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Special Issue "Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia"

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A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (1 September 2022) | Viewed by 27262

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Special Issue Editors

Prof. Dr. Anatoli Kheifets

E-Mail Website
Guest Editor

Research School of Physical Sciences, Australian National University, Canberra, ACT 2600, Australia
Interests: theoretical atomic and condensed matter physics

Dr. Gleb Gribakin
E-Mail Website
Guest Editor

School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK
Interests: many-body theory in atom; electron-atom scattering, negative ions, photodetachmen, multiphoton processes in strong laser fields

Prof. Dr. Vadim Ivanov

E-Mail Website
Guest Editor

Department of Physics, Peter the Great St. Petersburg Polytechnic University, St. Petersburg 195251, Russia
Interests: theoretical physics; condensed matter; physics of nanostructures; atomic and molecular physics

Special Issue Information

Dear Colleagues,

This Special Issue will contain contributions from numerous colleagues and collaborators of the late Prof. Miron Amusia, who had been a key figure in the international theoretical atomic physics community over the past half a century. The focus of the Special Issue will be on many-electron and multiphoton atomic processes which are at the forefront of contemporary atomic and molecular physics. Special attention will be given to many-electron correlation problems and its interplay with strong-field laser–atom interactions. Recent advances in the generation of short and intense laser pulses make this problem particularly topical. Although some recent topical issues have addressed strong laser physics and attosecond science (MDPI Applied Sciences 2019, IOP J.Phys & J.Photonics 2020), the many-electron correlation problem has never been the focus in this context. Therefore, the present proposal will usefully supplement existing literature and will be of interest to a large section of the atomic and strong laser physics community, both theoretically and experimentally.

Prof. Dr. Anatoli Kheifets
Dr. Gleb Gribakin
Prof. Dr. Vadim Ivanov
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atoms is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this special issue is free of charge. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

theoretical atomic and molecular physics
electronic structure of atoms and molecules
many-electron correlation
strong laser–atom interaction
attosecond science
high-order harmonic generation
tunneling and multi-photon ionization
electron scattering from atoms and molecules
endohedral atoms

Published Papers (22 papers)

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Editorial

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Open AccessEditorial

“Atoms” Special Issue (Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

Anatoli S. Kheifets

Gleb Gribakin

and

Vadim K. Ivanov

Atoms 2023, 11(2), 18; https://doi.org/10.3390/atoms11020018 - 20 Jan 2023

Viewed by 494

Abstract

The late Professor Miron Amusia was a key figure in theoretical atomic physics on the international stage for more than five decades [...] Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

Research

Jump to: Editorial, Review, Other

Open AccessArticle

Electron Correlations in Sequential Two-Photon Double Ionization of an Ar Atom

Nikolay M. Novikovskiy

Philipp V. Demekhin

and

Arno Ehresmann

Atoms 2022, 10(4), 139; https://doi.org/10.3390/atoms10040139 - 13 Nov 2022

Cited by 1 | Viewed by 791

Abstract

Sequential two-photon ionization is a process that is experimentally accessible due to the use of new free-electron laser sources for excitation. For the prototypical rare Ar gas atoms, a photoelectron spectrum (PES) corresponding to the second step of the sequential two-photon double ionization [...] Read more.

^{II}

) at a photon excitation energy of 65.3 eV was studied theoretically with a focus on the consequences of electron correlations in the considered process. The calculation predicts many intense lines at low photoelectron energies, which cannot be explained on the basis of a one-electron approximation. The processes that lead to the appearance of these lines include many-electron correlations, either in the first or second step of photoionization. A significant fraction of the intensity of the low-energy part of PES is associated with the Auger decay of the excited states formed at the second step of 2PDI. The shape of the low-energy part of the 2PDI

^{II}

PES is expected to be dependent on both the energy of photon excitations and the flux of the exciting beam. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Fock Expansion for Two-Electron Atoms: High-Order Angular Coefficients

Evgeny Z. Liverts

and

Rajmund Krivec

Atoms 2022, 10(4), 135; https://doi.org/10.3390/atoms10040135 - 07 Nov 2022

Cited by 1 | Viewed by 708

Abstract

The Fock expansion, which describes the properties of two-electron atoms near the nucleus, is studied. The angular Fock coefficients

ψ_{k, p} (α, θ)

with the maximum possible value of subscript p are calculated on examples of the coefficients [...] Read more.

