Gedeon S. The B-spline R-matrix method in theory of low-energy electron scattering on complex atoms

We developed the new BSR version of R-matrix method, based on the use of basis splines and term-dependent non-orthogonal orbitals. This version allows to investigate both an electronic structure of complex atoms and the elementary proccesses (such as elastic scattering, excitation and ionozation) of their interaction with photons and slow electrons. Using the example of low-energy electron scattering on calcium and aluminium as well as photodetachment of negative ions Ca– and Al–, we have shown, that proposed BSR approach allows one to obtain highly accurate results for non-relativistic collisions of electrons and photons with atoms and negative ions. To achieve this the close-coupling expansion must include all open channels. Also the basis set of configuration state functions should contain the electron configurations with excited core. It was shown, that the inclusion of core relaxation effects (using the term-dependent non-orthogonal orbitals) can significantly improve the corresponding binding energies as well as cross sections of elastic scattering and electron impact excitation of Ca atoms. We have determined that for the complex atoms (such as Ca and Al) the scattering cross sections are more sensitive to the electron correlations in the target, than to the short-range interactions with the incident electron. We found, that the energy dependence of the photodetachment cross section of Al– negative ion exhibits complex resonance structure caused by autoionizing states (AIS) of Al–. The positions and the widths of these AIS were obtained along with their classification. The predicted photodetachment cross sections provide new opportunities for future experimental and theoretical studies of the Al– negative ion. A large array of data for the scattering characteristics is obtained: integral and differential cross sections for elastic scattering and electron impact excitation of Ca and Al atoms, atomic collision parameters (so-called pseudo-Stokes parameters), oscillator strengths of selected transitions, electron impact ionization cross sections, cross sections of photodetachment of negative ions Ca– and Al–. The obtained results are in good agreement with the available experimental and theoretical data. The present calculations shown significantly better agreement with the absolute peak value of the Ca– photodetachment cross sections than other R-matrix calculations. Comparison of results obtained in our BSR-models with different numbers of target states provides an estimate regarding the likely accuracy of the present cross sections, which considered as converged to an accuracy of a few percent.