| 51. |
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| 52. |
- Li, Jiguang, et al.
(författare)
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MF -dependent Hyperfine Induced Transition Rates in an External Magnetic Field for Be-like 47Ti18
- 2011
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Ingår i: Physics Letters A. - : Elsevier. - 0375-9601 .- 1873-2429. ; 375:5, s. 914-917
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Tidskriftsartikel (refereegranskat)abstract
- Hyperfine induced 2s2pP03→2s2S01 transition rates in an external magnetic field for Be-like 47Ti were calculated based on the multiconfiguration Dirac-Fock method. It was found that the transition probability is dependent on the magnetic quantum number M of the excited state, even in the weak field. The present investigation clarifies that the difference of the hyperfine induced transition rate of Be-like Ti ions between experiment [Schippers, et al., Phys. Rev. Lett. 98 (2007) 033001(4)] and theory does not result from the influence of external magnetic field.
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| 53. |
- Li, Jiguang, et al.
(författare)
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On the breakdown of the Dirac kinetic energy operator for estimating normal mass shifts
- 2012
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Ingår i: European Physical Journal D. - : EDP Sciences. - 1434-6060 .- 1434-6079. ; 66, s. 290-297
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Tidskriftsartikel (refereegranskat)abstract
- The Dirac kinetic energy (DKE) form of the normal mass shift operator (me/M ∑i=1N Ti), which is an approximation of the (1/2M ∑i=1N pi2) operator built on the relativistic electron momenta, is widely used in relativistic atomic structure calculations. In the present paper, we illustrate the progressive breakdown of the Dirac kinetic energy form relatively to the momentum form when increasing the nuclear charge along the lithium isoelectronic sequence. Both forms are incorrect in the relativistic case but the DKE operator provides expectation values that are closer to the results obtained with the more complete relativistic recoil operator.
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| 54. |
- Li, Jiguang, et al.
(författare)
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Re-Evaluation of the Nuclear Magnetic Octupole Moment of Bi-209
- 2022
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- We modified the Hfs92 code of the GRASP package in order to describe the magnetic octupole hyperfine interaction. To illustrate the utility of the modified code, we carried out state-of-the-art calculations of the electronic factors of the magnetic octupole hyperfine interaction constants for levels in the ground configuration of the Bi atom. The nuclear magnetic octupole moment of the Bi-209 isotope was extracted by combining old measurements of the hyperfine structures of 6p(34)S(3/2)(o) [Hull, R.; Brink, G. Phys. Rev. A 1970, 1, 685] and 2P(3/2)(o) [Landman, D.A.; Lurio, A. Phys. Rev. A 1970, 1, 1330] using the atomic-beam magnetic-resonance technique with our theoretical electronic factors. The present extracted octupole moment was consistent with all the available values but the one obtained in the single-particle nuclear shell model approximation. This observation supports the previous finding that nuclear many-body effects, such as the core polarization, significantly contribute to the nuclear magnetic octupole moment in the case of Bi-209.
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| 55. |
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| 56. |
- Li, Jiguang, et al.
(författare)
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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
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:3
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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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| 57. |
- Li, Yanting, et al.
(författare)
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Fine-Tuning of Atomic Energies in Relativistic Multiconfiguration Calculations
- 2023
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculations sometimes do not reproduce the experimentally observed energy separations at a high enough accuracy. Fine-tuning of diagonal elements of the Hamiltonian matrix is a process which seeks to ensure that calculated energy separations of the states that mix are in agreement with experiment. The process gives more accurate measures of the mixing than can be obtained in ab initio calculations. Fine-tuning requires the Hamiltonian matrix to be diagonally dominant, which is generally not the case for calculations based on jj-coupled configuration state functions. We show that this problem can be circumvented by a method that transforms the Hamiltonian in jj-coupling to a Hamiltonian in LSJ-coupling for which fine-tuning applies. The fine-tuned matrix is then transformed back to a Hamiltonian in jj-coupling. The implementation of the method into the General Relativistic Atomic Structure Package is described and test runs to validate the program operations are reported. The new method is applied to the computation of the 2s(21)S(0)-2s2p(1,3)P(1) transitions in C III and to the computation of Rydberg transitions in B I, for which the 2s(2)p(22)S(1/2) perturber enters the 2s(2)ns(2)S(1/2) series. Improved convergence patterns and results are found compared with ab initio calculations.
