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Hubbard U

The on-site correction applied to localised d and f electrons in DFT+U.

No model yet

Quantity What it is Model
hubbard_u One value per species, eV none

Reference

Uhrin, Zadoks, Binci, Marzari and Timrov, Machine learning Hubbard parameters with equivariant neural networks, npj Computational Materials 11, 19 (2025). doi:10.1038/s41524-024-01501-5, code at camml-lab/hubbardml.

Equivariant network over atomic occupation matrices, targeting Hubbard parameters computed self-consistently by DFPT linear response.

Open before a model can exist

  • A place in Core. There is no Hubbard field in the calculation hints at all — no U, no species map, no projector.
  • A prediction type that is not one scalar. ModelPrediction carries a single value; one U per species does not fit. This is the first setting that forces the question.
  • A target contract pinning scheme, functional and projector. U is not a property of the material alone, and nothing in the number reveals which convention produced it — the same problem the k-distance 2π factor has.
  • A dataset with all three recorded rather than assumed.