The electron-atom (ion) collision excitation process is one of the most common inelastic scattering processes. It is of great significant in the fields of astrophysics and laboratory plasma. The relativistic distorted-wave method is a widely used theoretical tool for studying electron-atom (ion) collisions, with the aim of obtaining scattering parameters, such as impact cross sections and rate coefficients.
In recent years, we have developed a set of fully relativistic distorted-wave methods and programs for studying the electron-atom collision excitation processes. This method is based on the multi-configuration Dirac-Hartree-Fock (MCDHF) method, along with the corresponding packages GRASP 92/2K/2018 and RATIP. The present paper introduces the calculations of continuum state wave functions, total and differential cross sections, state multipoles, integral and differential Stokes parameters of the radiation photon following the impact excitation processes of polarized electrons and atoms. The influence of electron correlation effects, Breit interaction, and plasma screening effects on the excitation cross sections is discussed. The present methods and programs offer several advantages:
(1) In the calculations of the continuum electron wave functions, the direct and exchange interactions between the bound electron and the continuum electron are included. Then, the anti-symmetrized coupling wave functions, which is composed of the continuum electron and the ion wave functions, are utilized as the wave function of the system. This method has been employed to study the low to high energy electron scattering processes.
(2) In this method, the target state wave function is obtained using the MCDHF theory and the corresponding GRASP packages. The MCDHF method has the advantage of being able to consider the electron correlation effects, including valence-valence, core-valence, and core-core correlations, as well as the Breit interaction and quantum electrodynamics (QED) effects effect on the target state wave function. Furthermore, the calculation of the collision excitation matrix elements also incorporates the contribution of the Breit interaction. Consequently, the present method combines the advantages of both the MCDHF method and distorted-wave method, making it suitable for studying the scattering processes of highly charged ions. In addition, it facilitates the study of the influence of higher-order effects on the collision dynamics, thereby enabling the obtaining high-precision theoretical data.
(3) The current method and program can also be utilized to study the scattering cross section of electron-atom collision excitation processes, as well as the impact of plasma screening effects on collision excitation. Furthermore, the state multipoles, differential Stokes parameters, integral Stokes parameters and orientation parameters of electron-complex atom collision excitation can be studied in detail using the present method and program.