C++ NonbondedForce::addParticle方法代码示例

void testPeriodic() {
    System system;
    system.addParticle(1.0);
    system.addParticle(1.0);
    system.addParticle(1.0);
    VerletIntegrator integrator(0.01);
    NonbondedForce* nonbonded = new NonbondedForce();
    nonbonded->addParticle(1.0, 1, 0);
    nonbonded->addParticle(1.0, 1, 0);
    nonbonded->addParticle(1.0, 1, 0);
    nonbonded->addException(0, 1, 0.0, 1.0, 0.0);
    nonbonded->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
    const double cutoff = 2.0;
    nonbonded->setCutoffDistance(cutoff);
    system.setDefaultPeriodicBoxVectors(Vec3(4, 0, 0), Vec3(0, 4, 0), Vec3(0, 0, 4));
    system.addForce(nonbonded);
    Context context(system, integrator, platform);
    vector<Vec3> positions(3);
    positions[0] = Vec3(0, 0, 0);
    positions[1] = Vec3(2, 0, 0);
    positions[2] = Vec3(3, 0, 0);
    context.setPositions(positions);
    State state = context.getState(State::Forces | State::Energy);
    const vector<Vec3>& forces = state.getForces();
    const double eps = 78.3;
    const double krf = (1.0/(cutoff*cutoff*cutoff))*(eps-1.0)/(2.0*eps+1.0);
    const double crf = (1.0/cutoff)*(3.0*eps)/(2.0*eps+1.0);
    const double force = ONE_4PI_EPS0*(1.0)*(1.0-2.0*krf*1.0);
    ASSERT_EQUAL_VEC(Vec3(force, 0, 0), forces[0], TOL);
    ASSERT_EQUAL_VEC(Vec3(-force, 0, 0), forces[1], TOL);
    ASSERT_EQUAL_VEC(Vec3(0, 0, 0), forces[2], TOL);
    ASSERT_EQUAL_TOL(2*ONE_4PI_EPS0*(1.0)*(1.0+krf*1.0-crf), state.getPotentialEnergy(), TOL);
}

void testEwald2Ions() {
    System system;
    system.addParticle(1.0);
    system.addParticle(1.0);
    VerletIntegrator integrator(0.01);
    NonbondedForce* nonbonded = new NonbondedForce();
    nonbonded->addParticle(1.0, 1, 0);
    nonbonded->addParticle(-1.0, 1, 0);
    nonbonded->setNonbondedMethod(NonbondedForce::Ewald);
    const double cutoff = 2.0;
    nonbonded->setCutoffDistance(cutoff);
    nonbonded->setEwaldErrorTolerance(TOL);
    system.setDefaultPeriodicBoxVectors(Vec3(6, 0, 0), Vec3(0, 6, 0), Vec3(0, 0, 6));
    system.addForce(nonbonded);
    Context context(system, integrator, platform);
    vector<Vec3> positions(2);
    positions[0] = Vec3(3.048000,2.764000,3.156000);
    positions[1] = Vec3(2.809000,2.888000,2.571000);
    context.setPositions(positions);
    State state = context.getState(State::Forces | State::Energy);
    const vector<Vec3>& forces = state.getForces();

    ASSERT_EQUAL_VEC(Vec3(-123.711,  64.1877, -302.716), forces[0], 10*TOL);
    ASSERT_EQUAL_VEC(Vec3( 123.711, -64.1877,  302.716), forces[1], 10*TOL);
    ASSERT_EQUAL_TOL(-217.276, state.getPotentialEnergy(), 0.01/*10*TOL*/);
}

