[Wien] AFM LaMNO3 Symmetry

[Natalia Perkins]

Dear all,
We have  the following question:
Paramgnetic symmetry of LaMnO3 is Pnma, (ie, number 62 Int. Tab. Cryst.).
When AFM (A-phase) sets in at low temperature, the two glide planes (n and
a) are lost, because they are connected with time-reversal.
If we call Mn1 and Mn2 the ions with spin up and Mn3 and Mn4 the two
ions with spin down, the lost symmetries are those connecting Mn1 with Mn4
(the glide plane n) and Mn1 with Mn2 (the glide plane a), even if these
last two have the same spin !
On the contrary, Mn1 and Mn3 are still connected by the mirror plane m,
even if they have opposite spin (because the spin lies in the glide plane
and thus changes sign).
What symmetry group we should specify in the structure file for this
AFM-phase ???

Thanks in advance,
Natalia Perkins