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Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A...
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Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider

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

Deadline for manuscript submissions: closed (18 June 2025) | Viewed by 7690

Special Issue Editor

Dr. Nicolas Douguet

E-Mail Website
Guest Editor
Department of Physics, University of Central Florida, Orlando, FL 32816, USA
Interests: attosecond physics; strong-field physics; molecular dynamics

Special Issue Information

Dear Colleagues,

The development of ab initio methods is paramount for the theoretical description of atomic and molecular structures, and the interactions of such targets with other particles and fields. In recent years, many novel ab initio techniques have been developed to improve these calculations, thereby paving the way for new studies and applications that may support a plethora of experimental studies.

This Special Issue of Atoms, entitled "Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider", aims to collect papers (original articles and reviews) that focus on current advancements in ab initio calculations and their applications in the fields of atomic, molecular, and optical physics. At the same time, we decided to make it a tribute to our dear colleague, Barry I. Schneider, who passed away on 3 July 2024.

Research topics may include (but are not limited to) the following:

  • Atomic and molecular structures, including atoms and molecules in static fields;
  • Electron–atom, electron–ion, and electron–molecule collisions;
  • Molecular dynamics (dissociation, vibrational excitation, etc.);
  • Atomic and molecular photoionization;
  • Attosecond and strong field processes in atoms and molecules.

We are excited to receive your contributions.

Dr. Nicolas Douguet
Guest Editor

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 submissions that pass pre-check are 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 monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). 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

  • atomic and molecular structure
  • electron-atom and electron-molecule scattering
  • ultrafast physics
  • molecular spectroscopy
  • strong-field physics

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Further information on MDPI's Special Issue policies can be found here.

Published Papers (7 papers)

