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Sökning: WFRF:(Gaigalas Gediminas) > (2010)

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1.
  • Froese Fischer, Charlotte, et al. (författare)
  • Configuration interaction with separately optimized pair correlation functions
  • 2010
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
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2.
  • Jönsson, Per, et al. (författare)
  • Hyperfine structures, isotope shifts and transition rates of C II, N III, and O IV from relativistic configuration interaction calculations
  • 2010
  • Ingår i: Atomic Data and Nuclear Data Tables. - : Elsevier. - 0092-640X .- 1090-2090. ; 96:3, s. 271-298
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy levels, specific mass shift parameters, hyperfine interaction constants, Landé gJ factors, and transition probabilities between computed levels are reported for C II, N III, and O IV. Results include levels belonging to 2s22p,2s2p2,2p3,2s23s,2s23p,2s23d,2s2p3s and, in the case of C II, the 2s24s and 2s24p configurations. Wavefunctions were determined using the multiconfiguration Dirac–Hartree–Fock method and account for valence, core–valence, and core–core correlation effects.
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  • Li, Jiguang, et al. (författare)
  • Two-electron-one-photon M1 and E2 transitions between states of the 2p3 and 2s22p odd configurations of B-like ions with 18 ≤ Z ≤ 92
  • 2010
  • Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-electron–one-photon (TEOP) M1 and E2 transition energies, line strengths and transition probabilities between the states of the 2p3 and 2s22p odd configurations for B-like ions with 18 ≤ Z ≤ 92 have been calculated using the GRASP2K package based on the multiconfiguration Dirac–Hartree–Fock (MCDHF) method. Employing active-space techniques to expand the configuration list, we have systematically considered the valence, core–valence and core–core electron correlation effects. Breit interaction and quantum electrodynamical (QED) effects were also included to correct atomic state wavefunctions and the corresponding energies. Influences of electron correlation, Breit interaction and QED effects on transition energies and line strengths of the TEOP M1 and E2 transitions were analysed in detail. The present results were also compared with other theoretical and experimental values.
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  • Verdebout, Simon, et al. (författare)
  • Exploring Biorthonormal Transformations of Pair-Correlation Functions in Atomic Structure Variational Calculations
  • 2010
  • Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 43:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Multiconfiguration expansions frequently target valence correlation and correlation between valence electrons and the outermost core electrons. Correlation within the core is often neglected. A large orbital basis is needed to saturate both the valence and core–valence correlation effects. This in turn leads to huge numbers of configuration state functions (CSFs), many of which are unimportant. To avoid the problems inherent to the use of a single common orthonormal orbital basis for all correlation effects in the multiconfiguration Hartree–Fock (MCHF) method, we propose to optimize independent MCHF pair-correlation functions (PCFs), bringing their own orthonormal one-electron basis. Each PCF is generated by allowing single- and double-excitations from a multireference (MR) function. This computational scheme has the advantage of using targeted and optimally localized orbital sets for each PCF. These pair-correlation functions are coupled together and with each component of the MR space through a low dimension generalized eigenvalue problem. Nonorthogonal orbital sets being involved, the interaction and overlap matrices are built using biorthonormal transformation of the coupled basis sets followed by a counter-transformation of the PCF expansions. Applied to the ground state of beryllium, the new method gives total energies that are lower than the ones from traditional complete active space (CAS)-MCHF calculations using large orbital active sets. It is fair to say that we now have the possibility to account for, in a balanced way, correlation deep down in the atomic core in variational calculations.
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