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| 2. |
- Froese Fischer, Charlotte, et al.
(författare)
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Doublet-quartet energy separation in boron : a partitioned-correlationfunction- interaction method
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 88:6
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Tidskriftsartikel (refereegranskat)abstract
- No lines have been observed for transitions between the doublet and quartet levels of B I. Consequently, energy levels based on observation for the latter are obtained through extrapolation of wavelengths along the isoelectronic sequence for the 2s22p 2Po 3/2 – 2s2p2 4P5/2 transition. In this paper, accurate theoretical excitation energies from a partitioned-correlation-function-interaction (PCFI) method are reported for B I that include both relativistic effects in the Breit-Pauli approximation and a finite mass correction. Results are compared with extrapolated values from observed data. For B I our estimate of the excitation energy 28 959 ± 5 cm−1 is in better agreement with the values obtained by Edl´en et al. (1969) than those reported by Kramida and Ryabtsev (2007). Our method is validated by applying the same procedure to the separation of these levels in C II.
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| 3. |
- Jönsson, Per, et al.
(författare)
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Accurate Transition Probabilities from Large-Scale Multiconfiguration Calculations : a Tribute to Charlotte Froese Fischer
- 2013
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics (AIP). - 0094-243X .- 1551-7616. ; 1545, s. 266-278
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Tidskriftsartikel (refereegranskat)abstract
- The development of multiconfiguration computer packages for atomic structure calculations is reviewed with special attention to the work of Charlotte Froese Fischer. The underlying theory is described along with methodologies to choose basis expansions of configuration state functions. Calculations of energies and transitions rates are presented and the accuracy of the results is assessed. Limitations of multiconfiguration methods are discussed and it is shown how these limitations can be circumvented by a division of the original large-scale computational problem into a number of smaller problems.
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| 5. |
- Jönsson, Per, et al.
(författare)
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Energy levels and transition rates for the boron isoelectronic sequence : Si X, Ti XVIII – Cu XXV
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 559
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Tidskriftsartikel (refereegranskat)abstract
- Relativistic configuration interaction (RCI) calculations are performed for 291 states belonging to the configurations 1s22s22p, 1s22s2p2, 1s22p3, 1s22s23l, 1s22s2p3l, 1s22p23l, 1s22s24l , 1s22s2p4l , and 1s22p24l (l = 0, 1,2 and l = 0, 1, 2, 3) in boron-like ions Si X and Ti XVIII to Cu XXV. Electron correlation effects are represented in the wave functions by large configuration state function (CSF) expansions. States are transformed from j j-coupling to LS -coupling, and the LS -percentage compositions are used for labeling the levels. Radiative electric dipole transition rates are given for all ions, leading to massive data sets. Calculated energy levels are compared with other theoretical predictions and crosschecked against the Chianti database, NIST recommended values, and other observations. The accuracy of the calculations are high enough to facilitate the identification of observed spectral lines.
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| 6. |
- Jönsson, Per, et al.
(författare)
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New version : grasp2K relativistic atomic structure package
- 2013
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Ingår i: Computer Physics Communications. - : Elsevier. - 0010-4655 .- 1879-2944. ; 84:9, s. 2197-2203
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Tidskriftsartikel (refereegranskat)abstract
- A revised version of Grasp2K [P. Jönsson, X. He, C. Froese Fischer, I.P. Grant, Comput. Phys. Commun. 177 (2007) 597] is presented. It supports earlier non-block and block versions of codes as well as a new block version in which the njgraf library module [A. Bar-Shalom, M. Klapisch, Comput. Phys. Commun. 50 (1988) 375] has been replaced by the librang angular package developed by Gaigalas based on the theory of [G. Gaigalas, Z.B. Rudzikas, C. Froese Fischer, J. Phys. B: At. Mol. Phys. 30 (1997) 3747, G. Gaigalas, S. Fritzsche, I.P. Grant, Comput. Phys. Commun. 139 (2001) 263]. Tests have shown that errors encountered by njgraf do not occur with the new angular package. The three versions are denoted v1, v2, and v3, respectively. In addition, in v3, the coefficients of fractional parentage have been extended to j = 9/2, making calculations feasible for the lanthanides and actinides. Changes in v2 include minor improvements. For example, the new version of rci2 may be used to compute quantum electrodynamic (QED) corrections only from selected orbitals. In v3, a new program, jj2lsj, reports the percentage composition of the wave function in LSJ and the program rlevels has been modified to report the configuration state function (CSF) with the largest coefficient of an LSJ expansion. The bioscl2 and bioscl3 application programs have been modified to produce a file of transition data with one record for each transition in the same format as in Atsp2K [C. Froese Fischer, G. Tachiev, G. Gaigalas, 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. All versions of the codes have been adapted for 64-bit computer architecture.
