First-principles calculations of minimally twisted MoSe₂/WSe₂ bilayers

We present density functional theory (DFT) calculations of MoSe₂/WSe₂ bilayers twisted a small angle (~ 3^o-5^o) away from the commensurate 2H stacking.  As the twist angle decreases, our calculations show the emergence of flat bands in both conduction and valence bands.  The degeneracies of the flat bands suggest their origins in features of the 2H band structure.  We also analyze the atomic relaxation of the twisted MoSe₂/WSe₂ bilayer away from the rigid moiré structure. While full reconstruction is not achieved at the angles we study, we begin to see the increase in area of regions of low energy stacking.  We show that the states associated with the conduction and valence band flat bands are localized in different regions of local stacking.  The localization of states is pronounced even though reconstruction is incomplete.