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);
}
void testSwitchingFunction(NonbondedForce::NonbondedMethod method) {
ReferencePlatform platform;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(6, 0, 0), Vec3(0, 6, 0), Vec3(0, 0, 6));
system.addParticle(1.0);
system.addParticle(1.0);
VerletIntegrator integrator(0.01);
NonbondedForce* nonbonded = new NonbondedForce();
nonbonded->addParticle(0, 1.2, 1);
nonbonded->addParticle(0, 1.4, 2);
nonbonded->setNonbondedMethod(method);
nonbonded->setCutoffDistance(2.0);
nonbonded->setUseSwitchingFunction(true);
nonbonded->setSwitchingDistance(1.5);
nonbonded->setUseDispersionCorrection(false);
system.addForce(nonbonded);
Context context(system, integrator, platform);
vector<Vec3> positions(2);
positions[0] = Vec3(0, 0, 0);
double eps = SQRT_TWO;
// Compute the interaction at various distances.
for (double r = 1.0; r < 2.5; r += 0.1) {
positions[1] = Vec3(r, 0, 0);
context.setPositions(positions);
State state = context.getState(State::Forces | State::Energy);
// See if the energy is correct.
double x = 1.3/r;
double expectedEnergy = 4.0*eps*(std::pow(x, 12.0)-std::pow(x, 6.0));
double switchValue;
if (r <= 1.5)
switchValue = 1;
else if (r >= 2.0)
switchValue = 0;
else {
double t = (r-1.5)/0.5;
switchValue = 1+t*t*t*(-10+t*(15-t*6));
}
ASSERT_EQUAL_TOL(switchValue*expectedEnergy, state.getPotentialEnergy(), TOL);
// See if the force is the gradient of the energy.
double delta = 1e-3;
positions[1] = Vec3(r-delta, 0, 0);
context.setPositions(positions);
double e1 = context.getState(State::Energy).getPotentialEnergy();
positions[1] = Vec3(r+delta, 0, 0);
context.setPositions(positions);
double e2 = context.getState(State::Energy).getPotentialEnergy();
ASSERT_EQUAL_TOL((e2-e1)/(2*delta), state.getForces()[0][0], 1e-3);
}
}
void testArgonBox() {
const int gridSize = 8;
const double mass = 40.0; // Ar atomic mass
const double temp = 120.0; // K
const double epsilon = BOLTZ * temp; // L-J well depth for Ar
const double sigma = 0.34; // L-J size for Ar in nm
const double density = 0.8; // atoms / sigma^3
double cellSize = sigma / pow(density, 0.333);
double boxSize = gridSize * cellSize;
double cutoff = 2.0 * sigma;
// Create a box of argon atoms.
System system;
NonbondedForce* nonbonded = new NonbondedForce();
vector<Vec3> positions;
OpenMM_SFMT::SFMT sfmt;
init_gen_rand(0, sfmt);
const Vec3 half(0.5, 0.5, 0.5);
for (int i = 0; i < gridSize; i++) {
for (int j = 0; j < gridSize; j++) {
for (int k = 0; k < gridSize; k++) {
system.addParticle(mass);
nonbonded->addParticle(0, sigma, epsilon);
positions.push_back((Vec3(i, j, k) + half + Vec3(genrand_real2(sfmt), genrand_real2(sfmt), genrand_real2(sfmt))*0.1) * cellSize);
}
}
}
nonbonded->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
nonbonded->setCutoffDistance(cutoff);
system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
system.addForce(nonbonded);
VariableVerletIntegrator integrator(1e-5);
Context context(system, integrator, platform);
context.setPositions(positions);
context.setVelocitiesToTemperature(temp);
// Equilibrate.
integrator.stepTo(1.0);
// Simulate it and see whether energy remains constant.
State state0 = context.getState(State::Energy);
double initialEnergy = state0.getKineticEnergy() + state0.getPotentialEnergy();
for (int i = 0; i < 20; i++) {
double t = 1.0 + 0.05*(i+1);
integrator.stepTo(t);
State state = context.getState(State::Energy);
double energy = state.getKineticEnergy() + state.getPotentialEnergy();
ASSERT_EQUAL_TOL(initialEnergy, energy, 0.01);
}
}
/**
* Test an integrator that enforces constraints.