void testCutoff() {
    System system;
    system.addParticle(1.0);
    system.addParticle(1.0);
    system.addParticle(1.0);
    VerletIntegrator integrator(0.01);
    NonbondedForce* forceField = new NonbondedForce();
    forceField->addParticle(1.0, 1, 0);
    forceField->addParticle(1.0, 1, 0);
    forceField->addParticle(1.0, 1, 0);
    forceField->setNonbondedMethod(NonbondedForce::CutoffNonPeriodic);
    const double cutoff = 2.9;
    forceField->setCutoffDistance(cutoff);
    const double eps = 50.0;
    forceField->setReactionFieldDielectric(eps);
    system.addForce(forceField);
    Context context(system, integrator, platform);
    vector<Vec3> positions(3);
    positions[0] = Vec3(0, 0, 0);
    positions[1] = Vec3(0, 2, 0);
    positions[2] = Vec3(0, 3, 0);
    context.setPositions(positions);
    State state = context.getState(State::Forces | State::Energy);
    const vector<Vec3>& forces = state.getForces();
    const double krf = (1.0/(cutoff*cutoff*cutoff))*(eps-1.0)/(2.0*eps+1.0);
    const double crf = (1.0/cutoff)*(3.0*eps)/(2.0*eps+1.0);
    const double force1 = ONE_4PI_EPS0*(1.0)*(0.25-2.0*krf*2.0);
    const double force2 = ONE_4PI_EPS0*(1.0)*(1.0-2.0*krf*1.0);
    ASSERT_EQUAL_VEC(Vec3(0, -force1, 0), forces[0], TOL);
    ASSERT_EQUAL_VEC(Vec3(0, force1-force2, 0), forces[1], TOL);
    ASSERT_EQUAL_VEC(Vec3(0, force2, 0), forces[2], TOL);
    const double energy1 = ONE_4PI_EPS0*(1.0)*(0.5+krf*4.0-crf);
    const double energy2 = ONE_4PI_EPS0*(1.0)*(1.0+krf*1.0-crf);
    ASSERT_EQUAL_TOL(energy1+energy2, state.getPotentialEnergy(), TOL);
}

void testForceEnergyConsistency() {
    // Create a box of polarizable particles.
    
    const int gridSize = 3;
    const int numAtoms = gridSize*gridSize*gridSize;
    const double spacing = 0.6;
    const double boxSize = spacing*(gridSize+1);
    const double temperature = 300.0;
    const double temperatureDrude = 10.0;
    System system;
    vector<Vec3> positions;
    NonbondedForce* nonbonded = new NonbondedForce();
    DrudeForce* drude = new DrudeForce();
    system.addForce(nonbonded);
    system.addForce(drude);
    system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
    nonbonded->setNonbondedMethod(NonbondedForce::PME);
    nonbonded->setCutoffDistance(1.0);
    nonbonded->setUseSwitchingFunction(true);
    nonbonded->setSwitchingDistance(0.9);
    nonbonded->setEwaldErrorTolerance(5e-5);
    for (int i = 0; i < numAtoms; i++) {
        int startIndex = system.getNumParticles();
        system.addParticle(1.0);
        system.addParticle(1.0);
        nonbonded->addParticle(1.0, 0.3, 1.0);
        nonbonded->addParticle(-1.0, 0.3, 1.0);
        nonbonded->addException(startIndex, startIndex+1, 0, 1, 0);
        drude->addParticle(startIndex+1, startIndex, -1, -1, -1, -1.0, 0.001, 1, 1);
    }
    for (int i = 0; i < gridSize; i++)
        for (int j = 0; j < gridSize; j++)
            for (int k = 0; k < gridSize; k++) {
                Vec3 pos(i*spacing, j*spacing, k*spacing);
                positions.push_back(pos);
                positions.push_back(pos);
            }
    
    // Simulate it and check that force and energy remain consistent.
    
    DrudeLangevinIntegrator integ(temperature, 50.0, temperatureDrude, 50.0, 0.001);
    Platform& platform = Platform::getPlatformByName("Reference");
    Context context(system, integ, platform);
    context.setPositions(positions);
    State prevState;
    for (int i = 0; i < 100; i++) {
        State state = context.getState(State::Energy | State::Forces | State::Positions);
        if (i > 0) {
            double expectedEnergyChange = 0;
            for (int j = 0; j < system.getNumParticles(); j++) {
                Vec3 delta = state.getPositions()[j]-prevState.getPositions()[j];
                expectedEnergyChange -= 0.5*(state.getForces()[j]+prevState.getForces()[j]).dot(delta);
            }
            ASSERT_EQUAL_TOL(expectedEnergyChange, state.getPotentialEnergy()-prevState.getPotentialEnergy(), 0.05);
        }
        prevState = state;
        integ.step(1);
    }
}

void testWaterSystem() {
    ReferencePlatform platform;
    System system;
    static int numParticles = 648;
    const double boxSize = 1.86206;

    for (int i = 0 ; i < numParticles ; i++)
    {
       system.addParticle(1.0);
    }
    VerletIntegrator integrator(0.01);
    NonbondedForce* nonbonded = new NonbondedForce();
    for (int i = 0 ; i < numParticles/3 ; i++)
    {
      nonbonded->addParticle(-0.82, 1, 0);
      nonbonded->addParticle(0.41, 1, 0);
      nonbonded->addParticle(0.41, 1, 0);
    }
    nonbonded->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
    const double cutoff = 0.8;
    nonbonded->setCutoffDistance(cutoff);
    system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
    nonbonded->setEwaldErrorTolerance(EWALD_TOL);
    system.addForce(nonbonded);
    Context context(system, integrator, platform);
    vector<Vec3> positions(numParticles);
    #include "water.dat"
    context.setPositions(positions);
    State state1 = context.getState(State::Forces | State::Energy);
    const vector<Vec3>& forces = state1.getForces();

