Introduction: The theoretical analysis of ultrafast laser–matter interactions requires accurate methods for calculating time-dependent photoionization spectra. A common approach involves solving the time-dependent Schrödinger equation (TDSE) and projecting the final wave function onto the stationary continuum states of the unperturbed Hamiltonian. However, this projection often introduces large, unphysical oscillations into the energy spectrum, which are typically smoothed using convolution techniques like the window-operator method (WOM), a process that can inadvertently suppress genuine physical features.

Methods: We introduce a novel Scattering Projection Method (SPM) for one-dimensional ionization processes [1]. Instead of using stationary eigenstates, the SPM projects the time-evolved wave function onto a basis of scattering states with appropriate incoming or outgoing boundary conditions. We compare the SPM against the WOM for several systems: a simple square well, a jellium model of a metal surface, and a realistic band-structure-based potential modeling a crystalline aluminum surface.

Results: The SPM effectively eliminates the spurious oscillations that plague the standard projection method, yielding a smooth energy spectrum. Crucially, unlike the WOM, the SPM preserves fine physical structures such as Ramsauer–Townsend resonances, which are smeared out by window averaging. The method also naturally enables the calculation of directional emission, revealing asymmetries in photoelectron spectra driven by ultrashort and half-cycle pulses.

Conclusions: The Scattering Projection Method provides a superior alternative for extracting photoemission spectra from numerical TDSE solutions. It removes spurious numerical artifacts more effectively while faithfully preserving physically relevant spectral details. The SPM is particularly useful for studying systems where quantum interference effects or emission directionality are of interest, offering a robust tool for the analysis of ultrafast ionization dynamics in atoms and solid surfaces.

References:

[1] Barlari et al., Eur. Phys. J. D. 79, 93 (2025).

Introduction
Space radiation represents one of the most critical health challenges for astronauts during long-duration missions. Its effects stem from complex atomic and subatomic interactions involving heavy ions and high-energy photons that induce biological damage in tissues. Traditional computational dosimetry and Monte Carlo simulations have provided valuable insight, but their predictive capacity remains limited in highly variable radiation environments. Artificial Intelligence (AI) offers a transformative approach to modeling these atomic-scale processes and predicting their biomedical consequences with greater precision.

Methods
This systematic review followed PRISMA guidelines and analyzed studies indexed in PubMed, Scopus, IEEE Xplore, and NASA ADS from 2010 to 2025. The inclusion criteria focused on research employing machine learning (ML) or deep learning (DL) algorithms for atomic-level radiation modeling, dose prediction, or biological risk estimation. Extracted data included algorithm type, dataset source, atomic modeling scale, and biomedical applications.

Results and Discussion
Across 68 eligible studies, AI-based models outperformed traditional analytical or Monte Carlo methods in radiation prediction accuracy by an average of 25-40%. Neural networks and ensemble learning approaches showed superior performance in correlating atomic interaction data with biomarkers of DNA damage, oxidative stress, and neurocognitive decline. Hybrid AI frameworks integrating atomic collision data and biomedical endpoints demonstrated promising applications for astronaut health risk prediction and adaptive shielding design.

Conclusions
AI-driven modeling of atomic and space radiation interactions is redefining the landscape of space biomedicine. Integrating atomic data with biomedical outcomes enables more accurate and individualized radiation risk assessment, essential for future Moon and Mars missions. Future research should prioritize standardized datasets and explainable AI models to bridge atomic physics and biomedical prediction systems.

Ionization of atoms under charged heavy particle impact is a fundamental phenomenon, both from the point of view of theory and practical applications. The process of single ionization of helium presents a difficult few-body Coulomb problem above the break-up threshold for three freely charged particles.

We recently developed an approach based on the expansion in terms of parabolic convoluted quasi-Sturmians (CQSs). These basis functions are obtained by applying the Green's function operators of two models (named 2C and IIC in PRA, 111, 052812 (2025)), which involve the interaction of two pairs of particles using the corresponding Jacobi coordinates. Our goal here is to extend the CQS approach by including all Coulomb interactions when constructing the basis set. Specifically, we propose an ansatz for the three-body Green's function in the form of a modification of the 2C model operator by equipping the latter with factors that are consistent with the 3C model. In this work, to ensure the effectiveness of this approach, we restrict ourselves to the zeroth-order approximation, which directly reduces to the 3C model.

Calculations are performed for proton-impact ionization of atomic helium at 75 keV for different regimes that have been explored experimentally and theoretically. The ejected electron energies are taken to be below, nearly equal to, and above the cusp energy, i.e., the energy corresponding to the proton–electron velocity matching regime. Comparison of the results of the present 3C calculations with the cross-sections obtained with the 2C (for electron and proton velocities, which are quite different) and IIC models (for velocity matching) allows us to reveal the role of various pairwise interactions in the possible ionization mechanisms.

The achieved agreement between the calculated cross-sections and the results obtained by other theoretical methods, both perturbative and ab initio (e.g., WP-CCC), confirms the effectiveness of the developed approach.

