Material design of indium iodine compounds

We apply material design methodology and find a new indium iodine compound, CsInI3, which is thermodynamically stable but is not reported in Inorganic Crystal Structure Database (ICSD) yet. By using the ab initio evolutionary algorithm, we find several meta-stable structures of CsInI3 and investigate their physical properties. The ideal cubic perovskite structure, which is one of the meta-stable phases, shows the structural instability of the iodine breathing mode at zero temperature. However, the cubic perovskite is eventually stabilized at finite temperature due to the contribution of the phonon entropy. The cubic perovskite shows band inversion above the Fermi level, indicating that it is a topological material. Other meta-stable structures are derived from the cubic perovskite and have two different sizes of indium octahedrons, thereby presenting bond and charge disproportionation. The new compound of CsInI3 presents diverse physics including bond and charge disproportionation, topological nature, and a possible application for photovoltaics, thereby providing an ideal playground for these research fields.