OpenFF Force Fields

This repository contains force fields released by the Open Force Field Initiative. These force fields use the SMIRKS Native Open Force Field (SMIRNOFF) format. By convention these files use the .offxml file extension. The SMIRNOFF format has a specification and is discussed in a JCTC publication and associated pre-print.

The OpenFF Toolkit provides a reference implementation of the SMIRNOFF format. In particular, the ForceField class is used to load SMIRNOFF-format force fields and the create_openmm_system method enables the parametrization of small molecules into OpenMM objects.

Detailed usage examples can be found in the OpenFF Toolkit repository.

Each mainline force field is currently available in two forms -- both with and without bond constraints to hydrogen. The default version of each force field (i.e. openff-2.0.0.offxml) is suitable for typical molecular dynamics simulations with constrained bonds to hydrogen. The "unconstrained" version of each force field (i.e. openff_unconstrained-2.0.0.offxml) should be used when single-point energies are a major concern (e.g. geometry optimizations) and when comparing the force field to QM data.

This repository may also contain other useful force fields, data, or utilities, separate from mainline OpenFF force fields. More information on those can be found in the docs/ directory in this repository.

How to cite

To cite the Parsley line of force fields (openff-1.Y.Z) please use this citation.

To cite the Sage line of force fields (openff-2.Y.Z) please use this citation.

Optionally, consider also citing the version-specific Zenodo DOI for the particular force field from the table below.

Details for each OpenFF force field in this repository can be found on our website or in the following table:

| Filename | FF line | Release Date | Major format changes? | Fitting repo | DOI | |---------------------------------------------|---------|---------------|-----------------------|-------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------| | openff-2.2.1.offxml | Sage | Sep 11, 2024 | No | repo | | | openff_unconstrained-2.2.1.offxml | Sage | Sep 11, 2024 | No | repo | | | openff-2.2.1-rc1.offxml | Sage | Jul 22, 2024 | No | repo | | | openff_unconstrained-2.2.1-rc1.offxml | Sage | Jul 22, 2024 | No | repo | | | openff-2.2.0.offxml | Sage | Apr 18, 2024 | No | repo | | | openff_unconstrained-2.2.0.offxml | Sage | Apr 18, 2024 | No | repo | | | openff-2.2.0-rc1.offxml | Sage | Mar 6, 2024 | No | repo | | | openff_unconstrained-2.2.0-rc1.offxml | Sage | Mar 6, 2024 | No | repo | | | openff-2.1.1.offxml | Sage | Jan 22, 2024 | No | None | | | openff_unconstrained-2.1.1.offxml | Sage | Jan 22, 2024 | No | None | | | openff-2.1.0.offxml | Sage | May 2, 2023 | No | repo | | | openff_unconstrained-2.1.0.offxml | Sage | May 2, 2023 | No | repo | | | openff-2.1.0-rc.1.offxml | Sage | Apr 10, 2023 | No | repo | | | openff_unconstrained-2.1.0-rc.1.offxml | Sage | Apr 10, 2023 | No | repo | | | openff-2.0.0.offxml | Sage | Aug 16, 2021 | No | repo | | | openff_unconstrained-2.0.0.offxml | Sage | Aug 16, 2021 | No | repo | | | openff-2.0.0-rc.2.offxml | Sage | Aug 3, 2021 | No | None | | | openff_unconstrained-2.0.0-rc.2.offxml | Sage | Aug 3, 2021 | No | None | | | openff-2.0.0-rc.1.offxml | Sage | June 21, 2021 | No | repo | | | openff_unconstrained-2.0.0-rc.1.offxml | Sage | June 21, 2021 | No | repo | | | openff-1.3.1.offxml | Parsley | June 21, 2021 | No | None | | | openff_unconstrained-1.3.1.offxml | Parsley | June 21, 2021 | No | None | | | openff-1.3.1-alpha.1.offxml | Parsley | Apr 15, 2021 | No | None | | | openff_unconstrained-1.3.1-alpha.1.offxml | Parsley | Apr 15, 2021 | No | None | | | openff-1.3.0.offxml | Parsley | Oct 21, 2020 | No | repo | | | openff_unconstrained-1.3.0.offxml | Parsley | Oct 21, 2020 | No | repo | | | openff-1.2.1.offxml | Parsley | Sep 9, 2020 | No | None | | | openff_unconstrained-1.2.1.offxml | Parsley | Sep 9, 2020 | No | None | | | openff-1.2.0.offxml | Parsley | May 29, 2020 | No | repo | | | openff_unconstrained-1.2.0.offxml | Parsley | May 29, 2020 | No | repo | | | openff-1.1.1.offxml | Parsley | Apr 14, 2020 | No | None | | | openff_unconstrained-1.1.1.offxml | Parsley | Apr 14, 2020 | No | None | | | openff-1.1.0.offxml | Parsley | Mar 3, 2020 | No | repo | | | openff_unconstrained-1.1.0.offxml | Parsley | Mar 3, 2020 | No | repo | | | openff-1.0.1.offxml | Parsley | Apr 14, 2020 | No | None | | | openff_unconstrained-1.0.1.offxml | Parsley | Apr 14, 2020 | No | None | | | openff-1.0.0.offxml | Parsley | Oct 12, 2019 | No | repo | | | openff_unconstrained-1.0.0.offxml | Parsley | Oct 12, 2019 | No | repo | | | openff-1.0.0-RC2.offxml | None | Oct 4, 2019 | No | repo | | | openff_unconstrained-1.0.0-RC2.offxml | None | Oct 4, 2019 | No | repo | | | openff-1.0.0-RC1.offxml | None | Oct 4, 2019 | N/A | None | None | | openff_unconstrained-1.0.0-RC1.offxml | None | Oct 4, 2019 | N/A | None | None |

