Effect of bundling on the stability, equilibrium geometry, and electronic structure of Mo₆ S_9-x I_x nanowires

We use ab initio density-functional theory calculations to determine the effect of bundling on the equilibrium structure, electronic, and magnetic properties of Mo₆ S_9-x I_x nanowires with x=0,3,4.5,6. Each unit cell of these systems contains two S- and I-decorated Mo₆ clusters that are connected by S₃ linkages to form an ordered linear array. Due to the bistability of the sulfur linkages, the total energy of the nanowires exhibits typically many minima as a function of the wire length. We find the optimum interwire distance depends on composition and to a smaller degree on the orientation of the wires. Structural order is expected in bundles with x=0 and x=6, since there is no disorder in the decoration of the Mo clusters. In bundles with other stoichiometries we expect structural disorder to occur. We find that the electronic structure of some nanowires can be switched from metallic to semiconducting by changing the interwire separation. Also, we find that selected stable or metastable nanowire geometries exhibit ferromagnetic behavior.