Extensive resonance structures are manifest in R-Matrix ( RM ) calculations .
However , there exist a large number of highly excited electronic configurations that may contribute to background non-resonant bound-free opacity in high-temperature plasmas .
Since RM calculations are very complex , and not essential for background contributions , the Relativistic Distorted Wave ( RDW ) method is utilized to complement ( `` top-up '' ) photoionization cross sections of Fe XVII obtained using Close-Coupling Breit-Pauli R-Matrix ( CC-BPRM ) method .
There is good agreement between RDW and BPRM for background cross sections where resonances are not present , and individual fine structure levels can be correctly matched spectroscopically , though resonances are neglected in the RDW .
To ensure completeness , a high energy range up to 500 Ry above the ionization threshold for each level is considered .
Interestingly , the hydrogenic Kramer ’ s approximation also shows the same energy behavior as the RDW .
Grouping separately , the BPRM configurations consist of 454 bound levels with resonances corresponding to configurations 1 s ^ { 2 } 2 s ^ { 2 } 2 p ^ { 4 } nln ^ { \prime } l ^ { \prime } ( n \leq 3 , n ’ \leq 10 ) ; including RDW configurations there are 51,558 levels in total .
The topup contribution results in \sim 20 % increment , in addition to the 35 % enhancement from BPRM calculations over the Opacity Project value for the Rosseland Mean Opacity at the Z-temperature of 2.11 \times 10 ^ { 6 } K ( Pradhan & Nahar 2017 ) ..