H<sub>2</sub> Chemical Bond in a High-Pressure Crystalline Environment
Miriam Marqués, Miriam Peña‐Álvarez, Miguel Martínez-Canales, Graeme J. Ackland
Abstract
High Resolution Image Download MS PowerPoint Slide We show that the hydrogen in metal superhydride compounds can adopt two distinct states─atomic and molecular. At low pressures, the maximum number of atomic hydrogens is typically equal to the valency of the cation; additional hydrogens pair to form molecules with electronic states far below the Fermi energy causing low-symmetry structures with large unit cells. At high pressures, molecules become unstable, and all hydrogens become atomic. This study uses density functional theory, adopting BaH 4 as a reference compound, which is compared with other stoichiometries and other cations. Increased temperature and zero-point motion also favor high-symmetry atomic states, and picosecond-timescale breaking and remaking of the bond permutations via intermediate H 3 – units.