Iron K-shell lines are among the most prominent features in astronomical X-ray spectra. These lines are
observed in a wide variety of natural X-ray sources, including active galactic nuclei, X-ray binaries, stellar
corona, and supernova remnants. This project is dedicated to the continued development of relativistic
computational methods to generate high-precision atomic data for iron ions. The goal of the project
is to model Kα, Kβ, and Kγ lines from iron ions, as well as the ionisation rates. To do this, we
compute direct photoionization and resonant ionization cross-sections for both valence and inner-shell
electrons. The initial emphasis will be on iron ions in the highly charged states Fe XVII through Fe XXVI,
which dominate X-ray emissions in many hot cosmic environments. We employ the AUTOSTRUCTURE
computational package, which allows for the calculation of atomic structure and collisional data within a
relativistic framework, using distorted-wave and configuration interaction approaches. These results are
compared against data obtained from the Breit–Pauli R-matrix (BPRM) method. The resulting atomic
data will be of significant value to the astrophysical community, especially for modeling and interpreting
high-resolution X-ray spectra obtained from modern space telescopes.

Introduction

The non-relativistic quantum three-body problem, despite its century-long history, continues to challenge even experienced theorists due to the intricate coupling between angular and radial degrees of freedom. A systematic and pedagogically transparent route for eliminating angular dependence from the three-body Schrodinger equation (SE) is presented, following the spirit of the exposition by Bhatia and Temkin [1,2]. This leads us to the Reduced Schrodinger Equation (RSE)—a matrix-operator formulation that fully retains the generality of arbitrary particle masses, charges, total angular momentum (L), and parity.

Methods

The derivation beginning with the elimination of center-of-mass motion, followed by an analysis of the rotational invariance of the Hamiltonian. The angular basis is constructed from solid minimal bipolar harmonics (MBHs), providing a natural way to preserve the individual partial angular momenta of the constituent particles. The resulting RSE offers immediate insight into the coupling between different partial waves. The variational counterpart is derived, enabling accurate computation of bound-state energies and wave functions. The angular integrals are evaluated through a novel technique that expresses MBHs as linear combinations of Wigner D-functions.

Results

Numerical validation is provided for the low-lying singlet and triplet states of the helium atom—both of natural parity (for L<= 7) and unnatural parity (for L<=4). Explicitly correlated multi-exponent Hylleraas-type bases are employed within the framework of the Rayleigh–Ritz variational principle.

Conclusion

This work aims to unify and clarify results that have long been scattered across the literature, offering a self-contained and conceptually cohesive framework. The formalism not only simplifies the angular reduction process for three-body systems but also provides a transparent foundation for extending such treatments to many-body quantum systems.

References

[1] A. K. Bhatia and A. Temkin. Rev. Mod. Phys., 36:1050–1064 (1964).
[2] A. K. Bhatia and A. Temkin. Phys. Rev., 137:A1335–A1343, (1965).

The interaction between a system of charged particles can be strongly affected by the surrounding
media. While for free particles in vacuum, the interaction is described by the Coulomb potential, the
presence of polarizable surfaces introduces surface-particle forces, thus modifying interparticle
interactions. In a recent communication [Randazzo et al., 2024, Proc. R. Soc. A 480: 20240357],
these interactions are described by integrating the electromagnetic energy density of the electrical
system in a stationary approximation, a procedure which recovers the Coulomb interaction for free
particles in vacuum. As an illustration, concave and convex spherical conductor surface cases have
been considered, and analytical expressions could be derived.

In this work, we present the results of one- and two-electron atoms interacting with spherical conductor
surfaces. First, the dynamics of a single electron confined in a spherical cavity in a conductor and
surrounding a conductive sphere is considered. It is shown that for large surface radii, eigenstates
and eigenvalues can be accurately described by analytical expressions.
Then, one- and two-electron atomic systems are investigated. When compared to the corresponding
unconfined systems, the level structure and the charge density distributions are drastically changed
(see Morcillo-Arencibia et al. [2025, Proc. R. Soc. A, in press] for a case of a spherical cavity
in a conductor). This is also the case for the conducting sphere. The influence of such confinement is
also illustrated by studying the photoionization of electron nano sphere states.

The origin of elements heavier than iron remains a major open question in astrophysics. Roughly half of them are believed to have formed through the rapid neutron capture process, with neutron star mergers (NSMs) among the most promising sites. The 2017 detection of gravitational waves from an NSM (GW170817) and the observation of its electromagnetic counterpart—the kilonova (KN) AT2017gfo—provided the first direct evidence for heavy element production in NSMs. The luminosity and spectra of KNe depend critically on the ejecta opacity, which is dominated by millions of lines from r-process elements, especially lanthanides and actinides. Reliable atomic data and opacities for these elements are thus essential to model KNe and interpret these observations.

This work presents a large-scale computation of atomic data and opacities for all heavy elements (Z ≥ 20), with special attention paid to lanthanides and actinides, across a grid of typical KN ejecta conditions within one week after the merger (LTE photospheric phase) using the pseudo-relativistic Hartree–Fock (HFR) method as implemented in Cowan’s code. All resulting atomic and opacity data are publicly available (https://zenodo.org/records/14017952).