// Take a small step in the direction of the energy gradient.
    
    double norm = 0.0;
    for (int i = 0; i < numParticles; ++i) {
        Vec3 f = state1.getForces()[i];
        norm += f[0]*f[0] + f[1]*f[1] + f[2]*f[2];
    }


    norm = std::sqrt(norm);
    const double delta = 1e-3;
    double step = delta/norm;
    for (int i = 0; i < numParticles; ++i) {
        Vec3 p = positions[i];
        Vec3 f = state1.getForces()[i];
        positions[i] = Vec3(p[0]-f[0]*step, p[1]-f[1]*step, p[2]-f[2]*step);
    }
    context.setPositions(positions);
    
    // See whether the potential energy changed by the expected amount.
    
    nonbonded->setNonbondedMethod(NonbondedForce::Ewald);
    State state2 = context.getState(State::Energy);
    ASSERT_EQUAL_TOL(norm, (state2.getPotentialEnergy()-state1.getPotentialEnergy())/delta, 0.01)


}

void testLargeSystem() {
    const int numMolecules = 50;
    const int numParticles = numMolecules*2;
    const double cutoff = 2.0;
    const double boxSize = 5.0;
    const double tolerance = 5;
    System system;
    system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
    NonbondedForce* nonbonded = new NonbondedForce();
    nonbonded->setCutoffDistance(cutoff);
    nonbonded->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
    system.addForce(nonbonded);

    // Create a cloud of molecules.

    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);
    vector<Vec3> positions(numParticles);
    for (int i = 0; i < numMolecules; i++) {
        system.addParticle(1.0);
        system.addParticle(1.0);
        nonbonded->addParticle(-1.0, 0.2, 0.2);
        nonbonded->addParticle(1.0, 0.2, 0.2);
        positions[2*i] = Vec3(boxSize*genrand_real2(sfmt), boxSize*genrand_real2(sfmt), boxSize*genrand_real2(sfmt));
        positions[2*i+1] = Vec3(positions[2*i][0]+1.0, positions[2*i][1], positions[2*i][2]);
        system.addConstraint(2*i, 2*i+1, 1.0);
    }

    // Minimize it and verify that the energy has decreased.
    
    ReferencePlatform platform;
    VerletIntegrator integrator(0.01);
    Context context(system, integrator, platform);
    context.setPositions(positions);
    State initialState = context.getState(State::Forces | State::Energy);
    LocalEnergyMinimizer::minimize(context, tolerance);
    State finalState = context.getState(State::Forces | State::Energy | State::Positions);
    ASSERT(finalState.getPotentialEnergy() < initialState.getPotentialEnergy());

    // Compute the force magnitude, subtracting off any component parallel to a constraint, and
    // check that it satisfies the requested tolerance.

    double forceNorm = 0.0;
    for (int i = 0; i < numParticles; i += 2) {
        Vec3 dir = finalState.getPositions()[i+1]-finalState.getPositions()[i];
        double distance = sqrt(dir.dot(dir));
        dir *= 1.0/distance;
        Vec3 f = finalState.getForces()[i];
        f -= dir*dir.dot(f);
        forceNorm += f.dot(f);
        f = finalState.getForces()[i+1];
        f -= dir*dir.dot(f);
        forceNorm += f.dot(f);
    }
    forceNorm = sqrt(forceNorm/(4*numMolecules));
    ASSERT(forceNorm < 3*tolerance);
}

void testCutoffAndPeriodic() {
    ReferencePlatform platform;
    System system;
    system.addParticle(1.0);
    system.addParticle(1.0);
    LangevinIntegrator integrator(0, 0.1, 0.01);
    GBSAOBCForce* gbsa = new GBSAOBCForce();
    NonbondedForce* nonbonded = new NonbondedForce();
    gbsa->addParticle(-1, 0.15, 1);
    nonbonded->addParticle(-1, 1, 0);
    gbsa->addParticle(1, 0.15, 1);
    nonbonded->addParticle(1, 1, 0);
    const double cutoffDistance = 3.0;
    const double boxSize = 10.0;
    nonbonded->setCutoffDistance(cutoffDistance);
    gbsa->setCutoffDistance(cutoffDistance);
    system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
    system.addForce(gbsa);
    system.addForce(nonbonded);
    vector<Vec3> positions(2);
    positions[0] = Vec3(0, 0, 0);
    positions[1] = Vec3(2, 0, 0);

