Distinct metallization and atomization transitions in dense liquid hydrogen

TL;DR

This study uses advanced simulations to identify a transition in dense liquid hydrogen where it becomes metallic before fully dissociating, providing new insights into its phase behavior under extreme pressures.

Contribution

It reveals a previously unreported transition between molecular and mixed-atomic phases in dense hydrogen at around 400 GPa, indicating metallization occurs prior to complete atomization.

Findings

Identification of a transition at ~400 GPa with metallic behavior.

Metallization occurs in a partially dissociated molecular fluid.

Transition becomes a crossover at high temperature, matching experiments.

Abstract

We perform molecular dynamics simulations driven by accurate Quantum Monte Carlo forces on dense liquid hydrogen. Recently it has been reported a complete atomization transition between a mixed-atomic liquid and a completely dissociated fluid in an almost unaccessible pressure range {[\emph{Nat. Commun.} {\bf 5}, 3487 (2014)]}. Here instead, in a much more interesting pressure range, we identify a different transition between the fully molecular liquid and the mixed-atomic fluid at $\sim$ 400 GPa, with numerical evidence supporting its metallic behavior. Therefore we predict that the metallization at finite temperature occurs in this partially dissociated molecular fluid, well before the complete atomization of the liquid. At high temperature this first-order transition becomes a crossover, in very good agreement with the experimental observation. Several systematic tests supporting the quality of our large scale calculations are also reported.