*/
void testConstraints() {
const int numParticles = 8;
System system;
CustomIntegrator integrator(0.002);
integrator.addPerDofVariable("oldx", 0);
integrator.addComputePerDof("v", "v+dt*f/m");
integrator.addComputePerDof("oldx", "x");
integrator.addComputePerDof("x", "x+dt*v");
integrator.addConstrainPositions();
integrator.addComputePerDof("v", "(x-oldx)/dt");
integrator.setConstraintTolerance(1e-5);
NonbondedForce* forceField = new NonbondedForce();
for (int i = 0; i < numParticles; ++i) {
system.addParticle(i%2 == 0 ? 5.0 : 10.0);
forceField->addParticle((i%2 == 0 ? 0.2 : -0.2), 0.5, 5.0);
}
for (int i = 0; i < numParticles-1; ++i)
system.addConstraint(i, i+1, 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);
for (int j = 0; j < system.getNumConstraints(); ++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, 2e-5);
}
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);
}
}
/**
* Test getting and setting per-DOF variables.
*/
void testPerDofVariables() {
const int numParticles = 200;
const double boxSize = 10;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
NonbondedForce* nb = new NonbondedForce();
system.addForce(nb);
nb->setNonbondedMethod(NonbondedForce::CutoffNonPeriodic);
vector<Vec3> positions(numParticles);
OpenMM_SFMT::SFMT sfmt;
init_gen_rand(0, sfmt);
for (int i = 0; i < numParticles; i++) {
system.addParticle(1.5);
nb->addParticle(i%2 == 0 ? 1 : -1, 0.1, 1);
bool close = true;
while (close) {
positions[i] = Vec3(boxSize*genrand_real2(sfmt), boxSize*genrand_real2(sfmt), boxSize*genrand_real2(sfmt));
close = false;
for (int j = 0; j < i; ++j) {
Vec3 delta = positions[i]-positions[j];
if (delta.dot(delta) < 0.1)
close = true;
}
}
}
CustomIntegrator integrator(0.01);
integrator.addPerDofVariable("temp", 0);
integrator.addPerDofVariable("pos", 0);
integrator.addComputePerDof("v", "v+dt*f/m");
integrator.addComputePerDof("x", "x+dt*v");
integrator.addComputePerDof("pos", "x");
Context context(system, integrator, platform);
context.setPositions(positions);
vector<Vec3> initialValues(numParticles);
for (int i = 0; i < numParticles; i++)
initialValues[i] = Vec3(i+0.1, i+0.2, i+0.3);
integrator.setPerDofVariable(0, initialValues);
// Run a simulation, then query per-DOF values and see if they are correct.
vector<Vec3> values;
context.getState(State::Forces); // Cause atom reordering to happen before the first step
for (int i = 0; i < 200; ++i) {
integrator.step(1);
State state = context.getState(State::Positions);
integrator.getPerDofVariable(0, values);
for (int j = 0; j < numParticles; j++)
ASSERT_EQUAL_VEC(initialValues[j], values[j], 1e-5);
integrator.getPerDofVariable(1, values);
for (int j = 0; j < numParticles; j++)
ASSERT_EQUAL_VEC(state.getPositions()[j], values[j], 1e-5);
}
}
void testCoulomb() {
System system;
system.addParticle(1.0);
system.addParticle(1.0);
VerletIntegrator integrator(0.01);
NonbondedForce* forceField = new NonbondedForce();
forceField->addParticle(0.5, 1, 0);
forceField->addParticle(-1.5, 1, 0);
system.addForce(forceField);
Context context(system, integrator, platform);
vector<Vec3> positions(2);
positions[0] = Vec3(0, 0, 0);
positions[1] = Vec3(2, 0, 0);
context.setPositions(positions);
State state = context.getState(State::Forces | State::Energy);
const vector<Vec3>& forces = state.getForces();
