Path Integral Monte Carlo and Density Functional Molecular Dynamics Simulations of Hot, Dense Helium

TL;DR

This study combines path integral Monte Carlo and density functional molecular dynamics to derive a comprehensive equation of state for hot, dense helium, validating results against experiments and chemical models across a wide temperature and density range.

Contribution

The paper introduces a unified EOS for helium by integrating PIMC and DFT-MD data, including a thermodynamically consistent free energy fit and structural analysis.

Findings

Good agreement between PIMC and DFT-MD in intermediate temperatures

PIMC results converge to Debye-Hückel law at high temperatures

EOS matches shock wave experimental data

Abstract

Two first-principles simulation techniques, path integral Monte Carlo (PIMC) and density functional molecular dynamics (DFT-MD), are applied to study hot, dense helium in the density-temperature range of 0.387 - 5.35 g/cc and 500 K - 1.28x10^8 K. One coherent equation of state (EOS) is derived by combining DFT-MD data at lower temperatures with PIMC results at higher temperatures. Good agreement between both techniques is found in an intermediate temperature range. For the highest temperatures, the PIMC results converge to the Debye-Hueckel limiting law. In order derive the entropy, a thermodynamically consistent free energy fit is introduced that reproduces the internal energies and pressure derived from the first-principles simulations. The equation of state is presented in form of a table as well as a fit and is compared with chemical models. In addition, the structure of the fluid is analyzed using pair correlation functions. Shock Hugoniot curves are compared with recent laser shock wave experiments.