[Pw_forum] Seeking positive Laplacians in carbon nanotubes

[William Yim]

Hello,

This sounds an interesting issue. I couldn't see any obvious problem in
your input. Instead, I want to know what's the reason for a metallic
nanotuube to have a positive Laplacian at bond critical point. The C-C or
C=C BCP usually have negative Laplacian. Besides, if your expected BCP
falls within the cutoff radius, you will not be able to locate it using
planewave DFT, as AIM is an all-electron analysis.

Best regards,
William

On Thu, 4 Oct 2007, 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):
> 
> 
>    &CONTROL
>     title='N3_M3 calculation',
>     calculation='scf',
>     restart_mode='from_scratch',
>     prefix='N3_M3',
>     pseudo_dir='.'
>   /
>   &SYSTEM
>     ibrav = 4,
>     celldm(1)= 14.0125,
>     celldm(3)= 0.33169,
>     nat = 12,
>     ntyp = 1,
>     ecutwfc = 30,
>     ecutrho = 240,
>     occupations = 'smearing',
>     degauss = 0.03,
>     smearing = 'mv',
>     nbnd = 36
>   /
>   &ELECTRONS
>   /
> ATOMIC_SPECIES
> C 12.0107 C.pbe-rrkjus.UPF
> ATOMIC_POSITIONS {crystal}
> C    0.68812   0.81475   0.16090
> C    0.48031   0.76393   0.16090
> C    0.37337   0.68812   0.66090
> C    0.76393   0.78362   0.66090
> C    0.18525   0.37337   0.16090
> C    0.21638   0.48031   0.66090
> C    0.62663   0.31188   0.16090
> C    0.23607   0.21638   0.16090
> C    0.31188   0.18525   0.66090
> C    0.78362   0.51969   0.16090
> C    0.81475   0.62663   0.66090
> C    0.51969   0.23607   0.66090
> K_POINTS automatic
> 1 1 8 0 0 0
> 
> Many thanks in advance,
> Steve Kirk
> 

-- 
Dr. Wai-Leung Yim
Institut fuer Reine und Angewandte Chemie,
Theoretische Chemie,
Carl von Ossietzky Universtaet Oldenburg,
26129 Oldenburg,
Germany
Email: wlyim at puccini.che.pitt.edu             
Phone:	+49-441-798-3950 (office)              
Fax:	+49-441-798-3964