[Pw_forum] Problem in relaxing Si structure

[reza vatan]

Dear Lorenzo,

Thanks for replying. The single SCF step does not converge.
Any way by changing "occupations=smearing" to "occupations=fixed", I could
fix the convergence problem for both SCF cycle and relaxation, although I
don't know if this occupation mode is appropriate choice for semiconductor
or not.

Please let me know if you know what is the best choice for occupation mode
in the case of a semiconductor like Silicon.

Best,
Reza

On Tue, May 5, 2015 at 2:09 AM, Lorenzo Paulatto <
lorenzo.paulatto at impmc.upmc.fr> wrote:

> Dear Reza,
> what does not converge? The single SCF step or the relax calculation?
>
> Please not that you are not doing a relax calculation but a damped
> dynamic one. If your damped dynamics are not damped enough it will never
> converge.
>
> Use ion_dynamics="bfgs" instead (which is the default, do not play with
> parameters if the default ones work)
>
> regards!
>
> I also notice that you are using a smearing to integrate the Fermi
> surface of Silicon, but Silicon is not a metal. If fore some mysterious
> reason you want to use a smearing you may need more k-point, but the
> calculation SCF should converge regardless.
>
>
> On 04/05/15 23:42, reza vatan wrote:
> > Dear users,
> >
> > I have been trying to perform "calculation=relax" on Si bulk structure
> > generated by a super cell ( or unit cell) containing 8 atom repeating in
> > a simple cubic lattice (ibrav=1). I created this super cell, by cutting
> > a cell containing 8 atoms from perfect Si bulk structure obtained from
> > experimental and theoretical results. The problem is that my calculation
> > doesn't converge at all, although the structure seems to be relaxed. Is
> > there any one here knows where the problem is. I attached the input file
> > that I run.
> >
> > Best,
> > Reza
> >
> >
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>
> --
> 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/
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