Ion-ion dynamic structure factor, acoustic modes and equation of state of two-temperature warm dense aluminum

TL;DR

This study uses molecular dynamics with density functional theory-based potentials to analyze the ion-ion structure factor, acoustic modes, and equation of state of warm dense aluminum in a two-temperature state, revealing rapid ion correlation decay and increased sound speed.

Contribution

It introduces a parameter-free, density functional theory-based method to efficiently compute two-temperature properties of warm dense aluminum.

Findings

Ion-ion correlations decay faster than electron-ion relaxation time.

Increasing electron temperature raises the speed of sound in aluminum.

Good agreement with ab initio and average-atom calculations for equilibrium aluminum.

Abstract

The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasi-equilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasi-equilibrium situations. Analyzing the van Hove function, we find that ion-ion correlations vanish in a time significantly smaller than the electron-ion relaxation time so that dynamical properties have a physical meaning for the quasi-equilibrium state. A significant increase in the speed of sound is predicted from the modification of the dispersion relation of the ion acoustic mode as the electron temperature is increased. The two-temperature equation of state including the free energy, internal energy and pressure is also presented.