def test_periodic_torsion(self, n_particles=64, n_torsions=25, dim=3):
"""Randomly connect quadruples of particles, then validate the resulting PeriodicTorsion force"""
np.random.seed(125)
x = self.get_random_coords(n_particles, dim)
atom_idxs = np.arange(n_particles)
params = np.random.rand(n_torsions, 3).astype(np.float64)
torsion_idxs = []
for _ in range(n_torsions):
torsion_idxs.append(np.random.choice(atom_idxs, size=4, replace=False))
torsion_idxs = np.array(torsion_idxs, dtype=np.int32)
lamb = 0.0
box = np.eye(3) * 100
# specific to periodic torsion force
relative_tolerance_at_precision = {np.float32: 2e-5, np.float64: 1e-9}
for precision, rtol in relative_tolerance_at_precision.items():
test_potential = potentials.PeriodicTorsion(torsion_idxs)
ref_potential = functools.partial(bonded.periodic_torsion, torsion_idxs=torsion_idxs)
self.compare_forces(x, params, box, lamb, ref_potential, test_potential, rtol, precision=precision)
lamb_mult = np.random.randint(-5, 5, size=n_torsions, dtype=np.int32)
lamb_offset = np.random.randint(-5, 5, size=n_torsions, dtype=np.int32)
lamb = 0.35
for precision, rtol in relative_tolerance_at_precision.items():
test_potential = potentials.PeriodicTorsion(torsion_idxs, lamb_mult, lamb_offset)
ref_potential = functools.partial(
bonded.periodic_torsion, torsion_idxs=torsion_idxs, lamb_mult=lamb_mult, lamb_offset=lamb_offset
)
self.compare_forces(x, params, box, lamb, ref_potential, test_potential, rtol, precision=precision)
def parameterize_periodic_torsion(self, proper_params, improper_params):
"""
Parameterize all periodic torsions in the system.
"""
proper_params, proper_potential = self.parameterize_proper_torsion(
proper_params)
improper_params, improper_potential = self.parameterize_improper_torsion(
improper_params)
combined_params = jnp.concatenate([proper_params, improper_params])
combined_idxs = np.concatenate(
[proper_potential.get_idxs(),
improper_potential.get_idxs()])
proper_lambda_mult = proper_potential.get_lambda_mult()
proper_lambda_offset = proper_potential.get_lambda_offset()
if proper_lambda_mult is None:
proper_lambda_mult = np.zeros(len(proper_params))
if proper_lambda_offset is None:
proper_lambda_offset = np.ones(len(proper_params))
improper_lambda_mult = improper_potential.get_lambda_mult()
improper_lambda_offset = improper_potential.get_lambda_offset()
if improper_lambda_mult is None:
improper_lambda_mult = np.zeros(len(improper_params))
if improper_lambda_offset is None:
improper_lambda_offset = np.ones(len(improper_params))
combined_lambda_mult = np.concatenate(
[proper_lambda_mult, improper_lambda_mult]).astype(np.int32)
combined_lambda_offset = np.concatenate(
[proper_lambda_offset, improper_lambda_offset]).astype(np.int32)
combined_potential = potentials.PeriodicTorsion(
combined_idxs, combined_lambda_mult, combined_lambda_offset)
return combined_params, combined_potential
def parameterize_periodic_torsion(self, proper_params, improper_params):
"""
Parameterize all periodic torsions in the system.
"""
proper_params, proper_potential = self.parameterize_proper_torsion(
proper_params)
improper_params, improper_potential = self.parameterize_improper_torsion(
improper_params)
combined_params = jnp.concatenate([proper_params, improper_params])
combined_idxs = np.concatenate(
[proper_potential.get_idxs(),
improper_potential.get_idxs()])
combined_lambda_mult = np.concatenate([
proper_potential.get_lambda_mult(),
improper_potential.get_lambda_mult()
])
combined_lambda_offset = np.concatenate([
proper_potential.get_lambda_offset(),
improper_potential.get_lambda_offset()
])
combined_potential = potentials.PeriodicTorsion(
combined_idxs, combined_lambda_mult, combined_lambda_offset)
return combined_params, combined_potential
def parameterize_improper_torsion(self, ff_params):
params, idxs = self.ff.it_handle.partial_parameterize(ff_params, self.mol)
return params, potentials.PeriodicTorsion(idxs)
def combine_potentials(ff_handlers, guest_mol, host_system, precision):
"""
This function is responsible for figuring out how to take two separate hamiltonians
and combining them into one sensible alchemical system.
