Nonideal mixing effects in warm dense matter studied with first-principles computer simulations

Area of Science:

• * Condensed matter physics
• * Plasma physics
• * Computational materials science

Background:

• * Understanding nonideal mixing effects is crucial for accurately modeling matter under extreme conditions.
• * Warm dense matter (WDM) presents unique challenges due to high temperatures and densities, involving complex ionization states and interactions.
• * Existing methods for WDM mixture characterization are computationally intensive.

Purpose of the Study:

• * To investigate the validity of the ideal mixing approximation for predicting shock Hugoniot curves of WDM compounds.
• * To assess the accuracy of this approximation across different temperature and compression regimes.
• * To determine if WDM mixture properties can be derived from individual element equations of state.

Main Methods:

• * Calculation of shock Hugoniot curves using path integral Monte Carlo and density functional molecular dynamics.
• * Derivation of Hugoniot curves using the ideal mixing approximation from individual element equations of state.
• * Comparison of results from both methods to evaluate the approximation's accuracy.

Main Results:

• * The ideal mixing approximation accurately reproduces Hugoniot curves for BN, MgO, and MgSiO3 at temperatures above ~2 x 10^5 K and compression ratios > 3.2.
• * Ionization-induced compression features and maximum compression ratios are well-predicted by the approximation.
• * Deviations occur at lower temperatures (chemical bonding effects) and near L-shell ionization onset.

Conclusions:

• * The ideal mixing approximation is a reliable and computationally efficient tool for characterizing WDM and plasma mixtures.
• * WDM mixture properties can be effectively derived from individual element equations of state, simplifying complex simulations.
• * This approach significantly reduces the computational cost for studying binary and ternary mixtures in WDM regimes.