issue 620

620.ipynb

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     "text": [
      "Periodic: True, Combine: True\n",
      "\t[('NonbondedForce', 'PME')]\n",
      "Periodic: True, Combine: False\n",
      "\t[('CustomNonbondedForce', 'CutoffPeriodic'), ('NonbondedForce', 'PME')]\n",
      "Periodic: False, Combine: True\n",
      "\t[('NonbondedForce', 'NoCutoff')]\n",
      "Periodic: False, Combine: False\n",
      "\tWhen using `openmm.CustomNonbondedForce`, vdW and electrostatics cutoff methods must agree on whether or not periodic boundary conditions should be used.OpenMM will throw an error. Found vdw method 1, and electrostatics method 0, \n"
     ]
    }
   ],
   "source": [
    "import openmm\n",
    "from openff.toolkit import ForceField, Molecule, Topology\n",
    "from openff.units import unit\n",
    "\n",
    "from openff.interchange import Interchange\n",
    "from openff.interchange.exceptions import UnsupportedCutoffMethodError\n",
    "\n",
    "CUTOFFS = {\n",
    "    getattr(openmm.NonbondedForce, scheme): scheme\n",
    "    for scheme in [\"NoCutoff\", \"CutoffNonPeriodic\", \"CutoffPeriodic\", \"Ewald\", \"PME\"]\n",
    "}\n",
    "\n",
    "\n",
    "def get_topology(periodic: bool) -> Topology:\n",
    "    molecule = Molecule.from_smiles(\"CCO\")\n",
    "\n",
    "    topology = molecule.to_topology()\n",
    "\n",
    "    if periodic:\n",
    "        topology.box_vectors = unit.Quantity(\n",
    "            [4, 4, 4],\n",
    "            unit.nanometer,\n",
    "        )\n",
    "\n",
    "    return topology\n",
    "\n",
    "\n",
    "def get_nonbonded_methods(system: openmm.System) -> list[tuple[openmm.Force, str]]:\n",
    "    forces = list()\n",
    "\n",
    "    for force in system.getForces():\n",
    "        if isinstance(force, (openmm.NonbondedForce, openmm.CustomNonbondedForce)):\n",
    "            forces.append(\n",
    "                (\n",
    "                    force.__class__.__name__,\n",
    "                    CUTOFFS[force.getNonbondedMethod()],\n",
    "                )\n",
    "            )\n",
    "\n",
    "    return forces\n",
    "\n",
    "\n",
    "force_field = ForceField(\"openff-2.1.0.offxml\")\n",
    "\n",
    "for periodic in [True, False]:\n",
    "    for combine in [True, False]:\n",
    "        print(f\"Periodic: {periodic}, Combine: {combine}\")\n",
    "        try:\n",
    "            system = Interchange.from_smirnoff(\n",
    "                topology=get_topology(periodic),\n",
    "                force_field=force_field,\n",
    "            ).to_openmm(combine_nonbonded_forces=combine)\n",
    "\n",
    "            print(f\"\\t{get_nonbonded_methods(system)}\")\n",
    "        except UnsupportedCutoffMethodError as error:\n",
    "            print(f\"\\t{error}\")"
   ]
  },
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   "execution_count": 11,
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    {
     "data": {
      "text/plain": [
       "{0: 'NoCutoff',\n",
       " 1: 'CutoffNonPeriodic',\n",
       " 2: 'CutoffPeriodic',\n",
       " 3: 'Ewald',\n",
       " 4: 'PME'}"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "CUTOFFS"
   ]
  }
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