Atoms

11 pages, 351 KB

Open AccessEditor’s ChoiceArticle

Short–Range Hard–Sphere Potential and Coulomb Interaction: Deser–Trueman Formula for Rydberg States of Exotic Atomic Systems

by Gregory S. Adkins and Ulrich D. Jentschura

Atoms 2025, 13(9), 81; https://doi.org/10.3390/atoms13090081 - 11 Sep 2025

Cited by 2 | Viewed by 1121

Abstract

In exotic atomic systems with hadronic constituent particles, it is notoriously difficult to estimate the strong-interaction correction to energy levels. It is well known that, due to the strength of the nuclear interaction, the problem cannot be solved using Wigner–Brillouin perturbation theory alone. [...] Read more.

In exotic atomic systems with hadronic constituent particles, it is notoriously difficult to estimate the strong-interaction correction to energy levels. It is well known that, due to the strength of the nuclear interaction, the problem cannot be solved using Wigner–Brillouin perturbation theory alone. Recently, high-angular-momentum Rydberg states of exotic atomic systems with hadronic constituents have been identified as promising candidates in the search for new physics in the low-energy sector of the Standard Model. We thus derive a generalized Deser–Trueman formula for the induced energy shift for a general hydrogenic bound state with principal quantum number n and orbital angular momentum quantum number ℓ, and we find that the energy shift is given by the formula

δ E = 2 α_{n, ℓ} β_{ℓ} {(a_{h} / a_{0})}^{2 ℓ + 1} E_{h} / n^{3}

, where

α_{n, 0} = 1

,

α_{n, ℓ} = \prod_{s = 1}^{ℓ} (s^{- 2} - n^{- 2})

,

β_{ℓ} = (2 ℓ + 1) / {[(2 ℓ + 1)!!]}^{2}

,

E_{h}

is the Hartree energy,

a_{h}

is the hadronic radius and

a_{0}

is the generalized Bohr radius. The square of the double factorial,

{[(2 ℓ + 1)!!]}^{2}

, in the denominator implies a drastic suppression of the effect for higher angular momenta. Full article

(This article belongs to the Section Nuclear Theory and Experiments)

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13 pages, 3730 KB

Open AccessArticle

IKEBANA: Data-Driven Neural-Network Predictor of Electron-Impact K-Shell Ionization Cross Sections

by Darío M. Mitnik, Claudia C. Montanari, Silvina Segui, Silvina P. Limandri, Judith A. Guzmán, Alejo C. Carreras and Jorge C. Trincavelli

Atoms 2025, 13(9), 80; https://doi.org/10.3390/atoms13090080 - 11 Sep 2025

Viewed by 692

Abstract

A fully connected neural network was trained to model the K-shell ionization cross sections based on two input features: the atomic number and the incoming electron overvoltage. The training utilized a recent, updated compilation of experimental data covering elements from H to U, [...] Read more.

A fully connected neural network was trained to model the K-shell ionization cross sections based on two input features: the atomic number and the incoming electron overvoltage. The training utilized a recent, updated compilation of experimental data covering elements from H to U, and incident electron energies ranging from the threshold to relativistic values. The neural network demonstrated excellent predictive performance, compared with the experimental data, when available, and with full theoretical predictions. The developed model is provided in the ikebana code, which is openly available and requires only the user-selected atomic number and electron energy range as inputs. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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12 pages, 2083 KB

Open AccessArticle

Theoretical Study of Spectroscopic Properties of Fe(III)(acac)₃ Under All-Electron Scalar Relativistic Effects

by Luiz C. de Miranda and Nelson H. Morgon

Atoms 2025, 13(9), 79; https://doi.org/10.3390/atoms13090079 - 11 Sep 2025

Viewed by 1857

Abstract

Molecular geometry, infrared (IR) vibrational frequencies, and ultraviolet–visible (UV-Vis) electronic absorption spectra of the trivalent iron tris(acetylacetonate) complex, Fe(III)(acac)₃, were computed using hybrid meta-generalized gradient approximation (meta-GGA) density functional theory (DFT). Calculations employed the Jorge double-

ζ

valence plus polarization basis [...] Read more.

