Fully relativistic distorted-wave method of studying electron-atom collision excitation process

<sec>The electron-atom (ion) collision excitation process is one of the most common inelastic scattering processes. It is of great significance 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.</sec><sec>In recent years, we have developed a set of fully relativistic distorted-wave methods and programs of studying the electron-atom collision excitation processes. This method is based on the multi-configuration Dirac-Hartree-Fock (MCDHF) method, together with the corresponding packages GRASP 92/2K/2018 and RATIP. In the present work, continuum state wave functions, total and differential cross sections, state multipoles, integral and differential Stokes parameters of the radiation photon after the impact excitation processes of polarized electrons and atoms are calculated. The influences of electron correlation effects, Breit interaction, and plasma screening effects on the excitation cross sections are discussed. The present methods and programs possess several advantages below.</sec><sec>1) In the calculations of the continuum electron wave functions, the direct interaction and exchange interaction between the bound electron and the continuum electron are both included. Then, the anti-symmetrized coupling wave function, which is composed of the continuum electron wave function and the continuum ion wave function, is utilized as the wave function of the system. This method is employed to study the low-energy electron scattering process and medium energy electron scattering process.</sec><sec>2) In this method, the target state wave function is obtained form 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 influence of Breit interaction and quantum electrodynamics effect on the target state wave function. Furthermore, the calculation of the collision excitation matrix elements also includes the contribution of the Breit interaction. Consequently, the present method integrates the advantages of both the MCDHF method and distorted-wave method, thus is made 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 obtaining high-precision theoretical data.</sec><sec>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 influence 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 by using the present method and program.</sec>