Optimal helicity of single-walled carbon nanotube

We find that the optimal helical angle of the SWNT varies with its length f or the fixed number of carbon hexagons along the tubular perimeter. The lon ger the tube is, the larger the helical angle is, in which the helical angl e is defined with respect to the zigzag configuration. The armchair is the optimal helical configuration of the SWNT when its length is long enough. ( C) 2001 Elsevier Science B.V. All rights reserved.