    // Calculate the forces for both cutoff and periodic with two different atom positions.

    nonbonded->setNonbondedMethod(NonbondedForce::CutoffNonPeriodic);
    gbsa->setNonbondedMethod(GBSAOBCForce::CutoffNonPeriodic);
    Context context(system, integrator, platform);
    context.setPositions(positions);
    State state1 = context.getState(State::Forces);
    nonbonded->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
    gbsa->setNonbondedMethod(GBSAOBCForce::CutoffPeriodic);
    context.reinitialize();
    context.setPositions(positions);
    State state2 = context.getState(State::Forces);
    positions[1][0]+= boxSize;
    nonbonded->setNonbondedMethod(NonbondedForce::CutoffNonPeriodic);
    gbsa->setNonbondedMethod(GBSAOBCForce::CutoffNonPeriodic);
    context.reinitialize();
    context.setPositions(positions);
    State state3 = context.getState(State::Forces);
    nonbonded->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
    gbsa->setNonbondedMethod(GBSAOBCForce::CutoffPeriodic);
    context.reinitialize();
    context.setPositions(positions);
    State state4 = context.getState(State::Forces);

    // All forces should be identical, exception state3 which should be zero.

    ASSERT_EQUAL_VEC(state1.getForces()[0], state2.getForces()[0], 0.01);
    ASSERT_EQUAL_VEC(state1.getForces()[1], state2.getForces()[1], 0.01);
    ASSERT_EQUAL_VEC(state1.getForces()[0], state4.getForces()[0], 0.01);
    ASSERT_EQUAL_VEC(state1.getForces()[1], state4.getForces()[1], 0.01);
    ASSERT_EQUAL_VEC(state3.getForces()[0], Vec3(0, 0, 0), 0.01);
    ASSERT_EQUAL_VEC(state3.getForces()[1], Vec3(0, 0, 0), 0.01);
}

void testConstraints() {
    const int numMolecules = 10;
    const int numParticles = numMolecules*3;
    const int numConstraints = numMolecules*3;
    const double temp = 100.0;
    System system;
    LangevinIntegrator integrator(temp, 2.0, 0.001);
    integrator.setConstraintTolerance(1e-5);
    NonbondedForce* forceField = new NonbondedForce();
    for (int i = 0; i < numMolecules; ++i) {
        system.addParticle(16.0);
        system.addParticle(1.0);
        system.addParticle(1.0);
        forceField->addParticle(-0.82, 0.317, 0.65);
        forceField->addParticle(0.41, 1.0, 0.0);
        forceField->addParticle(0.41, 1.0, 0.0);
        system.addConstraint(i*3, i*3+1, 0.1);
        system.addConstraint(i*3, i*3+2, 0.1);
        system.addConstraint(i*3+1, i*3+2, 0.163);
    }
    system.addForce(forceField);
    Context context(system, integrator, platform);
    vector<Vec3> positions(numParticles);
    vector<Vec3> velocities(numParticles);
    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);

    for (int i = 0; i < numMolecules; ++i) {
        positions[i*3] = Vec3((i%4)*0.4, (i/4)*0.4, 0);
        positions[i*3+1] = positions[i*3]+Vec3(0.1, 0, 0);
        positions[i*3+2] = positions[i*3]+Vec3(-0.03333, 0.09428, 0);
        velocities[i*3] = Vec3(genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5);
        velocities[i*3+1] = Vec3(genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5);
        velocities[i*3+2] = Vec3(genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5);
    }
    context.setPositions(positions);
    context.setVelocities(velocities);

    // Simulate it and see whether the constraints remain satisfied.

    for (int i = 0; i < 1000; ++i) {
        integrator.step(1);
        State state = context.getState(State::Positions | State::Forces);
        for (int j = 0; j < numConstraints; ++j) {
            int particle1, particle2;
            double distance;
            system.getConstraintParameters(j, particle1, particle2, distance);
            Vec3 p1 = state.getPositions()[particle1];
            Vec3 p2 = state.getPositions()[particle2];
            double dist = std::sqrt((p1[0]-p2[0])*(p1[0]-p2[0])+(p1[1]-p2[1])*(p1[1]-p2[1])+(p1[2]-p2[2])*(p1[2]-p2[2]));
            ASSERT_EQUAL_TOL(distance, dist, 1e-5);
        }
    }
}

void testSerialization() {
    // Create a Force.

