[Pw_forum] ibrav for Bmmb group

[Gabriele Sclauzero]

Please have a look here:

http://www.quantum-espresso.org/user_guide/node50.html#SECTION0001110200000000000000

You can try to play a bit the cutoff or with the FFT mesh size to avoid this.

HTH

GS

Il giorno 29/nov/2010, alle ore 13.16, giacsport at libero.it ha scritto:

> Dear All,
>             I would like to calculate a structure whose symmetry group is 
> Bmmb. I know that is a orthorombic structure with the ab-plane adopted as a 2D  
> plane.
> The unit cell is 1 atom of Ti and 2 of oxygen.
>   Cartesian axes
>     site n.     atom                  positions (a_0 units)
>         1           Ti  tau(  1) = (   0.0000000   0.2500000   0.6800900  )
>         2           O   tau(  2) = (   0.0000000   0.2500000   0.3832200  )
>         3           O   tau(  3) = (   0.0000000   0.2500000   0.2180200  )
> 
> I tried setting ibrav = 8,     
>                         celldm(1)=a (bohr),
>                         celldm(2)=b/a,
>                         celldm(3)=c/a
> 
> and I got this message in the output
> 
>     ortho sub-group =    2*   2 procs
> 
>     warning: symmetry operation #  2 not allowed.   fractional translation:
>       0.0000000  0.3862661  0.0000000  in crystal coordinates
>     warning: symmetry operation #  7 not allowed.   fractional translation:
>       0.0000000  0.3862661  0.0000000  in crystal coordinates
> 
> Is the ibrav value not appropriate for the Bmmb space group? Can anybody 
> kindly help me?
> Very best,
> 
> Giacomo Giorgi,
> PhD. Tokyo University.
> 
> 
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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