---
license: mit
license_link: LICENSE
library_name: kups
tags:
  - chemistry
  - materials-science
  - molecular-dynamics
  - interatomic-potential
  - mlff
  - jax
  - mace
---

# MACE-MPA-0 medium — JAX build

This repository hosts a JAX export of [MACE-MPA-0 medium](https://github.com/ACEsuit/mace-foundations) for use with [kUPS](https://github.com/cusp-ai-oss/kups), a JAX-native molecular-simulation toolkit. The artefact is a self-contained `.zip` containing the serialized JAX computation graph, the original model parameters, and the minimal metadata needed to run inference.

**Important:** this is a **re-export, not a retraining.** Weights and architecture are the originals released by the MACE team. CuspAI's only contribution is converting the PyTorch reference implementation to JAX via [tojax](https://github.com/cusp-ai-oss/tojax). Every scientific claim, citation, and credit belongs to the original authors.

## Included model

| File | Upstream | License | Paper |
|------|----------|---------|-------|
| `mace-mpa-0-medium_32.zip` (40 MB) | [MACE-MPA-0 medium](https://github.com/ACEsuit/mace-foundations) | [MIT](LICENSE) | Batatia et al., *J. Chem. Phys.* **163**, 184110 (2024); [arXiv:2401.00096](https://arxiv.org/abs/2401.00096) |

Cutoff radius 6.0 Å. Schema: `AtomGraphInput` (positions, atomic numbers, cell, pbc, edge index, cell offsets, batch index, charge, spin).

## Quick start

```sh
pip install kups[cuda]
```

```python
from huggingface_hub import hf_hub_download
from kups.potential.mliap.tojax import TojaxedMliap

path = hf_hub_download(
    repo_id="CuspAI/kUPS-mace-jax",
    filename="mace-mpa-0-medium_32.zip",
)
model = TojaxedMliap.from_zip_file(path)
# model.cutoff, model.params, model.call(atom_graph_input) are now available.
```

kUPS ships CLI wrappers that take a YAML config pointing at this zip:

```sh
kups_relax_mlff --config relax_mace.yaml
```

Example configs live in the kUPS [examples/](https://github.com/cusp-ai-oss/kups/tree/main/examples) directory.

## What's in the `.zip`

- `model.jax` — JAX computation graph, serialized via `jax.export`.
- `params.msgpack` — parameters as a msgpack-encoded list of arrays.
- `metadata.json` — cutoff radius and supported atomic numbers.
- `dtypes.json` — input dtypes for `AtomGraphInput`.

Exported with symbolic shapes (`--symbolic NSE`); accepts variable atom, system, and edge counts without recompilation.

## Model details

**Upstream:** [ACEsuit/mace-foundations](https://github.com/ACEsuit/mace-foundations) · **Checkpoint:** `mace-mpa-0-medium.model`

MACE-MPA-0 is a foundation-model member of the MACE family (Multi-ACE, a higher-body-order message-passing equivariant neural network), trained on the MPtrj + sAlex materials dataset covering 89 chemical elements. The "medium" variant is the default recommendation from the MACE team for general-purpose materials simulation.

**Original authors:** Ilyes Batatia, Philipp Benner, Yuan Chiang, Alin M. Elena, Dávid P. Kovács, Janosh Riebesell, and the rest of the MACE team (~100 collaborators). Corresponding author: Gábor Csányi (Cambridge).

**Supported elements:** atomic numbers 1–83, 89–94 (see `metadata.json` inside the zip).

**Intended use and limitations:** general-purpose materials modelling (energies, forces, stresses) at DFT/PBE+U accuracy. Not trained for isolated molecules; for molecular systems refer to MACE-OFF. See the [upstream README](https://github.com/ACEsuit/mace-foundations) for authoritative guidance.

**Citation:**

```bibtex
@article{batatia2024foundation,
  title   = {A foundation model for atomistic materials chemistry},
  author  = {Batatia, Ilyes and Benner, Philipp and Chiang, Yuan and Elena, Alin M.
             and Kov{\'a}cs, D{\'a}vid P. and Riebesell, Janosh and others},
  journal = {The Journal of Chemical Physics},
  volume  = {163},
  number  = {18},
  pages   = {184110},
  year    = {2024},
  doi     = {10.1063/5.0230281},
  eprint  = {2401.00096},
  archivePrefix = {arXiv},
}
```

## Export pipeline and reproducibility

The archive was produced with the exporter in [tojax/examples/mlff/](https://github.com/cusp-ai-oss/tojax):

```sh
uv run python export_mace.py --output mace-mpa-0-medium_32.zip --symbolic NSE
```

tojax's export harness verifies numerical agreement with the PyTorch reference (default tolerances `rtol=1e-4`, `atol=1e-4`) before saving the archive.

## Changes from upstream

- **File format.** PyTorch `.model` → JAX-exported `.zip` (graph + msgpack params).
- **Weights.** Unchanged, bit-for-bit, from the upstream checkpoint.
- **Architecture.** Translated operation-for-operation; no approximations or substitutions.
- **Numerics.** Verified within `rtol=1e-4, atol=1e-4` against the PyTorch reference during export.
- **Cutoff and dtypes.** Preserved from upstream defaults (6.0 Å; float32 positions/cell/offsets, int64 indices, bool PBC).
- **Symbolic shapes.** Exports accept variable numbers of atoms, systems, and edges without recompilation.

## Attribution and license

This model exists because of the work of the MACE team. CuspAI's only contribution is the JAX export — we trained nothing, changed no weights, and designed none of the architecture. Please cite Batatia et al. (2024) when using this checkpoint in research.

The file `mace-mpa-0-medium_32.zip` is distributed under the MIT License; see [LICENSE](LICENSE) for the full text and [NOTICE](NOTICE) for attribution and modification details. The kUPS / tojax tooling citations:

```bibtex
@software{kups2026,
  author = {{CuspAI}},
  title  = {kUPS},
  year   = {2026},
  url    = {https://github.com/cusp-ai-oss/kups},
}

@software{tojax2026,
  author = {{CuspAI}},
  title  = {tojax},
  year   = {2026},
  url    = {https://github.com/cusp-ai-oss/tojax},
}
```

## Contact

- Issues with the JAX export or with kUPS: [github.com/cusp-ai-oss/kups/issues](https://github.com/cusp-ai-oss/kups/issues)
- Scientific questions about MACE: please direct to the upstream authors via [ACEsuit/mace-foundations](https://github.com/ACEsuit/mace-foundations).