Role of van der Waals interactions on the binding energies of 2D transition-metal dichalcogenides

Atomically-two-dimensional (2D) materials have out-of-plane van der Waals (vdW) interactions and in-plane covalent bonds, which enables the possibility to exfoliate and reassemble different 2D materials into arbitrarily stacked heterostructures. Here, we compare the atomic structures, binding energies, and dipole moments of transition-metal dichalcogenides (TMDCs) by different vdW-inclusive density functional theory (DFT) approaches. We found that the selection of the vdW-inclusive approaches largely affects the relaxed structure and the dipole moment of 2D systems. Specially, DFT-D3 takes chemical environments into account and reduces the double-counting effects at medium-range, and provides comparable binding energies for MoS2 with experimental results. This work highlights the importance of dispersion force and provides a guidance for selecting dispersion approaches in 2D device theoretical designs.