[Pw_forum] dipole correction-dipole field keep constant during optimization

[Fenggong Wang]

Dear Guido,
        Thank you for your quick reply.
         I think probably, as you said, first generating a good charge
density without dipole correction is a good idea. Actually, I was also
thinking of this.
         Maybe my previous idea is not good since the ititial guess is not
accurate.
          I will try a little more following your idea.
         If you happen to see Prof. Pachioni and Di valentin, please say
hello to them. I used to work in their group for one and a half years,
which was really good experience.
         Thank you very much.
         Fenggong

  On Tue, Oct 9, 2012 at 10:01 AM, Guido Fratesi <fratesi at mater.unimib.it>wrote:

> Dear Fenggong,
>
>  > Yes, it is a slab. The problem is it is difficult to converge if the
>  > dipole correction is added because in our system the charge density is
>  > changing too abruptly. Therefore, I was wondering whether adding a
>  > dipole correction which is keep constant during the scf convergence can
>  > improve the convergence problem. Of course, this will depends very much
>  > on the initial value of the dipole field.
>
>
> that happened to me at once when the sawtooth potential was mistakenly
> added at the wrong place, for example with the ramp inside the system
> rather than in vacuum.
>
> If this is not the case, "difficult" cases can be converged stepwise. E.g.:
>   1) do a scf calculation without dipfield (this converges, does it?)
>   2) set startingpot='file' and do a scf calculation with dipfield
> I did this several times to accelerate convergence for alkali atoms on
> metals. It also worked for structural relaxations (several scf steps),
> because once you had a good charge density the calculations went on
> smoothly.
>
> Or, as you suggest (I never tried)
>   1b) do a scf calculation with some guessed electric field ("external",
> variable eamp, no need to edit the code I guess)
>   2) as above, now with eamp=0.
>
> Please let us know if that solves your problem.
> Guido
>
> --
> Guido Fratesi
>
> Dipartimento di Scienza dei Materiali
> Universita` degli Studi di Milano-Bicocca
> via Cozzi 53, 20125 Milano, Italy
>
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-- 
Dr. Fenggong Wang
Postdoctoral Researcher

Department of Chemistry
University of Pennsylvania
231 South 34th Street, BOX 314
Philadelphia, PA 19104-6323
e-mail: wangfenggong at gmail.com; fenggong at sas.upenn.edu
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