Molecular Dynamic simulations of a double-walled carbon nanotube motor subjected to a sinusoidally varying electric field

Molecular Dynamics (MD) simulation results of a double-walled carbon nanotube (DWNT) motor, consisting of two coaxial carbon nanotubes, where the inner tube behaves as a shaft and the outer one as a sleeve are reported. The Brenner potential is used for the intra-tube interactions along with Nordlunds long range interaction term to account for the intertube interactions. Unit positive and negative charges are attached to two diametrically opposite atoms of the shaft. A sinusoidally varying electric field is then applied to these two atoms to induce rotational motion in the system as done by others. Two sets of simulations are performed. In the first set both the shaft and sleeve are free to move. Usual pendulum and motor like behavior is observed in this case. In the second set of the simulations the sleeve is held fixed. In the fixed sleeve case, two locked states, not aligned along the direction of the applied electric field, are observed in the angular orientation of the shaft inside the fixed sleeve. The frequency of shifts between locked states correspond to the frequency of the applied electric field. These states are explained in terms of the radial shape variations and the centroid shift of the shaft inside the fixed sleeve. These locked states are significant from the point of view of applications of DWNTs as nanomotors. We also observe that the motor breaks apart in the limit of no energy losses from the configuration.