double NonbondedForceImpl::calcDispersionCorrection(const System& system, const NonbondedForce& force) {
if (force.getNonbondedMethod() == NonbondedForce::NoCutoff || force.getNonbondedMethod() == NonbondedForce::CutoffNonPeriodic)
return 0.0;
// Identify all particle classes (defined by sigma and epsilon), and count the number of
// particles in each class.
map<pair<double, double>, int> classCounts;
for (int i = 0; i < force.getNumParticles(); i++) {
double charge, sigma, epsilon;
force.getParticleParameters(i, charge, sigma, epsilon);
pair<double, double> key = make_pair(sigma, epsilon);
map<pair<double, double>, int>::iterator entry = classCounts.find(key);
if (entry == classCounts.end())
classCounts[key] = 1;
else
entry->second++;
}
// Loop over all pairs of classes to compute the coefficient.
double sum1 = 0, sum2 = 0, sum3 = 0;
bool useSwitch = force.getUseSwitchingFunction();
double cutoff = force.getCutoffDistance();
double switchDist = force.getSwitchingDistance();
for (map<pair<double, double>, int>::const_iterator entry = classCounts.begin(); entry != classCounts.end(); ++entry) {
double sigma = entry->first.first;
double epsilon = entry->first.second;
double count = (double) entry->second;
count *= (count + 1) / 2;
double sigma2 = sigma*sigma;
double sigma6 = sigma2*sigma2*sigma2;
sum1 += count*epsilon*sigma6*sigma6;
sum2 += count*epsilon*sigma6;
if (useSwitch)
sum3 += count*epsilon*(evalIntegral(cutoff, switchDist, cutoff, sigma)-evalIntegral(switchDist, switchDist, cutoff, sigma));
}
for (map<pair<double, double>, int>::const_iterator class1 = classCounts.begin(); class1 != classCounts.end(); ++class1)
for (map<pair<double, double>, int>::const_iterator class2 = classCounts.begin(); class2 != class1; ++class2) {
double sigma = 0.5*(class1->first.first+class2->first.first);
double epsilon = sqrt(class1->first.second*class2->first.second);
double count = (double) class1->second;
count *= (double) class2->second;
double sigma2 = sigma*sigma;
double sigma6 = sigma2*sigma2*sigma2;
sum1 += count*epsilon*sigma6*sigma6;
sum2 += count*epsilon*sigma6;
if (useSwitch)
sum3 += count*epsilon*(evalIntegral(cutoff, switchDist, cutoff, sigma)-evalIntegral(switchDist, switchDist, cutoff, sigma));
}
double numParticles = (double) system.getNumParticles();
double numInteractions = (numParticles*(numParticles+1))/2;
sum1 /= numInteractions;
sum2 /= numInteractions;
sum3 /= numInteractions;
return 8*numParticles*numParticles*M_PI*(sum1/(9*pow(cutoff, 9))-sum2/(3*pow(cutoff, 3))+sum3);
}
void CpuCalcNonbondedForceKernel::initialize(const System& system, const NonbondedForce& force) {
// Identify which exceptions are 1-4 interactions.
numParticles = force.getNumParticles();
exclusions.resize(numParticles);
vector<int> nb14s;
for (int i = 0; i < force.getNumExceptions(); i++) {
int particle1, particle2;
double chargeProd, sigma, epsilon;
force.getExceptionParameters(i, particle1, particle2, chargeProd, sigma, epsilon);
exclusions[particle1].insert(particle2);
exclusions[particle2].insert(particle1);
if (chargeProd != 0.0 || epsilon != 0.0)
nb14s.push_back(i);
}
// Record the particle parameters.
num14 = nb14s.size();
bonded14IndexArray = new int*[num14];
for (int i = 0; i < num14; i++)
bonded14IndexArray[i] = new int[2];
bonded14ParamArray = new double*[num14];
for (int i = 0; i < num14; i++)
bonded14ParamArray[i] = new double[3];
particleParams.resize(numParticles);
double sumSquaredCharges = 0.0;
for (int i = 0; i < numParticles; ++i) {
double charge, radius, depth;
force.getParticleParameters(i, charge, radius, depth);
data.posq[4*i+3] = (float) charge;
particleParams[i] = make_pair((float) (0.5*radius), (float) (2.0*sqrt(depth)));
sumSquaredCharges += charge*charge;
}
// Recorded exception parameters.
