| 1. |
- Papoulia, Asimina, et al.
(författare)
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Ab initio electronic factors of the A and B hyperfine structure constants for the 5s(2)5p6s( 1,3)P(1)(0) states in Sn I
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant B were performed for the 5s(2)5p6s( 1,3)P(1)(0)excited states of neutral tin. To probe the sensitivity of B to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the 5s(2)5p6s( 1)P(1)(0) state, the final value of B/Q = 703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments Q for tin isotopes in the range Sn117-131 from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5s(2)5p6s( 1)P(1)(0) state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant A.
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| 2. |
- Papoulia, Asimina, et al.
(författare)
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Ab initio electronic factors of the A and B hyperfine structure constants for the 5s25p6s1,3P01 states in Sn I
- 2021
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Ingår i: Physical Review A. - 2469-9926. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant B were performed for the 5s25p6s1,3Po1 excited states of neutral tin. To probe the sensitivity of B to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the 5s25p6s 1Po1 state, the final value of B/Q=703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments Q for tin isotopes in the range 117−131Sn from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5s25p6s 1Po1 state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant A.
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| 3. |
- Papoulia, Asimina, et al.
(författare)
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Coulomb (Velocity) Gauge Recommended in Multiconfiguration Calculations of Transition Data Involving Rydberg Series
- 2019
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- Astronomical spectroscopy has recently expanded into the near-infrared (nIR) wavelength region, raising the demands on atomic transition data. The interpretation of the observed spectra largely relies on theoretical results, and progress towards the production of accurate theoretical data must continuously be made. Spectrum calculations that target multiple atomic states at the same time are by no means trivial. Further, numerous atomic systems involve Rydberg series, which are associated with additional difficulties. In this work, we demonstrate how the challenges in the computations of Rydberg series can be handled in large-scale multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) calculations. By paying special attention to the construction of the radial orbital basis that builds the atomic state functions, transition data that are weakly sensitive to the choice of gauge can be obtained. Additionally, we show that the Babushkin gauge should not always be considered as the preferred gauge, and that, in the computations of transition data involving Rydberg series, the Coulomb gauge could be more appropriate for the analysis of astrophysical spectra. To illustrate the above, results from computations of transitions involving Rydberg series in the astrophysically important C IV and C III ions are presented and analyzed.
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| 4. |
- Schiffmann, Sacha, et al.
(författare)
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Atomic Structure Calculations of Landé
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 923:2
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Tidskriftsartikel (refereegranskat)abstract
- We perform a detailed theoretical study of the atomic structure of ions with ns 2 np m ground configurations and focus on departures from LS coupling, which directly affect the Landé g factors of magnetic dipole lines between levels of the ground terms. Particular emphasis is given to astrophysically abundant ions formed in the solar corona (those with n = 2,3) with M1 transitions spanning a broad range of wavelengths. Accurate Landé g factors are needed to diagnose coronal magnetic fields using measurements from new instruments operating at visible and infrared wavelengths, such as the Daniel K. Inouye Solar Telescope. We emphasize an explanation of the dynamics of atomic structure effects for nonspecialists.
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| 5. |
- Schiffmann, Sacha
(författare)
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Computational Atomic Structures Toward Heavy Element Research
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We are interested in complex electronic structures of various atomic and ionics systems. We use an ab initioapproach, the multiconfigurational Dirac-Hartree-Fock (MCDHF), to compute atomic structures and properties.We contribute in three main ways to the already existent literature: by developing and implementing originalcomputer programs, by investigating possibilities of alternative computational methodologies and strategies, andfinally by performing accurate atomic structure calculations to support other research fields, i.e., nuclear physics,astrophysics or experimental physics, through the theoretical estimation of relevant atomic data.We raise questions about the choice of the optimal orbital basis by considering finite basis sets, MCDHF orbitalbases and natural-orbital bases. We demonstrate the promising potential of the latter in the context of hyperfinestructures and hope that others will find interest in pursuing our analysis. Ultimately, our work put forward someweaknesses of the traditional optimization strategy based on the layer-by-layer optimization strategy.We also perform large-scale calculations to determine accurate atomic properties such as energy levels, hyperfinestructures, isotope shifts, transition parameters, radiative lifetimes and Landé g factors. We show through thevariety of atomic properties and atomic systems studied, the difficulty of describing, in the relativistic framework,the correlation between the spatial position of electrons due to their Coulomb repulsion.This thesis is organized in two main parts. The first one is dedicated to the theoretical and computationalbackgrounds that are needed to understand the theoretical models and the interpretation of our results. Thesecond part presents and summarizes our articles and manuscripts. They are separated in four groups, A, B, C,and D, around the themes of the atomic orbital bases, the applications to nuclear physics, the applications toastrophysics, and investigations of negative ions.
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| 6. |
- Schiffmann, Sacha, et al.
(författare)
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Electronic isotope shift factors for the Ir 5d76s24F9/2→(odd,J=9/2) line at 247.587 nm
- 2021
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- We present the theoretical calculations of the electronic isotope shift factors of the 5d76s24F9/2→(odd,J=9/2) line at 247.587 nm, that were recently used to extract nuclear mean square radii and nuclear deformations of iridium isotopes [Mukai et al. (2020)]. The fully relativistic multiconfiguration Dirac-Hartree-Fock method and the relativistic configuration interaction method were used to perform the atomic structure calculations. Additional properties such as the sharing rule, Landé g factors or phase tracking were employed to ensure an adequate description of the targeted odd level.
