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Simulating Molecular Dynamics of
Nanotube-Based Structures

The last two decades have witnessed enormous development in the area of materials science and engineering, as many new classes of materials have been discovered, synthesized and fabricated. One of the most revolutionary materials has been the class of carbon structures referred to as fullerence structures.

Since their discovery, enormous effort has been made to explore their amazing properties and potential applications. For example, carbon nanotubes (CNTs) have extremely high strength, stiffness and resilience, and can be used as basic building units for nanoelectronicmechanical systems (NEMS). So far the mechanical properties of nanobearings, gigahertz oscillators, nanocones and nanosprings, etc. have not been fully understood. However, understanding and predicting their mechanical properties will be extremely important for the design, optimization and fabrications of these devices.

Due to the small size of these nanostructures, measurement and design of their mechanical properties are still challenging issues. However, these nanotube-based structures provide a suitable target for atomistic simulations. Recently, the second-generation reactive empirical bond order (REBO) potential has been proposed, which contains improved analytical functions and an extended database compared to the earlier version. This provides a much better description of chemical and mechanical properties for hydrocarbon molecules, nanotubes and diamonds. In addition, the long-range non-bonding interactions of these nanotube-based devices has also been described.

Figure 1: Simulation model of the C60- nanotube gigahertz oscillator. Due to the conversion between van der Waals interaction energy and kinetic energy, the C60 molecule oscillates, moving back and forth inside the nanotube.

Figure 2: Snapshots of a complete oscillation cycle of the (5,5)/(11,11)+(16,16) oscillator. Stable and smooth oscillators with a low decay rate can be obtained by choosing appropriate values of system parameters.

In our research work, a molecular dynamics simulation package based on the REBO potential and the non-bonding interactions has been developed to model the mechanical properties of CNT-based nanostructrues. Many important issues for various nanostructures have been investigated, for example, the oscillatory behavior of the C60-CNT based oscillators as shown in Figure 1, the double-walled and multi-walled CNT-based oscillators as shown in Figure 2, and the structures and stability of single-walled CNT rings as shown in Figure 3. In addition, the formation and stability of multi-walled CNT rings, the bending properties of double-walled nanotubes and tubular graphitic cones have been studied. Currently, the simulation package is being extended to investigate the nanoscale tribology and mass transport of carbon nanotube-based structures.

Figure 3: The deformation sequence of a zigzag (7,0) nanoring with an initial diameter of D=7.86nm, with cross-section torsion during relaxation. The buckling and formation of apexes can be clearly seen.

Contact Person : Assoc Prof Y. W Zhang

E-mail: msezyw@nus.edu.sg

Tel : 6516 1542
Fax: 6776 3604