Features

• Evaluates the energy, gradients (forces) and, for periodic systems, the stress of the current configuration, every configuration of a system, or a selection by name.

• Uses whatever Model Chemistry precedes it in the flowchart – a machine-learned force field from the xnn plug-in, MOPAC, xTB, ORCA, … – provided it can be driven as an MDI engine.

• Starts the program once and feeds it the structures over the warm MDI connection, so labelling hundreds or thousands of structures (e.g. the ensembles from the Normal Mode Sampling, Dimer Builder or Extract Clusters steps) costs one start-up: ~14 ms per water molecule with an xnn MACE model on a laptop CPU.

• Stores the results on each configuration – energy#Energy#<model>, gradients#Energy#<model>, stress#Energy#<model> – and the gradients on the atoms, so the Write Structure step’s extended XYZ output carries REF_energy and REF_forces for training.

• Writes energies.csv (energy, max/RMS force and timing per structure) in the step’s directory and can save any result to variables or tables.

Acknowledgements

This package was created with Cookiecutter and the molssi-seamm/cookiecutter-seamm-plugin project template.

Developed by the Molecular Sciences Software Institute (MolSSI), which receives funding from the National Science Foundation under award ACI-1547580

2026.9.18 (2026-09-18)

• Initial release. Evaluates the energy, gradients and (periodic) stress of one or many configurations with the upstream Model Chemistry driven as a resident MDI engine; results stored per configuration and on the atoms, with energies.csv and table/variable output. Validated with an xnn MACE model (1000 water configurations in 14 s) and with MOPAC PM6-ORG.

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