Zero-Temperature Structures of Atomic Metallic Hydrogen

TL;DR

This study uses ab initio methods to determine the zero-temperature atomic structures of metallic hydrogen across a wide pressure range, revealing phase transitions and structural similarities to other elements.

Contribution

It provides the first comprehensive ab initio prediction of atomic metallic hydrogen structures from 500 GPa to 5 TPa, including zero point motion effects.

Findings

Molecular hydrogen dissociates near 500 GPa into a body-centered tetragonal structure.

Hydrogen stabilizes in a planar structure similar to lithium at high pressures.

Hydrogen adopts a face-centered cubic lattice beyond 5 TPa.

Abstract

Ab initio random structure searching with density functional theory was used to determine the zero-temperature structures of atomic metallic hydrogen from 500 GPa to 5 TPa. Including zero point motion in the harmonic approximation, we estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (r_s = 1.225), which then remains stable to 2.5 TPa (r_s = 0.969). At higher pressures, hydrogen stabilizes in an ...ABCABC... planar structure that is remarkably similar to the ground state of lithium, which compresses to the face-centered cubic lattice beyond 5 TPa (r_s < 0.86). At this level of theory, our results provide a complete ab initio description of the atomic metallic structures of hydrogen, resolving one of the most fundamental and long outstanding issues concerning the structures of the elements.