def openff_openmm_pmd_gmx(
topology: Topology,
forcefield: ForceField,
box: ArrayQuantity,
prefix: str,
) -> None:
"""Pipeline to write GROMACS files from and OpenMM system through ParmEd"""
topology.box_vectors = box.to(unit.nanometer).magnitude * omm_unit.nanometer
omm_sys = forcefield.create_openmm_system(topology)
struct = pmd.openmm.load_topology(
system=omm_sys,
topology=topology.to_openmm(),
xyz=topology.topology_molecules[0].reference_molecule.conformers[0],
)
# Assign dummy residue names, GROMACS will not accept empty strings
# TODO: Patch upstream?
for res in struct.residues:
res.name = "FOO"
struct.save(prefix + ".gro")
struct.save(prefix + ".top")
def simulate(
force_field: ForceField,
topology: Topology,
positions: unit.Quantity,
box_vectors: Optional[unit.Quantity],
n_steps: int,
temperature: unit.Quantity,
pressure: Optional[unit.Quantity],
platform: Literal["Reference", "OpenCL", "CUDA", "CPU"] = "Reference",
output_directory: Optional[str] = None,
):
"""A helper function for simulating a system parameterised with a specific OpenFF
force field using OpenMM.
Parameters
----------
force_field
The force field to apply.
topology
The topology detailing the system to simulate.
positions
The starting coordinates of the molecules in the system.
box_vectors
The box vectors to use. These will overwrite the topology box vectors.
n_steps
The number of steps to simulate for.
temperature
The temperature to simulate at.
pressure
The pressure to simulate at.
platform
The platform to simulate using.
output_directory
The optional directory to store the simulation outputs in.
"""
assert pressure is None or (
pressure is not None and box_vectors is not None
), "box vectors must be provided when the pressure is specified."
topology.box_vectors = box_vectors
# Create an OpenMM system by applying the parameters to the topology.
omm_system, topology = force_field.create_openmm_system(
topology, return_topology=True)
if output_directory is not None:
os.makedirs(output_directory, exist_ok=True)
# Add the virtual sites to the OpenMM topology and positions.
omm_topology = topology.to_openmm()
omm_chain = [*omm_topology.chains()][0]
omm_residue = omm_topology.addResidue("", chain=omm_chain)
for particle in topology.topology_particles:
if isinstance(particle, TopologyAtom):
continue
omm_topology.addAtom(particle.virtual_site.name,
app.Element.getByMass(0), omm_residue)
positions = numpy.vstack(
[positions,
numpy.zeros((topology.n_topology_virtual_sites, 3))])
with temporary_cd(output_directory):
__simulate(
positions=positions * unit.angstrom,
box_vectors=box_vectors,
omm_topology=omm_topology,
omm_system=omm_system,
n_steps=n_steps,
temperature=temperature,
pressure=pressure,
platform=platform,
)
