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name: smirnoff-force-fields description: "Load, modify, inspect, serialize, label, and apply SMIRNOFF OFFXML force fields with OpenFF Toolkit ForceField APIs." disable-model-invocation: true metadata: disco-role: operating license: MIT

SMIRNOFF Force Fields

Use this sub-skill when a task centers on OpenFF Toolkit SMIRNOFF force fields: loading .offxml files, discovering installed force fields, inspecting or modifying parameter handlers, labeling molecules with assigned parameters, serializing edited force fields, combining sources, creating Interchange/OpenMM systems, or diagnosing SMIRNOFF parsing and handler errors.

Route First

• Use references/api-reference.md for the verified ForceField signatures, handler concepts, label shapes, serialization APIs, and Interchange/OpenMM boundary.
• Use references/workflows.md for copy-ready recipes: load installed or local .offxml, inspect available force fields, label molecules, edit a parameter, serialize/reload, and apply a force field.
• Use references/plugins-and-custom-parameters.md for custom ParameterHandler classes and entry-point plugin loading with load_plugins=True.
• Use references/troubleshooting.md when parsing, handler registration, force-field package discovery, charge assignment, virtual-site, Interchange, or OpenMM conversion fails.
• Use scripts/smoke_smirnoff_workflow.py for a safe local smoke probe that builds a molecule/topology, loads a force field, optionally labels parameters, and attempts Interchange if installed.

Boundaries

• For molecule construction, stereochemistry, conformers, file I/O, and mapped SMILES details, route to ../molecules-and-io/SKILL.md.
• For topology construction, PDB/OpenMM topology conversion, positions, boxes, and system-level preparation depth, route to ../topology-and-systems/SKILL.md.
• For optional backend installation, toolkit registries, charge toolkit availability, and dependency selection depth, route to ../toolkit-backends/SKILL.md.
• Do not rely on original repository docs, tests, examples, or notebooks at runtime; this sub-skill bundles the SMIRNOFF patterns needed for future agents.

Quick Start

from openff.toolkit import ForceField, Molecule, Topology
from openff.toolkit.typing.engines.smirnoff import get_available_force_fields

print(get_available_force_fields())
force_field = ForceField("openff-2.3.0.offxml")
molecule = Molecule.from_smiles("CCO")
topology = Topology.from_molecules([molecule])
labels = force_field.label_molecules(topology)
print(force_field.registered_parameter_handlers)
print(labels[0].keys())

If ForceField("openff-2.3.0.offxml") cannot find the file, inspect get_available_force_fields() and install or point to a local .offxml file rather than changing the molecule/topology workflow.