The Fock expansion, which describes the properties of two-electron atoms near the nucleus, is studied. The angular Fock coefficients

ψ_{k, p} (α, θ)

with the maximum possible value of subscript p are calculated on examples of the coefficients with

5 \leq k \leq 10

. The presented technique makes it possible to calculate such angular coefficients for any arbitrarily large k. The mentioned coefficients being leading in the logarithmic power series representing the Fock expansion, they may be indispensable for the development of simple methods for calculating the helium-like electronic structure. The theoretical results obtained are verified by other suitable methods. The Wolfram Mathematica is used extensively. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

Open AccessArticle

Spectroscopic Peculiarities at Ionization of Excited 2p⁵(²P_Jf)3s[K]_0,1,2 States of Ne: Cooper Minima and Autoionizing Resonances

and

Alexei N. Grum-Grzhimailo

Atoms 2022, 10(4), 102; https://doi.org/10.3390/atoms10040102 - 26 Sep 2022

Cited by 1 | Viewed by 771

Abstract

An extensive study of photoionization from neon excited states was performed. The R-matrix approach was applied to calculate a photoionization cross-section from the metastable

2 p^{5} (^{2} P_{J_{f}}) 3 s {[K]}_{0, 2}

and dipole-allowed [...] Read more.

An extensive study of photoionization from neon excited states was performed. The R-matrix approach was applied to calculate a photoionization cross-section from the metastable

2 p^{5} (^{2} P_{J_{f}}) 3 s {[K]}_{0, 2}

and dipole-allowed

2 p^{5} (^{2} P_{J_{f}}) 3 s {[K]}_{1}

states. The resonance structures and Cooper minimum accessible in photoionization from the excited states by the photons with energy below 30 eV were analyzed. The parameters of the lowest autoionizing states (AISs) of even parity were extracted by fitting of the photoionization cross-section. For the dipole-allowed states, calculations are presented for unpolarized, linearly and circularly polarized radiation. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

A Glimpse into Photodetachment Spectra of Giant and Nested Fullerene Anions

Valeriy K. Dolmatov

and

Steven T. Manson

Atoms 2022, 10(4), 99; https://doi.org/10.3390/atoms10040099 - 22 Sep 2022

Cited by 1 | Viewed by 723

Abstract

We focus on the study of the photodetachment of bare, i.e., single-cage

{(C_{N})}^{-}

as well as nested (multi-cage)

{(C_{N} @ C_{M} @ \dots)}^{-}

singly charged fullerene anions. We calculate the attached electron’s wavefunctions, energies, [...] Read more.

We focus on the study of the photodetachment of bare, i.e., single-cage

{(C_{N})}^{-}

as well as nested (multi-cage)

{(C_{N} @ C_{M} @ \dots)}^{-}

singly charged fullerene anions. We calculate the attached electron’s wavefunctions, energies, oscillator strengths and photodetachment cross sections of the

C_{60}^{-}

C_{240}^{-}

C_{540}^{-}

{(C_{60} @ C_{240})}^{-}

{(C_{60} @ C_{540})}^{-}

{(C_{240} @ C_{540})}^{-}

and

{(C_{60} @ C_{240} @ C_{540})}^{-}

fullerene anions, where the attached electron is captured into the ground s-state by the resultant external field provided by all fullerene cages in the anion. The goal is to gain insight into the changes in behavior ofphotodetachment of this valence electron as a function of the different geometries and potentials of the various underlying fullerenes or nested fullerenes (fullerene onions) both due to their increasing size and due to “stuffing” of a larger bare fullerene with smaller fullerenes. To meet this goal, we opt for a simple semi-empirical approximation to this problem: we approximate each individual fullerene cage by a rigid potential sphere of a certain inner radius, thickness and potential depth, as in numerous other model studies performed to date. The results reveal a number of rather significant differences in the wavefunctions, oscillator strengths and photodetachment cross sections among these fullerene anions, some of which are completely counter-intuitive. The results obtained can serve as a “zeroth-order-touchstone” for future studies of single-cage and nested fullerene anions by more rigorous theories and/or experiments to build upon this work to assess the importance of interactions omitted in the present study. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Calculation of Low-Energy Positron-Atom Scattering with Square-Integrable Wavefunctions

