Theoretical study of crystal and electronic structures of BiI₃

The electronic band structure as well as the crystal structure of the BiI3 semiconductor is investigated by performing first-principles pseudopotential calculations for the space group D3d1 or C3i2. The optimized structures were determined through total-energy calculations. The calculated results indicate that a rhombohedral structure (C3i2) forms a flatter band at the bottom of the conduction bands as compared to a hexagonal structure (D3d1). The lattice relaxation of the iodine atoms around a vacant site on the atomic plane of bismuth is found to play an important role on the conduction band bottom. It is proved that the rhombohedral BiI3 is an indirect semiconductor, while the hexagonal BiI3 has a direct band gap.