[Wien] A problem with symmetry

[delamora]

O A Yassin
    You do not describe the structure...
    There is a cubic Sr2MnTiO6 in the ICDD there the Mn and Ti are occupying the same positions with 0.5 each.
    What you can do is to make a supercel and put these two atoms in alternated positions.

This is what I get for the cubic perovskite cell:
                                                      
F   LATTICE,NONEQUIV.ATOMS:  4 225_Fm-3m                     
MODE OF CALC=RELA unit=ang 
 13.912170 13.912170 13.912170 90.000000 90.000000 90.000000
ATOM   1: X=0.25000000 Y=0.25000000 Z=0.25000000
ATOM   1:X= 0.75000000 Y=0.75000000 Z=0.75000000
Sr         NPT=  781  R0=0.00001000 RMT=    2.0000   Z: 38.0
ATOM   2: X=0.00000000 Y=0.00000000 Z=0.00000000
Ti         NPT=  781  R0=0.00005000 RMT=    2.0000   Z: 22.0
ATOM   3: X=0.50000000 Y=0.00000000 Z=0.00000000
Mn         NPT=  781  R0=0.00005000 RMT=    2.0000   Z: 25.0
ATOM   4: X=0.00000000 Y=0.25000000 Z=0.00000000
ATOM   4:X= 0.00000000 Y=0.75000000 Z=0.00000000
ATOM   4:X= 0.75000000 Y=0.00000000 Z=0.00000000
ATOM   4:X= 0.25000000 Y=0.00000000 Z=0.00000000
ATOM   4:X= 0.00000000 Y=0.00000000 Z=0.25000000
ATOM   4:X= 0.00000000 Y=0.00000000 Z=0.75000000
O          NPT=  781  R0=0.00010000 RMT=    2.0000   Z:  8.0

________________________________________
De: wien-bounces at zeus.theochem.tuwien.ac.at <wien-bounces at zeus.theochem.tuwien.ac.at> en nombre de Víctor Luaña Cabal <victor at fluor.quimica.uniovi.es>
Enviado: miércoles, 15 de octubre de 2014 05:13 p.m.
Para: A Mailing list for WIEN2k users
Asunto: Re: [Wien] A problem with symmetry

On Thu, Oct 16, 2014 at 12:25:22AM +0300, Osama Yassin wrote:
> In trying to generate the structure file of Sr2MnTiO6 in the space group
> I4/m (No 87), the Sr and the O positions do not split. The message
> "Splitting of equivalent positions not available.
> To split you must select a lattice type"
>
> I suspect some is corrupted because it was working well with Wien2k 13 and
> 14.
>
> How do I recover this problem.

There are several options, but there are years since I do not work with wien2k.
In principle FP-LAPW techniques do not average the potentials from ions in fractional
occupy positions so you have to replicate the cell and move the ions to
the different cells. You can do a statistical treatment of the different
posibilities. Hard but not imposible.

Probably the wien2k current programmers have studied other possibilities.

Regards,
       Dr. Víctor Luaña
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