Sarah Gregg

and

Gleb Gribakin

Atoms 2022, 10(4), 97; https://doi.org/10.3390/atoms10040097 - 22 Sep 2022

Cited by 1 | Viewed by 1065

Abstract

The variational method is applied to the low-energy positron scattering and annihilation problem. The ultimate aim of the investigation is to find a computationally economical way of accounting for strong electron–positron correlations, including the effect of virtual positronium formation. The method is applied to the study of elastic s-wave positron scattering from a hydrogen atom. A generalized eigenvalue problem is set up and solved to obtain s-wave positron–hydrogen scattering phase shifts within

8 \times 10^{- 3}

rad of accepted values. This is achieved using a small number of terms in the variational wavefunction; in particular, only nine terms that depend on the electron–positron distance are included. The annihilation parameter

Z_{eff}

is also calculated and is found to be in good agreement with benchmark calculations. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessEditor’s ChoiceArticle

Shake-Off Process in Non-Sequential Single-Photon Double Ionization of Closed-Shell Atomic Targets

Anatoli S. Kheifets

Atoms 2022, 10(3), 89; https://doi.org/10.3390/atoms10030089 - 07 Sep 2022

Cited by 3 | Viewed by 1041

Abstract

Amusia and Kheifets in 1984 introduced a Green’s function formalism to describe the effect of many-electron correlation on the ionization spectra of atoms. Here, we exploit this formalism to model the shake-off (SO) process, leading to the non-sequential single-photon two-electron ionization (double photoionization—DPI) of closed-shell atomic targets. We separate the SO process from another knock-out (KO) mechanism of DPI and show the SO prevalence away from the DPI threshold. We use this kinematic regime to validate our model by making a comparison with more elaborate techniques, such as convergent and time-dependent close coupling. We also use our model to evaluate the attosecond time delay associated with the SO process. Typically, the SO is very fast, taking only a few attoseconds to complete. However, it can take much longer in the DPI of strongly correlated systems, such as the H

^{-}

ion as well as the subvalent shells of the Ar and Xe atoms and Cl

^{-}

ion. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Absolute Double-Differential Cross Sections of Ultrasoft Isochromatic X-ray Radiation in Electron Scattering on Atoms

and

Atoms 2022, 10(3), 86; https://doi.org/10.3390/atoms10030086 - 24 Aug 2022

Cited by 1 | Viewed by 998

Abstract

We calculate double-differential cross sections of ultrasoft X-ray bremsstrahlung in electron scattering by Ar, Kr, and Xe atoms in the soft-photon approximation. The calculations are done for the isochromatic spectra (i.e., dependence on the electron energy at a fixed photon energy of 165 and 177 eV). The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (Phys. Rev. A 80, 022707 (2009)) for the above-mentioned photon energies. For low electron energies, our theoretical isochromatic spectra are in quantitative agreement with the experimental data for Ar. For Kr, the agreement is qualitative while agreement with the Xe data is poor. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Relativistic Two-Photon Matrix Elements for Attosecond Delays

Jimmy Vinbladh

Jan Marcus Dahlström

and

Eva Lindroth

Atoms 2022, 10(3), 80; https://doi.org/10.3390/atoms10030080 - 02 Aug 2022

Cited by 2 | Viewed by 1211

Abstract

The theory of one-photon ionization and two-photon above-threshold ionization is formulated for applications to heavy atoms in attosecond science by using Dirac–Fock formalism. A direct comparison of Wigner–Smith–Eisenbud delays for photoionization is made with delays from the Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBIT) method. Photoionization by an attosecond pulse train, consisting of monochromatic fields in the extreme ultraviolet range, is computed with many-body effects at the level of the relativistic random phase approximation (RRPA). Subsequent absorption and emission processes of infrared laser photons in RABBIT are evaluated by using static ionic potentials as well as asymptotic properties of relativistic Coulomb functions. As expected, light elements, such as argon, show negligible relativistic effects, whereas heavier elements, such a krypton and xenon, exhibit delays that depend on the fine-structure of the ionic target. The relativistic effects are notably close to ionization thresholds and Cooper minima with differences in fine-structure delays predicted to be as large as tens of attoseconds. The separability of relativistic RABBIT delays into a Wigner–Smith–Eisenbud delay and a universal continuum–continuum delay is studied with reasonable separability found for photoelectrons emitted along the laser polarization axis in agreement with prior non-relativistic results. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

