[Wien] change of lattice parameters while alloying

[Dr. K. C. Bhamu]

Dear Sir
For your first two points, I convinced but below suggestions triggered me
to ask/clarify my doubts more:


> Note that depending on what you want to compare in your series of
> calculations it probably is a good idea to do all calculations in the same
> space group - even if you are left with very low symmetry. Do this by
> giving all Cr in the pristine cell you want to substitute a different index
> (Cr1, Cr2 ...).
>

I tried to label all Cl with a number and then replaced all Cl one by one
with Br. But when I initialised the structure it gives me 1-P1 SG with
reduced basis vectors and all angles =60deg.
I wounder how to keep all six structure in the same space group?

I just had an discussion with experimentlist and he suggested me that
changing of basis vector and SG is normal but the key point I have to keep
in mind that the SG should not leave the the SG family belonging to that
class of (here perovskite) crystal structure. For example: we have various
SGs for perovskite family (225, 42, 44, 107..., etc.) and after replacing
any number of Cl with Br should stabilise in one the SG belongs to
perovskite structure.


>
> And remember that you do not calculate an (random) alloy, you calculate a
> periodic structure. Watch out for superstructure effects, perhaps by
> checking larger supercells with the same Br-concentration but different
> configuration.
>
>
Sir, I am doing for bulk only like ABCl_(1-x)Br_x.

Regards

Bhamu


> Martin Pieper
>
>
> Am 09.05.2017 01:55, schrieb Dr. K. C. Bhamu:
>
>> Dear Wien2k Users
>>
>> I am alloying a quaternery compound: replacing Cr with Br one by one.
>> What I see is, the pristine compound is cubic with 225 SG. When I
>> replace Cl by Br one by one then lattice parameters deviates from
>> cubic to different structure.
>> like a=b, c or a,b,c. SG also changes.
>> During initialisation I accepted the new structure suggested by the
>> w2web. Should I accept the suggested structure?
>> As per my understanding from previous posts from mailing list we
>> should accept the suggested structure which is with lower symmetry.
>>
>> Is the change of lattice parameters is normal behaviour of material or
>> I am doing any mistake?
>>
>> Sincerely
>>
>> Bhamu
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> ---
> Dr. Martin Pieper
> Karl-Franzens University
> Institute of Physics
> Universitätsplatz 5
> A-8010 Graz
> Austria
> Tel.: +43-(0)316-380-8564
>
>
>
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