[Pw_forum] K_POINTS automatic

[zahra vatankhah]

Dear Lorenzo,
I appreciate your help. I should study more and then continue.

Thanks,
Vatankhah

On Mon, Dec 3, 2012 at 8:32 PM, Lorenzo Paulatto <
lorenzo.paulatto at impmc.upmc.fr> wrote:

> On 3 December 2012 17:34, zahra vatankhah <vatankhah.z at gmail.com> wrote:
>
>> Dear Lorenzo,
>> For more detail, I performed the scf run for graphene/h-BN bilayer with
>> both 001 and 111. The Fermi energy was 1.4072 and 1.2002 eV for 111 and 001
>> respectively. Then I plot the DOS for both and I set the Fermi to zero, but
>> they were different. For 111, the Fermi is in the middle of the small gap
>> whereas the fermi crosses the states for 001.( The attached picture is the
>> total DOS with 001 without setting fermi to zero, the red line is the fermi
>> obtained from scf run with 001 and the green line is the fermi with
>> 111.(the correct fermi should be in the middl of the gap)).
>>
>
> Dear Zahra,
> it looks like the difference is very small, especially sine you have a
> gap. Keep in mind that, if you have a gap, in the limit of zero smearing
> the Fermi energy can  go anywhere in the gap. This is just a complicated
> way to say that there is no Fermi energy in insulators.
>
> On the other hand, both your calculations are wrong; if you want to
> simulate non-interacting planes - separated by some vacuum along Z - than
> you cannot shift the kpoints along Z. Be sure to have well understood this
> point before continuing, as it really is important. Check on some solid
> state book how the periodicity of wavefunctions is related to their
> k-point, and what kind of periodicity do you expect for your system
> (included the artificial periodicity along Z). By setting the shift along Z
> you force the wavefunctions from two artificial replicas of the graphene
> bilayer to hybridize with each other, which is an unphysical effect.
>
> bests
>
> --
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS & Université Paris 6
> phone: +33 (0)1 44275 084 / skype: paulatz
> www:   http://www-int.impmc.upmc.fr/~paulatto/
> mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
>
>
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