[Pw_forum] Problem in relaxing Si structure

[Lorenzo Paulatto]

DFT calculations assume zero temperature and a perfect crystal, Silicon is
an insulator under these conditions

Lorenzo Paulatto - Paris
On 10 May 2015 09:16, "reza vatan" <rezavatan64 at gmail.com> wrote:

> 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
>> >
>> >
>> > _______________________________________________
>> > Pw_forum mailing list
>> > Pw_forum at pwscf.org
>> > http://pwscf.org/mailman/listinfo/pw_forum
>> >
>>
>> --
>> 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 Cx 05
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
>>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150510/9550e021/attachment.html>