double force = ONE_4PI_EPS0*(-0.75)/4.0;
ASSERT_EQUAL_VEC(Vec3(-force, 0, 0), forces[0], TOL);
ASSERT_EQUAL_VEC(Vec3(force, 0, 0), forces[1], TOL);
ASSERT_EQUAL_TOL(ONE_4PI_EPS0*(-0.75)/2.0, state.getPotentialEnergy(), TOL);
}
void testConstraints() {
const int numParticles = 8;
const double temp = 100.0;
const double collisionFreq = 10.0;
const int numSteps = 15000;
System system;
VerletIntegrator integrator(0.004);
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);
system.addConstraint(0, 1, 1);
system.addConstraint(1, 2, 1);
system.addConstraint(2, 3, 1);
system.addConstraint(3, 0, 1);
system.addConstraint(4, 5, 1);
system.addConstraint(5, 6, 1);
system.addConstraint(6, 7, 1);
system.addConstraint(7, 4, 1);
AndersenThermostat* thermostat = new AndersenThermostat(temp, collisionFreq);
system.addForce(thermostat);
Context context(system, integrator, platform);
vector<Vec3> positions(numParticles);
positions[0] = Vec3(0, 0, 0);
positions[1] = Vec3(1, 0, 0);
positions[2] = Vec3(1, 1, 0);
positions[3] = Vec3(0, 1, 0);
positions[4] = Vec3(1, 0, 1);
positions[5] = Vec3(1, 1, 1);
positions[6] = Vec3(0, 1, 1);
positions[7] = Vec3(0, 0, 1);
context.setPositions(positions);
context.setVelocitiesToTemperature(temp);
// Let it equilibrate.
integrator.step(5000);
// Now run it for a while and see if the temperature is correct.
double ke = 0.0;
for (int i = 0; i < numSteps; ++i) {
State state = context.getState(State::Energy);
ke += state.getKineticEnergy();
integrator.step(1);
}
ke /= numSteps;
double expected = 0.5*(numParticles*3-system.getNumConstraints())*BOLTZ*temp;
ASSERT_USUALLY_EQUAL_TOL(expected, ke, 0.1);
}
void testErrorTolerance(NonbondedForce::NonbondedMethod method) {
// Create a cloud of random point charges.
const int numParticles = 51;
const double boxWidth = 5.0;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(boxWidth, 0, 0), Vec3(0, boxWidth, 0), Vec3(0, 0, boxWidth));
NonbondedForce* force = new NonbondedForce();
system.addForce(force);
vector<Vec3> positions(numParticles);
OpenMM_SFMT::SFMT sfmt;
init_gen_rand(0, sfmt);
for (int i = 0; i < numParticles; i++) {
system.addParticle(1.0);
force->addParticle(-1.0+i*2.0/(numParticles-1), 1.0, 0.0);
positions[i] = Vec3(boxWidth*genrand_real2(sfmt), boxWidth*genrand_real2(sfmt), boxWidth*genrand_real2(sfmt));
}
force->setNonbondedMethod(method);
ReferencePlatform platform;
// For various values of the cutoff and error tolerance, see if the actual error is reasonable.
for (double cutoff = 1.0; cutoff < boxWidth/2; cutoff *= 1.2) {
force->setCutoffDistance(cutoff);
vector<Vec3> refForces;
double norm = 0.0;
for (double tol = 5e-5; tol < 1e-3; tol *= 2.0) {
force->setEwaldErrorTolerance(tol);
VerletIntegrator integrator(0.01);
Context context(system, integrator, platform);
context.setPositions(positions);
State state = context.getState(State::Forces);
if (refForces.size() == 0) {
refForces = state.getForces();
for (int i = 0; i < numParticles; i++)
norm += refForces[i].dot(refForces[i]);
norm = sqrt(norm);
}
else {
double diff = 0.0;
for (int i = 0; i < numParticles; i++) {
Vec3 delta = refForces[i]-state.getForces()[i];
diff += delta.dot(delta);
}
diff = sqrt(diff)/norm;
ASSERT(diff < 2*tol);
}
}
}
}
/**
* Test a multiple time step r-RESPA integrator.
