Local structure in dense hydrogen at the liquid-liquid phase transition by Coupled Electron-Ion Monte Carlo

TL;DR

This study investigates the local structure of high-pressure hydrogen near the liquid-liquid phase transition using advanced Monte Carlo simulations, revealing insights into molecular formations and stability under extreme conditions.

Contribution

It applies the Coupled Electron-Ion Monte Carlo method to analyze hydrogen's local structure and molecular stability across the phase transition, providing new computational insights.

Findings

Identification of the liquid-liquid transition in high-pressure hydrogen.

Detection of transient H3+ ions that are not thermally stable.

Analysis of the molecular fraction in different phases.

Abstract

We present a study of the local structure of high pressure hydrogen around the liquid-liquid transition line based on results from the Coupled Electron-Ion Monte Carlo method. We report results for the Equation of State, for the radial distribution function between protons g(r) and results from a cluster analysis to detect the possible formation of stable molecular ions beyond the transition line, as well as above the critical temperature. We discuss various estimates for the molecular fraction in both phases and show that, although the presence of $H_3^+$ ions is suggested by the form of the g(r) they are not stable against thermal fluctuations.