Parameters
----------
ff_handlers: list of forcefield handlers
Small molecule forcefield handlers
guest_mol: Chem.ROMol
RDKit molecule
host_system: openmm.System
Host system to be deserialized
precision: np.float32 or np.float64
Numerical precision of the functional form
Returns
-------
tuple
Returns a list of lib.potentials objects, combined masses, and a list of
their corresponding vjp_fns back into the forcefield
"""
host_potentials, host_masses = openmm_deserializer.deserialize_system(
host_system, precision, cutoff=1.0)
host_nb_bp = None
combined_potentials = []
combined_vjp_fns = []
for bp in host_potentials:
if isinstance(bp, potentials.Nonbonded):
# (ytz): hack to ensure we only have one nonbonded term
assert host_nb_bp is None
host_nb_bp = bp
else:
combined_potentials.append(bp)
combined_vjp_fns.append([])
guest_masses = np.array([a.GetMass() for a in guest_mol.GetAtoms()],
dtype=np.float64)
num_guest_atoms = len(guest_masses)
num_host_atoms = len(host_masses)
combined_masses = np.concatenate([host_masses, guest_masses])
for handle in ff_handlers:
results = handle.parameterize(guest_mol)
if isinstance(handle, bonded.HarmonicBondHandler):
bond_idxs, (bond_params, vjp_fn) = results
bond_idxs += num_host_atoms
combined_potentials.append(
potentials.HarmonicBond(bond_idxs,
precision=precision).bind(bond_params))
combined_vjp_fns.append([(handle, vjp_fn)])
elif isinstance(handle, bonded.HarmonicAngleHandler):
angle_idxs, (angle_params, vjp_fn) = results
angle_idxs += num_host_atoms
combined_potentials.append(
potentials.HarmonicAngle(
angle_idxs, precision=precision).bind(angle_params))
combined_vjp_fns.append([(handle, vjp_fn)])
elif isinstance(handle, bonded.ProperTorsionHandler):
torsion_idxs, (torsion_params, vjp_fn) = results
torsion_idxs += num_host_atoms
combined_potentials.append(
potentials.PeriodicTorsion(
torsion_idxs, precision=precision).bind(torsion_params))
combined_vjp_fns.append([(handle, vjp_fn)])
elif isinstance(handle, bonded.ImproperTorsionHandler):
torsion_idxs, (torsion_params, vjp_fn) = results
torsion_idxs += num_host_atoms
combined_potentials.append(
potentials.PeriodicTorsion(
torsion_idxs, precision=precision).bind(torsion_params))
combined_vjp_fns.append([(handle, vjp_fn)])
elif isinstance(handle, nonbonded.AM1CCCHandler):
charge_handle = handle
guest_charge_params, guest_charge_vjp_fn = results
elif isinstance(handle, nonbonded.LennardJonesHandler):
guest_lj_params, guest_lj_vjp_fn = results
lj_handle = handle
else:
print("Warning: skipping handler", handle)
pass
# process nonbonded terms
combined_nb_params, (charge_vjp_fn, lj_vjp_fn) = nonbonded_vjps(
guest_charge_params, guest_charge_vjp_fn, guest_lj_params,
guest_lj_vjp_fn, host_nb_bp.params)
# these vjp_fns take in adjoints of combined_params and returns derivatives
# appropriate to the underlying handler
combined_vjp_fns.append([(charge_handle, charge_vjp_fn),
(lj_handle, lj_vjp_fn)])
# tbd change scale 14 for electrostatics
guest_exclusion_idxs, guest_scale_factors = nonbonded.generate_exclusion_idxs(
guest_mol, scale12=1.0, scale13=1.0, scale14=0.5)
# allow the ligand to be alchemically decoupled
# a value of one indicates that we allow the atom to be adjusted by the lambda value
guest_lambda_offset_idxs = np.ones(len(guest_masses), dtype=np.int32)
# use same scale factors until we modify 1-4s for electrostatics
guest_scale_factors = np.stack([guest_scale_factors, guest_scale_factors],
axis=1)
combined_lambda_offset_idxs = np.concatenate(
[host_nb_bp.get_lambda_offset_idxs(), guest_lambda_offset_idxs])
combined_exclusion_idxs = np.concatenate([
host_nb_bp.get_exclusion_idxs(), guest_exclusion_idxs + num_host_atoms
])
combined_scales = np.concatenate(
[host_nb_bp.get_scale_factors(), guest_scale_factors])
combined_beta = 2.0
combined_cutoff = 1.0 # nonbonded cutoff
combined_potentials.append(
potentials.Nonbonded(
combined_exclusion_idxs,
combined_scales,
combined_lambda_offset_idxs,
combined_beta,
combined_cutoff,
precision=precision,
).bind(combined_nb_params))
return combined_potentials, combined_masses, combined_vjp_fns
def from_rdkit(cls, mol, ff_handlers):
"""
Initialize a system from an RDKit ROMol.
