/*
* Verlet MD NVE integrator step
*
* This method implements the algorithm:
*
* vm(n) = v(n) + 0.5*a(n)*dt
* x(n+1) = x(n) + vm(n)*dt
*
* calculate acceleration a(n+1)
*
* v(n+1) = vm(n) + 0.5*a(n+1)*dt
*
* where x is position, v is velocity, and a is acceleration.
*/
void NveVvIntegrator::step()
{
Vector dv;
Vector dr;
System::MoleculeIterator molIter;
double prefactor;
int iSpecies, nSpecies;
nSpecies = simulation().nSpecies();
// 1st half velocity Verlet, loop over atoms
#if USE_ITERATOR
Molecule::AtomIterator atomIter;
for (iSpecies=0; iSpecies < nSpecies; ++iSpecies) {
system().begin(iSpecies, molIter);
for ( ; molIter.notEnd(); ++molIter) {
for (molIter->begin(atomIter); atomIter.notEnd(); ++atomIter) {
prefactor = prefactors_[atomIter->typeId()];
dv.multiply(atomIter->force(), prefactor);
atomIter->velocity() += dv;
dr.multiply(atomIter->velocity(), dt_);
atomIter->position() += dr;
}
}
}
#else
Atom* atomPtr;
int ia;
for (iSpecies=0; iSpecies < nSpecies; ++iSpecies) {
system().begin(iSpecies, molIter);
for ( ; molIter.notEnd(); ++molIter) {
for (ia=0; ia < molIter->nAtom(); ++ia) {
atomPtr = &molIter->atom(ia);
prefactor = prefactors_[atomPtr->typeId()];
dv.multiply(atomPtr->force(), prefactor);
atomPtr->velocity() += dv;
dr.multiply(atomPtr->velocity(), dt_);
atomPtr->position() += dr;
}
}
}
#endif
system().calculateForces();
// 2nd half velocity Verlet, loop over atoms
#if USE_ITERATOR
for (iSpecies=0; iSpecies < nSpecies; ++iSpecies) {
system().begin(iSpecies, molIter);
for ( ; molIter.notEnd(); ++molIter) {
for (molIter->begin(atomIter); atomIter.notEnd(); ++atomIter) {
prefactor = prefactors_[atomIter->typeId()];
dv.multiply(atomIter->force(), prefactor);
atomIter->velocity() += dv;
}
}
}
#else
for (iSpecies=0; iSpecies < nSpecies; ++iSpecies) {
system().begin(iSpecies, molIter);
for ( ; molIter.notEnd(); ++molIter)
{
for (ia=0; ia < molIter->nAtom(); ++ia) {
atomPtr = &molIter->atom(ia);
prefactor = prefactors_[atomPtr->typeId()];
dv.multiply(atomPtr->force(), prefactor);
atomPtr->velocity() += dv;
}
}
}
#endif
#ifndef INTER_NOPAIR
if (!system().pairPotential().isPairListCurrent()) {
system().pairPotential().buildPairList();
}
#endif
}
void NphIntegrator::step()
{
System::MoleculeIterator molIter;
double prefactor;
int iSpecies, nSpecies;
nSpecies = simulation().nSpecies();
/* perform the first half step of the explicitly reversible NPH integration scheme.
This follows from operator factorization
- orthorhombic case:
1) eta_alpha(t+dt/2) = eta_alpha(t) + dt/2 * V/L_alpha * ( P_{alpha,alpha}(t) - P_ext)
2) v' = v(t) + (1/2)a(t)*dt
3) L(t+dt/2) = L(t) + dt*eta(t+dt/2)/(2*W)
4) r'_alpha = r(t) + v'*dt* (L_{alpha}^2(t)/L_{alpha}^2(t+dt/2))
5a) L(t+dt) = L(t+dt/2) + dt*eta(t+dt/2)/2/W
5b) r_alpha(t+dt) = L_alpha(t+dt)/L_alpha(t)*r'_alpha
5c) v''_alpha = L_alpha(t)/L_alpha(t+dt) * v'_alpha
alpha denotes a cartesian index.
