[Pw_forum] Re : how to construct supercell for an fcc crystal compound

[Abdeslam Houari]

Hi;
Just look to your ZnSe face centered cubic unit cell with 2 atoms, as a simple cubic cell with 8 atoms (4 Zn abd 4 Se) .. If you multiply it (repeat it) 2 times along the three spatial directions (x, y and z axis) you will obtain a larger simple cubic cell which contain 8 unit cell, which mean with 8x8=64 atoms (32 Zn and 32 Se). You can by simple multiplication along the three dimension of the space create a cell as large as you want... not necessary cubic !! 
The next step is to do the substitution in this 64-atoms cell by taking off one Zn atom, for instance, and replace it by the desired one, let say Mn for instance. You will obtain the final desired unit cell that you will use in calculations, which now contains 31 Zn atoms, 32 Se atoms and 1 Mn atom.

The best way to proceed is to keep away the computer and do thing by hands, with three different color pencils on a paper sheet... When the procedure is well understood do it in computer...

Good luck
Abdus-salam 

=======================================
Abdesalem HOUARI
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Department of physics, Theoretical Physics Laboratory
University of Bejaia-06000. Algeria.
E-mail: abdeslam.houari at univ-bejaia.dz & habdslam at yahoo.fr
https://sites.google.com/site/houariabdeslam/homepage
Phone: +213 34 21 53 04
Fax: +213 34 21 59 86
Cell phone: +213 551 36 29 01 (emergency only !!)
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--- En date de : Jeu 15.12.11, bamidele ibrahim <bamideleibrahim at yahoo.com> a écrit :

De: bamidele ibrahim <bamideleibrahim at yahoo.com>
Objet: [Pw_forum] how to construct supercell for an fcc crystal compound
À: "pw_forum at pwscf.org" <pw_forum at pwscf.org>
Date: Jeudi 15 décembre 2011, 9h19

Dear all,   I have been working on series of zinc blende semiconductors materials in recent time. 
I am now interested in doping some of the compound with differents element in other to alterthe crystal structures(i.e introducing impurities). I know i need to build a supercell for my compound but, 
i don't understand how to do it. I went through all the examples files, but none was able to give the information. I willbe delighted if you can all come to my aid. for example ZnSe with atomic position of (0,0,0) and (0.25,0.25,0.25). 
How do i build a supercell for this compound?  Adetunji Bamidele Ibrahim
Department of
 physics,University of Agriculture,
Abeokuta, Ogun State,Nigeria.
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