Van der Waals interactions are examined through a semiempirical correction in the DFT functional and by comparing adatom-graphene calculations between 3% and 1.4% adatom coverages. Optimized adatom-graphene geometries identify the preferred adatom sites, whereas the adatom-graphene strength is correlated with the adsorption energy and the adatom distance from the graphene plane. Calculated electronic properties and structural parameters are obtained using hybrid functionals and a generalized gradient approximation functional paired with basis sets of various sizes. We found that due to long range electrostatic forces between the alkali/alkaline adatoms and the graphene monolayer, the adatom-graphene structural and electronic
Energy Technology Data Exchange (ETDEWEB)
Dimakis, Nicholas, E-mail: nicholas.dimakis@utrgv.edu [Department of Physics, University of Texas Rio Grande Valley, Edinburg, TX (United States); Valdez, Danielle; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade [Department of Physics, University of Texas Rio Grande Valley, Edinburg, TX (United States); Vargas, Sarah; Saenz, Justin [Robert Vela High School, Edinburg, TX (United States)
2017-08-15
Highlights: • Li, K, Na, and Ca graphene interaction is primarily ionic, whereas small covalent interactions also co-exist in these cases. • Van der Waals interactions are revealed by comparing adatom-graphene geometries between 1.4% and 3% adatom coverages and using Grimme corrections. • The Li, K, Na graphene interactions are accurately described by both PBE0 and PBE functionals. For Ca/graphene, the PBE0 functional should not be used. • For Li, K, and Na adsorbed on graphene, adatom-graphene interaction weakens as the adatom coverages increases. • The Ca-graphene interaction strength, which is stronger at high coverages, is opposite to increases in the Ca–4s orbital population. - Abstract: The adsorption of the alkali Li, K, and Na and the alkaline Ca on graphene is studied using periodic density functional theory (DFT) under various adatom coverages. The charge transfers between the adatom and the graphene sheet and the almost unchanged densities-of-states spectra in the energy region near and below the Fermi level support an ionic bond pattern between the adatom and the graphene atoms. However, the presence of small orbital overlap between the metal and the nearest graphene atom is indicative of small covalent bonding. Van der Waals interactions are examined through a semiempirical correction in the DFT functional and by comparing adatom-graphene calculations between 3% and 1.4% adatom coverages. Optimized adatom-graphene geometries identify the preferred adatom sites, whereas the adatom-graphene strength is correlated with the adsorption energy and the adatom distance from the graphene plane. Calculated electronic properties and structural parameters are obtained using hybrid functionals and a generalized gradient approximation functional paired with basis sets of various sizes. We found that due to long range electrostatic forces between the alkali/alkaline adatoms and the graphene monolayer, the adatom-graphene structural and electronic
Cascade calculation of K--p and K--d atoms
International Nuclear Information System (INIS)
Koike, T.; Harada, T.; Akaishi, Y.
1995-09-01
X-ray yields of K - -p and K - -d atoms are calculated as a function of the target density in order to find an optimum condition for experiments. The dependence of the yields on the energy level shift and absorption width due to the strong interaction is systematically investigated. (author)
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 cro...
DEFF Research Database (Denmark)
Ruud, K.; Helgaker, T.; Jørgensen, Poul
1994-01-01
We report a systematic investigation of the magnetizability of a series of small molecules. The use of London atomic orbitals ensures gauge invariance and a fast basis set convergence. Good agreement is obtained with experimental magnetizabilities, both isotropic and anisotropic. The calculations...
Direct nuclear reactions and the structure of atomic nuclei
International Nuclear Information System (INIS)
Osterfeld, F.
1985-01-01
The present thesis deals with two different aspects of direct nuclear reactions, namely on the one hand with the microscopic calculation of the imaginary optical potential for the elastic nucleon-nucleus scattering as well as on the other hand with the microscopic analysis of giant magnetic resonances in atomic nuclei which are excited by (p,n) charge-exchange reactions. In the first part of the thesis the imaginary part of the optical potential for the elastic proton- and neutron-nucleus scattering is microscopically calculated in the framework of the so called nuclear-structure approximation to the optical potential. The calculations are performed in the Feshbach formalism in second-order perturbation theory corresponding to an effective projectile-target-nucleon interaction. In the second part of this thesis in the framework of microscopic nuclear models a complete analysis of different A(p,n)B charge-exchange reactions at high incident energies 160 MeV 90 Zr(p,n) reaction three collective spin-isospin resonances could be uniquely identified. (orig./HSI) [de
International Nuclear Information System (INIS)
Dutchak, Ya.I.; Frenchko, V.S.; Voznyak, O.M.
1975-01-01
Certain models of the structure of three-component melts are considered: the ''quasi-eutectic'' one, the model of statistical distribution of atoms and the ''polystructural'' model. The analytical expressions are given for the area under the first maximum of the curve describing the radial distribution of atoms for certain versions of the ''polystructural'' model. On the example of In-Ga-Ga and Bi-Cd-Sn eutectic melts the possibility of estimating the nature of atomic ordering in three-component melts through checking the models under consideration has been demonstrated
Finite Bias Calculations to Model Interface Dipoles in Electrochemical Cells at the Atomic Scale
DEFF Research Database (Denmark)
Hansen, Martin Hangaard; Jin, Chengjun; Thygesen, Kristian Sommer
2016-01-01
The structure of an electrochemical interface is not determined by any external electrostatic field, but rather by external chemical potentials. This paper demonstrates that the electric double layer should be understood fundamentally as an internal electric field set up by the atomic structure...
Internal structure of reactor building for Madras Atomic Power Project
International Nuclear Information System (INIS)
Pandit, D.P.
1975-01-01
The structural configuration and analysis of structural elements of the internal structure of reactor building for the Madras Atomic Power Project has been presented. Two methods of analysis of the internal structure, viz. Equivalent Plane Frame and Finite Element Method, are explained and compared with the use of bending moments obtained. (author)
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.
Method of the reduced-added Green function in the calculation of atomic polarizabilities
International Nuclear Information System (INIS)
Chernov, V.E.; Dorofeev, D.L.; Kretinin, I.Yu.; Zon, B.A.
2005-01-01
The Green function in the quantum defect theory provides an exact account for high-excited and continuum electronic states. We modify it by taking into account the ground and low-excited states using their wave functions calculated ab initio. As an application, we present a simple and efficient semianalytical method for the calculation of atomic electric frequency-dependent scalar dipole polarizability, for both real and imaginary frequencies. The polarizabilities calculated for some atoms (Li, Na, K, Be, Mg, Ca, Si, P, S, O, Al, Ge, C, N, F, He, Ne, Ar, Kr, and Xe) are compared with existing methods of computational quantum chemistry and with experiments; good accuracy of the proposed method is demonstrated
Theoretical calculations of electron-impact and radiative processes in atoms
International Nuclear Information System (INIS)
Pindzola, M.S.
1975-01-01
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
Modeling of the atomic and electronic structures of interfaces
International Nuclear Information System (INIS)
Sutton, A.P.
1988-01-01
Recent tight binding and Car-Parrinello simulations of grain boundaries in semiconductors are reviewed. A critique is given of some models of embrittlement that are based on electronic structure considerations. The structural unit model of grain boundary structure is critically assessed using some results for mixed tilt and twist grain boundaries. A new method of characterizing interfacial structure in terms of bond angle distribution functions is described. A new formulation of thermodynamic properties of interfaces is presented which focusses on the local atomic environment. Effective, temperature dependent N-body atomic interactions are derived for studying grain boundary structure at elevated temperature
ARC: An open-source library for calculating properties of alkali Rydberg atoms
Šibalić, N.; Pritchard, J. D.; Adams, C. S.; Weatherill, K. J.
2017-11-01
We present an object-oriented Python library for the computation of properties of highly-excited Rydberg states of alkali atoms. These include single-body effects such as dipole matrix elements, excited-state lifetimes (radiative and black-body limited) and Stark maps of atoms in external electric fields, as well as two-atom interaction potentials accounting for dipole and quadrupole coupling effects valid at both long and short range for arbitrary placement of the atomic dipoles. The package is cross-referenced to precise measurements of atomic energy levels and features extensive documentation to facilitate rapid upgrade or expansion by users. This library has direct application in the field of quantum information and quantum optics which exploit the strong Rydberg dipolar interactions for two-qubit gates, robust atom-light interfaces and simulating quantum many-body physics, as well as the field of metrology using Rydberg atoms as precise microwave electrometers. Program Files doi:http://dx.doi.org/10.17632/hm5n8w628c.1 Licensing provisions: BSD-3-Clause Programming language: Python 2.7 or 3.5, with C extension External Routines: NumPy [1], SciPy [1], Matplotlib [2] Nature of problem: Calculating atomic properties of alkali atoms including lifetimes, energies, Stark shifts and dipole-dipole interaction strengths using matrix elements evaluated from radial wavefunctions. Solution method: Numerical integration of radial Schrödinger equation to obtain atomic wavefunctions, which are then used to evaluate dipole matrix elements. Properties are calculated using second order perturbation theory or exact diagonalisation of the interaction Hamiltonian, yielding results valid even at large external fields or small interatomic separation. Restrictions: External electric field fixed to be parallel to quantisation axis. Supplementary material: Detailed documentation (.html), and Jupyter notebook with examples and benchmarking runs (.html and .ipynb). [1] T.E. Oliphant
Protein crystal structure analysis using synchrotron radiation at atomic resolution
International Nuclear Information System (INIS)
Nonaka, Takamasa
1999-01-01
We can now obtain a detailed picture of protein, allowing the identification of individual atoms, by interpreting the diffraction of X-rays from a protein crystal at atomic resolution, 1.2 A or better. As of this writing, about 45 unique protein structures beyond 1.2 A resolution have been deposited in the Protein Data Bank. This review provides a simplified overview of how protein crystallographers use such diffraction data to solve, refine, and validate protein structures. (author)
Atomic fine structure in a space of constant curvature
International Nuclear Information System (INIS)
Bessis, N.; Bessis, G.; Shamseddine, R.
1982-01-01
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. (author)
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.
DFT computations of the lattice constant, stable atomic structure and ...
African Journals Online (AJOL)
This paper presents the most stable atomic structure and lattice constant of Fullerenes (C60). FHI-aims DFT code was used to predict the stable structure and the computational lattice constant of C60. These were compared with known experimental structures and lattice constants of C60. The results obtained showed that ...
Cui, S. T.
The stress-stress correlation function and the viscosity of a united-atom model of liquid decane are studied by equilibrium molecular dynamics simulation using two different formalisms for the stress tensor: the atomic and the molecular formalisms. The atomic and molecular correlation functions show dramatic difference in short-time behaviour. The integrals of the two correlation functions, however, become identical after a short transient period whichis significantly shorter than the rotational relaxation time of the molecule. Both reach the same plateau value in a time period corresponding to this relaxation time. These results provide a convenient guide for the choice of the upper integral time limit in calculating the viscosity by the Green-Kubo formula.
Atomic defects in monolayer WSe2 tunneling FETs studied by systematic ab initio calculations
Wu, Jixuan; Fan, Zhiqiang; Chen, Jiezhi; Jiang, Xiangwei
2018-05-01
Atomic defects in monolayer WSe2 tunneling FETs (TFETs) are studied through systematic ab initio calculations aiming at performance predictions and enhancements. The effects of various defect positions and different passivation atoms are characterized in WSe2 TFETs by rigorous ab initio quantum transport simulations. It is suggested that the Se vacancy (VSe) defect located in the gate-controlled channel region tends to increase the OFF current (I off), whereas it can be well suppressed by oxygen passivation. It is demonstrated that chlorine (Cl) passivation at the source-side tunneling region can largely suppress I off, leading to an impressively improved on–off ratio (I on/I off) compared with that without any defect. However, it is also observed that randomly positioned atomic defects tend to induce significant fluctuation of the TFET output. Further discussions are made with focus on the performance-variability trade-off for robust circuit design.
Max Auwaerter Price lecture: building and probing atomic structures
International Nuclear Information System (INIS)
Ternes, M.
2008-01-01
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)
Electronic Structure Calculation of Permanent Magnets using the KKR Green's Function Method
Doi, Shotaro; Akai, Hisazumi
2014-03-01
Electronic structure and magnetic properties of permanent magnetic materials, especially Nd2Fe14B, are investigated theoretically using the KKR Green's function method. Important physical quantities in magnetism, such as magnetic moment, Curie temperature, and anisotropy constant, which are obtained from electronics structure calculations in both cases of atomic-sphere-approximation and full-potential treatment, are compared with past band structure calculations and experiments. The site preference of heavy rare-earth impurities are also evaluated through the calculation of formation energy with the use of coherent potential approximations. Further, the development of electronic structure calculation code using the screened KKR for large super-cells, which is aimed at studying the electronic structure of realistic microstructures (e.g. grain boundary phase), is introduced with some test calculations.
Determination of diffusion coefficients of oxygen atoms in ZrO2 using first-principles calculations
International Nuclear Information System (INIS)
Segi, Takashi; Okuda, Takanari
2014-01-01
Density functional theory and nudged elastic band calculations were performed in order to determine the diffusion coefficient for oxygen from monoclinic ZrO 2 . The calculated values for monoclinic ZrO 2 at 1000 K and 1500 K were 5.88 × 10 -16 cm 2 s -1 and 2.91 × 10 -11 cm 2 s -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)
The effective atomic numbers of some biomolecules calculated by two methods: A comparative study
Energy Technology Data Exchange (ETDEWEB)
Manohara, S. R.; Hanagodimath, S. M.; Gerward, L. [Department of Physics, Gulbarga University, Gulbarga, Karnataka 585 106 (India); Department of Physics, Technical University of Denmark, Lyngby DK-2800 (Denmark)
2009-01-15
The effective atomic numbers Z{sub 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{sub eff} is given a new meaning by using a modern database of photon interaction cross sections (WinXCom). The results of the two methods are compared and discussed. It is shown that for all biomolecules the direct method gives larger values of Z{sub eff} than the interpolation method, in particular at low energies (1-100 keV) At medium energies (0.1-5 MeV), Z{sub eff} for both methods is about constant and equal to the mean atomic number of the material. Wherever possible, the calculated values of Z{sub eff} are compared with experimental data.
The effective atomic numbers of some biomolecules calculated by two methods: A comparative study
International Nuclear Information System (INIS)
Manohara, S. R.; Hanagodimath, S. M.; Gerward, L.
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 sections (WinXCom). The results of the two methods are compared and discussed. It is shown that for all biomolecules the direct method gives larger values of Z eff than the interpolation method, in particular at low energies (1-100 keV) At medium energies (0.1-5 MeV), Z eff for both methods is about constant and equal to the mean atomic number of the material. Wherever possible, the calculated values of Z eff are compared with experimental data.
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.)
Cluster model calculations of the solid state materials electron structure
International Nuclear Information System (INIS)
Pelikan, P.; Biskupic, S.; Banacky, P.; Zajac, A.; Svrcek, A.; Noga, J.
1997-01-01
Materials of the general composition ACuO 2 are the parent compounds of so called infinite layer superconductors. In the paper presented the electron structure of the compounds CaCuO 2 , SrCuO2, Ca 0.86 Sr 0.14 CuO2 and Ca 0.26 Sr 0.74 CuO 2 were calculated. The cluster models consisting of 192 atoms were computed using quasi relativistic version of semiempirical INDO method. The obtained results indicate the strong ionicity of Ca/Sr-O bonds and high covalency of Cu-bonds. The width of energy gap at the Fermi level increases as follows: Ca 0.26 Sr 0.74 CuO 2 0.86 Sr 0.14 CuO2 2 . This order correlates with the fact that materials of the composition Ca x Sr 1-x CuO 2 have have the high temperatures of the superconductive transition (up to 110 K). Materials partially substituted by Sr 2+ have also the higher density of states in the close vicinity at the Fermi level that ai the additional condition for the possibility of superconductive transition. It was calculated the strong influence of the vibration motions to the energy gap at the Fermi level. (authors). 1 tabs., 2 figs., 10 refs
Fine structure studies of terbium atoms
International Nuclear Information System (INIS)
Abhay Kumar; Bandyopadhyay, Krishnanath; Niraj Kumar
2012-01-01
Terbium (Z = 65) is a typical rare-earth element. Fine structure of spectural lines of terbium (Tb) are presented using the laser optogalvanic spectroscopic technique. Altogether eighty transitions in the 5686-6367 A range have been observed in the fine structure spectrum of 159 Tb. Wavelengths of all the observed transitions have been determined. Out of 80 transitions of Tb, a total of 59 transitions are being reported for the first time. Classifications of 39 new transitions have been provided using the known energy levels, Doppler-limited optogalvanic spectroscopic technique is employed to study the fine structure (fs) 159 Tb. (author)
Effective operators in nuclear-structure calculations
International Nuclear Information System (INIS)
Barrett, Bruce R
2005-01-01
A brief review of the history of the use of many-body perturbation theory to determine effective operators for shell-model calculations, i.e., for calculations in truncated model spaces, is given, starting with the ground-breaking work of Arima and Horie for electromagnetic moments. The problems encountered in utilizing this approach are discussed. New methods based on unitary-transformation approaches are introduced and analyzed. The old problems persist, but the new methods allow us to obtain a better insight into the nature of the physics involved in these processes
Classical calculation of radiative lifetimes of atomic hydrogen in a homogeneous magnetic field
International Nuclear Information System (INIS)
Horbatsch, M.W.; Hessels, E.A.; Horbatsch, M.
2005-01-01
Radiative lifetimes of hydrogenic atoms in a homogeneous magnetic field of moderate strength are calculated on the basis of classical radiation. The modifications of the Keplerian orbits due to the magnetic field are incorporated by classical perturbation theory. The model is complemented by a classical radiative decay calculation using the radiated Larmor power. A recently derived highly accurate formula for the transition rate of a field-free hydrogenic state is averaged over the angular momentum oscillations caused by the magnetic field. The resulting radiative lifetimes for diamagnetic eigenstates classified by n,m and the diamagnetic energy shift C compare well with quantum results
Block Tridiagonal Matrices in Electronic Structure Calculations
DEFF Research Database (Denmark)
Petersen, Dan Erik
in the Landauer–Büttiker ballistic transport regime. These calculations concentrate on determining the so– called Green’s function matrix, or portions thereof, which is the inverse of a block tridiagonal general complex matrix. To this end, a sequential algorithm based on Gaussian elimination named Sweeps...
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,…
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.
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.
Atomic structure of the SnO2 (110) surface
International Nuclear Information System (INIS)
Godin, T.J.; LaFemina, J.P.
1991-12-01
Using a tight-binding, total-energy model, we examine atomic relaxations of the ideal stoichiometric and reduced tin oxide (11) surfaces. In both cases we find a nearly bond-length conserving rumple of the top layer, and a smaller counter-relaxation of the second layer. These calculations show no evidence of surface states in the band gap for either surface
Synthesis and atomic structure determination of Al8V5 gamma-brass
International Nuclear Information System (INIS)
Mizutani, Uichiro
2006-01-01
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 Cu 5 Zn 8 and Cu 9 Al 4 , both being regarded as its prototype, and TM 2 Zn 11 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 Al 8 V 5 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)
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 structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)
International Nuclear Information System (INIS)
Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou
2005-01-01
The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed
The atomic structure of Fe100-xCux nanoalloys: X-ray absorption analysis
International Nuclear Information System (INIS)
Kravtsova, A.N.; Yalovega, G.E.; Soldatov, A.V.; Yan, W.S.; Wei, S.Q.
2009-01-01
The local atomic structure of Fe 100-x Cu x nanoalloys (x = 0, 10, 20, 40, 60, 70, 80 and 100%) has been investigated by X-ray absorption near edge structure (XANES) analysis. Local environment around copper and iron atoms in Fe 100-x Cu x has been studied by comparing the experimental XANES with corresponding theoretical spectra calculated for several structural models. It has been established that the most probable structure of the Fe 100-x Cu x nanoalloys for a low concentration of copper (x = 10-20%) is a homogenous bcc structure, for a high copper concentration (x = 60-80%)-a homogenous fcc structure, while at an intermediate copper concentration (about 40%) the nanoalloys have an inhomogeneous structure consisting of clusters of fcc solid solution (90%) and of clusters of bcc solid solution (10%)
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 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 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 charge...
Atomic structures of a monolayer of AlAs, GaAs, and InAs on Si(111)
International Nuclear Information System (INIS)
Lee, Geunjung; Yoon, Younggui
2010-01-01
We study atomic structures of a monolayer of AlAs, GaAs, and InAs on a Si(111) substrate from first-principles. The surface with the stacking sequence of ...SiSiMAsSiAs is energetically more stable than the surface with the stacking sequence of ...SiSiSiAsMAs, where M is Al, Ga, or In. The atomic structure of the three top layers of the low-energy surfaces are quite robust, irrespective of M, and the atomic structure of the AlAsSiAs terminated surface and that of the GaAsSiAs terminated surface are very similar. For the high-energy AsMAs terminated surfaces, the broken local tetrahedral symmetry plays an important role in the atomic structures. The calculated atomic structures of InAs on the Si(111) substrate depart most from the structure of crystalline Si.
International Nuclear Information System (INIS)
Hadek, J.
1999-01-01
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)
Calculation of the atomic electric dipole moment of Pb2+ induced by nuclear Schiff moment
Ramachandran, S. M.; Latha, K. V. P.; Meenakshisundaram, N.
2017-07-01
We report the atomic electric dipole moment induced by the P, T violating interactions in the nuclear/sub-nuclear level, for 207Pb2+ and 207Pb, owing to the recent interest in the ferroelectric crystal PbTiO3 as one of the candidates for investigating macroscopic P, T-odd effects. In this paper, we calculate the atomic electric dipole moments of 207Pb and Pb2+, parametrized in terms of the P, T-odd coupling parameter, the nuclear Schiff moment (NSM), S, in the frame-work of the coupled-perturbed Hartree-Fock theory. We estimate the Schiff moment of Pb2+ using the experimental result of a system, which is electronically similar to the Pb2+ ion. We present the dominant contributions of the electric dipole moment (EDM) matrix elements and the important correlation effects contributing to the atomic EDM of Pb2+. Our results provide the first ever calculated EDM of the Pb2+ ion, and an estimate of its NSM from which the P, T-odd energy shift in a PbTiO3 crystal can be evaluated.
Mapping energetics of atom probe evaporation events through first principles calculations.
Peralta, Joaquín; Broderick, Scott R; Rajan, Krishna
2013-09-01
The purpose of this work is to use atomistic modeling to determine accurate inputs into the atom probe tomography (APT) reconstruction process. One of these inputs is evaporation field; however, a challenge occurs because single ions and dimers have different evaporation fields. We have calculated the evaporation field of Al and Sc ions and Al-Al and Al-Sc dimers from an L1₂-Al₃Sc surface using ab initio calculations and with a high electric field applied to the surface. The evaporation field is defined as the electric field at which the energy barrier size is calculated as zero, corresponding to the minimum field that atoms from the surface can break their bonds and evaporate from the surface. The evaporation field of the surface atoms are ranked from least to greatest as: Al-Al dimer, Al ion, Sc ion, and Al-Sc dimer. The first principles results were compared with experimental data in the form of an ion evaporation map, which maps multi-ion evaporations. From the ion evaporation map of L1₂-Al₃Sc, we extract relative evaporation fields and identify that an Al-Al dimer has a lower evaporation field than an Al-Sc dimer. Additionally, comparatively an Al-Al surface dimer is more likely to evaporate as a dimer, while an Al-Sc surface dimer is more likely to evaporate as single ions. These conclusions from the experiment agree with the ab initio calculations, validating the use of this approach for modeling APT energetics. Copyright © 2013 Elsevier B.V. All rights reserved.
Atomic structures and mechanical properties of single-crystal GaN nanotubes
International Nuclear Information System (INIS)
Xu, B.; Lu, A.J.; Pan, B.C.; Yu, Q.X.
2005-01-01
An approach is proposed to theoretically construct a realistic single-crystal GaN nanotube at atomic scale. The generated atomic structures of the single-crystal GaN nanotubes match the structural aspects from experiment very well. Our energetic calculations show that a single-crystal GaN nanotube with [100]-oriented lateral facets is more stable than that with [110]-oriented lateral facets, when they have around the same wall thickness. For a specified orientation of the lateral facets on the single-crystal GaN nanotubes, the energetic stabilities of the tubes obey a P rule, in which P is the ratio of the number of four-coordinated atoms to the number of three-coordinated atoms. Furthermore, the Young's modulus of the considered GaN nanotubes decrease with increasing the ratio of the number of bulk atoms to the number of surface atoms in each type of tube. Our calculations and analysis demonstrate that the surface effect of a single-crystal nanotube enhances its Young's modulus significantly
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
Fundamental problem in the relativistic approach to atomic structure theory
International Nuclear Information System (INIS)
Kagawa, Takashi
1987-01-01
It is known that the relativistic atomic structure theory contains a serious fundamental problem, so-called the Brown-Ravenhall (BR) problem or variational collapse. This problem arises from the fact that the energy spectrum of the relativistic Hamiltonian for many-electron systems is not bounded from below because the negative-energy solutions as well as the positive-energy ones are obtained from the relativistic equation. This report outlines two methods to avoid the BR problem in the relativistic calculation, that is, the projection operator method and the general variation method. The former method is described first. The use of a modified Hamiltonian containing a projection operator which projects the positive-energy solutions in the relativistic wave equation has been proposed to remove the BR difficulty. The problem in the use of the projection operator method is that the projection operator for the system cannot be determined uniquely. The final part of this report outlines the general variation method. This method can be applied to any system, such as relativistic ones whose Hamiltonian is not bounded from below. (Nogami, K.)
Atomic structure of intracellular amorphous calcium phosphate deposits.
Betts, F; Blumenthal, N C; Posner, A S; Becker, G L; Lehninger, A L
1975-06-01
The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed.
Atomic structures and electronic properties of phosphorene grain boundaries
International Nuclear Information System (INIS)
Guo, Yu; Zhou, Si; Bai, Yizhen; Zhao, Jijun; Zhang, Junfeng
2016-01-01
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. (paper)
Structural atlas of dynein motors at atomic resolution.
Toda, Akiyuki; Tanaka, Hideaki; Kurisu, Genji
2018-04-01
Dynein motors are biologically important bio-nanomachines, and many atomic resolution structures of cytoplasmic dynein components from different organisms have been analyzed by X-ray crystallography, cryo-EM, and NMR spectroscopy. This review provides a historical perspective of structural studies of cytoplasmic and axonemal dynein including accessory proteins. We describe representative structural studies of every component of dynein and summarize them as a structural atlas that classifies the cytoplasmic and axonemal dyneins. Based on our review of all dynein structures in the Protein Data Bank, we raise two important points for understanding the two types of dynein motor and discuss the potential prospects of future structural studies.
International Nuclear Information System (INIS)
Demkin, V.P.; Pecheritsyn, A.A.
1995-01-01
Equations for the amplitudes and differential cross sections of electronic excitation and ionization of a helium atom are derived in the approximation of a open-quotes frozenclose quotes ion core. The wave functions of the discrete states are chosen in the form of generalized hydrogenlike orbitals. The radial wave functions of the continuous spectrum are determined by solving the equation of motion numerically. The differential excitation cross sections of excitation of the 2p, 3p, and 4p levels and ionization of a helium atom by electrons are calculated in the energy range up to 50 eV. Estimates are obtained for the nonorthogonal wave functions in the amplitudes of the excitation and ionization processes. It is shown that the given method is more compatible with experiment than the Born method
International Nuclear Information System (INIS)
Berrington, K.A.
