Development of a Reactive Force Field for VS2-Based 2D Materials: Modeling Defects, Melting, and Structural Transformations
To extend the study of vanadium disulfide (VS2) nanostructures beyond the system size and simulation time limits of ab initio methods, we introduce a new ReaxFF parameter set: ReaxFF VS2-2025. The ReaxFF VS2-2025 potential was parametrized against extensive quantum mechanical and experimental data, and it can accurately capture the energetic and physicochemical properties of two-dimensional (2D) VS2. Using this force field in molecular dynamics (MD) simulations, uniaxial tensile tests on 2H-VS2 yield Young’s moduli of 122.5 ± 0.1 GPa in the zigzag direction and 108.0 ± 0.2 GPa in the armchair direction, revealing an anisotropic elastic response. Defect formation energy calculations indicate that single sulfur vacancies are the most energetically favorable defect across the entire range of the allowed chemical potential for V and S, and single vanadium vacancies are more favorable than sulfur divacancies in sulfur-rich conditions, all consistent with density functional theory results. The melting simulations yield a melting temperature of 920 ± 50 K for monolayer 2H-VS2. Notably, during the melting process, VS2 shows a transient amorphous structure that has a drop in potential energy. This amorphous structure even shows a lower potential energy than that of the 2D VS2 in a follow-up relaxation at 0 K. These MD simulations confirm that the 2D 2H-VS2 is indeed metastable, explaining why synthesizing layered VS2 is experimentally difficult. Overall, this study offers insights into the structural and physicochemical behavior of VS2, providing a foundation for the rational design of VS2-based materials for catalytic, electronic, and electrochemical applications.