Interlayer translations in commensurately stacked transition metal dichalcogenide bilayers

Transition metal dichalcogenide (TMD) bilayers are promising candidates for optoelectronic device components. In addition to being semiconductors that are optically active in the visible light range, they can exist in a vast array of stacking orientations due to the weak van der Waals bonding between layers. To take advantage of this geometric flexibility, it is essential to understand how changes in stacking orientation affect the properties of TMD bilayers. In this work, we use density functional theory (DFT) to study the stacking variations brought about by interlayer translations in 0 and 180-degree stacked WSe₂/MoSe₂ and WS₂/MoS₂ bilayers. We show that the 180-degree stacked bilayers have a single ground state geometry, while the 0-degree stacked bilayers have two degenerate ground state stackings. We also describe how stacking orientation correlates with interlayer distance and electronic structure, and we suggest ways to probe stacking geometry in photoluminescence experiments.