[Wien] Laves C15 symmetry reduction

[Guo-ping Zhang]

Thank you very much, Dr. Blaha!

I will follow your suggestions to see how far I can go.

Guoping


On Mon, 27 Feb 2017, Peter Blaha wrote:

> The F cell is the correct cell !!!
>
> A "P" cell of an actually FCC cell is automatically a "supercell".
>
> However, with wien2k you cannot run (super)cells with the same symmetry as 
> the original cell, as wien2k has implemented on 48 symmetry operations. 
> Suppose you create a 10x10x10 cell and want to keep symmetry: it means that 
> now 1000 atoms would be "equivalent" and there must be 1000 symm.ops which 
> transforms the equivalent atoms into each other, ....
>
> So if you want to use a cell which has by construction 4 times more atoms, 
> you have to break the symmetry. Depending on how you do that, you can end up 
> in various subsymmetries, either a R cell (the R cell is the primitive cell 
> of every F-centered cell anyway), or, eventually in P1.
> If you are clever, you can probably keep the simple cubic lattice and some of 
> the symmetry operations, but you have to work this out and split/group 
> equivalent atoms yourself.
>
>
>
> On 02/27/2017 03:08 PM, Guo-ping Zhang wrote:
>> Dear Wien2k users and developers,
>> 
>> I encounter a problem with Wien symmetry operation that I could not find
>> an answer from mailing list.
>> 
>> I have an intermetallic rare-earth compound, CeFe2, which has C15 cubic
>> Laves phase of MgCu2, with group symmetry No. 227, and with Z=8 in the
>> conventional cell. But I need to contruct a simple cubic cell (P)
>> instead of fcc (F) one given by Wien2k. So I use x supercell to generate
>> P structure and then rename one Ce by Ce1 and one Fe by Fe1 or any
>> combination of them or increasing lattice constant along one direction.
>> If I allow Wien to use its generated structure, I ended up with
>> Rhombohedral structure, or even worse without symmetry. I have no
>> trouble with simple fcc structure, but have no experience with Laves phase.
>> 
>> Here is my structure
>> 
>> F                            2 27_F
>>              RELA
>>  13.800670 13.800670 13.800670 90.000000 90.000000 90.000000
>> ATOM  -1: X=0.12500000 Y=0.12500000 Z=0.12500000
>>           MULT= 2          ISPLIT=-2
>>       -1: X=0.87500000 Y=0.87500000 Z=0.87500000
>> Ce         NPT=  781  R0=.000010000 RMT=   2.50000   Z:  58.00000
>> LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
>>                      0.0000000 1.0000000 0.0000000
>>                      0.0000000 0.0000000 1.0000000
>> ATOM  -2: X=0.50000000 Y=0.50000000 Z=0.50000000
>>           MULT= 4          ISPLIT= 8
>>       -2: X=0.50000000 Y=0.75000000 Z=0.75000000
>>       -2: X=0.75000000 Y=0.75000000 Z=0.50000000
>>       -2: X=0.75000000 Y=0.50000000 Z=0.75000000
>> Fe         NPT=  781  R0=.000050000 RMT=   2.42000   Z:  26.00000
>> LOCAL ROT MATRIX:    0.0000000-0.7071068-0.7071068
>>                      0.0000000-0.7071068 0.7071068
>>                     -1.0000000 0.0000000 0.0000000
>> 
>> 
>> I would appreciate it if anyone can give me some hints on this as what
>> is the correct procedure to generate a correct structure.
>> 
>> Thank you very much!
>> 
>> Best regards,
>> 
>> Guoping
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>
> -- 
>
>                                      P.Blaha
> --------------------------------------------------------------------------
> 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
> WWW:   http://www.imc.tuwien.ac.at/TC_Blaha
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