Isotope shifts and relativistic shifts of Cr ii for the study of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>variation in quasar absorption spectra

Berengut, J. C.

doi:10.1103/physreva.84.052520

Cited by 13 publications

(22 citation statements)

References 35 publications

(90 reference statements)

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“…The two calculations presented here represent two computational regimes: a relatively smallscale calculation which requires only a single workstation or compute server, as well as a much larger scale calculation taking better advantage of modern HPC architecture. Both sets of calculations utilise emu CI and demonstrate that this technique allows for significantly higher accuracy than previous, standard CI+MBPT calculations [8].…”

Section: Example Calculation: Cr +mentioning

confidence: 97%

“…Subtraction diagrams are partially cancelled out by some two-and three-body diagrams in the MBPT expansion [8], necessitating the systematic inclusion of all one-, two-and three-body MBPT diagrams in the CI+MBPT procedure to ensure accurate spectra. Even given this cancellation, subtraction diagrams can grow large enough to be non-perturbative in open-shell systems, 8 which can significantly impact the accuracy of the resulting spectra [8]. Consequently, there is a tradeoff between the more "spectroscopic" orbitals produced by calculations in a V N potential and potentially large subtraction diagrams when V N DF = V N core ; the optimal choice will depend on the specifics of the target system.…”

Section: + Mbptmentioning

confidence: 99%

“…Despite these advantages, standard implementations, such as CI+MBPT of Kozlov et al [4], still require infeasibly large computational resources for 4 valence electrons [2]. Additionally, three-body MBPT corrections must be included to accurately treat systems with many valence electrons in this formalism [1,8,9]. The number of these three-body MBPT diagrams grows extremely rapidly with MBPT basis size and can significantly increase computation time [6,8], and are not included in the CI+MBPT code of Kozlov et al [4], for example.…”

Section: Introductionmentioning

confidence: 99%

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ambit: A programme for high-precision relativistic atomic structure calculations

Kahl¹,

Berengut²

2019

Computer Physics Communications

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We present the ambit software package for general atomic structure calculations. This software implements particle-hole configuration interaction with many-body perturbation theory (CI+MBPT) for fully relativistic calculations of atomic energy levels, electric-and magneticmultipole transition matrix elements, g-factors and isotope shifts. New numerical methods and modern high-performance computing techniques employed by this software allow for the calculation of open-shell systems with many valence-electrons (N ≥ 5) to a high degree of accuracy and in a highly computationally efficient manner. PROGRAM SUMMARYProgram Title: ambit Licensing provisions: GPLv3 Programming language: C++11 Program available from: https: // github. com/ drjuls/ AMBiT Nature of problem: Calculation of atomic/ionic spectra, including energy levels, electric and magnetic multipole transition matrix elements, and isotope shifts. Solution method: The program calculates energy levels and wavefunctions using either configuration interaction (CI) only, or CI with many-body perturbation theory (CI+MBPT) in the Brillouin-Wigner MBPT formalism. Restrictions: The program is not designed to treat highly-excited (Rydberg) states or continuum processes to a high degree of accuracy.

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Section: Example Calculation: Cr +mentioning

confidence: 97%

Section: + Mbptmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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ambit: A programme for high-precision relativistic atomic structure calculations

Kahl¹,

Berengut²

2019

Computer Physics Communications

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“…We include singleelectron excitations to 12spdf and double excitations up to 5spdf from the leading configurations (a similar strategy was used for CrII in [22]). Results using all single and double excitations to 7s6pdf were consistent, although the final energies were not as good.…”

mentioning

confidence: 99%

Limits on the Dependence of the Fine-Structure Constant on Gravitational Potential from White-Dwarf Spectra

