Theoretical investigation of novel electronic, optical, mechanical and thermal properties of metallic hydrogen at 495 GPa

TL;DR

This paper uses first-principles calculations to systematically investigate the electronic, optical, mechanical, and thermal properties of metallic hydrogen at 495 GPa, providing insights into its stability and behavior under extreme conditions.

Contribution

It presents a comprehensive theoretical analysis of metallic hydrogen's properties at high pressure, filling gaps where experimental methods are limited.

Findings

Metallic hydrogen exhibits metallic behavior confirmed by dielectric function and plasma frequency.

Mechanical stability is limited by shear modulus, with high Young's modulus indicating stiffness.

Lattice thermal conductivity is approximately 170-195 W/mK along different directions.

Abstract

Atomic metallic hydrogen has been produced in the laboratory at high pressure and low temperature, prompting further investigations of its different properties. However, purely experimental approaches are infeasible because of the extreme requirements in producing and preserving the metastable phase. Here we perform a systematic investigation of the electronic, optical, mechanical and thermal properties of $I4_1/amd$ hydrogen at 495 GPa using first-principles calculations. We calculate the electronic structure and dielectric function to verify the metallic behaviour of $I4_1/amd$ hydrogen. The calculated total plasma frequency from both intraband and interband transitions, 33.40 eV, agrees well with the experimental result. The mechanical properties including elastic stability and sound velocity are also investigated. The mechanical stability of $I4_1/amd$ hydrogen is limited by shear modulus other than bulk modulus, and the high Young's modulus indicates that $I4_1/amd$ hydrogen is a stiff material. After investigating the lattice vibrational properties, we study the thermodynamical properties and lattice anharmonicity to understand thermal behaviours in metallic hydrogen. Finally, the lattice thermal conductivity of $I4_1/amd$ hydrogen is calculated to be 194.72 W/mK and 172.96 W/mK along the $x$ and $z$ directions, respectively. Using metallic hydrogen as an example, we demonstrate that first-principles calculations can be a game-changing solution to understand a variety of material properties in extreme conditions.