Molecular geometry, infrared (IR) vibrational frequencies, and ultraviolet–visible (UV-Vis) electronic absorption spectra of the trivalent iron tris(acetylacetonate) complex, Fe(III)(acac)₃, were computed using hybrid meta-generalized gradient approximation (meta-GGA) density functional theory (DFT). Calculations employed the Jorge double-

ζ

valence plus polarization basis sets (standard DZP and relativistic DZP + DKH). Solvent effects were modeled using the SMD continuum solvation framework with acetonitrile as the dielectric medium. This charge-neutral complex exhibits predominantly ionic metal–ligand bonding character, which simplifies the computational treatment. Despite extensive DFT applications to coordination compounds, systematic benchmarks for this bidentate ligand system remain limited. The computed harmonic frequencies (

ν

) and electronic excitation energies (

λ_{\max}

) demonstrate excellent agreement with available experimental measurements. These results enable comparative analysis of IR and UV-Vis spectral features, both with and without all-electron scalar relativistic effects with the second-order Douglas–Kroll–Hess approach. Full article

(This article belongs to the Section Quantum Chemistry, Computational Chemistry and Molecular Physics)

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Graphical abstract

16 pages, 1203 KB

Open AccessArticle

Assessment of Absorbed Dose from a Positron Beam in Biological Tissue and Its Potential for Radiotherapy

by Andrezza O. Arêas and Maikel Y. Ballester

Atoms 2025, 13(9), 78; https://doi.org/10.3390/atoms13090078 - 10 Sep 2025

Viewed by 937

Abstract

Fast-charged particles have been used in diagnosis and treatment since the 19th century. Positrons are widely used in medical imaging through positron emission tomography, but their therapeutic potential remains underexplored due to technology limitations associated with the lack of research on their effectiveness [...] Read more.

Fast-charged particles have been used in diagnosis and treatment since the 19th century. Positrons are widely used in medical imaging through positron emission tomography, but their therapeutic potential remains underexplored due to technology limitations associated with the lack of research on their effectiveness against cancer. One way to understand their behavior is by calculating absorbed dose distributions in tissue, which can be safely and realistically done using computational simulations such as the Monte Carlo Method. This study investigates the interaction of a positron beam with brain tissue and a tumor through simulations using the TOPAS software. Depth dose profiles and absolute absorbed dose values were obtained in the range of 6–24 MeV. Validation was performed using data from the water phantom with electron beams. The results showed that, at certain depths in brain tissue, the absorbed dose by positrons was higher than that of electrons under the same conditions, ranging from 57% to 463% more. These findings suggest that positrons may offer advantages over conventional electron therapy and contribute to the development of novel therapeutic approaches. Full article

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16 pages, 1120 KB

Open AccessEditor’s ChoiceArticle

Simulated Photoabsorption Spectra for Singly and Multiply Charged Ions

by Stephan Fritzsche, Aloka Kumar Sahoo, Lalita Sharma and Stefan Schippers

Atoms 2025, 13(9), 77; https://doi.org/10.3390/atoms13090077 - 3 Sep 2025

Cited by 1 | Viewed by 951

Abstract

Simulated (or measured) photoabsorption spectra often provide the first indication of how matter interacts with light when irradiated by some radiation source. In addition to the direct, often slowly varying photoabsorption cross-section as a function of the incident photon frequency, such spectra typically [...] Read more.

Simulated (or measured) photoabsorption spectra often provide the first indication of how matter interacts with light when irradiated by some radiation source. In addition to the direct, often slowly varying photoabsorption cross-section as a function of the incident photon frequency, such spectra typically exhibit numerous resonances and edges arising from the interaction of the radiation field with the subvalence or even inner-shell electrons. Broadly speaking, these resonances reflect photoexcitation, with its subsequent fluorescence, or the autoionization of bound electrons. Here, a (relativistic) cascade model is developed for estimating the photoabsorption of (many) atoms and multiply charged ions with a complex shell structure across the periodic table. This model helps distinguish between level- and shell-resolved, as well as total photoabsorption, cross-sections, starting from admixtures of selected initial-level populations. Examples are shown for the photoabsorption of C⁺ ions near the 1s − 2p excitation threshold and for Xe²⁺ ions in the photon energy range from 10 to 200 eV. While the accuracy and resolution of the predicted photoabsortion spectra remain limited due to the additive treatment of resonances and because of missing electronic correlations in the representation of the levels involved, the present implementation is suitable for ions with quite different open-shell structures and may support smart surveys of resonances along different isoelectronic sequences. Full article

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10 pages, 784 KB

Open AccessArticle

Larmor Time for Trapezoidal Barrier

by Tengfei Li and Zhi Xiao

Atoms 2025, 13(9), 76; https://doi.org/10.3390/atoms13090076 - 29 Aug 2025

Viewed by 838

Abstract

In this paper, we explore the Larmor time for three types of trapezoidal barriers, and we find consistent results between the traditionally defined Larmor time and a newly defined one. We confirm that the transmission Larmor time for the trapezoidal barriers also satisfies [...] Read more.

