I am struggling with getting a correct band structure for even pristine graphene using SIESTA. The issue is almost certainly the K point path. My graphene sheet (128C atoms) isn't the traditional hexagonal cell. Here it is written in the ".fdf' style of siesta :

LatticeConstant 19.7473282 Ang

%block LatticeVectors

  1.0000000   0.0000000   0.0000000

  0.5000000   0.8666666   0.0000000

  0.0000000   0.0000000   2.0255851

%endblock LatticeVectors

And here is the Path I'm using

BandLinesScale pi/a

%block BandLines

1 0.0000 0.0000 0.0000 /Gamma

30 1.1547005 0.0000 0.0000 M

30 1.1547005 0.6667 0.0000 K

30 0.0000 0.0000 0.0000 /Gamma

%endblock BandLines

Can anyone help me determine the proper k point path with the correct high symmetry points for this type of structure just to at least be able to reproduce the graphene band structure we observe in literature ?

Let me just add that I've tried : More kpoints, better convergence criteria, different functionals and most other obvious solutions but I still can't get the proper band structure

  • $\begingroup$ it would be helpful if you could link to (or insert an image of) one of the band structures in literature that you are referring to? A few remarks on your geometry: I am not sure about SIESTA but in general the 21-th component of the lattice vector is -0.5 (not 0.5). Since you already mentioned you are not using the traditional cell, did you make sure by visualization that you are working on the correct geometry? Also, is the lattice constant that high!? 19 Angstrom!? $\endgroup$ Jun 14 at 18:12
  • 1
    $\begingroup$ You're talking about a single sheet of 128 carbons, but you have defined a bulk structure (periodic boundary conditions) with a huge lattice parameter. For an infinte sheet, only the $z$ component has to be very large to avoid an overlap or a graphite structure. $\endgroup$
    – M06-2x
    Jun 16 at 17:30
  • 1
    $\begingroup$ As @M06-2x said, is there a reason why you have 128 carbon atoms in the unit cell? If you compute the bands of this structure you will get nothing like the "typical" graphene bands, since your bands will be folded as many times as you have repeated the unit cell. And converting from that to the unit cell bands is not simple at all. You can look at this paper: arxiv.org/abs/1812.03925 to get an idea of the process. $\endgroup$
    – Pol Febrer
    Jun 26 at 10:10
  • $\begingroup$ Unless someone finds this question useful I will delete it. The cause is obviously band folding. Can't believe I didn't think of it or notice it. Sorry everyone for wasting your time.I will ask another question on advice to interpret band structures for doped graphene structures $\endgroup$
    – Elie H
    Jun 26 at 15:43


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