arXiv subjects

Rakesh Choubisa

Publications and source records attributed to Rakesh Choubisa.

10 recordsLinked to original sources

arXiv2026

Elastic scattering of twisted electrons by CO$_2$ molecules at high energies

Elastic scattering of a twisted (Bessel) electron beam by CO$_2$ molecules is studied theoretically at high energies. The molecule's structure is optimized using coupled cluster theory and density functional theory with correlation-consistent and Pople basis sets. Coulomb potentials are used in the static approximation. The differential and total scattering cross-sections are computed in the first Born approximation. All cross-sections are orientation-averaged using a passive rotational averaging technique. The scattering is studied by the impact of the twisted beam with topological charges in the range $m_l$ = 1 and $m_l$ = 20. The cross sections are, in addition, averaged over the target's impact parameters, which accounts for the cross sections of a large distribution of CO$_2$ molecules. Finally, the molecule's total cross-section by plane waves and twisted beams is reported. The proposed methodology can be applied to study any polyatomic molecule, regardless of its structure.

quant-ph↗

arXiv2026

Polarization Effects in Laser-Assisted (e,2e) Collision on H-atom by Twisted Electrons

The dynamics of fast (e, 2e) collisions, induced by the impact of twisted electron beams, on atomic hydrogen, is analyzed in the presence of a laser field with circular and linear polarization. For the (e,2e) differential cross-section calculations we use Volkov and Coulomb-Volkov wave functions for scattered and ejected electrons, respectively, while the laser-atom interaction is treated in first-order perturbation theory. The formalism is developed for the asymmetric coplanar geometry in the first Born approximation. We investigate the influence of laser field polarization and provide a comparative analysis of Triple Differential Cross-Sections (TDCS) for circularly and linearly polarized laser fields as a function of ejected electron angle. The overall magnitude of the cross-section is larger for circular polarization as compared to linear polarization. Some notable changes in the angular distributions of TDCS were also observed for the circular polarization as compared to that for linear polarization. We further extend the study to coherent superpositions of twisted electron beams to examine OAM effects for macroscopic target which shows that the TDCS$_{av}$ is strongly sensitive to the difference of the projectiles OAM as well as on the phase difference between them.

physics.atom-ph↗

arXiv2025

Triple differential cross-section for Laser-assisted (e,2e) process on $H_2O$ molecule by Plane and Twisted electrons Impact

Twisted electron-impact single ionization ((e,2e) process) of water molecule is theoretically studied in the presence of an external laser field. Calculations have been performed in the framework of the first Born approximation in coplanar asymmetric geometry. The wave functions for the fast (incident/scattered) electron and the ejected electron are described by the Volkov and Coulomb Volkov wave functions respectively which take into account the interaction of the laser field with incident/scattered and ejected electrons respectively. We calculate the triple differential cross section (TDCS) corresponding to the laser-assisted (e,2e) process for different orientations of the linearly polarised laser field. We describe the molecular state of $H_{2}O$ by the linear combination of atomic orbitals (self-consistent field LCAO method). The angular profile of the TDCS for plane wave electrons is strongly modified by the laser field compared to that of without laser field. However, for the twisted electrons with laser field the angular distribution is slightly changed from those of without laser field. We study the angular distribution of TDCS for laser field polarization parallel to the incident momentum ($\varepsilon_0$ $\parallel$ $k_i$), parallel to momentum transfer ($\varepsilon_0$ $\parallel$ $Δ$) and perpendicular to the momentum transfer ($\varepsilon_0$ $\perp$ $Δ$) and we observe that the $\varepsilon_0$ $\parallel$ $Δ$ has the highest magnitude of TDCS. For the orientations $\varepsilon_0$ $\parallel$ $k_i$ and $\varepsilon_0$ $\perp$ $Δ$, the laser-assisted plane wave studies shows oscillatory nature of TDCS but for the orientation $\varepsilon_0$ $\parallel$ $Δ$ we observe only recoil peak for $p-like$ character orbitals and dual peak, a recoil and binary peaks for the $s-like$ character orbital.

physics.atm-clus↗

arXiv2023

Laser-assisted (e,2e) study with twisted electron beam on H-atom

We study the laser-assisted twisted electron beam impact ionization of the hydrogen atom in coplanar asymmetric geometry. We develope the theoretical model in the first Born approximation. In the presence of the laser field, we treat the incident and scattered electrons as Volkov waves, the ejected electron, moving in the combined field of the laser and residual ion H + , is described by a Coulomb-Volkov wave function . In this communication, we compare the angular profile of triple differential cross-section (TDCS) for laser-assisted twisted electron beam incidence with the plane-wave, laser-assisted plane wave, and field-free twisted electron beam for (e,2e) processes, for different orbital angular momentum (OAM) number (m l ) values. We analyze the influence of the laser parameters (photon exchanged, intensity ) on the angular distribution of the TDCS. We study the (T DCS) av for macroscopic target to examine the effect of opening angle θ p of the twisted electron beam on the angular profile of TDCS. Our results clearly show the impact of laser parameters (electric field ? and number of photon exchanged (l)) and twisted electron beam parameters (OAM number (m l ) and opening angle (θ p )) on the angular distribution of TDCS.

physics.atom-ph↗

arXiv2022

MsSpec-DFM (Dielectric function module): Towards a multiple scattering approach to plasmon description

