Amorphization and Fracture in Silicon Selenium(2) Nanowires: Molecular-Dynamics Simulations on Parallel Computer Architectures.

The primary goal of this dissertation is to investigate the structural and mechanical properties and dynamical fracture in SiSe$\sb2$ nanowires using the molecular-dynamics (MD) simulation technique. The present work is the first study of SiSe$\sb2$ nanowires. Large-scale simulations reported in this thesis are carried out with parallel multiresolution schemes for the long-range Coulomb and the three-body covalent potentials. The multiresolution scheme reduces the computational complexity from O(N$\sp2$) to O(N). Using an effective interatomic potential containing both 2- and 3-body interactions, MD simulations are performed for SiSe$\sb2$ nanowires composed of finite (1-64) number of chains. Under small uniaxial strain, the nanowires are found to be highly crystalline and they remain in the elastic deformation regime. The macroscopic mechanical behavior is determined by intra-chain interactions. Under large uniaxial strain, we find local amorphization followed by fracture of nanowires. Initially broken edge-sharing bonds are found in the chains at the outermost layer. These broken bonds induce cross-linking among the neighboring chains and lead to the presence of corner-sharing tetrahedra. Results for the time evolution of amorphization and crack initiation and propagation are presented