Optimization of Stillinger Weber Potential Parameters for Monolayer ZnS

Abstract

We optimize a Stillinger–Weber (SW) interatomic potential for ZnS monolayers to enable reliable large-scale molecular dynamics across planar, disordered, and curved morphologies. Using force matching algorithm (POTFIT) incorporating referenced density-functional-theory (SIESTA/PBE) forces gathered from diverse finite-temperature trajectories of monolayer ZnS, we refit the parameters due to by Zhou et al. (optimized for bulk phases), yielding comparable cohesive energies and lattice constants for wurtzite, zinc-blende, and 2D phases. For the monolayer, the phonon dispersion closely tracks DFT, notably correcting the optical branches. Moreover, the curvature-law fit $(E_{\text{strain}}\propto 1/D^2$) to nanotube data extrapolates to negligible strain in the flat limit ($D\to \infty$), reinforcing the reliability of the optimized parameters for planar geometries. The optimized SW parameters demonstrate transferability, yielding an improved bonding network in 2D disordered geometries and thermally stable single-walled ZnS tubes. Quantitatively, curved-structure tests then yield an effective bending modulus $\approx 35\mathrm{eV}$ and thermal shape fluctuations scaling as $\text{RMSD}\propto 1/D$, indicating a practical stability threshold near $D\approx 38-$40 Å. Collectively, our optimized SW potential is a computationally efficient model that produces better vibrational, mechanical, and curvature energetics of various flat and curved geometries without sacrificing baseline thermodynamics. The model carries limitations due to the absence of explicit long-range electrostatics (and polarization).