Crystal structures, optical properties, and effective mass tensors of CH₃NH₃PbX₃ (X = i and Br) phases predicted from HSE06

The crystal structures are successfully established for tetragonal and orthorhombic CH₃NH₃PbX₃ (X = I and Br). The equilibrium lattice parameters are computed by the DFT+D2 method, and the results are compared to experimental values. The band dispersions and electronic densities of states are calculated by HSE06, showing that their band gaps are in the range from 1.63 to 2.3 eV. Although the calculated dielectric functions of MAPbX₃ compounds are similar to other semiconductors, the absorption spectra of their bulk crystals are drifted away from visible light spectrum. The effective mass tensors of holes and electrons are also evaluated in three principal directions at the ? point. The anisotropies in the effective masses of the hole and electron are illustrated for two orthorhombic phases.