Parameters
----------
mol: Chem.ROMol
RDKit ROMol. Should have graphical hydrogens in the topology.
ff_handlers: list of forcefield handlers.
openforcefield small molecule handlers.
"""
masses = np.array([a.GetMass() for a in mol.GetAtoms()], dtype=np.float64)
bound_potentials = []
for handle in ff_handlers:
results = handle.parameterize(mol)
if isinstance(handle, bonded.HarmonicBondHandler):
bond_params, bond_idxs = results
bound_potentials.append(potentials.HarmonicBond(bond_idxs).bind(bond_params))
elif isinstance(handle, bonded.HarmonicAngleHandler):
angle_params, angle_idxs = results
bound_potentials.append(potentials.HarmonicAngle(angle_idxs).bind(angle_params))
elif isinstance(handle, bonded.ProperTorsionHandler):
torsion_params, torsion_idxs = results
bound_potentials.append(potentials.PeriodicTorsion(torsion_idxs).bind(torsion_params))
elif isinstance(handle, bonded.ImproperTorsionHandler):
torsion_params, torsion_idxs = results
bound_potentials.append(potentials.PeriodicTorsion(torsion_idxs).bind(torsion_params))
elif isinstance(handle, nonbonded.AM1CCCHandler):
charge_handle = handle
charge_params = results
elif isinstance(handle, nonbonded.LennardJonesHandler):
lj_params = results
lj_handle = handle
else:
print("WARNING: skipping handler", handle)
pass
lambda_plane_idxs = np.zeros(len(masses), dtype=np.int32)
lambda_offset_idxs = np.zeros(len(masses), dtype=np.int32)
exclusion_idxs, scale_factors = nonbonded.generate_exclusion_idxs(
mol,
scale12=1.0,
scale13=1.0,
scale14=0.5
)
# use same scale factors until we modify 1-4s for electrostatics
scale_factors = np.stack([scale_factors, scale_factors], axis=1)
# (ytz) fix this later to not be so hard coded
alpha = 2.0 # same as ewald alpha
cutoff = 1.0 # nonbonded cutoff
qlj_params = jnp.concatenate([
jnp.reshape(charge_params, (-1, 1)),
jnp.reshape(lj_params, (-1, 2))
], axis=1)
bound_potentials.append(potentials.Nonbonded(
exclusion_idxs,
scale_factors,
lambda_plane_idxs,
lambda_offset_idxs,
alpha,
cutoff).bind(qlj_params))
return cls(masses, bound_potentials)
def deserialize_system(system, cutoff):
"""
Deserialize an OpenMM XML file
Parameters
----------
system: openmm.System
A system object to be deserialized
Returns
-------
list of lib.Potential, masses
Note: We add a small epsilon (1e-3) to all zero eps values to prevent
a singularity from occuring in the lennard jones derivatives
"""
masses = []
for p in range(system.getNumParticles()):
masses.append(value(system.getParticleMass(p)))
N = len(masses)
