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Atoms, Volume 12, Issue 11 (November 2024) – 6 articles

Cover Story (view full-size image): The electron transitions in atoms caused by charged particle impact are benchmarks in the study of electron dynamics. In this study, the focus is on the excitation of helium by proton and antiproton impacts. Both ab initio and perturbational calculations are performed, revealing the importance of electron correlations and higher-order effects. The influence of the projectile charge sign on the excitation cross section is also studied. View this paper
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8 pages, 287 KiB  
Article
Dataset for Optical Processes in Dense Astrophysical and Laboratory Plasmas
by Nenad M. Sakan, Vladimir A. Srećković, Zoran J. Simić and Momchil Dechev
Atoms 2024, 12(11), 59; https://doi.org/10.3390/atoms12110059 - 14 Nov 2024
Viewed by 811
Abstract
The interest in the modeling of laboratory and astrophysical plasma behavior from mid up to strong non-ideality (NI), e.g., plasma in which a Coulomb interaction becomes dominant, led us to further investigate the optical properties of such systems. An expanded set of results [...] Read more.
The interest in the modeling of laboratory and astrophysical plasma behavior from mid up to strong non-ideality (NI), e.g., plasma in which a Coulomb interaction becomes dominant, led us to further investigate the optical properties of such systems. An expanded set of results and properties like wave functions, dipole matrix elements, etc., for such systems is presented in this submission. The methodologies of our research, as well as the current and future elements of their applications, are explained. In addition to being helpful to other researchers for achieving a variety of goals, the data from this study could be useful the interdisciplinary fields of machine learning, astrochemistry and fusion physics. The dataset is available online at the repository Figshare. Full article
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9 pages, 430 KiB  
Article
On Resonance Enhancement of E1-E2 Nondipole Photoelectron Asymmetries in Low-Energy Ne 2p Photoionization
by Valeriy K. Dolmatov and Steven T. Manson
Atoms 2024, 12(11), 58; https://doi.org/10.3390/atoms12110058 - 7 Nov 2024
Viewed by 785
Abstract
Earlier, a significant enhancement of the nondipole parameters γ2p, δ2p, and ζ2p=γ2p+3δ2p in the photoelectron angular distribution for Ne 2p photoionization was predicted, owing to [...] Read more.
Earlier, a significant enhancement of the nondipole parameters γ2p, δ2p, and ζ2p=γ2p+3δ2p in the photoelectron angular distribution for Ne 2p photoionization was predicted, owing to resonance interference between dipole (E1) and quadrupole (E2) transitions. This enhancement manifests as narrow resonance spikes in the parameters due to the low-energy 2s3p and 2s4p dipole, as well as the 2s3d quadrupole autoionizing resonances. Given the unique nature of this predicted enhancement, it requires further validation, specifically regarding whether these narrow spikes in γ2p, δ2p and ζ2p will or will not retain their values for experimental observation if one accounts for a typical finite frequency spread in the ionizing radiation. To address this, we revisit the previous study, now incorporating the effect of frequency spread in the ionizing radiation, assuming a spread as large as 5 meV at the half-maximum of the radiation’s intensity. In the present paper we demonstrate that while the frequency spread does affect the resonance enhancement of γ2p, δ2p and ζ2p, these parameters still retain quantitatively significant values to be observed experimentally. The corresponding calculations were performed using the random phase approximation with exchange, which accounts for interchannel coupling in both dipole and quadrupole photoionization amplitudes. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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11 pages, 426 KiB  
Article
Excitation of Helium by Proton and Antiproton Impact
by Zsuzsánna Bálint, Sándor Borbély and Ladislau Nagy
Atoms 2024, 12(11), 57; https://doi.org/10.3390/atoms12110057 - 3 Nov 2024
Viewed by 790
Abstract
The electron transitions in atoms caused by charged particle impact are benchmarks for the study of electron dynamics. In the present paper we focus on the excitation of helium by proton and antiproton impact. We perform both ab initio and perturbational calculations, revealing [...] Read more.
