[Pw_forum] Calculated Gap smaller than ones calculated by other softwore

[lyzhao]

Dear all,
I ran a band structure calculation for the planar graphene-like SiC.
Using the following input, I got a direct gap of 2.16 eV at K symmetry point.

Now there is a question for me.
The literature generally report a direct gap of ~2.55 eV at K symmetry point.
I also tried ELK code (based on FP-LAPW method) and CASTEP code (based on norm conserving PBE pseudopotentials)
and, as expected, got a direct gap of ~2.55 eV at K symmetry point.

Note that, the following input is only for quick test.
I have calculated the whole band structure along the G-K-M-G path with 150 k-points, 
and gotten a direct gap of 2.16 eV at K symmetry point.
I have changed some parameters such as 'ecutwfc' and *.UPF, and no change was observed.

Any suggestions?

Best regards
Youzhao Lan

***************************
&control
  calculation='scf'
  prefix='SiC111'
 /
&system
ibrav=0,nat=2,ntyp=2
ecutwfc = 80.0
nbnd=8
 /
 &electrons
 /
ATOMIC_SPECIES
Si  28.06 Si.pbe-mt_fhi.UPF
C   12.01 C.pbe-mt_fhi.UPF
CELL_PARAMETERS (bohr)
 5.07289346   -2.92883646   0.00000000   
 0.00000000    5.85767273   0.00000000   
 0.00000000    0.00000000  37.80921171   
ATOMIC_POSITIONS (crystal)
 C     0.000000   0.000000   0.500000
 Si    0.333333  -0.333333   0.500000
K_POINTS (crystal)
 3
  0.000  0.000  0.000 1.0
  0.333  0.333  0.000 1.0
  0.500  0.000  0.000 1.0
**************************************
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