High-Pressure Structures and Superconductivity of Barium Iodide

Generally, pressure is a useful tool to modify the behavior of physical properties of materials due to the change in distance between atoms or molecules in the lattice. Barium iodide (BaI₂), as one of the simplest and most prototypical iodine compounds, has substantial high pressure investigation value. In this work, we explored the crystal structures of BaI₂ at a wide pressure range of 0-200 GPa using a global structure search methodology. A thermodynamical structure with tetragonal I4/mmm symmetry of BaI₂ was predicted to be stable at 17.1 GPa. Further electronic calculations indicated that I4/mmm BaI₂ exhibits the metallic feature via an indirect band gap closure under moderate pressure. We also found that the superconductivity of BaI₂ at 30 GPa is much lower than that of CsI at 180 GPa based on our electron-phonon coupling simulations. Our current simulations provide a step toward the further understanding of the high-pressure behavior of iodine compounds at extreme conditions.