- isotropic case:
only eta_x := eta is used and instead of step 1) we have
1') eta(t+dt/2) = eta(t) + dt/2 * (1/3*Tr P(t) - P_ext)
furthermore, in step 3) and 5a) L is replaced with V=L^3
- tetragonal case:
Lx := L_perp, Ly = Lz := L_par
eta_x := eta_perp, etay := eta_par, etaz unused
instead of step 1) we have
1'a) eta_perp(t+dt/2) = eta_perp + dt/2 * V/L_perp * ( P_xx(t) - P_ext)
1'b) eta_par(t+dt/2) = eta_par + dt/2 * V/L_par * ( P_yy(t) + P_zz(t) - 2*P_ext)
steps 3) and 5a) are split into two sub-steps
L_perp(i+1) = L_perp(i) + dt/(2*W)*eta_perp
L_par(i+1) = L_par(i) + dt/(4*W)*eta_par
*/
// obtain current stress tensor (diagonal components)
system().computeStress(currP_);
// obtain current box lengths
Vector lengths = system().boundary().lengths();
double volume = lengths[0]*lengths[1]*lengths[2];
double extP = system().boundaryEnsemble().pressure();
// advance eta(t)->eta(t+dt/2) (step one)
if (mode_ == Orthorhombic) {
double Vdthalf = 1.0/2.0 * volume * dt_;
eta_[0] += Vdthalf/lengths[0] * (currP_[0] - extP);
eta_[1] += Vdthalf/lengths[1] * (currP_[1] - extP);
eta_[2] += Vdthalf/lengths[2] * (currP_[2] - extP);
} else if (mode_ == Tetragonal) {
double Vdthalf = 1.0/2.0* volume * dt_;
eta_[0] += Vdthalf/lengths[0]*(currP_[0] - extP);
eta_[1] += Vdthalf/lengths[1]*(currP_[1] + currP_[2] - 2.0*extP);
} else if (mode_ == Cubic) {
eta_[0] += 1.0/2.0*dt_*(1.0/3.0*(currP_[0]+currP_[1]+currP_[2]) - extP);
}
// update the box length L(t) -> L(t+dt/2) (step three)
// (since we still keep the accelerations a(t) computed for box length L_alpha(t) in memory,
// needed in step two, we can exchange the order of the two steps)
// also pre-calculate L(t+dt) (step 5a, only depends on eta(t) of step one)
Vector lengthsOld = lengths;
Vector lengthsFinal;
double volumeFinal = 0.0;
double dthalfoverW = 1.0/2.0*dt_/W_;
if (mode_ == Orthorhombic) {
lengths[0] += dthalfoverW*eta_[0];
lengths[1] += dthalfoverW*eta_[1];
lengths[2] += dthalfoverW*eta_[2];
lengthsFinal[0] = lengths[0] + dthalfoverW*eta_[0];
lengthsFinal[1] = lengths[1] + dthalfoverW*eta_[1];
lengthsFinal[2] = lengths[2] + dthalfoverW*eta_[2];
volumeFinal = lengthsFinal[0]*lengthsFinal[1]*lengthsFinal[2];
} else if (mode_ == Tetragonal) {
lengths[0] += dthalfoverW*eta_[0];
lengths[1] += (1.0/2.0)*dthalfoverW*eta_[1];
lengths[2] = lengths[1];
lengthsFinal[0] = lengths[0] + dthalfoverW*eta_[0];
lengthsFinal[1] = lengths[1] + (1.0/2.0)*dthalfoverW*eta_[1];
lengthsFinal[2] = lengthsFinal[1];
volumeFinal = lengthsFinal[0]*lengthsFinal[1]*lengthsFinal[2];
} else if (mode_ == Cubic) {
volume += dthalfoverW*eta_[0];
lengths[0] = pow(volume,1.0/3.0); // Lx = Ly = Lz = V^(1/3)
lengths[1] = lengths[0];
lengths[2] = lengths[0];
volumeFinal = volume + dthalfoverW*eta_[0];
lengthsFinal[0] = pow(volumeFinal,1./3.);
lengthsFinal[1] = lengthsFinal[0];
lengthsFinal[2] = lengthsFinal[0];
}
// update simulation box
system().boundary().setOrthorhombic(lengthsFinal);
// update particles
Atom* atomPtr;
int ia;
Vector vtmp, dr, rtmp, dv;
Vector lengthsFac, dtLengthsFac2;
for (int i=0; i<3; i++) {
lengthsFac[i] = lengthsFinal[i]/lengthsOld[i];
dtLengthsFac2[i] = dt_ * lengthsOld[i]*lengthsOld[i]/lengths[i]/lengths[i];
}
for (iSpecies=0; iSpecies < nSpecies; ++iSpecies) {
system().begin(iSpecies, molIter);
for ( ; molIter.notEnd(); ++molIter) {
for (ia=0; ia < molIter->nAtom(); ++ia) {
atomPtr = &molIter->atom(ia);
prefactor = prefactors_[atomPtr->typeId()];
dv.multiply(atomPtr->force(), prefactor);
