Effect of different types of pseudopotentials on study of electronic dispersion for graphene and a (5,5) SWCNT |
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Authors: | B Khoshnevisan ZS Tabatabaean |
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Institution: | (1) Department of Physics, University of Kashan, Kashan, 87317-51167, Iran |
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Abstract: | We study the electronic dispersion for a graphene sheet and also a (5,5) single wall carbon nanotube (SWCNT) by using the
PWscf code from the ‘Quantum Espresso’ package. Two different types of pseudopotentials, ‘norm conserving’ and ‘ultra soft’,
have been employed and the results are more or less similar up to the Fermi level. By energy relaxation, it was found that,
if the inter-layer distance of graphite expands up to 4.5 times its in-layer (hexagonal) lattice constant, then each layer
can be considered as an individual graphene sheet and, in a bundle of (5,5) SWCNTs, the optimum separation between the tubes’
centers is about 19 a.u. and, if it expands to 22 a.u., then a single wall tube consideration can be made. The calculated
band structure and density of states (DOS) for the (5,5) SWCNT show that in the vicinity of the Fermi level there is no energy
gap (so that it is metallic) and there is a general agreement between them and zone-folding studies or other ab initio methods
in the literature. The effects of curvature on the band shifts and DOS have been considered, and they magnify the departure
from Mintmire and White’s universal prediction.
PACS 71.20.Tx; 71.15.Mb; 73.61.Wp |
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