a gap at K-point of graphene

[mcjung24]

I would like to check the SOC gap of graphene. Before that, looking at the PBE band structure, it seems that there is no Dirac point at the K-point and there is an energy gap between the occupied and unoccupied bands.(see attachment)
When I open EIGENVAL, I don't have occupancies of exactly 0.5 & 0.5 at the K point, probably because of this problem, the energy is not crossing at the Dirac point in the band structure.
Is there a way to solve this?

[pedro_melo]

Dear mcjung24,

I am not sure that this is the best way to check for a converged calculation on graphene. You seem to be using a very large supercell for a calculation that normally takes a primitive cell with two atoms. Any reason for this? Did you try first to run a calculation with the primitive or conventional cell of graphene? Did you get a significantly large gap there as well?

Also, just at first glance, did you perform geometric optimisation? Your supercell's lattice parameter has very few significant digits.

Kind regards,
Pedro

[mcjung24]

Dear pedro_melo,

Thanks for your reply.
I am trying to do a local strain effect in the supercell. In the first step,
I check the Dirac point of the original. Before creating the supercell, I did the optimization of the unit cell.
However, the unit cell also does not have the crossing point(Dirac point) at the K-point.

Regards,
Myung-Chul

[mcjung24]

I have attached the band structure in PBE and PBE+SOC.
A gap of a few micro-eV is shown at the K-point, as you can see in the attachment.

Is the gap real or a numerical error when plotting the figure?

Best regards,
Myung-Chul.