    NonbondedForce force;
    force.setNonbondedMethod(NonbondedForce::CutoffPeriodic);
    force.setCutoffDistance(2.0);
    force.setEwaldErrorTolerance(1e-3);
    force.setReactionFieldDielectric(50.0);
    force.setUseDispersionCorrection(false);
    force.addParticle(1, 0.1, 0.01);
    force.addParticle(0.5, 0.2, 0.02);
    force.addParticle(-0.5, 0.3, 0.03);
    force.addException(0, 1, 2, 0.5, 0.1);
    force.addException(1, 2, 0.2, 0.4, 0.2);

    // Serialize and then deserialize it.

    stringstream buffer;
    XmlSerializer::serialize<NonbondedForce>(&force, "Force", buffer);
    NonbondedForce* copy = XmlSerializer::deserialize<NonbondedForce>(buffer);

    // Compare the two forces to see if they are identical.

    NonbondedForce& force2 = *copy;
    ASSERT_EQUAL(force.getNonbondedMethod(), force2.getNonbondedMethod());
    ASSERT_EQUAL(force.getCutoffDistance(), force2.getCutoffDistance());
    ASSERT_EQUAL(force.getEwaldErrorTolerance(), force2.getEwaldErrorTolerance());
    ASSERT_EQUAL(force.getReactionFieldDielectric(), force2.getReactionFieldDielectric());
    ASSERT_EQUAL(force.getUseDispersionCorrection(), force2.getUseDispersionCorrection());
    ASSERT_EQUAL(force.getNumParticles(), force2.getNumParticles());
    for (int i = 0; i < force.getNumParticles(); i++) {
        double charge1, sigma1, epsilon1;
        double charge2, sigma2, epsilon2;
        force.getParticleParameters(i, charge1, sigma1, epsilon1);
        force2.getParticleParameters(i, charge2, sigma2, epsilon2);
        ASSERT_EQUAL(charge1, charge2);
        ASSERT_EQUAL(sigma1, sigma2);
        ASSERT_EQUAL(epsilon1, epsilon2);
    }
    ASSERT_EQUAL(force.getNumExceptions(), force2.getNumExceptions());
    for (int i = 0; i < force.getNumExceptions(); i++) {
        int a1, a2, b1, b2;
        double charge1, sigma1, epsilon1;
        double charge2, sigma2, epsilon2;
        force.getExceptionParameters(i, a1, b1, charge1, sigma1, epsilon1);
        force2.getExceptionParameters(i, a2, b2, charge2, sigma2, epsilon2);
        ASSERT_EQUAL(a1, a2);
        ASSERT_EQUAL(b1, b2);
        ASSERT_EQUAL(charge1, charge2);
        ASSERT_EQUAL(sigma1, sigma2);
        ASSERT_EQUAL(epsilon1, epsilon2);
    }
}

void testTruncatedOctahedron() {
    const int numMolecules = 50;
    const int numParticles = numMolecules*2;
    const float cutoff = 2.0;
    Vec3 a(6.7929, 0, 0);
    Vec3 b(-2.264163559406279, 6.404455775962287, 0);
    Vec3 c(-2.264163559406279, -3.2019384603140684, 5.54658849047036);

    System system;
    system.setDefaultPeriodicBoxVectors(a, b, c);
    NonbondedForce* force = new NonbondedForce();
    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);
    vector<Vec3> positions(numParticles);

    force->setCutoffDistance(cutoff);
    force->setNonbondedMethod(NonbondedForce::CutoffPeriodic);

    for (int i = 0; i < numMolecules; i++) {
        system.addParticle(1.0);
        system.addParticle(1.0);
        force->addParticle(-1, 0.2, 0.2);
        force->addParticle(1, 0.2, 0.2);
        positions[2*i] = a*(5*genrand_real2(sfmt)-2) + b*(5*genrand_real2(sfmt)-2) + c*(5*genrand_real2(sfmt)-2);
        positions[2*i+1] = positions[2*i] + Vec3(1.0, 0.0, 0.0);
        system.addConstraint(2*i, 2*i+1, 1.0);
    }
    system.addForce(force);