1991-01-01
A progress report on R-matrix calculations of electron impact excitation and opacity data for ionized Fe is given. This paper discusses aspects of modern calculations of the electron excitation process in atoms and ions. The Belfast Atomic Data Bank holds much data in this area, including data recommended in regular Atomic Data Workshops held to evaluate atomic data for the applications community: electron excitation data for Fe ions recommended at recent Workshops is summarised. The main R-matrix programs currently in use are described, and some recent R-matrix calculations on electron excitation in Fe ions are highlighted. Photoabsorption data for all elements up to Fe are also calculated using the R-matrix programs in the international Opacity Project, and a summary is given of the atomic data expected from the Project. Finally some possible future directions are outlined. (orig.)
Lobato, I.; Rojas, J.; Landauro, C. V.; Torres, J.
2008-01-01
The structural evolution and dynamics of silver nanodrops Ag${}_{2896}$ (4.4 nm in diameter) during rapid cooling conditions has been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modeled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique is applied to reveal the structural transition in the process of solidifica...
Relativistic many-body theory of atomic structures
International Nuclear Information System (INIS)
Cheng, K.T.
1983-01-01
The main objective of this program is to improve our understanding of the effect of relativity and electron correlations on atomic processes. Current efforts include hyperfine structure (hfs) studies using the multiconfiguration Dirac-Fock (MCDF) technique. Atomic hfs are known to be sensitive to relativity and electron correlations, and provide important tests of relativistic atomic many-body theories. Preliminary results on the hfs of the 4f 12 3 H ground state of 68 Er 167 are shown and are in good agreement with experiment. This shows that the MCDF technique can be an efficient and powerful method for atomic hfs studies. Further tests of this method are in progress. We are also studying the absorption spectra for Xe-like ions in the region of 4d → nf, epsilonf transitions
Lara, A; Riquelme, M; Vöhringer-Martinez, E
2018-05-11
Partition coefficients serve in various areas as pharmacology and environmental sciences to predict the hydrophobicity of different substances. Recently, they have also been used to address the accuracy of force fields for various organic compounds and specifically the methylated DNA bases. In this study, atomic charges were derived by different partitioning methods (Hirshfeld and Minimal Basis Iterative Stockholder) directly from the electron density obtained by electronic structure calculations in a vacuum, with an implicit solvation model or with explicit solvation taking the dynamics of the solute and the solvent into account. To test the ability of these charges to describe electrostatic interactions in force fields for condensed phases, the original atomic charges of the AMBER99 force field were replaced with the new atomic charges and combined with different solvent models to obtain the hydration and chloroform solvation free energies by molecular dynamics simulations. Chloroform-water partition coefficients derived from the obtained free energies were compared to experimental and previously reported values obtained with the GAFF or the AMBER-99 force field. The results show that good agreement with experimental data is obtained when the polarization of the electron density by the solvent has been taken into account, and when the energy needed to polarize the electron density of the solute has been considered in the transfer free energy. These results were further confirmed by hydration free energies of polar and aromatic amino acid side chain analogs. Comparison of the two partitioning methods, Hirshfeld-I and Minimal Basis Iterative Stockholder (MBIS), revealed some deficiencies in the Hirshfeld-I method related to the unstable isolated anionic nitrogen pro-atom used in the method. Hydration free energies and partitioning coefficients obtained with atomic charges from the MBIS partitioning method accounting for polarization by the implicit solvation model
Theoretical atomic physics code development I: CATS: Cowan Atomic Structure Code
International Nuclear Information System (INIS)
Abdallah, J. Jr.; Clark, R.E.H.; Cowan, R.D.
1988-12-01
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
The fifth Atomic Energy Research dynamic benchmark calculation with HEXTRAN-SMABRE
International Nuclear Information System (INIS)
Haenaelaeinen, Anitta
1998-01-01
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)
Vortex-ring-fractal Structure of Atom and Molecule
International Nuclear Information System (INIS)
Osmera, Pavel
2010-01-01
This chapter is an attempt to attain a new and profound model of the nature's structure using a vortex-ring-fractal theory (VRFT). Scientists have been trying to explain some phenomena in Nature that have not been explained so far. The aim of this paper is the vortex-ring-fractal modeling of elements in the Mendeleev's periodic table, which is not in contradiction to the known laws of nature. We would like to find some acceptable structure model of the hydrogen as a vortex-fractal-coil structure of the proton and a vortex-fractal-ring structure of the electron. It is known that planetary model of the hydrogen atom is not right, the classical quantum model is too abstract. Our imagination is that the hydrogen is a levitation system of the proton and the electron. Structures of helium, oxygen, and carbon atoms and a hydrogen molecule are presented too.
Calculations of relativistic effects in atoms and molecules from the Schroedinger wave function
International Nuclear Information System (INIS)
Detrich, J.H.; Roothaan, C.C.J.
1981-01-01
The traditional method for dealing with relativistic effects in atoms and molecules consists of a somewhat heuristic combination of quantum electrodynamics and a many-electron quantum mechanics generalized from the one-electron Dirac theory. On the whole, results calculated from this theory agree with experimental data. Nevertheless, the theory is by no means entirely satisfactory; in its development, certain ambiguities and divergencies must be resolved by somewhat arbitrary and/or questionable means. This paper illuminates - and sidesteps - some of the more questionable aspects of the traditional method, by reformulating electromagnetic interactions between particles in a different way
Gulvi, Nitin R.; Patel, Priyanka; Badani, Purav M.
2018-04-01
Pathway for dissociation of multihalogenated alkyls is observed to be competitive between molecular and atomic elimination products. Factors such as molecular structure, temperature and pressure are known to influence the same. Hence present work is focussed to explore mechanism and kinetics of atomic (Br) and molecular (HBr and Br2) elimination upon pyrolysis of 1,1- and 1,2-ethyl dibromide (EDB). For this purpose, electronic structure calculations were performed at DFT and CCSD(T) level of theory. In addition to concerted mechanism, an alternate energetically efficient isomerisation pathway has been exploited for molecular elimination. Energy calculations are further complimented by detailed kinetic investigation, over wide range of temperature and pressure, using suitable models like Canonical Transition State Theory, Statistical Adiabatic Channel Model and Troe's formalism. Our calculations suggest high branching ratio for dehydrohalogentation reaction, from both isomers of EDB. Fall off curve depicts good agreement between theoretically estimated and experimentally reported values.
Atomic structure of graphene supported heterogeneous model catalysts
International Nuclear Information System (INIS)
Franz, Dirk
2017-04-01
Graphene on Ir(111) forms a moire structure with well defined nucleation centres. Therefore it can be utilized to create hexagonal metal cluster lattices with outstanding structural quality. At diffraction experiments these 2D surface lattices cause a coherent superposition of the moire cell structure factor, so that the measured signal intensity scales with the square of coherently scattering unit cells. This artificial signal enhancement enables the opportunity for X-ray diffraction to determine the atomic structure of small nano-objects, which are hardly accessible with any experimental technique. The uniform environment of every metal cluster makes the described metal cluster lattices on graphene/Ir(111) an attractive model system for the investigation of catalytic, magnetic and quantum size properties of ultra-small nano-objects. In this context the use of x-rays provides a maximum of flexibility concerning the possible sample environments (vacuum, selected gases, liquids, sample temperature) and allows in-situ/operando measurements. In the framework of the present thesis the structure of different metal clusters grown by physical vapor deposition in an UHV environment and after gas exposure have been investigated. On the one hand the obtained results will explore many aspects of the atomic structure of these small metal clusters and on the other hand the presented results will proof the capabilities of the described technique (SXRD on cluster lattices). For iridium, platinum, iridium/palladium and platinum/rhodium the growth on graphene/Ir(111) of epitaxial, crystalline clusters with an ordered hexagonal lattice arrangement has been confirmed using SXRD. The clusters nucleate at the hcp sites of the moire cell and bind via rehybridization of the carbon atoms (sp"2 → sp"3) to the Ir(111) substrate. This causes small displacements of the substrate atoms, which is revealed by the diffraction experiments. All metal clusters exhibit a fcc structure, whereupon
Learning Approach on the Ground State Energy Calculation of Helium Atom
International Nuclear Information System (INIS)
Shah, Syed Naseem Hussain
2010-01-01
This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function.The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.
Energy Technology Data Exchange (ETDEWEB)
Bross, David H.; Parmar, Payal; Peterson, Kirk A., E-mail: kipeters@wsu.edu [Department of Chemistry, Washington State University, Pullman, Washington 99164-4630 (United States)
2015-11-14
The first 6 ionization potentials (IPs) of the uranium atom have been calculated using multireference configuration interaction (MRCI+Q) with extrapolations to the complete basis set limit using new all-electron correlation consistent basis sets. The latter was carried out with the third-order Douglas-Kroll-Hess Hamiltonian. Correlation down through the 5s5p5d electrons has been taken into account, as well as contributions to the IPs due to the Lamb shift. Spin-orbit coupling contributions calculated at the 4-component Kramers restricted configuration interaction level, as well as the Gaunt term computed at the Dirac-Hartree-Fock level, were added to the best scalar relativistic results. The final ionization potentials are expected to be accurate to at least 5 kcal/mol (0.2 eV) and thus more reliable than the current experimental values of IP{sub 3} through IP{sub 6}.
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.
Calculation of the atomic states energies in the Thomas - Fermi approximation
Directory of Open Access Journals (Sweden)
S. N. Fedotkin
2017-12-01
Full Text Available A method for calculating the energies of levels for many-electron neutral atoms is proposed. In this case, in addition to the Coulomb field of the nucleus, an important contribution to the energy is connected with the interaction between the electrons. This interaction is taken into account approximately by perturbation theory in the framework of the Thomas - Fermi statistical model. Using the Taytz approximation for the mean potential the analytical expressions for the energies of s-states are obtained with principal quantum numbers n = 1, 2, 3, 4. The energies are calculated for the nuclear charges in the interval 1 < Z ≤ 100. A good agreement with the experimental values of the energies was obtained.
Inner-shell correlations and Sturm expansions in coupled perturbation calculations of atomic systems
International Nuclear Information System (INIS)
Sherstyuk, A.I.; Solov'eva, G.S.
1995-01-01
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
Classroom: inexpensive models for teaching atomic structure and ...
African Journals Online (AJOL)
Classroom: inexpensive models for teaching atomic structure and compounds at junior secondary school level of education. WHK Hordzi, BA Mensah. Abstract. No Abstract. Global Journal of Educational Research Vol. 2(1&2) 2003: 33-40. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL ...
Workshop on foundations of the relativistic theory of atomic structure
International Nuclear Information System (INIS)
1981-03-01
The conference is an attempt to gather state-of-the-art information to understand the theory of relativistic atomic structure beyond the framework of the original Dirac theory. Abstracts of twenty articles from the conference were prepared separately for the data base
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...
Electronic structure of graphene nanoribbons doped with nitrogen atoms: a theoretical insight.
Torres, A E; Fomine, S
2015-04-28
The electronic structure of graphene nanoribbons doped with a graphitic type of nitrogen atoms has been studied using B3LYP, B2PLYP and CAS methods. In all but one case the restricted B3LYP solutions were unstable and the CAS calculations provided evidence for the multiconfigurational nature of the ground state with contributions from two dominant configurations. The relative stability of the doped nanoribbons depends mostly on the mutual position of the dopant atoms and notably less on the position of nitrogen atoms within the nanoribbon. N-graphitic doping affects cationic states much more than anionic ones due the participation of the nitrogen atoms in the stabilization of the positive charge, resulting in a drop in ionization energies (IPs) for N-graphitic doped systems. Nitrogen atoms do not participate in the negative charge stabilization of anionic species and, therefore, the doping does not affect the electron affinities (EAs). The unrestricted B3LYP method is the method of choice for the calculation of IPs and EAs. Restricted B3LYP and B2PLYP produces unreliable results for both IPs and EAs while CAS strongly underestimates the electron affinities. This is also true for the reorganization energies where restricted B3LYP produces qualitatively incorrect results. Doping changes the reorganization energy of the nanoribbons; the hole reorganization energy is generally higher than the corresponding electron reorganization energy due to the participation of nitrogen atoms in the stabilization of the positive charge.
Calculation of Ion Charge State Distributions After Inner-Shell Ionization in Xe Atom
International Nuclear Information System (INIS)
Mohammedein, A.M.; Ghoneim, A.A.; Kandil, M.K.; Kadad, I.M.
2009-01-01
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, L 1 , L 2,3 , M 1 , M 2,3 and M 4,5 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 Xe 7+ , Xe 8+ , Xe 9+ and Xe 1 0 + ions, and the charged X 8+ ions are the highest. The main product from the L 1 shell ionization is found to be Xe 8+ , Xe 9+ ions, while the charged Xe 8+ ions predominate at L 2,3 hole states. The charged Xe 6+ , Xe 7+ and Xe 8+ ions mainly yield from 3s 1/2 and 3p 1/2 , 3/2 ionization, while Xe in 3d 3/2 , 5/2 hole states mainly turns into Xe 4+ and Xe 5+ ions. The present results are found to agree well with the experimental data. (author)
On the electronic and geometrical structures of small atomic clusters
International Nuclear Information System (INIS)
Malrieu, J.P.; Maynau, D.
1987-01-01
This paper recalls the main challenges and difficulties of the theoretical study of small clusters of atoms. It briefly summarizes some informations concerning rare-gas clusters and clusters of normal elements such as C or Si. The main discussion is devoted to the small clusters of the simplest metal (Li), comparing the agreement and discrepancies between two crude models - the jellium model and the tight-binding one - with the most refined ab initio calculations. 28 refs
The general atomic and molecular electronic structure system HONDO: Version 7.0
International Nuclear Information System (INIS)
Dupuis, M.; Watts, J.D.; Villar, H.O.; Hurst, G.J.B.
1989-01-01
We describe a computer program for ab initio quantum mechanical calculations of atomic and molecular wavefunctions and energies. Capabilities for the calculation of energy gradients and second derivatives with respect to nuclear coordinates are provided for several types of wavefunctions. Calculations of many molecular properties based on the electron density are possible. The program contains automated algorithms for the determination of equilibrium structures, saddle points, reaction pathways, vibrational spectra including infrared and Raman intensities. We illustrate the capabilities of the program by highlighting research problems recently investigated with the present program. (orig.)
Atomic-level structure and structure-property relationship in metallic glass
Cheng, Yongqiang
One of the key tasks in material science is to understand the structure and structure-property relationship. The recently emerging bulk metallic glasses (BMGs) have demonstrated unique properties, especially intriguing mechanical properties such as their high strength and high propensity to localize deformation in shear bands. However, a comprehensive understanding of the structure of BMGs has been hindered by the complexity of these amorphous materials. Even more challenging is the structure-property correlation, which has been well established in crystals but has been seriously lacking for BMGs. This thesis presents a systematic study of the atomic-level structures of two representative BMGs, Cu-Zr and Cu-Zr-Al. The interpenetrating Cu-centered icosahedral clusters have been identified to be the primary structural feature. The fraction of icosahedra increases with increasing Cu or Al contents, and with decreasing cooling rate. The effect of Al in improving the icosahedral order is two-fold: the geometric effect due to the atomic-size mismatch and the chemical effect originated from the Cu-Al bond shortening. The resolved structure is used to study the structure-property relationship. The full icosahedra are found to be responsible for the dynamical slowdown of the supercooled liquid, which underlies the non-Arrhenius behavior, and explains the composition dependence of glass transition temperature, glass forming ability, and the room temperature strength. By simulated deformation, the initiation of plasticity and tendency for strain localization are also investigated. The full icosahedra are found to be the most rigid and resistant cluster with solid-like character, while the unstable clusters with liquid-like character serve as the fertile sites for initiating shear transformations. In addition, the elastic moduli are calculated and analyzed, and the origins of the different configurational dependence of shear modulus (G) and bulk modulus ( B) are explained. The
Surface structure investigations using noncontact atomic force microscopy
International Nuclear Information System (INIS)
Kolodziej, J.J.; Such, B.; Goryl, M.; Krok, F.; Piatkowski, P.; Szymonski, M.
2006-01-01
Surfaces of several A III B V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination
Energy Technology Data Exchange (ETDEWEB)
Kong, Ki-jeong [Korea Research Institute of Chemical Technology, P.O.Box 107, Yuseong, Daejeon 305-600 (Korea, Republic of)]. E-mail: kong@krict.re.kr; Choi, Youngmin [Korea Research Institute of Chemical Technology, P.O.Box 107, Yuseong, Daejeon 305-600 (Korea, Republic of); Ryu, Beyong-Hwan [Korea Research Institute of Chemical Technology, P.O.Box 107, Yuseong, Daejeon 305-600 (Korea, Republic of); Lee, Jeong-O [Korea Research Institute of Chemical Technology, P.O.Box 107, Yuseong, Daejeon 305-600 (Korea, Republic of); Chang, Hyunju [Korea Research Institute of Chemical Technology, P.O.Box 107, Yuseong, Daejeon 305-600 (Korea, Republic of)
2006-07-15
The potential of carbon-related materials, such as carbon nanotubes (CNTs) and graphite nanofibers (GNFs), supported metal catalysts as an electrode for fuel cell application was investigated using the first-principle electronic structure calculations. The stable binding geometries and energies of metal catalysts are determined on the CNT surface and the GNF edge. The catalyst metal is more tightly bound to the GNF edge than to the CNT surface because of the existence of active dangling bonds of edge carbon atoms. The diffusion barrier of metal atoms on the surface and edge is also obtained. From our calculation results, we have found that high dispersity is achievable for GNF due to high barrier against the diffusion of metal atoms, while CNT appears less suitable. The GNF with a large edge-to-wall ratio is more suitable for the high-performance electrode than perfect crystalline graphite or CNT.
International Nuclear Information System (INIS)
Kong, Ki-jeong; Choi, Youngmin; Ryu, Beyong-Hwan; Lee, Jeong-O; Chang, Hyunju
2006-01-01
The potential of carbon-related materials, such as carbon nanotubes (CNTs) and graphite nanofibers (GNFs), supported metal catalysts as an electrode for fuel cell application was investigated using the first-principle electronic structure calculations. The stable binding geometries and energies of metal catalysts are determined on the CNT surface and the GNF edge. The catalyst metal is more tightly bound to the GNF edge than to the CNT surface because of the existence of active dangling bonds of edge carbon atoms. The diffusion barrier of metal atoms on the surface and edge is also obtained. From our calculation results, we have found that high dispersity is achievable for GNF due to high barrier against the diffusion of metal atoms, while CNT appears less suitable. The GNF with a large edge-to-wall ratio is more suitable for the high-performance electrode than perfect crystalline graphite or CNT
Soil structure interaction calculations: a comparison of methods
International Nuclear Information System (INIS)
Wight, L.; Zaslawsky, M.
1976-01-01
Two approaches for calculating soil structure interaction (SSI) are compared: finite element and lumped mass. Results indicate that the calculations with the lumped mass method are generally conservative compared to those obtained by the finite element method. They also suggest that a closer agreement between the two sets of calculations is possible, depending on the use of frequency-dependent soil springs and dashpots in the lumped mass calculations. There is a total lack of suitable guidelines for implementing the lumped mass method of calculating SSI, which leads to the conclusion that the finite element method is generally superior for calculative purposes
Soil structure interaction calculations: a comparison of methods
Energy Technology Data Exchange (ETDEWEB)
Wight, L.; Zaslawsky, M.
1976-07-22
Two approaches for calculating soil structure interaction (SSI) are compared: finite element and lumped mass. Results indicate that the calculations with the lumped mass method are generally conservative compared to those obtained by the finite element method. They also suggest that a closer agreement between the two sets of calculations is possible, depending on the use of frequency-dependent soil springs and dashpots in the lumped mass calculations. There is a total lack of suitable guidelines for implementing the lumped mass method of calculating SSI, which leads to the conclusion that the finite element method is generally superior for calculative purposes.
First-principles calculations of the interaction between hydrogen and 3d alloying atom in nickel
Energy Technology Data Exchange (ETDEWEB)
Liu, Wenguan, E-mail: liuwenguan@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Qian, Yuan; Zhang, Dongxun [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Liu, Wei, E-mail: liuwei@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Han, Han [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China)
2015-10-15
Knowledge of the behavior of hydrogen (H) in Ni-based alloy is essential for the prediction of Tritium behavior in Molten Salt Reactor. First-principles calculations were performed to investigate the interaction between H and 3d transition metal (TM) alloying atom in Ni-based alloy. H prefers the octahedral interstitial site to the tetrahedral interstitial site energetically. Most of the 3d TM elements (except Zn) attract H. The attraction to H in the Ni–TM–H system can be mainly attributed to the differences in electronegativity. With the large electronegativity, H and Ni gain electrons from the other TM elements, resulting in the enhanced Ni–H bonds which are the source of the attraction to H in the Ni–TM–H system. The obviously covalent-like Cr–H and Co–H bindings are also beneficial to the attraction to H. On the other hand, the repulsion to H in the Ni–Zn–H system is due to the stable electronic configuration of Zn. We mainly utilize the results calculated in 32-atom supercell which corresponds to the case of a relatively high concentration of hydrogen. Our results are in good agreement with the experimental ones.
Calculation of nuclear-spin-relaxation rate for spin-polarized atomic hydrogen
International Nuclear Information System (INIS)
Ahn, R.M.C.; Eijnde, J.P.H.W.V.; Verhaar, B.J.
1983-01-01
Approximations introduced in previous calculations of spin relaxation for spin-polarized atomic hydrogen are investigated by carrying out a more exact coupled-channel calculation. With the exception of the high-temperature approximation, the approximations turn out to be justified up to the 10 -3 level of accuracy. It is shown that at the lowest temperatures for which experimental data are available, the high-temperature limit underestimates relaxation rates by a factor of up to 2. For a comparison with experimental data it is also of interest to pay attention to the expression for the atomic hydrogen relaxation rates in terms of transition amplitudes for two-particle collisions. Discrepancies by a factor of 2 among previous derivations of relaxation rates are pointed out. To shed light on these discrepancies we present two alternative derivations in which special attention is paid to identical-particle aspects. Comparing with experiment, we find our theoretical volume relaxation rate to be in better agreement with measured values than that obtained by other groups. The theoretical surface relaxation rate, however, still shows a discrepancy with experiment by a factor of order 50
International Nuclear Information System (INIS)
Varandas, A.J.C.
1980-01-01
A suggestion is made for using the zeroth-order exchange term, at the one-exchange level, in the perturbation development of the interaction energy as a criterion for optmizing the atomic basis sets in interatomic force calculations. The approach is illustrated for the case of two helium atoms. (orig.)
International Nuclear Information System (INIS)
Korecki, P.; Tolkiehn, M.; Dąbrowski, K. M.; Novikov, D. V.
2011-01-01
A method for a direct measurement of X-ray projections of the atomic structure is described. Projections of the atomic structure around Nb atoms in a LiNbO 3 single crystal were obtained from a white-beam X-ray absorption anisotropy pattern detected using Nb K fluorescence. Projections of the atomic structure around Nb atoms in a LiNbO 3 single crystal were obtained from a white-beam X-ray absorption anisotropy (XAA) pattern detected using Nb K fluorescence. This kind of anisotropy results from the interference of X-rays inside a sample and, owing to the short coherence length of a white beam, is visible only at small angles around interatomic directions. Consequently, the main features of the recorded XAA corresponded to distorted real-space projections of dense-packed atomic planes and atomic rows. A quantitative analysis of XAA was carried out using a wavelet transform and allowed well resolved projections of Nb atoms to be obtained up to distances of 10 Å. The signal of nearest O atoms was detected indirectly by a comparison with model calculations. The measurement of white-beam XAA using characteristic radiation indicates the possibility of obtaining element-sensitive projections of the local atomic structure in more complex samples
Energy Technology Data Exchange (ETDEWEB)
Kim, Young Soon; Nam, Baek Il [Myongji University, Seoul (Korea, Republic of)
1995-08-01
We have developed computer programs to calculate 2-and 3-step selective resonant multiphoton ionization of atoms. Autoionization resonances in the final continuum can be put into account via B-Spline basis set method. 8 refs., 5 figs. (author)
International Nuclear Information System (INIS)
Belianinov, Alex; Ganesh, Panchapakesan; Lin, Wenzhi; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V.; Sales, Brian C.; Sefat, Athena S.
2014-01-01
Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe 0.55 Se 0.45 (T c = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe 1−x Se x structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces
Finding the Atomic Configuration with a Required Physical Property in Multi-Atom Structures
International Nuclear Information System (INIS)
d'Avezac, M.; Zunger, A.
2007-01-01
In many problems in molecular and solid state structures one seeks to determine the energy-minimizing decoration of sites with different atom types. In other problems, one is interested in finding a decoration with a target physical property (e.g. alloy band gap) within a certain range. In both cases, the sheer size of the configurational space can be horrendous. We present two approaches which identify either the minimum-energy configuration or configurations with a target property for a fixed underlying Bravais lattice. We compare their efficiency at locating the deepest minimum energy configuration of face centered cubic Au-Pd alloy. We show that a global-search genetic-algorithm approach with diversity-enhancing constraints and reciprocal-space mating can efficiently find the global optimum, whereas the local-search virtual-atom approach presented here is more efficient at finding structures with a target property
The development of high-resolution spectroscopic methods and their use in atomic structure studies
International Nuclear Information System (INIS)
Poulsen, O.
1984-01-01
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 51 V I, and in 235 U 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.)
Atomic physics. Introduction to quantum physics and structure of the atomic system. 2. ed.
International Nuclear Information System (INIS)
Cagnac, Bernard; Pebay-Peyroula, J.-C.
1975-01-01
This lecture is intended for providing experimental foundations to the basic principles of quantum mechanics, from descriptions of some characteristic experiments which emphasize the limitations of the classical theory. The basic laws that govern the internal structure of atomic systems are exposed (waves and photons, the planetary model and principal quantum number, and the spatial classification of kinetic momenta and magnetic moments). Experimental studies presently in progress are reviewed and their aims are outlined [fr
Development of the simulation package 'ELSES' for extra-large-scale electronic structure calculation
International Nuclear Information System (INIS)
Hoshi, T; Fujiwara, T
2009-01-01
An early-stage version of the simulation package 'ELSES' (extra-large-scale electronic structure calculation) is developed for simulating the electronic structure and dynamics of large systems, particularly nanometer-scale and ten-nanometer-scale systems (see www.elses.jp). Input and output files are written in the extensible markup language (XML) style for general users. Related pre-/post-simulation tools are also available. A practical workflow and an example are described. A test calculation for the GaAs bulk system is shown, to demonstrate that the present code can handle systems with more than one atom species. Several future aspects are also discussed.
Determination of Krypton Diffusion Coefficients in Uranium Dioxide Using Atomic Scale Calculations.
