Mechanical enhancement and weakening in Mo ₆S ₆ nanowire by twisting

The torsional, bending and tensile mechanical properties of Mo ₆S ₆ nanowire are examined by molecular dynamics (MD) simulations with a first-principles-based reactive force field (ReaxFF). It is found that Mo ₆S ₆ nanowire shows unique mechanical properties such as high torsional and bending flexibility, high Young’s modulus and strength, and negative Poisson’s ratio. The Mo ₆S ₆ nanowire can be strengthened or weakened via twisting, depending on the twist angle. The Mo ₆S ₆ nanowire with a slight twist angle shows brittle failure, whereas it with a large twist angle exhibits ductile failure and necking behavior. Twisted Mo ₆S ₆ 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 °/nm. The negative Poisson’s ratio and the crossover are explained by the bond transform that makes zero angles to the wire cross-section.