void testPeriodicTorsions() {
ReferencePlatform platform;
System system;
system.addParticle(1.0);
system.addParticle(1.0);
system.addParticle(1.0);
system.addParticle(1.0);
VerletIntegrator integrator(0.01);
PeriodicTorsionForce* forceField = new PeriodicTorsionForce();
forceField->addTorsion(0, 1, 2, 3, 2, PI_M/3, 1.1);
system.addForce(forceField);
ASSERT(!forceField->usesPeriodicBoundaryConditions());
ASSERT(!system.usesPeriodicBoundaryConditions());
Context context(system, integrator, platform);
vector<Vec3> positions(4);
positions[0] = Vec3(0, 1, 0);
positions[1] = Vec3(0, 0, 0);
positions[2] = Vec3(1, 0, 0);
positions[3] = Vec3(1, 0, 2);
context.setPositions(positions);
State state = context.getState(State::Forces | State::Energy);
{
const vector<Vec3>& forces = state.getForces();
double torque = -2*1.1*std::sin(2*PI_M/3);
ASSERT_EQUAL_VEC(Vec3(0, 0, torque), forces[0], TOL);
ASSERT_EQUAL_VEC(Vec3(0, 0.5*torque, 0), forces[3], TOL);
ASSERT_EQUAL_VEC(Vec3(forces[0][0]+forces[1][0]+forces[2][0]+forces[3][0], forces[0][1]+forces[1][1]+forces[2][1]+forces[3][1], forces[0][2]+forces[1][2]+forces[2][2]+forces[3][2]), Vec3(0, 0, 0), TOL);
ASSERT_EQUAL_TOL(1.1*(1+std::cos(2*PI_M/3)), state.getPotentialEnergy(), TOL);
}
// Try changing the torsion parameters and make sure it's still correct.
forceField->setTorsionParameters(0, 0, 1, 2, 3, 3, PI_M/3.2, 1.3);
forceField->updateParametersInContext(context);
state = context.getState(State::Forces | State::Energy);
{
const vector<Vec3>& forces = state.getForces();
double dtheta = (3*PI_M/2)-(PI_M/3.2);
double torque = -3*1.3*std::sin(dtheta);
ASSERT_EQUAL_VEC(Vec3(0, 0, torque), forces[0], TOL);
ASSERT_EQUAL_VEC(Vec3(0, 0.5*torque, 0), forces[3], TOL);
ASSERT_EQUAL_VEC(Vec3(forces[0][0]+forces[1][0]+forces[2][0]+forces[3][0], forces[0][1]+forces[1][1]+forces[2][1]+forces[3][1], forces[0][2]+forces[1][2]+forces[2][2]+forces[3][2]), Vec3(0, 0, 0), TOL);
ASSERT_EQUAL_TOL(1.3*(1+std::cos(dtheta)), state.getPotentialEnergy(), TOL);
}
}
void testHbond() {
// Create a system using a CustomHbondForce.
System customSystem;
customSystem.addParticle(1.0);
customSystem.addParticle(1.0);
customSystem.addParticle(1.0);
customSystem.addParticle(1.0);
customSystem.addParticle(1.0);
CustomHbondForce* custom = new CustomHbondForce("0.5*kr*(distance(d1,a1)-r0)^2 + 0.5*ktheta*(angle(a1,d1,d2)-theta0)^2 + 0.5*kpsi*(angle(d1,a1,a2)-psi0)^2 + kchi*(1+cos(n*dihedral(a3,a2,a1,d1)-chi0))");
custom->addPerDonorParameter("r0");
custom->addPerDonorParameter("theta0");
custom->addPerDonorParameter("psi0");
custom->addPerAcceptorParameter("chi0");
custom->addPerAcceptorParameter("n");
custom->addGlobalParameter("kr", 0.4);
custom->addGlobalParameter("ktheta", 0.5);
custom->addGlobalParameter("kpsi", 0.6);
custom->addGlobalParameter("kchi", 0.7);
vector<double> parameters(3);
parameters[0] = 1.5;
parameters[1] = 1.7;
parameters[2] = 1.9;
custom->addDonor(1, 0, -1, parameters);
parameters.resize(2);
parameters[0] = 2.1;
parameters[1] = 2;
custom->addAcceptor(2, 3, 4, parameters);
custom->setCutoffDistance(10.0);
customSystem.addForce(custom);
// Create an identical system using HarmonicBondForce, HarmonicAngleForce, and PeriodicTorsionForce.
System standardSystem;
standardSystem.addParticle(1.0);
standardSystem.addParticle(1.0);
standardSystem.addParticle(1.0);
standardSystem.addParticle(1.0);
standardSystem.addParticle(1.0);
HarmonicBondForce* bond = new HarmonicBondForce();
bond->addBond(1, 2, 1.5, 0.4);
standardSystem.addForce(bond);
HarmonicAngleForce* angle = new HarmonicAngleForce();
angle->addAngle(0, 1, 2, 1.7, 0.5);
angle->addAngle(1, 2, 3, 1.9, 0.6);
standardSystem.addForce(angle);
PeriodicTorsionForce* torsion = new PeriodicTorsionForce();
torsion->addTorsion(1, 2, 3, 4, 2, 2.1, 0.7);
standardSystem.addForce(torsion);
// Set the atoms in various positions, and verify that both systems give identical forces and energy.
OpenMM_SFMT::SFMT sfmt;
init_gen_rand(0, sfmt);
vector<Vec3> positions(5);
VerletIntegrator integrator1(0.01);
VerletIntegrator integrator2(0.01);
Context c1(customSystem, integrator1, platform);
Context c2(standardSystem, integrator2, platform);
for (int i = 0; i < 10; i++) {
for (int j = 0; j < (int) positions.size(); j++)
positions[j] = Vec3(2.0*genrand_real2(sfmt), 2.0*genrand_real2(sfmt), 2.0*genrand_real2(sfmt));
c1.setPositions(positions);
c2.setPositions(positions);
State s1 = c1.getState(State::Forces | State::Energy);
State s2 = c2.getState(State::Forces | State::Energy);
for (int i = 0; i < customSystem.getNumParticles(); i++)
ASSERT_EQUAL_VEC(s2.getForces()[i], s1.getForces()[i], TOL);
ASSERT_EQUAL_TOL(s2.getPotentialEnergy(), s1.getPotentialEnergy(), TOL);
}
// Try changing the parameters and make sure it's still correct.
parameters.resize(3);
parameters[0] = 1.4;
parameters[1] = 1.7;
parameters[2] = 1.9;
custom->setDonorParameters(0, 1, 0, -1, parameters);
parameters.resize(2);
parameters[0] = 2.2;
parameters[1] = 2;
custom->setAcceptorParameters(0, 2, 3, 4, parameters);
bond->setBondParameters(0, 1, 2, 1.4, 0.4);
torsion->setTorsionParameters(0, 1, 2, 3, 4, 2, 2.2, 0.7);
custom->updateParametersInContext(c1);
bond->updateParametersInContext(c2);
torsion->updateParametersInContext(c2);
State s1 = c1.getState(State::Forces | State::Energy);
State s2 = c2.getState(State::Forces | State::Energy);
for (int i = 0; i < customSystem.getNumParticles(); i++)
ASSERT_EQUAL_VEC(s2.getForces()[i], s1.getForces()[i], TOL);
ASSERT_EQUAL_TOL(s2.getPotentialEnergy(), s1.getPotentialEnergy(), TOL);
}