Further sulf(on)amide improvements

Background and goal

As a class, OpenFF force fields have repeatedly had issues with reproducing the geometries of sulfonamides and sulfones. Additional reading and documentation can be found at:

• Sulfonamide issue in Parsley

• MSM as a better initial guess

• https://openforcefieldgroup.slack.com/archives/CK5MQG0TC/p1661707855604879

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Sage 2.1 aimed to fix these parameters in multiple targeted ways:

• Using initial parameters derived from QM values, rather than the previous force field

• changing the partitioning of chemistries between different sulfonamide angles (a31, a32)

However, the problems still persist for some chemistries:

@Pavan Behara re-fit a force field that appears to address these issues as the initial basis for Sage 2.2. The only changes here so far are tightening priors to keep values more similar to the initial MSM guesses. (more reading in Slack: ).

To prevent this issue from re-occurring in the future, we should:

• set up a test suite of diverse molecules, and known problematic chemistries, especially of sulfonamides and other hypervalent sulfurs

• Check to see if the above issue #64 is actually closed by Sage 2.2

  • If so, we can potentially release the above FF immediately, perhaps as 2.1.1