The ABINIT Users Mailing List ( CLOSED )

[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

Hello

I _believe_ that what gaussian is actually doing is the following: no
symmetries are used, and all the original ones are broken, but at the
end the resulting structure is analysed with a very lax tolerance for
symmetry fulfillment, and the approximate symmetries are found (8 of
them). You may even be able to re-symmetrize to enforce these for
good. We are considering adding this to abinit (it should already be
possible to change the tolerance, in a subsequent run, but I have not
found the input variable). There is no timeline as yet: if someone
wants to volunteer, it should be easy to implement.

Matthieu

On Fri, Apr 24, 2009 at 9:15 PM, farah marsusi <fmarsusi@yahoo.com> wrote:
> Dear Angelade,
>
> Thank you for your response. I have run the abinit with three diferent nsyms
> in the input file. As you mentioned if I don't define nsym for abinit, it
> keeps original symmetry. If I define nsym=1, it breaks all symmetry unless
> identity, and the resulted geometry is very different from corresponding
> geometry resulted from GAUSSIAN pakage in both cases. GAUSSIAN predicts C1
> final symmetric for the system ( I enter full optimization with nosymm
> command to GAUSSIAN).This means nsym=8. With this nsym abinit results nearly
> the same geometry as GAUSSIAN. This is a question for me, how abinit can
> underestand the final symmetry. In my case nsym=1, breaks all of 24 initial
> symmetry unless identity, while GAUSSIAN keeps 8 of them. So I should run
> one time GAUSSIAN to find final geometry, then abinit to find plane wave
> orbitals.
>
> Best wishes,
> Farah
>
>
> --- On Fri, 4/24/09, Anglade Pierre-Matthieu <anglade@gmail.com> wrote:
>
> From: Anglade Pierre-Matthieu <anglade@gmail.com>
> Subject: Re: [abinit-forum] symmetry
> To: forum@abinit.org
> Date: Friday, April 24, 2009, 1:19 PM
>
> Dear Farah,
>
> I'm not quite sure to understand your question. Yet, I'll try an answer :
> By default Abinit keeps the original symmetry of your system because
> it exploit them to the maximum ; that is it can not find even a force
> that breaks the symmetry.
>
> If you tell abinit to use a lower level of symmetry than the actual
> one, it may finds forces that break the actual symmetry. But still it
> can't break the chosen level of symmetry.
>
> In case you want a completely general relaxation you must impose "nsym
> 1" so that Abinit really computes forces in a general manner. In this
> way you could reach any "natural" symmetry of your relaxed system by
> performing a complete relaxation.
>
> Am I answering your question?
>
> Regards,
>
> PMA
>
> On Wed, Apr 22, 2009 at 9:21 AM, farah marsusi <fmarsusi@yahoo.com> wrote:
>> Dear all,
>>
>>
>>
>> I know the initial symmetry of the system (Td), but do not know what is
>> the
>> final symmetry after let the system to relax by ionmov=3.  The symmetry of
>> the system after relaxation is again Td, if I do not define the nsym of
>> the
>> system in the input file.
>>
>>
>>
>> I repeated the problem with the GAUSSIAN package, and did not impose to
>> system to hold its symmetry during relaxation. The final symmetry of the
>> system was C1.
>>
>>
>>
>> If I enter the command nsym=8 (relates to C1 symmetric) with its
>> corresponding symrel in abinit input file the final geometry of abinit
>> will
>> be the same as GAUSSIAN.
>>
>>
>>
>> Is it anyway I can understand abinit to find final symmetry of the system
>> by
>> itself.
>>
>> Best wishes,
>>
>> Farah
>>
>
>
>
> --
> Pierre-Matthieu Anglade
>
>
>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF)
Dpto. Fisica de Materiales,
U. del Pais Vasco,
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390

Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500