运用分子动力学方法模拟了锯齿型双壁碳纳米管体系的振荡行为,其中旋转的内管施加了不同大小的螺旋上升长度.不同于以前关于扶手椅型碳纳米管的工作(Zeng Y H, et al.2016 Nanotechnology 2795705),锯齿型的内管在施加了不同大小的螺旋上升长度之后,其管壁结构会产生畸变或缺陷.模拟过程中,锯齿型内管在施加一定的旋转速度以后保持自由,而固定的外管为无任何缺陷的理想锯齿型碳纳米管.分子动力学模拟结果显示锯齿型内管的轴向振荡行为与内管施加的螺旋上升长度密切相关.内管的振荡频率随着内管螺旋上升长度的增加而增加.但当内管的螺旋上升长度较大时,由于螺旋上升所引起的内管缺陷结构造成整个内管的破裂,从而导致其无法进行稳定的轴向振荡.模拟结果还显示,对于无螺旋上升的理想锯齿型碳管,虽然其轴向振荡效果非常微弱,但却可以作为一种具有恒定旋转频率的旋转致动器.此外,对螺旋上升长度为0.5 nm的内管在不同温度下的振荡性能进行了模拟分析,结果表明内管振荡的幅度随温度的升高而相应地增加,但当温度超过一定的临界值后,内管不能保持稳定的振荡.%Oscillation behaviors of oscillators consisting of defect-free multi-walled carbon nanotubes (MWCNTs) have been extensively studied, owing to the operating frequency of the nanotubes being able to reach up to gigahertz. However, there exist defects in most carbon nanotubes, which will affect the friction force between the walls of nanotubes. It is therefore critical to investigate the oscillation characteristics of the MWCNT-based oscillators containing a distorted or defective rotating tube, for the design of MWCNTs-based oscillators. Unlike the case in the armchair carbon nanotubes (Zeng Y H, et al. 2016 Nanotechnology 27 95705), the existence of the helical rise in the zigzag-type nanotubes can induce aberrant or defective shell structures. In this paper, the oscillatory behaviors of zigzag@zigzag double-wall carbon nanotubes containing a rotating inner tube with different helical rises are investigated using the molecular dynamics method. In all the simulation modes, the adaptive intermolecular reactive empirical bond order potential is used in this work for both the covalent bond between carbon atoms and the long-range van der Waals interaction of the force field. The perfect zigzag outer tube is assumed to be fixed while the zigzag inner tube is free after it has been rotated by a torque. At the beginning of the simulation, the whole system is heat bathed at a temperature around 300 K for 60 ps, to gently increase the whole system temperature to around 300 K after the energy minimization. The total number of particles, the system volume, and the absolute temperature are kept unchanged for 60 ps. Then we apply a torque of 30 eV to the inner tube under the constant temperature. After the rotation frequency of the inner tube reaches around 300 GHz, we remove the torque of inner tube and let the whole system be under a constant energy condition. The time steps for all simulations are all chosen to be 1 fs. The total time for the simulation is 3000 ps. It is found that the oscillatory behavior of the inner tube is dependent on the helical rise. The simulation results show that the oscillation frequency of the inner tube increases with the length of helical rise increasing. However, as the helical rise is further increased, the oscillation becomes awful because of the breakage of the inner tube with defects. Moreover, the zigzag@zigzag double-wall carbon nanotubes without any helical rise may be used as an ideal rotating actuator because the inner tube can rotate at an approximately constant rotational frequency. The influence of the system temperature on the oscillatory behavior of inner tube with a helical rise of 0.5 nm is also investigated. The results show that the oscillation amplitude of the inner tube increases with temperature increasing, but the oscillation of the inner tube is extremely unstable if the temperature is higher than a critical value.
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