A numerical re-look at the partial separation model for stacking fault energy

Stacking fault energies (SFEs) are fundamental to deformation mechanisms in crystalline materials, yet discrepancies between theoretical predictions and experiment remain. Here we evaluate the Olson–Cohen (OC), Ising, and partial separation (PS) models using a unified EAM/MEAM interatomic potential framework to enable a controlled comparison of the different approaches. For most fcc metals, the PS model predicts SFEs consistent with the OC and Ising models, whereas larger deviations occur when equilibrium partial separations are too small for the model to remain valid. Similar material-dependent behavior is observed for concentrated alloys. Simulations of Ni reveal that finite specimen thickness can influence the apparent PS-based SFE, a size effect expected to intensify in materials with wider separations. Furthermore, simulations of metastable fcc Co demonstrate that the apparent partial separation is sensitive to boundary conditions. These results clarify the applicability and limitations of the PS approach and highlight the importance of carefully verifying specimen size and boundary conditions when determining SFEs from partial separations.