Stability comparison of simulated double-walled carbon nanotube structures

The focus of this research is to systematically study and classify electronic energy trends in different double-walled carbon nanotube (DWCNT) structures through ab initio simulations. Simulations comparing the stability of DWCNTs with different interwall spacings, tube types (armchair or zigzag), lengths, diameters, and endcaps were performed at a variety of computational levels. These simulations showed that DWCNTs nucleate from end caps and become energetically more stable as length and diameter increase. Another finding of this research was that the interwall spacing is dependent on which type of tube is in the outer position of the DWCNT. High stability configurations occurred when the interwall spacing was approximately 3.3 angstrom and a zigzag tube was in the outer position or when the interwall spacing was approximately 3.5 angstrom and an armchair tube was in the outer position. It was also seen that endcaps affected which tube combinations were more stable; the armchair@armchair DWCNT was the most energetically stable combination for capped tubes, while the armchair@zigzag DWCNT had the highest stability of uncapped tubes. Understanding if there is a preferred structural motif for DWCNTs and clarifying which nucleation and growth paths are favored by nanotubes will elucidate if controlled fabrication can be achieved. (C) 2008 Elsevier Ltd. All rights reserved.