*/
void testRespa() {
const int numParticles = 8;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(4, 0, 0), Vec3(0, 4, 0), Vec3(0, 0, 4));
CustomIntegrator integrator(0.002);
integrator.addComputePerDof("v", "v+0.5*dt*f1/m");
for (int i = 0; i < 2; i++) {
integrator.addComputePerDof("v", "v+0.5*(dt/2)*f0/m");
integrator.addComputePerDof("x", "x+(dt/2)*v");
integrator.addComputePerDof("v", "v+0.5*(dt/2)*f0/m");
}
integrator.addComputePerDof("v", "v+0.5*dt*f1/m");
HarmonicBondForce* bonds = new HarmonicBondForce();
for (int i = 0; i < numParticles-2; i++)
bonds->addBond(i, i+1, 1.0, 0.5);
system.addForce(bonds);
NonbondedForce* nb = new NonbondedForce();
nb->setCutoffDistance(2.0);
nb->setNonbondedMethod(NonbondedForce::Ewald);
for (int i = 0; i < numParticles; ++i) {
system.addParticle(i%2 == 0 ? 5.0 : 10.0);
nb->addParticle((i%2 == 0 ? 0.2 : -0.2), 0.5, 5.0);
}
nb->setForceGroup(1);
nb->setReciprocalSpaceForceGroup(0);
system.addForce(nb);
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 monitor energy conservations.
double initialEnergy = 0.0;
for (int i = 0; i < 1000; ++i) {
State state = context.getState(State::Energy);
double energy = state.getKineticEnergy()+state.getPotentialEnergy();
if (i == 1)
initialEnergy = energy;
else if (i > 1)
ASSERT_EQUAL_TOL(initialEnergy, energy, 0.05);
integrator.step(2);
}
}
/**
* Test a System where multiple virtual sites are all calculated from the same particles.
*/
void testOverlappingSites() {
System system;
system.addParticle(1.0);
system.addParticle(1.0);
system.addParticle(1.0);
NonbondedForce* nonbonded = new NonbondedForce();
system.addForce(nonbonded);
nonbonded->addParticle(1.0, 0.0, 0.0);
nonbonded->addParticle(-0.5, 0.0, 0.0);
nonbonded->addParticle(-0.5, 0.0, 0.0);
vector<Vec3> positions;
positions.push_back(Vec3(0, 0, 0));
positions.push_back(Vec3(10, 0, 0));
positions.push_back(Vec3(0, 10, 0));
for (int i = 0; i < 20; i++) {
system.addParticle(0.0);
double u = 0.1*((i+1)%4);
double v = 0.05*i;
system.setVirtualSite(3+i, new ThreeParticleAverageSite(0, 1, 2, u, v, 1-u-v));
nonbonded->addParticle(i%2 == 0 ? -1.0 : 1.0, 0.0, 0.0);
positions.push_back(Vec3());
}
VerletIntegrator i1(0.002);
VerletIntegrator i2(0.002);
Context c1(system, i1, Platform::getPlatformByName("Reference"));
Context c2(system, i2, platform);
c1.setPositions(positions);
c2.setPositions(positions);
c1.applyConstraints(0.0001);
c2.applyConstraints(0.0001);
State s1 = c1.getState(State::Positions | State::Forces);
State s2 = c2.getState(State::Positions | State::Forces);
for (int i = 0; i < system.getNumParticles(); i++)
ASSERT_EQUAL_VEC(s1.getPositions()[i], s2.getPositions()[i], 1e-5);
for (int i = 0; i < 3; i++)
ASSERT_EQUAL_VEC(s1.getForces()[i], s2.getForces()[i], 1e-5);
}
void testPMEParameters() {
// Create a cloud of random point charges.
