Abstract
There are a number of approaches to study interactions of positrons and electrons with hydrogenic targets. Among the most commonly used are the method of polarized orbital, the close-coupling approximation, and the R-matrix formulation. The last two approaches take into account the short-range and long-range correlations. The method of polarized orbital takes into account only long-range correlations but is not variationally correct. This method has recently been modified to take into account both types of correlations and is variationally correct. It has been applied to calculate phase shifts of scattering from hydrogenic systems like H, He+, and Li2+. The phase shifts obtained using this method have lower bounds to the exact phase shifts and agree with those obtained using other approaches. This approach has also been applied to calculate resonance parameters in two-electron systems obtaining results which agree with those obtained using the Feshbach projection-operator formalism. Furthermore this method has been employed to calculate photodetachment and photoionization of two-electron systems, obtaining very accurate cross sections which agree with the experimental results. Photodetachment cross sections are particularly useful in the study of the opacity of the sun. Recently, excitation of the atomic hydrogen by electron impact and also by positron impact has been studied by this method.
Highlights
An incoming wave behaves like a particle in Recent Advances in Nanophotonics-Fundamentals and Applications processes like Compton scattering and photoabsorption
We find that in the hybrid theory, the He singlet resonance is at ER = 57.8481 eV with respect to the ground state of He and Γ = 0.1233 eV
Theories which provide variational bounds on the calculated phase shifts are preferable because improved results can be obtained when the number of functions in the closed channels is increased
Summary
The discovery of an electron by J.J. Thomson in 1897 led to the development of physics beyond the classical physics. The polarization is possible only when the incident electron is outside the target, according to the method of polarized orbitals [3] This method includes only the long-range À1/r4 potential and not the short-range correlations, and the method is not variationally correct. A method called the hybrid theory [6] has been introduced in which the short-range and long-range correlations are taken into account at the same time and the polarization takes place whether the incident electron is outside or inside the target. The equations for the scattering function are very detailed and are given in [6]
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