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[Masayoshi Mikami <mmikami@rc.m-kagaku.co.jp>]

Dear all,

I have had an interesting situation with ABINIT v.5.3.4.
An input for Pbnm (#62) may not work ? Instead,
the same input for Pnma (converted from Pbnm) works...

Here is my story:
I just tried a computation of Mg2SiO4(forsterite).
The original CIF data is available on the WEB:
http://rruff.geo.arizona.edu/AMS/xtal_data/CIFfiles/00268.cif

1) First, I made an input like this:
## geom part starts ##
spgroup 62
acell 4.79 10.19 5.85 angstrom
angdeg 90 90 90
spgxor 2 spgorig 1 brvltt 1 # Pbnm
nsym  0
natrd 6
typat 2*1 1*2 3*3
xred
  0.00000   0.00000   0.00000 # Mg
  0.00560   0.26320   0.75000 # Mg
  0.09450   0.40780   0.25000  # Si
  0.24990   0.09070   0.75000  # O
  0.28320   0.05780   0.25000  # O
  0.23120   0.33700   0.47070  # O
## geom part ends ##
znucl 12.0 14.0 8.0
ntypat 3  ecut 50
natom  28
ntime 80
ixc 11
ionmov 3
toldff  5.0d-5
tolmxf  5.0d-4

Then, I had an error like this:
operat : ERROR -
  The number of atoms obtained from symmetries,  44
  is greater than the input number of atoms, natom=     28
  This is not allowed.
  Action : modify natom or the symmetry data in the input file.

N.B. This unit cell contains 4 times (2+1+4), i.e. 28 !

2) Second, I made "P1" input, i.e., making all xred
from the Pbnm input, with no spgroup information.

## geom part starts ##
acell 4.79 10.19 5.85 angstrom
angdeg 90 90 90
nsym  0
typat 8*1 4*2 16*3
xred
    0.00000   0.00000   0.00000   # Mg
    0.50000   0.50000   0.00000   # Mg
    0.00000   0.00000   0.50000   # Mg
    0.50000   0.50000   0.50000   # Mg
    0.00560   0.26320   0.75000   # Mg
    0.50560   0.23680   0.25000   # Mg
    0.99440   0.73680   0.25000   # Mg
    0.49440   0.76320   0.75000   # Mg
    0.09450   0.40780   0.25000   # Si
    0.59450   0.09220   0.75000   # Si
    0.90550   0.59220   0.75000   # Si
    0.40550   0.90780   0.25000   # Si
    0.23120   0.33700   0.47070   # O
    0.73120   0.16300   0.52930   # O
    0.76880   0.66300   0.97070   # O
    0.26880   0.83700   0.02930   # O
    0.76880   0.66300   0.52930   # O
    0.26880   0.83700   0.47070   # O
    0.23120   0.33700   0.02930   # O
    0.73120   0.16300   0.97070   # O
    0.28320   1.05780   0.25000   # O
    0.78320   0.44220   0.75000   # O
    0.71680  -0.05780   0.75000   # O
    0.21680   0.55780   0.25000   # O
    0.24990   0.09070   0.75000   # O
   -0.25010   0.40930   0.25000   # O
    0.75010   0.90930   0.25000   # O
    1.25010   0.59070   0.75000   # O
## geom part ends ##

The ABINIT recognize this crystal as "Pnma" (#62)
in the output, and run without any errors like Case 1).

3) Finally, I converted the Pbnm data into Pnma
(thanks to Material Studio), and make Pnma-based input:

## geom part starts ##
spgroup 62
acell 10.1900 5.8500 4.7900 angstrom
angdeg 90 90 90
spgxor 1 spgorig 1 brvltt 1 # Pnma
nsym  0
natrd 6
typat 2*1 1*2 3*3
xred
   -0.50000  -0.00000   0.00000   # Mg
   -0.76320   0.75000  -0.00560   # Mg
   -0.90780   0.25000  -0.09450   # Si
   -0.59070   0.75000  -0.24990   # O
   -0.55780   0.25000  -0.28320   # O
   -0.83700   0.47070  -0.23120   # O
## geom part ends ##

Then, I had no problems with this again...

Thus, I am just wondering ...
When I looked into the routine,
12geometry/gensymspgr.F90,
I noticed a message (around l.470),
---------
!Orientations for the orthorhombic space groups
!WARNING : XG 000620 : I am not sure that this coding is correct !!
if (spgroup>15 .and. spgroup <75) then
  select case (spgaxor)
        (snip)
---------

How do you think ?
I will be back if/when I notice something to be added here.

Regards,
Masayoshi

N.B.
(Pbnm)
loop_
_symmetry_equiv_pos_as_xyz
  'x,y,z'
  'x,y,1/2-z'
  '-x,-y,1/2+z'
  '1/2+x,1/2-y,1/2+z'
  '1/2-x,1/2+y,1/2-z'
  '1/2-x,1/2+y,z'
  '1/2+x,1/2-y,-z'
  '-x,-y,-z'

(Pnma)
loop_
_symmetry_equiv_pos_as_xyz
  x,y,z
  -x+1/2,-y,z+1/2
  -x,y+1/2,-z
  x+1/2,-y+1/2,-z+1/2
  -x,-y,-z
  x+1/2,y,-z+1/2
  x,-y+1/2,z
  -x+1/2,y+1/2,z+1/2