R-Matrix calculations for opacities: IV. Convergence, completeness, and comparison of relativistic R-matrix and distorted wave calculations for FeXVII and FeXVIII

TL;DR

This paper compares relativistic R-matrix and distorted wave calculations for FeXVII and FeXVIII to assess their completeness and convergence, ensuring accurate opacity data through cross-method validation and top-up procedures.

Contribution

It introduces a comprehensive comparison and validation of BPRM and RDW methods for high-$n ext{ } ext{and} ext{ }l$ levels, enhancing the accuracy of opacity calculations.

Findings

Good agreement between BPRM and RDW in background cross sections

Configuration interaction significantly affects background cross sections

High-$n ext{ } ext{levels} $ have negligible impact on opacities due to low population

Abstract

To investigate the completeness of coupled channel (CC) Breit-Pauli R-Matrix (BPRM) calculations for opacities, we employ the relativistic distorted wave (RDW) method to complement (``top-up'') and compare the BPRM photoionization cross sections for high-$n\ell$ levels of both FeXVII and FeXVIII. Good agreement is found in background photoionization cross sections using these two methods, which also ensures correct matching of bound level cross sections for completeness. In order to top-up the CC-BPRM calculations, bound-bound transitions involving additional bound levels, and a large number of doubly-excited quasi-bound levels corresponding to BPRM autoionizing resonances described in paper RMOPII, are calculated using the RDW method. Photoionization cross sections in the high energy region are also computed and compared up to about 500 $Ry$, and contributions from higher core level excitations than BPRM are considered. The effect of configuration interaction is investigated, which plays a significant role in correctly reproducing some background cross sections. Owing to the fact that the additional RDW levels correspond to high-$n\ell$ bound levels that are negligibly populated according to the Mihalas-Hummer-D\"{a}ppen equation-of-state (Paper I), the effect on opacities is expected to be small.