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.