Characteristics of ground state electronic structures of ionized atoms and rules of their orbital competitions
Authors: Jin Rui  , Gao Xiang  , Zeng De-Ling  , Gu Chun  , Yue Xian-Fang  , Li Jia-Ming  ,   Center for Atomic and Molecular Nanosciences, Department of Physics, Tsinghua University, Beijing 100084, China;,   Beijing Computational Science Research Center, Beijing 100084, China;,   Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100084, China;,   Department of Physics and Information Engineering, Jining University, Jining 273155, China
Published: December 2020

Ionized atoms widely exist in plasmas, and studies of properties of ionized atoms are the foundations of frontier science researches such as astrophysics and controlled nuclear fusions. For example, the information about the ground configurations of atoms is required for accurately calculating the physical quantities such as energy levels and dynamical processes. The configurations for different ionized atoms can be obtained with the photo-electron energy spectrum experiment, however it is very time-consuming to obtain so many data of all ions. Therefore the more economical theoretical study will be of great importance. As is well known, the configurations of neutral atoms can be determined according to Mendeleev order while those of highly ionized atoms are hydrogen-like due to the strong Coulombic potential of their nuclei. Then with the variations of ionization degree and atomic number along the periodic table, there would appear the interesting competitions between electronic orbitals. Although some theoretical results exist for ions 3 Z 118, 3 Ne 105 (where Z is the atomic number and Ne is the electron number), there are many errors in the results for highly ionized atoms. Therefore, the ground configurations of ionized atoms and their orbital competitions still deserve to be systematically studied. Based on the independent electron approximation, we calculate the energy levels of all possible competition configurations of all the neutral and ionized atoms in the extended periodic tables (2 Z 119) by Dirac-Slater method. Then the ground configurations are determined by calculating the chosen lowest total energy. The advantages of Dirac- Slater method are as follows. 1) It has been shown that the Dirac-Slater calculation is accurate enough for studying the ground properties of atoms, such as the 1st threshold, and that higher accuracy will be obtained for highly ionized atoms, because the electron correlation becomes less important. 2) Furthermore, with Dirac-Slater method we can obtain the localized self-consistent potential, thereby we can study the orbital competition rules for different atoms. Using the three of our designed atomic orbital competition graphs, all of our calculated ground configurations for over 7000 ionized atoms are conveniently expressed. We systematically summarize the rules of orbital competitions for different elements in different periods. We elucidate the mechanism of orbital competition (i.e., orbital collapsing) with the help of self-consistent atomic potential of ionized atoms. Also we compare the orbital competition rules for different periods of transition elements, the rare-earth and transuranium elements with the variation of the self-consistent filed for different periods. On this basis, we summarize the relationship between the orbital competitions and some bulk properties for some elements, such as the superconductivity, the optical properties, the mechanical strength, and the chemistry activities. We find that there exist some abnormal orbital competitions for some lowly ionized and neutral atoms which may lead to the unique bulk properties for the element. With the ground state electronic structures of ionized atoms, we can construct the basis of accurate quasi-complete configuration interaction (CI) calculations, and further accurately calculate the physical quantities like the energy levels, transition rates, collision cross section, etc. Therefore we can meet the requirements of scientific researches such as the analysis of high-power free-electron laser experiments and the accurate measurement of the mass of nuclei.