void testIdealGas() { const int numParticles = 64; const int frequency = 10; const int steps = 1000; const double pressure = 1.5; const double pressureInMD = pressure*(AVOGADRO*1e-25); // pressure in kJ/mol/nm^3 const double temp[] = {300.0, 600.0, 1000.0}; const double initialVolume = numParticles*BOLTZ*temp[1]/pressureInMD; const double initialLength = std::pow(initialVolume, 1.0/3.0); // Create a gas of noninteracting particles. ReferencePlatform platform; System system; system.setDefaultPeriodicBoxVectors(Vec3(initialLength, 0, 0), Vec3(0, 0.5*initialLength, 0), Vec3(0, 0, 2*initialLength)); vector<Vec3> positions(numParticles); OpenMM_SFMT::SFMT sfmt; init_gen_rand(0, sfmt); for (int i = 0; i < numParticles; ++i) { system.addParticle(1.0); positions[i] = Vec3(initialLength*genrand_real2(sfmt), 0.5*initialLength*genrand_real2(sfmt), 2*initialLength*genrand_real2(sfmt)); } MonteCarloBarostat* barostat = new MonteCarloBarostat(pressure, temp[0], frequency); system.addForce(barostat); ASSERT(barostat->usesPeriodicBoundaryConditions()); ASSERT(system.usesPeriodicBoundaryConditions()); // Test it for three different temperatures. for (int i = 0; i < 3; i++) { barostat->setTemperature(temp[i]); LangevinIntegrator integrator(temp[i], 0.1, 0.01); Context context(system, integrator, platform); context.setPositions(positions); // Let it equilibrate. integrator.step(10000); // Now run it for a while and see if the volume is correct. double volume = 0.0; for (int j = 0; j < steps; ++j) { Vec3 box[3]; context.getState(0).getPeriodicBoxVectors(box[0], box[1], box[2]); volume += box[0][0]*box[1][1]*box[2][2]; ASSERT_EQUAL_TOL(0.5*box[0][0], box[1][1], 1e-5); ASSERT_EQUAL_TOL(2*box[0][0], box[2][2], 1e-5); integrator.step(frequency); } volume /= steps; double expected = (numParticles+1)*BOLTZ*temp[i]/pressureInMD; ASSERT_USUALLY_EQUAL_TOL(expected, volume, 3/std::sqrt((double) steps)); } }
void testRandomSeed() { const int numParticles = 8; const double temp = 100.0; const double pressure = 1.5; ReferencePlatform platform; System system; system.setDefaultPeriodicBoxVectors(Vec3(8, 0, 0), Vec3(0, 8, 0), Vec3(0, 0, 8)); VerletIntegrator integrator(0.01); NonbondedForce* forceField = new NonbondedForce(); forceField->setNonbondedMethod(NonbondedForce::CutoffPeriodic); 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); MonteCarloBarostat* barostat = new MonteCarloBarostat(pressure, temp, 1); system.addForce(barostat); ASSERT(barostat->usesPeriodicBoundaryConditions()); ASSERT(system.usesPeriodicBoundaryConditions()); 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. barostat->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. barostat->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]); } } }