# this should not be a dict since we may have more than one instance of a given
# force.
bps = []
for force in system.getForces():
if isinstance(force, mm.HarmonicBondForce):
bond_idxs = []
bond_params = []
for b_idx in range(force.getNumBonds()):
src_idx, dst_idx, length, k = force.getBondParameters(b_idx)
length = value(length)
k = value(k)
bond_idxs.append([src_idx, dst_idx])
bond_params.append((k, length))
bond_idxs = np.array(bond_idxs, dtype=np.int32)
bond_params = np.array(bond_params, dtype=np.float64)
bps.append(potentials.HarmonicBond(bond_idxs).bind(bond_params))
if isinstance(force, mm.HarmonicAngleForce):
angle_idxs = []
angle_params = []
for a_idx in range(force.getNumAngles()):
src_idx, mid_idx, dst_idx, angle, k = force.getAngleParameters(
a_idx)
angle = value(angle)
k = value(k)
angle_idxs.append([src_idx, mid_idx, dst_idx])
angle_params.append((k, angle))
angle_idxs = np.array(angle_idxs, dtype=np.int32)
angle_params = np.array(angle_params, dtype=np.float64)
bps.append(potentials.HarmonicAngle(angle_idxs).bind(angle_params))
if isinstance(force, mm.PeriodicTorsionForce):
torsion_idxs = []
torsion_params = []
for t_idx in range(force.getNumTorsions()):
a_idx, b_idx, c_idx, d_idx, period, phase, k = force.getTorsionParameters(
t_idx)
phase = value(phase)
k = value(k)
torsion_params.append((k, phase, period))
torsion_idxs.append([a_idx, b_idx, c_idx, d_idx])
torsion_idxs = np.array(torsion_idxs, dtype=np.int32)
torsion_params = np.array(torsion_params, dtype=np.float64)
bps.append(
potentials.PeriodicTorsion(torsion_idxs).bind(torsion_params))
if isinstance(force, mm.NonbondedForce):
num_atoms = force.getNumParticles()
charge_params = []
lj_params = []
for a_idx in range(num_atoms):
charge, sig, eps = force.getParticleParameters(a_idx)
charge = value(charge) * np.sqrt(constants.ONE_4PI_EPS0)
sig = value(sig)
eps = value(eps)
# increment eps by 1e-3 if we have eps==0 to avoid a singularity in parameter derivatives
# override default amber types
# this doesn't work for water!
# if eps == 0:
# print("Warning: overriding eps by 1e-3 to avoid a singularity")
# eps += 1e-3
# charge_params.append(charge_idx)
charge_params.append(charge)
lj_params.append((sig, eps))
charge_params = np.array(charge_params, dtype=np.float64)
# print("Protein net charge:", np.sum(np.array(global_params)[charge_param_idxs]))
lj_params = np.array(lj_params, dtype=np.float64)
# 1 here means we fully remove the interaction
# 1-2, 1-3
# scale_full = insert_parameters(1.0, 20)
# 1-4, remove half of the interaction
# scale_half = insert_parameters(0.5, 21)
exclusion_idxs = []
scale_factors = []
all_sig = lj_params[:, 0]
all_eps = lj_params[:, 1]
# validate exclusions/exceptions to make sure they make sense
for a_idx in range(force.getNumExceptions()):
# tbd charge scale factors
src, dst, new_cp, new_sig, new_eps = force.getExceptionParameters(
a_idx)
new_sig = value(new_sig)
new_eps = value(new_eps)
src_sig = all_sig[src]
dst_sig = all_sig[dst]
src_eps = all_eps[src]
dst_eps = all_eps[dst]
expected_sig = (src_sig + dst_sig) / 2
expected_eps = np.sqrt(src_eps * dst_eps)
exclusion_idxs.append([src, dst])
# sanity check this (expected_eps can be zero), redo this thing
# the lj_scale factor measures how much we *remove*
if expected_eps == 0:
if new_eps == 0:
lj_scale_factor = 1
else:
raise RuntimeError(
"Divide by zero in epsilon calculation")
else:
lj_scale_factor = 1 - new_eps / expected_eps
scale_factors.append(lj_scale_factor)
# tbd fix charge_scale_factors using new_cp
if new_eps != 0:
np.testing.assert_almost_equal(expected_sig, new_sig)
exclusion_idxs = np.array(exclusion_idxs, dtype=np.int32)
lambda_plane_idxs = np.zeros(N, dtype=np.int32)
lambda_offset_idxs = np.zeros(N, dtype=np.int32)
# cutoff = 1000.0
nb_params = np.concatenate(
[np.expand_dims(charge_params, axis=1), lj_params], axis=1)
# optimizations
nb_params[:, 1] = nb_params[:, 1] / 2
nb_params[:, 2] = np.sqrt(nb_params[:, 2])
beta = 2.0 # erfc correction
# use the same scale factors for electrostatics and lj
scale_factors = np.stack([scale_factors, scale_factors], axis=1)
bps.append(
potentials.Nonbonded(exclusion_idxs, scale_factors,
lambda_plane_idxs, lambda_offset_idxs,
beta, cutoff).bind(nb_params))
# nrg_fns.append(('Exclusions', (exclusion_idxs, scale_factors, es_scale_factors)))
return bps, masses