THEORETICAL COMPLEX ENERGIES OF STARK RESONANCES IN LITHIUM BY OPERATOR PERTURBATION THEORY APPROACH

The theoretical complex energies of the Stark resonances in the lithium atom (non-hydrogenic atomic system) in a DC electric are calculated within the operator form of the modified perturbation theory for the non-H atomic systems. The method includes the physically reasonable distorted-waves approximation in the frame of the formally exact quantum-mechanical procedure. The calculated Stark resonances energies and widths in the lithium atom are calculated and compared with results of calculations on the basis of the method of complex eigenvalue Schrödinger equation by Themelis-Nicolaides, the complex absorbing potential method by Sahoo-Ho and the B-spline-based coordinate rotation method approach by Hui-Yan Meng et al.

Angular distributions in the double ionization of argon by fast electron impact

A model describing the two electrons ejected by distorted waves is applied to the study of the double ionization of argon by fast electrons (~ 5500 eV). The correlation is also partially taken into account both in the final state and in the initial state. The results obtained by our model as well as by other models also based on the first Born approximation are compared with the available experimental data.

Elastic scattering of electrons by barium atoms using the distorted wave method

Differential and integral cross sections of elastic scattering of electrons by barium atoms at intermediate energies (10 – 200 eV) were calculated using the distorted wave method. Being an elastic scattering both the initial and final distortion potentials were taken as the static potential of a barium atom in the initial state. The distorted waves are determined by the partial wave expansion method by expanding them in terms of spherical harmonics while the radial equation corresponding to distorted waves is evaluated using the Numerov method. A computer program DWBA1, for scattering was modified to perform numerical calculations for scattering and the results obtained are compared with the experimental and theoretical results available. The present integral cross sections are in good qualitative agreement with the experimental results and most of the theoretical results. For energies in the range 30 – 100 eV the present differential cross sections are in satisfactory agreement with the other theoretical and experimental results.

A new approach to wide-angle dynamical X-ray diffraction by deformed crystals

A new approach is proposed for X-ray dynamical diffraction theory in distorted crystals. The theory allows one to perform dynamical diffraction simulations between Bragg peaks for non-ideal crystals, using a simple approach of two distorted waves. It can be directly applied for reciprocal-space simulation. The formalism is used to analyse high-resolution X-ray diffraction data, obtained for an InSb/InGaSb/InSb/InAs superlattice grown on top of a GaSb buffer layer on a (001) GaSb substrate.

Distorted waves with exact nonlocal exchange: A canonical function approach

The Canonical Function Method (CFM) is developed and applied, for the first time, to the distorted wave problem with exact nonlocal exchange. In electron impact ionization of hydrogenic systems, the latter originates from the Pauli exclusion principle that leads, in the Hartree–Fock approximation, to a radial Schrodinger equation of an integro-differential type. The application of the CFM with static and polarization potentials allows us to obtain the phaseshifts and scattering lengths in the s-wave singlet and triplet states at high (≥5 eV) and low energies (≤0.1 eV). The results are compared with those obtained by other methods based on exact exchange, local equivalent-exchange potentials and recently developed spectral integral equation methods (S-IEM). The accuracy, stability, and speed of convergence of the CFM are analysed and compare favorably with other methods including the highly accurate S-IEM. At very low energies, the CFM is superior to all known methods.PACS Nos.: 34.00.00, 34.50.–s, 03.65.–w, 02.60.Nm, 02.60.–x