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["Dr.N. Choudhury" <dynamics@apsara.barc.ernet.in>]

Hi,

I used ABINIT (v433)  for study of a monoclinic perovskite supercell.
While ABINIT assigns space group Pm for the structure enclosed below,
FINDSYM (http://physics1.byu.edu/cgi-bin/findsym.cgi ) assigns space group
Cm. The polarization has [aab] type symmetry (Cartesian) which Vanderbilt
and Cohen, (Phys. Rev. B.63, 094108 (2001)) assign to Cm symmetry.

Why are the space groups assigned different?

Please note that I have used high precision for the struc generator
in both ABINIT and FINDSYM, but  FINDSYM  rounds off after 5 decimals


Thanks,
Narayani

Narayani Choudhury
Solid State Physics Division, Bhabha Atomic Research Centre
Trombay, Mumbai 400 085, India; email: dynamics@apsara.barc.ernet.in

----------------------ABINIT output----------------

 Symmetries : space group Pm (#  6); Bravais mP (primitive monocl.)
 -outvars: echo values of preprocessed input variables --------
     acell    7.5750500000E+00  7.5750500000E+00  7.5750500000E+00 Bohr

--------------------------input----------------------

natom  15
zatnum  82 12 41 8
ntypat  4
typat  3*1 2 3 3 9*4


acell  7.575050000000  7.575050000000  7.575050000000 bohr
rprim   -1.0000000000E+00  1.0000000000E+00  0.0000000000E+00
         1.0000000000E+00  0.0000000000E+00 -1.0000000000E+00
        -1.0000000000E+00 -1.0000000000E+00 -1.0000000000E+00
  xred
      -0.008253014832     -0.016506029663      0.028847579430
       0.338922207334      0.677844414668      0.376809307100
       0.657818540271      0.315637080542      0.695594078496
       0.004127585516      0.008255171033      0.501593982286
       0.335458731829      0.670917463658      0.822699448570
       0.670012783206      0.340025566412      0.178160687640
       0.195533819060      0.852848567790      0.651961413108
       0.182652980040      0.365305960080      0.655117167878
       0.657314748729      0.852848567790      0.651961413108
       0.340346287589      0.182806789804      0.307936353485
       0.842460502214      0.182806789804      0.307936353485
       0.841619583639      0.683239167278      0.303155130920
       0.520333634997      0.040667269994     -0.024745916460
       0.007490563929      0.530790515976     -0.019574729467
       0.523299952046      0.530790515976     -0.019574729467

----------------------------------------------------------------

FINDSYM, Version 3.1, November 2004
Written by Harold T. Stokes and Dorian M. Hatch
Brigham Young University

PMN
Tolerance:    0.00001
Lattice parameters, a,b,c,alpha,beta,gamma:
   7.57505   7.57505   7.57505  90.00000  90.00000 120.00000
Centering: P
Number of atoms in unit cell:
 15
Type of each atom:
  1  1  1  2  3  3  4  4  4  4  4  4  4  4  4
Position of each atom (dimensionless coordinates)
   1  -0.00825  -0.01651   0.02885
   2   0.33892   0.67784   0.37681
   3   0.65782   0.31564   0.69559
   4   0.00413   0.00826   0.50159
   5   0.33546   0.67092   0.82270
   6   0.67001   0.34003   0.17816
   7   0.19553   0.85285   0.65196
   8   0.18265   0.36531   0.65512
   9   0.65731   0.85285   0.65196
  10   0.34035   0.18281   0.30794
  11   0.84246   0.18281   0.30794
  12   0.84162   0.68324   0.30316
  13   0.52033   0.04067  -0.02475
  14   0.00749   0.53079  -0.01957
  15   0.52330   0.53079  -0.01957
Using settings with unique axis b
Using settings with cell choice 1
Using settings with origin choice 2
Using settings with hexagonal axes
------------------------------------------
Space Group   8  Cs-3      Cm
Origin at    0.00000   0.00000   0.00000
Vectors a,b,c:
  -1.00000  -2.00000   0.00000
   1.00000   0.00000   0.00000
   0.00000   0.00000   1.00000
Values of a,b,c,alpha,beta,gamma:
  13.12037   7.57505   7.57505  90.00000  90.00000  90.00000
Atomic positions in terms of a,b,c:
Wyckoff position a, x =  0.00825, z =  0.02885
   1   0.50825   0.50000   0.02885
Wyckoff position a, x = -0.33892, z =  0.37681
   2   0.16108   0.50000   0.37681
Wyckoff position a, x =  0.34218, z = -0.30441
   3   0.84218   0.50000   0.69559
Wyckoff position a, x = -0.00413, z = -0.49841
   4   0.49587   0.50000   0.50159
Wyckoff position a, x = -0.33546, z = -0.17730
   5   0.16454   0.50000   0.82270
Wyckoff position a, x =  0.32999, z =  0.17816
   6   0.82999   0.50000   0.17816
Wyckoff position b, x =  0.07358, y =  0.26911, z = -0.34804
   7   0.07358   0.26911   0.65196
   9   0.07358   0.73089   0.65196
Wyckoff position a, x = -0.18265, z = -0.34488
   8   0.31735   0.50000   0.65512
Wyckoff position b, x = -0.09140, y =  0.24894, z =  0.30794
  10   0.90860   0.24894   0.30794
  11   0.90860   0.75106   0.30794
Wyckoff position a, x =  0.15838, z =  0.30316
  12   0.65838   0.50000   0.30316
Wyckoff position a, x =  0.47967, z = -0.02475
  13   0.97967   0.50000   0.97525
Wyckoff position b, x =  0.23460, y =  0.24210, z = -0.01957
  14   0.23460   0.24210   0.98043
  15   0.23460   0.75790   0.98043