The electron transitions in atoms caused by charged particle impact are benchmarks for the study of electron dynamics. In the present paper we focus on the excitation of helium by proton and antiproton impact. We perform both ab initio and perturbational calculations, revealing the importance of electron correlations and higher-order effects. The influence of the projectile charge sign on the excitation cross section is also studied. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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14 pages, 361 KiB  
Article
On a Study of Photoionization of Atoms and Ions from Endohedral Anions
by Valeriy K. Dolmatov, Larissa V. Chernysheva and Victor G. Yarzhemsky
Atoms 2024, 12(11), 56; https://doi.org/10.3390/atoms12110056 - 30 Oct 2024
Viewed by 874
Abstract
We study the relationship between the results of two qualitatively different semi-empirical models for photoionization cross sections, σn, of neutral atoms (A) and their cations (A+) centrally encapsulated inside a fullerene anion, CNq [...] Read more.
We study the relationship between the results of two qualitatively different semi-empirical models for photoionization cross sections, σn, of neutral atoms (A) and their cations (A+) centrally encapsulated inside a fullerene anion, CNq, where q represents the negative excess charge on the shell. One of the semi-empirical models, broadly employed in previous studies, assumes a uniform excess negative charge distribution over the entire fullerene cage, by analogy with a charged metallic sphere. The other model, presented here, considers the quantum states of the excess electrons on the shell, determined by specific n and values of their quantum numbers. Remarkably, both models yield similar photoionization cross sections for the encapsulated species. Consequently, we find that the photoionization of the encapsulated atoms or cations inside the CNq anion is influenced only slightly by the quantum states of the excess electrons on the fullerene cage. Furthermore, we demonstrate that the influence decreases even further as the size of the fullerene cage increases. All this holds true at least under the assumption that the encapsulated atom or cation is compact, i.e., its electron density remains primarily within itself rather than being drawn into the fullerene shell. This remarkable finding results from Hartree–Fock calculations combined with a popular modeling of the fullerene shell which is simulated by an attractive spherical annular potential. Full article
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12 pages, 5333 KiB  
Article
Impact of Calcium Doping on the Electronic and Optical Characteristics of Strontium Hydride (SrH2): A DFT Study
by Hamza Errahoui, Mohamed Karouchi, Abdelkebir Ejjabli, Aymane El haji, Abdelmounaim Laassouli, Omar Ait El Alia, Salah Chaji, Youssef Lachtioui and Omar Bajjou
Atoms 2024, 12(11), 55; https://doi.org/10.3390/atoms12110055 - 29 Oct 2024
Cited by 3 | Viewed by 1003
Abstract
This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH2) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band [...] Read more.
This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH2) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band structure, density of states (DOS), and optical absorption spectra of SrH2. Our results show that Ca doping significantly alters the electronic properties of SrH2, notably increasing the indirect bandgap from 1.3 eV to 1.6 eV. The DOS analysis reveals new states near the Fermi level, primarily from Ca 3d orbitals. Moreover, the optical absorption spectra display enhanced absorption in the visible range, suggesting the potential for optoelectronic applications. This research highlights the feasibility of tuning the electronic and optical characteristics of SrH2 through Ca doping, thus opening the way for the generation of advanced materials with tailored properties. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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17 pages, 354 KiB  
Article
Gordon Decomposition of the Magnetizability of a Dirac One-Electron Atom in an Arbitrary Discrete Energy State
by Patrycja Stefańska
Atoms 2024, 12(11), 54; https://doi.org/10.3390/atoms12110054 - 25 Oct 2024
Viewed by 4238
Abstract
We present a Gordon decomposition of the magnetizability of a Dirac one-electron atom in an arbitrary discrete energy eigenstate, with a pointlike, spinless, and motionless nucleus of charge Ze. The external magnetic field, by which the atomic state is perturbed, is [...] Read more.
We present a Gordon decomposition of the magnetizability of a Dirac one-electron atom in an arbitrary discrete energy eigenstate, with a pointlike, spinless, and motionless nucleus of charge Ze. The external magnetic field, by which the atomic state is perturbed, is assumed to be weak, static, and uniform. Using the Sturmian expansion of the generalized Dirac–Coulomb Green function proposed by Szmytkowski in 1997, we derive a closed-form expressions for the diamagnetic (χd) and paramagnetic (χp) contributions to χ. Our calculations are purely analytical; the received formula for χp contains the generalized hypergeometric functions 3F2 of the unit argument, while χd is of an elementary form. For the atomic ground state, both results reduce to the formulas obtained earlier by other author. This work is a prequel to our recent article, where the numerical values of χd and χp for some excited states of selected hydrogenlike ions with 1Z137 were obtained with the use of the general formulas derived here. Full article
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