    VerletIntegrator integrator(0.01);
    Context context(system, integrator, Platform::getPlatformByName("Reference"));
    context.setPositions(positions);
    State initialState = context.getState(State::Positions | State::Energy, true);
    for (int i = 0; i < numMolecules; i++) {
        Vec3 center = (initialState.getPositions()[2*i]+initialState.getPositions()[2*i+1])*0.5;
        ASSERT(center[0] >= 0.0);
        ASSERT(center[1] >= 0.0);
        ASSERT(center[2] >= 0.0);
        ASSERT(center[0] <= a[0]);
        ASSERT(center[1] <= b[1]);
        ASSERT(center[2] <= c[2]);
    }
    double initialEnergy = initialState.getPotentialEnergy();

    context.setState(initialState);
    State finalState = context.getState(State::Positions | State::Energy, true);
    double finalEnergy = finalState.getPotentialEnergy();

    ASSERT_EQUAL_TOL(initialEnergy, finalEnergy, 1e-4);
}

void testEwaldExact() {

//    Use a NaCl crystal to compare the calculated and Madelung energies

    const int numParticles = 1000;
    const double cutoff = 1.0;
    const double boxSize = 2.82;

    ReferencePlatform platform;
    System system;

    for (int i = 0; i < numParticles/2; i++)
        system.addParticle(22.99);
    for (int i = 0; i < numParticles/2; i++)
        system.addParticle(35.45);
    VerletIntegrator integrator(0.01);
    NonbondedForce* nonbonded = new NonbondedForce();
    for (int i = 0; i < numParticles/2; i++)
        nonbonded->addParticle(1.0, 1.0,0.0);
    for (int i = 0; i < numParticles/2; i++)
        nonbonded->addParticle(-1.0, 1.0,0.0);
    nonbonded->setNonbondedMethod(NonbondedForce::Ewald);
    nonbonded->setCutoffDistance(cutoff);
    system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
    nonbonded->setEwaldErrorTolerance(EWALD_TOL);
    system.addForce(nonbonded);
    Context context(system, integrator, platform);
    vector<Vec3> positions(numParticles);
    #include "nacl_crystal.dat"
    context.setPositions(positions);

    State state = context.getState(State::Forces | State::Energy);
    const vector<Vec3>& forces = state.getForces();

//   The potential energy of an ion in a crystal is 
//   E = - (M*e^2/ 4*pi*epsilon0*a0),
//   where 
//   M            :    Madelung constant (dimensionless, for FCC cells such as NaCl it is 1.7476)
//   e            :    1.6022 × 10−19 C
//   4*pi*epsilon0:     1.112 × 10−10 C²/(J m)
//   a0           :    0.282 x 10-9 m (perfect cell)
// 
//   E is then the energy per pair of ions, so for our case
//   E has to be divided by 2 (per ion), multiplied by N(avogadro), multiplied by number of particles, and divided by 1000 for kJ
    double exactEnergy        = - (1.7476 * 1.6022e-19 * 1.6022e-19  * 6.02214e+23 * numParticles) / (1.112e-10 * 0.282e-9 * 2 * 1000);
    //cout << "exact\t\t: " << exactEnergy << endl;
    //cout << "calc\t\t: " << state.getPotentialEnergy() << endl;
    ASSERT_EQUAL_TOL(exactEnergy, state.getPotentialEnergy(), 100*EWALD_TOL);

}

void testTriclinic() {
    // Create a triclinic box containing eight particles.

    System system;
    system.setDefaultPeriodicBoxVectors(Vec3(2.5, 0, 0), Vec3(0.5, 3.0, 0), Vec3(0.7, 0.9, 3.5));
    for (int i = 0; i < 8; i++)
        system.addParticle(1.0);
    NonbondedForce* force = new NonbondedForce();
    system.addForce(force);
    force->setNonbondedMethod(NonbondedForce::PME);
    force->setCutoffDistance(1.0);
    force->setPMEParameters(3.45891, 32, 40, 48);
    for (int i = 0; i < 4; i++)
        force->addParticle(-1, 0.440104, 0.4184); // Cl parameters
    for (int i = 0; i < 4; i++)
        force->addParticle(1, 0.332840, 0.0115897); // Na parameters
    vector<Vec3> positions(8);
    positions[0] = Vec3(1.744, 2.788, 3.162);
    positions[1] = Vec3(1.048, 0.762, 2.340);
    positions[2] = Vec3(2.489, 1.570, 2.817);
    positions[3] = Vec3(1.027, 1.893, 3.271);
    positions[4] = Vec3(0.937, 0.825, 0.009);
    positions[5] = Vec3(2.290, 1.887, 3.352);
    positions[6] = Vec3(1.266, 1.111, 2.894);
    positions[7] = Vec3(0.933, 1.862, 3.490);

    // Compute the forces and energy.

