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pymatgen Import Errors

  • Updated

Upgrading packages like Matlantis CSP (mtcsp) can break your pymatgen environment due to breaking changes introduced in pymatgen  v2026.2.24 and later. (Note: mtcsp supports pymatgen v2026.x from version v1.4.1 onwards.)

 

 

 

Situation:

The February 2026 update split pymatgen's core features into a separate package called pymatgen-core(Official Change log: v2026.2.24; see also the Pro-Tip below). This architectural shift can cause conflicts between stale download caches and outdated dependency trees, potentially leading to import failures across various pymatgen modules.



Example Errors:

ModuleNotFoundError: No module named 'pymatgen.core.graphs'

 

ModuleNotFoundError: No module named 'pymatgen.io.ase'

 

ModuleNotFoundError: No module named 'pymatgen.core.composition'

 

ModuleNotFoundError: No module named 'pymatgen.analysis.phase_diagram'

 

How to Fix:

Run the following command wipe the outdated cache and force a clean reinstall of pymatgen and its dependencies. We highly recommend restarting your kernel after running this command.

 

%pip install --force-reinstall --no-cache-dir pymatgen

 

 

Pro-Tip:

Since pymatgen's core features were split into the separate pymatgen-core package, you can now pinpoint and import only the specific classes you need. This significantly reduces memory usage during MTCSP search/exploration tasks. (Applicable to mtcsp v1.4.1 and later)

 

 

 

Reference:

 

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