Importance of the completeness of the configuration interaction and close coupling expansions in Rmatrix calculations for highly charged ions: electronimpact excitation of Fe^{20+}
Abstract
We have carried out two intermediate coupling frame transformation (ICFT) Rmatrix calculations for the electronimpact excitation of {{C}}like {{Fe}}^{20+}, both of which use the same expansions for their configuration interaction (CI) and closecoupling (CC) representations. The first expansion arises from the configurations 2{{{s}}}^{2} 2{{{p}}}^{2},2{{s}} 2{{{p}}}^{3},2{{{p}}}^{4}, \{2{{{s}}}^{2} 2{{p}},2{{s}} 2{{{p}}}^{2},2{{{p}}}^{3}\} {nl}, with n = 3, 4, for l=03, which give rise to 564 CI/CC levels. The second adds configurations 2{{{s}}}^{2} 2{{p}} 5{{l}}, for l=02, which give rise to 590 CI/CC levels in total. Comparison of oscillator strengths and effective collision strengths from these two calculations demonstrates the lack of convergence in data for n = 4 from the smaller one. Comparison of results for the 564 CI/CC level calculation with an earlier ICFT Rmatrix calculation which used the exact same CI expansion but truncated the CC expansion to only 200 levels demonstrates the lack of convergence of the earlier data, particularly for n = 3 levels. Also, we find that the results of our 590 CC Rmatrix calculation are significantly and systematically larger than those of an earlier comparable DWplusresonances calculation. Thus, it is important still to take note of the (lack of) convergence in both atomic structural and collisional data, even in such a highly charged ion as Fe^{20+}, and to treat resonances nonperturbatively. This is of particular importance for Fe ions given their importance in the spectroscopic diagnostic modelling of astrophysical plasmas.
 Publication:

Journal of Physics B Atomic Molecular Physics
 Pub Date:
 April 2016
 DOI:
 10.1088/09534075/49/8/085203
 arXiv:
 arXiv:1511.05776
 Bibcode:
 2016JPhB...49h5203F
 Keywords:

 Physics  Atomic Physics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 17 pages, 6 tables, 26 figures, 38 bibliographic references. Pac numbers 34.50.Fa, 52.20.Fs, 95.30.Ky