const int numParticles = 51;
const double boxWidth = 4.7;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(boxWidth, 0, 0), Vec3(0, boxWidth, 0), Vec3(0, 0, boxWidth));
NonbondedForce* force = new NonbondedForce();
system.addForce(force);
vector<Vec3> positions(numParticles);
OpenMM_SFMT::SFMT sfmt;
init_gen_rand(0, sfmt);
for (int i = 0; i < numParticles; i++) {
system.addParticle(1.0);
force->addParticle(-1.0+i*2.0/(numParticles-1), 1.0, 0.0);
positions[i] = Vec3(boxWidth*genrand_real2(sfmt), boxWidth*genrand_real2(sfmt), boxWidth*genrand_real2(sfmt));
}
force->setNonbondedMethod(NonbondedForce::PME);
ReferencePlatform platform;
// Compute the energy with an error tolerance of 1e-3.
force->setEwaldErrorTolerance(1e-3);
VerletIntegrator integrator1(0.01);
Context context1(system, integrator1, platform);
context1.setPositions(positions);
double energy1 = context1.getState(State::Energy).getPotentialEnergy();
// Try again with an error tolerance of 1e-4.
force->setEwaldErrorTolerance(1e-4);
VerletIntegrator integrator2(0.01);
Context context2(system, integrator2, platform);
context2.setPositions(positions);
double energy2 = context2.getState(State::Energy).getPotentialEnergy();
// Now explicitly set the parameters. These should match the values that were
// used for tolerance 1e-3.
force->setPMEParameters(2.49291157051793, 32, 32, 32);
VerletIntegrator integrator3(0.01);
Context context3(system, integrator3, platform);
context3.setPositions(positions);
double energy3 = context3.getState(State::Energy).getPotentialEnergy();
ASSERT_EQUAL_TOL(energy1, energy3, 1e-6);
ASSERT(fabs((energy1-energy2)/energy1) > 1e-5);
}
void testConstraints() {
const int numParticles = 8;
const int numConstraints = 5;
const double temp = 20.0;
System system;
BrownianIntegrator integrator(temp, 2.0, 0.001);
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, 0, 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.
for (int i = 0; i < 1000; ++i) {
State state = context.getState(State::Positions);
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);
}
integrator.step(1);
}
}
void testMotionRemoval() {
const int numParticles = 8;
const double temp = 100.0;
const double collisionFreq = 10.0;
ReferencePlatform platform;
System system;
VerletIntegrator integrator(0.01);
HarmonicBondForce* bonds = new HarmonicBondForce();
bonds->addBond(2, 3, 2.0, 0.5);
system.addForce(bonds);
NonbondedForce* nonbonded = new NonbondedForce();
for (int i = 0; i < numParticles; ++i) {
system.addParticle(i+1);
nonbonded->addParticle((i%2 == 0 ? 1.0 : -1.0), 1.0, 5.0);
}
system.addForce(nonbonded);
CMMotionRemover* remover = new CMMotionRemover();
system.addForce(remover);
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 == 0 ? 2 : -2), (i%4 < 2 ? 2 : -2), (i < 4 ? 2 : -2));
velocities[i] = Vec3(genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5);
}
context.setPositions(positions);
context.setVelocities(velocities);
// Now run it for a while and see if the center of mass remains fixed.
Vec3 cmPos = calcCM(context.getState(State::Positions).getPositions(), system);
for (int i = 0; i < 1000; ++i) {
integrator.step(1);
State state = context.getState(State::Positions | State::Velocities);
Vec3 pos = calcCM(state.getPositions(), system);
ASSERT_EQUAL_VEC(cmPos, pos, 1e-2);
Vec3 vel = calcCM(state.getVelocities(), system);
ASSERT_EQUAL_VEC(Vec3(0, 0, 0), vel, 1e-2);
}
}
/**
* Test an integrator with an AndersenThermostat to see if updateContextState()
* is being handled correctly.
*/
void testWithThermostat() {
const int numParticles = 8;
const double temp = 100.0;
const double collisionFreq = 20.0;
const int numSteps = 5000;
System system;
CustomIntegrator integrator(0.003);
integrator.addUpdateContextState();
integrator.addComputePerDof("v", "v+dt*f/m");
integrator.addComputePerDof("x", "x+dt*v");
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);
integrator.setRandomNumberSeed(thermostat->getRandomNumberSeed());
Context context(system, integrator, platform);
vector<Vec3> positions(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));
context.setPositions(positions);
context.setVelocitiesToTemperature(temp);
// Let it equilibrate.
integrator.step(10000);
// Now run it for a while and see if the temperature is correct.
double ke = 0.0;
for (int i = 0; i < numSteps; ++i) {
State state = context.getState(State::Energy);
ke += state.getKineticEnergy();
integrator.step(10);
}
ke /= numSteps;
double expected = 0.5*numParticles*3*BOLTZ*temp;
ASSERT_USUALLY_EQUAL_TOL(expected, ke, 0.1);
}
/**
* Test the ComputeSum operation.
