Study on New High-Pressure Phases and Electronic Properties of Iodine Chloride Employing Ab Initio Calculations

In regards to the crystal structure of the halogen compound iodine chloride (ICl), only the experimental and theoretical structure P 2 1 / c under ambient pressure is known up to now. However, the insulator material under ambient pressure may have a metal phase transition under high pressure, resulting in more excellent properties. Here, by employing the first-principles computations and the Crystal structure AnaLYsis with Particle Swarm Optimization (CALYPSO) structure prediction technique, we studied the structure and electronic properties of ICl under high pressure. The phase sequence of ICl was established, and two high-pressure phases ( Imma and P 4/ mmm ) with six and eight coordinations, respectively, were proposed. The structure optimization demonstrated that ICl sustained the following phase transitions at high pressure: P 2 1 / c → Imma → P 4/ mmm , which occurred at ~14 GPa and ~46 GPa, respectively. We also found that the P 2 1 / c phase was a mixed compound containing both covalent and ionic bonds, and the Imma and P 4/ mmm phases were ionic compounds. Finally, the mechanical and dynamical stabilities of all phases were confirmed by the calculations.