[Pw_forum] The number of bands increases with c-axial

[sreekar guddeti]

>
> Dear all,
>

 Respected Mr. Huang


> When I computed the band structure of bi-layer graphene.
>
> I found that if I fix the displacement of two layers (3.3A) and other
> parameters. Change the c-axial (celldm(3)) only.
>
> The number of bands will be different.
>
>
> The only possible way I can interpret this (I may be wrong) is the
variation in the d-like bands (clutter of bands just above the Fermi level).
I did a quick(ecut 30,360 Ry) calculation using your 'c' parameters and I
got a similar band structure (I restricted #of bands to 20). I think you may
not have scaled the z-coordinates accordingly. To confirm the d-character of
the clutter-bands, perform k-resolved DOS calculations... the output is
really soothing to the eyes :P. If you intend to perform a precise
calculation (of order of 1 meV as your ecut suggests), I may suggest
convergence with degauss.

Finally, as I too am learning the code, I would like to ask if there is any
issue to use other Bravais lattice instead of ibrav=0?

24.62 A    equals to the result from VASP (should be the correct one)
>
why should VASP be 'the correct one'... I wouldnt see it as an authority ;)

PS: Let me know if I am wrong.
Sincerely,
Sreekar Guddeti
Undergraduate (5th year)
IIT Bombay
India
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