High-pressure phases of magnesium selenide and magnesium telluride

The electronic structure, the charge density, and the total energy of MgSe and MgTe in the rocksalt (B1), cesium chloride (B2), zinc blende (B3), wurtzite (B4), nickel arsenide (B8₁ ), and iron silicide (B28) structures are studied using first-principles self-consistent local-density calculations in a large plane-wave basis employing soft nonlocal pseudopotentials. Experimentally for MgSe a transition was observed from the rocksalt to the iron silicide structure at 107 GPa. We find this transition between the same structures at 160 GPa. For MgTe the experimental ground state is the wurtzite structure, while the nickel arsenide structure obtained at 1–3.5 GPa persists after unloading to normal pressure. Up to 60 GPa no other transition was observed. Theoretically we find a nickel arsenide ground state and a transition to the cesium chloride structure at 69.6 GPa. The wurtzite and nickel arsenide structures are energetically very close. The difference at the minimal energy in these two structures is only 20.3 meV per atom.