| 1. |
- Wang, Kai, et al.
(författare)
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Calculations with spectroscopic accuracy for energies, transition rates, hyperfine interaction constants, and Landé gJ-factors in nitrogen-like Kr XXX
- 2017
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier. - 0022-4073 .- 1879-1352. ; 187, s. 375-402
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Tidskriftsartikel (refereegranskat)abstract
- Extensive self-consistent multi-configuration Dirac-Fock(MCDF) calculations and second-order many- body perturbation theory (MBPT) calculations are performed for the lowest 272 states belonging to the 2s22p3, 2s2p4, 2p5, 2s22p23l, and2s2p33l (l¼s, p, d) configurations of N-like KrXXX.Complete and consistent datasets of level energies,wavelengths,line strengths, oscillator strengths,lifetimes, AJ, BJ hyperfine interaction constants,Landé gJ-factors, and electric dipole(E1),magnetic dipole(M1),electric quadrupole(E2),magnetic quadrupole(M2) transition rates among all these levels are given.The present MCDF and MBPTresults are compared with each other and with other available experimental and theoretical results.The mean relative difference between our two sets of level energies is only about 0.003% for these 272 levels.The accuracy of the present calculations are high enough to facilitate identification of many observed spectral lines.These accurate data can be served as benchmark for other calculations and can be useful for fusion plasma research and astrophysical applications.
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| 2. |
- Andersson, Martin, et al.
(författare)
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The anomalous hyperfine structure of Al II
- 2012
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 45:13
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Tidskriftsartikel (refereegranskat)abstract
- The hyperfine structure of a large number of transitions in Al II cannot be described using A and B hyperfine constants and the hyperfine structure is therefore said to be anomalous. In this paper, we have studied the hyperfine structure of a few transitions in Al II, 3s5s(3)S-3s5p(3)P, 3s4d(3)D-3s5p(3)P and 3s5p(3)P-3s5d(3)D, by combining theory and experiment. It is shown that the anomalous hyperfine structure is due to strong off-diagonal hyperfine interaction resulting not only in a deplacement of the energies of the hyperfine levels, but also resulting in large intensity redistribution among the individual hyperfine lines. It is shown that the hyperfine mixing in 3s4d(3)D and 3s5d(3)D is very large, whereas small but not negligible in 3s5p(3)P. By combining experimental spectra and theory we could obtain accurate wavefunctions for the 3s4d(3)D and 3s5d(3)D hyperfine levels which were used to calculate the gf-values of all individual hyperfine transitions not only for 3s5p(3)P, but also for 3s3p(3)P and 3s4p(3)P, where the off-diagonal hyperfine interaction leads to negligible intensity redistribution.
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| 3. |
- Guo, Xueling, et al.
(författare)
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Energy levels and radiative data for Kr-like W38+ from MCDHF and RMBPT calculations
- 2016
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:13
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Tidskriftsartikel (refereegranskat)abstract
- Energies, transition rates, line strengths and lifetimes have been computed for all levels of the 4p 6 and 4p 54d configurations of W38+ by using the multi-configuration Dirac-Hartree-Fock (MCDHF) method as well as relativistic many-body perturbation theory. We investigate systematically correlation, relativistic and quantum electro-dynamical (QED) effects of different properties, including excitation energies and transition rates. We demonstrate that it is important to include the core-valence correlation of rather deep subshells (including 3d and 3p) to reach close to spectroscopic accuracy for the transition energies. We also show that high-multipole transitions (E3, M2) are important for the lifetime of some metastable levels of 4p 54d (). The present results are in good agreement with experiments and of considerably higher accuracy than those achieved in previous theoretical works.
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| 4. |
- Li, Wenxian, et al.
(författare)
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A Novel Method to Determine Magnetic Fields in Low-density Plasma Facilitated Through Accidental Degeneracy of Quantum States in Fe9
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X. ; 807:1
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new method to determine magnetic fields, by using the magnetic-field-induced electric dipole transition 3p(4) 3d D-4(7/2) -> 3p(5) P-3/2 in Fe9+ ions. This ion has a high abundance in astrophysical plasma and is therefore well suited for direct measurements of even rather weak fields in, e.g., solar flares. This transition is induced by an external magnetic field and its rate is proportional to the square of the magnetic field strength. We present theoretical values for what we will label the reduced rate and propose that the critical energy difference between the upper level in this transition and the close-to-degenerate 3p(4) 3d D-4(5/2) should be measured experimentally since it is required to determine the relative intensity of this magnetic line for different magnetic fields.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Tang, Rulin, et al.
