Is this a monoclinic or orthorhombic crystal system?

Materials Project
,
1

I would like to report an apparent inconsistency in the space group assignments for two materials in your database:
MP-1271198 https://next-gen.materialsproject.org/materials/mp-1271198?chemsys=Fe))

Observed Discrepancy:

  1. Both materials are listed with the orthorhombic space group Cmcm on their MP entries.
  2. However:
  • The automatically generated description of lattice parameters (particularly β ≠ 90°) suggest monoclinic symmetry .
  • Independent symmetry analysis using pymatgen (symprec=0.01 Å) and VESTA consistently identifies these structures as P21/m.
    Verification Steps Taken:
    Confirmed the P21/m assignment via SpacegroupAnalyzer in pymatgen.
    • Cross-validated using FINDSYM (tolerance=0.001 Å), which also indicates monoclinic symmetry.
    1. Could you verify whether:
    • The Cmcm assignment is intentional (e.g., due to specific calculation settings)?
    • This might be a database entry error?
    1. If confirmed as P21/m, could the entries be updated?
    2. Attachments:
    • CIF files for both materials (downloaded from MP).
2

This is a commonly encountered issue with space group determination. The default symmetry tolerance (symprec) in pymatgen is 0.01, whereas it is 0.1 in emmet, which is used to build data entries in the Materials Project.

For both structures, if you run the following code, you’ll see that decreasing symprec lowers the interpreted space group from Cmcm to P2_1/m

from mp_api.client import MPRester

with MPRester() as mpr:
    summ_docs = mpr.materials.summary.search(material_ids=["mp-1271198","mp-10021"])
for doc in summ_docs:
    for symprec in (0.1, 0.01,):
        print(f"MPID: {doc.material_id}, symprec={symprec}, space group: {doc.structure.get_space_group_info(symprec=symprec)}")

MPID: mp-10021, symprec=0.1, space group: (‘Cmcm’, 63)
MPID: mp-10021, symprec=0.01, space group: (‘P2_1/m’, 11)
MPID: mp-1271198, symprec=0.1, space group: (‘Cmcm’, 63)
MPID: mp-1271198, symprec=0.01, space group: (‘P2_1/m’, 11)