Equation of State of Hot, Dense Magnesium Derived with First-PrinciplesComputer Simulations

TL;DR

This study uses first-principles simulations to determine the equation of state of magnesium under extreme conditions relevant to planetary interiors and fusion, revealing ionization behaviors and shock compression characteristics.

Contribution

First-principles methods are applied to derive magnesium's equation of state across a wide range of densities and temperatures, highlighting ionization mechanisms and shock response.

Findings

Mg's L-shell electrons merge at high density.

Single broad shock compression region with ratio ~4.9.

Differences in ionization and shock behavior compared to MgO, Si, and Al.

Abstract

Using two first-principles computer simulation techniques, path integral Monte-Carlo and density functional theory molecular dynamics, we derive the equation of state of magnesium in the regime of warm dense matter, with densities ranging from 0.43 to 86.11~g/cm$^3$~and temperatures from 20,000 K to $5\times10^8$~K. These conditions are relevant for the interiors of giant planets and stars as well as for shock compression measurements and inertial confinement fusion experiments. We study ionization mechanisms and electronic structure of magnesium as a function of density and temperature. We show that the L shell electrons 2s and 2p energy bands merge at high density. This results into a gradual ionization of the L-shell with increasing density and temperature. In this regard, Mg differs from MgO, which is also reflected in the shape of its principal shock Hugoniot curve. For Mg, we predict a single broad pressure-temperature region where the shock compression ratio is approximately 4.9. Mg thus differs from Si and Al plasma that exhibit two well-separated compression maxima on the Hugoniot curve for L and K shell ionizations. Finally we study multiple shocks and effects of preheat and precompression.