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| 7. |
- Schiffmann, Sacha, et al.
(författare)
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Natural orbitals in multiconfiguration calculations of hyperfine-structure parameters
- 2020
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 101:6
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Tidskriftsartikel (refereegranskat)abstract
- We are reinvestigating the hyperfine structure of sodium using a fully relativistic multiconfiguration approach. In the fully relativistic approach, the computational strategy somewhat differs from the original nonrelativistic counterpart used by P. Jonsson et al., Phys. Rev. A 53, 4021 (1996). Numerical instabilities force us to use a layer-by-layer approach that has some broad unexpected effects. Core correlation is found to be significant and therefore should be described in an adequate orbital basis. The natural-orbital basis provides an interesting alternative to the orbital basis from the layer-by-layer approach, allowing us to overcome some deficits of the latter, giving rise to magnetic dipole hyperfine structure constant values, in excellent agreement with observations. Effort is made to assess the reliability of the natural-orbital bases and to illustrate their efficiency.
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| 8. |
- Schiffmann, Sacha, et al.
(författare)
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POLALMM : A program to compute polarizabilities for nominal one-electron systems using the Lagrange-mesh method
- 2020
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 256
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Tidskriftsartikel (refereegranskat)abstract
- We present a program to compute polarizabilities of nominal one-electron systems using the Lagrange-mesh method (LMM) (Baye, 2015), that was used by Filippin et al., (2018). A semiempirical-core-potential approach is implemented, ultimately solving a Dirac-like equation by diagonalizing the corresponding Hamiltonian matrix. In order to build the core potential, the core orbitals are obtained from independent calculations using the GRASP2018 package (Fischer et al., 2019). Therefore we provide an easy-to-use interface between the GRASP2018 package and the LMM complete finite basis, allowing to switch easily from one one-electron basis to the other. Program summary: Program Title: POLALMM CPC Library link to program files: http://dx.doi.org/10.17632/6mw5gdwfkt.1 Licensing provisions: MIT license Programming language: Fortran90 Nature of problem: Determination of the dipole and quadrupole polarizabilities. Solution method: We combine a semiempirical-core-potential approach with the numerical Lagrange-mesh method to solve a Dirac-like one-electron equation [2]. The building of the core potential requires the prior knowledge of core orbitals provided by GRASP [3]. Two free parameters are optimized by fitting the computed single-electron valence energies to their experimental reference value. References: [1] The Lagrange-mesh method, D. Baye, Phys. Rep. 565 (2015) 1-107 [2] Relativistic semiempirical-core-potential calculations in Ca+, Ba+ and Sr+ ions on Lagrange meshes, L. Filippin, S. Schiffmann, J. Dohet-Eraly, D. Baye and M. Godefroid, Phys. Rev. A 97 (2018) 012506 [3] GRASP2018 - A Fortran 95 version of the General Relativistic Atomic Structure Package, C. Froese Fischer, G. Gaigalas, P. Jönsson and J. Bieroń, Comput. Phys. Commun. 237 (2019) 184-187
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| 9. |
- Si, Ran, et al.
(författare)
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Ab initio multiconfiguration Dirac-Hartree-Fock calculations of the in and Tl electron affinities and their isotope shifts
- 2021
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Ingår i: Physical Review A. - 2469-9926. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- We report multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations on the thallium (Tl) electron affinity, as well as on the excited energy levels arising from the ground configuration of Tl-. The results are compared with the available experimental values and further validated by extending the study to its homologous, lighter element, indium (In), belonging to group 13 (III.A) of the Periodic Table. The calculated electron affinities of In and Tl, 383.4 and 322.8 meV, agree with the latest measurements by within 1%. Three bound states 3P0,1,2 are confirmed in the 5s25p2 configuration of In-, while only the ground state 3P0 is bound in the 6s26p2 configuration of Tl-. The isotope shifts on the In and Tl electron affinities are also estimated. The E2 and M1 intraconfiguration radiative transition rates within 5s25p2 3P0,1,2 of In- are used to calculate the radiative lifetimes of the metastable 3P1,2 levels.
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| 10. |
- Yordanov, Deyan T., et al.
(författare)
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Structural trends in atomic nuclei from laser spectroscopy of tin
- 2020
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Ingår i: Communications Physics. - : Springer Nature. - 2399-3650. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Tin is the chemical element with the largest number of stable isotopes. Its complete proton shell, comparable with the closed electron shells in the chemically inert noble gases, is not a mere precursor to extended stability; since the protons carry the nuclear charge, their spatial arrangement also drives the nuclear electromagnetism. We report high-precision measurements of the electromagnetic moments and isomeric differences in charge radii between the lowest 1/2(+), 3/2(+), and 11/2(-) states in Sn117-131, obtained by collinear laser spectroscopy. Supported by state-of-the-art atomic-structure calculations, the data accurately show a considerable attenuation of the quadrupole moments in the closed-shell tin isotopes relative to those of cadmium, with two protons less. Linear and quadratic mass-dependent trends are observed. While microscopic density functional theory explains the global behaviour of the measured quantities, interpretation of the local patterns demands higher-fidelity modelling. Measurements of the hyperfine structure of chemical elements isotopes provide unique insight into the atomic nucleus in a nuclear model-independent way. The authors present collinear laser spectroscopy data obtained at the CERN ISOLDE and measure hyperfine splitting along a long chain of odd-mass tin isotopes.
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