[Pw_forum] phonon calculation for optimized geometry -one subtle confusion

[Ngoc Linh Nguyen]

> Dear Hanyu !
>                      Thanks for your reply. As you now the default value
> for
> the pressure in PWSCF is 0.5.

This value should be 0.0 as the default value (see in input PW website)

> I am using that value as convergence
> threshold
> but when I am doing scf calculation with the geometrical parameters value
> obtained from the vc-relax calculation the pressure value is different
> from
> vc-relax final run. And as you know pressure will effect the phonon
> dispresion relation..Can you please give me any suggestion,

Before doing scf calculations, have you changed the cell-parameters in scf
input file as same as the converged cell-parameters from vc-relax?

Best regards,

Linh



>
> Thanks alot,
> MOHNISH
>
> On Sun, Apr 18, 2010 at 3:00 PM, Hanyu <ouuing at gmail.com> wrote:
>
>> dear mohnish :
>> I think you should check it carefully again. I don't think it should
>> be happen. In fact, the stress of scf and vc-relax should be the same.
>> but if the stress is not the hydrostatic pressure, the result is not
>> be believed. you have to relax the structure until the stress of the
>> phase is what you want.
>>
>> best regards.
>>
>> Hanyu
>>
>> On Sun, Apr 18, 2010 at 11:16 AM, mohnish pandey
>> <mohnish.iitk at gmail.com>
>> wrote:
>> > Dear users,
>> >                   I want to do phonon calculation for some structures,
>> but
>> > after geometry optimization when I am using optimized geometry
>> parameters
>> > for scf calculation there is difference in stress of scf calculation
>> and
>> > vc-relax calculation which is changing phonon dispersion. Can anybody
>> please
>> > tell me if there is any option to use the data of relax or vc-relax
>> > calculation for phonon dispersion.. Or can I doing phonon calculation
>> along
>> > with relax or vc-relax calculation.?
>> > Thanks a lot in advance,
>> >
>> > --
>> > Regards,
>> > MOHNISH,
>> > -----------------------------------------------------------------
>> > Mohnish Pandey
>> > Y6927262,4th Year dual degree student,
>> > Department of Chemical Engineering,
>> > IIT KANPUR
>> > 09235721300
>> > -----------------------------------------------------------------
>> >
>> > _______________________________________________
>> > Pw_forum mailing list
>> > Pw_forum at pwscf.org
>> > http://www.democritos.it/mailman/listinfo/pw_forum
>> >
>> >
>>
>>
>>
>> --
>> -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=**=-=**=-=**=-=*=-=*=-=*=-=*=-=*=-
>>  Hanyu Liu(刘寒雨),
>>  MS.
>>  State key  Laboratory of Superhard Materials, Jilin University, China
>>  Email: liuhanyu08 at mails.jlu.edu.cn    ouuing at gmail.com
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
>>
>
>
>
> --
> Regards,
> MOHNISH,
> -----------------------------------------------------------------
> Mohnish Pandey
> Y6927262,4th Year dual degree student,
> Department of Chemical Engineering,
> IIT KANPUR
> 09235721300
> -----------------------------------------------------------------
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>


-----------------------------------------------------
 Nguyen Ngoc Linh, PhD Student
 c/o:   SISSA & CNR-INFM Democritos,
        via Beirut 2-4, 34014 Trieste (Italy)
 email: nnlinh at sissa.it
 phone: +39 04 03787 319
 skype: ngoclinh84phys
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"The physics is theoretical but the fun is real"


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