First-principles study of commensurate twisted MoS₂/MoSe₂ heterobilayers: Structural, electronic, and elastic properties

This study investigates the structural, electronic and elastic properties of commensurate twisted MoS_2/MoSe_2 heterobilayers across five specific twist angles through first-principles calculations. We identify a critical angle (30^\circ) that yields an exceptionally flat interface, characterized by a minimal interlayer spacing variation of only 0.017 Å. This distinctive planar morphology originates from a high-symmetry moiré superlattice with spatially uniform stacking configurations. Furthermore, we reveal that the variation in interlayer binding energy is governed by the lattice corrugation, reflected by a larger difference between maximum and minimum bilayer thicknesses. A more pronounced corrugation enables the system to maximize the fractional area of strongly coupled, low-energy stacking domains (e.g., AB-1) while minimizing that of weakly coupled, high-energy regions (e.g., AA). Electronically, the system exhibits a twist-angle-dependent transition between direct and indirect band gaps, while maintaining a robust type-II band alignment across all angles, with band edges localized in the MoSe_2 and MoS_2 layers, respectively. Elastic properties remain nearly unchanged at twist angles greater than 9^\circ, but the Young's moduli of these heterobilayers surpass those of silicene and phosphorene. These findings highlight the potential of twisted MoS_2/MoSe_2 heterobilayers as a tunable platform for advanced optoelectronic devices.