[Pw_forum] Seeking positive Laplacians in carbon nanotubes

[Steven Kirk]

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. Steven R. Kirk           <Steven.Kirk at hv.se, S.R.Kirk at physics.org>
Dept. of Technology, Mathematics & Computer Science  (P)+46 520 223215
University West                                      (F)+46 520 223299
P.O. Box 957 Trollhattan 461 29 SWEDEN       http://taconet.webhop.org