ABSTRACTA first-principle calculations based on van der Waals-corrected Density Functional Theory (vdW-DFT) is performed to investigate atomic structure of methyl ammonium lead iodine (CH3NH3PbI3) which is a key material for high efficiency solid-state solar cell. A temperature dependent symmetry was previously reported which also included in this study. DFT calculation of electronic and optical properties are systematically studied with semi-local, non-local exchange-correlation and post-DFT approximation including PBE, HSE06 hybrid functional and GW. Relativistic effect in lead ion was taken into account by incorporating spin-orbit coupling (SOC) effect to obtain more accurate band gap of this material. With GW-SOC functional, our results of band gap calculations showed good agreement between DFT calculations and experimental studies which confirmed that this computational scheme is suitable for high accuracy material design, e.g. for solar cell applications.