[QE-users] Simple cubic to fcc cubic

[Giovanni Cantele]

I would add, to support this suggestion, that this forum is, in my opinion,
a very precious resource, for both those who are beginners and those who
are less beginners
because not only there is a more than reasonable response "rate" to posed
problems and questions but also, browsing past threads, you might discover
lot of
tricks, explanations, suggestions that might result helpful for you!
Giovanni

-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home


Il giorno mar 27 feb 2024 alle ore 11:46 Stefano Baroni <BARONI at sissa.it>
ha scritto:

> Thank you Giovanni. May I suggest that in this and other similar cases
> help from the Quantum ESPRESSO Community is properly acknowledged in any
> work (thesis, paper, report) that has benefited from it? Thanks — Stefano
>
>
> On 27 Feb 2024, at 11:36, Giovanni Cantele <giovanni.cantele at spin.cnr.it>
> wrote:
>
> Let us suppose that we have a fcc crystal, with one atom per cell, at
> (0,0,0), for the sake of simplicity.
>
> The unit cell sides are in the form (a/2,a/2,0) (a=side of the cubic
> cell), with unit cell volume a^3 / 4.
>
> Now, let us move from fcc to sc unit cell.
> Each of the 8 atoms at the corners is shared by 8 cubic cells, and thus we
> should consider only one of these atoms.
> On the other hand, atoms at the center of the cube faces are shared by two
> unit cells, and count as 1/2. Since we have
> 6 faces, 3 out of these 6 atoms must be considered.
> As a result, the sc unit cell will contain 4 atoms and a volume 4 times
> larger, a^3 as you would expect.
>
> To go back from sc to fcc you should therefore keep 1/4 of your atoms,
> because those that are associated to the centers of three faces,
> that should be explicitly considered in sc, now become equivalent (that
> is, connected by a lattice vector) to other atoms in fcc.
>
> The code correctly finds overlapped atoms, e.g. in the example of one atom
> per unit cell, in sc you would have (0,0,0), (a/2,a/2,0), (a/2,0,a/2),
> (0,a/2,a/2)
> and the last three in fcc are obtained from (0,0,0) after a lattice
> translation by (a/2,a/2,0), (a/2,0,a/2), (0,a/2,a/2), respectively.
>
> Giovanni
>
> --
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: https://sites.google.com/view/giovanni-cantele/home
>
>
> Il giorno mar 27 feb 2024 alle ore 11:14 Ms. Chandrika K. via users <
> users at lists.quantum-espresso.org> ha scritto:
>
>> Need help in understanding
>>
>>    1. I am currently working on Co3O4 structure,from literature it is
>>    very evident that it belongs to space group Fd3m(cubic fcc).
>>    2. I have referred to Co3O4 Fd3m cubic structure from materials
>>    project it is represented as simple cubic structure but Fd3m space group
>>    refers to cubic fcc.
>>    3. As it is simple cubic ibrav =1,when i change ibrav =2(cubic fcc) i
>>    am getting warning message
>>    "WARNING: Atom 381 and atom 444 are very close !!!   Atom 444 deleted
>>    !!!"
>>    ATOMIC_POSITIONS (angstrom)
>>
>> I would like to know how to change the structure from simple cubic to fcc
>> cubic
>>
>>
>> chandrika yadav k
>>
>>
>> _______________________________________________
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>> effects that the Russian military offensive has on their
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>> and economic cooperation amongst peoples
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> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
> —
> Stefano Baroni - Trieste —  http://stefano.baroni.me
>
>
>
>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
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