Metallization of magnesium polyhydrides under pressure

Abstract

Evolutionary structure searches are used to predict stable phases with unique stoichiometries in the hydrogen-rich region of the magnesium/hydrogen phase diagram under pressure. MgH4, MgH12, and MgH 16 are found to be thermodynamically stable with respect to decomposition into MgH2 and H2 near 100 GPa, and all lie on the convex hull by 200 GPa. MgH4 contains two H- anions and one H2 molecule per Mg2+ cation, whereas the hydrogenic sublattices of MgH12 and MgH16 are composed solely of H2δ- molecules. The high-hydrogen content stoichiometries have a large density of states at the Fermi level, and the Tc of MgH 12 at 140 GPa is calculated to be nearly three times greater than that of the classic hydride, MgH2, at 180 GPa. © 2013 American Physical Society.