[Wien] After supercell, add impurity... x sgroup change space group

[Serhat Ayık]

Thank you for your feedback
As you said, I have clustered the Al on one side of supercell and "layered"
like distribution.
I've tried different distributions before. I have had some attempts where
"x sgroup" gives different space groups.
For example, on my last attempt, I replaced the 1st, 4th, 5th, 8th, 9th,
12th, 13th and 18th of the 16 In atoms with Al atoms. (Total: 8 Al + 8 In)
- x nn
- copy case.struct_nn case.struct (9 atoms: 2 Ag, 1 Al, 1 In, 5 S)
- x nn
- copy  case.struct_nn case.struct (I repeated this step one more time
because "x nn" gave warning again). This time 10 atoms: 2 Ag, 1 Al, 1 In, 6
S
- x nn
- x sgroup
And finally the space group turns 20 (C 2 2 21) Orthorombic C-base centered.
As a result, a different space group from the original struct
file(122_I-42d) was created.
In the struct file, the result appears to be OK.
2 Ag: at 4 different positions=8 Ag,
1 Al: at 4 different positions= 4 Al,
1 In: at 4 different positions=4 In,
6 S: at 2+2+4+4+2+2 different positions=16 S
I viewed the structure in the xcrysden program. Al and In atoms appear to
be homogeneously distributed.
I continue the calculation with this struct file and space group. I will
share the result with you.


Peter Blaha <pblaha at theochem.tuwien.ac.at>, 25 Oca 2021 Pzt, 21:35
tarihinde şunu yazdı:

> It is VERY important to check which In atoms you replace by Al.
> View your structure and check: Did you cluster the Al on one side of the
> supercell ?  Did you introduce a "layered" like distribution ? ....
>
> Most likely you want a "random" substitution, without any ordering
> (otherwise experiment might have found some order).
>
> Most likely, the "ideal" randomly substituted structure will even have
> P1 spacegroup, i.e. all symmetry operations are lost (at least for a
> larger supercell).
>
> PS: Experiment measures an "average structure", and therefore find a
> high symmetry SG. They put on the same position half a In and half a Al
> atom.
> Of course, this is not reality.
>
> Am 24.01.2021 um 21:31 schrieb Serhat Ayık:
> > Dear Wien2k users,
> > In my original struct file, I have (B Lattice) 3 non equiv. atoms
> > (Chemical form: AgInS2), space group 122_I-42d, and 8 number of symmetry
> > operations.
> > I do 2x2x2, P lattice type supercell and I have 48 non equiv. (16 Ag, 16
> > In, 16 S) atoms. I want chemical form like AgAl(0.5)In(0.5)S2. I am
> > replacing 8 In atoms with 8 Al atoms. Finally, I have 16 Ag, 8 Al, 8 In
> > and 16 S in struct file.
> > Then, I do
> > - x nn (nn-bondlength factor:2)
> > copy case.struct_nn to case.struct. (After this step, I have 7 atoms "2
> > Ag, 1 Al, 1 In, 3 S" in case.struct)
> > - repeat x nn
> > -  x sgroup
> > warning: !!! Number of inequivalent atoms has changed. !!! Old value= 48
> > New value= 7 warning: !!! Unit cell has been reduced.
> > sgroup found: 17 (P 2 2 21)
> >
> > I think the space group shouldn't change.
> > Is it true that the space group changes? Or am I making a mistake
> somewhere?
> >
> > Regards
> >
> >
> >
> >
> >
> >
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>
> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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