    VerletIntegrator integ(0.001);
    Context context(system, integ, platform);
    context.setPositions(positions);
    State state = context.getState(State::Forces | State::Energy);

    // Compare them to values computed by Gromacs.

    double expectedEnergy = -963.370;
    vector<Vec3> expectedForce(8);
    expectedForce[0] = Vec3(4.25253e+01, -1.23503e+02, 1.22139e+02);
    expectedForce[1] = Vec3(9.74752e+01, 1.68213e+02, 1.93169e+02);
    expectedForce[2] = Vec3(-1.50348e+02, 1.29165e+02, 3.70435e+02);
    expectedForce[3] = Vec3(9.18644e+02, -3.52571e+00, -1.34772e+03);
    expectedForce[4] = Vec3(-1.61193e+02, 9.01528e+01, -7.12904e+01);
    expectedForce[5] = Vec3(2.82630e+02, 2.78029e+01, -3.72864e+02);
    expectedForce[6] = Vec3(-1.47454e+02, -2.14448e+02, -3.55789e+02);
    expectedForce[7] = Vec3(-8.82195e+02, -7.39132e+01, 1.46202e+03);
    for (int i = 0; i < 8; i++) {
        ASSERT_EQUAL_VEC(expectedForce[i], state.getForces()[i], 1e-4);
    }
    ASSERT_EQUAL_TOL(expectedEnergy, state.getPotentialEnergy(), 1e-4);
}

void testConstraints() {
    const int numParticles = 8;
    const int numConstraints = 5;
    System system;
    VariableVerletIntegrator integrator(1e-5);
    integrator.setConstraintTolerance(1e-5);
    NonbondedForce* forceField = new NonbondedForce();
    for (int i = 0; i < numParticles; ++i) {
        system.addParticle(10.0);
        forceField->addParticle((i%2 == 0 ? 0.2 : -0.2), 0.5, 5.0);
    }
    system.addConstraint(0, 1, 1.0);
    system.addConstraint(1, 2, 1.0);
    system.addConstraint(2, 3, 1.0);
    system.addConstraint(4, 5, 1.0);
    system.addConstraint(6, 7, 1.0);
    system.addForce(forceField);
    Context context(system, integrator, platform);
    vector<Vec3> positions(numParticles);
    vector<Vec3> velocities(numParticles);
    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);

    for (int i = 0; i < numParticles; ++i) {
        positions[i] = Vec3(i/2, (i+1)/2, 0);
        velocities[i] = Vec3(genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5);
    }
    context.setPositions(positions);
    context.setVelocities(velocities);

    // Simulate it and see whether the constraints remain satisfied.

    double initialEnergy = 0.0;
    for (int i = 0; i < 1000; ++i) {
        State state = context.getState(State::Positions | State::Energy | State::Velocities | State::Forces);
            for (int j = 0; j < numConstraints; ++j) {
                int particle1, particle2;
                double distance;
                system.getConstraintParameters(j, particle1, particle2, distance);
                Vec3 p1 = state.getPositions()[particle1];
                Vec3 p2 = state.getPositions()[particle2];
                double dist = std::sqrt((p1[0]-p2[0])*(p1[0]-p2[0])+(p1[1]-p2[1])*(p1[1]-p2[1])+(p1[2]-p2[2])*(p1[2]-p2[2]));
                ASSERT_EQUAL_TOL(distance, dist, 1e-4);
            }
        double energy = state.getKineticEnergy()+state.getPotentialEnergy();
        if (i == 1)
            initialEnergy = energy;
        else if (i > 1)
            ASSERT_EQUAL_TOL(initialEnergy, energy, 0.01);
        integrator.step(1);
    }
    double finalTime = context.getState(State::Positions).getTime();
    ASSERT(finalTime > 0.1);

    // Now try the stepTo() method.

    finalTime += 0.5;
    integrator.stepTo(finalTime);
    ASSERT_EQUAL(finalTime, context.getState(State::Positions).getTime());
}

void testRandomSeed() {
    const int numParticles = 8;
    const double temp = 100.0;
    const double collisionFreq = 10.0;
    System system;
    VerletIntegrator integrator(0.01);
    NonbondedForce* forceField = new NonbondedForce();
    for (int i = 0; i < numParticles; ++i) {
        system.addParticle(2.0);
        forceField->addParticle((i%2 == 0 ? 1.0 : -1.0), 1.0, 5.0);
    }
    system.addForce(forceField);
    AndersenThermostat* thermostat = new AndersenThermostat(temp, collisionFreq);
    system.addForce(thermostat);
    vector<Vec3> positions(numParticles);
    vector<Vec3> velocities(numParticles);
    for (int i = 0; i < numParticles; ++i) {
        positions[i] = Vec3((i%2 == 0 ? 2 : -2), (i%4 < 2 ? 2 : -2), (i < 4 ? 2 : -2));
        velocities[i] = Vec3(0, 0, 0);
    }

