incorrect result in 2D structure

[lishuzhong123]

I have tested a 2D structure with space group No. 187. The result from amcheck shows an altmagnetic configuration, but the actual magnetic ordering is antiferromagnetic due to the [C₂∥Mz] symmetry operation.

Here is the POSCAR:
Ru Cl O
1.0000000000000000
3.2570514862548787 0.0000000000000001 0.0000000000000000
-1.6285257431274391 2.8206893285305865 0.0000000000000000
0.0000000000000000 0.0000000000000000 33.1899986267000173
Ru Cl O
2 2 1
Direct
0.3333333333333357 0.6666666666666643 0.4576427307039594
0.3333333333333357 0.6666666666666643 0.5423572692960406
0.0000000000000000 0.0000000000000000 0.4059153552002215
0.0000000000000000 0.0000000000000000 0.5940846447997785
0.0000000000000000 0.0000000000000000 0.5000000000000000

The amcheck result is :

[lisz@master01 ~/gpu/n6/bilayerRuCl2_O/m0/afm/isp_band/test]$ amcheck POSCAR

Processing: POSCAR

Spacegroup: P-6m2 (187)

Writing the used structure to auxiliary file: check POSCAR_amcheck.vasp.

Orbit of Ru atoms at positions:
1 (1) [0.33333333 0.66666667 0.45764273]
2 (2) [0.33333333 0.66666667 0.54235727]
Type spin (u, U, d, D, n, N, nn or NN) for each of them (space separated):
u d

Orbit of Cl atoms at positions:
3 (1) [0. 0. 0.40591536]
4 (2) [0. 0. 0.59408464]
Type spin (u, U, d, D, n, N, nn or NN) for each of them (space separated):
nn

Orbit of O atoms at positions:
5 (1) [0. 0. 0.5]
Only one atom in the orbit: skipping.
Group of non-magnetic atoms (Cl): skipping.
Only one atom in the orbit: skipping.

Altermagnet? True

[asmolyanyuk]

Unfortunately, in the current implementation the pure 2D systems are not supported.
I might consider adding such a support in the future version, but currently I'm busy with other tasks.