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 (BaI), 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 BaI at a wide pressure range of 0-200 GPa using a global structure search methodology. A thermodynamical structure with tetragonal 4/ symmetry of BaI was predicted to be stable at 17.1 GPa. Further electronic calculations indicated that 4/ BaI exhibits the metallic feature via an indirect band gap closure under moderate pressure. We also found that the superconductivity of BaI 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.