Vathonne, Emerson; Andersson, David A; Freyss, Michel; Perriot, Romain; Cooper, Michael W D; Stanek, Christopher R; Bertolus, Marjorie
2017-01-03
We present a study of the diffusion of krypton in UO 2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT+U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO 2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μ O or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO 2 , migration is assisted by the bound Schottky defect and the charged uranium vacancy, V U 4- . Around stoichiometry, migration assisted by the charged uranium-oxygen divacancy (V UO 2- ) and V U 4- is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two V U 4- dominates. Kr migration is enhanced at higher μ O , and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. The mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.
International Nuclear Information System (INIS)
Oliveira, L.E.M.C. de.
1976-01-01
The electronic structure of the interstitial hydrogen atom in alkaline-earth fluorides has been studied using the self-consistent-field multiple-scattering Xα method. In the calculations a cluster constituted by the hydrogen atom and its first anion and cation neighbors has been used. The contact parameters with the proton and the fluorine nuclei have been evaluated. The agreement obtained with the experimental results is in general good and indicates that this method is also appropriate to study defects in ionic crystals. (author) [pt
Grid-based electronic structure calculations: The tensor decomposition approach
Energy Technology Data Exchange (ETDEWEB)
Rakhuba, M.V., E-mail: rakhuba.m@gmail.com [Skolkovo Institute of Science and Technology, Novaya St. 100, 143025 Skolkovo, Moscow Region (Russian Federation); Oseledets, I.V., E-mail: i.oseledets@skoltech.ru [Skolkovo Institute of Science and Technology, Novaya St. 100, 143025 Skolkovo, Moscow Region (Russian Federation); Institute of Numerical Mathematics, Russian Academy of Sciences, Gubkina St. 8, 119333 Moscow (Russian Federation)
2016-05-01
We present a fully grid-based approach for solving Hartree–Fock and all-electron Kohn–Sham equations based on low-rank approximation of three-dimensional electron orbitals. Due to the low-rank structure the total complexity of the algorithm depends linearly with respect to the one-dimensional grid size. Linear complexity allows for the usage of fine grids, e.g. 8192{sup 3} and, thus, cheap extrapolation procedure. We test the proposed approach on closed-shell atoms up to the argon, several molecules and clusters of hydrogen atoms. All tests show systematical convergence with the required accuracy.
Atomic structure of non-stoichiometric transition metal carbides
International Nuclear Information System (INIS)
Moisy-Maurice, Virginie.
1981-10-01
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 770 0 C- 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 Ti 2 Csub(1+x) and Nb 6 C 5 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 [fr
Influence of the plasma environment on atomic structure using an ion-sphere model
Belkhiri, Madeny; Fontes, Christopher J.; Poirier, Michel
2015-09-01
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 multiconfiguration Dirac-Fock value of B. Saha and S. Fritzsche [J. Phys. B 40, 259 (2007), 10.1088/0953-4075/40/2/002]. Last, the present model is compared to experimental data in titanium measured on the terawatt Astra facility and provides values for electron temperature and density in agreement with the maria code.
International Nuclear Information System (INIS)
Hua Manyu; Li Yimin; Long Chunguang; Li Xia
2012-01-01
The structural, electronic and elastic properties of potassium hexatitanate (K 2 Ti 6 O 13 ) whisker were investigated using first-principles calculations. The calculated cell parameters of K 2 Ti 6 O 13 including lattice constants and atomic positions are in good agreement with the experimental data. The obtained formation enthalpy (-61.1535 eV/atom) and cohesive energy (-137.4502 eV/atom) are both negative, showing its high structural stability. Further analysis of the electronic structures shows that the potassium hexatitanate is a wide-band semiconductor. Within K 2 Ti 6 O 13 crystal, the Ti---O bonding interactions are stronger than that of K---O, while no apparent K---Ti bonding interactions can be observed. The structural stability of K 2 Ti 6 O 13 was closely associated with the covalent bond interactions between Ti (d) and O (p) orbits. Further calculations on elastic properties show that K 2 Ti 6 O 13 is a high stiffness and brittle material with small anisotropy in shear and compression.
Inductance calculation of 3D superconducting structures with ground plane
International Nuclear Information System (INIS)
Teh, C.H.; Kitagawa, M.; Okabe, Y.
1999-01-01
An inductance calculation method, which is based on calculating the current distribution of a fluxoid-trapped superconducting loop by using the expression of momentum and the Maxwell equations, is reconstructed to enable calculation of arbitrary 3D structures which have a ground plane (GP). Calculation of the mutual inductances of the superconductor system is also incorporated into the algorithm. The method of images is used to save computational resources, and the mirror plane is demonstrated to be just at the effective penetration depth below the upper boundary of the GP. The algorithm offers accurate results with reasonable calculation time. (author)
Structures and Stability of Metal Amidoboranes (MAB): Density Functional Calculations
International Nuclear Information System (INIS)
Li Cailin; Wu Chaoling; Chen Yungui; Zhou Jingjing; Zheng Xin; Pang Lijuan; Deng Gang
2010-01-01
Molecule geometry structures, frequencies, and energetic stabilities of ammonia borane (AB, NH 3 BH 3 ) and metal amidoboranes (MAB, MNH 2 BH 3 ), formed by substituting H atom in AB with one of main group metal atoms, have been investigated by density-functional theory and optimized at the B3LYP levels with 6-311G++ (3df, 3pd) basic set. Their structural parameters and infrared spectrum characteristic peaks have been predicted, which should be the criterion of a successfully synthesized material. Several parameters such as binding energies, vibrational frequencies, and the energy gaps between the HOMO and the LUMO have been adopted to characterize and evaluate their structure stabilities. It is also found that the binding energies and HOMO-LUMO energy gaps of the MAB obviously change with the substitution of the atoms. MgAB has the lowest binding energy and is easier to decompose than any other substitutional structures under same conditions, while CaAB has the highest chemical activity. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
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.
Lupinetti, Concetta; Thakkar, Ajit J
2005-01-22
Accurate static dipole polarizabilities and hyperpolarizabilities are calculated for the ground states of the Al, Si, P, S, Cl, and Ar atoms. The finite-field computations use energies obtained with various ab initio methods including Moller-Plesset perturbation theory and the coupled cluster approach. Excellent agreement with experiment is found for argon. The experimental alpha for Al is likely to be in error. Only limited comparisons are possible for the other atoms because hyperpolarizabilities have not been reported previously for most of these atoms. Our recommended values of the mean dipole polarizability (in the order Al-Ar) are alpha/e(2)a(0) (2)E(h) (-1)=57.74, 37.17, 24.93, 19.37, 14.57, and 11.085 with an error estimate of +/-0.5%. The recommended values of the mean second dipole hyperpolarizability (in the order Al-Ar) are gamma/e(4)a(0) (4)E(h) (-3)=2.02 x 10(5), 4.31 x 10(4), 1.14 x 10(4), 6.51 x 10(3), 2.73 x 10(3), and 1.18 x 10(3) with an error estimate of +/-2%. Our recommended polarizability anisotropy values are Deltaalpha/e(2)a(0) (2)E(h) (-1)=-25.60, 8.41, -3.63, and 1.71 for Al, Si, S, and Cl respectively, with an error estimate of +/-1%. The recommended hyperpolarizability anisotropies are Deltagamma/e(4)a(0) (4)E(h) (-3)=-3.88 x 10(5), 4.16 x 10(4), -7.00 x 10(3), and 1.65 x 10(3) for Al, Si, S, and Cl, respectively, with an error estimate of +/-4%. (c) 2005 American Institute of Physics.
International Nuclear Information System (INIS)
Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Endo, Tatsuro; Higuchi, Kenji; Ogata, Shigenobu; Kimizuka, Hajime
2012-01-01
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)
International Nuclear Information System (INIS)
Damla, N.; Baltas, H.; Celik, A.; Kiris, E.; Cevik, U.
2008-01-01
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, 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. (authors)
Use of spatial symmetry in atomic--integral calculations: an efficient permutational approach
International Nuclear Information System (INIS)
Rouzo, H.L.
1979-01-01
The minimal number of independent nonzero atomic integrals that occur over arbitrarily oriented basis orbitals of the form R(r).Y/sub lm/(Ω) is theoretically derived. The corresponding method can be easily applied to any point group, including the molecular continuous groups C/sub infinity v/ and D/sub infinity h/. On the basis of this (theoretical) lower bound, the efficiency of the permutational approach in generating sets of independent integrals is discussed. It is proved that lobe orbitals are always more efficient than the familiar Cartesian Gaussians, in the sense that GLOS provide the shortest integral lists. Moreover, it appears that the new axial GLOS often lead to a number of integrals, which is the theoretical lower bound previously defined. With AGLOS, the numbers of two-electron integrals to be computed, stored, and processed are divided by factors 2.9 (NH 3 ), 4.2 (C 5 H 5 ), and 3.6 (C 6 H 6 ) with reference to the corresponding CGTOS calculations. Remembering that in the permutational approach, atomic integrals are directly computed without any four-indice transformation, it appears that its utilization in connection with AGLOS provides one of the most powerful tools for treating symmetrical species. 34 references
Insights inot the atomic many-particle dynamics of scattering processes by ab-initio calculations
International Nuclear Information System (INIS)
Zapukhlyak, Myroslav
2008-01-01
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, He 2+ -He, and Ar q+ -He (q=15-18) [de
Self-consistent average-atom scheme for electronic structure of hot and dense plasmas of mixture
International Nuclear Information System (INIS)
Yuan Jianmin
2002-01-01
An average-atom model is proposed to treat the electronic structures of hot and dense plasmas of mixture. It is assumed that the electron density consists of two parts. The first one is a uniform distribution with a constant value, which is equal to the electron density at the boundaries between the atoms. The second one is the total electron density minus the first constant distribution. The volume of each kind of atom is proportional to the sum of the charges of the second electron part and of the nucleus within each atomic sphere. By this way, one can make sure that electrical neutrality is satisfied within each atomic sphere. Because the integration of the electron charge within each atom needs the size of that atom in advance, the calculation is carried out in a usual self-consistent way. The occupation numbers of electron on the orbitals of each kind of atom are determined by the Fermi-Dirac distribution with the same chemical potential for all kinds of atoms. The wave functions and the orbital energies are calculated with the Dirac-Slater equations. As examples, the electronic structures of the mixture of Au and Cd, water (H 2 O), and CO 2 at a few temperatures and densities are presented
Self-consistent average-atom scheme for electronic structure of hot and dense plasmas of mixture.
Yuan, Jianmin
2002-10-01
An average-atom model is proposed to treat the electronic structures of hot and dense plasmas of mixture. It is assumed that the electron density consists of two parts. The first one is a uniform distribution with a constant value, which is equal to the electron density at the boundaries between the atoms. The second one is the total electron density minus the first constant distribution. The volume of each kind of atom is proportional to the sum of the charges of the second electron part and of the nucleus within each atomic sphere. By this way, one can make sure that electrical neutrality is satisfied within each atomic sphere. Because the integration of the electron charge within each atom needs the size of that atom in advance, the calculation is carried out in a usual self-consistent way. The occupation numbers of electron on the orbitals of each kind of atom are determined by the Fermi-Dirac distribution with the same chemical potential for all kinds of atoms. The wave functions and the orbital energies are calculated with the Dirac-Slater equations. As examples, the electronic structures of the mixture of Au and Cd, water (H2O), and CO2 at a few temperatures and densities are presented.
Hydrogen atoms in protein structures: high-resolution X-ray diffraction structure of the DFPase
2013-01-01
Background Hydrogen atoms represent about half of the total number of atoms in proteins and are often involved in substrate recognition and catalysis. Unfortunately, X-ray protein crystallography at usual resolution fails to access directly their positioning, mainly because light atoms display weak contributions to diffraction. However, sub-Ångstrom diffraction data, careful modeling and a proper refinement strategy can allow the positioning of a significant part of hydrogen atoms. Results A comprehensive study on the X-ray structure of the diisopropyl-fluorophosphatase (DFPase) was performed, and the hydrogen atoms were modeled, including those of solvent molecules. This model was compared to the available neutron structure of DFPase, and differences in the protein and the active site solvation were noticed. Conclusions A further examination of the DFPase X-ray structure provides substantial evidence about the presence of an activated water molecule that may constitute an interesting piece of information as regard to the enzymatic hydrolysis mechanism. PMID:23915572
International Nuclear Information System (INIS)
Ho, T.S.; Lieber, M.; Chan, F.T.
1981-01-01
We have employed the eikonal method to calculate the cross section for the capture of an electron into an arbitrary nl subshell in collisions between hydrogen atoms and fast projectiles. the projectiles were protons, C 6+ , O 8+ , and Fe 24+ . The energy ranges considered were 20--100 keV in the proton case, and 40--200 keV per nucleon in the other cases. These projectiles were selected because of their importance in fusion plasmas. For the highly charged case of Fe 24+ we found that our formulas, while exact, involved a high degree of cancellation and produced unreliable numerical results, so that a numerical integration of the penultimate formula was substituted. In the proton case agreement with recent experimental data is excellent
Convergence of configuration-interaction single-center calculations of positron-atom interactions
International Nuclear Information System (INIS)
Mitroy, J.; Bromley, M. W. 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 ΔX 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
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)
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite ... The Kohn–Sham equations were solved using the ... RMTKmax = 7 was used for all the investigated systems,.
Convergent Close-Coupling Calculations for Electron-Atom and Electron-Molecule Scattering
International Nuclear Information System (INIS)
Fursa, Dmitry; Zammit, M.C.; Bostock, C.J.; Bray, I.
2014-01-01
The Convergent Close-Coupling (CCC) method developed in our group has been applied extensively to study electron-atom/ion collisions and recently has been extended to electron collisions with diatomic molecules. This approach relies on the ability to represent the infinite number of target bound states and its continuum via a finite number of states obtained by a diagonalization of the target in a square-integrable (Sturmian) one-electron basis. We normally use a Laguerre basis though other choices are possible, for example a boxed-based basis or a B-spline basis. The choice of the basis is governed by the physical problem under consideration. As the size of a Sturmian basis increases the calculated negative energy states (relative to the corresponding ionization stage of the target) converge to the target true bound states and the positive energy states provide an increasingly dense representation of the target continuum. We then perform a multichannel expansion of the total (projectile plus target electrons) wave function and formulate a set of close-coupling equations. These equations are transformed into momentum space where they take the form of the Lippmann-Schwinger equations for the T-matrix. A solution of the T-matrix equations is obtained at each total energy E by converting them into a set of linear equations that are solved by standard techniques. We perform a partial-wave expansion of the projectile wave function and take into account the symmetry of the scattering system (e.g, total spin, parity, etc.) in order to reduce the size of the coupled equations and make calculations feasible. As soon as the T-matrix is obtained we can evaluate scattering amplitudes and cross sections for the transitions of interest. For the case of molecular targets the formulation is done within the fixed-nuclei approximation. We adopt a single-centre approach in CCC calculations. This allows us to utilize a great deal of computational development thoroughly tested for
Atomic and electronic structures of novel silicon surface structures
Energy Technology Data Exchange (ETDEWEB)
Terry, J.H. Jr.
1997-03-01
The modification of silicon surfaces is presently of great interest to the semiconductor device community. Three distinct areas are the subject of inquiry: first, modification of the silicon electronic structure; second, passivation of the silicon surface; and third, functionalization of the silicon surface. It is believed that surface modification of these types will lead to useful electronic devices by pairing these modified surfaces with traditional silicon device technology. Therefore, silicon wafers with modified electronic structure (light-emitting porous silicon), passivated surfaces (H-Si(111), Cl-Si(111), Alkyl-Si(111)), and functionalized surfaces (Alkyl-Si(111)) have been studied in order to determine the fundamental properties of surface geometry and electronic structure using synchrotron radiation-based techniques.
Theoretical and experimental investigation of atomic radiative lifetimes and hyperfine structures
International Nuclear Information System (INIS)
Joensson, Per.
1992-01-01
Atomic radiative lifetimes and hyperfine structures as well as other properties, such as total energy and specific mass shift, have been studied theoretically and experimentally. Computer programs to calculate hyperfine structure constants from non-relativistic multiconfiguration Hartree-Fock (MCHF) and relativistic multi-configuration Dirac-Fock (MCDF) wavefunctions have been written. Using these programs large-scale calculations of hyperfine structures in lithium and sodium have been performed. It is shown, that the MCHF method is able to predict hyperfine structures to an accuracy of a few per mille in lithium, whereas for the more complex hyperfine structures to an accuracy of a few per mille in lithium, whereas for the more complex sodium atom an accuracy of a few per cent is obtainable. For lithium convergence of the total energy, ionization energy, specific mass shift and hyperfine parameters has been studied with the MCHF method. 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 curves following VUV excitation, the radiative lifetimes and hyperfine structures of the 7p 2 P states in silver were measured. The delayed-coincidence technique has been used to make very accurate measurements of the radiative lifetimes and hyperfine structures of the lowest P states in sodium and silver
Ab initio calculations of the electronic structure and bonding characteristics of LaB6
International Nuclear Information System (INIS)
Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.
2005-01-01
Lanthanum hexaboride (LaB 6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB 6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB 6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB 6 system and partially explains its high efficiency as a thermionic emitter
International Nuclear Information System (INIS)
Saito, M.; Suzuki, S.; Kimura, M.; Suzuki, T.; Kihira, H.; Waseda, Y.
2005-01-01
Quantitative X-ray structural analysis coupled with anomalous X-ray scattering has been used for characterizing the atomic-scale structure of rust formed on steel surfaces. Samples were prepared from rust layers formed on the surfaces of two commercial steels. X-ray scattered intensity profiles of the two samples showed that the rusts consisted mainly of two types of ferric oxyhydroxide, α-FeOOH and γ-FeOOH. The amounts of these rust components and the realistic atomic arrangements in the components were estimated by fitting both the ordinary and the environmental interference functions with a model structure calculated using the reverse Monte Carlo simulation technique. The two rust components were found to be the network structure formed by FeO 6 octahedral units, the network structure itself deviating from the ideal case. The present results also suggest that the structural analysis method using anomalous X-ray scattering and the reverse Monte Carlo technique is very successful in determining the atomic-scale structure of rusts formed on the steel surfaces
Atomic structure of diamond {111} surfaces etched in oxygen water vapor
International Nuclear Information System (INIS)
Theije, F.K. de; Reedijk, M.F.; Arsic, J.; Enckevort, W.J.P. van; Vlieg, E.
2001-01-01
The atomic structure of the {111} diamond face after oxygen-water-vapor etching is determined using x-ray scattering. We find that a single dangling bond diamond {111} surface model, terminated by a full monolayer of -OH fits our data best. To explain the measurements it is necessary to add an ordered water layer on top of the -OH terminated surface. The vertical contraction of the surface cell and the distance between the oxygen atoms are generally in agreement with model calculations and results on similar systems. The OH termination is likely to be present during etching as well. This model experimentally confirms the atomic-scale mechanism we proposed previously for this etching system
International Nuclear Information System (INIS)
Zhang Min; Shi Jun-Jie
2014-01-01
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 4μ B 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)
Atomic and magnetic structure of MnF3
International Nuclear Information System (INIS)
Hunter, B.A.; Kennedy, B.J.; Vogt, T.
2003-01-01
Full text: The magnetic and atomic structure of MnF 3 has been determined from 4K to 300K using neutron powder diffraction. The MnF 3 compound is the archetypical Mn-based colossal magnetoresistive compound. A Neel temperature of approximately 40K was observed from the temperature variation of the magnetic moment. Below the Neel temperature a large negative thermal expansion was observed, in striking similarity to other Mn-based colossal magnetoresistive compounds. The variation in structure is discussed in relation to other Mn-based compounds, particularly as this compound cannot support charge ordering
Large-dimension configuration-interaction calculations of positron binding to the group-II atoms
International Nuclear Information System (INIS)
Bromley, M. W. J.; Mitroy, J.
2006-01-01
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
Atom exchange between aqueous Fe(II) and structural Fe in clay minerals.
Neumann, Anke; Wu, Lingling; Li, Weiqiang; Beard, Brian L; Johnson, Clark M; Rosso, Kevin M; Frierdich, Andrew J; Scherer, Michelle M
2015-03-03
Due to their stability toward reductive dissolution, Fe-bearing clay minerals are viewed as a renewable source of Fe redox activity in diverse environments. Recent findings of interfacial electron transfer between aqueous Fe(II) and structural Fe in clay minerals and electron conduction in octahedral sheets of nontronite, however, raise the question whether Fe interaction with clay minerals is more dynamic than previously thought. Here, we use an enriched isotope tracer approach to simultaneously trace Fe atom movement from the aqueous phase to the solid ((57)Fe) and from the solid into the aqueous phase ((56)Fe). Over 6 months, we observed a significant decrease in aqueous (57)Fe isotope fraction, with a fast initial decrease which slowed after 3 days and stabilized after about 50 days. For the aqueous (56)Fe isotope fraction, we observed a similar but opposite trend, indicating that Fe atom movement had occurred in both directions: from the aqueous phase into the solid and from the solid into aqueous phase. We calculated that 5-20% of structural Fe in clay minerals NAu-1, NAu-2, and SWa-1 exchanged with aqueous Fe(II), which significantly exceeds the Fe atom layer exposed directly to solution. Calculations based on electron-hopping rates in nontronite suggest that the bulk conduction mechanism previously demonstrated for hematite1 and suggested as an explanation for the significant Fe atom exchange observed in goethite2 may be a plausible mechanism for Fe atom exchange in Fe-bearing clay minerals. Our finding of 5-20% Fe atom exchange in clay minerals indicates that we need to rethink how Fe mobility affects the macroscopic properties of Fe-bearing phyllosilicates and its role in Fe biogeochemical cycling, as well as its use in a variety of engineered applications, such as landfill liners and nuclear repositories.
Calculation of coupling factor for double-period accelerating structure
International Nuclear Information System (INIS)
Bian Xiaohao; Chen Huaibi; Zheng Shuxin
2005-01-01
In the design of the linear accelerating structure, the coupling factor between cavities is a crucial parameter. The error of coupling factor accounts for the electric or magnetic field error mainly. To accurately design the coupling iris, the accurate calculation of coupling factor is essential. The numerical simulation is widely used to calculate the coupling factor now. By using MAFIA code, two methods have been applied to calculate the dispersion characteristics of the single-period structure, one method is to simulate the traveling wave mode by the period boundary condition; another method is to simulate the standing wave mode by the electrical boundary condition. In this work, the authors develop the two methods to calculate the coupling factor of double-period accelerating structure. Compared to experiment, the results for both methods are very similar, and in agreement with measurement within 15% deviation. (authors)
Electric field gradient calculation at atomic site of In implanted ZnO samples
International Nuclear Information System (INIS)
Abreu, Y.; Cruz, C. M.; Leyva, A.; Pinnera; Van Espen, P.; Perez, C.
2011-01-01
The electric field gradient (EFG) calculated for 111 In→ 111 Cd implanted ZnO samples is reported. The study was made for ideal hexagonal ZnO structures and super-cells considering the In implantation environment at the cation site using the 'WIEN2k' code within the GGA(+U) approximation. The obtained EFG values are in good agreement with the experimental reports for ideal ZnO and 111 In→ 111 Cd implanted structures; measured by perturbed angular correlation (PAC) and Moessbauer spectroscopy. The attribution of substitutional incorporation of 111 In at the ZnO cation site after annealing was confirmed. (Author)
Atomic structure of graphene supported heterogeneous model catalysts
Energy Technology Data Exchange (ETDEWEB)
Franz, Dirk
2017-04-15
Graphene on Ir(111) forms a moire structure with well defined nucleation centres. Therefore it can be utilized to create hexagonal metal cluster lattices with outstanding structural quality. At diffraction experiments these 2D surface lattices cause a coherent superposition of the moire cell structure factor, so that the measured signal intensity scales with the square of coherently scattering unit cells. This artificial signal enhancement enables the opportunity for X-ray diffraction to determine the atomic structure of small nano-objects, which are hardly accessible with any experimental technique. The uniform environment of every metal cluster makes the described metal cluster lattices on graphene/Ir(111) an attractive model system for the investigation of catalytic, magnetic and quantum size properties of ultra-small nano-objects. In this context the use of x-rays provides a maximum of flexibility concerning the possible sample environments (vacuum, selected gases, liquids, sample temperature) and allows in-situ/operando measurements. In the framework of the present thesis the structure of different metal clusters grown by physical vapor deposition in an UHV environment and after gas exposure have been investigated. On the one hand the obtained results will explore many aspects of the atomic structure of these small metal clusters and on the other hand the presented results will proof the capabilities of the described technique (SXRD on cluster lattices). For iridium, platinum, iridium/palladium and platinum/rhodium the growth on graphene/Ir(111) of epitaxial, crystalline clusters with an ordered hexagonal lattice arrangement has been confirmed using SXRD. The clusters nucleate at the hcp sites of the moire cell and bind via rehybridization of the carbon atoms (sp{sup 2} → sp{sup 3}) to the Ir(111) substrate. This causes small displacements of the substrate atoms, which is revealed by the diffraction experiments. All metal clusters exhibit a fcc structure
MODY - calculation of ordered structures by symmetry-adapted functions
Białas, Franciszek; Pytlik, Lucjan; Sikora, Wiesława
2016-01-01
In this paper we focus on the new version of computer program MODY for calculations of symmetryadapted functions based on the theory of groups and representations. The choice of such a functional frame of coordinates for description of ordered structures leads to a minimal number of parameters which must be used for presentation of such structures and investigations of their properties. The aim of this work is to find those parameters, which are coefficients of a linear combination of calculated functions, leading to construction of different types of structure ordering with a given symmetry. A spreadsheet script for simplification of this work has been created and attached to the program.
International Nuclear Information System (INIS)
Singh, Janpreet; Singh, Satvinder; Tripathi, S. K.; Singh, Gurinder; Kaura, Aman
2016-01-01
The atomic arrangements and chemical bonding of stable Ge_4Sb_2Te_7 (GeTe rich), a phase-change material, have been investigated by means of ab initio total energy calculations. To study the atomic arrangement, GeTe block is considered into -TeSbTeSbTe- block and -Te-Te- layer in the stacking I and II respectively. The stacking I is energetically more stable than the stacking II. The reason for more stability of the stacking I has been explained. The chemical bonding has been studied with the electronic charge density distribution around the atomic bonds. The quantity of electronic charge loosed or gained by atoms has been calculated using the Bader charge analysis. The metallic character has been studied using band structures calculations. The band gap for the stacking I and II is 0.463 and 0.219 eV respectively.
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.
Ab-initio electronic band structure calculations for beryllium chalcogenides
International Nuclear Information System (INIS)
Kalpana, G.; Pari, G.; Yousuf, Mohammad
1997-01-01
The first principle tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties, structural phase transition and pressure dependence of band gap of BeS, BeSe and BeTe. We have calculated the energy-volume relations for these compounds in the B3 and B8 phases. The calculated lattice parameters, bulk modulus and the pressure-volume relation were found to be in good agreement with the recent experimental results. The calculated B3→B8 structural transition pressure for BeS, BeSe and BeTe agree well with the recent experimental results. Our calculations show that these compounds are indirect band gap (Γ-X) semiconductors at ambient conditions. The calculated band gap values are found to be underestimated by 20-30% which is due to the usage of LDA. After the structural transition to the B8 phase, BeS continues to be indirect band gap semiconductors and ultimately above 100 GPa it metallises, BeSe and BeTe are metallic at the B3→B8 structural transition. (author)
Structure formation in atom lithography using geometric collimation
Meijer, T.; Beardmore, J.P.; Fabrie, C.G.C.H.M.; van Lieshout, J.P.; Notermans, R.P.M.J.W.; Sang, R.T.; Vredenbregt, E.J.D.; Leeuwen, van K.A.H.
