Solid atomic hydrogen: Point defect formation and elastic stability

Abstract

Within the framework of the density functional theory, the resistance of solid atomic hydrogen with an I41/amd crystal structure to the formation of point defects, such as a vacancy, an interstitial site, and a double vacancy, was studied. At the pressures below 265 GPa, the equilibrium vacancy concentration per atom reaches a critical value, even near the temperature of liquid helium. Thus, the destruction of the metastable atomic state occurs at higher pressures than predicted by the calculations based on the phonon spectra. For atomic hydrogen at room temperature, pressures exceeding 280 GPa are required. The elastic stability of the I41/amd atomic phase in the pressure range from 250–600 GPa was investigated. It is shown that there are regions of instability of the I41/amd atomic hydrogen phase, where a transition to the structure with FDDD symmetry occurs.