Taking the Convergent Close-Coupling Method beyond Helium: The Utility of the Hartree-Fock Theory

Igor Bray,Sudhakar Pamidighantam,Xavier Weber,Alisher S Kadyrov,Dmitry V Fursa,Anatoli S Kheifets,Barry I Schneider,Maciej Cytowski

doi:10.3390/atoms10010022

Abstract

The convergent close-coupling (CCC) method was initially developed to describe electron scattering on atomic hydrogen and the hydrogenic ions such as He+. The latter allows implementation of double photoionization (DPI) of the helium atom. For more complex single valence-electron atomic and ionic targets, the direct and exchange interaction with the inner electron core needs to be taken into account. For this purpose, the Hartree-Fock (HF) computer codes developed in the group of Miron Amusia have been adapted. In this brief review article, we demonstrate the utility of the HF technique by examples of electron scattering on Li and the DPI of the H− and Li− ions. We also discuss that modern-day computer infrastructure allows the associated CCC code, and others, to be readily run directly via the Atomic, Molecular and Optical Science Gateway.

Highlights

Collisions between particles on the atomic scale are ubiquitous throughout the universe
The latter include astrophysics, fusion, lighting, nanolithography, and medical imaging and therapy. It is of great concern whenever there are substantial discrepancies between theory and experiment that are not understood. One such case was the discrepancy for the angular correlation parameters in the fundamental Coulomb three-body collision problem of e-H excitation of the 2p state [1,2]
The details of the implementation of the convergent close-coupling (CCC) theory to electron scattering on quasi one-electron targets, such as the alkalis, have been given by Bray [18]

Summary

Introduction

Collisions between particles on the atomic scale are ubiquitous throughout the universe. The group of Miron Amusia generously provided the Hartree-Fock computational code [16,17] for a self-consistent treatment of the core electrons This allowed the reduction of the electron–alkali atom collision problem to be a Coulomb three-body problem, albeit with some more complicated nonlocal potentials [18]. The utility of the HF theory was instrumental to describe the valence-shell DPI of alkaline– earth metal atoms [35] These calculations were later found in good agreement with experiments [36]. We shall demonstrate the agreement between theory and experiment by focusing on just the simplest electron–alkali collision system, that of e-Li scattering This collision system is a key component in calculating the DPI of Li−, as upon single or double photoionization the e-Li wave-function corresponds to the final state of Li−. The CCC computer codes utilize modern computational infrastructure including massive parallelism and GPU acceleration and are readily accessible for execution via the Atomic, Molecular and Optical Science Gateway, https://amosgateway.org (accessed on 4 February 2022) [42]

Theory

Electron-Lithium Excitation

Double Photoionisation

Conclusions