Details for various water models and other force fields ported to SMIRNOFF format can be found in the table below:

| Filename | FF line | Release Date | Major format changes? | Fitting repo | DOI | |---------------------------------------------|---------|---------------|-----------------------|-------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------| | tip5p-1.0.0.offxml | Ports | Nov 6, 2023 | No | None | see docs/water-models.md | | spce-1.0.0.offxml | Ports | Nov 6, 2023 | No | None | see docs/water-models.md | | tip4p_ew-1.0.0.offxml | Ports | Nov 6, 2023 | No | None | see docs/water-models.md | | opc-1.0.2.offxml | Ports | Aug 9, 2023 | No | None | see docs/water-models.md | | opc3-1.0.1.offxml | Ports | Aug 9, 2023 | No | None | see docs/water-models.md | | tip3p_fb-1.1.1.offxml | Ports | Aug 9, 2023 | No | None | see docs/water-models.md | | tip3p-1.0.1.offxml | Ports | Aug 9, 2023 | No | None | see docs/water-models.md | | tip4p_fb-1.0.1.offxml | Ports | Aug 9, 2023 | No | None | see docs/water-models.md | | opc-1.0.1.offxml | Ports | May 24, 2023 | No | None | see docs/water-models.md | | opc3-1.0.0.offxml | Ports | May 24, 2023 | No | None | see docs/water-models.md | | tip3p_fb-1.1.0.offxml | Ports | May 24, 2023 | No | None | see docs/water-models.md | | tip4p_fb-1.0.0.offxml | Ports | May 24, 2023 | No | None | see docs/water-models.md | | opc-1.0.0.offxml | Ports | May 1, 2023 | No | None | see docs/water-models.md | | tip3p_fb-1.0.0.offxml | Ports | Feb 27, 2023 | No | None | see docs/water-models.md | | tip3p-1.0.0.offxml | Ports | Feb 27, 2023 | No | None | see docs/water-models.md |

Installation

shell conda install -c conda-forge openff-forcefields

Use

Installing this package exposes an entry point that makes the openforcefields/offxml/ directory easily accessible by other packages in the same Python installation. If the OpenFF Toolkit is installed, it will automatically detect and use this entry point when loading OFFXML files:

python from openff.toolkit.typing.engines.smirnoff import ForceField ff = ForceField('openff-2.0.0.offxml')

