[Wien] IRREP and SYMMETSO with ferromagnetic materials

[Fecher, Gerhard]

Hi Peter,
Maybe this is a little longer but I hope it helps to correct or improve SYMMETSO and IRREP.
It concerns for example
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg14673.html
I did not realise that I was sticking with that problem not that long ago
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg14671.html
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg14673.html

As already mentioned before, in the ferromagnetic case or when a magnetic field
is applied along [001] the symmetry of cubic elements Fe (bcc) or Ni (fcc)
results in the "colored" space group I 4/mm'm' with the colored point group
D4h(C4h). (Please check also my old posts). The problem can be generalised
to many other ferromagnetic systems where the basic symmetry of the crystal
structure is not compatible to that of a magnetic field applied in a given direction.
(not only [001] but also others e.g. [111] will indeed result in a different colored group)

PROBLEM ************************************************************************
IRREP seems to fail finding the irreducible representations already for very simple ferromagnets, e.g.: Fe, Ni.

DIAGNOSTICS *********************************************************************
SYMMETSO writes the "new" symmetry operations into the structure file. It uses
however the non-colored notation I 4/mmm with 16 operations (D4h), further it 
gives the type of the operation (if not C)
  A (keep magnetisation)
  B (revert the magnetisation)
that is it distinguishes principally the colored groups,
here, A+B belong to the D4h part and only A to C4h. 

IRREP reads the symmetry operations from the structure file, and finds the
number of symmetry operations for the unprimed and the primed
operations (A+B). It also does not make use of the types of operations.
In the present example it thus finds the point group D4h
that contains all B operations that change the magnetisation.

A short workaround would be to change to a lower symmetry that is compatible
with the direction of magnetisation or to change the number of symmetry operations in the
struct file such that it matches the number of the allowed A operations. In that
case IRREP will find C4h instead of D4h and is able to assign all irreps
correctly.

SOLUTION ************************************************************************
IRREP needs to read also the type of the operation
line 52 of of init.f :   Read (20,514) NOIORD ......
and should correct for the number of "allowed" operations.

Unfortunately, SYMMETSO does not always write the type into the structure file,
that is it needs also to be corrected. Presently type A seems not to be written
if all operations are of type A, this should be changed such that it is always
given.

I suggest that SYMMETSO writes also the number of a type operations, that is:
   A+B   A      NUMBER OF SYMMETRY OPERATIONS 
here it would then be
   16    8      NUMBER OF SYMMETRY OPERATIONS 
IRREP should then read in init.f line 49
      READ(20,*) IORD, IORDA
instead of       READ(20,*) IORD
this should allow to provide (together with the information on the type) in the
"DO 14 I=1,IORD" loop the information to find the full colored group.
It would also be great if both, SYMMETSO and IRREP, give the color group and not
just the simple point group that is here D4h(C4h) and not only D4h or C4h, it
would be rather confusing if symmetso reports D4h but IRREP C4h.

OPEN questions: ****************************************************************

What about the L M components in case.in2 ? 
in D4h one has 
0 0  2 0  4 0  4 4  6 0  6 4 
in C4h one has some additional components 
0 0  2 0  4 0  4 4 -4 4  6 0  6 4 -6 4 
(the potential should always belong to the fully symmetric irrep a1g (a1), that
differ in D4h and C4h)
(Note the - sign does not mean a negative L (!) but assigns whether the real
spherical harmonic is of sine (odd) or cosine (even) type)
Here this was for the simple case, it becomes more complicated if certain atoms 
of a compound occupy sites with lower symmetry.

IRREP works using I 4/m or say better C4h in the present case (elemental Fe or
Ni), however, spaghetti fails for certain directions and one receives (using w2web)
the message:
ERROR in comprel: cannot find com.rel


It is not mystery it is symetry (hMMM soMething seeMs to be Missing) 
Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0_Fe_SO-test.struct
Type: application/octet-stream
Size: 1183 bytes
Desc: 0_Fe_SO-test.struct
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20170720/b9050fcf/attachment-0001.obj>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: Fe_SymmetryOperations.txt
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20170720/b9050fcf/attachment-0001.txt>