[Pw_forum] (no subject)

[Axel Kohlmeyer]

On Wed, Dec 11, 2013 at 7:47 PM, Reza Behjatmanesh-Ardakani
<reza_b_m_a at yahoo.com> wrote:
> Suppose, we have a simple fcc unit cell. Do we need to introduce one
> particle position (original particle) or 14 particles (8 on corners and 6 on
> the faces). I think only originals needed. Other particles can be produced
> by symmetry operators.

nope.

a fcc lattice has only one atom. that is in the *primitive* cell
(which is what QE uses). what you describe is the conventional cell,
which would be a simple cubic lattice but that would not have 14 atoms
but 4 atoms (1 in the corner and 3 in the faces, because the corners
are shared by 8 cells and the faces by 2).

i suggest you re-read the chapters covering these topics in your
favorite book on crystallography to work this out.

axel.
>
> With the Best Regards
>
>
> Reza Behjatmanesh-Ardakani
> Associate Professor of Physical Chemistry
> Address:
> Department of Chemistry,
> School of Science,
> Payame Noor University (PNU),
> Ardakan,
> Yazd,
> Iran.
> E-mails:
> 1- reza_b_m_a at yahoo.com (preferred),
> 2- behjatmanesh at pnu.ac.ir,
> 3- reza.b.m.a at gmail.com.
>
>
> On Wednesday, December 11, 2013 7:19 PM, Paolo Giannozzi
> <paolo.giannozzi at uniud.it> wrote:
> On Wed, 2013-12-11 at 07:12 -0800, Reza Behjatmanesh-Ardakani wrote:
>
>> 1- For preparing the input file, if you introduce a symmetry in your
>> input's structure, only original particles
>>    should be defined in the input file. Is it right?
>
> no: you need to supply all atoms in a unit cell.
>
>
> P.
>
> --
> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
>
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-- 
Dr. Axel Kohlmeyer  akohlmey at gmail.com  http://goo.gl/1wk0
International Centre for Theoretical Physics, Trieste. Italy.