The Thermodynamical Instability Induced by Pressure Ionization in Fluid Helium

Abstract

A systematic study of pressure ionization is carried out in the chemical picture by the example of fluid helium. By comparing the variants of the chemical model, it is demonstrated that the behavior of pressure ionization depends on the construction of the free energy function. In the chemical model with the Coulomb free energy described by the Padé interpolation formula, thermodynamical instability induced by pressure ionization is found to be manifested by a discontinuous drop or a continuous fall and rise along the pressure-density curve as well as the pressure-temperature curve, which is very much like the first order liquid-liquid phase transition of fluid hydrogen from the first principles simulations. In contrast, in the variant chemical model with the Coulomb free energy term empirically weakened, no thermodynamical instability is induced when pressure ionization occurs, and the resulting equation of state achieves good agreement with the first principles simulations of fluid helium.

arXiv comment9 pages, 15 figures

References in corpus (10)

• FPEOS: A First-Principles Equation of State Table of Deuterium for Inertial Confinement Fusion Applications
• Hydrogen-Helium Mixtures in the Interiors of Giant Planets
• Equation of state of fully ionized electron-ion plasmas
• First Principles Calculations of Shock Compressed Fluid Helium
• Path Integral Monte Carlo and Density Functional Molecular Dynamics Simulations of Hot, Dense Helium
• Analysis of laser shock experiments on precompressed samples using a quartz reference and application to warm dense hydrogen and helium
• Quantum molecular dynamics simulations for the nonmetal-to-metal transition in fluid helium
• Quantum Monte Carlo Simulation of the High-Pressure Molecular-Atomic Crossover in Fluid Hydrogen
• Free-energy model for fluid helium at high density
• Wide range equation of state for fluid hydrogen within density functional theory