[QE-users] changing cell size 1x1 to 3x3 does not provide same DOS & BS

[Lorenzo Paulatto]

Dear Wenusara,

the 3x3 supercell has a much larger amount of vacuum, this is a typical 
source of problems with graphene, as one electron may like to wonder out 
in the vacuum.  Sticking to 5-10Å of vacuum is enough and should work 
fine, i.e. when you multiply celldm(1) by 3, you should also divide 
celldm(3) by the same amount to keep vacuum constant. Also, your plane 
wave cutoff seems a bit low, I assume you have tested convergence properly.

kind regards

On 23/02/2024 17:48, wenusaras wrote:
> hi,
>
> I am new to QE.
> I start with the simple pw scf code of graphene 1x1 unit cell (i.e. 
> nat=2) then the DOS and BS was obtained.
> After that pw scf code was changed to 3x3 cell (i.e. nat =18) then the 
> obtained DOS and BS was not similar to 1x1 (changing the number of 
> kpoints was not make two BS (or DOS) similar).
>
> Herewith I have attached the both pw scf & nscf files.
>
> I am curious to know what is the reason for this?
> Is there a way to make this both DOS and BS for both 1x1 and 3x3 to 
> similar?
>
>
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-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
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