[QE-users] Detecting all symmetry operations in AFM systems

[DIRK, PAUL]

Dear all,

I am having some difficulties related to the symmetry detection for antiferromagnetic materials in QE 7.4. I want to run a spin-polarised (collinear) structural relaxation for Ca2FeAlO5 with G-type AFM order (magnetic space group Ima’2’, number 46.244) has 2 magnetic Fe-sites in the primitive unit cell, which should have opposite magnetic moments. For this space group I am expecting 4 symmetry operations, which QE does correctly detect when running a calculation with ferromagnetic configuration (see attached files labelled with ‘FM’).

However, when running the antiferromagnetic system, I believe I have to specify the sites of opposite moments with different labels, so that I can initialize the moments by setting starting_magnetization(i) accordingly (see attached files labelled with ‘AFM’). Unfortunately, it appears that the two Fe-sites are then treated as completely distinct sites during the symmetry detection and 2 of the 4 symmetry operations cannot be found anymore even though they should be present. In particular, it seems to affect operations that involve fractional translations.

I understand this limitation has been discussed previously for other AFM systems with non-symmorphic space groups (e.g. https://lists.quantum-espresso.org/pipermail/developers/2020-May/002220.html ), so I wonder whether it has been fixed yet or if there is some kind of workaround?

Thanks in advance for your help and for your hard work!

Best wishes,
Paul Dirk
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