[QE-developers] Finding all symmetry operations correctly

[박민규]

Dear all developers,

This is about whether QE can figure out all possible symmetry operations including time reversal or not.
I don’t know whether this is already discussed before.

Imagine I want to calculate antiferromagnetic MnF2.
Its space group is P4_2/mnm (136). F is located at Wyckoff position 4f and Mn at 2a.
The magnetic space group of MnF2 is known as P4_2’/mnm’ (136.499).
This is taken from section 8.7.1 of Burns and Glazer, Space Groups for Solid State Scientists 2013.

Now if I run a calculation without magnetic moments, QE correctly lists up all symmetry operations of corresponding space group. One can easily compare the result using Bilbao Crystallographic Server.
However if I give a magnetic moment to Mn atoms, QE shows only part of the symmetry operations.
Symmetry operations related with fractional translations are missing in this case.

I think the problem occurs because QE treats each type of atom (ntyp) differently even though they are actually same species.
This can also be verified if you do nonmagnetic calculation of MnF2 with one Mn type and two Mn type.
They give different symmetry operations.
I guess this problem only arises for non-symmorphic space groups.

Since the symmetry detection of QE works very well for other cases, small modifications to the code might improve this behavior.
But unfortunately I have no experience at all about coding, I would like to request it to the experts.

I attach input and output files for quick check.

Thanks for reading.
Best regards,
============================================
Minkyu Park
Research Institute of Basic Sciences, University of Ulsan,
93, Daehak-ro, Nam-gu, Ulsan, 44610 Republic of Korea
minkyupark at ulsan.ac.kr<mailto:minkyupark at ulsan.ac.kr>
+82-52-259-1473
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