[Pw_forum] Seeking positive Laplacians in carbon nanotubes

Nicola Marzari marzari at MIT.EDU
Thu Oct 4 19:17:46 CEST 2007

Hi Steve,

presuming the calculation converged successfully, and your geometry
is correct, what does your charge density look like ?

EMetallic nanotubes are very different from a traditional metal,
and in particular there is not going to be, in my opinion, any 
qualitative difference in the charge density of a metallic nanotube
from that of a semiconducting nanotube having the same diameter (a part 
from the obvious ocmment that the bonds will be oriented differently
depending on chirality).

Another way to say this is that the transverse polarizability is
independent of chirality - along a transverse cut, there is no 
difference in the response between a metal CNT and an insulating one.

Would be very interested to see if you find any difference.


Steven Kirk wrote:
> Hello,
> I am using Quantum Espresso to try to see if I can find metallic (e.g. 
> (3,3)) carbon nanotubes with positive values of the Laplacian of the 
> charge density at the bond critical points (using RFW Bader's AIM 
> approach). I am extracting Laplacians from gridded charge density data 
> exported to the Integrity package. So far I am finding that the 
> corresponding Laplacians are negative, which is not in line with what 
> they are supposed to be for a metal, and simply increasing the number of 
> grid points in the unit cell and increasing the ecutrho parameter do not 
> seem to help the situation. I have looked at some of Nicola Marzari's 
> publications for guidance on possible input parameters, and searched the 
> mailing list archives for advice. I would therefore be very grateful if 
> you have any advice on how I might change my input parameters (for a 
> single point calculation on a (3,3) SWNT):

Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

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