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Analysis of band-gap formation in squashed armchair carbon nanotubes H. Mehrez, A. Svizhenko, and M. P. Anantram

Summary: Analysis of band-gap formation in squashed armchair carbon nanotubes
H. Mehrez, A. Svizhenko, and M. P. Anantram
Mail Stop: 229-1, Center for NanoTechnology and NASA Advanced Supercomputing Division, NASA Ames Research Center,
Moffett Field, California 94035-1000, USA
M. Elstner and T. Frauenheim
Theoretische Physik, Universitat Paderborn, D-33098 Paderborn, Germany
Received 6 December 2004; published 28 April 2005
The electronic properties of deformed armchair carbon nanotubes are modeled using constraint free density
functional tight binding molecular dynamics simulations. Independent from CNT diameter, deforming path can
be divided into three regimes. In the first regime, the nanotube deforms with negligible force. In the second
one, there is significantly more resistance to deforming with the force being 40100 nN/per CNT unit cell.
In the last regime, the CNT loses its hexagonal structure resulting in force drop-off followed by substantial
force enhancement upon deforming. We compute the change in band gap as a function of deforming and our
main results are: i A band gap initially opens due to interaction between atoms at the top and bottom sides of
CNT. The -orbital approximation is successful in modeling the band-gap opening at this stage. ii In the
second regime of deforming, large - interaction at the edges becomes important, which can lead to band-gap
oscillation. iii Contrary to a common perception, nanotubes with broken mirror symmetry can have zero band
gap. iv All armchair nanotubes become metallic in the third regime of deforming. Finally, we discuss both
differences and similarities obtained from the tight binding and density functional approaches.
DOI: 10.1103/PhysRevB.71.155421 PACS number s : 73.63.Fg, 61.46. w, 73.22. f


Source: Anantram, M. P. - Department of Electrical Engineering, University of Washington at Seattle


Collections: Materials Science; Computer Technologies and Information Sciences