Ternary superconducting hydrides in the La-Mg-H system

Ternary or more complex hydrogen-rich hydrides are the main hope of reaching room-temperature superconductivity at high pressures. Their chemical space is vast and its exploration is challenging. Here we report the investigation of the La-Mg-H ternary system using the evolutionary algorithm USPEX at pressures in the range 150-300 GPa. Several ternary superconducting hydrides were found, including thermodynamically stable P6/ mmm-LaMg3H28 with TC = 164 K at 200 GPa, P/2m-LaMgH8, C2/m-La2MgH12 and P2/m-La3MgH16. In addition, novel binary hydrides were predicted to be stable at various pressures, such as Cm-Mg6H11, P1-MgH26, Fmm2MgH30, P1-MgH38 and R3m-LaH13. We also report several novel low-enthalpy metastable phases, both ternary and binary ones. Finally, we demonstrate important methods of exploring very large chemical spaces and show how they can improve crystal structure prediction.