Disable the barostat during FIRE minimization

[hannahbaumann]

Description

As has been described here (#557), box vectors can change during energy minimization using the FIRE minimizer, leading to instabilities. This PR temporarily disables the barostat for the minimization.

Changelog message

 Disable the barostat during FIRE minimization #773 

[hannahbaumann]

@ijpulidos @mikemhenry : This seems to be solving the issues with random crashes when starting NPT equilibration after FIRE minimization that I mentioned on Tuesday. On some short test calculations I'm not seeing any crashes.

[hannahbaumann]

I removed this as I had seen this (openmm/openmm#1237 (comment)), but in test calculations I don't see crashes if we update the context state so this may not be necessary?

[hannahbaumann]

Actually, as @jthorton pointed out, removing the self.addUpdateContextState() and setting the pressure to None should both have the same effect, so we could do either!

[mikemhenry]

I like setting the pressure to None as it is a bit more clear IMHO

[mikemhenry]

looks like we have a test that checks that actually FAILED openmmtools/tests/test_integrators.py::test_update_context_state_calls - AssertionError: Integrator 'FIREMinimizationIntegrator' has 0 calls to addUpdateContextState(), while there should be only one.

[mikemhenry]

I can't edit this PR, @hannahbaumann can you check the box described here? https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.06%. Comparing base (5cdd135) to head (49c7c07).
Report is 5 commits behind head on main.

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