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Sökning: WFRF:(Gaigalas Gediminas) > Engelska > Annan publikation

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1.
  • Bengtsson, Peter, et al. (författare)
  • Energy structure and transition rates in the Ne-like sequence from relativistic CI calculations
  • 2012
  • Ingår i: Europhysics Conference Abstracts;36C. - European Physical Society. - 2-914771-75-4 ; :36C
  • Annan publikation (övrigt vetenskapligt)abstract
    • Atomic data are important in astrophysical applications and transition rates can be used in the determination of element abundances and plasma diagnostics. To provide for the extensive data needs a number of general computer codes such as SUPERSTRUCTURE, CIV3, and ATSP2K have been developed. As an alternative to these codes, which all rely on the Breit-Pauli approximation, the fully relativistic GRASP2K code can be used. GRASP2K is based on the multiconfiguration Dirac-Hartree-Fock method and implements a bi-orthogonal transformation method that permits initial and final states in a transition array to be optimized separately, which, in many cases, leads to more accurate values of the resulting rates. The GRASP2K package also contains modules to compute diagonal and off-diagonal hyperfine interaction constants, isotope shifts, Land´e gJ factors, and splittings of magnetic sub-state in intermediate and strong magnetic fields. In this work, GRASP2K has been applied to provide highly accurate spectroscopic data for ions in the Ne-like sequence between Mg III and Kr XXVII. Valence, core-valence, and core-core correlation effects were accounted for through SD-MR expansions to increasing sets of active orbitals. In Mg III, Al IV, Si V, P VI, S VII, and Ar IX, for which experimental energies are known to high accuracy, the mean error in the calculated energies is only 0.011%. For ions with no available experimental energy levels the calculated values should be most valuable in various applications. The high accuracy of the calculated energies makes it possible, in some cases, to to point out experimental values that are in error. Babushkin (length) and Coulomb (velocity) forms of transition rates are computed and agree to within a few percent for the majority of the allowed transitions. Computed lifetimes for states belonging to the 2p33s and 2p53d configurations are in good agreement with values from beam-foil measurements as well as from accurate MCHF Breit-Pauli calculations.
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2.
  • Bieron, Jacek, et al. (författare)
  • Computational Atomic Structure
  • 2012
  • Ingår i: Program and Abstracts : Eighth International Conference on Atomic and Molecular Data and Their Applications: ICAMDATA 8.
  • Annan publikation (övrigt vetenskapligt)abstract
    • There is an increasing demand for accurate atomic data due to advancements in experimental techniques and investments in large scale research facilities. In astrophysics the quality and resolution of solar and stellar spectra has so improved that the accuracy of atomic data is frequently a limiting factor in the interpretation. Accurate atomic data are also required in plasma physics and in other emerging areas such as laser spectroscopy on isotope separators, X-ray lithography, and lighting research. The needs include accurate transition energies, fine- and hyperfine structures, isotope shifts as well as parameters related to interaction with external magnetic fields. Also there is a constant need for transition rates between excited states. Data are needed for a wide range of elements and ionization stages. To meet the demands for accurate atomic data the COMPutational Atomic Structure (COMPAS) group has been formed. The group is involved in developing state of the art computer codes for atomic calculations in the non-relativistic scheme with relativistic corrections in the Breit-Pauli approximation [1] as well as in the fully relativistic domain. Here we describe new developments of the GRASP2K relativistic atomic structure code [2, 3]. We present results for a number of systems and properties to illustrate the potential and restriction of computational atomic structure. Among the properties are hyperfine structures and hyperfine quenched rates, Zeeman splittings in intermediate fields, isotope shifts and transition rates [4]. We also discuss plans for future code developments.
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3.
  • Froese Fischer, Charlotte, et al. (författare)
  • Configuration interaction with separately optimized pair correlation functions
  • 2010
  • Annan publikation (övrigt vetenskapligt)abstract
    • Variational methods produce one-electron radial functions that minimize the total energy of the system. Independent pair correlation functions (PCFs) designed to represent a specific correlation effect – valence, core-valence, or core-core – can be obtained from multiconfiguration Hartree-Fock (MCHF) or Dirac-Hartree-Fock (MCDHF) calculations [1,2]. These separately optimized and nonorthogonal PCFs may then be coupled by solving the associated generalized eigenproblem. In the present study, the Hamiltonian and overlap matrix elements are evaluated through biorthonormal orbital transformations and efficient counter-transformation of the configuration interaction eigenvectors [3]. The ground state of Be atom has been thoroughly tested by this method for various computational strategies and correlation models. It has been shown that the energy convergence is faster than with the usual SD-MCHF method of optimizing a single, orthonormal, one-electron orbital basis spanning the complete configuration space. Beryllium is a small system for which basis saturation can be achieved through complete active space MCHF expansions. But for larger systems describing electron correlation in all space by optimizing a common orthonormal set becomes hopeless whereas the calculation of additional PCFs is straight forward. Our independent optimization scheme, raises many questions related in the choice of the zero-order model to be used when building the interaction matrix. The present study is the first step in the current development of the extension of the atsp2K and grasp2K packages [1,2] that will adopt the biorthonormal treatment for energies, isotope shifts, hyperfine structures and transition probabilities.
4.
  • Gaigalas, Gediminas, et al. (författare)
  • Energies for States of the 2s22p5 and 2s2p6 in Fluorine-like Ions Between Si VI and W LXVI
  • 2012
  • Ingår i: Program and Abstracts : Eighth International Conference on Atomic and Molecular Data and Their Applications: ICAMDATA 8.
