Stability: E binding ≈ 5 eV/atom

1. IEEE 2009 Poster session EF EF We investigate the equilibrium geometry and electronic structure of Mo12S9I9 nanowires using ab initio density functional calculations. The skeleton of these unusually stable nanowires consists of rigid, functionalized Mo octahedra, connected by flexible, bistable sulfur bridges. This structural flexibility translates into a capability to stretch up to 20% at almost no energy cost. The nanowires change from conductors to narrow-gap magnetic semiconductors in one of their structural isomers. • Advantages over carbon nanotubes: • easy to synthesize / disperse • uniform structure • very stable • “Intriguing properties”: • optical nonlinear polarizability, • superconductivity • possibly magnetism Small Θ: short bridge Large Θ: long bridge 2 grouped angles  3 minima in E(a): a= 13.80 Å  12.30 Å  11.00 Å Long-long  Short-long  short-short BUT What’s its atomic structure? What makes its electronic properties special? band structure (3 isomers) Atomic structure (Experimentalist suggested) d a Mo I S Molybdenum-6 octahedral are decorated by sulfur or iodine and connected by the bridges of sulfur atoms. One octahedral rotates 180 degrees to get the 2nd one and these two octahedral get one unit cell with 30 atoms in. The diameter d is about 0.98 nm. Interplay between structure and magnetism in Mo6S9-xIx nanowires Teng Yang1,2, Shinya Okano2, Savas Berber3, David Tománek21 Magnetism and Magnetic Materials Division, IMR, CAS, China 2 Physics and Astronomy Department, Michigan State University, USA 3 Physics Department, Gebze Institute of Technology (GYTE), Turkey At different lattice constants a, we optimized the structures by conjugate gradient methods and obtained the cohesive energies as function of a. Ebinding(eV/unit cell) An interesting band trend that the band dispersion decreases with the decreased lattice constant, was observed. The reduction of Mo-S-Mo bridge angle or the bond bending results in a weaker hybridization and therefore decreases the band dispersion when nanowire is compressed. a (Å) • Stability: Ebinding≈ 5 eV/atom • Flexibility: about 30% stretch by virtually no • energy cost! • Unusual:3 minima in E(a) !! • a = 11.00 Å, 12.30 Å and 13.80 Å Magnetism (a = 11.00 Å) • Smaller fraction of the magnetic moment is on 4d orbitals of Molybdenum atoms • Magnetic moment resides mostly on 3p orbitals of bridging Sulfur atoms Take-home message: compress this nanowires, d1 d2 metallic semi-conducting non-magneticmagnetic Change a • Mo6 octahedra are rigid; • Structural changes occur only in S bridges