The brittle-ductile behavior of cracks has long been an area of intensive study. In particular, body centered cubic (bcc) iron has been studied often in the recent past in the framework of continuum (e.g. Rice
]) and atomistic models (e.g. Mullins
]), and as well in experiments (e.g. Marsh
], Šmida and Bošansk models consider usually plane strain conditions (2D) along the crack front and temperature of 0 K. However, free sample surface (where plane stress conditions are expected in the normal direction) may influence the ductile-brittle behavior, as well as the thermal atomic motion. Such studies require 3D atomistic simulations.