  • Annan publikation (övrigt vetenskapligt)abstract
    • The experimental energy levels and computed energies from the largest RCI calculations including QED corrections are displayed in Table 1. The computed energies agree very well with experimental values. Starting from Si VI the energy differences rapidly goes down to a few hundred cm−1 , which corresponds to an error of around 0.02 %. From Sr XXX to Sn XLII experimental energies are given with error bars between 1000 and 2000 cm−1 . The calculated values are within the stated experimental error bars except for Cd XL and Sn XLII. The reason for the difference in these two ions is not known. Experimental data for ions from Sb XLIII to Ta LXV are not available. For the W LXVI ion, the differences between theoretical and experimental transition energies are a few thousand cm−1 . As discussed by Kramida [1] the total uncertainties of the measured energies in W LXVI were dominated by the calibration uncertainties and varied in the range 1.0 - 2.3 eV, which translates to 8000 - 20000 cm−1 . Based on the comparison between theory and experiment for the lighter ions as well as for W LXVI we estimate that the errors in the calculated transition energies for ions in the range Sb XLIII - Ta LXV, for which no experimental data are available, are less than 0.08 %.
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5.
  • Jönsson, Per, et al. (författare)
  • Accurate Transition Probabilities from Large-scale Multiconfiguration Calculations
  • 2012
  • Ingår i: Program and Abstracts : Eighth International Conference on Atomic and Molecular Data and Their Applications: ICAMDATA 8.
  • Annan publikation (övrigt vetenskapligt)abstract
    • The quality and resolution of solar, stellar, and other types of plasma observations, has so improved that the accuracy of atomic data is frequently a limiting factor in the interpretation of these new observations. An obvious need is for accurate transition probabilities. Laboratory measurements, e.g. using ion/traps, beam-foil or laser techniques, have been performed for isolated transitions and atoms, but no systematic laboratory study exists or is in progress. Instead the bulk of these atomic data must be calculated. Multiconfiguration methods, either non-relativistic with Breit-Pauli corrections (MCHF+BP) or fully relativistic (MCDHF), are useful to this end. The main advantage of multiconfiguration methods is that they are readily applicable to excited and openshell systems, including open f-shells, across the whole periodic table, thus allowing for mass production of atomic data. The accuracy of these calculations depends on the complexity of the shell structure and on the underlying model for describing electron correlation. By systematically increasing the number of basis functions in large-scale calculations, as well as exploring different models for electron correlation, it is often possible to provide both transition energies and transition probabilities with some error estimate. The success of the calculations also depends on available computer software. In this talk we will describe a collaborative effort to continue the important and acclaimed work of Prof. Charlotte Froese Fischer and to develop state-of-the-art multiconfiguration codes. In the latest versions of the non-relativistic (ATSP2K) and relativistic (GRASP2K) multiconfiguration codes angular integration is performed using second quantization in the coupled tensorial form, angular momentum theory in three spaces (orbital, spin and quasispin), and a generalized graphical technique that allows open f-shells. In addition it is possible to transform results given in the relativistic j j-coupling to the more useful LSJ-coupling. Biorthogonal transformation techniques are implemented and initial and final states in a transition can be separately optimized. The main parts of the codes are also adapted for parallel execution using MPI. Results from recent large-scale calculations using these codes will be presented for systems of different complexity. Of special interest are spectrum calculations, where all states up to a certain level are computed at the same time. Finally, we look at new computational developments that allow basis functions in multiconfiguration methods to be built on several independent and non-orthogonal sets of one-electron orbitals. Initial calculations indicate that the increased flexibility of the orbital sets allows transition energies, as well as other atomic properties, to be predicted to a much higher accuracy than before.
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8.
  • Jönsson, Per, et al. (författare)
  • The ATSP2K and GRASP2K Multiconfiguration Atomic Structure Program Packages
  • 2013
  • Ingår i: Book of abstracts. - Institute of Modern Physics, Chinese Academy of Sciences.
  • Annan publikation (övrigt vetenskapligt)abstract
    • Synopsis The ATSP2K and GRASP2K program packages for large scale atomic calculations are presented. A number of applications are given to illustrate the potential and restriction of the packages.
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10.
  • Li, Jiguang, et al. (författare)
  • Mass and field isotope shift parameters for the 2s-2p resonance doublet of Lithium-like ions
  • 2012
  • Ingår i: Book of Abstracts : 16th International Conference Physics of Highly Charged Ions.
  • Annan publikation (övrigt vetenskapligt)abstract
    • Recently, it was shown that the dielectronic recombination measurements can be used for accurately inferring changes in the nuclear mean-square charge radii of highly-charged lithium-like neodymium [1]. To make use of this method for other elements and isotopes, mass and field isotope shift calculations are required in order to derive information about the nuclear charge distributions. In this work [2], we estimate the relativistic mass and field isotope shift factors for the two 2s2 S1/2−2p 2Po 1/2,3/2 transitions along the lithium isoelectronic sequence using the GRASP2K package [3, 4] based on the multiconfiguration Dirac-Hartree-Fock method. The detailed comparisons with the MCDF-gme [5] calculations and others will be illustrated. Adopting the calculated electronic parameters of isotope shifts, we analyze the competition between the mass and field shift contributions for the 2s − 2p resonance doublet along the isoelectronic sequence, with the assistance of the empirical relations between Z and the nuclear properties. It is found that the mass shifts and the field shifts possess similar orders of magnitude in the Z < 40 range, so that one should consider both of them for a relevant analysis of isotope shifts. The field shift contribution grows rapidly towards the high-Z region and becomes quickly dominant. Discussions are also made for the 2s 2S1/2 − 2p 2Po 1/2,3/2 line isotope shifts in the case of 150,142 Nd 57+ where the experimental values are available. The present results show that the higher-order nuclear moments often neglected in the calculation of the field shift should be considered for very highly charged ions in order to extract the δ⟨r2⟩ values from experiments.
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