On Producing Long-Lived Spin Polarized Metastable Atoms—Feasibility of Storing Electric Energy

Horst Schmidt-Böcking

and

Gernot Gruber

Atoms 2022, 10(3), 76; https://doi.org/10.3390/atoms10030076 - 18 Jul 2022

Cited by 1 | Viewed by 1400

Abstract

We describe a method of producing long-lived multiply excited spin polarized atoms or ions, the decay of which is strongly delayed or even blocked by intra-ionic magnetic stabilization. Special configurations with huge internal magnetic fields capture only spin polarized electrons in collisions with spin aligned atomic hydrogen gas targets. It is expected that the spin aligned configuration yields an extremely high internal magnetic field which will effectively block spin flip transitions. By this the lifetime of inner shell vacancies is expected to strongly increase. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Satellite Excitations and Final State Interactions in Atomic Photoionization

Victor G. Yarzhemsky

and

Yury A. Teterin

Atoms 2022, 10(3), 73; https://doi.org/10.3390/atoms10030073 - 14 Jul 2022

Cited by 1 | Viewed by 1077

Abstract

Satellite excitations and final state configuration interactions appear due to the many-electron correlations and result in a photoelectron spectrum complex final state structure instead of single lines corresponding to one-hole states. In the present work, both processes are considered in a framework of the many-body perturbation theory, and two techniques, namely the spectral function and CI (configuration interaction) methods are considered. It is shown that for the calculation of satellite lineshapes and low-energy Auger decay, the spectral function method is more appropriate, but in the case of strong final state interactions, the methods of solution of Dyson equation or secular matrix are superior. The results obtained for satellites and low energy Auger decay in the Ne 1s, Ne 2p photoelectron spectra, the Co 3s, and the Th 5p photoelectron spectra are in agreement with the experimental data. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Graphical abstract

Open AccessArticle

Photoionization of Atomic Systems Using the Random-Phase Approximation Including Relativistic Interactions

Pranawa C. Deshmukh

and

Steven T. Manson

Atoms 2022, 10(3), 71; https://doi.org/10.3390/atoms10030071 - 11 Jul 2022

Cited by 1 | Viewed by 1232

Abstract

Approximation methods are unavoidable in solving a many-electron problem. One of the most successful approximations is the random-phase approximation (RPA). Miron Amusia showed that it can be used successfully to describe atomic photoionization processes of many-electron atomic systems. In this article, the historical reasons behind the term “random-phase approximation” are revisited. A brief introduction to the relativistic RPA (RRPA) developed by Walter Johnson and colleagues is provided and some of its illustrative applications are presented. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Strong-Field Ionization Amplitudes for Atomic Many-Electron Targets

Stephan Fritzsche

and

Birger Böning

Atoms 2022, 10(3), 70; https://doi.org/10.3390/atoms10030070 - 30 Jun 2022

Cited by 2 | Viewed by 1316

Abstract

The strong-field approximation (SFA) has been widely applied in the literature to model the ionization of atoms and molecules by intense laser pulses. A recent re-formulation of the SFA in terms of partial waves and spherical tensor operators helped adopt this approach to account for realistic atomic potentials and pulses of different shape and time structure. This re-formulation also enables one to overcome certain limitations of the original SFA formulation with regard to the representation of the initial-bound and final-continuum wave functions of the emitted electrons. We here show within the framework of Jac, the Jena Atomic Calculator, how the direct SFA ionization amplitude can be readily generated and utilized in order to compute above-threshold ionization (ATI) distributions for many-electron targets and laser pulses of given frequency, intensity, polarization, pulse duration and carrier–envelope phase. Examples are shown for selected ATI energy, angular as well as momentum distributions in the strong-field ionization of atomic krypton. We also briefly discuss how this approach can be extended to incorporate rescattering and high-harmonic processes into the SFA amplitudes. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Quasifree Photoionization under the Reaction Microscope

and

Atoms 2022, 10(3), 68; https://doi.org/10.3390/atoms10030068 - 28 Jun 2022

Cited by 1 | Viewed by 1302

Abstract

We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H

_{2}

at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by [...] Read more.

