Dynamics of the Structural Transformation of Crystalline Hydrogen upon the Transition into the Conductive State under Compression

Abstract

The structural transformation of solid hydrogen under compression along the isotherm of 100 K in the region of transition into the conductive state was studied within the density functional theory. The pressure, the pair correlation function of protons, the density of electron states, and the electrical conductivity were calculated within a range of hydrogen densities from 1.14 to 2.11 g/cm³. The transition of the monoclinic structure of molecular solid hydrogen into the orthorhombic Cmca structure with 12 hydrogen atoms in a unit cell was revealed. In this case, the electrical conductivity was observed to grow, though hydrogen remained molecular. Hydrogen molecules decomposed under compression to the density of 1.563 g/cm³. A unit cell, the thus-formed quasi-tetrahedron, was built of five protons with a distance of 0.92 Å from the central proton to the four others.