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    COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS
        Institute for Computational Sciences and Informatics
	                      (CSI 898-Sec 001) 

            Carbon Nanotubes: Band Structure with a Twist

                           J. W. Mintmire 
              Naval Research Laboratory Washington, DC 

Our research group at the Naval Research Laboratory has been active 
in theoretical studies of the electronic and structural properties of 
carbon nanotubes over most of this decade.  Single-wall carbon nanotubes—
which can be visualized as constructed from rolled-up graphitic sheets—
exhibit helical symmetries that can be used to reduce the computational 
effort needed for electronic band structure calculations of these materials.  
We have carried out extensive first-principles calculations on these 
materials using a local-density functional approach developed at NRL 
for helical chain polymers.  We discuss both our early work that 
predicted all armchair nanotubes should be conducting and more recent 
simulations on achiral and chiral nanotubes.  More recently we developed 
a simple analytical model that predicts the density-of-states (and band 
gap, etc.) near the Fermi level should depend only on whether the nanotubes 
are semiconducting or metallic.  This relationship also explains the 
observed spacing of STM-measured DOS peaks of single-wall nanotubes, 
providing further confirmation of the band structure theory of these 
nanowires.  We compare the predictions of this model with densities of 
states calculated directly using our first-principles band structure method.  
These comparisons show that this model works well for energies within about 
1 eV of the Fermi level.  

	                  Monday , November 1 1999
                                  4:30 pm
                         Room 206, Science & Tech. I

Refreshments will be served.
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Find the schedule at http://www.csi.gmu.edu/lcdm/seminar/schedule.html