2011-01-01
Atom lithography uses standing wave light fields as arrays of lenses to focus neutral atom beams into line patterns on a substrate. Laser cooled atom beams are commonly used, but an atom beam source with a small opening placed at a large distance from a substrate creates atom beams which are locally
SGO: A fast engine for ab initio atomic structure global optimization by differential evolution
Chen, Zhanghui; Jia, Weile; Jiang, Xiangwei; Li, Shu-Shen; Wang, Lin-Wang
2017-10-01
As the high throughout calculations and material genome approaches become more and more popular in material science, the search for optimal ways to predict atomic global minimum structure is a high research priority. This paper presents a fast method for global search of atomic structures at ab initio level. The structures global optimization (SGO) engine consists of a high-efficiency differential evolution algorithm, accelerated local relaxation methods and a plane-wave density functional theory code running on GPU machines. The purpose is to show what can be achieved by combining the superior algorithms at the different levels of the searching scheme. SGO can search the global-minimum configurations of crystals, two-dimensional materials and quantum clusters without prior symmetry restriction in a relatively short time (half or several hours for systems with less than 25 atoms), thus making such a task a routine calculation. Comparisons with other existing methods such as minima hopping and genetic algorithm are provided. One motivation of our study is to investigate the properties of magnetic systems in different phases. The SGO engine is capable of surveying the local minima surrounding the global minimum, which provides the information for the overall energy landscape of a given system. Using this capability we have found several new configurations for testing systems, explored their energy landscape, and demonstrated that the magnetic moment of metal clusters fluctuates strongly in different local minima.
International Nuclear Information System (INIS)
Rubin, Yu.V.; Belous, L.F.
2012-01-01
Self-associates of nucleic acid components (stacking trimers and tetramers of the base pairs of nucleic acids) and short fragments of nucleic acids are nanoparticles (linear sizes of these particles are more than 10 A). Modern quantum-mechanical methods and softwares allow one to perform ab initio calculations of the systems consisting of 150-200 atoms with enough large basis sets (for example, 6-31G * ). The aim of this work is to reveal the peculiarities of molecular and electronic structures, as well as the energy features of nanoparticles of nucleic acid components. We had carried out ab initio calculations of the molecular structure and interactions in the stacking dimer, trimer, and tetramer of nucleic base pairs and in the stacking (TpG)(ApC) dimer and (TpGpC) (ApCpG) trimer of nucleotides, which are small DNA fragments. The performed calculations of molecular structures of dimers and trimers of nucleotide pairs showed that the interplanar distance in the structures studied is equal to 3.2 A on average, and the helical angle in a trimer is approximately equal to 30 o : The distance between phosphor atoms in neighboring chains is 13.1 A. For dimers and trimers under study, we calculated the horizontal interaction energies. The analysis of interplanar distances and angles between nucleic bases and their pairs in the calculated short oligomers of nucleic acid base pairs (stacking dimer, trimer, and tetramer) has been carried out. Studies of interactions in the calculated short oligomers showed a considerable role of the cross interaction in the stabilization of the structures. The contribution of cross interactions to the horizontal interactions grows with the length of an oligomer. Nanoparticle components get electric charges in nanoparticles. Longwave low-intensity bands can appear in the electron spectra of nanoparticles.
Characterization of Structural and Configurational Properties of DNA by Atomic Force Microscopy.
Meroni, Alice; Lazzaro, Federico; Muzi-Falconi, Marco; Podestà, Alessandro
2018-01-01
We describe a method to extract quantitative information on DNA structural and configurational properties from high-resolution topographic maps recorded by atomic force microscopy (AFM). DNA molecules are deposited on mica surfaces from an aqueous solution, carefully dehydrated, and imaged in air in Tapping Mode. Upon extraction of the spatial coordinates of the DNA backbones from AFM images, several parameters characterizing DNA structure and configuration can be calculated. Here, we explain how to obtain the distribution of contour lengths, end-to-end distances, and gyration radii. This modular protocol can be also used to characterize other statistical parameters from AFM topographies.
Chain-Branching Control of the Atomic Structure of Alkanethiol-Based Gold–Sulfur Interfaces
DEFF Research Database (Denmark)
Wang, Yun; Chi, Qijin; Zhang, Jingdong
2011-01-01
Density functional theory structure calculations at 0 K and simulations at 300 K of observed high-resolution in situ scanning tunneling microscopy (STM) images reveal three different atomic-interface structures for the self-assembled monolayers (SAMs) of three isomeric butanethiols on Au(111......): direct binding to the Au(111) surface without pitting, binding to adatoms above a regular surface with extensive pitting, and binding to adatoms with local surface vacancies and some pitting. Thermal motions are shown to produce some observed STM features, with a very tight energy balance controlling...
Atomic and electronic structure of the CdTe(111)B–(2√3 × 4) orthogonal surface
Energy Technology Data Exchange (ETDEWEB)
Bekenev, V. L., E-mail: bekenev@ipms.kiev.ua; Zubkova, S. M. [National Academy of Sciences of Ukraine, Frantsevych Institute for Problems of Materials Science (Ukraine)
2017-01-15
The atomic and electronic structure of four variants of Te-terminated CdTe(111)B–(2√3 × 4) orthogonal polar surface (ideal, relaxed, reconstructed, and reconstructed with subsequent relaxation) are calculated ab initio for the first time. The surface is modeled by a film composed of 12 atomic layers with a vacuum gap of ~16 Å in the layered superlattice approximation. To close Cd dangling bonds on the opposite side of the film, 24 fictitious hydrogen atoms with a charge of 1.5 electrons each are added. Ab initio calculations are performed using the Quantum Espresso program based on density functional theory. It is demonstrated that relaxation leads to splitting of the four upper layers. The band energy structures and total and layer-by-layer densities of electronic states for the four surface variants are calculated and analyzed.
Snyder, David A.; Grullon, Jennifer; Huang, Yuanpeng J.; Tejero, Roberto; Montelione, Gaetano T.
2014-01-01
Maximizing the scientific impact of NMR-based structure determination requires robust and statistically sound methods for assessing the precision of NMR-derived structures. In particular, a method to define a core atom set for calculating superimpositions and validating structure predictions is critical to the use of NMR-derived structures as targets in the CASP competition. FindCore (D.A. Snyder and G.T. Montelione PROTEINS 2005;59:673–686) is a superimposition independent method for identifying a core atom set, and partitioning that set into domains. However, as FindCore optimizes superimposition by sensitively excluding not-well-defined atoms, the FindCore core may not comprise all atoms suitable for use in certain applications of NMR structures, including the CASP assessment process. Adapting the FindCore approach to assess predicted models against experimental NMR structures in CASP10 required modification of the FindCore method. This paper describes conventions and a standard protocol to calculate an “Expanded FindCore” atom set suitable for validation and application in biological and biophysical contexts. A key application of the Expanded FindCore method is to identify a core set of atoms in the experimental NMR structure for which it makes sense to validate predicted protein structure models. We demonstrate the application of this Expanded FindCore method in characterizing well-defined regions of 18 NMR-derived CASP10 target structures. The Expanded FindCore protocol defines “expanded core atom sets” that match an expert’s intuition of which parts of the structure are sufficiently well-defined to use in assessing CASP model predictions. We also illustrate the impact of this analysis on the CASP GDT assessment scores. PMID:24327305
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.
Electronic structure calculations on nitride semiconductors and their alloys
International Nuclear Information System (INIS)
Dugdale, D.
2000-09-01
Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)
Dissociative recombination of interstellar ions: electronic structure calculations for HCO+
International Nuclear Information System (INIS)
Kraemer, W.P.; Hazi, A.U.
1985-01-01
The present study of the interstellar formyl ion HCO + is the first attempt to investigate dissociative recombination for a triatomic molecular ion using an entirely theoretical approach. We describe a number of fairly extensive electronic structure calculations that were performed to determine the reaction mechanism of the e-HCO + process. Similar calculations for the isoelectronic ions HOC + and HN 2 + are in progress. 60 refs
Yin, Na; Dai, Ying; Wei, Wei; Huang, Baibiao
2018-04-01
A lot of efforts have been made towards the band gap opening in two-dimensional silicene, the silicon version of graphene. In the present work, the electronic structures of single atom doped (B, N, Al and P) and codoped (B/N and Al/P) silicene monolayers are systematically examined on the base of density functional electronic calculations. Our results demonstrate that single atom doping can realize electron or hole doping in the silicene; while codoping, due to the syergistic effects, results in finite band gap in silicene at the Dirac point without significantly degrading the electronic properties. In addition, the characteristic of band gap shows dependence on the doping concentration. Importantly, we predict a new two-dimensional Dirac structure, the graphene-like Si3C, which also shows linear band dispersion relation around the Fermi level. Our results demonstrates an important perspective to engineer the electronic and optical properties of silicene.
Variable temperature investigation of the atomic structure of gold nanoparticles
International Nuclear Information System (INIS)
Young, N P; Kirkland, A I; Huis, M A van; Zandbergen, H W; Xu, H
2010-01-01
The characterisation of nanoparticle structures is the first step towards understanding and optimising their utility in important technological applications such as catalysis. Using newly developed in-situ transmission electron microscopy (TEM) specimen holders, the temperature dependent atomic structure of gold nanoparticles in the size range 5-12 nm has been investigated. In this size interval, the decahedral morphology has been identified as the most favourable structure at or above room temperature, while particle surface roughening becomes evident above 600 0 C. An icosahedral transition has also been identified at low temperature in particles under 9 nm in diameter. These experimental results are consistent with recently published temperature dependent equilibrium phase maps for gold nanoparticles.
Variable temperature investigation of the atomic structure of gold nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Young, N P; Kirkland, A I [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Huis, M A van; Zandbergen, H W [Kavli Insitute of Nanoscience, Delft University of Technolgy, Lorentzweg 1, NL-2628CJ, Delft (Netherlands); Xu, H, E-mail: neil.young@materials.ox.ac.u [Department of Geology and Geophysics, and Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin (United States)
2010-07-01
The characterisation of nanoparticle structures is the first step towards understanding and optimising their utility in important technological applications such as catalysis. Using newly developed in-situ transmission electron microscopy (TEM) specimen holders, the temperature dependent atomic structure of gold nanoparticles in the size range 5-12 nm has been investigated. In this size interval, the decahedral morphology has been identified as the most favourable structure at or above room temperature, while particle surface roughening becomes evident above 600{sup 0}C. An icosahedral transition has also been identified at low temperature in particles under 9 nm in diameter. These experimental results are consistent with recently published temperature dependent equilibrium phase maps for gold nanoparticles.
Semiclassical calculation of ionisation rate for Rydberg helium atoms in an electric field
International Nuclear Information System (INIS)
Wang De-Hua
2011-01-01
The ionisation of Rydberg helium atoms in an electric field above the classical ionisation threshold has been examined using the semiclassical method, with particular emphasis on discussing the influence of the core scattering on the escape dynamics of electrons. The results show that the Rydberg helium atoms ionise by emitting a train of electron pulses. Unlike the case of the ionisation of Rydberg hydrogen atom in parallel electric and magnetic fields, where the pulses of the electron are caused by the external magnetic field, the pulse trains for Rydberg helium atoms are created through core scattering. Each peak in the ionisation rate corresponds to the contribution of one core-scattered combination trajectory. This fact further illustrates that the ionic core scattering leads to the chaotic property of the Rydberg helium atom in external fields. Our studies provide a simple explanation for the escape dynamics in the ionisation of nonhydrogenic atoms in external fields. (atomic and molecular physics)
Calculation of the 1s-2s two-photon excitation cross-section in atomic hydrogen
Energy Technology Data Exchange (ETDEWEB)
Celik, G.; Celik, E.; Kilic, H.S. [Selcuk Univ., Dept. of Physics, Faculty of Arts and Science (Turkey)
2008-12-15
The two-photon excitation cross-section of atomic hydrogen is calculated using explicit summation over intermediate states within the framework of dipole approximation. The matrix element for two-photon excitation is transformed into finite sums, consisting of the product of a radial and angular part. Nine intermediate states are employed in the calculation of the transition matrix element. The two-photon excitation cross-section obtained for the transition 1s{sup 2}S{sub 1/2}-2s{sup 2}S{sub 1/2} in atomic hydrogen is in good agreement with the literature. (authors)
Calculation of the 1s-2s two-photon excitation cross-section in atomic hydrogen
International Nuclear Information System (INIS)
Celik, G.; Celik, E.; Kilic, H.S.
2008-01-01
The two-photon excitation cross-section of atomic hydrogen is calculated using explicit summation over intermediate states within the framework of dipole approximation. The matrix element for two-photon excitation is transformed into finite sums, consisting of the product of a radial and angular part. Nine intermediate states are employed in the calculation of the transition matrix element. The two-photon excitation cross-section obtained for the transition 1s 2 S 1/2 -2s 2 S 1/2 in atomic hydrogen is in good agreement with the literature. (authors)
The influence of the surface atomic structure on surface diffusion
International Nuclear Information System (INIS)
Ghaleb, Dominique
1984-03-01
This work represents the first quantitative study of the influence of the surface atomic structure on surface diffusion (in the range: 0.2 Tf up 0.5 Tf; Tf: melting temperature of the substrate). The analysis of our results on a microscopic scale shows low formation and migration energies for adatoms; we can describe the diffusion on surfaces with a very simple model. On (110) surfaces at low temperature the diffusion is controlled by the exchange mechanism; at higher temperature direct jumps of adatoms along the channels contribute also to the diffusion process. (author) [fr
Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method
International Nuclear Information System (INIS)
Osadchy, A V; Obraztsova, E D; Volotovskiy, S G; Golovashkin, D L; Savin, V V
2016-01-01
In this paper we present the results of band structure computer simulation of GaSe- based nanostructures using the empirical pseudopotential method. Calculations were performed using a specially developed software that allows performing simulations using cluster computing. Application of this method significantly reduces the demands on computing resources compared to traditional approaches based on ab-initio techniques and provides receiving the adequate comparable results. The use of cluster computing allows to obtain information for structures that require an explicit account of a significant number of atoms, such as quantum dots and quantum pillars. (paper)
International Nuclear Information System (INIS)
Bradley, C.R.; Zaluzec, N.J.
1987-08-01
The development of medium voltage electron microscopes having high brightness electron sources and ultra-high vacuum environments has been anticipated by the microscopy community now for several years. The advantages of such a configuration have been discussed to great lengths, while the potential disadvantages have for the most part been neglected. The most detrimental of these relative to microcharacterization are the effects of electron sputtering and atomic displacement to the local specimen composition. These effects have in the past been considered mainly in the high voltage electron microscope regime and generally were ignored in lower voltage instruments. Recent experimental measurements have shown that the effects of electron sputtering as well as radiation induced segregation can be observed in conventional transmission electron microscopes. It is, therefore, important to determine at what point the effects will begin to manifest themselves in the new generation of medium voltage analytical electron microscopes. In this manuscript we present new calculations which allow the individual experimentalist to determine the potential threshold levels for a particular elemental system and thus avoid the dangers of introducing artifacts during microanalysis. 12 refs., 3 figs
All-atom molecular dynamics calculation study of entire poliovirus empty capsids in solution
Energy Technology Data Exchange (ETDEWEB)
Andoh, Y.; Yoshii, N.; Yamada, A.; Kojima, H.; Mizutani, K.; Okazaki, S., E-mail: okazaki@apchem.nagoya-u.ac.jp [Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Fujimoto, K. [Department of Pharmacy, College of Pharmaceutical Sciences, Ritsumeikan University, Nojihigashi, Kusatsu, Shiga 525-8577 (Japan); Nakagawa, A. [Institute for Protein Research, Osaka University, Yamadaoka, Suita, Osaka 565-0871 (Japan); Nomoto, A. [Institute of Microbial Chemistry, Kamiosaki, Shinagawa-ku, Tokyo 141-0021 (Japan)
2014-10-28
Small viruses that belong, for example, to the Picornaviridae, such as poliovirus and foot-and-mouth disease virus, consist simply of capsid proteins and a single-stranded RNA (ssRNA) genome. The capsids are quite stable in solution to protect the genome from the environment. Here, based on long-time and large-scale 6.5 × 10{sup 6} all-atom molecular dynamics calculations for the Mahoney strain of poliovirus, we show microscopic properties of the viral capsids at a molecular level. First, we found equilibrium rapid exchange of water molecules across the capsid. The exchange rate is so high that all water molecules inside the capsid (about 200 000) can leave the capsid and be replaced by water molecules from the outside in about 25 μs. This explains the capsid's tolerance to high pressures and deactivation by exsiccation. In contrast, the capsid did not exchange ions, at least within the present simulation time of 200 ns. This implies that the capsid can function, in principle, as a semipermeable membrane. We also found that, similar to the xylem of trees, the pressure of the solution inside the capsid without the genome was negative. This is caused by coulombic interaction of the solution inside the capsid with the capsid excess charges. The negative pressure may be compensated by positive osmotic pressure by the solution-soluble ssRNA and the counter ions introduced into it.
All-atom molecular dynamics calculation study of entire poliovirus empty capsids in solution
Andoh, Y.; Yoshii, N.; Yamada, A.; Fujimoto, K.; Kojima, H.; Mizutani, K.; Nakagawa, A.; Nomoto, A.; Okazaki, S.
2014-10-01
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.
International Nuclear Information System (INIS)
Miyasaka, Yasuhiko
1979-01-01
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)
Andoh, Y.; Yoshii, N.; Yamada, A.; Kojima, H.; Mizutani, K.; Okazaki, S.; Fujimoto, K.; Nakagawa, A.; Nomoto, A.
2014-01-01
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 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
Structure of the Balmer jump. The isolated hydrogen atom
Calvo, F.; Belluzzi, L.; Steiner, O.
2018-06-01
Context. The spectrum of the hydrogen atom was explained by Bohr more than one century ago. We revisit here some of the aspects of the underlying quantum structure, with a modern formalism, focusing on the limit of the Balmer series. Aims: We investigate the behaviour of the absorption coefficient of the isolated hydrogen atom in the neighbourhood of the Balmer limit. Methods: We analytically computed the total cross-section arising from bound-bound and bound-free transitions in the isolated hydrogen atom at the Balmer limit, and established a simplified semi-analytical model for the surroundings of that limit. We worked within the framework of the formalism of Landi Degl'Innocenti & Landolfi (2004, Astrophys. Space Sci. Lib., 307), which permits an almost straight-forward generalization of our results to other atoms and molecules, and which is perfectly suitable for including polarization phenomena in the problem. Results: We analytically show that there is no discontinuity at the Balmer limit, even though the concept of a "Balmer jump" is still meaningful. Furthermore, we give a possible definition of the location of the Balmer jump, and we check that this location is dependent on the broadening mechanisms. At the Balmer limit, we compute the cross-section in a fully analytical way. Conclusions: The Balmer jump is produced by a rapid drop of the total Balmer cross-section, yet this variation is smooth and continuous when both bound-bound and bound-free processes are taken into account, and its shape and location is dependent on the broadening mechanisms.
Calculation of coupling factor for the heterogeneous accelerating structure
International Nuclear Information System (INIS)
Bian Xiaohao; Chen Huaibi; Zheng Shuxin
2006-01-01
The converging part of electron accelerator is designed to converge the phase of injecting electrons, improving the beam quality of the accelerator. It is very crucial to calculate the coupling factor between cavities and to design the geometry structure of the coupling irises. By the E module of code MAFIA, the authors calculate the frequency of every single resonant cavity and the two eigenfrequencies of two-cavitiy line. Then we get the coupling factor between the two cavities. This method can be used to design the geometry structure of the coupling isises between every two cavities. Compared to experiment, the results of the method is very accurate. (authors)
International Nuclear Information System (INIS)
Shepard, J. R.
2007-01-01
Three-body recombination rates for cold 4 He are calculated with a method which exploits the simple relationship between the imaginary part of the atom-dimer elastic scattering phase shift and the S-matrix for recombination. The elastic phase shifts are computed above breakup threshold by solving a three-body Faddeev equation in momentum space with inputs based on a variety of modern atom-atom potentials. Recombination coefficients for the HFD-B3-FCII potential agree very well with the only previously published results. Since the elastic scattering and recombination processes for 4 He are governed by 'Efimov physics', they depend on universal functions of a scaling variable. The computed recombination coefficients for potentials other than HFD-B3-FCII make it possible to determine these universal functions
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...... and use their knowledge to design new materials for a vast range of applications. Todays hottest topics are, amongst many others, better materials for energy conversion (e.g. solar cells), energy storage (batteries) and catalysts for the removal of environmentally dangerous exhausts. The mentioned...... properties are to a large extent governed by the physics on the atomic scale, that means pure quantum mechanics. For many decades, Density Functional Theory has been the computational method of choice, since it provides a fairly easy and yet accurate way of determining electronic structures and related...
REFLOS, Fuel Loading and Cost from Burnup and Heavy Atomic Mass Flow Calculation in HWR
International Nuclear Information System (INIS)
Boettcher, W.; Schmidt, E.
1969-01-01
1 - Nature of physical problem solved: REFLOS is a programme for the evaluation of fuel-loading schemes in heavy water moderated reactors. The problems involved in this study are: a) Burn-up calculation for the reactor cell. b) Determination of reactivity behaviour, power distribution, attainable burn-up for both the running-in period and the equilibrium of a 3-dimensional heterogeneous reactor model; investigation of radial fuel movement schemes. c) Evaluation of mass flows of heavy atoms through the reactor and fuel cycle costs for the running-in, the equilibrium, and the shut down of a power reactor. If the subroutine for treating the reactor cell were replaced by a suitable routine, other reactors with weakly absorbing moderators could be analyzed. 2 - Method of solution: Nuclear constants and isotopic compositions of the different fuels in the reactor are calculated by the cell-burn-up programme and tabulated as functions of the burn-up rate (MWD/T). Starting from a known state of the reactor, the 3-dimensional heterogeneous reactor programme (applying an extension of the technique of Feinberg and Galanin) calculates reactivity and neutron flux distribution using one thermal and one or two fast neutron groups. After a given irradiation time, the new state of the reactor is determined, and new nuclear constants are assigned to the various defined locations in the reactor. Reloading of fuel may occur if the prescribed life of the reactor is reached or if the effective multiplication factor or the power form factor falls below a specified level. The scheme of reloading to be carried out is specified by a load vector, giving the number of channels to be discharged, the kind of movement from one to another channel and the type of fresh fuel to be charged for each single reloading event. After having determined the core states characterizing the equilibrium period, and having decided the fuel reloading scheme for the running-in period of the reactor life, the fuel
Dynamic calculation of structures in seismic zones. 2. ed.
International Nuclear Information System (INIS)
Capra, Alain; Davidovici, Victor
1982-01-01
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 [fr
Atomic Structure of Type VI Contractile Sheath from Pseudomonas aeruginosa.
Salih, Osman; He, Shaoda; Planamente, Sara; Stach, Lasse; MacDonald, James T; Manoli, Eleni; Scheres, Sjors H W; Filloux, Alain; Freemont, Paul S
2018-02-06
Pseudomonas aeruginosa has three type VI secretion systems (T6SSs), H1-, H2-, and H3-T6SS, each belonging to a distinct group. The two T6SS components, TssB/VipA and TssC/VipB, assemble to form tubules that conserve structural/functional homology with tail sheaths of contractile bacteriophages and pyocins. Here, we used cryoelectron microscopy to solve the structure of the H1-T6SS P. aeruginosa TssB1C1 sheath at 3.3 Å resolution. Our structure allowed us to resolve some features of the T6SS sheath that were not resolved in the Vibrio cholerae VipAB and Francisella tularensis IglAB structures. Comparison with sheath structures from other contractile machines, including T4 phage and R-type pyocins, provides a better understanding of how these systems have conserved similar functions/mechanisms despite evolution. We used the P. aeruginosa R2 pyocin as a structural template to build an atomic model of the TssB1C1 sheath in its extended conformation, allowing us to propose a coiled-spring-like mechanism for T6SS sheath contraction. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Mokhtari, A.; Akbarzadeh, H
2003-09-01
The electronic and structural properties of beryllium nitride (alpha and beta), magnesium- and calcium-nitrides were investigated using first principle full potential-linearized augmented plane wave method within density functional theory. We used Perdew and Wang-generalized gradient approximation, which is based on exchange correlation energy optimization, to calculate the total energy and the Engel-Vosko's GGA formalism, which optimize the corresponding potential, for band structure calculations. We also optimized internal parameters by relaxing the atomic positions in the force directions. Our results including lattice parameter, bulk modulus and it's pressure derivative, cohesive energy, band structure and density of states are compared with the experimental and other theoretical (Hartree-Fock approximation with a posteriori density functional correction) data.
International Nuclear Information System (INIS)
Mokhtari, A.; Akbarzadeh, H.
2003-01-01
The electronic and structural properties of beryllium nitride (alpha and beta), magnesium- and calcium-nitrides were investigated using first principle full potential-linearized augmented plane wave method within density functional theory. We used Perdew and Wang-generalized gradient approximation, which is based on exchange correlation energy optimization, to calculate the total energy and the Engel-Vosko's GGA formalism, which optimize the corresponding potential, for band structure calculations. We also optimized internal parameters by relaxing the atomic positions in the force directions. Our results including lattice parameter, bulk modulus and it's pressure derivative, cohesive energy, band structure and density of states are compared with the experimental and other theoretical (Hartree-Fock approximation with a posteriori density functional correction) data
Calculation of surface acoustic waves in a multilayered piezoelectric structure
International Nuclear Information System (INIS)
Zhang Zuwei; Wen Zhiyu; Hu Jing
2013-01-01
The propagation properties of the surface acoustic waves (SAWs) in a ZnO—SiO 2 —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—SiO 2 —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—SiO 2 —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. (semiconductor physics)
The electronic structure of Ga As1-xPx and Ga Sb1-xPx calculated using the recursion method
International Nuclear Information System (INIS)
El-Hasan, M.; Tomak, M.
1988-10-01
The electronic structure calculation of Ga As 1-x P x and Ga Sb 1-x P x alloys using the recursion method is reported. A five orbitals, sp 3 s*, per atom model is used in the tight-binding representation of the Hamiltonian. The local density of states are calculated for Ga, As, Sb and P-sites, in a cluster of 216 atoms, the results are reasonably in good agreement with previous calculations. (author). 12 refs, 8 figs, 1 tab
International Nuclear Information System (INIS)
Auffray, J.P.
1997-01-01
The atom through centuries, has been imagined, described, explored, then accelerated, combined...But what happens truly inside the atom? And what are mechanisms who allow its stability? Physicist and historian of sciences, Jean-Paul Auffray explains that these questions are to the heart of the modern physics and it brings them a new lighting. (N.C.)
First principles calculations of structural, electronic and thermal ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 37; Issue 5. First principles calculations of structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and PbTe compounds. N Boukhris H Meradji S Amara Korba S Drablia S Ghemid F El Haj Hassan. Volume 37 Issue 5 August 2014 pp 1159-1166 ...
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ... functional theory (DFT) combined with the quasi-harmonic .... is consistent with Vegard's law which assumes that the lat- tice constant varies .... reflects a charge-transfer effect which is due to the different.
