Stability and electronic structure of magnesium hydride and magnesium deuteride under high pressure

Abstract

Metal polyhydrides have attracted interest because some of them transform into metals under high pressure, while others initiate a phase transition to become superconductors. It was recently discovered that some superconducting metal polyhydrides have a high critical temperature (Tc ) under pressure. We calculate the structures of MgH2 (FCC), MgH2 (HCP), and MgH3 under pressures ranging from 0-300 GPa in order to determine the formation enthalpy and electronic properties under high pressure. We also replaced the hydrogen atoms with deuterium (D). The convex hulls of MgH2 (FCC), MgH2 (HCP), and MgH3 (FCC) calculated at pressures from 0 to 300 GPa. At all pressures, MgH2 (HCP) is unstable, whereas MgH3 is stable between 100 and 300 GPa. MgH2 (FCC) is thermodynamically stable between 0 and 200 GPa. MgH3 is dynamically stable at high pressure, according to phonon calculations, while MgD3 's phonon frequencies are 1/√2 times lower than MgH3 's due to the isotope effect. The MgH2 and MgD2 results are unstable under pressures ranging from 0 to 200 GPa. The band structures and density of states of MgH3 and MgD3 were also described, which appear to be similar, as well as MgH2 and MgD2.