[Wien] why hexagonal goes to monoclinic C-base or triclinic within initialization?
Peter Blaha
pblaha at theochem.tuwien.ac.at
Wed Nov 5 09:10:29 CET 2014
Let me first start out, that something like this can happen in general.
You mix the concepts of a pure "bravais lattice" (a,a,c,90,90,120
=HEXAGONAL) with the concept of space groups.
Take the simplest case, a "cubic" cell (a=b=c, angles=90), but put into
this "cubic box" a couple of different atoms at random (x,y,z)
positions. The resulting space group will be "P1", i.e. a TRICLINIC
Space group, although of course the bravais lattice is still "cubic".
In some other cases, sgroup will transform your structure to some
"default setting" (like F <--> B-centered tetragonal lattices, which are
again "equivalent").
-----------------------------------------
In your specific case. my sgroup version finds the space group 156 (P 3
m 1), but then fails with some error message, because it has apparently
problems with internal accuracy.
The reason is that your input struct file is "inaccurate" (it seems
Quantum Espresso does not exactly preserve symmetry):
Your first atomic positions are:
> ATOM 1: X=0.11107924 Y=0.22215827 Z=0.24924470
> MULT= 3 ISPLIT= 8
> ATOM 1: X=0.11107924 Y=0.88892053 Z=0.24924470
> ATOM 1: X=0.77784149 Y=0.88892053 Z=0.24924470
but SG 156 requires for the "3d" Wyckoff-position:
(x,-x,z), (x,2x,z) and (2-x,-x,z).
In other words: 0.88892053 --> 0.88892076
and: 0.77784149 --> 0.77784173
is required in order to fulfill the symmetry requirements.
Most likely, similar inaccuracies happen for other positions and
depending on the numerics of your computer (compiler options, WIEN2k
version?) you may end up with some SG (although, strictly speaking, P1
would be the correct SG for this input).
Solution:
a) Fix all positions by hand (tedious)
b) Provided that P3m1 is the correct SG (I think it is, but I have not
checked all positions), setup a new struct file (w2web or
makestruct) and enter the "first" positions of your nine
non-equivalent atoms (copy-paste). The equivalent positions should
then be generated automatically (and hopefully with rounding errors
only in the last digit).
On 11/04/2014 07:10 PM, Martin Gmitra wrote:
> Dear Wien2k users,
>
> I am wondering why sgroup transfers input hexagonal system (see
> attachment or below a part of the slab that reduces symmetry in Wien2k)
> within initialization process to monoclinic B-base centered one while
> symmetry finds 6 symmetry operations for the original hexagonal system.
> If I reduce multiplicity of the atoms (to 27) the initialization goes
> with triclinic (P 90 90 120) and one operation symmetry. I have
> transferred the structure from plane wave calculations using Quantum
> Espresso code where the system is treated as hexagonal with 6 symmetry
> operations.
>
> Do you have an idea why Wien2k does not treat the system as hexagonal?
>
> Best regards,
> Martin Gmitra, Uni Regensburg
>
> H LATTICE,NONEQUIV. ATOMS 9
> MODE OF CALC=RELA unit=
> 18.064563 18.064563 37.794523 90.000000 90.000000120.000000
> ATOM 1: X=0.11107924 Y=0.22215827 Z=0.24924470
> MULT= 3 ISPLIT= 8
> ATOM 1: X=0.11107924 Y=0.88892053 Z=0.24924470
> ATOM 1: X=0.77784149 Y=0.88892053 Z=0.24924470
> Mo NPT= 781 R0=0.00001000 RMT= 2.4161 Z: 42.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 2: X=0.22214961 Y=0.11107481 Z=0.32975565
> MULT= 3 ISPLIT= 8
> ATOM 2: X=0.88892486 Y=0.11107481 Z=0.32975565
> ATOM 2: X=0.88892486 Y=0.77785005 Z=0.32975565
> S NPT= 781 R0=0.00010000 RMT= 2.0975 Z: 16.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 3: X=0.22234728 Y=0.11117364 Z=0.16891605
> MULT= 3 ISPLIT= 8
> ATOM 3: X=0.88882603 Y=0.11117364 Z=0.16891605
> ATOM 3: X=0.88882603 Y=0.77765239 Z=0.16891605
> S NPT= 781 R0=0.00010000 RMT= 2.0969 Z: 16.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 4: X=0.44443301 Y=0.22221629 Z=0.24939272
> MULT= 3 ISPLIT= 8
> ATOM 4: X=0.77778348 Y=0.22221629 Z=0.24939272
> ATOM 4: X=0.77778348 Y=0.55556676 Z=0.24939272
> Mo NPT= 781 R0=0.00001000 RMT= 2.4196 Z: 42.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 5: X=0.55534152 Y=0.11068338 Z=0.32969156
> MULT= 3 ISPLIT= 8
> ATOM 5: X=0.55534152 Y=0.44465814 Z=0.32969156
> ATOM 5: X=0.88931628 Y=0.44465814 Z=0.32969156
> S NPT= 781 R0=0.00010000 RMT= 2.0976 Z: 16.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 6: X=0.55573535 Y=0.11147104 Z=0.16887573
> MULT= 3 ISPLIT= 8
> ATOM 6: X=0.55573535 Y=0.44426431 Z=0.16887573
> ATOM 6: X=0.88852863 Y=0.44426431 Z=0.16887573
> S NPT= 781 R0=0.00010000 RMT= 2.0962 Z: 16.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 7: X=0.11106993 Y=0.55553475 Z=0.24900148
> MULT= 3 ISPLIT= 8
> ATOM 7: X=0.44446502 Y=0.55553475 Z=0.24900148
> ATOM 7: X=0.44446502 Y=0.88892983 Z=0.24900148
> Mo NPT= 781 R0=0.00001000 RMT= 2.4161 Z: 42.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 8: X=0.22237477 Y=0.44474987 Z=0.32919385
> MULT= 3 ISPLIT= 8
> ATOM 8: X=0.22237477 Y=0.77762490 Z=0.32919385
> ATOM 8: X=0.55524980 Y=0.77762490 Z=0.32919385
> S NPT= 781 R0=0.00010000 RMT= 2.0944 Z: 16.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 9: X=0.22210430 Y=0.44420894 Z=0.16867867
> MULT= 3 ISPLIT= 8
> ATOM 9: X=0.22210430 Y=0.77789536 Z=0.16867867
> ATOM 9: X=0.55579073 Y=0.77789536 Z=0.16867867
> S NPT= 781 R0=0.00010000 RMT= 2.0975 Z: 16.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> 0 NUMBER OF SYMMETRY OPERATIONS
>
>
>
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--
P.Blaha
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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
WWW: http://www.imc.tuwien.ac.at/staff/tc_group_e.php
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