A ReaxFF Force Field for 2D-WS2 and Its Interaction with Sapphire

We present a new ReaxFF reactive force field parameter set enabling large-scale computational synthesis and characterization of 2D-WS2, guided by an extensive quantum mechanical data set on both periodic and nonperiodic systems and validated against ADF-STEM experiments. This potential is designed to capture the most essential features of a WS2 thin film, such as the 2H → 1T displacive phase transition, S-vacancy migration, and the energetics of various point and line defects, e.g., ripplocations in a WS2 monolayer, thus enabling cost-effective simulations supporting phase and defect engineering of 2D-WS2. Additionally, the new ReaxFF description accurately describes the nucleation of a finite 1T phase on the 2H basal plane or edges, the rotational and translational grain boundaries, and the coupled effect of chemical potential and edge stability on the formation of S- and W-oriented grain boundaries. Because the epitaxial relationship between the substrate and 2D flakes plays a key role in controlling the growth direction and thus the crystal quality of a 2D film, this potential is trained further for the WS2/sapphire interface and therefore can provide valuable insights into the morphological changes observed in a coalesced WS2 grown film on sapphire.