Beyond a week post-merger, the KN ejecta enters the nebular phase, where NLTE effects become important, so that every radiative and collisional process must be considered to derive level populations and, hence, the opacity of each element within the KN ejecta, making the spectral modelling highly complex. Due to the scarcity of atomic data for collisional processes in heavy elements, radiative transfer simulations rely on crude empirical formulae to model nebular-phase KN spectra. To improve the situation both in terms of completeness and accuracy, we benchmarked an efficient and scalable approach based on the Plane-Wave Born approximation within the HFR framework. The results are compared with more sophisticated R-Matrix calculations and with existing empirical prescriptions, demonstrating a good balance between computational feasibility and accuracy.

Vortex structures in atomic ionization processes have been the subject of recent studies. In positron-hydrogen [Navarrete, F. O. et al, J. Phys. B, 48 (5), 055201, 2015] and proton–-helium [Guarda, T. A. et al, Atoms 13, 3, 2025], the appearance of a vortex in the vicinity of the electron capture peak in momentum space has been observed. Although the exact position has not been completely elucidated, the coincidence between the angles pointing the vortex and the angle corresponding to one of the Thomas mechanisms—describing kinematic conditions for electron capture—is remarkable. This apparent connection is not completely understood yet.

In order to shine some light upon this mystery, we have carried out several calculations of ionisation differential cross-sections of hydrogen-like targets, using projectiles of different masses. Using an automated algorithm to find the position of the vortices in momentum space, we can compare the angles arising from the different kinds of Thomas mechanisms and the saddle point position.

Atomic systems interacting with quantized modes of the electromagnetic field (cavity QED) have been extensively studied in the literature. The set of field–matter states (polaritons) can be described by the Pauli–Fierz (PF) Hamiltonian, which is derived from the minimal coupling scheme in the Coulomb gauge and the second quantization of the transverse components of the electromagnetic field under confinement. The longitudinal field components are accounted for through interaction potentials between charged particles. Despite the significant simplifications involved in its derivation, the PF equation has a broad range of validity, enabling the description of optical, molecular, and condensed matter systems.

After the seminal work of E. Jaynes and F. Cummings, the literature on the subject is rich with analytical models and simple numerical calculations. However, even with exact knowledge of the material (atomic) states and the field states (cavity modes), a rigorous treatment requires a full -or at least a converged- consideration of all possible field-matter configurations. Furthermore, the longitudinal field component describing interactions between material particles must be consistent with the transverse modes, which are affected by the confinement; this interaction is not necessarily the simple Coulomb potential.

In this work, we present a Configuration–Interaction (CI) method for the eigenstates of the Pauli–Fierz Hamiltonian for atomic systems in spherical cavities. The longitudinal field components (matter interactions) are consistent with the field's boundary conditions inside the conductor. In the case of spherical confinement, this results in a substantial modification of the Coulomb interactions doubt to the coupling with surface polarization, as well as an image potential for the interaction between each charge and the surface. For large cavities, the radial components of the material states tend towards well-defined surface image states, and the material dynamics become 2D, restricted to the surface of the sphere.

The ionization of water molecules is a relevant reaction in fields such as plasma physics, fusion experiments, astrophysics, and radiobiology. We perform a theoretical study of the simple ionization of liquid and gas-phase molecules via fast-electron impact. We employ a first-order perturbative model and consider asymmetric collisions in a coplanar geometry. The reaction observables, i.e., the cross-sections, are obtained via numerical calculation [1-3]. We compute triple-differential cross-sections for the liquid and the gaseous phases. To describe the bound states of liquid-phase water molecules, we utilize a Wannier orbital formalism [4] . Localized orbitals for individual molecules are generated, which include information regarding their interactions with the surrounding liquid environment. The initial bound state of the molecule in the gas phase is represented by linear combinations of Gaussian functions centered on each atom of the water molecule (this approach provides a representation of the multicenter structure of the molecule). The fast-incident and scattered electrons in the reaction are described by plane waves, whereas the ejected electron at low energy is described by a Coulomb wave.
We compare our predictions with experimental data, theoretical calculations, and previous calculations for liquid-phase water [5,6 and references therein] of triple-differential, double-differential, single-differential, and total cross-sections. We find qualitative agreement with the different data. Although the physical properties of the phases are different, the scarse available results nevertheless show little difference.
References
[1] M.L. de Sanctis et al, J. Phys. B (2012) 45, 045206
[2] M.L. de Sanctis et al, J. Phys. B (2015) 48, 0155201.
[3] M.L. de Sanctis et al, Eur. Phys. J.D (2017) 71, 125
[4] P. Hunt et al, Chem. Phys. Lett. (2003) 376, 68
[5] C. Champion Phys. Med. Biol. 55 (2010) 11–32
[6] Mi-Young Song et al, J. Phys. Chem. (2021) Ref. Data 50 , 023103