  The outstanding optoelectronics and photovoltaic properties of metal halide
perovskites, including high carrier motilities, low carrier recombination
rates, and the tunable spectral absorption range are attributed to the unique
electronic properties of these materials. While DFT provides reliable
structures and stabilities of perovskites, it performs poorly in electronic
structure prediction. The relativistic GW approximation has been demonstrated
to be able to capture electronic structure accurately, but at an extremely high
computational cost. Here we report efficient and accurate band gap calculations
of halide metal perovskites by using the approximate quasiparticle DFT-1/2
method. Using AMX3 (A = CH3NH3, CH2NHCH2, Cs; M = Pb, Sn, X=I, Br, Cl) as
demonstration, the influence of the crystal structure (cubic, tetragonal or
orthorhombic), variation of ions (different A, M and X) and relativistic
effects on the electronic structure are systematically studied and compared
with experimental results. Our results show that the DFT-1/2 method yields
accurate band gaps with the precision of the GW method with no more
computational cost than standard DFT. This opens the possibility of accurate
electronic structure prediction of sophisticated halide perovskite structures
and new materials design for lead-free materials.
