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Nanowires and nanotubes: computer simulations

Carbon nanotubes are a topic of research in very attractive and already well developed area of condensed matter science. Cylindrical nanostructures made of other materials are also studied. Recent experimental and computer simulation investigations have shown that gold nanowires exist in several unusual forms, such as multi-shell nanowires and STM suspended monatomic chains. In the first part of my talk I will present the results of classical molecular dynamics computer simulation studies of structural, thermal, vibrational, and mechanical properties for gold nanowires [1, 2]. My simulations are based on a realistic, well-tested embedded-atom potential. In molecular dynamics simulations the equations of motion for the system of particles in a required configuration are solved numerically using suitable algorithms. Both infinite (where the periodic boundary conditions are used along the wire axis), and finite nanowires are studied. The systems analyzed are in the range of radii R = (0.5 - 1.5) nm, the lengths of finite nanowires are L = (4 - 12) nm, and the numbers of particles are N = (300 - 2100). In this size range multi-shell cylindrical nanostructures often form. These multi-wall structures are stable up to rather high temperatures T ~ 900 K. It was also found that compressed nanowires recover their initial lengths and radii even after large structural deformations. However, in contrast to the case of carbon nanotubes, in gold nanowires irreversible local atomic rearrangements occur even under small compressions. In the second part of the talk I will show the results for cylindrical oxide nanostructures. The density functional theory calculations based on the plane waves and pseudopotentials are used. Finite MgO nanotubes and infinite silica nanowires are investigated and their structural and electronic properties, as well as related experimental results, will be presented [3]. [1] G. Bilalbegović, Structure and stability of finite gold nanowires, Phys. Rev. B 58, 15412 (1998) ; Multishelled Gold Nanowires, Molecular Simulation 24, 87 (2000) ; Structures and Melting in Infinite Gold Nanowires, Solid State Communications 115, 73 (2000) ; Metallic nanowires: multi-shelled or filled ?, Computational Materials Science 18, 333 (2000) ; Multi-shell gold nanowires under compression, Journal of Physics: Condensed Matter 13, 11531 (2001) ; Gold nanotube: structure and melting, Vacuum 71, 165 (2003) ; Assemblies of gold icosahedra, Computational Materials Science 31, 181 (2004). [2] J. Stepanić and G. Bilalbegović, Nanometer-scale capacitors, Fizika A 8(4), 261 (1999). [3] G. Bilalbegović, Structural and electronic properties of MgO nanotube clusters, Phys. Rev. B 70, 045407 (2004) ; unpublished

nanowires; nanotubes; nanotechnology; molecular dynamics simulation; density functional electronic structure calculations

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