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A novel scattering formalism, the multi-configuration Dirac–Fock partial wave analysis (MCDF-PWA), is presented in this study. This approach extends the conventional Dirac partial wave analysis by incorporating multiple atomic configurations of the target scatterer. The newly formulated methodology is employed to compute the cross-sections in elastic e-atom scattering. The analysis is performed for a few atomic targets like Mg, Ca, and Ba.

A complex optical potential, in the framework of Dirac partial wave analysis, is employed to study the minima in the differential cross sections (DCSs) and the spin polarization due to the elastic scattering of electron by Pb atom. In addition, integral, momentum-transfer, absorption, viscosity and total cross sections are also reported for the energy region 6 eV ≤ Ei ≤10 keV. This complex optical potential comprises the static, exchange, polarization and absorption components. We obtain, in total, 12 critical minima (CM) positions, where DCS attains its smallest values and 22 points with of the maximum values of spin polarization (MSP). CM and MSP are found to be correlated in terms of Ei and scattering angles where the spin-flip amplitude overrides the magnitude of their direct counterpart. As per as we know, there is neither any experimental nor any theoretical study on CM of e-Pb scattering available in the literature. A detailed comparison shows a good agreement between our predicted results with the available experimental and other theoretical findings.

This article reports on the scattering of unpolarized and spin polarized electrons and positrons from 28Ni58,29Cu63,46Pd108, and 78Pt196, covering light to heavy precious metal targets. To cover the wide energy domain of 1 eV ≤Ei≤300 MeV, Dirac partial-wave phase-shift analysis is employed, using a complex optical potential for Ei≤1 MeV and a potential derived from the nuclear charge distribution for Ei>1 MeV. Results are presented for the differential and integral cross-sections, including elastic, momentum transfer, and viscosity cross-sections. In addition, the inelastic, ionization, and total (elastic + inelastic) cross-section results are provided, together with mean free path estimates. Moreover, the polarization correlations S,T, and U, which are sensitive to phase-dependent interference effects, are considered. Scaling laws with respect to collision energy, scattering angle, and nuclear charge number at ultrahigh energies are derived using the equivalence between elastic scattering and tip bremsstrahlung emission. In addition, a systematic analysis of the critical minima in the differential cross-section and the corresponding total polarization points in the Sherman function S is carried out. A comparison with existing experimental data and other theoretical findings is made in order to test the merit of the present approach in explaining details of the measurements.

Superheavy elements are an ideal testbed for studying relativistic, exchange, and correlation effects in scattering phenomena. In this work, we investigate electron scattering from copernicium (Z=112) and oganesson (Z=118) atoms. Both the relativistic Dirac and non-relativistic partial wave methods are employed to analyze the scattering dynamics, with the interaction between the projectile and target atom modeled within the framework of the optical potential approach. Our results demonstrate that relativistic, exchange, and correlation effects play a significant role in modifying the scattering cross-sections and scattering length, highlighting the influence of these interactions on the scattering processes from superheavy atomic systems. The work also attempts to identify common features of the scattering cross-section by comparing those of lighter elements in the same group.

The spin-polarization S and the spin-polarization parameters U and T of the elastically scattered electrons from Hg atoms have been computed for scattering angles 0°-180° in the energy range 1 eV ≤ E i ≤ 2 keV . An optical model approach is employed using a complex optical potential within the framework of the Dirac relativistic partial wave analysis. We compare our results with recent experiments and available theoretical calculations and find a reasonable agreement with experiments over a wide range of energies.

We study a class of periodic Schrödinger operators, which in distinguished cases can be proved to have linear band-crossings or “Dirac points”. We then show that the introduction of an “edge”, via adiabatic modulation of these periodic potentials by a domain wall, results in the bifurcation of spatially localized “edge states”. These bound states are associated with the topologically protected zero-energy mode of an asymptotic one-dimensional Dirac operator. Our model captures many aspects of the phenomenon of topologically protected edge states for two-dimensional bulk structures such as the honeycomb structure of graphene. The states we construct can be realized as highly robust TM-electromagnetic modes for a class of photonic waveguides with a phase-defect.

In this paper, we propose a recurrent neural network numerical method with the finite element method for partial differential equations to study the band gap structure and Dirac points in two-dimensional photonic crystals. Electromagnetic wave propagation is governed by Maxwell’s equations. We transform the partial differential equations into large-scale generalized eigenvalue problems by spatially discretising them using the finite element method. Compared with traditional numerical computation methods, neural networks can perform high-speed parallel computation. Existing neural network-based eigenvalue solvers are typically restricted to computing extremal eigenvalues of real symmetric matrix pairs. To overcome this limitation, we develop a novel RNN-based numerical scheme tailored for solving the band structure problem in photonic crystals. We validate our method by computing the dispersion relations of photonic crystals with periodic dielectric columns, achieving excellent agreement with the plane-wave expansion method. In addition, we calculate the Dirac points at the center of the Brillouin zone, which is crucial for understanding the unique optical properties of photonic crystals. We determine the precise filling ratios at which these Dirac points appear, thus providing insight into the relationship between geometrical and material parameters and the appearance of Dirac points.

AbstractIn the current research, we use the hydrodynamic model of electron-ion plasmas with a very general Fermi–Dirac equation of state for electrons in order to investigate the modulational behaviour of ion acoustic (IA) excitation in environments relevant to a wide range of parameters from laboratory to astrophysical phenomena. The reductive perturbation method is used to reduce the model equations into the nonlinear Schrödinger equation from which the dispersion of modulated IA excitations is evaluated and the stability criterion for nonlinear envelope excitations is obtained in terms of normalized electron temperature and chemical potential, applicable to a wide range of parametric space from solid state and inertial-confined fusion plasmas up to the compact stellar objects like white dwarf stars. It is shown that both kinds of bright and dark envelop solitons can exist in warm dense matter, and their stability depends strongly on electron fluid parameters.Graphic abstract

We present four frequently used finite difference methods and establish the error bounds for the discretization of the Dirac equation in the massless and nonrelativistic regime, involving a small dimensionless parameter 0 < ε ≪ 1 inversely proportional to the speed of light. In the massless and nonrelativistic regime, the solution exhibits rapid motion in space and is highly oscillatory in time. Specifically, the wavelength of the propagating waves in time is at O ( ε ), while in space, it is at O (1) with the wave speed at O ( ε − 1 ). We adopt one leap-frog, two semi-implicit, and one conservative Crank-Nicolson finite difference methods to numerically discretize the Dirac equation in one dimension and establish rigorously the error estimates which depend explicitly on the time step τ , mesh size h , and the small parameter ε . The error bounds indicate that, to obtain the “correct” numerical solution in the massless and nonrelativistic regime, i.e., 0 < ε ≪ 1, all these finite difference methods share the same ε -scalability as time step τ = O ( ε 3/2 ) and mesh size h = O ( ε 1/2 ). A large number of numerical results are reported to verify the error estimates.

A new integral equation formulation is presented for the Maxwell transmission problem in Lipschitz domains. It builds on the Cauchy integral for the Dirac equation, is free from false eigenwavenumbers for a wider range of permittivities than other known formulations, can be used for magnetic materials, is applicable in both two and three dimensions, and does not suffer from any low-frequency breakdown. Numerical results for the two-dimensional version of the formulation, including examples featuring surface plasmon waves, demonstrate competitiveness relative to state-of-the-art integral formulations that are constrained to two dimensions. However, our Dirac integral equation performs equally well in three dimensions, as demonstrated in a companion paper.