*/
void testSum() {
const int numParticles = 200;
const double boxSize = 10;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(boxSize, 0, 0), Vec3(0, boxSize, 0), Vec3(0, 0, boxSize));
NonbondedForce* nb = new NonbondedForce();
system.addForce(nb);
vector<Vec3> positions(numParticles);
OpenMM_SFMT::SFMT sfmt;
init_gen_rand(0, sfmt);
for (int i = 0; i < numParticles; i++) {
system.addParticle(i%10 == 0 ? 0.0 : 1.5);
nb->addParticle(i%2 == 0 ? 0.1 : -0.1, 0.1, 1);
bool close = true;
while (close) {
positions[i] = Vec3(boxSize*genrand_real2(sfmt), boxSize*genrand_real2(sfmt), boxSize*genrand_real2(sfmt));
close = false;
for (int j = 0; j < i; ++j) {
Vec3 delta = positions[i]-positions[j];
if (delta.dot(delta) < 1)
close = true;
}
}
}
CustomIntegrator integrator(0.005);
integrator.addGlobalVariable("ke", 0);
integrator.addComputePerDof("v", "v+dt*f/m");
integrator.addComputePerDof("x", "x+dt*v");
integrator.addComputeSum("ke", "m*v*v/2");
Context context(system, integrator, platform);
context.setPositions(positions);
// See if the sum is being computed correctly.
for (int i = 0; i < 100; ++i) {
State state = context.getState(State::Energy);
ASSERT_EQUAL_TOL(state.getKineticEnergy(), integrator.getGlobalVariable(0), 1e-5);
integrator.step(1);
}
}
void testChangingBoxSize() {
ReferencePlatform platform;
System system;
system.setDefaultPeriodicBoxVectors(Vec3(4, 0, 0), Vec3(0, 5, 0), Vec3(0, 0, 6));
system.addParticle(1.0);
NonbondedForce* nb = new NonbondedForce();
nb->setNonbondedMethod(NonbondedForce::CutoffPeriodic);
nb->setCutoffDistance(2.0);
nb->addParticle(1, 0.5, 0.5);
system.addForce(nb);
LangevinIntegrator integrator(300.0, 1.0, 0.01);
Context context(system, integrator, platform);
vector<Vec3> positions;
positions.push_back(Vec3());
context.setPositions(positions);
Vec3 x, y, z;
context.getState(State::Forces).getPeriodicBoxVectors(x, y, z);
ASSERT_EQUAL_VEC(Vec3(4, 0, 0), x, 0);
ASSERT_EQUAL_VEC(Vec3(0, 5, 0), y, 0);
ASSERT_EQUAL_VEC(Vec3(0, 0, 6), z, 0);
context.setPeriodicBoxVectors(Vec3(7, 0, 0), Vec3(0, 8, 0), Vec3(0, 0, 9));
context.getState(State::Forces).getPeriodicBoxVectors(x, y, z);
ASSERT_EQUAL_VEC(Vec3(7, 0, 0), x, 0);
ASSERT_EQUAL_VEC(Vec3(0, 8, 0), y, 0);
ASSERT_EQUAL_VEC(Vec3(0, 0, 9), z, 0);
// Shrinking the box too small should produce an exception.
context.setPeriodicBoxVectors(Vec3(7, 0, 0), Vec3(0, 3.9, 0), Vec3(0, 0, 9));
bool ok = true;
try {
context.getState(State::Forces).getPeriodicBoxVectors(x, y, z);
ok = false;
}
catch (exception& ex) {
}
ASSERT(ok);
}