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Research

Jump to: Review

18 pages, 2231 KiB  
Article
Comparative DFT Study of K2AgSbBr6 and K2NaScBr6: Exploring the Role of B′B″ Cation Substitution on Material Properties
by Abdelkebir Ejjabli, Mohamed Karouchi, Hamza Errahoui, Abdelmounaim Laassouli, Aymane El haji, Youssef Lachtioui and Omar Bajjou
Atoms 2025, 13(6), 53; https://doi.org/10.3390/atoms13060053 - 13 Jun 2025
Cited by 1 | Viewed by 967
Abstract
The effects of cation substitution are the main emphasis of this investigation into the structural, mechanical, electronic, and optical properties of double perovskites K2AgSbBr6 and K2NaScBr6. Outwardly favorable tolerance and octahedral factors and negative formation energy [...] Read more.
The effects of cation substitution are the main emphasis of this investigation into the structural, mechanical, electronic, and optical properties of double perovskites K2AgSbBr6 and K2NaScBr6. Outwardly favorable tolerance and octahedral factors and negative formation energy confirmed structural stability and thermodynamic feasibility. Mechanical analysis showed that K2AgSbBr6 possesses greater volumetric stability and rigidity, while K2NaScBr6 exhibits greater ductility and isotropic characteristics. The electronic properties determined based on density functional theory (DFT) calculations indicate that K2AgSbBr6 has an indirect bandgap of 0.857 eV, making it suitable for applications using visible light, and K2NaScBr6 has a direct bandgap of 3.107 eV, making it ideal for UV-specific technologies. Optical analyses demonstrate complementary characteristics, particularly in terms of the dielectric function, absorption, reflectivity, energy loss function, refractive index, extinction coefficient, and optical conductivity. K2AgSbBr6 exhibits strong visible light absorptivity. 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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14 pages, 1754 KiB  
Article
The Single-Active-Electron Approximation with Angular-Momentum-Dependent Potentials: Application to the Helium Atom
by Juan Carlos del Valle and Klaus Bartschat
Atoms 2025, 13(5), 43; https://doi.org/10.3390/atoms13050043 - 14 May 2025
Viewed by 1191
Abstract
We discuss an extension of the Single-Active-Electron (SAE) approximation in atoms by allowing the model potential to depend on the angular-momentum quantum number ℓ. We refer to this extension as the ℓ-SAE approximation. The main ideas behind ℓ-SAE are illustrated [...] Read more.
We discuss an extension of the Single-Active-Electron (SAE) approximation in atoms by allowing the model potential to depend on the angular-momentum quantum number ℓ. We refer to this extension as the ℓ-SAE approximation. The main ideas behind ℓ-SAE are illustrated using the helium atom as a benchmark system. We show that introducing ℓ-dependent potentials improves the accuracy of key quantities in atomic structure computed from the Time-Independent Schrödinger Equation (TISE), including energies, oscillator strengths, and static and dynamic polarizabilities, compared to the standard SAE approach. Additionally, we demonstrate that the ℓ-SAE approximation is suitable for quantum simulations of light−atom interactions described by the Time-Dependent Schrödinger Equation (TDSE). As an illustration, we simulate High-order Harmonic Generation (HHG) and the three-sideband (3SB) version of the Reconstruction of Attosecond Beating by Interference of Two-photon Transitions (RABBITT) technique, achieving enhanced accuracy comparable to that obtained in all-electron calculations. One of the main advantages of the ℓ-SAE approach is that existing SAE codes can be easily adapted to handle ℓ-dependent potentials without any additional computational cost. 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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5 pages, 278 KiB  
Article
Benchmark Calculations for Near-Threshold Electron-Impact Excitation of the (1s3s)3,1S States of Helium
by Klaus Bartschat, Igor Bray and Dmitry V. Fursa
Atoms 2025, 13(4), 27; https://doi.org/10.3390/atoms13040027 - 31 Mar 2025
Viewed by 444
Abstract
We revisit the current status of high-precision calculations for electron-impact excitation of the (1s3s)3,1S states in helium in the low-energy near-threshold regime that is characterized by a large number of resonance features. Having noticed [...] Read more.
We revisit the current status of high-precision calculations for electron-impact excitation of the (1s3s)3,1S states in helium in the low-energy near-threshold regime that is characterized by a large number of resonance features. Having noticed discrepancies between predictions from two previous large-scale calculations for this problem, we report new results and make recommendations regarding the absolute cross-sections that should be used in modeling applications. 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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19 pages, 495 KiB  
Article
State-Selective Double Photoionization of Atomic Carbon and Neon
by Frank L. Yip
Atoms 2024, 12(12), 70; https://doi.org/10.3390/atoms12120070 - 16 Dec 2024
Viewed by 1080
Abstract
Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, [...] Read more.
Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, and efforts continue to explore many-electron targets with the same level of detail to understand the angular distributions of the ejected electrons in full dimensionality. Expanding on previous results, we consider here the double photoionization of two 2p valence electrons of atomic carbon and neon and explore the possible continuum states that are connected by dipole selection rules to the coupling of the outgoing electrons in 3P, 1D, and 1S initial states of the target atoms. Carbon and neon share these possible symmetries for the coupling of their valence electrons. Results are presented for the energy-sharing single differential cross section (SDCS) and triple differential cross section (TDCS), further elucidating the impact of the initial state symmetry in determining the angular distributions that are impacted by the correlation that drives the DPI process. 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, 456 KiB  
Article
Mutual Neutralization in Collisions of Li+ with O−
by Åsa Larson and Ann E. Orel
Atoms 2024, 12(12), 61; https://doi.org/10.3390/atoms12120061 - 28 Nov 2024
Viewed by 691
Abstract
The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li+ with O− were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration [...] Read more.
The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li+ with O− were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration interaction method. The final state distributions favored channels with excited oxygen states, indicating a strong effect of electron correlation, and the electron transfer could not be described by a simple one-electron exchange process. 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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15 pages, 3029 KiB  
Article
Efficient Time-Dependent Method for Strong-Field Ionization of Atoms with Smoothly Varying Radial Steps
by Nicolas Douguet, Mikhail Guchkov, Klaus Bartschat and Samantha Fonseca dos Santos
Atoms 2024, 12(7), 34; https://doi.org/10.3390/atoms12070034 - 3 Jul 2024
Cited by 4 | Viewed by 1597
Abstract
We present an efficient numerical method to solve the time-dependent Schrödinger equation in the single-active electron picture for atoms interacting with intense optical laser fields. Our approach is based on a non-uniform radial grid with smoothly increasing steps for the electron distance from [...] Read more.
We present an efficient numerical method to solve the time-dependent Schrödinger equation in the single-active electron picture for atoms interacting with intense optical laser fields. Our approach is based on a non-uniform radial grid with smoothly increasing steps for the electron distance from the residual ion. We study the accuracy and efficiency of the method, as well as its applicability to investigate strong-field ionization phenomena, the process of high-order harmonic generation, and the dynamics of highly excited Rydberg states. 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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Review

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13 pages, 359 KiB  
Review
Numerical Methods for the Time-Dependent Schrödinger Equation: Beyond Short-Time Propagators
by Ryan Schneider and Heman Gharibnejad
Atoms 2025, 13(8), 70; https://doi.org/10.3390/atoms13080070 - 28 Jul 2025
Viewed by 266
Abstract
This article reviews several numerical methods for the time-dependent Schrödinger Equation (TDSE). We consider both the most commonly used approach—short-time propagation, which solves the TDSE by assuming that the Hamiltonian is time-independent over sufficiently small (time) intervals—as well as a number of higher-order [...] Read more.
This article reviews several numerical methods for the time-dependent Schrödinger Equation (TDSE). We consider both the most commonly used approach—short-time propagation, which solves the TDSE by assuming that the Hamiltonian is time-independent over sufficiently small (time) intervals—as well as a number of higher-order alternatives. Our goal is to dispel the notion that the latter are too computationally demanding for practical use. To that end, we cover methods whose numerical building blocks are shared by short-time propagators or can be handled by standard libraries. Moreover, we make the case that these methods are best positioned to take advantage of parallel computing environments. One of the alternatives considered is a “double DVR” solver, which applies an expansion in a product basis of functions in space and time to obtain a solution (over all space and at multiple time points simultaneously) with a single linear system solve. To our knowledge, and despite its simplicity, this approach has not previously been applied to the TDSE. 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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