We present here the MsSpec Dielectric Function module (MsSpec-DFM), which generates dielectric functions in an electron gas or a liquid, either isolated or embedded into an environment. In addition to standard models such as the plasmon pole and the RPA, this module also provides more involved methods incorporating local field corrections (in order to account for correlations), Boltzmann-Vlasov hydrodynamical methods, the relaxation-damped Mermin and the diffusion-damped Hu-O'Connell methods, as well as moment-based methods using either a Nevanlinna function or a memory function. Ultimately, through the use of form factors, the MsSpec-DFM module will be able to address a wide range of materials such as metals, semiconductors, including inversion layers, hetero-structures, superconductors, quantum wells, quantum wires, quantum dots, Dirac materials such as graphene, and liquids.

cond-mat.other↗

arXiv2022

Model dielectric functions for fluctuation potential calculations in electron gas: a critical assessment

In this article, we report a critical assessment of dielectric function calculations in electron gas through the comparison of different modelling methods. This work is motivated by the fact that the dielectric function is a key quantity in the multiple scattering description of plasmon features in various electron-based spectroscopies. Starting from the standard random phase approximation (RPA) expression, we move on to correlation-augmented RPA, then damped RPA models. Finally, we study the reconstruction of the dielectric function from its moments, using the Nevanlinna and memory function approaches. We find the memory function method to be the most effective, being highly flexible and customizable.

cond-mat.other↗

arXiv2021

Semi-relativistic (e,2e) study with twisted electron beam on Cu and Ag

In this communication, we report our calculations of Triple Differential Cross-Section (TDCS) for the relativistic (e,2e) process with a twisted electron beam on Cu and Ag atomic targets in coplanar asymmetric geometry mode. The theoretical formalism has been developed in the first Born approximation (FBA) in which we use the Dirac plane wave as well as the twisted electron wave for the incident electron beam to study the effect of various parameters of the twisted electron beam on the (e,2e) process. We use Dirac plane wave, semi relativistic Coulomb wave and Darwin wave function for the scattered, ejected and K-shell electron respectively. We compare the angular profiles of the TDCS of the twisted electron impact (e,2e) process with that of the plane wave. We segregate the TDCS for charge-charge interaction and current-current interaction with their interference term and study the effect of different parameters of the twisted electron beam on them. The study is also extended to the macroscopic Cu and Ag targets to further investigate the effect of the opening angle of the twisted electron beam on TDCS. The spin asymmetry in TDCS caused by polarized incident electron beam is also studied to elucidate the effects of the twisted electron beam on the (e,2e) process.

physics.atom-ph↗

arXiv2021

Twisted electron impact single ionization coincidence cross-sections for noble gas atoms

We present the angular profiles of the triple differential cross-section (TDCS) for the (e,2e) process on the noble gas atoms, namely He (1s), Ne (2s and 2p), and Ar (3p) for the plane wave and the twisted electron impact. We develop the theoretical formalism in the first-born approximation. The present study compares the TDCS for different values of orbital angular momentum number $m$ and opening angles $θ_p$ of the twisted electron beam with that of the plane wave beam. In addition, we also investigate the TDCS for macroscopic atomic targets to explore the influence of opening angle $θ_p$ of the twisted electron beam on the TDCS. Our results show that the peaks in binary and recoil region shift from the momentum transfer direction. The results also show that for larger opening angles the peaks for $p$-type orbitals split into double-peak structures which are not observed in the plane wave results for the given kinematics. The angular profiles for averaged cross-section show the dependence of TDCS on the opening angles which are significantly different from the plane wave TDCS.

physics.atom-ph↗

arXiv2021

Triple differential cross-section for the twisted electron impact ionization of water molecule

In this communication, we present the results of the triple differential cross-section (TDCS) for the (e,2e) process on H2O molecule for the plane wave and the twisted electron beam impact. The formalism is developed in the first Born approximation. We describe the plane/twisted wave, plane wave, the linear combination of atomic orbitals (LCAO) (self-consistent field LCAO method) and Coulomb wave for the incident electron, scattered electron, the molecular state of H2O, and the ejected electron, respectively. We investigate the angular profiles of the TDCS for the outer orbitals 1B1, 3A1, 1B2, and 2A1 of the water molecule. We compare the angular profiles of the TDCS for the different values of orbital angular momentum (OAM) number m of the twisted electron beam with that of the plane wave beam. We also study the TDCS for macroscopic H2O target to explore the effect of opening angle θp of the twisted electron beam on the TDCS. Our results clearly show the effect of the twisted electron's OAM number (m) and the opening angle θp on the TDCS of the water molecule.

physics.chem-ph↗

arXiv2020

Electron impact single ionization of hydrogen molecule by twisted electron beam

In this communication, we present the results of the Five-fold Differential Cross Section (5DCS) and Triple Differential Cross Section (TDCS) for the (e,2e) process on molecular hydrogen ($H_2$) by the plane wave and the twisted electron beam impact. The formalism is developed within the first Born approximation using the plane wave and the twisted wave for the incident electron beam. We describe the plane wave, Heitler-London type wave function and Coulomb wave for the scattered electron, $H_2$ molecular state, and the ejected electron respectively. We compare the angular profiles of the 5DCS and TDCS for the different values of Orbital Angular Momentum (OAM) number {\it m} of the twisted electron beam with that of the plane wave beam. We also present the 5DCS for different molecular orientations and study the effect of {\it m} on the 5DCS. We further investigate the influence of the twisted electron beam on the (e,2e) process on the $H_2$ molecule from the perspective of the "Young-type" interference of the scattered waves, emanating from the two atomic centers of the $H_2$ molecule. We also study the TDCS for macroscopic $H_2$ target to explore the effect of opening angle ($θ_p$) of the twisted electron beam on the TDCS. Our results clearly show the effect of the twisted electron's OAM number (m) and the opening angle ($θ_p$) on the 5DCS and TDCS of the molecular hydrogen.

physics.atom-ph↗