Release History

Releases follow the major.minor.micro scheme recommended by PEP440, where

  • major increments denote a change that may break API compatibility with previous major releases
  • minor increments add features but do not break API compatibility
  • micro increments represent bugfix releases or improvements in documentation


This version of the toolkit introduces many new features on the way to a 1.0.0 release.

New features

  • Major overhaul, resulting in the creation of the 0.2 SMIRNOFF specification and its XML representation
  • Updated API and infrastructure for reference SMIRNOFF ForceField implementation
  • Implementation of modular ParameterHandler classes which process the topology to add all necessary forces to the system..
  • Implementation of modular ParameterIOHandler classes for reading/writing different serialized SMIRNOFF forcefield representations
  • Introduction of Molecule and Topology classes for representing molecules and biomolecular systems
  • New ToolkitWrapper interface to RDKit, OpenEye, and AmberTools toolkits, managed by ToolkitRegistry
  • API improvements to more closely follow PEP8 guidelines
  • Improved documentation and examples


This is an early preview release of the toolkit that matches the functionality described in the preprint describing the SMIRNOFF v0.1 force field format: [DOI].

New features

This release features additional documentation, code comments, and support for automated testing.


Treatment of improper torsions

A significant (though currently unused) problem in handling of improper torsions was corrected. Previously, non-planar impropers did not behave correctly, as six-fold impropers have two potential chiralities. To remedy this, SMIRNOFF impropers are now implemented as three-fold impropers with consistent chirality. However, current force fields in the SMIRNOFF format had no non-planar impropers, so this change is mainly aimed at future work.