[Pw_forum] problem with symmetry recognition
pascal boulet
pascal.boulet at univ-provence.fr
Sun Jul 10 12:10:22 CEST 2011
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Dear Vic, Stefano and Giuseppe,
Thank you for your help and sorry for this lengthy post.
Following Stefano's comment I need to provide ALL the atomic positions,
which I did not do! I gave only the positions in the primitive unit cell
(UC).
But then, if I provide all the positions (I guess in the full UC) why
should QE fill the others?
In addition, I did some calculations on Mg2Si (FCC, 12 atoms in the full
UC) by providing only the 3 atoms of the primitive UC. QE found 48
symmetry elements, which is correct, and the optimized cell parameters
seemed OK. So, still, is it wrong?
I have just tried Mn4Si7 with the full UC (44 atoms) and QE found 8
symmetry operations which is correct.
I also checked with the Bilbao Jmol applet that my structure is correct.
BTW, I also noticed something that looks strange to me. The coordinates
reported by QE in the output are not those I give in the input: X and Y
are the same but not Z which is scaled by c/a. So, for me, the distance
between the atoms is changed in the Z direction(?). That could explain
why the SCF converge is so difficult...(?) See the second set of
coordinates I copied from QE output, below.
For those who are interested, I provide here all the positions (cell
parameters: celldm(1)=10.46100d0,celldm(3)=3.17100d0, ibrav=6). The atom
positions with more digits are those of the atoms in the reduced UC (I
generated all the positions with the Bilbao website).
Input file:
ATOMIC_POSITIONS crystal
Si 0.16270000 0.67910000 0.18150000
Si 0.837300 0.320900 0.181500
Si 0.679100 0.837300 0.818500
Si 0.320900 0.162700 0.818500
Si 0.162700 0.320900 0.681500
Si 0.837300 0.679100 0.681500
Si 0.679100 0.162700 0.318500
Si 0.320900 0.837300 0.318500
Si 0.19330000 0.15070000 0.11290000
Si 0.806700 0.849300 0.112900
Si 0.150700 0.806700 0.887100
Si 0.849300 0.193300 0.887100
Si 0.193300 0.849300 0.612900
Si 0.806700 0.150700 0.612900
Si 0.150700 0.193300 0.387100
Si 0.849300 0.806700 0.387100
Si 0.34360000 0.22790000 0.54090000
Si 0.656400 0.772100 0.540900
Si 0.227900 0.656400 0.459100
Si 0.772100 0.343600 0.459100
Si 0.343600 0.772100 0.040900
Si 0.656400 0.227900 0.040900
Si 0.227900 0.343600 0.959100
Si 0.772100 0.656400 0.959100
Si 0.333333333333333 0.333333333333333 0.25000000
Si 0.666666666666667 0.666666666666667 0.2500
Si 0.333333333333333 0.666666666666667 0.7500
Si 0.666666666666667 0.333333333333333 0.7500
Mn 0.00000000 0.50000000 0.06250000
Mn 0.500000 0.000000 0.937500
Mn 0.000000 0.500000 0.562500
Mn 0.500000 0.000000 0.437500
Mn 0.00000000 0.50000000 0.31250000
Mn 0.500000 0.000000 0.687500
Mn 0.000000 0.500000 0.812500
Mn 0.500000 0.000000 0.187500
Mn 0.50000000 0.50000000 0.12500000
Mn 0.500000 0.500000 0.875000
Mn 0.500000 0.500000 0.625000
Mn 0.500000 0.500000 0.375000
Mn 0.00000000 0.00000000 0.00000000
Mn 0.000000 0.000000 0.500000
Mn 0.00000000 0.00000000 0.25000000
Mn 0.000000 0.000000 0.750000
- From output file:
[...]
8 Sym.Ops. (no inversion)
Cartesian axes
site n. atom positions (alat units)
1 Si tau( 1) = ( 0.1627000 0.6791000 0.5755365 )
2 Si tau( 2) = ( 0.8373000 0.3209000 0.5755365 )
3 Si tau( 3) = ( 0.6791000 0.8373000 2.5954635 )
4 Si tau( 4) = ( 0.3209000 0.1627000 2.5954635 )
5 Si tau( 5) = ( 0.1627000 0.3209000 2.1610365 )
6 Si tau( 6) = ( 0.8373000 0.6791000 2.1610365 )
7 Si tau( 7) = ( 0.6791000 0.1627000 1.0099635 )
8 Si tau( 8) = ( 0.3209000 0.8373000 1.0099635 )
9 Si tau( 9) = ( 0.1933000 0.1507000 0.3580059 )
10 Si tau( 10) = ( 0.8067000 0.8493000 0.3580059 )
11 Si tau( 11) = ( 0.1507000 0.8067000 2.8129941 )
12 Si tau( 12) = ( 0.8493000 0.1933000 2.8129941 )
13 Si tau( 13) = ( 0.1933000 0.8493000 1.9435059 )
14 Si tau( 14) = ( 0.8067000 0.1507000 1.9435059 )
15 Si tau( 15) = ( 0.1507000 0.1933000 1.2274941 )
16 Si tau( 16) = ( 0.8493000 0.8067000 1.2274941 )
17 Si tau( 17) = ( 0.3436000 0.2279000 1.7151939 )
18 Si tau( 18) = ( 0.6564000 0.7721000 1.7151939 )
19 Si tau( 19) = ( 0.2279000 0.6564000 1.4558061 )
20 Si tau( 20) = ( 0.7721000 0.3436000 1.4558061 )
21 Si tau( 21) = ( 0.3436000 0.7721000 0.1296939 )
22 Si tau( 22) = ( 0.6564000 0.2279000 0.1296939 )
23 Si tau( 23) = ( 0.2279000 0.3436000 3.0413061 )
24 Si tau( 24) = ( 0.7721000 0.6564000 3.0413061 )
25 Si tau( 25) = ( 0.3333333 0.3333333 0.7927500 )
26 Si tau( 26) = ( 0.6666667 0.6666667 0.7927500 )
27 Si tau( 27) = ( 0.3333333 0.6666667 2.3782500 )
28 Si tau( 28) = ( 0.6666667 0.3333333 2.3782500 )
29 Mn tau( 29) = ( 0.0000000 0.5000000 0.1981875 )
30 Mn tau( 30) = ( 0.5000000 0.0000000 2.9728125 )
31 Mn tau( 31) = ( 0.0000000 0.5000000 1.7836875 )
32 Mn tau( 32) = ( 0.5000000 0.0000000 1.3873125 )
33 Mn tau( 33) = ( 0.0000000 0.5000000 0.9909375 )
34 Mn tau( 34) = ( 0.5000000 0.0000000 2.1800625 )
35 Mn tau( 35) = ( 0.0000000 0.5000000 2.5764375 )
36 Mn tau( 36) = ( 0.5000000 0.0000000 0.5945625 )
37 Mn tau( 37) = ( 0.5000000 0.5000000 0.3963750 )
38 Mn tau( 38) = ( 0.5000000 0.5000000 2.7746250 )
39 Mn tau( 39) = ( 0.5000000 0.5000000 1.9818750 )
40 Mn tau( 40) = ( 0.5000000 0.5000000 1.1891250 )
41 Mn tau( 41) = ( 0.0000000 0.0000000 0.0000000 )
42 Mn tau( 42) = ( 0.0000000 0.0000000 1.5855000 )
43 Mn tau( 43) = ( 0.0000000 0.0000000 0.7927500 )
44 Mn tau( 44) = ( 0.0000000 0.0000000 2.3782500 )
Yours
Pascal
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