    // Try twice with the same random seed.

    thermostat->setRandomNumberSeed(5);
    Context context(system, integrator, platform);
    context.setPositions(positions);
    context.setVelocities(velocities);
    integrator.step(10);
    State state1 = context.getState(State::Positions);
    context.reinitialize();
    context.setPositions(positions);
    context.setVelocities(velocities);
    integrator.step(10);
    State state2 = context.getState(State::Positions);

    // Try twice with a different random seed.

    thermostat->setRandomNumberSeed(10);
    context.reinitialize();
    context.setPositions(positions);
    context.setVelocities(velocities);
    integrator.step(10);
    State state3 = context.getState(State::Positions);
    context.reinitialize();
    context.setPositions(positions);
    context.setVelocities(velocities);
    integrator.step(10);
    State state4 = context.getState(State::Positions);

    // Compare the results.

    for (int i = 0; i < numParticles; i++) {
        for (int j = 0; j < 3; j++) {
            ASSERT(state1.getPositions()[i][j] == state2.getPositions()[i][j]);
            ASSERT(state3.getPositions()[i][j] == state4.getPositions()[i][j]);
            ASSERT(state1.getPositions()[i][j] != state3.getPositions()[i][j]);
        }
    }
}

void testParallelComputation(NonbondedForce::NonbondedMethod method) {
    System system;
    const int numParticles = 200;
    for (int i = 0; i < numParticles; i++)
        system.addParticle(1.0);
    NonbondedForce* force = new NonbondedForce();
    for (int i = 0; i < numParticles; i++)
        force->addParticle(i%2-0.5, 0.5, 1.0);
    force->setNonbondedMethod(method);
    system.addForce(force);
    system.setDefaultPeriodicBoxVectors(Vec3(5,0,0), Vec3(0,5,0), Vec3(0,0,5));
    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);
    vector<Vec3> positions(numParticles);
    for (int i = 0; i < numParticles; i++)
        positions[i] = Vec3(5*genrand_real2(sfmt), 5*genrand_real2(sfmt), 5*genrand_real2(sfmt));
    for (int i = 0; i < numParticles; ++i)
        for (int j = 0; j < i; ++j) {
            Vec3 delta = positions[i]-positions[j];
            if (delta.dot(delta) < 0.1)
                force->addException(i, j, 0, 1, 0);
        }
    
    // Create two contexts, one with a single device and one with two devices.
    
    VerletIntegrator integrator1(0.01);
    Context context1(system, integrator1, platform);
    context1.setPositions(positions);
    State state1 = context1.getState(State::Forces | State::Energy);
    VerletIntegrator integrator2(0.01);
    string deviceIndex = platform.getPropertyValue(context1, CudaPlatform::CudaDeviceIndex());
    map<string, string> props;
    props[CudaPlatform::CudaDeviceIndex()] = deviceIndex+","+deviceIndex;
    Context context2(system, integrator2, platform, props);
    context2.setPositions(positions);
    State state2 = context2.getState(State::Forces | State::Energy);
    
    // See if they agree.
    
    ASSERT_EQUAL_TOL(state1.getPotentialEnergy(), state2.getPotentialEnergy(), 1e-5);
    for (int i = 0; i < numParticles; i++)
        ASSERT_EQUAL_VEC(state1.getForces()[i], state2.getForces()[i], 1e-5);
    
    // Modify some particle parameters and see if they still agree.

    for (int i = 0; i < numParticles; i += 5) {
        double charge, sigma, epsilon;
        force->getParticleParameters(i, charge, sigma, epsilon);
        force->setParticleParameters(i, 0.9*charge, sigma, epsilon);
    }
    force->updateParametersInContext(context1);
    force->updateParametersInContext(context2);
    state1 = context1.getState(State::Forces | State::Energy);
    state2 = context2.getState(State::Forces | State::Energy);
    ASSERT_EQUAL_TOL(state1.getPotentialEnergy(), state2.getPotentialEnergy(), 1e-5);
    for (int i = 0; i < numParticles; i++)
        ASSERT_EQUAL_VEC(state1.getForces()[i], state2.getForces()[i], 1e-5);
}