Features

• Advertises every xnn checkpoint found in the directories listed in xnn.ini to the Model Chemistry step as xnn:MLFF@<model>.

• Launches xnn mdi – the checkpoint served as a resident MDI engine – for any step that drives a model chemistry over MDI: Energy (single points for many structures), LAMMPS (MD with the MLFF as the QM engine), Dimer Builder, Normal Mode Sampling.

• Molecular and periodic systems (energy, forces and stress); runs on the CPU or a GPU (device in xnn.ini).

• There is no xnn step to place in a flowchart: the models are used through Model Chemistry + Energy (or LAMMPS).

Note: xnn is published on PyPI under the name xnns; the import name and the xnn command are unchanged.

Acknowledgements

This package was created with the molssi-seamm/cookiecutter-seamm-plugin tool, which is based on the excellent Cookiecutter.

Developed by the Molecular Sciences Software Institute (MolSSI), which receives funding from the National Science Foundation under award CHE-2136142.

2026.9.18 (2026-09-18)

• Initial release. Provides xnn machine-learned force fields as xnn:MLFF@<model> model chemistries (checkpoints discovered from the directories in xnn.ini) and launches xnn mdi as the MDI engine for the Energy, LAMMPS and other MDI-driving steps. Includes xnn-step-installer for the seamm-xnn conda environment.

• Plug-in created using the SEAMM plug-in cookiecutter.