void MonteCarloBarostatImpl::updateContextState(ContextImpl& context) {
if (++step < owner.getFrequency() || owner.getFrequency() == 0)
return;
step = 0;
// Compute the current potential energy.
double initialEnergy = context.getOwner().getState(State::Energy).getPotentialEnergy();
// Modify the periodic box size.
Vec3 box[3];
context.getPeriodicBoxVectors(box[0], box[1], box[2]);
double volume = box[0][0]*box[1][1]*box[2][2];
double deltaVolume = volumeScale*2*(genrand_real2(random)-0.5);
double newVolume = volume+deltaVolume;
double lengthScale = std::pow(newVolume/volume, 1.0/3.0);
kernel.getAs<ApplyMonteCarloBarostatKernel>().scaleCoordinates(context, lengthScale, lengthScale, lengthScale);
context.getOwner().setPeriodicBoxVectors(box[0]*lengthScale, box[1]*lengthScale, box[2]*lengthScale);
// Compute the energy of the modified system.
double finalEnergy = context.getOwner().getState(State::Energy).getPotentialEnergy();
double pressure = context.getParameter(MonteCarloBarostat::Pressure())*(AVOGADRO*1e-25);
double kT = BOLTZ*context.getParameter(MonteCarloBarostat::Temperature());
double w = finalEnergy-initialEnergy + pressure*deltaVolume - context.getMolecules().size()*kT*std::log(newVolume/volume);
if (w > 0 && genrand_real2(random) > std::exp(-w/kT)) {
// Reject the step.
kernel.getAs<ApplyMonteCarloBarostatKernel>().restoreCoordinates(context);
context.getOwner().setPeriodicBoxVectors(box[0], box[1], box[2]);
volume = newVolume;
}
else
numAccepted++;
numAttempted++;
if (numAttempted >= 10) {
if (numAccepted < 0.25*numAttempted) {
volumeScale /= 1.1;
numAttempted = 0;
numAccepted = 0;
}
else if (numAccepted > 0.75*numAttempted) {
volumeScale = std::min(volumeScale*1.1, volume*0.3);
numAttempted = 0;
numAccepted = 0;
}
}
}
void MonteCarloAnisotropicBarostatImpl::updateContextState(ContextImpl& context) {
if (++step < owner.getFrequency() || owner.getFrequency() == 0)
return;
if (!owner.getScaleX() && !owner.getScaleY() && !owner.getScaleZ())
return;
step = 0;
// Compute the current potential energy.
double initialEnergy = context.getOwner().getState(State::Energy).getPotentialEnergy();
double pressure;
// Choose which axis to modify at random.
int axis;
while (true) {
double rnd = genrand_real2(random)*3.0;
if (rnd < 1.0) {
if (owner.getScaleX()) {
axis = 0;
pressure = context.getParameter(MonteCarloAnisotropicBarostat::PressureX())*(AVOGADRO*1e-25);
break;
}
} else if (rnd < 2.0) {
if (owner.getScaleY()) {
axis = 1;
pressure = context.getParameter(MonteCarloAnisotropicBarostat::PressureY())*(AVOGADRO*1e-25);
break;
}
} else if (owner.getScaleZ()) {
axis = 2;
pressure = context.getParameter(MonteCarloAnisotropicBarostat::PressureZ())*(AVOGADRO*1e-25);
break;
}
}
// Modify the periodic box size.
Vec3 box[3];
context.getPeriodicBoxVectors(box[0], box[1], box[2]);
double volume = box[0][0]*box[1][1]*box[2][2];
double deltaVolume = volumeScale[axis]*2*(genrand_real2(random)-0.5);
double newVolume = volume+deltaVolume;
Vec3 lengthScale(1.0, 1.0, 1.0);
lengthScale[axis] = newVolume/volume;
kernel.getAs<ApplyMonteCarloBarostatKernel>().scaleCoordinates(context, lengthScale[0], lengthScale[1], lengthScale[2]);
context.getOwner().setPeriodicBoxVectors(box[0]*lengthScale[0], box[1]*lengthScale[1], box[2]*lengthScale[2]);
// Compute the energy of the modified system.
double finalEnergy = context.getOwner().getState(State::Energy).getPotentialEnergy();
double kT = BOLTZ*owner.getTemperature();
double w = finalEnergy-initialEnergy + pressure*deltaVolume - context.getMolecules().size()*kT*std::log(newVolume/volume);
if (w > 0 && genrand_real2(random) > std::exp(-w/kT)) {
// Reject the step.
kernel.getAs<ApplyMonteCarloBarostatKernel>().restoreCoordinates(context);
context.getOwner().setPeriodicBoxVectors(box[0], box[1], box[2]);
volume = newVolume;
}
else
numAccepted[axis]++;
numAttempted[axis]++;
if (numAttempted[axis] >= 10) {
if (numAccepted[axis] < 0.25*numAttempted[axis]) {
volumeScale[axis] /= 1.1;
numAttempted[axis] = 0;
numAccepted[axis] = 0;
}
else if (numAccepted[axis] > 0.75*numAttempted[axis]) {
volumeScale[axis] = std::min(volumeScale[axis]*1.1, volume*0.3);
numAttempted[axis] = 0;
numAccepted[axis] = 0;
}
}
}