We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H

_{2}

at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by Miron Amusia more than four decades ago. We found the distinct four-fold symmetry in the angular emission pattern of QFM electrons from H

_{2}

double ionization that has previously only been observed for He. Furthermore, we provide experimental evidence that the photon momentum is not imparted onto the center of mass in quasifree photoionization, which is in contrast to the situation in single ionization and in double ionization mediated by the shake-off and knock-out mechanisms. This finding is substantiated by numerical results obtained by solving the system’s full-dimensional time-dependent Schrödinger equation beyond the dipole approximation. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Spin Polarization of Electrons in Two-Color XUV + Optical Photoionization of Atoms

Nikolay M. Kabachnik

and

Irina P. Sazhina

Atoms 2022, 10(2), 66; https://doi.org/10.3390/atoms10020066 - 20 Jun 2022

Cited by 1 | Viewed by 1168

Abstract

The spin polarization of photoelectrons in two-color XUV + optical multiphoton ionization is theoretically considered using strong field approximation. We assume that both the XUV and the optical radiation are circularly polarized. It is shown that the spin polarization is basically determined by the XUV photoabsorption and that the sidebands are spin polarized as well. Their polarization may be larger or smaller than that of the central photoelectron line depending on the helicity of the dressing field. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Taking the Convergent Close-Coupling Method beyond Helium: The Utility of the Hartree-Fock Theory

Sudhakar Pamidighantam

Maciej Cytowski

and

Anatoli S. Kheifets

Atoms 2022, 10(1), 22; https://doi.org/10.3390/atoms10010022 - 11 Feb 2022

Cited by 2 | Viewed by 1713

Abstract

The convergent close-coupling (CCC) method was initially developed to describe electron scattering on atomic hydrogen and the hydrogenic ions such as He

^{+}

. The latter allows implementation of double photoionization (DPI) of the helium atom. For more complex single valence-electron atomic and [...] Read more.

The convergent close-coupling (CCC) method was initially developed to describe electron scattering on atomic hydrogen and the hydrogenic ions such as He

^{+}

. The latter allows implementation of double photoionization (DPI) of the helium atom. For more complex single valence-electron atomic and ionic targets, the direct and exchange interaction with the inner electron core needs to be taken into account. For this purpose, the Hartree-Fock (HF) computer codes developed in the group of Miron Amusia have been adapted. In this brief review article, we demonstrate the utility of the HF technique by examples of electron scattering on Li and the DPI of the H

^{-}

and Li

^{-}

ions. We also discuss that modern-day computer infrastructure allows the associated CCC code, and others, to be readily run directly via the Atomic, Molecular and Optical Science Gateway. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Accurate Exponential Representations for the Ground State Wave Functions of the Collinear Two-Electron Atomic Systems

Evgeny Z. Liverts

and

Nir Barnea

Atoms 2022, 10(1), 4; https://doi.org/10.3390/atoms10010004 - 29 Dec 2021

Cited by 1 | Viewed by 1473

Abstract

In the framework of the study of helium-like atomic systems possessing the collinear configuration, we propose a simple method for computing compact but very accurate wave functions describing the relevant S-state. It is worth noting that the considered states include the well-known states of the electron–nucleus and electron–electron coalescences as a particular case. The simplicity and compactness imply that the considered wave functions represent linear combinations of a few single exponentials. We have calculated such model wave functions for the ground state of helium and the two-electron ions with nucleus charge

1 \leq Z \leq 5

. The parameters and the accompanying characteristics of these functions are presented in tables for number of exponential from 3 to 6. The accuracy of the resulting wave functions are confirmed graphically. The specific properties of the relevant codes by Wolfram Mathematica are discussed. An example of application of the compact wave functions under consideration is reported. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Time Delay in Electron Collision with a Spherical Target as a Function of the Scattering Angle

Miron Ya. Amusia

Arkadiy S. Baltenkov

and

Igor Woiciechowski

Atoms 2021, 9(4), 105; https://doi.org/10.3390/atoms9040105 - 01 Dec 2021

Cited by 2 | Viewed by 1716

Abstract

We have studied the angular time delay in slow-electron elastic scattering by spherical targets as well as the average time delay of electrons in this process. It is demonstrated how the angular time delay is connected to the Eisenbud–Wigner–Smith (EWS) time delay. The specific features of both angular and energy dependencies of these time delays are discussed in detail. The potentialities of the derived general formulas are illustrated by the numerical calculations of the time delays of slow electrons in the potential fields of both absolutely hard-sphere and delta-shell potential well of the same radius. The conducted studies shed more light on the specific features of these time delays. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Review

