First‐Principles Calculation of the Electronic Structure of CH3NH3PbI3 under High Pressure

Under the framework of density functional theory (DFT) based on first principles, the local density approximation (LDA) and generalized gradient approximation (GGA) are used to analyze the phase‐transition pressure, band structure, density of states, atom populations, and bond populations of the five phases of CH3NH3PbI3. From the enthalpy of the five phases as a function of pressure, the 2H‐phase transforms into the O‐phase under 2 GPa, and the T‐phase transforms into the C‐phase under 0.3 GPa. The charge density and the charge population analysis show that methyl ammonia is connected by covalent bonds, and the PbI6 octahedron has both ionic and covalent bonds. As the pressure increases, the covalency of the CH and NH bonds in methyl ammonia decreases, while the covalency of the CN bond increases. From the charge density and the density of states, the 2H‐phase and 4H‐phase have indirect bandgaps, while C‐, O‐, and T‐phases have direct bandgaps. The valence band of CH3NH3PbI3 is mainly determined by the I‐5p and Pb‐6s orbitals, and the conduction band is mainly determined by the Pb‐6p orbitals. In addition, this study shows that the bandgap decreases with increasing pressure, and the ideal bandgap can be achieved by adjusting the pressure.