vtmp.add(atomPtr->velocity(),dv);
dr[0] = vtmp[0] * dtLengthsFac2[0];
dr[1] = vtmp[1] * dtLengthsFac2[1];
dr[2] = vtmp[2] * dtLengthsFac2[2];
rtmp.add(atomPtr->position(), dr);
rtmp[0] *= lengthsFac[0];
rtmp[1] *= lengthsFac[1];
rtmp[2] *= lengthsFac[2];
atomPtr->position() = rtmp;
vtmp[0] /= lengthsFac[0];
vtmp[1] /= lengthsFac[1];
vtmp[2] /= lengthsFac[2];
atomPtr->velocity() = vtmp;
}
}
}
#ifndef INTER_NOPAIR
if (!system().pairPotential().isPairListCurrent()) {
system().pairPotential().buildPairList();
}
#endif
system().calculateForces();
/* the second step of the explicitly reversible integrator consists of the following to sub-steps
6) v(t+dt) = v'' + 1/2 * a(t+dt)*dt
7) eta(t+dt/2) -> eta(t+dt)
*/
// v(t+dt) = v'' + 1/2 * a(t+dt)*dt
for (iSpecies=0; iSpecies < nSpecies; ++iSpecies) {
system().begin(iSpecies, molIter);
for ( ; molIter.notEnd(); ++molIter)
{
for (ia=0; ia < molIter->nAtom(); ++ia) {
atomPtr = &molIter->atom(ia);
prefactor = prefactors_[atomPtr->typeId()];
dv.multiply(atomPtr->force(), prefactor);
atomPtr->velocity() += dv;
}
}
}
// now compute pressure tensor with updated virial and velocities
system().computeStress(currP_);
// advance eta(t+dt/2) -> eta(t+dt)
if (mode_ == Orthorhombic) {
double Vdthalf = 1.0/2.0 * volumeFinal * dt_;
eta_[0] += Vdthalf/lengthsFinal[0] * (currP_[0] - extP);
eta_[1] += Vdthalf/lengthsFinal[1] * (currP_[1] - extP);
eta_[2] += Vdthalf/lengthsFinal[2] * (currP_[2] - extP);
} else if (mode_ == Tetragonal) {
double Vdthalf = 1.0/2.0 * volumeFinal * dt_;
eta_[0] += Vdthalf/lengthsFinal[0]*(currP_[0] - extP);
eta_[1] += Vdthalf/lengthsFinal[1]*(currP_[1] + currP_[2] - 2.0*extP);
} else if (mode_ == Cubic) {
eta_[0] += 1.0/2.0*dt_*(1.0/3.0*(currP_[0]+currP_[1]+currP_[2]) - extP);
}
#ifndef INTER_NOPAIR
if (!system().pairPotential().isPairListCurrent()) {
system().pairPotential().buildPairList();
}
#endif
/*
// debug output
double P;
system().computeStress(P);
std::cout << system().boundary() << std::endl;
std::cout << "P = " << P << " ";
std::cout << "Ekin = " << system().kineticEnergy() << " ";
std::cout << "Epot = " << system().potentialEnergy() << " ";
std::cout << "PV = " << extP * system().boundary().volume() << " ";
std::cout << "Ebaro = " << barostatEnergy() << " ";
std::cout << "H = " << system().potentialEnergy() + system().kineticEnergy() +
extP * system().boundary().volume() + barostatEnergy() << std::endl;
*/
}
// Create links and print.
void Crosslinker::sample(long iStep)
{
if (isAtInterval(iStep)) {
// Clear the cellList
cellList_.clear();
// Add every atom in this System to the CellList
System::MoleculeIterator molIter;
Atom* atomPtr;
for (int iSpec=0; iSpec < system().simulation().nSpecies(); ++iSpec) {
for (system().begin(iSpec, molIter); molIter.notEnd(); ++molIter) {
for (int ia=0; ia < molIter->nAtom(); ++ia) {
atomPtr = &molIter->atom(ia);
system().boundary().shift(atomPtr->position());
cellList_.addAtom(*atomPtr);
}
}
}
//Use the cell list to find neighbours and create links
CellList::NeighborArray cellNeighbor;
Vector iPos, jPos;
Atom *iAtomPtr, *jAtomPtr;
double dRSq, cutoffSq=cutoff_*cutoff_;
int nCellNeighbor, nCellAtom, totCells;
int ic, ip, iAtomId, jp, jAtomId;
// Loop over cells containing primary atom. ic = cell index
totCells = cellList_.totCells();
for (ic = 0; ic < totCells; ++ic) {
// Get Array cellNeighbor of Ids of neighbor atoms for cell ic.
// Elements 0,..., nCellAtom - 1 contain Ids for atoms in cell ic.
