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

[Alex Shearer]

If you know the form of the basic repeating unit (The un-doped 
zincblende structure would be a good place to start), it may be useful 
to use a molecule building program that has tools designed for periodic 
systems. I have had success with gaussview; the GUI is relatively 
intuitive and the coordinates stored in the .com file of the supercell 
you create can be copied directly into the corresponding section of the 
PW script (though be mindful of what length units are being used). The 
key to gview is the PBC (periodic boundary conditions) menu; there are 
several tutorials online with detailed instructions regarding this part 
of the program. If gaussview isn't available, I have heard good reviews 
of other programs that may have similar or even better features - the 
one that comes to mind is Avogadro but I'm sure there are others too.

  All that being said, I agree with professor Baroni that trying the 
construction by hand is educational; as a new user of QE I tried by hand 
a couple times for different crystal faces before 'cheating' and using a 
program.

Best of luck,

Alex Shearer
C.B. Harris Group
University of California, Berkeley



On 12/15/2011 1:11 AM, Stefano Baroni wrote:
> The same way you would "by hands". First draw (physically with pencil 
> and paper, or just mentally if you have a good 3D imagination) a 
> zincblende crystal structure with many unit cells repeated in the 
> three dimensions. Give different atoms different colors. ZnSe can be 
> colored with just two colors (say, green and red, plus possibly black 
> to draw bonds). Then highlight the atoms that you want to turn into 
> impurities using a different color (say, blue), arranging them in 
> periodic array (i.e. one every 2/3/you-name-it elementary cells). 
> Which crystal structure has the artificial crystal you have built? The 
> unit cell of this artificial crystal will be your unit cell: it will 
> contain many atoms ... Do it by yourself: you will learn a lot ... 
> (and it may be fun!) - SB
>
> On Dec 15, 2011, at 9:19 AM, bamidele ibrahim wrote:
>
>> 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 alter
>> the 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 will
>> be 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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> ---
> Stefano Baroni - SISSA&DEMOCRITOS National Simulation Center - Trieste
> http://stefano.baroni.me <http://stefano.baroni.me/> [+39] 040 3787 
> 406 (tel) -528 (fax) / stefanobaroni (skype)
>
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> de la pensée - Jean Piaget
>
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