Structural phase stability, elastic properties, and electronic structure of pressure-induced CaC2: A first-principles study

This work investigates the structural phase transition of CaC2 material under 0-150 GPa pressure by using firstprinciples calculation. The enthalpy difference results suggest that the C2/c structure transforms into the Cmcm structure at 0.08 GPa, while the C2/m structure transforms into the Cmcm structure at 0.11 GPa. The Cmcm structure transforms into the Immm structure at 13.70 GPa and the P6/mmm structure at 110.65 GPa. Moreover, the enthalpy values of C2/c, C2/m, I4/mmm, and Cmcm are very close between 0 and 0.11 GPa, indicating that these four structures may coexist in this pressure range. The change of volume with pressure shows that the volume decreases with the increased pressure, especially it decreases sharply at the pressure transition point. In addition, the results show that the elastic modulus of different structures increases linearly with the increase of pressure in their respective pressure stable ranges, but it will increase sharply at the pressure transition point, indicating that CaC2 exhibits better stiffness under high pressure than under low pressure. Finally, the change of the electronic structure of CaC2 with pressure is also analyzed, the results show that C2/c and C2/m are indirect band gap semiconductor structures between 0-0.11 GPa, but the band gap becomes 0 eV at the first pressure transition point 0.11 GPa, and it is always 0 eV in the pressure range of 0.11-150 GPa, which means that it becomes a metal phase. This work will provide a valuable reference for the experiment and application of CaC2 under high pressure.