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: bl...@theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
WWW: http://www.imc.tuwien.ac.at/TC_Blaha
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