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Open AccessEditor’s ChoiceReview

Recent Progress in Low-Energy Electron Elastic-Collisions with Multi-Electron Atoms and Fullerene Molecules

Alfred Z. Msezane

and

Zineb Felfli

Atoms 2022, 10(3), 79; https://doi.org/10.3390/atoms10030079 - 29 Jul 2022

Cited by 3 | Viewed by 1281

Abstract

We briefly review recent applications of the Regge pole analysis to low-energy 0.0 ≤ E ≤ 10.0 eV electron elastic collisions with large multi-electron atoms and fullerene molecules. We then conclude with a demonstration of the sensitivity of the Regge pole-calculated Ramsauer–Townsend minima and shape resonances to the electronic structure and dynamics of the Bk and Cf actinide atoms, and their first time ever use as novel and rigorous validation of the recent experimental observation that identified Cf as a transitional element in the actinide series. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessReview

Peculiar Physics of Heavy-Fermion Metals: Theory versus Experiment

Vasily R. Shaginyan

Alfred Z. Msezane

and

George S. Japaridze

Atoms 2022, 10(3), 67; https://doi.org/10.3390/atoms10030067 - 23 Jun 2022

Cited by 2 | Viewed by 1637

Abstract

This review considers the topological fermion condensation quantum phase transition (FCQPT) that leads to flat bands and allows the elucidation of the special behavior of heavy-fermion (HF) metals that is not exhibited by common metals described within the framework of the Landau Fermi liquid (LFL) theory. We bring together theoretical consideration within the framework of the fermion condensation theory based on the FCQPT with experimental data collected on HF metals. We show that very different HF metals demonstrate universal behavior induced by the FCQPT and demonstrate that Fermi systems near the FCQPT are controlled by the Fermi quasiparticles with the effective mass

M^{*}

strongly depending on temperature T, magnetic field B, pressure P, etc. Within the framework of our analysis, the experimental data regarding the thermodynamic, transport and relaxation properties of HF metal are naturally described. Based on the theory, we explain a number of experimental data and show that the considered HF metals exhibit peculiar properties such as: (1) the universal

T / B

scaling behavior; (2) the linear dependence of the resistivity on T,

ρ (T) \propto A_{1} T

(with

A_{1}

is a temperature-independent coefficient), and the negative magnetoresistance; (3) asymmetrical dependence of the tunneling differential conductivity (resistivity) on the bias voltage; (4) in the case of a flat band, the superconducting critical temperature

T_{c} \propto g

with g being the coupling constant, while the

M^{*}

becomes finite; (5) we show that the so called Planckian limit exhibited by HF metals with

ρ (T) \propto T

is defined by the presence of flat bands. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessReview

ATOM Program System and Computational Experiment

Larissa V. Chernysheva

and

Vadim K. Ivanov

Atoms 2022, 10(2), 52; https://doi.org/10.3390/atoms10020052 - 24 May 2022

Cited by 1 | Viewed by 1175

Abstract

The article is devoted to a brief description of the ATOM computer program system, designed to study the structure, transition probabilities and cross sections of various processes in multielectron atoms. The theoretical study was based on the concept of a computational experiment, the main provisions of which are discussed in the article. The main approximate methods used in the system of programs for taking many-electron correlations into account and determining their role in photoionization processes, elastic and inelastic electron scattering, the decay of vacancies, and many others are presented. The most significant results obtained with this software are listed. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Probing C₆₀ Fullerenes from within Using Free Electron Lasers

Nora Berrah

Atoms 2022, 10(3), 75; https://doi.org/10.3390/atoms10030075 - 14 Jul 2022

Cited by 1 | Viewed by 1135

Abstract

Fullerenes, such as C₆₀, are ideal systems to investigate energy redistribution following substantial excitation. Ultra-short and ultra-intense free electron lasers (FELs) have allowed molecular research in a new photon energy regime. FELs have allowed the study of the response of fullerenes to X-rays, which includes femtosecond multi-photon processes, as well as time-resolved ionization and fragmentation dynamics. This perspective: (1) provides a general introduction relevant to C₆₀ research using photon sources, (2) reports on two specific X-ray FEL-based photoionization investigations of C₆₀, at two different FEL fluences, one static and one time-resolved, and (3) offers a brief analysis and recommendations for future research. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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