  The properties of Mo_6S_3I_6 nanowires were investigated with ab initio
calculations based on the density-functional theory. The molecules build weakly
coupled one-dimensional chains with three sulfur atoms in the bridging planes
between the Mo octahedra, each dressed with six iodines. Upon uniaxial strain
along the wires, each bridging plane shows two energy minima, one in the ground
state with the calculated Young modulus Y=82 GPa, and one in the stretched
state with Y=94 GPa. Both values are at least four times smaller than the
experimental values and the origin of the discrepancy remains a puzzle. The
ideal tensile strength is about 8.4 GPa, the chains break in the Mo-Mo bonds
within the octahedra and not in the S bridges. The charge-carrier conductivity
is strongly anisotropic and the Mo_6S_3I_6 nanowires behave as
quasi-one-dimensional conductors in the whole range of investigated strains.
The conductivity is extremely sensitive to strain, making this material very
suitable for stain gauges. Very clean nanowires with good contacts may be
expected to behave as ballistic quantum wires over lengths of several $\mu $m.
On the other hand, with high-impedance contacts they are good candidates for
the observation of Luttinger liquid behaviour. The pronounced 1D nature of the
Mo_6S_3I_6 nanowires makes them a uniquely versatile and user-friendly system
for the investigation of 1D physics.
