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 (B8(1)), and iron silicide (B28) structures are studied using first-principles self-consistent local-de nsity calculations in a large plane-wave basis employing soft nonlocal pseudopotentials. Experimentally for MgSe a transition was observed f rom the rock-salt to the iron silicide structure at 107 GPa. We find t his transition between the same structures at 160 GPa. For MgTe the ex perimental ground state is the wurtzite structure, while the nickel ar senide structure obtained at 1-3.5 GPa persists after unloading to nor mal pressure. Up to 60 GPa no other transition was observed. Theoretic ally we find a nickel arsenide ground state and a transition to the ce sium 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.