[Pw_forum] MoO3 input

[Michael Mehl]

You've listed the Wyckoff positions of the atoms, which generate all of the
atoms in the unit cell.  The space group for MoO3 is #62.  Those points are
(4c) Wyckoff positions, which means that there are 16 atoms in the unit
cell.

There are two ways to handle this:

1) Investigate the crystal_sg option for ATOMIC_POSITIONS
2) Use the space group tables to unfold the (4c) sites

To do either, you'll need to know which orientation of space group 62 your
reference is using:  there are 6 possibilities (see
http://img.chem.ucl.ac.uk/sgp/large/ortho.htm, and look for 62).  The
reference you are using should tell you which one it is, or give you some
clue by describing nearest neighbor distances.  You'll have to do some
research.

Unfortunately we don't have MoO3 up on the prototype web page yet, so I
can't really tell you any more than that.  We have some updates coming, and
this isn't the first time MoO3 has been mentioned, so I'll try to add it in
soon.

If you look at the examples in
http://www.aflowlib.org/CrystalDatabase/orthorhombic_spacegroup.html  under
Pnma (#62) you'll see how to convert (x 1/4 z) coordinates to multiple
atoms for the Pnma orientation, but be warned that the relationship is
different for other orientations.


On Thu, Jul 20, 2017 at 3:09 PM, hamed asadi <hasadi at mail.kntu.ac.ir> wrote:

> dear all,
> I have try to make MoO3 bulk unit cell but the resulted structure is not
> like the published one. The input file which I made it from papers:
>
>
> &CONTROL
>                  calculation = 'scf' ,
>                 restart_mode = 'from_scratch' ,
>                 etot_conv_thr = 1.0E-8  ,
>                forc_conv_thr = 1.0D-8 ,
>                   outdir='/home/asa/Desktop/MoO3/out',
>                pseudo_dir = '/home/asa/Desktop/MoO3/pp',
> wf_collect=.true.
>                 tprnfor   = .true.
>                 tstress = .true.
> verbosity= 'low',
>  /
>  &SYSTEM
>                         ibrav = 9,
>    celldm(1) =7.48501621,
>                     celldm(2) =3.498447323,
>    celldm(3) =0.932944533,
>                      nbnd = 30,
>                          nat = 4,
>                         ntyp = 2,
>                      ecutwfc = 40 ,
>                      ecutrho = 400,
>                  occupations = 'smearing' ,
>                  degauss= 0.01 ,
>                  smearing= 'gaussian',
>
>  /
>  &ELECTRONS
>  mixing_beta = 0.7
>                   conv_thr = 1.D-8 ,
>  /
> &IONS
>                  ion_dynamics= 'bfgs'
>
> /
>  &CELL
>    cell_dynamics = 'bfgs' ,
>    cell_factor = 2
>  /
> ATOMIC_SPECIES
> Mo    95.94   Mo.pbe-spn-rrkjus_psl.0.2.UPF
> O     15.999  O.pbe-rrkjus.UPF
> ATOMIC_POSITIONS {crystal}
> Mo 0.077 0.25 0.501
> O 0.1003 0.25 0.075
> O 0.2242 0.25 0.068
> O 0.4328 0.25 0.443
> K_POINTS {automatic}
> 30 30 1   0 0 0
>
>
> I try ibrave 8 to 11 for this case but anyone does not looks like the
> correct structure. Please help me to get the right structure.
> Thank you in advance.
> H. Asadi
> K. N. Toosi university of technology
>
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-- 

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Michael J. Mehl, Ph.D.

Kinnear Chair in Physics

The United States Naval Academy

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mmehl at usna.edu

Library of Crystallographic Prototypes <http://aflow.org/CrystalDatabase/>
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