Role of boundary conditions and thermostats in the uniaxial tensile loading of silicon nanowires

WT Xu and WK Kim, COMPUTATIONAL MATERIALS SCIENCE, 178, 109636 (2020).

DOI: 10.1016/j.commatsci.2020.109636

The size-dependent brittle-to-ductile transition of silicon has been observed with nanowire structures in experiments and many research efforts have focused on revealing its underlying physical mechanisms through both experimental and simulation approaches. While most simulation studies using molecular dynamics have considered the influence of various factors such as strain rate, temperature, and size, etc., little is known about the effect of boundary conditions and simulation types, i.e. constant energy vs. constant temperature simulations. In this work, we study the effects of boundary conditions and thermostats on the failure behavior of silicon nanowires by performing the molecular dynamics simulation of the uniaxial tensile test with three modified embedded-atom-method potentials. The nanowires are subjected to either periodic boundary conditions or fixed-end boundary conditions and the simulation is conducted under either the constant energy or constant temperature conditions by Langevin thermostat. The simulations reveal that Young's modulus and tensile strength exhibit little dependence on the boundary condition and thermostat while the failure strain of the nanowires increases with fixed boundary conditions compared to the nanowires subjected to periodic boundary conditions. The failure behaviors, which are quantified by our novel ductility failure probability parameter, exhibit larger, but limited variations depending on the boundary condition, but the trend is mixed and not conclusive.

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