// Elements nCellAtom,..., nCellNeighbor-1 are from neighboring cells.
cellList_.getCellNeighbors(ic, cellNeighbor, nCellAtom);
nCellNeighbor = cellNeighbor.size();
// Loop over atoms in cell ic
for (ip = 0; ip < nCellAtom; ++ip) {
iAtomPtr = cellNeighbor[ip];
iPos = iAtomPtr->position();
iAtomId = iAtomPtr->id();
// Loop over atoms in all neighboring cells, including cell ic.
for (jp = 0; jp < nCellNeighbor; ++jp) {
jAtomPtr = cellNeighbor[jp];
jPos = jAtomPtr->position();
jAtomId = jAtomPtr->id();
// Avoid double counting: only count pairs with jAtomId > iAtomId
if ( jAtomId > iAtomId ) {
// Exclude bonded pairs
if (!iAtomPtr->mask().isMasked(*jAtomPtr)) {
// Calculate distance between atoms i and j
dRSq = system().boundary().distanceSq(iPos, jPos);
if (dRSq < cutoffSq) {
if(system().simulation().random().uniform(0.0, 1.0) < probability_){
//create a link between i and j atoms
system().linkMaster().addLink(*iAtomPtr, *jAtomPtr, 0);
}
}
}
} // end if jAtomId > iAtomId
} // end for jp (j atom)
} // end for ip (i atom)
} // end for ic (i cell)
// Construct a string representation of integer nSample
std::stringstream ss;
std::string nSampleString;
ss << nSample_;
nSampleString = ss.str();
// Construct new fileName: outputFileName + char(nSample)
std::string filename;
filename = outputFileName();
filename += nSampleString;
// Open output file, write data, and close file
fileMaster().openOutputFile(filename, outputFile_);
system().writeConfig(outputFile_);
outputFile_.close();
nSample_++;
// Clear the LinkMaster
system().linkMaster().clear();
} // end isAtInterval
}
/*
* Evaluate change in energy, add Boltzmann factor to accumulator.
*/
void McMuExchange::sample(long iStep)
{
if (isAtInterval(iStep)) {
// Preconditions
if (!system().energyEnsemble().isIsothermal()) {
UTIL_THROW("EnergyEnsemble is not isothermal");
}
if (nMolecule_ != system().nMolecule(speciesId_)) {
UTIL_THROW("nMolecule has changed since setup");
}
McPairPotential& potential = system().pairPotential();
const CellList& cellList = potential.cellList();
System::MoleculeIterator molIter;
Atom* ptr0 = 0; // Pointer to first atom in molecule
Atom* ptr1 = 0; // Pointer to flipped atom
Atom* ptr2 = 0; // Pointer to neighboring atom
Mask* maskPtr = 0; // Mask of flipped atom
double rsq, dE, beta, boltzmann;
int j, k, nNeighbor, nFlip;
int i1, i2, id1, id2, t1, t2, t1New, iMol;
beta = system().energyEnsemble().beta();
nFlip = flipAtomIds_.size();
// Loop over molecules in species
iMol = 0;
system().begin(speciesId_, molIter);
for ( ; molIter.notEnd(); ++molIter) {
dE = 0.0;
ptr0 = &molIter->atom(0);
// Loop over flipped atoms
for (j = 0; j < nFlip; ++j) {
i1 = flipAtomIds_[j];
t1New = newTypeIds_[i1];
ptr1 = &molIter->atom(i1);
id1 = ptr1->id();
t1 = ptr1->typeId();
maskPtr = &(ptr1->mask());
// Loop over neighboring atoms
cellList.getNeighbors(ptr1->position(), neighbors_);
nNeighbor = neighbors_.size();
for (k = 0; k < nNeighbor; ++k) {
ptr2 = neighbors_[k];
id2 = ptr2->id();
// Check if atoms are identical
if (id2 != id1) {
// Check if pair is masked
if (!maskPtr->isMasked(*ptr2)) {
rsq = boundary().distanceSq(ptr1->position(),
ptr2->position());
t2 = ptr2->typeId();
if (&(ptr1->molecule()) != &(ptr2->molecule())) {
// Intermolecular atom pair
dE -= potential.energy(rsq, t1, t2);
dE += potential.energy(rsq, t1New, t2);
} else {
// Intramolecular atom pair
if (id2 > id1) {
dE -= potential.energy(rsq, t1, t2);
i2 = (int)(ptr2 - ptr0);
t2 = newTypeIds_[i2];
dE += potential.energy(rsq, t1New, t2);
} else {
i2 = (int)(ptr2 - ptr0);
if (!isAtomFlipped_[i2]) {
dE -= potential.energy(rsq, t1, t2);
t2 = newTypeIds_[i2];
dE += potential.energy(rsq, t1New, t2);
}
}
}
}
}
} // end loop over neighbors
} // end loop over flipped atoms
boltzmann = exp(-beta*dE);
accumulators_[iMol].sample(boltzmann);
++iMol;
} // end loop over molecules
}
}