Atoms

20 pages, 1930 KiB

Open AccessArticle

Elastic Electron Scattering from Be, Mg, and Ca

by Mehrdad Adibzadeh, Constantine E. Theodosiou and Nicholas J. Harmon

Atoms 2024, 12(6), 33; https://doi.org/10.3390/atoms12060033 - 18 Jun 2024

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We present a comprehensive set of theoretical results for differential, integrated, and momentum transfer cross sections for the elastic scattering of electrons by beryllium, magnesium, and calcium at energies below 1 keV. In addition, we provide Sherman function values for elastic electron scattering from calcium in the same energy range. This study extends the application of our method of calculations, already employed for barium and strontium, to all stable alkaline-earth-metal atoms. Our semi-empirical approach to treating target polarization has produced in our earlier work a satisfactory agreement with experimental values and precise theoretical results such as convergent close-coupling calculations for barium. The present data are expected to be of similar high accuracy, based on our previous success in similar calculations for barium and all inert gases. Full article

(This article belongs to the Special Issue Calculations and Measurements of Atomic and Molecular Collisions)

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19 pages, 2622 KiB

Open AccessArticle

Sensitivity of a Point-Source-Interferometry-Based Inertial Measurement Unit Employing Large Momentum Transfer and Launched Atoms

by Jinyang Li, Timothy Kovachy, Jason Bonacum and Selim M. Shahriar

Atoms 2024, 12(6), 32; https://doi.org/10.3390/atoms12060032 - 11 Jun 2024

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Abstract

We analyze theoretically the sensitivity of accelerometry and rotation sensing with a point source interferometer employing large momentum transfer (LMT) and present a design of an inertial measurement unit (IMU) that can measure rotation around and acceleration along each of the three axes. In this design, the launching technique is used to realize the LMT process without the need to physically change directions of the Raman pulses, thus significantly simplifying the apparatus. We also describe an explicit scheme for such an IMU. Full article

(This article belongs to the Special Issue Advances in and Prospects for Matter Wave Interferometry)

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26 pages, 723 KiB

Open AccessReview

Time-Dependent Density Functional Theory for Atomic Collisions: A Progress Report

by Tom Kirchner

Atoms 2024, 12(6), 31; https://doi.org/10.3390/atoms12060031 - 1 Jun 2024

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Abstract

In this paper, the current status of time-dependent density functional theory (TDDFT)-based calculations for ion–atom collision problems is reviewed. Most if not all reported calculations rely on the semiclassical approximation of heavy particle collision physics and the time-dependent Kohn–Sham (TDKS) scheme for computing the electronic density of the system. According to the foundational Runge–Gross theorem, all information available about the electronic many-body system is encoded in the density; however, in practice it is often not known how to extract it without resorting to modelling and approximations. This is in addition to a necessarily approximate implementation of the TDKS scheme due to the lack of precise knowledge about the potential that drives the equations. Notwithstanding these limitations, an impressive body of work has been accumulated over the past few decades. A sample of the results obtained for various collision systems is discussed here, in addition to the formal underpinnings and theoretical and practical challenges of the application of TDDFT to atomic collision problems, which are expounded in mostly nontechnical terms. Open problems and potential future directions are outlined as well. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Atomic Collision and Atomic Spectroscopy)

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16 pages, 386 KiB

Open AccessArticle

Natural Orbitals and Targeted Non-Orthogonal Orbital Sets for Atomic Hyperfine Structure Multiconfiguration Calculations

by Mingxuan Ma, Yanting Li, Michel Godefroid, Gediminas Gaigalas, Jiguang Li, Jacek Bieroń, Chongyang Chen, Jianguo Wang and Per Jönsson

Atoms 2024, 12(6), 30; https://doi.org/10.3390/atoms12060030 - 29 May 2024

Cited by 1 | Viewed by 1399

Abstract

Hyperfine structure constants have many applications, but are often hard to calculate accurately due to large and canceling contributions from different terms of the hyperfine interaction operator, and also from different closed and spherically symmetric core subshells that break up due to electron correlation effects. In multiconfiguration calculations, the wave functions are expanded in terms of configuration state functions (CSFs) built from sets of one-electron orbitals. The orbital sets are typically enlarged within the layer-by-layer approach. The calculations are energy-driven, and orbitals in each new layer of correlation orbitals are spatially localized in regions where the weighted total energy decreases the most, overlapping and breaking up different closed core subshells in an irregular pattern. As a result, hyperfine structure constants, computed as expectation values of the hyperfine operators, often show irregular or oscillating convergence patterns. Large orbital sets, and associated large CSF expansions, are needed to obtain converged values of the hyperfine structure constants. We analyze the situation for the states of the

{2 s^{2} 2 p^{3}, 2 s^{2} 2 p^{2} 3 p, 2 s^{2} 2 p^{2} 4 p}

odd and

{2 s^{2} 2 p^{2} 3 s, 2 s 2 p^{4}, 2 s^{2} 2 p^{2} 4 s, 2 s^{2} 2 p^{2} 3 d}

even configurations in N I, and show that the convergence with respect to the increasing sets of orbitals is radically improved by introducing separately optimized orbital sets targeted for describing the spin- and orbital-polarization effects of the

1 s

and

2 s

core subshells that are merged with, and orthogonalized against, the ordinary energy-optimized orbitals. In the layer-by-layer approach, the spectroscopic orbitals are kept frozen from the initial calculation and are not allowed to relax in response to the introduced layers of correlation orbitals. To compensate for this lack of variational freedom, the orbitals are transformed to natural orbitals prior to the final calculation based on single and double substitutions from an increased multireference set. The use of natural orbitals has an important impact on the states of the

2 s^{2} 2 p^{2} 3 s

configuration, bringing the corresponding hyperfine interaction constants in closer agreement with experiment. Relying on recent progress in methodology, the multiconfiguration calculations are based on configuration state function generators, cutting down the time for spin-angular integration by factors of up to 50, compared to ordinary calculations. Full article

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Atoms, Volume 12, Issue 6 (June 2024) – 4 articles

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