Inverse boundary element calculations based on structural modes
DEFF Research Database (Denmark)
Juhl, Peter Møller
2007-01-01
The inverse problem of calculating the flexural velocity of a radiating structure of a general shape from measurements in the field is often solved by combining a Boundary Element Method with the Singular Value Decomposition and a regularization technique. In their standard form these methods sol...
Calculation of forces arising from impacting projectiles upon yielding structures
International Nuclear Information System (INIS)
Drittler, K.; Gruner, P.; Krivy, J.
1977-01-01
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.)
Design guide for calculating fluid damping for circular cylindrical structures
International Nuclear Information System (INIS)
Chen, S.S.
1983-06-01
Fluid damping plays an important role for structures submerged in fluid, subjected to flow, or conveying fluid. This design guide presents a summary of calculational procedures and design data for fluid damping for circular cylinders vibrating in quiescent fluid, crossflow, and parallel flow
A sub-structure method for multidimensional integral transport calculations
International Nuclear Information System (INIS)
Kavenoky, A.; Stankovski, Z.
1983-03-01
A new method has been developed for fine structure burn-up calculations of very heterogeneous large size media. It is a generalization of the well-known surface-source method, allowing coupling actual two-dimensional heterogeneous assemblies, called sub-structures. The method has been applied to a rectangular medium, divided into sub-structures, containing rectangular and/or cylindrical fuel, moderator and structure elements. The sub-structures are divided into homogeneous zones. A zone-wise flux expansion is used to formulate a direct collision probability problem within it (linear or flat flux expansion in the rectangular zones, flat flux in the others). The coupling of the sub-structures is performed by making extra assumptions on the currents entering and leaving the interfaces. The accuracies and computing times achieved are illustrated by numerical results on two benchmark problems
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.
Calculation of forces arising from impacting projectiles upon yielding structures
International Nuclear Information System (INIS)
Drittler, K.; Gruner, P.; Krivy, J.
1977-01-01
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
Calculation of the electric potential around two identical atoms or ions
International Nuclear Information System (INIS)
Salzmann, D.
1994-01-01
Problems of diatomic molecules and atom-atom collisions, in which two identical atoms take part, or nearest-neighbor interactions in hot plasmas require the computations of the electric potential and the electron charge distribution around such a two-centered object. The electric potential around two such identical atoms or ions fulfills special symmetry conditions. These symmetries include a cylindrical symmetry around the line connecting the centers of the two atoms and a reflection symmetry around the plane perpendicular to this line halfway between the two atoms. When the two atoms are far apart, the asymptotic behavior of the charge-state distribution and the potential are those of two separated isolated atoms each of which can be expanded into multipole components around its nucleus. We define a set of new functions T mk (y,y n ) Eq. (2.25), which connect the various multipole components of the electric potential to those of the electron charge distribution in such a two-identical-atom problem, and which take into account all the above symmetry conditions. The great advantage of these transformation functions is the fact that by accounting for the above symmetry conditions, the three-dimensional integration required for the computation of the local electric microfield directly from the Poisson equation is practically reduced to a one-dimensional one. It is shown that the use of these functions greatly reduces the complexity and computation times of problems in which two identical atoms are involved, particularly for high-Z atoms. Explicit exact formulas are given for the computation of the T mk functions. An example is given which illustrates the use of these functions in first-order perturbation theory. For this special class of problems the procedure presented here results in a closed recursive equation, in which the interatomic distance is the only free parameter
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
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…
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.
Ab initio MCHF structural calculations of Mg-like cerium
Wajid, Abdul; Jabeen, S.; Husain, Abid
2018-05-01
Energy levels and emission line wavelengths of high-Z materials are useful for impurity diagnostics in the next generation fusion devices. For this here we have calculated E1, M2 transitions, oscillator strengths, and transition probabilities for transitions among the terms belonging to the 2p63s2, 2p63s3p, 2p63p2 and 2p63s3d for the Magnesium like cerium (Ce XLVII) using the GRASP2K package based on the fully relativistic multi-configuration Dirac-Fock method. The electron correlation effects, Breit interaction and quantum electrodynamics effects to the atomic state wave functions and the corresponding energies have been taken into account.
Energy Technology Data Exchange (ETDEWEB)
Feller, D.F.
1979-01-01
The behavior of the two exponential parameters in an even-tempered gaussian basis set is investigated as the set optimally approaches an integral transform representation of the radial portion of atomic and molecular orbitals. This approach permits a highly accurate assessment of the Hartree-Fock limit for atoms and molecules.
Evaluation of calculational and material models for concrete containment structures
International Nuclear Information System (INIS)
Dunham, R.S.; Rashid, Y.R.; Yuan, K.A.
1984-01-01
A computer code utilizing an appropriate finite element, material and constitutive model has been under development as a part of a comprehensive effort by the Electric Power Research Institute (EPRI) to develop and validate a realistic methodology for the ultimate load analysis of concrete containment structures. A preliminary evaluation of the reinforced and prestressed concrete modeling capabilities recently implemented in the ABAQUS-EPGEN code has been completed. This effort focuses on using a state-of-the-art calculational model to predict the behavior of large-scale reinforced concrete slabs tested under uniaxial and biaxial tension to simulate the wall of a typical concrete containment structure under internal pressure. This paper gives comparisons between calculations and experimental measurements for a uniaxially-loaded specimen. The calculated strains compare well with the measured strains in the reinforcing steel; however, the calculations gave diffused cracking patterns that do not agree with the discrete cracking observed in the experiments. Recommendations for improvement of the calculational models are given. (orig.)
Wavelets in self-consistent electronic structure calculations
International Nuclear Information System (INIS)
Wei, S.; Chou, M.Y.
1996-01-01
We report the first implementation of orthonormal wavelet bases in self-consistent electronic structure calculations within the local-density approximation. These local bases of different scales efficiently describe localized orbitals of interest. As an example, we studied two molecules, H 2 and O 2 , using pseudopotentials and supercells. Considerably fewer bases are needed compared with conventional plane-wave approaches, yet calculated binding properties are similar. Our implementation employs fast wavelet and Fourier transforms, avoiding evaluating any three-dimensional integral numerically. copyright 1996 The American Physical Society
Microscopic calculations of nuclear structure and nuclear correlations
International Nuclear Information System (INIS)
Wiringa, R.B.
1992-01-01
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
Atomic and electronic structures of an extremely fragile liquid.
Kohara, Shinji; Akola, Jaakko; Patrikeev, Leonid; Ropo, Matti; Ohara, Koji; Itou, Masayoshi; Fujiwara, Akihiko; Yahiro, Jumpei; Okada, Junpei T; Ishikawa, Takehiko; Mizuno, Akitoshi; Masuno, Atsunobu; Watanabe, Yasuhiro; Usuki, Takeshi
2014-12-18
The structure of high-temperature liquids is an important topic for understanding the fragility of liquids. Here we report the structure of a high-temperature non-glass-forming oxide liquid, ZrO2, at an atomistic and electronic level. The Bhatia-Thornton number-number structure factor of ZrO2 does not show a first sharp diffraction peak. The atomic structure comprises ZrO5, ZrO6 and ZrO7 polyhedra with a significant contribution of edge sharing of oxygen in addition to corner sharing. The variety of large oxygen coordination and polyhedral connections with short Zr-O bond lifetimes, induced by the relatively large ionic radius of zirconium, disturbs the evolution of intermediate-range ordering, which leads to a reduced electronic band gap and increased delocalization in the ionic Zr-O bonding. The details of the chemical bonding explain the extremely low viscosity of the liquid and the absence of a first sharp diffraction peak, and indicate that liquid ZrO2 is an extremely fragile liquid.
DFT study of the structures and energetics of 98-atom AuPd clusters.
Bruma, Alina; Ismail, Ramli; Paz-Borbón, L Oliver; Arslan, Haydar; Barcaro, Giovanni; Fortunelli, Alessandro; Li, Z Y; Johnston, Roy L
2013-01-21
The energetics, structures and segregation of 98-atom AuPd nanoclusters are investigated using a genetic algorithm global optimization technique with the Gupta empirical potential (comparing three different potential parameterisations) followed by local minimizations using Density Functional Theory (DFT) calculations. A shell optimization program algorithm is employed in order to study the energetics of the highly symmetric Leary Tetrahedron (LT) structure and optimization of the chemical ordering of a number of structural motifs is carried out using the Basin Hopping Monte Carlo approach. Although one of the empirical potentials is found to favour the LT structure, it is shown that Marks Decahedral and mixed FCC-HCP motifs are lowest in energy at the DFT level.
Michael Faraday and the concept of atomic structure
International Nuclear Information System (INIS)
Pocock, R.F.
1991-01-01
Written to commemorate the bicentenary of Faraday's birth, this article surveys his influence on atomic theory during the 19th and early 20th centuries. It identifies which developments were derived from projects which he had started; it shows that his ideas and methods determined the direction of researches which he had not himself initiated. The account is in the form of a chronological narrative. This is based entirely on published sources, and the treatment is non-mathematical. In consequence it contains no new factual data. The presentation of Faraday's work in this particular context is, however, original. Although not covering studies of the nucleus - which were mostly later than the period considered -this article describes the origins of modern theories of atomic structure reasonably completely. It is a useful overview for engineers unfamiliar with details of the history of physics. In addition, it is a case-study of the persistence of scientific ideas in researches occupying a century or more. (author)
Tailoring atomic structure to control the electronic transport in zigzag graphene nanoribbon
International Nuclear Information System (INIS)
Zeng, Hui; Zhao, Jun; Wei, Jianwei; Zeng, Xianliang; Xu, Yang
2012-01-01
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.
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.
Electronic and atomic structure of the AlnHn+2 clusters
DEFF Research Database (Denmark)
Martinez, Jose Ignacio; Alonso, J.A.
2008-01-01
The electronic and atomic structure of the family of hydrogenated Al clusters AlnHn+2 with n=4-11 has been studied using the density functional theory with the generalized gradient approximation (GGA) for exchange and correlation. All these clusters have substantial gaps between the highest...... a polyhedron of n vertices and n H atoms form strong H-Al terminal bonds; one pair of electrons is involved in each of those bonds. The remaining n+1 electron pairs form a delocalized cloud over the surface of the Al cage. The clusters fulfilling the Wade-Mingos rule have wider HOMO-LUMO gaps...... and are chemically more stable. The trends in the gap have some reflections in the form of the photoabsorption spectra, calculated in the framework of time-dependent density functional theory using the GGA single-particle energies and orbitals and a local density approximation exchange-correlation kernel....
DEFF Research Database (Denmark)
Pawlowski, F; Jorgensen, P; Olsen, Jeppe
2002-01-01
A detailed study is carried out of the accuracy of molecular equilibrium geometries obtained from least-squares fits involving experimental rotational constants B(0) and sums of ab initio vibration-rotation interaction constants alpha(r)(B). The vibration-rotation interaction constants have been...... calculated for 18 single-configuration dominated molecules containing hydrogen and first-row atoms at various standard levels of ab initio theory. Comparisons with the experimental data and tests for the internal consistency of the calculations show that the equilibrium structures generated using Hartree......-Fock vibration-rotation interaction constants have an accuracy similar to that obtained by a direct minimization of the CCSD(T) energy. The most accurate vibration-rotation interaction constants are those calculated at the CCSD(T)/cc-pVQZ level. The equilibrium bond distances determined from these interaction...
Mechanical deformation of atomic-scale metallic contacts: Structure and mechanisms
DEFF Research Database (Denmark)
Sørensen, Mads Reinholdt; Brandbyge, Mads; Jacobsen, Karsten Wedel
1998-01-01
We have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain using molecular dynamics and effective medium theory potentials. The evolution of the structure of the contacts and the underlying deformation mechanisms are described along with the calculated......, but vacancies can be permanently present. The transition states and energies for slip mechanisms have been determined using the nudged elastic band method, and we find a size-dependent crossover from a dislocation-mediated slip to a homogeneous slip when the contact diameter becomes less than a few nm. We show...
Experimental determination of the relativistic fine-structure splitting in pionic Ti and Fe atoms
International Nuclear Information System (INIS)
Wang, K.; Boehm, F.; Bovet, E.; Hahn, A.A.; Henrikson, H.E.; Miller, J.P.; Powers, R.J.; Vogel, P.; Vuilleumier, J.; Kunselman, A.R.
1980-01-01
Using a high-resolution crystal spectrometer we have measured the relativistic angular-momentum splittings of the 5g-4f and 5f-4d transitions in pionic Ti and Fe atoms. The observed fine-structure splittings of 85.3 +- 3.0 eV in π - Ti and 158.5 +- 7.8 eV in π - Fe agree with the calculated splittings of 88.5 and 167.6 eV, respectively, arising from the Klein-Gordon equation and from small corrections due to vacuum polarization, strong interaction, and electron screening
On-the-Fly Machine Learning of Atomic Potential in Density Functional Theory Structure Optimization
Jacobsen, T. L.; Jørgensen, M. S.; Hammer, B.
2018-01-01
Machine learning (ML) is used to derive local stability information for density functional theory calculations of systems in relation to the recently discovered SnO2 (110 )-(4 ×1 ) reconstruction. The ML model is trained on (structure, total energy) relations collected during global minimum energy search runs with an evolutionary algorithm (EA). While being built, the ML model is used to guide the EA, thereby speeding up the overall rate by which the EA succeeds. Inspection of the local atomic potentials emerging from the model further shows chemically intuitive patterns.
Tuning the electronic structure of graphene through alkali metal and halogen atom intercalation
Ahmad, Sohail; Miró, Pere; Audiffred, Martha; Heine, Thomas
2018-04-01
The deposition, intercalation and co-intercalation of heavy alkali metals and light halogens atoms in graphene mono- and bilayers have been studied using first principles density-functional calculations. Both the deposition and the intercalation of alkali metals gives rise to n-type doping due to the formation of M+-C- pairs. The co-intercalation of a 1:1 ratio of alkali metals and halogens derives into the formation of ionic pairs among the intercalated species, unaltering the electronic structure of the layered material.
International Nuclear Information System (INIS)
Cohen, J.S.; Struensee, M.C.
1991-01-01
The improved adiabatic representation is used in calculations of elastic and isotopic-exchange cross sections for asymmetric collisions of pμ, dμ, and tμ with bare p, d, and t nuclei and with H, D, and T atoms. This formulation dissociates properly, correcting a well-known deficiency of the standard adiabatic method for muonic-atom collisions, and includes some effects at zeroth order that are normally considered nonadiabatic. The electronic screening is calculated directly and precisely within the improved adiabatic description; it is found to be about 30% smaller in magnitude than the previously used value at large internuclear distances and to deviate considerably from the asymptotic form at small distances. The reactance matrices, needed for calculations of molecular-target effects, are given in tables
Calculation of the mean-square velocities of atom oscillations in the Moessbauer experiment
International Nuclear Information System (INIS)
Semenov, Ya.S.; Lebedev, M.P.
2005-01-01
To study mechanical and physical properties of solid bodies, it is important to know the behavior of rms velocities of atomic oscillations. Binary iron alloys in the vicinity of phase transition temperatures were investigated using the Moessbauer spectroscopy. The rms velocities of atomic oscillations demonstrate that 3d-3p direct chemical bonds for Si and 3d-4p direct chemical bonds for Ge are broken (formed) at the phase transition temperature; as a consequence, the velocities of atomic oscillations increase abruptly [ru
International Nuclear Information System (INIS)
Kaliambos, L.A.
2008-01-01
Fundamental interactions of spinning electrons at an interelectron separation less than 578.8 fm yield attractive electromagnetic forces with S = 0 creating vibrations under a motional emf. They explain the indistinguishability of electrons and give a vibration energy able for calculating the ground-state energies of many-electron atoms without using any perturbative approximation. Such forces create two-electron orbitals able to account for the exclusion principal and the mechanism of covalent bonds. In the outer subshells of atoms the penetrating orbitals interact also as pair-pair systems and deform drastically the probability densities of the quantum mechanical electron clouds. Such a dynamics of deformation removes the degeneracy and leads to the deviation from the shell scheme. However in the interior of atoms the large nuclear charge leads to a spherically symmetric potential with non-interacting pairs for creating shells of degenerate states giving an accurate explanation of the X-ray lines. On the other hand, considerable charge distributions in nucleons as multiples of 2e/3 and - e/3 determined by the magnetic moments, interact for creating the nuclear structure with p-n bonds. Such spin-spin interactions show that the dominant concept of the untisymmetric wave function for fermions is inapplicable not only in the simple p-n, p-p, and n-n systems but also in the LS coupling of atoms in which the electrons interact from different quantum states giving either S = 0 or S = l. (author)
A massively-parallel electronic-structure calculations based on real-space density functional theory
International Nuclear Information System (INIS)
Iwata, Jun-Ichi; Takahashi, Daisuke; Oshiyama, Atsushi; Boku, Taisuke; Shiraishi, Kenji; Okada, Susumu; Yabana, Kazuhiro
2010-01-01
Based on the real-space finite-difference method, we have developed a first-principles density functional program that efficiently performs large-scale calculations on massively-parallel computers. In addition to efficient parallel implementation, we also implemented several computational improvements, substantially reducing the computational costs of O(N 3 ) operations such as the Gram-Schmidt procedure and subspace diagonalization. Using the program on a massively-parallel computer cluster with a theoretical peak performance of several TFLOPS, we perform electronic-structure calculations for a system consisting of over 10,000 Si atoms, and obtain a self-consistent electronic-structure in a few hundred hours. We analyze in detail the costs of the program in terms of computation and of inter-node communications to clarify the efficiency, the applicability, and the possibility for further improvements.
On the nodal structure of atomic and molecular Wigner functions
International Nuclear Information System (INIS)
Dahl, J.P.; Schmider, H.
1996-01-01
In previous work on the phase-space representation of quantum mechanics, we have presented detailed pictures of the electronic one-particle reduced Wigner function for atoms and small molecules. In this communication, we focus upon the nodal structure of the function. On the basis of the simplest systems, we present an expression which relates the oscillatory decay of the Wigner function solely to the dot product of the position and momentum vector, if both arguments are large. We then demonstrate the regular behavior of nodal patterns for the larger systems. For the molecular systems, an argument analogous to the open-quotes bond-oscillatory principleclose quotes for momentum densities links the nuclear framework to an additional oscillatory term in momenta parallel to bonds. It is shown that these are visible in the Wigner function in terms of characteristic nodes
International Nuclear Information System (INIS)
Hay, P.J.; Wadt, W.R.
1985-01-01
Ab initio effective core potentials (ECP's) have been generated to replace the Coulomb, exchange, and core-orthogonality effects of the chemically inert core electron in the transition metal atoms Sc to Hg. For the second and third transition series relative ECP's have been generated which also incorporate the mass--velocity and Darwin relativistic effects into the potential. The ab initio ECP's should facilitate valence electron calculations on molecules containing transition-metal atoms with accuracies approaching all-electron calculations at a fraction of the computational cost. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3d,4s,4p), (4d,5s,5p), and (5d,6s,6p) orbitals of the first, second, and third transition series atoms, respectively. All-electron and valence-electron atomic excitation energies are also compared for the low-lying states of Sc--Hg, and the valence-electron calculations are found to reproduce the all-electron excitation energies (typically within a few tenths of an eV)
Development and application of advanced methods for electronic structure calculations
DEFF Research Database (Denmark)
Schmidt, Per Simmendefeldt
. For this reason, part of this thesis relates to developing and applying a new method for constructing so-called norm-conserving PAW setups, that are applicable to GW calculations by using a genetic algorithm. The effect of applying the new setups significantly affects the absolute band positions, both for bulk......This thesis relates to improvements and applications of beyond-DFT methods for electronic structure calculations that are applied in computational material science. The improvements are of both technical and principal character. The well-known GW approximation is optimized for accurate calculations...... of electronic excitations in two-dimensional materials by exploiting exact limits of the screened Coulomb potential. This approach reduces the computational time by an order of magnitude, enabling large scale applications. The GW method is further improved by including so-called vertex corrections. This turns...
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.
Numerical comparison of atomic binding energies calculated by Thomas-Fermi like formulas
International Nuclear Information System (INIS)
Donnamaria, M.C.; Castro, E.A.; Fernandez, F.M.
1985-01-01
We apply in an exhaustive way formulas of Thomas-Fermi nature to determine atomic ground state energies. Results are compared with Hartree-Fock SCF data and the different methods are analysed in a comparative fashion. (authors)
International Nuclear Information System (INIS)
Vargin, A.N.; Ganina, N.A.; Konyukhov, V.K.; Selyakov, V.I.
1975-01-01
The problem of calculation of collisional probabilities of rotational transitions (CPRT) in molecule-molecule and molecule-atom interactions in a three-dimensional space has been solved in this paper. A quasiclassical approach was used. The calculation of collisional probabilities of rotational transitions trajectory was carried out in the following way. The particle motion trajectory was calculated by a classical method and the time dependence of the perturbation operator was obtained, its averaging over wave functions of initial and finite states produced CPRT. The classical calculation of the molecule motion trajectory was justified by triviality of the de Broglie wavelength, compared with characteristic atomic distances, and by triviality of a transfered rotational quantum compared with the energy of translational motion of particles. The results of calculation depend on the chosen interaction potential of collisional particles. It follows from the Messy criterion that the region of nonadiabaticity of interaction may be compared with internuclear distances of a molecule. Therefore, for the description of the interaction a short-range potential is required. Analytical expressions were obtained appropriate for practical calculations for one- and two-quantum rotational transitions of diatomic molecules. The CPRT was averaged over the Maxwell distribution over velocities and analytical dependences on a gas temperature were obtained. The results of the numerical calculation of probabilities for the HCl-HCl, HCl-He, CO-CO interactions are presented to illustrate the method
International Nuclear Information System (INIS)
Parkhomenko, A.I.; yachev, S.P."" >Podyachev, S.P.; Privalov, T.I.; Shalagin, A.M.
1997-01-01
Absorption line of monochromatic radiation by atoms nonselective excitation by velocities under conditions of optical excitation of components of superfine structure of the basic electron state is considered. It is shown that the absorption line has unusual substructures for certain values of the basic state superfine desintegration. These substructures in the absorption spectrum may be pointed out by accounting the superfine structure of the electron excited state. The absorption spectra of monochromatic radiation close tot he D 1 - and D 2 -lines of the atomic rubidium are calculated
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.
Calculation of hyperfine structure constants of small molecules using
Indian Academy of Sciences (India)
The Z-vector method in the relativistic coupled-cluster framework is employed to calculate the parallel and perpendicular components of the magnetic hyperfine structure constant of a few small alkaline earth hydrides (BeH, MgH, and CaH) and fluorides (MgF and CaF). We have compared our Z-vector results with the values ...
Thick-Restart Lanczos Method for Electronic Structure Calculations
International Nuclear Information System (INIS)
Simon, Horst D.; Wang, L.-W.; Wu, Kesheng
1999-01-01
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
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
Lu, Shih-I.
2018-01-01
We use the discrete solvent reaction field model to evaluate the linear and second-order nonlinear optical susceptibilities of 3-methyl-4-nitropyridine-1-oxyde crystal. In this approach, crystal environment is created by supercell architecture. A self-consistent procedure is used to obtain charges and polarizabilities for environmental atoms. Impact of atomic polarizabilities on the properties of interest is highlighted. This approach is shown to give the second-order nonlinear optical susceptibilities within error bar of experiment as well as the linear optical susceptibilities in the same order as experiment. Similar quality of calculations are also applied to both 4-N,N-dimethylamino-3-acetamidonitrobenzene and 2-methyl-4-nitroaniline crystals.
Dopant distributions in n-MOSFET structure observed by atom probe tomography
International Nuclear Information System (INIS)
Inoue, K.; Yano, F.; Nishida, A.; Takamizawa, H.; Tsunomura, T.; Nagai, Y.; Hasegawa, M.
2009-01-01
The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted.
Dopant distributions in n-MOSFET structure observed by atom probe tomography.
Inoue, K; Yano, F; Nishida, A; Takamizawa, H; Tsunomura, T; Nagai, Y; Hasegawa, M
2009-11-01
The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted.
Structure and transport at grain boundaries in polycrystalline olivine: An atomic-scale perspective
Mantisi, Boris; Sator, Nicolas; Guillot, Bertrand
2017-12-01
Structure and transport properties at grain boundaries in polycrystalline olivine have been investigated at the atomic scale by molecular dynamics simulation (MD) using an empirical ionocovalent interaction potential. On the time scale of the simulation (a few tens of nanoseconds for a system size of ∼650,000 atoms) grain boundaries and grain interior were identified by mapping the atomic displacements along the simulation run. In the investigated temperature range (1300-1700 K) the mean thickness of the grain boundary phase is evaluated between 0.5 and 2 nm, a value which depends on temperature and grain size. The structure of the grain boundary phase is found to be disordered (amorphous-like) and is different from the one exhibited by the supercooled liquid. The self-diffusion coefficients of major elements in the intergranular region range from ∼10-13 to 10-10 m2/s between 1300 and 1700 K (with DSigb Kubo relation expressing the viscosity as function of the stress tensor time correlation function. In spite of a slow convergence of the calculation by MD, the grain boundary viscosity was estimated about ∼105 Pa s at 1500 K, a value in agreement with high-temperature viscoelastic relaxation data. An interesting information gained from MD is that sliding at grain boundaries is essentially controlled by the internal friction between the intergranular phase and the grain edges.
Relaxation and final-state structure in XPS of atoms, molecules, and metals
International Nuclear Information System (INIS)
Shirley, D.A.; Martin, R.L.; McFeely, F.R.; Kowalczyk, S.P.; Ley, L.
1975-03-01
Photoemission from a many-electron system is a many-electron process, even though the transition operator may affect only one electron directly. Relaxation and ''shake-up'' structure are related by a sum rule. When one is present, the other must be also. Shake-up structure is shown to be accurately predictable in atomic neon and molecular HF if the CI calculations are done carefully. In metals the sum rule also applies but final-state effects usually appear as relaxation energy, which is large even for valence electrons. Finally, in rare-earth metals discrete shake-up structure is observable in the 4p region. (7 figs, 30 refs) (auth)
Korecki, P.; Tolkiehn, M.; Dąbrowski, K. M.; Novikov, D. V.
2011-01-01
Projections of the atomic structure around Nb atoms in a LiNbO3 single crystal were obtained from a white-beam X-ray absorption anisotropy (XAA) pattern detected using Nb K fluorescence. This kind of anisotropy results from the interference of X-rays inside a sample and, owing to the short coherence length of a white beam, is visible only at small angles around interatomic directions. Consequently, the main features of the recorded XAA corresponded to distorted real-space projections of dense-packed atomic planes and atomic rows. A quantitative analysis of XAA was carried out using a wavelet transform and allowed well resolved projections of Nb atoms to be obtained up to distances of 10 Å. The signal of nearest O atoms was detected indirectly by a comparison with model calculations. The measurement of white-beam XAA using characteristic radiation indicates the possibility of obtaining element-sensitive projections of the local atomic structure in more complex samples. PMID:21997909
Iron phosphate glasses: Bulk properties and atomic scale structure
Energy Technology Data Exchange (ETDEWEB)
Joseph, Kitheri; Stennett, Martin C.; Hyatt, Neil C.; Asuvathraman, R.; Dube, Charu L.; Gandy, Amy S.; Govindan Kutty, K. V.; Jolley, Kenny; Vasudeva Rao, P. R.; Smith, Roger
2017-10-01
Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137Cs to 137Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10-6 K-1 to 13.4 × 10-6 K-1, when 25 wt. % of Cs2O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The FeII content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The FeII content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data.
