Car-parrinello molecular dynamics simulations of tensile tests on Si〈001〉 nanowires

Theoretical simulations of tensile tests on Si〈001〉 nanowires have been carried out using Car-Parrinello molecular dynamics. H-passivation was used to model experimentally occurring passivation in Si nanowires. First-principle molecular dynamics simulations at ambient temperature reveal the governing role of size, overall shape, and composition of the surface layer for the mechanical properties. Our results indicate that SiH₂ groups in the outer layer and the octahedral shape of the wire soften Young's modulus and allow wire to handle larger transverse strains than SiH groups in wires with the tetrahedral shape. The importance of the overall shape of the wire has been discussed by comparing the behavior of surface layers of {100} and {110} facets. The presence of the {100} facets helps to relax the transverse strain during tension. On the basis of changes in structural parameters, we have presented the schematic motion of Si atoms in core and surface layers before the fracture appeared.