Ground-state structures of atomic metallic hydrogen

Area of Science:

• Condensed matter physics
• Materials science
• Quantum mechanics

Background:

• Understanding the behavior of hydrogen under extreme pressure is crucial for astrophysics and materials science.
• Previous studies have explored various phases of hydrogen, but definitive ground-state structures at high pressures remain debated.

Purpose of the Study:

• To determine the ground-state structures of atomic metallic hydrogen at pressures ranging from 500 GPa to 5 TPa.
• To investigate the structural transitions of hydrogen under extreme compression.

Main Methods:

• Utilized ab initio random structure searching.
• Employed density functional theory (DFT) for electronic structure calculations.
• Included proton zero-point motion within the harmonic approximation.

Main Results:

• Identified a monatomic body-centered tetragonal structure for metallic hydrogen stable from 500 GPa to 1 TPa.
• Observed dissociation of molecular hydrogen into this monatomic phase near 500 GPa.
• Discovered a novel planar ABCABC structure emerging at higher pressures, similar to lithium's ground state.
• Found a transition to a face-centered cubic lattice near 3.5 TPa.

Conclusions:

• The ground-state structure of hydrogen undergoes significant transformations under extreme pressure.
• The identified structures provide new insights into the phase diagram of hydrogen.
• These findings have implications for understanding planetary interiors and developing new materials.