On the effect of supercell size and strain localization in computational tensile tests

Atomistic simulations of tensile test are often employed in studies of cleavage or decohesion of crystals and interfaces. However, the particular numerical implementation differ from model to model. Each individual model is characterized not only by a particular computational procedure but also by different loading conditions and the way the crystal breaks. Therefore, calculated values of strength can substantially differ and the particular choice of the model affects the predictions made. This paper is intended to illustrate differences in computational models and their results. Particular attention is paid to differences in computed values of fracture stress and its dependence on the size of computational supercell. It is shown that the fracture stress computed in models considering uniform stress distribution does not depend on the supercell size. On the other hand, the fracture stress decreases with increasing supercell size in models with localized strain.