Atomic transition energies and the variation of the fine-structure constant α
International Nuclear Information System (INIS)
Borschevsky, Anastasia; Eliav, Ephraim; Ishikawa, Yasuyuki; Kaldor, Uzi
2006-01-01
Relativistic energy shifts of atomic excitation energies, showing the dependence of these energies on the value of the fine-structure constant α, are needed to extract past changes in α from spectra of distant quasars. These shifts are calculated by the Fock-space coupled cluster method and its extrapolated intermediate Hamiltonian extension, which allow high-accuracy treatment of electron correlation. The accuracy of the method is tested by comparing 33 transition energies in heavy atoms (obtained with the laboratory α) with experiment; the average error is 258 cm -1 , and the largest error is 711 cm -1 . This may be compared with an average error of 432 cm -1 and a maximum error of 2150 cm -1 in the work of Dzuba et al., who reported most of the available energy shift calculations. The enhanced accuracy is due to more extensive inclusion of electron correlation. To obtain the energy shifts, we repeated the calculations with different values of α (within 0.1% of the current value). Our shifts differ by up to 30% from the values given by Dzuba et al., with an average difference of 9%. Based on the better quality of the present-day excitation energies, we believe the energy shifts reported here are more accurate than earlier work
The trapping of K and Na atoms by a clean W(110) surface. Dynamic trajectory calculations. ch.3
International Nuclear Information System (INIS)
Hurkmans, A.; Overbosch, E.G.; Los, J.
1976-01-01
The fraction of K and Na atoms which are initially trapped by a clean W(110) surface has been measured as a function of incident energy (0.5 < approximately Esub(i) < approximately 15 eV) at several angles of incidence. At the same time the desorption energies Qsub(i) of the trapped potassium and sodium atoms were measured: Qsub(i) = 2.05 +- 0.02 eV and Qsub(i) = 2.60 +- 0.04 eV respectively. The measured trapping probabilities can be described well by Trillings 'partially screened spherical cap' model, except fos the small angles of incidence. Dynamic trajectory calculations were performed for a particle scattered from a diatomic molecule to explain the screening and the descrepancy at normal incidence. The calculations give good quantitative agreement with the measured trapping probability at small angles both for potassium and sodium atoms and show that simultaneous interaction with two adjacent surface atoms affects the trapping particularly at small angles of incidence. (Auth.)
Finite-temperature stress calculations in atomic models using moments of position
Parthasarathy, Ranganathan; Misra, Anil; Ouyang, Lizhi
2018-07-01
Continuum modeling of finite temperature mechanical behavior of atomic systems requires refined description of atomic motions. In this paper, we identify additional kinematical quantities that are relevant for a more accurate continuum description as the system is subjected to step-wise loading. The presented formalism avoids the necessity for atomic trajectory mapping with deformation, provides the definitions of the kinematic variables and their conjugates in real space, and simplifies local work conjugacy. The total work done on an atom under deformation is decomposed into the work corresponding to changing its equilibrium position and work corresponding to changing its second moment about equilibrium position. Correspondingly, we define two kinematic variables: a deformation gradient tensor and a vibration tensor, and derive their stress conjugates, termed here as static and vibration stresses, respectively. The proposed approach is validated using MD simulation in NVT ensembles for fcc aluminum subjected to uniaxial extension. The observed evolution of second moments in the MD simulation with macroscopic deformation is not directly related to the transformation of atomic trajectories through the deformation gradient using generator functions. However, it is noteworthy that deformation leads to a change in the second moment of the trajectories. Correspondingly, the vibration part of the Piola stress becomes particularly significant at high temperature and high tensile strain as the crystal approaches the softening limit. In contrast to the eigenvectors of the deformation gradient, the eigenvectors of the vibration tensor show strong spatial heterogeneity in the vicinity of softening. More importantly, the elliptic distribution of local atomic density transitions to a dumbbell shape, before significant non-affinity in equilibrium positions has occurred.
Photonic band structure calculations using nonlinear eigenvalue techniques
International Nuclear Information System (INIS)
Spence, Alastair; Poulton, Chris
2005-01-01
This paper considers the numerical computation of the photonic band structure of periodic materials such as photonic crystals. This calculation involves the solution of a Hermitian nonlinear eigenvalue problem. Numerical methods for nonlinear eigenvalue problems are usually based on Newton's method or are extensions of techniques for the standard eigenvalue problem. We present a new variation on existing methods which has its derivation in methods for bifurcation problems, where bordered matrices are used to compute critical points in singular systems. This new approach has several advantages over the current methods. First, in our numerical calculations the new variation is more robust than existing techniques, having a larger domain of convergence. Second, the linear systems remain Hermitian and are nonsingular as the method converges. Third, the approach provides an elegant and efficient way of both thinking about the problem and organising the computer solution so that only one linear system needs to be factorised at each stage in the solution process. Finally, first- and higher-order derivatives are calculated as a natural extension of the basic method, and this has advantages in the electromagnetic problem discussed here, where the band structure is plotted as a set of paths in the (ω,k) plane
International Nuclear Information System (INIS)
Ghanbari Adivi, E.; Kanjuri, F.; Bolorizadeh, M.
2006-01-01
The positronium formation differential cross sections in collision of the high-energy but non-relativistic electrons with anti-hydrogen atoms are calculated by using the three-body Faddeev-Watson-Lovelace formalism. In a second-order approximation, the inter-nuclear and nuclear-electronic partial amplitudes therein the Faddeev-Watson series are calculated, analytically, in the range of 0-180 degrees of the scattering angles. The presence of the T homas peak a t 45 d egree i s investigated. The results are discussed for 1 and 10 keV impact energies and for electron transition from anti-hydrogen ground state into the different states therein the K-, L- and M- shells of the positronium atoms.
Chodkiewicz, Michał L; Migacz, Szymon; Rudnicki, Witold; Makal, Anna; Kalinowski, Jarosław A; Moriarty, Nigel W; Grosse-Kunstleve, Ralf W; Afonine, Pavel V; Adams, Paul D; Dominiak, Paulina Maria
2018-02-01
It has been recently established that the accuracy of structural parameters from X-ray refinement of crystal structures can be improved by using a bank of aspherical pseudoatoms instead of the classical spherical model of atomic form factors. This comes, however, at the cost of increased complexity of the underlying calculations. In order to facilitate the adoption of this more advanced electron density model by the broader community of crystallographers, a new software implementation called DiSCaMB , 'densities in structural chemistry and molecular biology', has been developed. It addresses the challenge of providing for high performance on modern computing architectures. With parallelization options for both multi-core processors and graphics processing units (using CUDA), the library features calculation of X-ray scattering factors and their derivatives with respect to structural parameters, gives access to intermediate steps of the scattering factor calculations (thus allowing for experimentation with modifications of the underlying electron density model), and provides tools for basic structural crystallographic operations. Permissively (MIT) licensed, DiSCaMB is an open-source C++ library that can be embedded in both academic and commercial tools for X-ray structure refinement.
Adsorption of SO{sub 2} on Li atoms deposited on MgO (1 0 0) surface: DFT calculations
Energy Technology Data Exchange (ETDEWEB)
Eid, Kh.M., E-mail: Kheid98@hotmail.com [Physics Department, Faculty of Education, Ain Shams University, Cairo 11757 (Egypt); Ammar, H.Y. [Department of Physics, Faculty of Science, Najran University, Najran 1988 (Saudi Arabia)
2011-05-01
The adsorption of sulfur dioxide molecule (SO{sub 2}) on Li atom deposited on the surfaces of metal oxide MgO (1 0 0) on both anionic and defect (F{sub s}-center) sites located on various geometrical defects (terrace, edge and corner) has been studied using density functional theory (DFT) in combination with embedded cluster model. The adsorption energy (E{sub ads}) of SO{sub 2} molecule (S-atom down as well as O-atom down) in different positions on both of O{sup -2} and F{sub s} sites is considered. The spin density (SD) distribution due to the presence of Li atom is discussed. The geometrical optimizations have been done for the additive materials and MgO substrate surfaces (terrace, edge and corner). The oxygen vacancy formation energies have been evaluated for MgO substrate surfaces. The ionization potential (IP) for defect free and defect containing of the MgO surfaces has been calculated. The adsorption properties of SO{sub 2} are analyzed in terms of the E{sub ads}, the electron donation (basicity), the elongation of S-O bond length and the atomic charges on adsorbed materials. The presence of the Li atom increases the catalytic effect of the anionic O{sup -2} site of MgO substrate surfaces (converted from physisorption to chemisorption). On the other hand, the presence of the Li atom decreases the catalytic effect of the F{sub s}-site of MgO substrate surfaces. Generally, the SO{sub 2} molecule is strongly adsorbed (chemisorption) on the MgO substrate surfaces containing F{sub s}-center.
Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces
McBriarty, Martin E.
Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.
Fartab, Dorsa S.; Kordbacheh, Amirhossein Ahmadkhan
2018-06-01
The first-principles calculations based on spin-polarized density functional theory is carried out to investigate the structural, electronic and magnetic properties of a hexagonal boron nitride sheet (h-BNS) doped by one or two lithium atom(s). Moreover, a vacancy in the neighborhood of one Li-substituted atom is introduced into the system. All optimized structures indicate significant local deformations with Li atom(s) protruded to the exterior of the sheet. The defects considered at N site are energetically more favorable than their counterpart structures at B site. The spin-polarized impurity states appear within the bandgap region of the pristine h-BNS, which lead to a spontaneous magnetization with the largest magnetic moments of about 2 μB in where a single or two B atom(s) are replaced by Li atom(s). Furthermore, the Li substitution for a single B atom increases the density of holes compared to that of electrons forming a p-type semiconductor. More interestingly, the structure in which two Li are substituted two neighboring B atoms appears to show desired half-metallic behavior that may be applicable in spintronic. The results provide a way to enhance the conductivity and magnetism of the pristine h-BNS for potential applications in BN-based nanoscale devices.
Atomic Resolution Imaging of Nanoscale Structural Ordering in a Complex Metal Oxide Catalyst
Zhu, Yihan; Wang, Qingxiao; Zhao, Lan; Teng, Baiyang; Lu, Weimin; Han, Yu
2012-01-01
The determination of the atomic structure of a functional material is crucial to understanding its "structure-to-property" relationship (e.g., the active sites in a catalyst), which is however challenging if the structure possesses complex
Seibert, Jakob; Bannwarth, Christoph; Grimme, Stefan
2017-08-30
A fully quantum mechanical (QM) treatment to calculate electronic absorption (UV-vis) and circular dichroism (CD) spectra of typical biomolecules with thousands of atoms is presented. With our highly efficient sTDA-xTB method, spectra averaged along structures from molecular dynamics (MD) simulations can be computed in a reasonable time frame on standard desktop computers. This way, nonequilibrium structure and conformational, as well as purely quantum mechanical effects like charge-transfer or exciton-coupling, are included. Different from other contemporary approaches, the entire system is treated quantum mechanically and neither fragmentation nor system-specific adjustment is necessary. Among the systems considered are a large DNA fragment, oligopeptides, and even entire proteins in an implicit solvent. We propose the method in tandem with experimental spectroscopy or X-ray studies for the elucidation of complex (bio)molecular structures including metallo-proteins like myoglobin.
Ab initio random structure search for 13-atom clusters of fcc elements
International Nuclear Information System (INIS)
Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M
2013-01-01
The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd 13 and Au 13 , we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au 13 , which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons. (paper)
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.
Plane-wave electronic structure calculations on a parallel supercomputer
International Nuclear Information System (INIS)
Nelson, J.S.; Plimpton, S.J.; Sears, M.P.
1993-01-01
The development of iterative solutions of Schrodinger's equation in a plane-wave (pw) basis over the last several years has coincided with great advances in the computational power available for performing the calculations. These dual developments have enabled many new and interesting condensed matter phenomena to be studied from a first-principles approach. The authors present a detailed description of the implementation on a parallel supercomputer (hypercube) of the first-order equation-of-motion solution to Schrodinger's equation, using plane-wave basis functions and ab initio separable pseudopotentials. By distributing the plane-waves across the processors of the hypercube many of the computations can be performed in parallel, resulting in decreases in the overall computation time relative to conventional vector supercomputers. This partitioning also provides ample memory for large Fast Fourier Transform (FFT) meshes and the storage of plane-wave coefficients for many hundreds of energy bands. The usefulness of the parallel techniques is demonstrated by benchmark timings for both the FFT's and iterations of the self-consistent solution of Schrodinger's equation for different sized Si unit cells of up to 512 atoms
International Nuclear Information System (INIS)
Boesten, L.G.J.
1978-01-01
Calculations on the threshold ionization of H, He + and Li 2+ by electrons have been performed to study the so-called 'post-collision interaction' (P.C.I.) effects which appear to affect the threshold ionization process significantly. These effects are caused by the long range Coulomb interactions between the two electrons as they move away from the nucleus. The long range interactions are fully taken into account in the classical three-body collision theory. In quantum mechanical theories, however, it is difficult to account for these interactions. This theory has been used to study the ionization of He + -ions by electron impact up to much higher energies (up till ten times the threshold energy). The results are compared with experimental results of Dolder et al. (1961) and with results of quantum mechanical calculations. Results are given for ionization of helium atoms by electron or proton impact. This collision process, in which four particles are involved, can under certain circumstances be treated as a collision process in which only three particles are involved. Calculations are performed concerning: a) cross sections for ionization of metastable helium atoms by electron impact, b) cross sections for ionization of ground-state helium atoms by fast proton impact (energy and angular distributions of ejected electrons), c) generalized oscillator strengths for ionization of helium by fast proton impact
International Nuclear Information System (INIS)
Branda, M.M.; Ferullo, R.; Castellani, N.J.
1990-01-01
The application of an atomic Hartree-Fock-Slater method is exposed in the present work for the simultaneous obtainment of all parameters used in the extended Hueckel method with charge interaction (IEH): The diagonal elements of the Hamiltonian, the constants of the quadratic relation between. (Author). 16 refs., 3 tabs
Lattice location of dopant atoms: An N-body model calculation
Indian Academy of Sciences (India)
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 ...
Calculation of high rydberg levels of atom Zn with the WBEPM theory
International Nuclear Information System (INIS)
Zheng, Nengwu; Li, Zhengquan; Fan, Jing; Ma, Dongxia; Zhou, Tao
2002-01-01
Within the weakest bound electron potential model theory, we treat the many-valance electron system of atom Zn single electron and use the extended martin's expression to determine parameters. The results are satisfying with deviations no more than 1cm -1 compared with the experimental values. (author)
Coupled-channels calculations of excitation and ionization in ion-atom collisions
International Nuclear Information System (INIS)
Martir, M.H.
1981-01-01
A numerical method has been used to compute excitation and ionization cross sections for ion-atom collisions. The projectile is treated classically and follows a straight line, constant velocity path (unless indicated otherwise). The wave function that describes the atom is expanded about the target in a truncated Hilbert space. The interaction between the projectile and the target atom is treated as a time dependent perturbation. A unitary time development operator, U, propagates the wave function from a time prior to the collision to a time after the collision in small time steps. Contrary to first-order theories, coupling between states is allowed. This method has been improved so that any number of partial waves can be included in the wave function expansion. This method has been applied to study negatively charged projectiles. Cross sections are obtained for collisions of antiprotons on atomic hydrogen (30 keV to 372 keV) and compared with cross sections of protons on atomic hydrogen to explore the Z/sub P/ dependence. The antiproton-hydrogen results were converted into electron-hydrogen values with E/sub e/ = E/sub P/(m/sub e//m/sub P/) (15 eV to 200 eV) and compared to experimental values. The method is then applied to study vacancy production from the L-shell. The partial wave convergence of the cross sections was carefully studied for s through g waves. Collisions between protons (and alpha-particles) and argon are studied to explore the Z/sub P/ dependence of the cross sections. The cross section ratio sigma(α)/(4sigma(p)) is compared to experiment
Structure and stability of semiconductor tip apexes for atomic force microscopy
International Nuclear Information System (INIS)
Pou, P; Perez, R; Ghasemi, S A; Goedecker, S; Jelinek, P; Lenosky, T
2009-01-01
The short range force between the tip and the surface atoms, that is responsible for atomic-scale contrast in atomic force microscopy (AFM), is mainly controlled by the tip apex. Thus, the ability to image, manipulate and chemically identify single atoms in semiconductor surfaces is ultimately determined by the apex structure and its composition. Here we present a detailed and systematic study of the most common structures that can be expected at the apex of the Si tips used in experiments. We tackle the determination of the structure and stability of Si tips with three different approaches: (i) first principles simulations of small tip apexes; (ii) simulated annealing of a Si cluster; and (iii) a minima hopping study of large Si tips. We have probed the tip apexes by making atomic contacts between the tips and then compared force-distance curves with the experimental short range forces obtained with dynamic force spectroscopy. The main conclusion is that although there are multiple stable solutions for the atomically sharp tip apexes, they can be grouped into a few types with characteristic atomic structures and properties. We also show that the structure of the last atomic layers in a tip apex can be both crystalline and amorphous. We corroborate that the atomically sharp tips are thermodynamically stable and that the tip-surface interaction helps to produce the atomic protrusion needed to get atomic resolution.
International Nuclear Information System (INIS)
Wang, Lin-Wang; Zhao, Zhengji; Meza, Juan
2006-01-01
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(N 3 ) 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
Calculation of hadronic part of photon structure function in QCD
International Nuclear Information System (INIS)
Gorskij, A.S.; Ioffe, B.L.; Oganesyan, A.G.; Khodzhamiryan, A.Yu.
1989-01-01
The photon structure function in QCD in the intermediate region of the Bjorken variable 0.2 2 /2pq, where q 2 is the hard photon virtuality, p is the soft photon momentum) is calculated. It is shown that without introduction of fitting parameters the experimental data can be described in the range 3GeV 2 ≤Q 2 2 /Q 2 =-q 2 /not taking account for the leading logarithmic corrections. It is demonstrated that the corrections proportional to μ ν 2 > to the hard photon scattering amplitude on the longitudinal soft photon and to the Callan-Gross relation vanish. 16 refs.; 6 figs
Comparison of optimization methods for electronic-structure calculations
International Nuclear Information System (INIS)
Garner, J.; Das, S.G.; Min, B.I.; Woodward, C.; Benedek, R.
1989-01-01
The performance of several local-optimization methods for calculating electronic structure is compared. The fictitious first-order equation of motion proposed by Williams and Soler is integrated numerically by three procedures: simple finite-difference integration, approximate analytical integration (the Williams-Soler algorithm), and the Born perturbation series. These techniques are applied to a model problem for which exact solutions are known, the Mathieu equation. The Williams-Soler algorithm and the second Born approximation converge equally rapidly, but the former involves considerably less computational effort and gives a more accurate converged solution. Application of the method of conjugate gradients to the Mathieu equation is discussed
Design and structural calculation of nuclear power plant mechanical components
International Nuclear Information System (INIS)
Amaral, J.A.R. do
1986-01-01
The mechanical components of a nuclear power plant must show high quality and safety due to the presence of radioactivity. Besides the perfect functioning during the rigid operating conditions, some postulated loadings are foreseen, like earthquake and loss of coolant accidents, which must be also considered in the design. In this paper, it is intended to describe the design and structural calculations concept and development, the interactions with the piping and civil designs, as well as their influences in the licensing process with the authorities. (Author) [pt
Coupling structure calculations for ion cyclotron heating of Tore Supra
International Nuclear Information System (INIS)
Bannelier, P.
1986-12-01
Two structures are studied: antennas and waveguides. After some recalls on transmission lines with losses, the theory is applied to antennas with inner adaptation: the problem is to calculate the impedance necessary for complete adaptation of antenna to the power line and the generator. The Faraday screen role is detailed and studied: the per-unit length loss resistance due to ohmic losses in the screen which lower the plasma-coupled maximum power. Waveguide coupling theory is also presented. Coupling between wave guide and plasma is evaluated [fr
The calculation of the electron structure and optical properties of TiNi martensite
International Nuclear Information System (INIS)
Kul'kova, S.E.; Beketov, K.A.; Egorushkin, V.E.; Muryzhnikova, O.N.
1995-01-01
The self-consistent calculation of NiTi B2 and B19' phases have been performed by the linear muffin-tin orbital method in atomic sphere approximation (LMTO-ASA). Two approaches for calculation of B2-phase band structure have been used and the essential differences in the Fermi surface have been pointed out. The alterations of NiTi electron characteristics at the martensitic transition have been analyzed. The optical spectra and their peculiarities in B2 and monoclinic B19' phases have been discussed. In the frames of first principles method electron-positron annihilation characteristics in B2-NiTi have been investigated too. It was shown that a rather satisfactory agreement with experimental results for NiTi was achieved. (orig.)
International Nuclear Information System (INIS)
Ba, Yaye Awa; Wenger, Christian; Surleau, Romain; Boudon, Vincent; Rotger, Maud; Daumont, Ludovic; Bonhommeau, David A.; Tyuterev, Vladimir G.; Dubernet, Marie-Lise
2013-01-01
Two spectroscopic relational databases, denoted MeCaSDa and ECaSDa, have been implemented for methane and ethene, and included in VAMDC (Virtual Atomic and Molecular Data Centre, (http://portal.vamdc.eu/vamdc_portal/home.seam)). These databases collect calculated spectroscopic data from the accurate analyses previously performed for the electronic ground state of methane, ethene, and some of their isotopologues: 12 CH 4 , 13 CH 4 , and 12 C 2 H 4 . Both infrared absorption and Raman scattering lines are included. The polyad structures are reported and the transitions are precisely described by their energy, their intensity and the full description of the lower and upper states involved in the transitions. The relational schemas of ECaSDa and MeCaSDa databases are equivalent and optimised to enable the better compromise between data retrieval and compatibility with the XSAMS (XML Schema for Atoms, Molecules, and Solids) format adopted within the VAMDC European project. -- Highlights: • We present two new spectroscopic databases, MeCaSDa and ECaSDa. • They contain calculated line lists for methane and ethene, respectively. • They collect data from accurate analyses previously preformed. • They are included in the Virtual Atomic and Molecular Data Centre (VAMDC)
Nuclear structure of light thallium isotopes as deduced from laser spectroscopy on a fast atom beam
International Nuclear Information System (INIS)
Bounds, J.A.
1985-08-01
After optimizing the system by experiments on /sup 201,203,205/Tl, the neutron-deficient isotopes 189-193 Tl have been studied using the collinear fast atom beam laser spectroscopy system at UNISOR on-line to the Holifield Heavy Ion Research Facility. A sensitive system for the measurements was developed since the light isotopes were available in mass-separated beams of only 7 x 10 4 to 4 x 10 5 atoms per second. By laser excitation of the 535 nm atomic transitions of atoms in the beam, the 6s 2 7s 2 S/sub 1/2/ and 6s 2 6s 2 P/sub 3/2/ hyperfine structures were measured, as were the isotope shifts of the 535 nm transitions. From these, the magnetic dipole moments, spectroscopic quadrupole moments and isotopic changes in mean-square charge radius were deduced. The magnetic dipole moments are consistent with previous data. The /sup 190,192/Tl isotopes show a considerable difference in quadrupole deformations as well as an anomalous isotope shift with respect to 194 Tl. A large isomer shift in 193 Tl is observed implying a larger deformation in the 9/2 - isomer than in the 1/2 + ground state. The /sup 189,191,193/Tl isomers show increasing deformation away from stability. A deformed shell model calculation indicates that this increase in deformation can account for the dropping of the 9/2 - band in these isotopes while an increase in neutron pairing correlations, having opposite and compensating effects on the rotational moment of inertia, maintains the 9/2 - strong-coupled band structure. 105 refs., 27 figs
First principle calculations of alkali hydride electronic structures
International Nuclear Information System (INIS)
Novakovic, N; Radisavljevic, I; Colognesi, D; Ostojic, S; Ivanovic, N
2007-01-01
Electronic structure, volume optimization, bulk moduli, elastic constants, and frequencies of the transversal optical vibrations in LiH, NaH, KH, RbH, and CsH are calculated using the full potential augmented plane wave method, extended with local orbitals, and the full potential linearized augmented plane wave method. The obtained results show some common features in the electronic structure of these compounds, but also clear differences, which cannot be explained using simple empirical trends. The differences are particularly prominent in the electronic distributions and interactions in various crystallographic planes. In the light of these findings we have elaborated some selected experimental results and discussed several theoretical approaches frequently used for the description of various alkali hydride properties
Distinct atomic structures of the Ni-Nb metallic glasses formed by ion beam mixing
International Nuclear Information System (INIS)
Tai, K. P.; Wang, L. T.; Liu, B. X.
2007-01-01
Four Ni-Nb metallic glasses are obtained by ion beam mixing and their compositions are measured to be Ni 77 Nb 23 , Ni 55 Nb 45 , Ni 31 Nb 69 , and Ni 15 Nb 85 , respectively, suggesting that a composition range of 23-85 at. % of Nb is favored for metallic glass formation in the Ni-Nb system. Interestingly, diffraction analyses show that the structure of the Nb-based Ni 31 Nb 69 metallic glass is distinctly different from the structure of the Nb-based Ni 15 Nb 85 metallic glass, as the respective amorphous halos are located at 2θ≅38 and 39 deg. To explore an atomic scale description of the Ni-Nb metallic glasses, an n-body Ni-Nb potential is first constructed with an aid of the ab initio calculations and then applied to perform the molecular dynamics simulation. Simulation results determine not only the intrinsic glass forming range of the Ni-Nb system to be within 20-85 at. % of Nb, but also the exact atomic positions in the Ni-Nb metallic glasses. Through a statistical analysis of the determined atomic positions, a new dominant local packing unit is found in the Ni 15 Nb 85 metallic glass, i.e., an icositetrahedron with a coordination number to be around 14, while in Ni 31 Nb 69 metallic glasses, the dominant local packing unit is an icosahedron with a coordination number to be around 12, which has been reported for the other metallic glasses. In fact, with increasing the irradiation dose, the Ni 31 Nb 69 metallic glasses are formed through an intermediate state of face-centered-cubic-solid solution, whereas the Ni 15 Nb 85 metallic glass is through an intermediate state of body-centered-cubic-solid solution, suggesting that the structures of the constituent metals play an important role in governing the structural characteristics of the resultant metallic glasses
Takano, Yu; Kobayashi, Nobuhiko; Morikawa, Yoshitada
2018-06-01
Through computer simulations using atomistic models, it is becoming possible to calculate the atomic structures of localized defects or dopants in semiconductors, chemically active sites in heterogeneous catalysts, nanoscale structures, and active sites in biological systems precisely. Furthermore, it is also possible to clarify physical and chemical properties possessed by these nanoscale structures such as electronic states, electronic and atomic transport properties, optical properties, and chemical reactivity. It is sometimes quite difficult to clarify these nanoscale structure-function relations experimentally and, therefore, accurate computational studies are indispensable in materials science. In this paper, we review recent studies on the relation between local structures and functions for inorganic, organic, and biological systems by using atomistic computer simulations.