Otherwise, the entry point can be accessed by querying the openforcefield.smirnoff_forcefield_directory entry point group.

```python from importlib.metadata import entry_points

for entrypoint in iterentrypoints(group='openforcefield.smirnoffforcefielddirectory'): print(entrypoint.load()()) ```

For convenience, the OpenFF Toolkit also has a standalone function get_available_force_fields that lists the force fields discered by this entry point group:

```pycon

from openff.toolkit.typing.engines.smirnoff.forcefield import getavailableforcefields getavailableforcefields() ['smirnoff99Frosst-1.0.2.offxml', 'smirnoff99Frosst-1.0.0.offxml', 'smirnoff99Frosst-1.1.0.offxml', 'smirnoff99Frosst-1.0.4.offxml', 'smirnoff99Frosst-1.0.8.offxml', 'smirnoff99Frosst-1.0.6.offxml', 'smirnoff99Frosst-1.0.3.offxml', 'smirnoff99Frosst-1.0.1.offxml', 'smirnoff99Frosst-1.0.5.offxml', 'smirnoff99Frosst-1.0.9.offxml', 'smirnoff99Frosst-1.0.7.offxml', 'ff14sboffimpropers0.0.2.offxml', 'ff14sb0.0.1.offxml', 'ff14sb0.0.3.offxml', 'ff14sboffimpropers0.0.1.offxml', 'ff14sboffimpropers0.0.3.offxml', 'ff14sb0.0.2.offxml', 'openff-1.0.1.offxml', 'openff-1.1.1.offxml', 'openff-1.0.0-RC1.offxml', 'openff-1.2.0.offxml', 'openff-1.3.0.offxml', 'openffunconstrained-2.0.0-rc.1.offxml', 'openffunconstrained-1.3.1.offxml', 'openffunconstrained-1.2.1.offxml', 'openff-2.0.0-rc.2.offxml', 'openffunconstrained-1.0.0-RC2.offxml', 'openffunconstrained-1.1.0.offxml', 'openffunconstrained-1.0.0.offxml', 'openff-2.0.0.offxml', 'openffunconstrained-2.0.0.offxml', 'openffunconstrained-2.0.0-rc.2.offxml', 'openff-1.1.0.offxml', 'openff-1.0.0.offxml', 'openff-1.0.0-RC2.offxml', 'openff-1.3.1.offxml', 'openff-1.2.1.offxml', 'openff-1.3.1-alpha.1.offxml', 'openffunconstrained-1.0.0-RC1.offxml', 'openffunconstrained-1.2.0.offxml', 'openffunconstrained-1.3.0.offxml', 'openff-2.0.0-rc.1.offxml', 'openffunconstrained-1.0.1.offxml', 'openffunconstrained-1.1.1.offxml', 'openffunconstrained-1.3.1-alpha.1.offxml'] ```

History

Force fields in the Parsley and Sage lines are descended from the SMIRNOFF99Frosst line of force fields. The first official release (openff-1.0.0.offxml, code name "Parsley") was made in September 2019 as a result of the Open Force Field Initiative's refitting efforts.

General versioning guidelines

Applicable in general to SMIRNOFF-format FFs produced by the Open Force Field Consortium

Force fields moving forward will be called name-X.Y.Z

• X denotes some major change in functional form or fitting strategy.
• Y is the parameterization epoch / generation, or a minor change that can affect energy.
• Z is a bugfix version -- e.g. something we've caught and corrected.

Versions

• v1.0.0 Parsley : First major forcefield release.

• v1.0.1 Parsley: This bugfix release contains following changes: (1) Addition of monatomic ion LibraryCharges.

• v1.1.0 Parsley: This minor release contains following changes: (1) Addition of new proper torsions and improper torsions for tetrazole; (2) Corrections to N-N bond rotation periodicity; (3) Removal of redundant periodicity component in t19; (4) Addition of three new bond and angle terms, a22a, b14a and b36a.

• v1.1.1 Parsley: This bugfix release contains following changes: (1) Addition of monatomic ion LibraryCharges.

