[Pw_forum] Defining an antiferromagnetic graphene nanoribbon

[Hande Ustunel]

Dear Roberto,

If I may jump in, I don't suppose it would be terribly costly to repeat one
of your calculations with a cutoff that is slightly higher once you are
done with the lower cutoff. You can compare whichever quantities you are
interested in between the two cutoffs and decide whether the error is
within a threshold that is self-determined/acceptable by the community at
large. This would verify once and for all the appropriateness of your
cutoff. Keep in mind however that for a system such as a graphene ribbon
the cutoff may not be the only parameter to optimize. There's still the
smearing and the amount of vaccum to worry about. For this reason, you
should consider an isolated preliminary cutoff convergence study in a
simpler system such as diamond or better still graphene as suggested in
previous replies to your post.

Best wishes,
Hande

On Sun, 11 May 2008, Roberto G. A. Veiga wrote:

> Hi, Stefano:
> 
> as far as I understand, if I use a cutoff for a system made of carbons and I find it is appropriate, I should use the same cutoff for another system also made of carbons. I mean, if I use 20 Ry for carbon nanotubes and the results are fine, I could use 20 Ry for diamond, or graphene. Is it wrong my assumption?
> 
> []s,
> 
> Roberto
> 
> Stefano Baroni <baroni at sissa.it> wrote: The kinetic-energy cutoff is a property of the atomic core, NOT of the specific system (to a large extent).SB
> 
> On May 10, 2008, at 6:11 PM, Roberto G. A. Veiga wrote:
> 
> Dear Stefano:
> 
> I'm using Ultrasoft PPs. My question was because this cutoff (20 Ry) seemed to be appropriate for other carbonic systems.
> 
> []s,
> 
> Roberto
> 
> Stefano Baroni <baroni at sissa.it> wrote: 
> On May 9, 2008, at 10:42 PM, Roberto G. A. Veiga wrote:
> 
> Hi, Konstantin:
> 
> thank you very much. Such a large cutoff (80 Ry) is necessary for convergence? Or maybe I'm using one quite small (20 Ry)...
> 
> it depends on the PP you are using, I guess, and certainly NOT on the actual structure you are studying. 80 Ry seems like an appropriate cutoff for moderately hard norm-conserving PP's, whereas 20 Ry sounds like appriate for many US PP's. In either case, you better check the aprporiateness by yourself, through thorough convergence tests.
> 
> 
> Stefano
> 
> 
> 
> 
> 
> []s,
> 
> Roberto
> 
> Konstantin Kudin <konstantin_kudin at yahoo.com> wrote:  Hi Roberto,
> 
>  Here is a ribbon input that works for sure:
> https://kiev.princeton.edu/misc/rg_07.scf.in
>  (get PPs from the PWSCF website)
> 
>  Good luck!
>  Kostya
>  ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
> 
> 
> La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget
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> 
> 
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> 
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>  ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
> 
> 
> La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget
> 
> 
> 
> Please, if possible, don't  send me MS Word or PowerPoint attachments
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-- 
Hande Ustunel
Department of Physics
Office 439
Middle East Technical University
Ankara 06531, Turkey
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