Calculation of inelastic helium atom scattering from H2/ NaCl(001)
DEFF Research Database (Denmark)
Bruch, L.W.; Hansen, Flemming Yssing; Traeger, F.
2011-01-01
The one-phonon inelastic low energy helium atom scattering theory is adapted to cases where the target monolayer is a p(1 × 1) commensurate square lattice. Experimental data for para-H2/NaCl(001) are re-analyzed and the relative intensities of energy loss peaks in the range 6 to 9 meV are determi......The one-phonon inelastic low energy helium atom scattering theory is adapted to cases where the target monolayer is a p(1 × 1) commensurate square lattice. Experimental data for para-H2/NaCl(001) are re-analyzed and the relative intensities of energy loss peaks in the range 6 to 9 me...
The multi-scattering-Xα method for analysis of the electronic structure of atomic clusters
International Nuclear Information System (INIS)
Bahurmuz, A.A.; Woo, C.H.
1984-12-01
A computer program, MSXALPHA, has been developed to carry out a quantum-mechanical analysis of the electronic structure of molecules and atomic clusters using the Multi-Scattering-Xα (MSXα) method. The MSXALPHA program is based on a code obtained from the University of Alberta; several improvements and new features were incorporated to increase generality and efficiency. The major ones are: (1) minimization of core memory usage, (2) reduction of execution time, (3) introduction of a dynamic core allocation scheme for a large number of arrays, (4) incorporation of an atomic program to generate numerical orbitals used to construct the initial molecular potential, and (5) inclusion of a routine to evaluate total energy. This report is divided into three parts. The first discusses the theory of the MSXα method. The second gives a detailed description of the program, MSXALPHA. The third discusses the results of calculations carried out for the methane molecule (CH 4 ) and a four-atom zirconium cluster (Zr 4 )
Comparison of self-consistent calculations of the static polarizability of atoms and molecules
International Nuclear Information System (INIS)
Moullet, I.; Martins, J.L.
1990-01-01
The static dipole polarizabilities and other ground-state properties of H, H 2 , He, Na, and Na 2 are calculated using five different self-consistent schemes: Hartree--Fock, local spin density approximation, Hartree--Fock plus local density correlation, self-interaction-corrected local spin density approximation, and Hartree--Fock plus self-interaction-corrected local density correlation. The inclusion of the self-interaction corrected local spin density approximation in the Hartree--Fock method improves dramatically the calculated dissociation energies of molecules but has a small effect on the calculated polarizabilities. Correcting the local spin density calculations for self-interaction effects improves the calculated polarizability in the cases where the local spin density results are mediocre, and has only a small effect in the cases where the local spin density values are in reasonable agreement with experiment
Observations of resonance-like structures for positron-atom scattering at intermediate energies
International Nuclear Information System (INIS)
Dou, L.
1993-01-01
Absolute values of elastic differential cross sections (DCS's) are measured for position (e + ) scattering by argon (8.7-300 eV) krypton (6.7-400 eV) and also neon (13.6-400 eV) using a crossed-beam experimental setup. When the DCS's are plotted at fixed scattering angles of 30 degrees, 60 degrees, 90 degrees and 120 degrees versus energy it has been found that well-defined resonance-like structures are found at an energy of 55-60 eV for argon and at 25 and 200 eV for krypton, with a broader structure found between 100-200 eV for neon. These observed resonance-like structures are unusual because they occur at energies well above the known inelastic thresholds for these atoms. They may represent examples of open-quotes coupled channel shape resonancesclose quotes, first predicted by Higgins and Burke [1] for e + -H scattering in the vicinity of 36 eV (width ∼ 4 eV), which occurs only when both the elastic and positronium formation scattering channels are considered together. A more recent e + -H calculation by Hewitt et al. [2] supports the Higgins and Burke prediction. These predictions and the present observations suggest the existence of a new type of atomic scattering resonance
International Nuclear Information System (INIS)
Dou, L.; Kauppila, W.E.; Kwan, C.K.; Stein, T.S.
1993-01-01
We have measured absolute values of elastic differential cross sections (DCS's) for positron (e + ) scattering by argon (8.7-300 eV), krypton (6.7-400 eV), and also neon (13.6-400 eV) using a crossed-beam experimental setup. When the DCS's are plotted at fixed scattering angles of 30 degrees, 60 degrees, 90 degrees, and 120 degrees versus energy it has been found that well-defined resonance-like structures were found at an energy of 55-60 eV for argon and at 25 and 200 eV for krypton, with a broader structure found between 100-200 eV for neon. These observed resonance-like structures are unusual because they occur at energies well above the known inelastic thresholds for these atoms. They may represent examples of open-quotes coupled channel shape resonancesclose quotes, first predicted by Higgins and Burke for e + -H scattering in the vicinity of 36 eV (width ∼ 4 eV), which occurs only when both the elastic and positronium formation scattering channels are considered together. A more recent e + -H calculation by Hewitt et al. supports the Higgins and Burke prediction. These predictions and the present observations suggest the existence of a new type of atomic scattering resonance
Damianos, Konstantina; Ferrando, Riccardo
2012-02-21
The structural modifications of small supported gold clusters caused by realistic surface defects (steps) in the MgO(001) support are investigated by computational methods. The most stable gold cluster structures on a stepped MgO(001) surface are searched for in the size range up to 24 Au atoms, and locally optimized by density-functional calculations. Several structural motifs are found within energy differences of 1 eV: inclined leaflets, arched leaflets, pyramidal hollow cages and compact structures. We show that the interaction with the step clearly modifies the structures with respect to adsorption on the flat defect-free surface. We find that leaflet structures clearly dominate for smaller sizes. These leaflets are either inclined and quasi-horizontal, or arched, at variance with the case of the flat surface in which vertical leaflets prevail. With increasing cluster size pyramidal hollow cages begin to compete against leaflet structures. Cage structures become more and more favourable as size increases. The only exception is size 20, at which the tetrahedron is found as the most stable isomer. This tetrahedron is however quite distorted. The comparison of two different exchange-correlation functionals (Perdew-Burke-Ernzerhof and local density approximation) show the same qualitative trends. This journal is © The Royal Society of Chemistry 2012
Directory of Open Access Journals (Sweden)
FANG FANG JIAN
2010-09-01
Full Text Available The main aim of this study was to investigate the relationship between mIn tA new Ni(II complex of bisglycinato-bis[p-(hydroxylmethylpy-ridine] was synthesized and characterized by elemental analysis, IR, UV–Vis spectroscopy and X-ray single crystal diffraction analysis. The thermal stability of the title complex was also determined. The complex adopts a distorted octahedral geometry and possesses inversion symmetry with the Ni(II ion as the center of inversion. Density function theory (DFT calculations of the structure, electronic absorption spectra, electron structure and natural population analysis (NPA at the B3LYP/LANL2DZ level of theory were performed. The predicted geometric parameters and electronic spectra were compared with the experimental values and they supported each other. The NPA results indicate that the electronic transitions were mainly derived from the contribution of an intra-ligand (IL transition, a ligand-to-metal charge transfer (LMCT transition and a d-d transition. The electron structure calculations suggest that the central Ni(II ion uses its 4s and 3d orbitals to form covalent bonds with coordinated N and O atoms. The calculated bond orders are also consistent with the thermal decomposition results. Based on vibrational analysis, the thermodynamic properties of the title complex were predicted and the correlative equations between these thermodynamic properties and temperature are also reported.
Compton profiles and band structure calculations of CdS and CdTe
International Nuclear Information System (INIS)
Heda, N.L.; Mathur, S.; Ahuja, B.L.; Sharma, B.K.
2007-01-01
In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci 137 Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
First-principles calculations of BC{sub 4}N nanostructures: stability and electronic structure
Energy Technology Data Exchange (ETDEWEB)
Freitas, A.; Azevedo, S. [Universidade Federal da Paraiba, CCEN, Departamento de Fisica, Joao Pessoa, PB (Brazil); Machado, M. [Universidade Federal de Pelotas, Departamento de Fisica, Pelotas, RS (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitoria da Conquista, Vitoria da Conquista, BA (Brazil)
2012-07-15
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC{sub 4}N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 A, or cut and bent to form nanocones, with 60 and 120 disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B-N and C-C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D {sup 2} law. The results show that the 60 disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. (orig.)
Electronic structure of SnS deduced from photoelectron spectra and band-structure calculations
Ettema, A.R.H.F.; Groot, R.A. de; Haas, C.; Turner, T.S.
1992-01-01
SnS is a layer compound with a phase transition from a high-temperature β phase to a low-temperature α phase with a lower symmetry. Ab initio band-structure calculations are presented for both phases. The calculations show that the charge distributions in the two phases are very similar. However,
Energy Technology Data Exchange (ETDEWEB)
Bencs, László, E-mail: bencs.laszlo@wigner.mta.hu [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Laczai, Nikoletta [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Ajtony, Zsolt [Institute of Food Science, University of West Hungary, H-9200 Mosonmagyaróvár, Lucsony utca 15–17 (Hungary)
2015-07-01
A combination of former convective–diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass — m{sub 0}) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m{sub 0} values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm{sup 3} min{sup −1}) of the internal sheath gas during atomization. The theoretical and experimental ratios of m{sub 0}(mini-flow)-to-m{sub 0}(stop-flow) were closely similar for each study analyte. Likewise, the calculated m{sub 0} data gave a fairly good agreement with the corresponding experimental m{sub 0} values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology. - Highlights: • A calculation scheme for convective–diffusive vapor loss in GFAAS is described. • Residence time (τ) formulas were compared for sensitivity (m{sub 0}) in a THGA furnace. • Effects of the sample/platform dimension and dosing hole on τ were assessed. • Theoretical m{sub 0} of 18 analytes were
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed
2012-08-20
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed; Anciaux-Sedrakian, Ani; Rozanska, Xavier; Klahr, Diego; Guignon, Thomas; Fleurat-Lessard, Paul
2012-01-01
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Development of the simulation package 'ELSES' for extra-large-scale electronic structure calculation
Energy Technology Data Exchange (ETDEWEB)
Hoshi, T [Department of Applied Mathematics and Physics, Tottori University, Tottori 680-8550 (Japan); Fujiwara, T [Core Research for Evolutional Science and Technology, Japan Science and Technology Agency (CREST-JST) (Japan)
2009-02-11
An early-stage version of the simulation package 'ELSES' (extra-large-scale electronic structure calculation) is developed for simulating the electronic structure and dynamics of large systems, particularly nanometer-scale and ten-nanometer-scale systems (see www.elses.jp). Input and output files are written in the extensible markup language (XML) style for general users. Related pre-/post-simulation tools are also available. A practical workflow and an example are described. A test calculation for the GaAs bulk system is shown, to demonstrate that the present code can handle systems with more than one atom species. Several future aspects are also discussed.
Grimme, Stefan; Brandenburg, Jan Gerit; Bannwarth, Christoph; Hansen, Andreas
2015-08-07
and reach that of triple-zeta AO basis set second-order perturbation theory (MP2/TZ) level at a tiny fraction of computational effort. Periodic calculations conducted for molecular crystals to test structures (including cell volumes) and sublimation enthalpies indicate very good accuracy competitive to computationally more involved plane-wave based calculations. PBEh-3c can be applied routinely to several hundreds of atoms on a single processor and it is suggested as a robust "high-speed" computational tool in theoretical chemistry and physics.
International Nuclear Information System (INIS)
Grimme, Stefan; Brandenburg, Jan Gerit; Bannwarth, Christoph; Hansen, Andreas
2015-01-01
methods and reach that of triple-zeta AO basis set second-order perturbation theory (MP2/TZ) level at a tiny fraction of computational effort. Periodic calculations conducted for molecular crystals to test structures (including cell volumes) and sublimation enthalpies indicate very good accuracy competitive to computationally more involved plane-wave based calculations. PBEh-3c can be applied routinely to several hundreds of atoms on a single processor and it is suggested as a robust “high-speed” computational tool in theoretical chemistry and physics
Li, Xiaolong; Zhou, Zhaobo; Hu, Riming; Zhou, Xiaolong; Yu, Jie; Liu, Manmen
2018-04-01
The Phase stability, electronic structure, elastic properties and hardness of Ru-Ir alloys with different B concentration were investigated by first principles calculations. The calculated formation enthaplies and cohesive energies show that these compounds are all thermodynamically stable. Information on electronic structure indicates that they possess metallic characteristic and Ru-Ir-B alloys were composed of the Ru-B and Ir-B covalent bond. The elastic properties were calculated, which included bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and hardness. The calculated results reveal that the plastic of Ru-Ir-B alloys increase with the increase of the content of B atoms, but the hardness of Ru-Ir-B alloys have no substantial progress with the increase of the content of B atoms. However, it is interesting that the hardness of the Ru-Ir-B compound was improved obviously as the B content was higher than 18 atoms because of a phase structure transition.
Quantum chemical calculations in the structural analysis of phloretin
Gómez-Zavaglia, Andrea
2009-07-01
In this work, a conformational search on the molecule of phloretin [2',4',6'-Trihydroxy-3-(4-hydroxyphenyl)-propiophenone] has been performed. The molecule of phloretin has eight dihedral angles, four of them taking part in the carbon backbone and the other four, related with the orientation of the hydroxyl groups. A systematic search involving a random variation of the dihedral angles has been used to generate input structures for the quantum chemical calculations. Calculations at the DFT(B3LYP)/6-311++G(d,p) level of theory permitted the identification of 58 local minima belonging to the C 1 symmetry point group. The molecular structures of the conformers have been analyzed using hierarchical cluster analysis. This method allowed us to group conformers according to their similarities, and thus, to correlate the conformers' stability with structural parameters. The dendrogram obtained from the hierarchical cluster analysis depicted two main clusters. Cluster I included all the conformers with relative energies lower than 25 kJ mol -1 and cluster II, the remaining conformers. The possibility of forming intramolecular hydrogen bonds resulted the main factor contributing for the stability. Accordingly, all conformers depicting intramolecular H-bonds belong to cluster I. These conformations are clearly favored when the carbon backbone is as planar as possible. The values of the νC dbnd O and νOH vibrational modes were compared among all the conformers of phloretin. The redshifts associated with intramolecular H-bonds were correlated with the H-bonds distances and energies.
Relativistic calculations of one-photon bound-free transition amplitudes in hydrogenic atoms
International Nuclear Information System (INIS)
Simo, E.; Kwato Njock, M.G.
2005-04-01
Photoionization transition matrix of hydrogenic systems are investigated theoretically within the framework of the tensorial formalism with relativistic arguments. Calculations are carried out exactly, without approximation. We derive continuum second-order Dirac-Coulomb Sturmian functions. The numerical simulation of our results is performed in the dipole approximation. We test our theory on selected nucleus from the Periodic Table. The results of the fully relativistic calculations are compared with those of the quasi-relativistic calculations. A conclusion is drawn about the level of reliability of the quite simplified quasi-relativistic approach. (author)
Kadioglu, Yelda; Santana, Juan A.; Özaydin, H. Duygu; Ersan, Fatih; Aktürk, O. Üzengi; Aktürk, Ethem; Reboredo, Fernando A.
2018-06-01
We have studied the structural stability of monolayer and bilayer arsenene (As) in the buckled (b) and washboard (w) phases with diffusion quantum Monte Carlo (DMC) and density functional theory (DFT) calculations. DMC yields cohesive energies of 2.826(2) eV/atom for monolayer b-As and 2.792(3) eV/atom for w-As. In the case of bilayer As, DMC and DFT predict that AA-stacking is the more stable form of b-As, while AB is the most stable form of w-As. The DMC layer-layer binding energies for b-As-AA and w-As-AB are 30(1) and 53(1) meV/atom, respectively. The interlayer separations were estimated with DMC at 3.521(1) Å for b-As-AA and 3.145(1) Å for w-As-AB. A comparison of DMC and DFT results shows that the van der Waals density functional method yields energetic properties of arsenene close to DMC, while the DFT + D3 method closely reproduced the geometric properties from DMC. The electronic properties of monolayer and bilayer arsenene were explored with various DFT methods. The bandgap values vary significantly with the DFT method, but the results are generally qualitatively consistent. We expect the present work to be useful for future experiments attempting to prepare multilayer arsenene and for further development of DFT methods for weakly bonded systems.
Tewari, Sumit; Bastiaans, Koen M; Allan, Milan P; van Ruitenbeek, Jan M
2017-01-01
Scanning tunneling microscopes (STM) are used extensively for studying and manipulating matter at the atomic scale. In spite of the critical role of the STM tip, procedures for controlling the atomic-scale shape of STM tips have not been rigorously justified. Here, we present a method for preparing tips in situ while ensuring the crystalline structure and a reproducibly prepared tip structure up to the second atomic layer. We demonstrate a controlled evolution of such tips starting from undefined tip shapes.
Atomic structure of machined semiconducting chips: An x-ray absorption spectroscopy study
Energy Technology Data Exchange (ETDEWEB)
Paesler, M.; Sayers, D.
1988-12-01
X-ray absorption spectroscopy (XAS) has been used to examine the atomic structure of chips of germanium that were produced by single point diamond machining. It is demonstrated that although the local (nearest neighbor) atomic structure is experimentally quite similar to that of single crystal specimens information from more distant atoms indicates the presence of considerable stress. An outline of the technique is given and the strength of XAS in studying the machining process is demonstrated.
Kohri, Kumiko; Yoshida, Eiko; Yasuike, Shuji; Fujie, Tomoya; Yamamoto, Chika; Kaji, Toshiyuki
2015-06-01
Organic-inorganic hybrid molecules, which are composed of an organic structure and metal(s), are indispensable for synthetic chemical reactions; however, their toxicity has been incompletely understood. In the present study, we discovered two cytotoxic organobismuth compounds whose cytotoxicity diminished upon replacement of the intramolecular bismuth atom with an antimony atom. The intracellular accumulation of the organobismuth compounds was much higher than that of the organoantimony compounds with the corresponding organic structures. We also showed that both the organic structure and bismuth atom are required for certain organobismuth compounds to exert their cytotoxic effect, suggesting that the cytotoxicity of such a compound is a result of an interaction between the organic structure and the bismuth atom. The present data suggest that organobismuth compounds with certain molecular structures exhibit cytotoxicity via an interaction between the molecular structure and the bismuth atom, and this cytotoxicity can be diminished by replacing the bismuth atom with an antimony atom, resulting in lower intracellular accumulation.
A theoretical inquiry into the question of W and Ta (100) atomic structures
International Nuclear Information System (INIS)
Treglia, G.; Spanjaard, D.
1983-01-01
In spite of the very large number of experiments (LEED, AES, UPS, MeV He + scattering, work function, FIM) carried out on W (100), no structural model consistent with all the data has been proposed yet: in particular, the question of the reconstruction thermally induced when the sample is cooled below room temperature remains a puzzling problem. Furthermore, from a theoretical point of view, no definitive answer has been given. Actually, either the mechanism invoked for the reconstruction is too weak, or some contributions are omitted or calculated without sufficient care. The surface energy of W (100) is computed taking into account the band term treated in the tight binding approximation, a pairwise repulsive potential of the Born-Mayer type and the electronic correlation contribution obtained from a perturbation treatment of the Hubbard model in the band limit. This energy is then fully minimised with respect to all coordinates of surface atoms, keeping all atoms neutral for any displace,ment. It is found that the unreconstructed surface is the most stable at T = 0 K and discuss this unexpected result. A similar calculation for Ta (100) leads to opposite conclusions. (author)
Donval, Gaël; Moreau, Philippe; Danet, Julien; Larbi, Séverine Jouanneau-Si; Bayle-Guillemaud, Pascale; Boucher, Florent
2017-01-04
Most of the recent developments in EELS modelling has been focused on getting a better agreement with measurements. Less work however has been dedicated to bringing EELS calculations to larger structures that can more realistically describe actual systems. The purpose of this paper is to present a hybrid approach well adapted to calculating the whole set of localised EELS core-loss edges (at the XAS level of theory) on larger systems using only standard tools, namely the WIEN2k and VASP codes. We illustrate the usefulness of this method by applying it to a set of amorphous silicon structures in order to explain the flattening of the silicon L 2,3 EELS edge peak at the onset. We show that the peak flattening is actually caused by the collective contribution of each of the atoms to the average spectrum, as opposed to a flattening occurring on each individual spectrum. This method allowed us to reduce the execution time by a factor of 3 compared to a usual-carefully optimised-WIEN2k calculation. It provided even greater speed-ups on more complex systems (interfaces, ∼300 atoms) that will be presented in a future paper. This method is suited to calculate all the localized edges of all the atoms of a structure in a single calculation for light atoms as long as the core-hole effects can be neglected.
Formation and structural phase transition in Co atomic chains on a Cu(775) surface
International Nuclear Information System (INIS)
Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L.
2017-01-01
The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.
Formation and structural phase transition in Co atomic chains on a Cu(775) surface
Energy Technology Data Exchange (ETDEWEB)
Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L., E-mail: klavsyuk@physics.msu.ru [Moscow State University (Russian Federation)
2017-01-15
The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.
International Nuclear Information System (INIS)
Prudnikov, O. N.; Taichenachev, A. V.; Tumaikin, A. M.; Yudin, V. I.
2007-01-01
Generally, conditions for deep sub-Doppler laser cooling do not match conditions for strong atomic localization, that takes place in a deeper optical potential and leads to higher temperature. Moreover, for a given detuning in a deep optical potential the secular approximation, which is frequently used for a quantum description of laser cooling, fails. Here we investigate the atomic localization in optical potential, using a full quantum approach for atomic density matrix beyond the secular approximation. It is shown that laser cooling in a deep optical potential, created by a light field with polarization gradients, can be used as an alternative method for the formation of high contrast spatially localized structures of atoms for the purposes of atom lithography and atomic nanofabrication. Finally, we analyze possible limits for the width and contrast of localized atomic structures that can be reached in this type of light mask
Convergent close-coupling calculations of low-energy positron-atomic-hydrogen scattering
International Nuclear Information System (INIS)
Bray, I.; Stelbovics, A.T.
1993-07-01
The convergent close coupling approach developed by the authors is applied to positron scattering from atomic hydrogen below the first excitation threshold. In this approach the multi-channel expansion one-electron states are obtained by diagonalizing the target Hamiltonian in a large Laguerre basis. It is demonstrated that this expansion of the scattering wave function is sufficient to reproduce the very accurate low-energy variational results, provided target states with l≤ 15 are included in the expansions. 10 refs., 1 tab
Tests and calculation of the seismic behaviour of concrete structures
International Nuclear Information System (INIS)
Gauvain, J.; Hoffman, A.; Jeandidier, C.; Livolant, M.
1979-01-01
This paper deals with the frame type buildings, which are generally the most sensible to earthquakes. Its objectives are to describe the main phenomena governing the behaviour of such structures, when the earthquake level increases up to the structure collapse, to point out what type of calculation model shall be used to obtain good results and to give an estimation of the safety factors corresponding to the usual design practice. Extended experimental research on the behaviour of reinforced concrete beams and frames submitted to monotonic or cyclic loading has been done. These tests are very useful to build constitutive laws models, but as they do not reproduce the earthquake loads, they do not simulate directly what happens to the structure during an earthquake. For that reason, since 1966, dynamics tests were performed using vibration generators or shaking-tables. As an example of that type of test and of the corresponding results, we describe here with more details the tests made at the Saclay Center, on a shaking-table called VESUVE, on simple beams and frames
International Nuclear Information System (INIS)
Mitroy, J.; Bromley, M.W.J.
2003-01-01
The van der Waals coefficients, C 6 , C 8 , and C 10 for the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are estimated by a combination of ab initio and semiempirical methods. Polarizabilities and atom-wall coefficients are given as a diagnostic check, and the lowest order nonadiabatic dispersion coefficient, D 8 and the three-body coefficient, C 9 are also presented. The dispersion coefficients are in agreement with the available relativistic many-body perturbation theory calculations. The contribution from the core was included by using constrained sum rules involving the core polarizability and Hartree-Fock expectation values to estimate the f-value distribution
Software for relativistic atomic structure theory: The grasp project at oxford
International Nuclear Information System (INIS)
Parpia, F.A.; Grant, I.P.
1991-01-01
GRASP is an acronym for General-purpose Relativistic Atomic Structure Program. The objective of the GRASP project at Oxford is to produce user-friendly state-of-the-art multiconfiguration Dirac-Fock (MCDF) software packages for rleativistic atomic structure theory
Atomic structure affects the directional dependence of friction
Czech Academy of Sciences Publication Activity Database
Weymouth, A.J.; Meuer, D.; Mutombo, Pingo; Wutscher, T.; Ondráček, Martin; Jelínek, Pavel; Giessibl, F.J.
2013-01-01
Roč. 111, č. 12 (2013), "126103-1"-"126103-4" ISSN 0031-9007 R&D Projects: GA ČR(CZ) GPP204/11/P578 Grant - others:GA AV(CZ) M100101207 Institutional support: RVO:68378271 Keywords : atomic scale friction * atomic force microscopy * silicon surface Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.728, year: 2013
Lindahl, Erik; Azuara, Cyril; Koehl, Patrice; Delarue, Marc
2006-07-01
Normal mode analysis (NMA) is an efficient way to study collective motions in biomolecules that bypasses the computational costs and many limitations associated with full dynamics simulations. The NOMAD-Ref web server presented here provides tools for online calculation of the normal modes of large molecules (up to 100,000 atoms) maintaining a full all-atom representation of their structures, as well as access to a number of programs that utilize these collective motions for deformation and refinement of biomolecular structures. Applications include the generation of sets of decoys with correct stereochemistry but arbitrary large amplitude movements, the quantification of the overlap between alternative conformations of a molecule, refinement of structures against experimental data, such as X-ray diffraction structure factors or Cryo-EM maps and optimization of docked complexes by modeling receptor/ligand flexibility through normal mode motions. The server can be accessed at the URL http://lorentz.immstr.pasteur.fr/nomad-ref.php.
Smallest Nanoelectronic with Atomic Devices with Precise Structures
Yamada, Toshishige
2000-01-01
Since its invention in 1948, the transistor has revolutionized our everyday life - transistor radios and TV's appeared in the early 1960s, personal computers came into widespread use in the mid-1980s, and cellular phones, laptops, and palm-sized organizers dominated the 1990s. The electronics revolution is based upon transistor miniaturization; smaller transistors are faster, and denser circuitry has more functionality. Transistors in current generation chips are 0.25 micron or 250 nanometers in size, and the electronics industry has completed development of 0.18 micron transistors which will enter production within the next few years. Industry researchers are now working to reduce transistor size down to 0.13 micron - a thousandth of the width of a human hair. However, studies indicate that the miniaturization of silicon transistors will soon reach its limit. For further progress in microelectronics, scientists have turned to nanotechnology to advance the science. Rather than continuing to miniaturize transistors to a point where they become unreliable, nanotechnology offers the new approach of building devices on the atomic scale [see sidebar]. One vision for the next generation of miniature electronics is atomic chain electronics, where devices are composed of atoms aligned on top of a substrate surface in a regular pattern. The Atomic Chain Electronics Project (ACEP) - part of the Semiconductor Device Modeling and Nanotechnology group, Integrated Product Team at the NAS Facility has been developing the theory of understanding atomic chain devices, and the author's patent for atomic chain electronics is now pending.
