[Pw_forum] Band Structure/graphene

[nazari at iasbs.ac.ir]

 Dear All,

 I wish to get the band structure and band gap for graphene nanoribbon.
 In the following you can find the input for 2*2 graphene nanoribbon.
 In litrature the reported band gap for such  structure is in the range
  of 0.5-0.6. I get such value for small  number  of k-point but by
 increasing the number of kpoint the band gap  decrases  and this not
compatible with litratue. Is there probelm in the input.

 regards
 Fariba nazari
 IASBS

Input for small band gap:

&control
    calculation='nscf'
    prefix='graphene'
    pseudo_dir = '/lhome/aa/espresso-4.0.2/pseudo/',
    outdir='/lhome/aa/tmp/'
 /
 &system
   ibrav= 8, celldm(1)=9.302, celldm(2)=3.864, celldm(3)=2.844, nat=12,
ntyp=2,
   occupations='smearing', degauss=0.02, ecutwfc =30.0, ecutrho
=300.0,nbnd=28,
/
 &electrons
    conv_thr =  1.0d-6
    mixing_beta = 0.7
 /
&IONS
  ion_dynamics = 'bfgs'
/
ATOMIC_SPECIES
C 12.0107 C.pbe-van_bm.UPF
H 1.00794 H.pbe-van_ak.UPF
ATOMIC_POSITIONS {angstrom}
C        1.769889031   1.322946944  -0.012817900
C        1.770489086   4.159733324  -0.022135401
C        0.539682313   3.462493413  -0.021948354
C        0.539180075   2.020040405  -0.016808553
H        1.769947891   0.229915494  -0.001367763
H        1.774772992   5.252856855  -0.017605292
C        4.231096346   1.322960286  -0.012817558
C        4.231696827   4.159712177  -0.022136595
C        3.000909807   3.462494493  -0.021949575
C        3.000394654   2.020036555  -0.016806896
H        4.231213438   0.229870885  -0.001367555
H        4.236032200   5.252906248  -0.017606218
K_POINTS
 15
 0.00 0.00 0.00 1
 0.0173 0.0 0.00 1
 0.0273 0.0 0.0 1
 0.0373  0.0 0.0 1
 0.0473  0.0 0.0 1
 0.0573  0.0 0.0 1
 0.0673  0.0 0.0 1
 0.0773  0.0 0.0 1
 0.0873  0.0 0.0 1
 0.0973  0.0 0.0 1
 0.137  0.0 0.0  1
 0.173  0.0 0.00 1
 0.2754 0.0 0.0 1
 0.334  0.0 0.0 1
 0.50 0.00 0.00 1
Input for  band gap in the range of 0.5-0.6:


 &control
    calculation='nscf'
    prefix='graphene'
    pseudo_dir = '/lhome/aa/espresso-4.0.2/pseudo/',
    outdir='/lhome/aa/tmp/'
 /
 &system
   ibrav= 8, celldm(1)=9.302, celldm(2)=3.864, celldm(3)=2.844, nat=12,
ntyp=2,
   occupations='smearing', degauss=0.02, ecutwfc =30.0, ecutrho
=300.0,nbnd=28,
/
 &electrons
    conv_thr =  1.0d-6
    mixing_beta = 0.7
 /
&IONS
  ion_dynamics = 'bfgs'
/
ATOMIC_SPECIES
C 12.0107 C.pbe-van_bm.UPF
H 1.00794 H.pbe-van_ak.UPF
ATOMIC_POSITIONS {angstrom}
C        1.769889031   1.322946944  -0.012817900
C        1.770489086   4.159733324  -0.022135401
C        0.539682313   3.462493413  -0.021948354
C        0.539180075   2.020040405  -0.016808553
H        1.769947891   0.229915494  -0.001367763
H        1.774772992   5.252856855  -0.017605292
C        4.231096346   1.322960286  -0.012817558
C        4.231696827   4.159712177  -0.022136595
C        3.000909807   3.462494493  -0.021949575
C        3.000394654   2.020036555  -0.016806896
H        4.231213438   0.229870885  -0.001367555
H        4.236032200   5.252906248  -0.017606218
K_POINTS
5
 0.00 0.00 0.00 1
 0.137  0.0 0.0  1
 0.173  0.0 0.00 1
 0.2754 0.0 0.0 1
 0.50 0.00 0.00 1











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