# Prediction of a Mobile Solid State in Dense Hydrogen under High Pressures

## TL;DR

This paper reports the discovery of a novel dense hydrogen state at extremely high pressures that combines solid-like order with liquid-like mobility, challenging traditional views on phase states.

## Contribution

The study introduces a new classical regime supersolid-like state in dense hydrogen, identified through advanced ab initio simulations at high pressures.

## Key findings

- Existence of a long-range ordered yet mobile dense hydrogen state at 1-1.5 TPa
- This state may be (meta-)stable at ultra-low temperatures
- Characterization of its stability and melting behavior

## Abstract

Solid rigidity and liquid-scale mobility are thought incompatible in elemental substances. One cannot have an elemental solid that is long-range positionally ordered wherein the atoms flow like in a liquid simultaneously. The only exception might be the hypothetical supersolid state of 4He. In this work, we demonstrate that such exotic state could exist even in the classical regime. Using ab initio molecular dynamics (AIMD) and ab initio path integral molecular dynamics (AI-PIMD), a novel state of dense hydrogen which simultaneously has both long-range spatial ordering and liquid-scale atomic mobility is discovered at 1~1.5 TPa (1 TPa=10000000 atmospheric pressures). The features distinct from a normal solid and liquid are carefully characterized, with the stability and melting behavior are investigated. Extensive AI-PIMD simulations further revealed that this state might be (meta-)stable even at ultra-low temperatures, suggesting an emerging candidate for an alternative type of supersolid state in dense metallic hydrogen.

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Source: https://tomesphere.com/paper/1702.00211