Directory of Open Access Journals (Sweden)
Alberto Milani
2015-02-01
Full Text Available Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanced technological applications due to the different coordination of carbon atoms and to the possibility of π-conjugation. In this context, atomic-scale wires comprised of sp-hybridized carbon atoms represent ideal 1D systems to potentially downscale devices to the atomic level. Carbon-atom wires (CAWs can be arranged in two possible structures: a sequence of double bonds (cumulenes, resulting in a 1D metal, or an alternating sequence of single–triple bonds (polyynes, expected to show semiconducting properties. The electronic and optical properties of CAWs can be finely tuned by controlling the wire length (i.e., the number of carbon atoms and the type of termination (e.g., atom, molecular group or nanostructure. Although linear, sp-hybridized carbon systems are still considered elusive and unstable materials, a number of nanostructures consisting of sp-carbon wires have been produced and characterized to date. In this short review, we present the main CAW synthesis techniques and stabilization strategies and we discuss the current status of the understanding of their structural, electronic and vibrational properties with particular attention to how these properties are related to one another. We focus on the use of vibrational spectroscopy to provide information on the structural and electronic properties of the system (e.g., determination of wire length. Moreover, by employing Raman spectroscopy and surface enhanced Raman scattering in combination with the support of first principles calculations, we show that a detailed understanding of the charge transfer between CAWs and metal nanoparticles may open the possibility to tune the electronic structure from alternating to equalized bonds.
Energy Technology Data Exchange (ETDEWEB)
Clade, P
2005-10-15
From a measurement of the recoil velocity of an atom absorbing a photon, it is possible to deduce a determination of the ratio h/m between the Planck constant and the mass of the atoms and then to deduce a value of the fine structure constant alpha. To do this measurement, we use the technique of Bloch oscillations, which allows us to transfer a large number of recoils to atoms. A velocity sensor, based on velocity selective Raman transition, enables us to measure the momentum transferred to the atoms. A measurement with a statistical uncertainty of 4.4 10{sup -9}, in conjunction with a careful study of systematic effects (5 10{sup -9}), has led us to a determination of alpha with an uncertainty of 6.7 10{sup -9}: {alpha}{sup -1}(Rb) = 137.03599878 (91). This uncertainty is similar to the uncertainty of the best determinations of alpha based on atom interferometry. (author)
Term structure of 4d-electron configurations and calculated spectrum in Sn-isonuclear sequence
International Nuclear Information System (INIS)
Al-Rabban, Moza M.
2006-01-01
Theoretical calculations of term structure are carried out for the ground configurations 4d w , 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 4p 5 4d n+1 , 4d n-1 4f 1 , and 4d n-1 5p 1 with respect to the ground configuration 4d n , 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 4d n -4p 5 4d n+1 and 4d n -4d n-1 4f 1
A relativistic point coupling model for nuclear structure calculations
International Nuclear Information System (INIS)
Buervenich, T.; Maruhn, J.A.; Madland, D.G.; Reinhard, P.G.
2002-01-01
A relativistic point coupling model is discussed focusing on a variety of aspects. In addition to the coupling using various bilinear Dirac invariants, derivative terms are also included to simulate finite-range effects. The formalism is presented for nuclear structure calculations of ground state properties of nuclei in the Hartree and Hartree-Fock approximations. Different fitting strategies for the determination of the parameters have been applied and the quality of the fit obtainable in this model is discussed. The model is then compared more generally to other mean-field approaches both formally and in the context of applications to ground-state properties of known and superheavy nuclei. Perspectives for further extensions such as an exact treatment of the exchange terms using a higher-order Fierz transformation are discussed briefly. (author)
Lobato, I; Rojas, J; Landauro, C V; Torres, J
2009-02-04
The structural evolution and dynamics of silver nanodrops Ag(2869) (4.4 nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 × 10(13) K s(-1) the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 × 10(12) K s(-1)), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the face centred cubic and hexagonal close packed structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small, but in correspondence with the structural changes.
Auxiliary basis expansions for large-scale electronic structure calculations.
Jung, Yousung; Sodt, Alex; Gill, Peter M W; Head-Gordon, Martin
2005-05-10
One way to reduce the computational cost of electronic structure calculations is to use auxiliary basis expansions to approximate four-center integrals in terms of two- and three-center integrals, usually by using the variationally optimum Coulomb metric to determine the expansion coefficients. However, the long-range decay behavior of the auxiliary basis expansion coefficients has not been characterized. We find that this decay can be surprisingly slow. Numerical experiments on linear alkanes and a toy model both show that the decay can be as slow as 1/r in the distance between the auxiliary function and the fitted charge distribution. The Coulomb metric fitting equations also involve divergent matrix elements for extended systems treated with periodic boundary conditions. An attenuated Coulomb metric that is short-range can eliminate these oddities without substantially degrading calculated relative energies. The sparsity of the fit coefficients is assessed on simple hydrocarbon molecules and shows quite early onset of linear growth in the number of significant coefficients with system size using the attenuated Coulomb metric. Hence it is possible to design linear scaling auxiliary basis methods without additional approximations to treat large systems.
An intrinsic representation of atomic structure: From clusters to periodic systems
Li, Xiao-Tian; Xu, Shao-Gang; Yang, Xiao-Bao; Zhao, Yu-Jun
2017-10-01
We have improved our distance matrix and eigen-subspace projection function (EPF) [X.-T. Li et al., J. Chem. Phys. 146, 154108 (2017)] to describe the atomic structure for periodic systems. Depicting the local structure of an atom, the EPF turns out to be invariant with respect to the choices of the unit cell and coordinate frame, leading to an intrinsic representation of the crystal with a set of EPFs of the nontrivial atoms. The difference of EPFs reveals the difference of atoms in local structure, while the accumulated difference between two sets of EPFs can be taken as the distance between configurations. Exemplified with the cases of carbon allotropes and boron sheets, our EPF approach shows exceptional rationality and efficiency to distinguish the atomic structures, which is crucial in structure recognition, comparison, and analysis.
Yoshizawa, Terutaka; Zou, Wenli; Cremer, Dieter
2017-04-01
A new method for calculating nuclear magnetic resonance shielding constants of relativistic atoms based on the two-component (2c), spin-orbit coupling including Dirac-exact NESC (Normalized Elimination of the Small Component) approach is developed where each term of the diamagnetic and paramagnetic contribution to the isotropic shielding constant σi s o is expressed in terms of analytical energy derivatives with regard to the magnetic field B and the nuclear magnetic moment 𝝁 . The picture change caused by renormalization of the wave function is correctly described. 2c-NESC/HF (Hartree-Fock) results for the σiso values of 13 atoms with a closed shell ground state reveal a deviation from 4c-DHF (Dirac-HF) values by 0.01%-0.76%. Since the 2-electron part is effectively calculated using a modified screened nuclear shielding approach, the calculation is efficient and based on a series of matrix manipulations scaling with (2M)3 (M: number of basis functions).
International Nuclear Information System (INIS)
Eskandari, M.R.; Rezaie, B.
2005-01-01
A calculation of the ground-state energy and average distance between particles in the nonsymmetric muonic 3 He atom is given. We have used a wave function with one free parameter, which satisfies boundary conditions such as the behavior of the wave function when two particles are close to each other or far away. In the proposed wave function, the electron-muon correlation function is also considered. It has a correct behavior for r 12 tending to zero and infinity. The calculated values for the energy and expectation values of r 2n are compared with the multibox variational approach and the correlation function hyperspherical harmonic method. In addition, to show the importance and accuracy of approach used, the method is applied to evaluate the ground-state energy and average distance between the particles of nonsymmetric muonic 4 He atom. Our obtained results are very close to the values calculated by the mentioned methods and giving strong indications that the proposed wave functions, in addition to being very simple, provide relatively accurate values for the energy and expectation values of r 2n , emphasizing the importance of the local properties of the wave function
International Nuclear Information System (INIS)
Song, W.; Appen, J. von; Choi, P.; Dronskowski, R.; Raabe, D.; Bleck, W.
2013-01-01
Carbide precipitation during upper and lower bainite formation in high-carbon bearing steel 100Cr6 is characterized using transmission electron microscopy and atom probe tomography. The results reveal that both ε and θ carbides precipitate in lower bainite isothermally held at 260 °C and only θ precipitates form in upper bainite isothermally held at 500 °C. ε and θ precipitate under paraequilibrium condition at 260 °C in lower bainite and θ precipitates under negligible partitioning local equilibrium condition in upper bainite at 500 °C. In order to theoretically study ε and θ precipitation and the ε → θ transition in bainite, thermodynamic calculations have been carried out using ab initio techniques. We find that ε and θ carbides in ferrite have almost identical thermodynamic stability, and hence have similar formation probability. In austenite, however, cementite formation is clearly preferred: it is favored by 5 kJ mol −1 at room temperature and still by 4 kJ mol −1 at 500 °C. Hence, the thermodynamic predictions agree well with the atom probe tomography results
Bakkari, Karim; Fersi, Riadh; Kebir Hlil, El; Bessais, Lotfi; Thabet Mliki, Najeh
2018-03-01
First-principle calculations combining density functional theory and the full-potential linearized augmented plane wave (FP-LAPW) method are performed to investigate the electronic and magnetic structure of Pr2Co7 in its two polymorphic forms, (2:7 H) and (2:7 R), for the first time. This type of calculation was also performed for PrCo5 and PrCo2 intermetallics. We have computed the valence density of states separately for spin-up and spin-down states in order to investigate the electronic band structure. This is governed by the strong contribution of the partial DOS of 3d-Co bands compared to the partial DOS of the 4f-Pr bands. Such a high ferromagnetic state is discussed in terms of the strong spin polarization observed in the total DOS. The magnetic moments carried by the Co and Pr atoms located in several sites for all compounds are computed. These results mainly indicate that cobalt atoms make a dominant contribution to the magnetic moments. The notable difference in the atomic moments of Pr and Co atoms between different structural slabs is explained in terms of the magnetic characteristics of the PrCo2 and PrCo5 compounds and the local chemical environments of the Pr and Co atoms in different structural slabs of Pr2Co7. From spin-polarized calculations we have simulated the 3d and 4f band population to estimate the local magnetic moments. These results are in accordance with the magnetic moments calculated using the FP-LAPW method. In addition, the exchange interactions J ij are calculated and used as input for M(T) simulations. Involving the data obtained from the electronic structure calculations, the appropriate Padé Table is applied to simulate the magnetization M(T) and to estimate the mean-field Curie temperature. We report a fairly good agreement between the ab initio calculation of magnetization and Curie temperature with the experimental data.
Optical properties and band structure of atomically thin MoS2
Shan, Jie; Mak, Kin Fai; Lee, Changgu; Hone, James; Heinz, Tony
2010-03-01
Atomically thin layers of materials can be expected to exhibit distinct electronic structure and novel properties compared to their bulk counterparts. Layered compounds, for which stable atomically thin samples can be produced, are ideal candidates for such studies. Graphene, a monolayer slice of the graphite crystal, is an illustrative example of both the stability and of the interest and importance of such materials. Here we report a study of thin layers of MoS2, a hexagonal layered bulk semiconductor with an indirect band gap of 1.3 eV. MoS2 samples with layer thickness N down to a monolayer were obtained by mechanical exfoliation. We observed an enhancement of the luminescence quantum yield by more than a factor of 100 in monolayer MoS2 compared to the bulk material. The combination of absorption, photoluminescence, and photoconductivity measurements indicates that a transition to a direct-gap material occurs in the limit of the single MoS2 layer. This result is supported by an earlier first-principles calculation [J. Phys. Chem. C 2007, 111, 16192]. Further, by varying the thickness of the samples, we were able to probe the evolution of the electronic structure for N = 1 -- 6 layers.
Piotrowski, Maurício J; Piquini, Paulo; Cândido, Ladir; Da Silva, Juarez L F
2011-10-14
The crystalline structure of transition-metals (TM) has been widely known for several decades, however, our knowledge on the atomic structure of TM clusters is still far from satisfactory, which compromises an atomistic understanding of the reactivity of TM clusters. For example, almost all density functional theory (DFT) calculations for TM clusters have been based on local (local density approximation--LDA) and semilocal (generalized gradient approximation--GGA) exchange-correlation functionals, however, it is well known that plain DFT fails to correct the self-interaction error, which affects the properties of several systems. To improve our basic understanding of the atomic and electronic properties of TM clusters, we report a DFT study within two nonlocal functionals, namely, the hybrid HSE (Heyd, Scuseria, and Ernzerhof) and GGA+U functionals, of the structural and electronic properties of the Co(13), Rh(13), and Hf(13) clusters. For Co(13) and Rh(13), we found that improved exchange-correlation functionals decrease the stability of open structures such as the hexagonal bilayer (HBL) and double simple-cubic (DSC) compared with the compact icosahedron (ICO) structure, however, DFT-GGA, DFT-GGA+U, and DFT-HSE yield very similar results for Hf(13). Thus, our results suggest that the DSC structure obtained by several plain DFT calculations for Rh(13) can be improved by the use of improved functionals. Using the sd hybridization analysis, we found that a strong hybridization favors compact structures, and hence, a correct description of the sd hybridization is crucial for the relative energy stability. For example, the sd hybridization decreases for HBL and DSC and increases for ICO in the case of Co(13) and Rh(13), while for Hf(13), the sd hybridization decreases for all configurations, and hence, it does not affect the relative stability among open and compact configurations.
Ab initio calculations of the structure and conformations of 2,6-lutidine
International Nuclear Information System (INIS)
Porcinai, S.; Foggi, P.
1997-01-01
Ab initio molecular orbital calculations at the SCF level have been utilized to determine the structure and the electronic and vibrational properties of 2,6-lutidine (2,6-dimethyl-pyridine) in the ground electronic state. Comparative calculations have been performed on the parent molecule pyridine. Structure predictions of both molecules are in good agreement with experimental data. The most stable rotamer of 2,6-lutidine has C 2v symmetry with one of the C-H bonds of both the methyl groups lying in the plane of the aromatic ring and pointing in the opposite direction with respect to the nitrogen atom. This is the result of the minimization of competing forces deriving from steric hindrance and electronic stabilization. Vibrational frequencies and oscillator strengths of C-H stretching in the fundamental region have been calculated for both pyridine and the most stable rotamer of 2,6-lutidine and compared to IR data obtained in pure liquids. The potential energy profile of the C-H bond in and out of plane has been investigated up to five times the equilibrium distance. The trend of the potential curves confirms that the C-H bond lying in the plane has a higher dissociation energy than that of the in-plane bonds as observed in experiments on vibrational overtones
Kim, Jeongnim; Baczewski, Andrew D.; Beaudet, Todd D.; Benali, Anouar; Chandler Bennett, M.; Berrill, Mark A.; Blunt, Nick S.; Josué Landinez Borda, Edgar; Casula, Michele; Ceperley, David M.; Chiesa, Simone; Clark, Bryan K.; Clay, Raymond C., III; Delaney, Kris T.; Dewing, Mark; Esler, Kenneth P.; Hao, Hongxia; Heinonen, Olle; Kent, Paul R. C.; Krogel, Jaron T.; Kylänpää, Ilkka; Li, Ying Wai; Lopez, M. Graham; Luo, Ye; Malone, Fionn D.; Martin, Richard M.; Mathuriya, Amrita; McMinis, Jeremy; Melton, Cody A.; Mitas, Lubos; Morales, Miguel A.; Neuscamman, Eric; Parker, William D.; Pineda Flores, Sergio D.; Romero, Nichols A.; Rubenstein, Brenda M.; Shea, Jacqueline A. R.; Shin, Hyeondeok; Shulenburger, Luke; Tillack, Andreas F.; Townsend, Joshua P.; Tubman, Norm M.; Van Der Goetz, Brett; Vincent, Jordan E.; ChangMo Yang, D.; Yang, Yubo; Zhang, Shuai; Zhao, Luning
2018-05-01
QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater–Jastrow type trial wavefunctions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary-field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit and graphical processing unit systems. We detail the program’s capabilities, outline its structure, and give examples of its use in current research calculations. The package is available at http://qmcpack.org.
A suggested periodic table up to Z≤ 172, based on Dirac-Fock calculations on atoms and ions.
Pyykkö, Pekka
2011-01-07
Extended Average Level (EAL) Dirac-Fock calculations on atoms and ions agree with earlier work in that a rough shell-filling order for the elements 119-172 is 8s Periodic Table develops further that of Fricke, Greiner and Waber [Theor. Chim. Acta 1971, 21, 235] by formally assigning the elements 121-164 to (nlj) slots on the basis of the electron configurations of their ions. Simple estimates are made for likely maximum oxidation states, i, of these elements M in their MX(i) compounds, such as i = 6 for UF(6). Particularly high i are predicted for the 6f elements.
QED Based Calculation of the Fine Structure Constant
Energy Technology Data Exchange (ETDEWEB)
Lestone, John Paul [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-10-13
Quantum electrodynamics is complex and its associated mathematics can appear overwhelming for those not trained in this field. Here, semi-classical approaches are used to obtain a more intuitive feel for what causes electrostatics, and the anomalous magnetic moment of the electron. These intuitive arguments lead to a possible answer to the question of the nature of charge. Virtual photons, with a reduced wavelength of λ, are assumed to interact with isolated electrons with a cross section of πλ^{2}. This interaction is assumed to generate time-reversed virtual photons that are capable of seeking out and interacting with other electrons. This exchange of virtual photons between particles is assumed to generate and define the strength of electromagnetism. With the inclusion of near-field effects the model presented here gives a fine structure constant of ~1/137 and an anomalous magnetic moment of the electron of ~0.00116. These calculations support the possibility that near-field corrections are the key to understanding the numerical value of the dimensionless fine structure constant.
International Nuclear Information System (INIS)
Loevvik, O.M.; Prytz, O.
2004-01-01
The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP 3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP 3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P 3 skutterudite structures are promising materials for thermoelectric applications
Femtosecond structural dynamics on the atomic length scale
Energy Technology Data Exchange (ETDEWEB)
Zhang, Dongfang
2014-03-15
This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm{sup 2}) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO{sub 2} and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been
Electronic and atomic structure at metal-oxide heterointerfaces
Energy Technology Data Exchange (ETDEWEB)
Schlueter, Christoph Friedrich
2013-07-01
The results of a series of investigations on modern oxide materials using hard X-ray photoelectron spectroscopy (HAXPES) combined with the X-ray standing wave (XSW) method are described in this thesis. The combination of hard X-ray photoelectron spectroscopy and X-ray standing waves enables the electronic structure to be measured with a spatial resolution in the picometer range. Under suitable preparation conditions, a quasi two-dimensional electron gas (2DEG) is formed at the heterointerfaces of strontium titanate (SrTiO{sub 3}) with polar oxides, such as lanthanum aluminate (LaAlO{sub 3}) or lanthanum gallate (LaGaO{sub 3}). Samples were grown at the ESRF and in Naples and surface X-ray diffraction confirmed the excellent epitaxial quality of the films. The XSW-method was used to reconstruct images of the structure of LaAlO{sub 3} layers in real space. These images give evidence of distortions in the LaAlO{sub 3} structure which facilitate the compensation of the potential differences. Furthermore, XSW/HAXPES measurements permit the Ti and Sr,O contributions to the 2DEG close to the Fermi level to be identified unambiguously. The analysis shows that the 3d band crosses the Fermi level and that some density of states is associated with oxygen vacancies. Superlattices of SrTiO{sub 3} with polar calcium cuprate (CaCuO{sub 2}) were investigated by HAXPES. Similar to the case of SrTiO{sub 3}/LaAlO{sub 3}, the polarity of CaCuO{sub 2} should lead to a diverging surface potential. The core level spectra from Ca, Sr, and Ti show that there is a redistribution mechanism for oxygen which compensates the potential differences. When the oxygen concentration is enhanced these superstructures become superconducting (T{sub C} = 40 K). The increased oxidation of the superconducting material is revealed by the additional components in the core level spectra of the metal atoms and in the appearance of a new screening channel in Cu 2p core level spectra, which signals the hole
Electronic and atomic structure at metal-oxide heterointerfaces
International Nuclear Information System (INIS)
Schlueter, Christoph Friedrich
2013-01-01
The results of a series of investigations on modern oxide materials using hard X-ray photoelectron spectroscopy (HAXPES) combined with the X-ray standing wave (XSW) method are described in this thesis. The combination of hard X-ray photoelectron spectroscopy and X-ray standing waves enables the electronic structure to be measured with a spatial resolution in the picometer range. Under suitable preparation conditions, a quasi two-dimensional electron gas (2DEG) is formed at the heterointerfaces of strontium titanate (SrTiO 3 ) with polar oxides, such as lanthanum aluminate (LaAlO 3 ) or lanthanum gallate (LaGaO 3 ). Samples were grown at the ESRF and in Naples and surface X-ray diffraction confirmed the excellent epitaxial quality of the films. The XSW-method was used to reconstruct images of the structure of LaAlO 3 layers in real space. These images give evidence of distortions in the LaAlO 3 structure which facilitate the compensation of the potential differences. Furthermore, XSW/HAXPES measurements permit the Ti and Sr,O contributions to the 2DEG close to the Fermi level to be identified unambiguously. The analysis shows that the 3d band crosses the Fermi level and that some density of states is associated with oxygen vacancies. Superlattices of SrTiO 3 with polar calcium cuprate (CaCuO 2 ) were investigated by HAXPES. Similar to the case of SrTiO 3 /LaAlO 3 , the polarity of CaCuO 2 should lead to a diverging surface potential. The core level spectra from Ca, Sr, and Ti show that there is a redistribution mechanism for oxygen which compensates the potential differences. When the oxygen concentration is enhanced these superstructures become superconducting (T C = 40 K). The increased oxidation of the superconducting material is revealed by the additional components in the core level spectra of the metal atoms and in the appearance of a new screening channel in Cu 2p core level spectra, which signals the hole doping of the CaCuO 2 blocks. Magnetoresistive
Femtosecond structural dynamics on the atomic length scale
International Nuclear Information System (INIS)
Zhang, Dongfang
2014-03-01
This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm 2 ) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO 2 and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been deeply involved in
International Nuclear Information System (INIS)
Serezhkin, V.N.; Buslaev, Yu.A.; Mikhajlov, Yu.N.
1997-01-01
New method for determination of coordination numbers (CN) of atoms in crystal structures, based on the model of interatomic interaction, within the frames whereof each atom is approximated by two spheres with the common center in the atom nuclei, is proposed. One of the spheres specifies conditionally isolated (chemically unbound) atom and its radius is a constant, which for atoms of the given chemical sort in the structure of any compound is equal to quasi-orbital Sleiter radius. The sphere of the other radius specifies chemically bound atom and coincides with the sphere, the volume whereof is equal to the volume of the Voronoj-Dirichlet polyhedron of the corresponding atom in the structure of the concrete crystal. Using a series of examples, workability of the given method for CN determination of atoms in structures of both simple substances and chemical compounds (alkali, transition metals, U, Th). Good agreement of the obtained results with the generally accepted CN s of atoms for the considered crystals is noted and a number of principal advantages of the new method, as compared to classical one of the CNs evaluation, is demonstrated
Evangelisti, Luca; Pate, Brooks
2017-06-01
A study of the minimally exciting topic of agreement between experimental and measured rotational constants of molecules was performed on a set of large molecules with 16-18 heavy atoms (carbon and oxygen). The molecules are: nootkatone (C_{15}H_{22}O), cedrol (C_{15}H_{26}O), ambroxide (C_{16}H_{28}O), sclareolide (C_{16}H_{22}O_{2}), and dihydroartemisinic acid (C_{15}H_{24}O_{2}). For this set of molecules we obtained 13C-subsitution structures for six molecules (this includes two conformers of nootkatone). A comparison of theoretical structures and experimental substitution structures was performed in the spirit of the recent work of Grimme and Steinmetz.[1] Our analysis focused the center-of-mass distance of the carbon atoms in the molecules. Four different computational methods were studied: standard DFT (B3LYP), dispersion corrected DFT (B3LYP-D3BJ), hybrid DFT with dispersion correction (B2PLYP-D3), and MP2. A significant difference in these theories is how they handle medium range correlation of electrons that produce dispersion forces. For larger molecules, these dispersion forces produce an overall contraction of the molecule around the center-of-mass. DFT poorly treats this effect and produces structures that are too expanded. MP2 calculations overestimate the correction and produce structures that are too compact. Both dispersion corrected DFT methods produce structures in excellent agreement with experiment. The analysis shows that the difference in computational methods can be described by a linear error in the center-of-mass distance. This makes it possible to correct poorer performing calculations with a single scale factor. We also reexamine the issue of the "Costain error" in substitution structures and show that it is significantly larger in these systems than in the smaller molecules used by Costain to establish the error limits. [1] Stefan Grimme and Marc Steinmetz, "Effects of London dispersion correction in density functional theory on
International Nuclear Information System (INIS)
Gverdtsiteli, I.G.; Guldamashvili, A.I.; Sadagashvili, M.I.
1989-01-01
Single analytic relations are derived for calculating relative contributions of different profile components (unchanneled, partly channeled and well channeld ions) produced by multiple scattering of incident ions in an amorphous surface layer of a target. Calculated values of profile components are in good agreement with available experimental data at different values of ion energies, angles and incident planes of ions, crystallographic orientation, depth of the amorphous surface layer of target, orientation exactness and ion beam divergence. Those analytical relations permit to give account of features and nature of profile shape behaviour as a function of experimental conditions and to make an optimal choice parameters of ion alloying to obtain a profile of required shape
International Nuclear Information System (INIS)
Shein, I.R.; Ivanovskii, A.L.
2014-01-01
Highlights: • α and β polymorphs of BaZn 2 As 2 as a parent phase of the new DMSs are examined. • Structural, elastic, electronic properties are evaluated from first principles. • Inter-atomic bonding picture is discussed. -- Abstract: Very recently, on the example of hole- and spin-doped BaZn 2 As 2 , quite an unexpected area of potential applications of 122-like phases was proposed as a promising platform for searching the new diluted magnetic semiconductors (DMSs) (2013; K. Zhao, et al, Nature Commun. 4:1442). Herein, by means of the first-principles calculations, we have examined in detail the basic structural, elastic, electronic properties and the peculiarities of the inter-atomic bonding in α and β polymorphs of 122-like BaZn 2 As 2 – a parent phase of the new DMSs. Our characterization of these materials covers the optimized structural parameters, the main elastic parameters (elastic constants, bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropy indexes, and Pugh’s criterion), as well as electronic bands and densities of electronic states
Czech Academy of Sciences Publication Activity Database
Vackář, Jiří; Šipr, Ondřej; Šimůnek, Antonín
2008-01-01
Roč. 77, č. 4 (2008), 045112/1-045112/6 ISSN 1098-0121 R&D Projects: GA AV ČR IAA100100514; GA AV ČR(CZ) IAA100100637 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z10100521 Keywords : core levels * ab-initio calculations * electronic states * ground state properties Subject RIV: BE - Theoretical Physics Impact factor: 3.322, year: 2008
Energy Technology Data Exchange (ETDEWEB)
Shamim, Md; Harbola, Manoj K, E-mail: sami@iitk.ac.i, E-mail: mkh@iitk.ac.i [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)
2010-11-14
Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.
International Nuclear Information System (INIS)
Shamim, Md; Harbola, Manoj K
2010-01-01
Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.