Add center-of-mass motion remover in OpenMM export

.github/workflows/ci.yaml

@@ -97,7 +97,7 @@ jobs:
       if: ${{ matrix.openeye == true && matrix.openmm == true }}
       run: |
         micromamba install "deepdiff =5" rich click -c conda-forge
-        python -m pip install git+https://github.com/openforcefield/interchange-regression-testing.git@fa07b62824c39af591142b402bd68103f4043f8b
+        python -m pip install git+https://github.com/openforcefield/interchange-regression-testing.git@83067d7cce37a0f21b028651a7d98ec063572063
 
         create_openmm_systems \
           --input             "regression_tests/small-molecule/input-topologies.json" \

docs/releasehistory.md

@@ -13,6 +13,10 @@ Please note that all releases prior to a version 1.0.0 are considered pre-releas
 
 ## Current development
 
+### Behavior changes
+
+* #1132 Methods that return an `openmm.System` object now include a `openmm.CMMotionRemover` "force" within it.
+
 ### New features
 
 * #1053 Logs, at the level of `logging.INFO`, how charges are assigned by SMIRNOFF force fields to each atom and virtual site.

docs/using/edges.md

@@ -67,6 +67,10 @@ For more, see [issue #1005](https://github.com/openforcefield/openff-interchange
 
 Keywords: OpenMM, GROMACS, constraints, bond constraints, rigid water
 
+### Center-of-mass motion remover ignored
+
+If present, an `openmm.CMMotionRemover` "force" is ignored when loading a system. An `Interchange` object does not store this information. Note that exported systems from `Interchange.to_openmm_system` include this force by default.
+
 ## Quirks with GROMACS
 
 ### Residue indices must begin at 1

openff/interchange/_tests/interoperability_tests/test_openmm.py

@@ -318,22 +318,22 @@ def test_openmm_no_valence_forces_with_no_handler(self, sage, ethanol):
         original_system = Interchange.from_smirnoff(sage, [ethanol]).to_openmm(
             combine_nonbonded_forces=True,
         )
-        assert original_system.getNumForces() == 4
+        assert original_system.getNumForces() == 5
 
         sage.deregister_parameter_handler("Constraints")
         sage.deregister_parameter_handler("Bonds")
 
         no_bonds = Interchange.from_smirnoff(sage, [ethanol]).to_openmm(
             combine_nonbonded_forces=True,
         )
-        assert no_bonds.getNumForces() == 3
+        assert no_bonds.getNumForces() == 4
 
         sage.deregister_parameter_handler("Angles")
 
         no_angles = Interchange.from_smirnoff(sage, [ethanol]).to_openmm(
             combine_nonbonded_forces=True,
         )
-        assert no_angles.getNumForces() == 2
+        assert no_angles.getNumForces() == 3
 
     def test_openmm_only_electrostatics_no_vdw(self):
         force_field_only_charges = ForceField(get_test_file_path("no_vdw.offxml"))
@@ -605,10 +605,10 @@ def test_valence_term_paticle_index_offsets(self, water, tip5p):
             combine_nonbonded_forces=True,
         )
 
-        # NonbondedForce and HarmonicBondForce; no HarmonicAngleForce (even if there were force
-        # field parameters added, the current implementation would not add an angle force because
-        # H-O-H is fully constrained)
-        assert out.getNumForces() == 2
+        # NonbondedForce, HarmonicBondForce, CMMotionRemover; no HarmonicAngleForce (even if there
+        # were force field parameters added, the current implementation would not add an angle
+        # force because H-O-H is fully constrained)
+        assert out.getNumForces() == 3
 
         # Particle indexing is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
         #                      O, H, H, O, H, H, VS, VS, VS, VS

openff/interchange/_tests/unit_tests/interop/openmm/test_openmm.py

@@ -28,6 +28,16 @@ def compare(smiles: str) -> float:
 
 @skip_if_missing("openmm")
 class TestToOpenMM:
+    def test_cmm_remover_included(self, sage, basic_top):
+        import openmm
+
+        system = sage.create_interchange(basic_top).to_openmm_system()
+
+        assert isinstance(
+            system.getForce(system.getNumForces() - 1),
+            openmm.CMMotionRemover,
+        )
+
     def test_combine_nonbonded_forces_vdw_14(self, sage_unconstrained):
         molecule = Molecule.from_mapped_smiles("[C:2](#[C:3][Br:4])[Br:1]")
         molecule.generate_conformers(n_conformers=1)

openff/interchange/_tests/unit_tests/interop/test_openmm.py

@@ -12,6 +12,7 @@
 
 if has_package("openmm"):
     from openmm import (
+        CMMotionRemover,
         HarmonicAngleForce,
         HarmonicBondForce,
         NonbondedForce,
@@ -46,6 +47,8 @@ def test_no_nonbonded_force(self, sage):
                 assert force.getNumBonds() == 4
             elif isinstance(force, HarmonicAngleForce):
                 assert force.getNumAngles() == 6
+            elif isinstance(force, CMMotionRemover):
+                pass
             else:
                 pytest.fail(f"Unexpected force found, type: {type(force)}")
 

openff/interchange/components/interchange.py

@@ -920,6 +920,10 @@ def from_openmm(
         interchange : Interchange
             An Interchange object representing the contents of the OpenMM objects.
 
+        Notes
+        -----
+        An `openmm.CMMotionRemover` force, if present, is ignored.
+
         """
         from openff.interchange.interop.openmm._import._import import from_openmm
 

openff/interchange/interop/openmm/__init__.py

@@ -147,6 +147,8 @@ def to_openmm_system(
             except NotImplementedError:
                 continue
 
+    system.addForce(openmm.CMMotionRemover())
+
     return system