In this paper, we explore the Larmor time for three types of trapezoidal barriers, and we find consistent results between the traditionally defined Larmor time and a newly defined one. We confirm that the transmission Larmor time for the trapezoidal barriers also satisfies certain properties of mirror-symmetric barriers. Consistent with our expectations, we also find that: 1. as the barrier height increases, the peak of the Larmor time shifts to the right (higher energy); and 2. as the barrier width increases, the peak becomes larger in coincidence with the classical expectation that a particle needs more time to cross a longer path of the same height/inclination. Full article

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9 pages, 549 KB

Open AccessEditor’s ChoiceArticle

Interfacing the B-Spline R-Matrix and R-Matrix with Time Dependence Computer Codes: An Update

by Juan C. Del Valle, Aaron T. Bondy, Soumyajit Saha, Kathryn R. Hamilton and Klaus Bartschat

Atoms 2025, 13(9), 75; https://doi.org/10.3390/atoms13090075 - 29 Aug 2025

Viewed by 949

Abstract

As a continuation of Schneider et al., Atoms 2022 10, 26, we report recent progress in the development and deployment of the interface between the computational codes B-Spline R-matrix (BSR) and R-Matrix with Time dependence (RMT). These advances have been achieved within [...] Read more.

As a continuation of Schneider et al., Atoms 2022 10, 26, we report recent progress in the development and deployment of the interface between the computational codes B-Spline R-matrix (BSR) and R-Matrix with Time dependence (RMT). These advances have been achieved within the context of the

L S

-coupling scheme. In its current state, the interface handles atomic target states described by single configurations and supports the Fano–Racah phase convention, as required by RMT. As first example of an application, we use the interface to investigate multiphoton single ionization of helium exposed to a linearly polarized laser field with wavelengths between 280 and 316 nm and a peak intensity of

3 \times 10^{14}

W/cm². As a second example, we consider high-order harmonic generation (HHG) in carbon, driven by an intense 30-cycle laser field at 800 nm and a peak intensity of

1 \times 10^{12}

W/cm². Full article

(This article belongs to the Special Issue Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider)

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12 pages, 1240 KB

Open AccessEditor’s ChoiceArticle

State-Selective Differential Cross Sections for Single-Electron Capture in Slow He⁺–He Collisions

by Shucheng Cui, Kaizhao Lin, Dadi Xing, Ling Liu, Dongmei Zhao, Dalong Guo, Yong Gao, Shaofeng Zhang, Yong Wu, Chenzhong Dong, Xiaolong Zhu and Xinwen Ma

Atoms 2025, 13(9), 74; https://doi.org/10.3390/atoms13090074 - 28 Aug 2025

Viewed by 963

Abstract

A combined experimental and theoretical study is carried out on the single-electron capture process in He⁺–He collisions at energies ranging from 0.5 keV/u to 5 keV/u. Using cold target recoil ion momentum spectroscopy, we obtain state-selective cross sections and angular differential [...] Read more.

A combined experimental and theoretical study is carried out on the single-electron capture process in He⁺–He collisions at energies ranging from 0.5 keV/u to 5 keV/u. Using cold target recoil ion momentum spectroscopy, we obtain state-selective cross sections and angular differential cross sections. Within the entire studied energy range, the dominant channel is the electron captured into the ground-state, and the relative contribution of the dominant channel shows a decreasing trend with increasing energy. The angular differential cross sections of ground-state capture exhibit obvious oscillatory structures. To understand the oscillatory structures of the differential cross sections, we also performed theoretical calculations using the two-center atomic orbital close-coupling method, which well reproduced the oscillatory structures. The results indicate that these structures are strongly correlated to the oscillatory structures of the impact parameter dependence of electron probability. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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Atoms, Volume 13, Issue 9 (September 2025) – 8 articles

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