[Pw_forum] Help in using xcrysden for making structures

[Duy Le]

If
1. you know there are 18 atoms in a unit cell
2. AND if you know their Cartesian coordinates
3. AND if you don't want to use the Bravais-lattice index,

you could use
1. ibrav=0
2. AND define your unit cell (using  CELL_PARAMETERS): nothing more than the
3 "primitive" lattice vectors
3. AND ATOMIC_POSITIONS: I suggest that you should use crystal coordinates
instead of using Cartesian coordinates.

You can find description in
http://www.quantum-espresso.org/input-syntax/INPUT_PW.html

:)

On Fri, Sep 4, 2009 at 12:14 PM, Neel Singh <neelphysics at yahoo.in> wrote:

>  hi,
> I need some help in drawing crystal using xcrysden. Sir/Madam, let us take
> the case of FCC for which ibrav=2, and celldm(1)=9.000. Now if i know that i
> have 18 atoms in my unit cell and i know the Cartesian co-ordinates{x,y,z}
> of each atom in angstrom/bhor. I want to know that how can i draw my unit
> cell with giving positions of all the atoms without using the symmetries by
> xcrysden??. Means like if i specifiy,
> & system
> ibrav=2, celldm(1)=9.00, nat=1,......
> ATOMIC POSITIONS{angstrom}
> A  0  4.5 0
>
> now if we visualise this type of structure with Xcrysden, we found a number
> of atoms genrated due to symmetry. If i make a file like
>  & system
> ibrav=2, celldm(1)=9.00, nat=18,......
> ATOMIC POSITIONS{angstrom}
> A  0  4.5 0
> /
> 18 times we have specified the co-ordinates
> /
> /
> A  4.5 0 0
> Xcrysden will give warning like atom 10 and 90 are very close like that.
> Sir i want to know is there any way so that i can make my PWSCF input file
> with angstrom/bohr postions such that with one atomic postion Xcrysden will
> show only one atom??
> Means i will give 18 atomic postions and xcrysden will produce 18 atom unit
> cell without using symmatries.
>
> Thanks for your help,
> Neel Singh,
> Univeristy of Delhi,
> India
>
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-- 
--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.
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