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

Area of Science:

• Plasma Physics
• Quantum Mechanics
• Materials Science

Background:

• Accurate optical property calculations are crucial for understanding warm dense matter (WDM).
• Existing methods for WDM opacity calculations have limitations.
• Free-energy density functional theory (DFT) offers a promising approach.

Purpose of the Study:

• To apply a novel DFT-based methodology for calculating L-shell opacity of iron (Fe) and chromium (Cr) at high temperatures (182 eV).
• To investigate the influence of exchange-correlation (XC) functionals on WDM optical properties at elevated temperatures.
• To compare DFT predictions with other theoretical models and experimental data.

Main Methods:

• Utilized Mermin-Kohn-Sham DFT with temperature-dependent generalized gradient approximation XC functionals.
• Calculated L-shell opacity for Fe and Cr at T = 182 eV.
• Compared results with dense plasma models, real-space Green's function methods, and experimental measurements.

Main Results:

• DFT predictions showed good agreement with other theoretical methods for both Fe and Cr.
• DFT results for Cr opacity, particularly in the bound-continuum region, closely matched experimental data.
• Discrepancies between DFT and experimental Fe opacity persisted, similar to those observed with plasma-physics models.
• The contribution of XC functionals to the total free energy was found to be negligible at high temperatures.

Conclusions:

• The developed free-energy DFT methodology is a reliable tool for WDM optical property calculations.
• The negligible role of XC functionals at high temperatures simplifies WDM opacity calculations.
• Further refinements are needed to address discrepancies in Fe opacity predictions compared to experimental data.