Mechanical enhancement and weakening in Mo6S6 nanowire by twisting

The torsional, bending and tensile mechanical properties of Mo6S6 nanowire are examined by molecular dynamics (MD) simulations with a first-principles-based reactive force field (ReaxFF). It is found that Mo6S6 nanowire shows unique mechanical properties such as high torsional and bending flexibility, high Young's modulus and strength, and negative Poisson's ratio. The Mo6S6 nanowire can be strengthened or weakened via twisting, depending on the twist angle. The Mo6S6 nanowire with a slight twist angle shows brittle failure, whereas it with a large twist angle exhibits ductile failure and necking behavior. Twisted Mo6S6 nanowires show a crossover in the negative Poisson's ratio at critical strains, that is, Poisson's ratio first decreases but then increases, with a minimum value down to around -0.8 at the strain of 0.01 as the twist angle is 21.0 degrees/nm. The negative Poisson's ratio and the crossover are explained by the bond transform that makes zero angles to the wire cross-section.