Structural and Electronic Properties of Mo$_{6}$S$_x$I$_{9-x}$ Nanowires.

We investigate the equilibrium geometry and electronic structure of recently synthesized Mo$_{6}$S$_x$I$_{9-x}$ nanowires using {\em ab initio} Density Functional calculations. Our structure optimization calculations suggest a well-defined atomic structure within these nanowires, which are energetically unusually stable in view of their sub-nanometer diameter. For particular stoichiometries, we find the Mo$_{6}$S$_x$I$_{9-x}$ nanowires to be rather soft with respect to axial compression, and also to be metallic. We characterize the quantum conductance in these nanowires using a self-consistent nonequilibrium Green's function approach within the Landauer-Buttiker formalism. We find the charge density near the Fermi level to be delocalized along the wires, suggesting a high polarizability. For particular metastable geometries, the nanowires also exhibit a magnetic instability. Combination of atomic-scale perfection with a high structural stability and unusual electronic and transport properties lends itself to potential applications of these nanowires as unique building blocks in hierarchically assembled electronic nanocircuits.