Spacegroup P212121 does not give a valid pointgroup

[lopsided]

Python version

Python 3.9.18

Pymatgen version

2024.2.8

Operating system version

Fedora 38

Current behavior

Loading the SpaceGroup P212121 works fine, but the point_group symbol it reports (D2^4) is not recognised. I believe it should be 222. The issue appears to be here: https://github.com/materialsproject/pymatgen/blob/81dc677462d164182115903e28318cb5cf2ea804/pymatgen/symmetry/groups.py#L223 as the symbol P212121 is not in SpaceGroup.sg_encoding - instead it appears there with the underscores P2_12_12_1 and the correct pointgroup (222). As it can't find it here it uses the schoenflies entry of the spacegroup (D2^4) instead. I don't know what this is, or how to use it to find the 222 space group..?

At the top of this class some effort is made to duplicate entries for the SG_SYMBOLS so they also contain copies without underscores. If this was also done for the sg_encoding then the problem would be fixed, but I don't know if that is a reasonable thing to do or if it would cause other problems?

Expected Behavior

I should be able to instantiate a PointGroup from a SpaceGroup by using the associated point_group symbol

Minimal example

sg = SpaceGroup('P212121')
pg = PointGroup(sg.point_group)  # Fails

Relevant files to reproduce this bug

No response

[hongyi-zhao]

The complete bug reproduction code snippet is shown below:

In [12]: from pymatgen.symmetry.groups import SpaceGroup, PointGroup
    ...: 
    ...: # Create an instance of the SpaceGroup for 'P212121'
    ...: sg = SpaceGroup('P212121')
    ...: 
    ...: # Fetch the point group symbol from the space group
    ...: point_group_symbol = sg.point_group
    ...: 
    ...: # Display the space group and its point group symbol
    ...: print(f"Space Group: {sg.symbol}")
    ...: print(f"Point Group Symbol: {point_group_symbol}")
    ...: 
    ...: # Now let's try creating the PointGroup.
    ...: try:
    ...:     pg = PointGroup(point_group_symbol)
    ...:     print(f"Processed Point Group: {pg}")
    ...: except Exception as e:
    ...:     print(f"Error: {e}")
    ...: 
Space Group: P212121
Point Group Symbol: D2^4
Error: 'D2^4'