  We present a detailed first-principles analysis of the (001) surface of
methylammonium lead triiodide (MAPbI3). With density-functional theory we
investigate the atomic and electronic structure of the tetragonal (I4cm) phase
of MAPbI3. We analysed surfaces models with MAI- (MAI-T) and
PbI2-terminations(PbI2-T). For both terminations, we studied the clean-surface
and a series of surface reconstructions. We find that the clean MAI-T model is
more stable than its PbI2-T counterpart. For the MAI
termination,reconstructions with added or removed units of nonpolar MAI and
PbI2 are most stable. The corresponding band structures reveal surface states
originating from the conduction band. Despite the presence of such additional
surface states, our stable reconstructed surface models do not introduce new
states within the band gap.