et al. 2013

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We propose a new probe of the dependence of the fine-structure constant on a strong gravitational field using metal lines in the spectra of white-dwarf stars. Comparison of laboratory spectra with far-UV astronomical spectra from the white-dwarf star G191-B2B recorded by the Hubble Space Telescope Imaging Spectrograph gives limits of Á = ¼ ð4:2 AE 1:6Þ Â 10 À5 and ðÀ6:1 AE 5:8Þ Â 10 À5 from FeV and NiV spectra, respectively, at a dimensionless gravitational potential relative to Earth of Á % 5 Â 10 À5 . With better determinations of the laboratory wavelengths of the lines employed these results could be improved by up to 2 orders of magnitude. DOI: 10.1103/PhysRevLett.111.010801 PACS numbers: 06.20.Jr, 31.15.am, 32.30.Jc, 97.20.Rp Light scalar fields can appear very naturally in modern cosmological models and theories of high-energy physics, changing parameters of the standard model such as fundamental coupling constants and mass ratios. Like the gravitational charge, the scalar charge is purely additive, so near massive objects such as white dwarfs the effect of the scalar field can change. For objects that are not too relativistic, such as stars and planets, both the total mass and the total scalar charge are simply proportional to the number of nucleons in the object. However, different types of coupling between the scalar field and other fields can lead to an increase or decrease in scalar coupling strengths near gravitating massive bodies [1]. For small variations, the scalar field variation at distance r from such an object of mass M is proportional to the change in dimensionless gravitational potential ¼ GM=rc 2 , and we express this proportionality by introducing the sensitivity parameter k [2]. Specifically, for changes in the fine-structure ''constant'' , we writeThis dependence can be seen explicitly in particular theories of varying , such as those of Bekenstein [3] and Barrow-Sandvik-Magueijo [4], and their generalizations [5], where can increase (Á = > 0) or decrease (Á = < 0) on approach to a massive object depending on the balance between electrostatic and magnetic energy in the ambient matter fields [1]. The most sensitive current limits on k come from measurements of two Earth-bound clocks over the course of a year [2,[6][7][8][9][10][11][12]. The sensitivity is entirely due to ellipticity in Earth's orbit, which gives a 3% seasonal variation in the gravitational potential at Earth due to the Sun. The peak-to-trough sinusoidal change in the potential has magnitude Á ¼ 3 Â 10 À10 . Each clock has a different sensitivity to variation, and so Á = can be measured and hence k extracted.Because of the high precision of atomic clocks, k is determined very precisely despite the relatively small seasonal change in the gravitational potential. By contrast, we examine a ''medium strength'' field, where Á is 5 orders of magnitude larger than in the Earth-bound experiments, and the distance between the probe and the source is $10 4 times smaller than 1 AU. This allows us to probe nonlinear coupling of Á...

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“…Details of the ambit code can be found in Refs. [61][62][63][64]. To begin our discussion of the ambit treatment of the problem, first consider the 5d 2 D5 ⁄2 and 4d 9 5s 2 2 D5 ⁄2 levels as a two-level system.…”

Section: B L > Lcore Configurationsmentioning

confidence: 99%

Energy-level structure ofSn3+ions

et al. 2018

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Laser-produced Sn plasma sources are used to generate extreme ultraviolet (EUV) light in stateof-the-art nanolithography. An ultraviolet and optical spectrum is measured from a droplet-based laser-produced Sn plasma, with a spectrograph covering the range 200 -800 nm. This spectrum contains hundreds of spectral lines from lowly charged tin ions Sn 1+ -Sn 4+ of which a major fraction was hitherto unidentified. We present and identify a selected class of lines belonging to the quasi-one-electron, Ag-like ([Kr]4d 10 nl electronic configuration), Sn 3+ ion, linking the optical lines to a specific charge state by means of a masking technique. These line identifications are made with iterative guidance from cowan code calculations. Of the 53 lines attributed to Sn 3+ , some 20 were identified from previously known energy levels, and 33 lines are used to determine previously unknown level energies of 13 electronic configurations, i.e., 7p, (7, 8)d, (5, 6)f , (6 − 8)g, (6 − 8)h, (7,8)i. The consistency of the level energy determination is verified by the quantum-defect scaling procedure. The ionization limit of Sn 3+ is confirmed and refined to 328 908.4 cm -1 with an uncertainty of 2.1 cm -1 . The relativistic Fock space coupled cluster (FSCC) calculation of the measured level energies are generally in good agreement with experiment, but fail to reproduce the anomalous behavior of the 5d 2 D and nf 2 F terms. By combining the strengths of FSCC, cowan code calculations, and configuration interaction many-body perturbation theory (CI+MBPT), this behavior is shown to arise from interactions with doubly-excited configurations.

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Isotope shifts and relativistic shifts of Cr ii for the study ofαvariation in quasar absorption spectra

Cited by 13 publications

References 35 publications

ambit: A programme for high-precision relativistic atomic structure calculations

ambit: A programme for high-precision relativistic atomic structure calculations

Limits on the Dependence of the Fine-Structure Constant on Gravitational Potential from White-Dwarf Spectra

Energy-level structure ofSn3+ions

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