Isoelectronic trends of line strength data in the Li and Be isoelectronic sequences

Curtis, L. J.

doi:10.1088/0031-8949/74/3/n02

Cited by 13 publications

(26 citation statements)

References 82 publications

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“…An independent measurement has been realized by Schnabel and Kock [37] using the cascade-free laser induced fluorescence method, yielding the original beamfoil result but with a smaller uncertainty, namely 1.34 ± 0.03. Amazingly, this value escaped to the attention of the authors of a rather complete compilation [39]. Table 1 shows that the present SD-MR-DPCFI results confirm the previous theoretical value [33], with a difference between the two gauges that is much smaller than the accuracy rating 'A' attributed by Fuhr and Wiese [40] to all transitions where this difference is smaller than 1.5%.…”

Section: The Beryllium Resonance Linesupporting

confidence: 81%

JJGEN: A flexible program for generating lists of jj-coupled configuration state functions

Sturesson

Jönsson

Fischer

2007

Computer Physics Communications

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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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Section: The Beryllium Resonance Linesupporting

confidence: 81%

JJGEN: A flexible program for generating lists of jj-coupled configuration state functions

Sturesson

Jönsson

Fischer

2007

Computer Physics Communications

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“…Lifetimes for long-lived states of the ground configuration or the lowest excited configurations have been determined in accurate storage-ring and trapping experiments (see for example, the review by Träbert [59]) and are used for benchmarking. Lifetimes for a large range of short-lived states have been determined using beam-foil spectroscopy [60]. However, even if these beam-foil data are very valuable, they are in general not accurate enough to discriminate between different computational approaches.…”

Section: Transition Probabilitiesmentioning

confidence: 99%

Multiconfiguration Dirac-Hartree-Fock Calculations with Spectroscopic Accuracy: Applications to Astrophysics

Jönsson

Gaigalas

Rynkun

et al. 2017

Atoms

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Abstract:Atomic data, such as wavelengths, spectroscopic labels, broadening parameters and transition rates, are necessary for many applications, especially in plasma diagnostics, and for interpreting the spectra of distant astrophysical objects. The experiment with its limited resources is unlikely to ever be able to provide a complete dataset on any atomic system. Instead, the bulk of the data must be calculated. Based on fundamental principles and well-justified approximations, theoretical atomic physics derives and implements algorithms and computational procedures that yield the desired data. We review progress and recent developments in fully-relativistic multiconfiguration Dirac-Hartree-Fock methods and show how large-scale calculations can give transition energies of spectroscopic accuracy, i.e., with an accuracy comparable to the one obtained from observations, as well as transition rates with estimated uncertainties of a few percent for a broad range of ions. Finally, we discuss further developments and challenges.

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“…Such lifetimes are routinely measured by beam-foil spectroscopy (see [13]), but a naively obtained apparent lifetime result taken at face value may be severely misleading, if the upper level is not selectively excited, but is suffering from cascade repopulation. This problem and its treatment (by measuring the decay curves of the cascades and performing a correlated analysis, for example in the ANDC scheme [14][15][16][17], or by employing a cascade model fit) have been discussed repeatedly [17][18][19][20][21] and need not be replayed here beyond mentioning their existence (see discussion below). The 2s 2 1 S 0 -2s2p 3 P o 1 intercombination decay rate, in contrast, is several orders of magnitude smaller than the resonance decay rate and relates (for low-Z ions) to level lifetimes in the second to millisecond range.…”

Section: Be-like Ionsmentioning

confidence: 99%

Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View

Trabert

2014

Atoms

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The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with "the other side" before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.

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Isoelectronic trends of line strength data in the Li and Be isoelectronic sequences

Cited by 13 publications

References 82 publications

JJGEN: A flexible program for generating lists of jj-coupled configuration state functions

JJGEN: A flexible program for generating lists of jj-coupled configuration state functions

Multiconfiguration Dirac-Hartree-Fock Calculations with Spectroscopic Accuracy: Applications to Astrophysics

Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View

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