Accurate force-field methodology capturing atomic reconstructions in transition metal dichalcogenide moiré system

In this work, a generalized force-field methodology for the relaxation of large moire heterostructures is proposed. The force-field parameters are optimized to accurately reproduce the structural degrees of freedom of some computationally manageable cells relaxed using density functional theory. The parameters can then be used to handle large moire systems. We specialize in the case of 2H-phased twisted transition-metal dichalcogenide homo-and heterobilayers using a combination of the Stillinger-Weber intralayer and the Kolmogorov-Crespi interlayer potential. Force-field parameters are developed for all combinations of MX2 for M & ISIN; {Mo, W} and X & ISIN; {S, Se, Te}. The results show agreement within 20 meV in terms of band structure between density functional theory and force-field relaxation. Using the relaxed structures, a simplified and systematic scheme for the extraction of the interlayer moire potential is presented for both R-and H-stacked systems. We show that in-plane and out-of-plane relaxation effects on the moire potential, which is made both deeper and wider after relaxation, are essential. An interpolation based methodology for the calculation of the interlayer binding energy is also proposed. Finally, we show that atomic reconstruction, which is captured by the force-field method, becomes especially prominent for angles below 4 degrees -5 degrees, when there is no mismatch in lattice constant between layers.