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| 7. |
- Jönsson, Per, et al.
(författare)
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The ATSP2K and GRASP2K Multiconfiguration Atomic Structure Program Packages
- 2013
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Ingår i: Book of abstracts. - : Institute of Modern Physics, Chinese Academy of Sciences.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 8. |
- Naze, Cedric, et al.
(författare)
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RIS3 : a program for relativistic isotope shift calculations
- 2013
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Ingår i: Computer Physics Communications. - : Elsevier. - 0010-4655 .- 1879-2944. ; 184:9, s. 2187-2196
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Tidskriftsartikel (refereegranskat)abstract
- An atomic spectral line is characteristic of the element producing the spectrum. The line also depends on the isotope. The program ris3 (Relativistic Isotope Shift) calculates the electron density at the origin and the normal and speci c mass shift parameters. Combining these electronic quantities with available nuclear data, isotope-dependent energy level shifts are determined
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| 9. |
- Rynkun, Pavel, et al.
(författare)
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Energies and E1, M1, E2, and M2 transition rates for states of the 2s22p4, 2s2p5, and 2p6 configurations in oxygen-like ions between F II and Kr XXIX
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; A136:557
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Tidskriftsartikel (refereegranskat)abstract
- Based on relativistic wave functions from multiconfiguration Dirac-Hartree-Fock and configuration interaction calculations, E1, M1, E2, M2 transition rates, weighted oscillator strengths, and lifetimes are evaluated for the states of the (1s2)2s22p4, 2s2p5, and 2p6 configurations in all oxygen-like ions between F II and Kr XXIX. Valence and core-valence correlation effects were accounted for through single-double multireference (SD-MR) expansions to increasing sets of active orbitals. Computed energies are compared with the NIST recommended values, generally differing by less than 600 cm−1. For some spectra, significantly larger differences are found and our results are in better agreement with Edlén interpolated values. For levels where experimental lifetimes are available, the agreement is within experimental uncertainty for all but a few lowly ionized spectra. Complete Online tables of energy levels and transition data are available.
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| 10. |
- Verdebout, Simon, et al.
(författare)
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A Partitioned Correlation Function Interaction approach for describing electron correlation in atoms
- 2013
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Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 46:8
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Tidskriftsartikel (refereegranskat)abstract
- The traditional multiconfiguration Hartree–Fock (MCHF) and configuration interaction (CI) methods are based on a single orthonormal orbital basis. For atoms with many closed core shells, or complicated shell structures, a large orbital basis is needed to saturate the different electron correlation effects such as valence, core–valence and correlation within the core shells. The large orbital basis leads to massive configuration state function (CSF) expansions that are difficult to handle, even on large computer systems. We show that it is possible to relax the orthonormality restriction on the orbital basis and break down the originally very large calculations into a series of smaller calculations that can be run in parallel. Each calculation determines a partitioned correlation function (PCF) that accounts for a specific correlation effect. The PCFs are built on optimally localized orbital sets and are added to a zero-order multireference (MR) function to form a total wave function. The expansion coefficients of the PCFs are determined from a low dimensional generalized eigenvalue problem. The interaction and overlap matrices are computed using a biorthonormal transformation technique (Verdebout et al 2010 J. Phys. B: At. Mol. Phys. 43 074017). The new method, called partitioned correlation function interaction (PCFI), converges rapidly with respect to the orbital basis and gives total energies that are lower than the ones from ordinary MCHF and CI calculations. The PCFI method is also very flexible when it comes to targeting different electron correlation effects. Focusing our attention on neutral lithium, we show that by dedicating a PCF to the single excitations from the core, spin- and orbital-polarization effects can be captured very efficiently, leading to highly improved convergence patterns for hyperfine parameters compared with MCHF calculations based on a single orthogonal radial orbital basis. By collecting separately optimized PCFs to correct the MR function, the variational degrees of freedom in the relative mixing coefficients of the CSFs building the PCFs are inhibited. The constraints on the mixing coefficients lead to small off-sets in computed properties such as hyperfine structure, isotope shift and transition rates, with respect to the correct values. By (partially) deconstraining the mixing coefficients one converges to the correct limits and keeps the tremendous advantage of improved convergence rates that comes from the use of several orbital sets. Reducing ultimately each PCF to a single CSF with its own orbital basis leads to a non-orthogonal CI approach. Various perspectives of the new method are given.
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