def compare_energy_components(rest_system,
other_system,
positions,
platform=REFERENCE_PLATFORM):
"""
Get energy components of a given system
"""
platform = configure_platform(platform)
# Create thermodynamic state and sampler state for non-rest system
thermostate_other = ThermodynamicState(system=other_system,
temperature=temperature)
# Create context for non-rest system
integrator_other = openmm.VerletIntegrator(1.0 * unit.femtosecond)
context_other = thermostate_other.create_context(integrator_other)
context_other.setPositions(positions)
# Get energy components for non-rest system
components_other = [
component[1]
for component in compute_potential_components(context_other, beta=beta)
]
# Create thermodynamic state for rest_system
thermostate_rest = ThermodynamicState(system=rest_system,
temperature=temperature)
# Create context forrest system
integrator_rest = openmm.VerletIntegrator(1.0 * unit.femtosecond)
context_rest = thermostate_rest.create_context(integrator_rest)
context_rest.setPositions(positions)
# Get energy components for rest system
components_rest = [
component[1]
for component in compute_potential_components(context_rest, beta=beta)
]
# Check that bond, angle, and torsion energies match
for other, rest in zip(components_other[:3], components_rest[:3]):
assert np.isclose(
[other], [rest]
), f"The energies do not match for the {other[0]}: {other[1]} (other system) vs. {rest[1]} (REST system)"
# Check that nonbonded energies match
print(components_rest)
nonbonded_other = np.array(components_other[3:]).sum()
nonbonded_rest = np.array(components_rest[3:]).sum()
assert np.isclose(
[nonbonded_other], [nonbonded_rest]
), f"The energies do not match for the NonbondedForce: {nonbonded_other} (other system) vs. {nonbonded_rest} (REST system)"
def compare_energies(REST_system, other_system, positions, rest_atoms, T_min, T):
# Create thermodynamic state
lambda_zero_alchemical_state = RESTState.from_system(REST_system)
thermostate = ThermodynamicState(REST_system, temperature=T_min)
compound_thermodynamic_state = CompoundThermodynamicState(thermostate,
composable_states=[lambda_zero_alchemical_state])
# Set alchemical parameters
beta_0 = 1 / (kB * T_min)
beta_m = 1 / (kB * T)
compound_thermodynamic_state.set_alchemical_parameters(beta_0, beta_m)
# Minimize and save energy
integrator = openmm.VerletIntegrator(1.0 * unit.femtosecond)
context = compound_thermodynamic_state.create_context(integrator)
context.setPositions(positions)
sampler_state = SamplerState.from_context(context)
REST_energy = compound_thermodynamic_state.reduced_potential(sampler_state)
# Compute energy for non-RESTified system
# Determine regions and scaling factors
solute = rest_atoms
solvent = [i for i in range(other_system.getNumParticles()) if i not in solute]
solute_scaling = beta_m / beta_0
inter_scaling = np.sqrt(beta_m / beta_0)
# Scale the terms in the bond force appropriately
bond_force = other_system.getForce(0)
for bond in range(bond_force.getNumBonds()):
p1, p2, length, k = bond_force.getBondParameters(bond)
if p1 in solute and p2 in solute:
bond_force.setBondParameters(bond, p1, p2, length, k * solute_scaling)
elif (p1 in solute and p2 in solvent) or (p1 in solvent and p2 in solute):
bond_force.setBondParameters(bond, p1, p2, length, k * inter_scaling)
# Scale the terms in the angle force appropriately
angle_force = other_system.getForce(1)
for angle_index in range(angle_force.getNumAngles()):
p1, p2, p3, angle, k = angle_force.getAngleParameters(angle_index)
if p1 in solute and p2 in solute and p3 in solute:
angle_force.setAngleParameters(angle_index, p1, p2, p3, angle, k * solute_scaling)
elif set([p1, p2, p3]).intersection(set(solute)) != set() and set([p1, p2, p3]).intersection(
set(solvent)) != set():
angle_force.setAngleParameters(angle_index, p1, p2, p3, angle, k * inter_scaling)
# Scale the terms in the torsion force appropriately
torsion_force = other_system.getForce(2)
for torsion_index in range(torsion_force.getNumTorsions()):
p1, p2, p3, p4, periodicity, phase, k = torsion_force.getTorsionParameters(torsion_index)
if p1 in solute and p2 in solute and p3 in solute and p4 in solute:
torsion_force.setTorsionParameters(torsion_index, p1, p2, p3, p4, periodicity, phase, k * solute_scaling)
elif set([p1, p2, p3, p4]).intersection(set(solute)) != set() and set([p1, p2, p3, p4]).intersection(
set(solvent)) != set():
torsion_force.setTorsionParameters(torsion_index, p1, p2, p3, p4, periodicity, phase, k * inter_scaling)
# Scale the exceptions in the nonbonded force appropriately
nb_force = other_system.getForce(3)
for nb_index in range(nb_force.getNumExceptions()):
p1, p2, chargeProd, sigma, epsilon = nb_force.getExceptionParameters(nb_index)
if p1 in solute and p2 in solute:
nb_force.setExceptionParameters(nb_index, p1, p2, solute_scaling * chargeProd, sigma, solute_scaling * epsilon)
elif (p1 in solute and p2 in solvent) or (p1 in solvent and p2 in solute):
nb_force.setExceptionParameters(nb_index, p1, p2, inter_scaling * chargeProd, sigma, inter_scaling * epsilon)
# Scale nonbonded interactions for solute-solute region by adding exceptions for all pairs of atoms
exception_pairs = [tuple(sorted([nb_force.getExceptionParameters(nb_index)[0], nb_force.getExceptionParameters(nb_index)[1]])) for nb_index in range(nb_force.getNumExceptions())]
solute_pairs = set([tuple(sorted(pair)) for pair in list(itertools.product(solute, solute))])
for pair in list(solute_pairs):
p1 = pair[0]
p2 = pair[1]
p1_charge, p1_sigma, p1_epsilon = nb_force.getParticleParameters(p1)
p2_charge, p2_sigma, p2_epsilon = nb_force.getParticleParameters(p2)
if p1 != p2:
if pair not in exception_pairs:
nb_force.addException(p1, p2, p1_charge * p2_charge * solute_scaling, 0.5 * (p1_sigma + p2_sigma),
np.sqrt(p1_epsilon * p2_epsilon) * solute_scaling)
# Scale nonbonded interactions for inter region by adding exceptions for all pairs of atoms
for pair in list(itertools.product(solute, solvent)):
p1 = pair[0]
p2 = int(pair[1]) # otherwise, will be a numpy int
p1_charge, p1_sigma, p1_epsilon = nb_force.getParticleParameters(p1)
p2_charge, p2_sigma, p2_epsilon = nb_force.getParticleParameters(p2)
if tuple(sorted(pair)) not in exception_pairs:
nb_force.addException(p1, p2, p1_charge * p2_charge * inter_scaling, 0.5 * (p1_sigma + p2_sigma), np.sqrt(p1_epsilon * p2_epsilon) * inter_scaling)
# Get energy
thermostate = ThermodynamicState(other_system, temperature=T_min)
integrator = openmm.VerletIntegrator(1.0 * unit.femtosecond)
context = thermostate.create_context(integrator)
context.setPositions(positions)
sampler_state = SamplerState.from_context(context)
nonREST_energy = thermostate.reduced_potential(sampler_state)
assert REST_energy - nonREST_energy < 1, f"The energy of the REST system ({REST_energy}) does not match " \
f"that of the non-REST system with terms manually scaled according to REST2({nonREST_energy})."
