Strain in atomistic models of nanocrystalline clusters.

Strain, as an easy and clearly defined concept in continuum mechanics, has no direct counterpart in atomistic models. Existing methods, relying on the concept of atomic coordination number, do not provide a complete description of volumetric and deviatoric strains across metallic nanocrystalline microstructures. To overcome those limitations a new method is proposed: the Voronoi Cell deformation (VCD) fully accounts for the local geometry and provides a description of the strain field independent of the atomic coordination. As a typical case of study, a large atomic cluster of 200 Al grains (ca 2 million atoms) and overall size of 33 cubic nanometres was considered.