• v1.2.0 Parsley: This minor release contains following changes: (1) New, carefully designed quantum chemical dataset was utilized in training valence parameters in the force field and (2) Removal of redundancy in t108 SMIRKS pattern

• v1.2.1 Parsley: This bugfix release manually changes two bond force constants to resolve an issue seen in propyne substituents when using hydrogen mass repartitioning with a 4fs timestep. Full details are available at https://github.com/openforcefield/openforcefields/issues/19.

• v1.3.0 Parsley: This minor release contains a fix of amide-related issues; (1) a poor performance of v1.2 in reproducing amide torsional energy profiles and (2) absence of appropriate torsion parameters for dialkyl amides.

• v1.3.1-alpha.1 Parsley: The new force field files in this release are adapted from the openff-1.3.0 release, except that two angle parameters have been reverted to their original values from smirnoff99Frosst 1.1.0, in an attempt to fix sulphonamide geometries.

• v1.3.1 Parsley: This release is identical to v1.3.1-alpha.1 Parsley.

• v2.0.0-rc.1 Sage: This major release candidate contains both refit valence and vdW terms. Full details are available at https://github.com/openforcefield/openff-sage/releases/tag/2.0.0-rc.1

• v2.0.0-rc.2 Sage: This major release candidate is identical to v2.0.0-rc.1 Sage except that the angle value for a16 has been changed to 180.0 * degree, as the previous value of 183... * degree causes geometry optimizers to fail to converge.

• v2.0.0 Sage: This major release contains the same physical parameters as v2.0.0-rc.2 Sage, but has the parameter ids changed. For more information see the openff-sage repository.

• 2023.02.1: This release switches to a calendar-versioning system and adds tip3p-1.0.0.offxml and tip3p-fb-1.0.0.offxml, as well as tip3p.offxml and tip3p-fb.offxml, which will always point to the latest files in their respective lines.

• 2023.04.1: This release adds openff-2.1.0-rc.1.offxml Sage 2.1.0 Release Candidate 1, with several small parameter fixes and improvements.

• 2023.05.0: This release adds the opc-1.0.0.offxml, our initial port of the OPC water model.

• 2023.05.1: This release adds openff-2.1.0.offxml, Sage 2.1.0, with identical physics parameters to openff-2.1.0-rc.1.offxml.

• 2023.06.0: This release adds opc-1.0.1.offxml, standardizing the use of the string "kilocaloriepermole". It also adds tip3p-fb-1.1.0.offxml, which fixes a unit error in the geometric constraints and adds additional ion parameters. Finally, it adds opc3-1.0.0.offxml and tip4p_fb-1.0.0.offxml.

• 2024.01.0: This release adds openff-2.1.1.offxml and openff_unconstrained-2.1.1.offxml, Sage 2.1.1, which has identical parameters to Sage 2.1.0 (originally released in version 2023.05.1 of the openff-forcefields package) but adds Xe van der Waals parameters from Tang, K.T., Toennies, J.P. New combining rules for well parameters and shapes of the van der Waals potential of mixed rare gas systems. Z Phys D - Atoms, Molecules and Clusters 1, 91–101 (1986).

• 2024.03.0: This release adds openff-2.2.0-rc1.offxml and openff_unconstrained-2.2.0-rc1.offxml, Sage 2.2.0 Release Candidate 1, which modifies some small ring internal angles and remedies issues with sulfamide geometries.

• 2024.04.0: This release adds openff-2.2.0.offxml and openff_unconstrained-2.2.0.offxml, Sage 2.2.0, with identical parameters to openff-2.2.0-rc1.offxml.

• 2024.07.0: This release adds openff-2.2.1-rc1.offxml and openff_unconstrained-2.2.1-rc1.offxml, which contains re-fit valence parameters where linear angles have been pinned to linear equilibrium values.

• 2024.09.0 This release adds the Sage 2.2.1 force field with openff-2.2.1.offxml and openff_unconstrained-2.2.1.offxml, with identifical parameters to 2.2.1-rc1.

Acknowledgements

Project based on the Computational Molecular Science Python Cookiecutter version 1.0.