[Pw_forum] XCRYSDEN Primitive cell: Reg

[Tone Kokalj]

On Tue, 2016-01-19 at 13:48 +0530, Suresh A wrote:
> Dear All,
>             Herewith I have included two primitive cell input filefor anatase strucutre. Between them XCRYSDEN shows correct structure for file one where atomic positions are in angstrom unit and for another structure it shows wrong strucutre where atomic positions are  in relative crystal coordinate. Will you please point out where the problem is? And I am using xcrysden-1.5.60-semishared linux 


Typically such problems stem from the following reason: the user and
the program have a different idea of the unit-cell. In particular,
there are two flavors of these problems:

(i) the crystallographic vectors are chosen differently between the
user and the program (in such cases specified Cartesian coordinates do
not give correct structure)

(ii) the crystallographic coordinates refers to different set of
vectors, e.g, primitive vs. conventional (in such cases the specified
crystal coordinates do not give the correct structure)

In your case it is the second problem. You have specified the crystal
coordinates with respect to conventional vectors, but the pw.x expects
the coordinates wrt primitive vectors (and consequently also xcrysden
interprets the QE input this way).

------------------
Excerpt from the pw.x documentation:
------------------
crystal : atomic positions are in crystal coordinates, i.e.
          in relative coordinates of the primitive lattice
          vectors as defined either in card CELL_PARAMETERS
          or via the ibrav + celldm / a,b,c... variables
--------------------


Best regards, Tone

-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

Please, if possible, avoid sending me Word or PowerPoint attachments.
See:  http://www.gnu.org/philosophy/no-word-attachments.html