[Pw_forum] Work function of Carbon nanotube

[loc duong ding]

Dear all,

I try to calculate the work function of CNT. I follow all steps in the work function example and no error in the calculation steps. I compare my result with some papers and I see my results is smaller and the dependence of work function in diameter is inverted. My results is 4.2, 3.8, 3.6 eV for (4,4), (5,5) and (6,6) tube. It looks strange. 
 
This is my input file:

input_pw

&CONTROL
      calculation = 'scf',
      prefix='CNT0404',
      restart_mode = 'restart',
      pseudo_dir ='./',
      outdir='./'
      tstress = .true. ,
      tprnfor = .true. ,
      nstep =  100  ,
      etot_conv_thr = 1.0E-4 ,
      forc_conv_thr = 1.0D-3 ,
      dt = 20 ,
/
&SYSTEM
      ibrav= 0,  celldm(1) = 47.259, nat = 16, ntyp = 1, nspin=1,
      ecutwfc =35, ecutrho = 210, occupations='smearing', degauss=0.0001,
      starting_magnetization(1) = 0.0,
      starting_magnetization(2) = 0.3,
      starting_magnetization(3) = 0.5    
/
&ELECTRONS
    startingwfc = 'atomic'
    mixing_mode = 'plain'
    mixing_beta = 0.6
    conv_thr = 1.0e-6
    electron_maxstep= 150
/
&IONS
    upscale = 15
/
&CELL
   cell_dynamics = 'bfgs' ,
   press = 0.00 ,
   wmass =  0.00150000  ,
/
ATOMIC_SPECIES
 C  12.011  C.pbe-rrkjus.UPF
ATOMIC_POSITIONS {angstrom}
C    6.553412225   2.494247153   0.724930481
C    6.384209537   3.189335516   1.955034374
C    4.921037485   4.725404700   0.724938769
C    5.532498571   4.353613294   1.955042803
C    1.264191320   3.317569203   0.724981489
C    3.495616015   4.948134701   0.724939100
C    2.800526187   4.779818582   1.955052266
C    1.043153150   1.891599899   0.724952105
C    1.212815843   1.196984732   1.955055225
C    1.636733754   3.927573140   1.955082857
C    2.673787862  -0.341212987   0.724950680
C    2.063329729   0.030888435   1.955053025
C    6.331514885   1.068488114   0.724935334
C    4.099852762  -0.563295810   0.724948544
C    4.794456495  -0.394248320   1.955057038
C    5.959864180   0.457099648   1.955045909
K_POINTS {automatic}
1 1 9 0 0 0
CELL_PARAMETERS
 1.0   0.0   0.0
 0.0   1.0   0.0
 0.0   0.0   0.09838 

input_pp

&inputPP
 prefix='CNT0404' 
  outdir='./'
  plot_num= 1
  filplot='CNT0404' 
/
&plot
  iflag=3,
  output_format=3
  fileout='CNT0404.total.potential.xsf'
/ 


input_average

1       
CNT0404 
1 
500 
1 
2


Could you please give me some sugestions to adjust the calculations? What factors should I change? 
I great appreciate for your help.

Best regards,-----------------------------------------------
Loc Duong Dinh
Ms-Ph.D Student
Sungkyunkwan Advanced Institute of Nanotechnology,
Sungkyunkwan University,
Suwon, 440-746, Korea 
Email: mambom1902 at yahoo.com