On a representative atomistic volume for a grain embedded in a polycrystal

A new concept of a representative atomistic volume for a grain (RAVG), defined as a crystal having random shape, random crystallographic orientation, and a specific number of atoms, is introduced and investigated numerically. The grain is embedded into a 3D polycrystal with a fixed number of similar size grains of body-centered cubic lattice (iron). The computer generated polycrystals comprised of such grains are subjected to tensile tests using a molecular statics approach and the Morse pairwise potential. Two sizes of polycrystals were considered: the 8-grain (two-by-two-by-two) and the 27-grain one (three-by-three-by-three). For each type and a specific grain size 15 structurally random polycrystal samples were generated to assess the Young’s modulus and its scatter. It is shown that the grain size having 12 lattice constant units (around 3.4 nm with 3270 atoms per grain) is sufficient to describe its meso-scale properties and thus can be accepted as a representative atomistic volume for a grain embedded in a polycrystal.