First-principles study of L -shell iron and chromium opacity at stellar interior temperatures

Abstract

Recently developed free-energy density functional theory (DFT)-based methodology for optical property calculations of warm dense matter has been applied for studying L-shell opacity of iron and chromium at T = 182 eV. We use Mermin-Kohn-Sham density functional theory with a groundstate and a fully temperature-dependent generalized gradient approximation exchange-correlation (XC) functionals. It is demonstrated that the role of XC at such a high-T is negligible due to the total free-energy of interacting system being dominated by the noninteracting free-energy term in agreement with estimations for the homogeneous electron gas. Our DFT predictions are compared to the radiative emissivity and opacity of dense plasmas model, to the real-space Green's function method, and to experimental measurements. Good agreement is found between all three theoretical methods, and in the bound-continuum region for Cr when compared to the experiment, while the discrepancy between direct DFT calculations and the experiment for Fe remains essentially the same as for plasma-physics models.

Radiation burnthrough measurements to infer opacity at conditions close to the solar radiative zone–convective zone boundary

“…Treating the opacity of iron as a free parameter in modelling other astrophysical phenomena (17,18) is also ruled out by these findings. The authors note recently published theoretical work using density functional theory to calculate iron at the Z conditions indicates no enhancement in the opacity of iron [47]. Furthermore, a recent development in the debate about the solar elemental abundance is the publication of a reanalysis of solar photospheric data producing abundances that differ from Asplund and remove the discrepancy with helioseismic data [48].…”