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| 58. |
- Li, Yanting, et al.
(författare)
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Independently Optimized Orbital Sets in GRASP : The Case of Hyperfine Structure in Li I
- 2023
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- In multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations, there is a strong coupling between the localization of the orbital set and the configuration state function (CSF) expansion used to determine it. Furthermore, it is well known that an orbital set resulting from calculations, including CSFs describing core-core correlation and other effects, which aims to lower the weighted energies of a number of targeted states as much as possible, may be inadequate for building CSFs that account for correlation effects that are energetically unimportant but decisive for computed properties, e.g., hyperfine structures or transition rates. This inadequacy can be traced in irregular or oscillating convergence patterns of the computed properties as functions of the increasing orbital set. In order to alleviate the above problems, we propose a procedure in which the orbital set is obtained by merging several separately optimized, and mutually non-orthogonal, orbital sets. This computational strategy preserves the advantages of capturing electron correlation on the total energy through the variational MCDHF method and allows to target efficiently the correlation effects on the considered property. The orbital sets that are merged are successively orthogonalized against each other to retain orthonormality. The merged orbital set is used to build CSFs that efficiently lower the energy and also adequately account for the correlation effects that are important for the property. We apply the procedure to compute the hyperfine structure constants for the 1s(2)2s (2)S1/2 and 1s(2)2p (2Po)(1/2, 3/2) states in Li-7 and show that it leads to considerably improved convergence patterns with respect to the increasing orbital set compared to standard calculations based on a single orbital set, energy optimized in the variational procedure. The perspectives of the new procedure are discussed in a broader context in the summary.
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| 59. |
- Li, Yanting, et al.
(författare)
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Performance Tests and Improvements on the rmcdhf and rci Programs of GRASP
- 2023
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The latest published version of GRASP (General-purpose Relativistic Atomic Structure Package), i.e., GRASP2018, retains a few suboptimal subroutines/algorithms, which reflect the limited memory and file storage of computers available in the 1980s. Here we show how the efficiency of the relativistic self-consistent-field (SCF) procedure of the multiconfiguration-Dirac-Hartree-Fock (MCDHF) method and the relativistic configuration-interaction (RCI) calculations can be improved significantly. Compared with the original GRASP codes, the present modified version reduces the CPU times by factors of a few tens or more. The MPI performances for all the original and modified codes are carefully analyzed. Except for diagonalization, all computational processes show good MPI scaling.
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| 60. |
- Li, Yan Ting, et al.
(författare)
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Reducing the computational load : atomic multiconfiguration calculations based on configuration state function generators
- 2023
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Ingår i: Computer Physics Communications. - : Elsevier. - 0010-4655 .- 1879-2944. ; 283, s. 108562-108562
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Tidskriftsartikel (refereegranskat)abstract
- In configuration interaction (CI) calculations the atomic wave functions are given as expansions over configuration state functions (CSFs) built on relativistic one-electron orbitals. The expansion coefficients of the configuration state functions are obtained by constructing and diagonalizing the Hamiltonian matrix. Here we show how a regrouping of the configuration state functions and the introduction of configuration state function generators (CSFGs) allow for a substantial reduction of the computational load in relativistic CI calculations. The computational methodology based on configuration state function generators, recently implemented in the General Relativistic Atomic Structure package (Grasp2018, Froese Fischer et al. (2019) [16]), is applied to a number of atomic systems and correlation models with increasing sets of one-electron orbitals. We demonstrate a reduction of the CPU time with factors between 10 and 14 for the largest CI calculations. The inclusion of the Breit interaction into the calculations is time consuming. By applying restrictions on the Breit integrals we show that it is possible to further reduce the CPU times with factors between 2 and 3, with negligible changes to the computed excitation energies. We also demonstrate that the introduction of configuration state function generators allows for efficient a priori condensation techniques, with reductions of the expansions sizes with factors between 1.5 and 2.5 and the CPU time with factors between 2.5 and 4.5, again with negligible changes to the excitation energies. In total we demonstrate reductions of the CPU time with factors up to 68 for CI calculations based on configuration state function generators, restrictions on the Breit integrals and with a priori condensed expansions compared to ordinary CI calculations without restrictions on the Breit integrals and with full expansions. Further perspectives of the new methodology based on configuration state function generators are given.
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