(författare)
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Candidate for Laser Cooling of a Negative Ion : High-Resolution Photoelectron Imaging of Th
- 2019
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Ingår i: Physical Review Letters. - 0031-9007. ; 123:20
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Tidskriftsartikel (refereegranskat)abstract
- Laser cooling is a well-established technique for the creation of ensembles of ultracold neutral atoms or positive ions. This ability has opened many exciting new research fields over the past 40 years. However, no negatively charged ions have been directly laser cooled because a cycling transition is very rare in atomic anions. Efforts of more than a decade currently have La- as the most promising candidate. We report on experimental and theoretical studies supporting Th- as a new promising candidate for laser cooling. The measured and calculated electron affinities of Th are, respectively, 4901.35(48) cm-1 and 4832 cm-1, or 0.607 690(60) and 0.599 eV, almost a factor of 2 larger than the previous theoretical value of 0.368 eV. The ground state of Th- is determined to be 6d37s2 F43/2e rather than 6d27s27p G45/2o. The consequence of this is that there are several strong electric dipole transitions between the bound levels arising from configurations 6d37s2 and 6d27s27p in Th-. The potential laser-cooling transition is S1/2o2↔F43/2e with a wavelength of 2.6 μm. The zero nuclear spin and hence lack of hyperfine structure in Th- reduces the potential complications in laser cooling as encountered in La-, making Th- a new and exciting candidate for laser cooling.
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| 9. |
- Tang, Rulin, et al.
(författare)
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Observation of electric-dipole transitions in the laser-cooling candidate Th- And its application for cooling antiprotons
- 2021
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Ingår i: Physical Review A. - 2469-9926. ; 103:4
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Tidskriftsartikel (refereegranskat)abstract
- Despite the fact that the laser-cooling method is a well-established technique to obtain ultracold neutral atoms and atomic cations, it has rarely if ever been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade have until recently only resulted in La- as a promising anion candidate for laser cooling, but our previous work [Tang et al., Phys. Rev. Lett. 123, 203002 (2019)10.1103/PhysRevLett.123.203002] showed that Th- is also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the frequencies and rates, as well as branching ratios, for the relevant transitions in Th-. The resonant frequency of the laser-cooling transition is determined to be ν=123.455(30) THz [λ=2428.4(6)nm]. The transition rate is calculated as A=1.17×104s-1. Since the branching fraction to dark states is negligible, 1.47×10-10, this represents an ideal closed cycle in Th- for laser cooling. Furthermore, the zero nuclear spin of Th232 makes the cooling process possible in a Penning trap, which can be used to confine both antiprotons and Th- ions. The presented ion dynamics simulations show that the laser-cooled Th- anions can effectively cool antiprotons to a temperature around 10 mK.
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| 10. |
- Wenxian, Li, et al.
(författare)
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A Novel Method to Determine Magnetic Fields in low-density Plasma eg Solar Flares Facilitated Through Accidental Degeneracy of Quantum States in Fe 9
- 2015
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Ingår i: Astrophysical Journal. - : Bibliopolis, Edizioni di Filosofia e Scienze. - 0004-637X .- 1538-4357. ; 807:1
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new method to determine magnetic fields, by using the magnetic-field-induced electric dipole transition 3p4 3d 4D 7 2 3p P 5 2 3 2 in Fe9+ ions. This ion has a high abundance in astrophysical plasma and is therefore well suited for direct measurements of even rather weak fields in, e.g., solar flares. This transition is induced by an external magnetic field and its rate is proportional to the square of the magnetic field strength. We present theoretical values for what we will label the reduced rate and propose that the critical energy difference between the upper level in this transition and the close-to-degenerate 3p4 3d 4D 5 2 should be measured experimentally since it is required to determine the relative intensity of this magnetic line for different magnetic fields.
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