Thermodynamic Modeling of Fluid Polyamorphism in Hydrogen at Extreme Conditions

TL;DR

This paper develops a thermodynamic model for fluid polyamorphism in high-pressure hydrogen, capturing the phase transition between insulating and conducting states using experimental data and simulations.

Contribution

It presents the first thermodynamic model of hydrogen's fluid-fluid phase transition at extreme conditions, integrating experimental and simulation data.

Findings

The model predicts phase coexistence and reaction equilibrium accurately.

The law of corresponding states can unify different hydrogen models.

The approach provides insights into hydrogen's behavior at high pressures.

Abstract

Fluid polyamorphism, the existence of multiple amorphous fluid states in a single-component system, has been observed or predicted in a variety of substances. A remarkable example of this phenomenon is the fluid-fluid phase transition in high-pressure hydrogen between insulating and conducting high-density fluids. This transition is induced by the reversible dimerization/dissociation of the molecular and atomistic states of hydrogen. In this work, we present the first attempt to thermodynamically model the fluid-fluid phase transition in hydrogen at extreme conditions. Our predictions for the phase coexistence and the reaction equilibrium of the two alternative forms of fluid hydrogen are based on experimental data and supported by the results of simulations. {Remarkably, we find that the law of corresponding states can be utilized to construct a unified equation of state combining the available computational results for different models of hydrogen and the experimental data.