First-principles simulations of warm dense lithium fluoride

Area of Science:

• Condensed matter physics
• Computational physics
• Materials science

Background:

• Understanding warm dense matter (WDM) is crucial for various fields, including inertial confinement fusion and planetary science.
• Lithium fluoride (LiF) is a model system for studying WDM due to its simple ionic structure.

Purpose of the Study:

• To investigate the warm dense matter states of LiF using advanced computational methods.
• To accurately model the Hugoniot curve and ionization processes in LiF.
• To provide benchmark data for existing equation-of-state (EOS) models and tables.

Main Methods:

• First-principles path integral Monte Carlo (PIMC) simulations.
• Density functional theory molecular dynamics (DFT-MD) calculations.
• Simulations covered densities from 2.08-15.70 g/cm³ and temperatures from 10⁴-10⁹ K.

Main Results:

• Identified a pronounced compression maximum and a shoulder on the principal Hugoniot curve of LiF, attributed to K-shell and L-shell ionization.
• Computed pair-correlation functions revealing evolving plasma structure driven by thermal and pressure ionization.
• Electronic density of states calculations showed that the electronic gap in liquid LiF can remain open up to 15.7 g/cm³.

Conclusions:

• The study provides accurate PIMC and DFT-MD data for LiF WDM states, serving as a benchmark for EOS tables like SESAME and LEOS.
• Observed ionization effects significantly influence the Hugoniot curve, highlighting the importance of accurate electronic structure treatment.
• LiF maintains an electronic gap at high densities and temperatures, impacting its conductive properties in extreme environments.