Atomistic Calculation of Mechanical Behavior

Mechanical behavior is stress-related behavior. This can mean the material response is driven by externally applied stress (or partially), or the underlying processes are mediated by an internal stress field; very often both are true. Due to defects and their collective behavior [1], the spatiotemporal spectrum of stress field in a real material tends to have very large spectral width, with non-trivial coupling between different scales, which is another way of saying that the mechanical behavior of real materials tends to be multiscale. The concept of stress field is usually valid when coarse-grained above a few nm; in favorable circumstances like when crystalline order is preserved locally, it may be applicable down to sub-nm lengthscale [2]. But overall, the atomic scale is where the stress concept breaks down, and atomistic simulations [3–5] provide very important termination or matching condition for stress-based theories. Large-scale atomistic simulations (Chap. 2.25) are approaching μm lengthscale and are starting to reveal the collective behavior of defects [6]. But studying defect unit processes is still a main task of atomistic simulation. It is infeasible to list the current developments in this area to any degree of completeness, so only a few highlights are given. A somewhat more detailed review can be found in Ref. [5]. • The study of deformation [7–11], grain growth [12] and fracture [13, 14] in nanocrystalline materials. • Atomistic simulation of adhesion and friction [15, 16], and nanoindentation [17–20]. • The study of dislocation core structure and Peierls stress in BCC metals [21], semiconductors [22] and intermetallics [23]. A proper definition of dislocation core energy and numerically precise ways [24, 25] to extract