Abstract
The electronic properties of zigzag (n,0) and armchair (n,n) single wall carbon nanotubes (SWCNTs) have been studied using ab-initio density functional theory. We investigate the effect of diameter/length on binding energy/atom and Homo-Lumo gap of zigzag SWNTs from (3,0) to (7,0) and armchair SWNTs from (3,3) to (7,7) with two ends open. B.E/atom decreases with increase in length of all the tubes leading to the stability of long tubes. Band gap decreases with increasing length of zigzag and armchair CNTs, but decrease is not monotonic. The ab-initio calculations were performed using SIESTA code using generalized gradient approximation (GGA).