for (int i = 0; i < num14; ++i) {
int particle1, particle2;
double charge, radius, depth;
force.getExceptionParameters(nb14s[i], particle1, particle2, charge, radius, depth);
bonded14IndexArray[i][0] = particle1;
bonded14IndexArray[i][1] = particle2;
bonded14ParamArray[i][0] = static_cast<RealOpenMM>(radius);
bonded14ParamArray[i][1] = static_cast<RealOpenMM>(4.0*depth);
bonded14ParamArray[i][2] = static_cast<RealOpenMM>(charge);
}
// Record other parameters.
nonbondedMethod = CalcNonbondedForceKernel::NonbondedMethod(force.getNonbondedMethod());
nonbondedCutoff = force.getCutoffDistance();
if (nonbondedMethod == NoCutoff)
useSwitchingFunction = false;
else {
useSwitchingFunction = force.getUseSwitchingFunction();
switchingDistance = force.getSwitchingDistance();
}
if (nonbondedMethod == Ewald) {
double alpha;
NonbondedForceImpl::calcEwaldParameters(system, force, alpha, kmax[0], kmax[1], kmax[2]);
ewaldAlpha = alpha;
}
else if (nonbondedMethod == PME) {
double alpha;
NonbondedForceImpl::calcPMEParameters(system, force, alpha, gridSize[0], gridSize[1], gridSize[2]);
ewaldAlpha = alpha;
}
if (nonbondedMethod == Ewald || nonbondedMethod == PME)
ewaldSelfEnergy = -ONE_4PI_EPS0*ewaldAlpha*sumSquaredCharges/sqrt(M_PI);
else
ewaldSelfEnergy = 0.0;
rfDielectric = force.getReactionFieldDielectric();
if (force.getUseDispersionCorrection())
dispersionCoefficient = NonbondedForceImpl::calcDispersionCorrection(system, force);
else
dispersionCoefficient = 0.0;
lastPositions.resize(numParticles, Vec3(1e10, 1e10, 1e10));
data.isPeriodic = (nonbondedMethod == CutoffPeriodic || nonbondedMethod == Ewald || nonbondedMethod == PME);
}
void testSerialization() {
// Create a Force.
NonbondedForce force;
force.setForceGroup(3);
force.setNonbondedMethod(NonbondedForce::CutoffPeriodic);
force.setSwitchingDistance(1.5);
force.setUseSwitchingFunction(true);
force.setCutoffDistance(2.0);
force.setEwaldErrorTolerance(1e-3);
force.setReactionFieldDielectric(50.0);
force.setUseDispersionCorrection(false);
double alpha = 0.5;
int nx = 3, ny = 5, nz = 7;
force.setPMEParameters(alpha, nx, ny, nz);
double dalpha = 0.8;
int dnx = 4, dny = 6, dnz = 7;
force.setLJPMEParameters(dalpha, dnx, dny, dnz);
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);
force.addGlobalParameter("scale1", 1.0);
force.addGlobalParameter("scale2", 2.0);
force.addParticleParameterOffset("scale1", 2, 1.5, 2.0, 2.5);
force.addExceptionParameterOffset("scale2", 1, -0.1, -0.2, -0.3);
// 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.getForceGroup(), force2.getForceGroup());
ASSERT_EQUAL(force.getNonbondedMethod(), force2.getNonbondedMethod());
ASSERT_EQUAL(force.getSwitchingDistance(), force2.getSwitchingDistance());
ASSERT_EQUAL(force.getUseSwitchingFunction(), force2.getUseSwitchingFunction());
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());
ASSERT_EQUAL(force.getNumExceptions(), force2.getNumExceptions());
ASSERT_EQUAL(force.getNumGlobalParameters(), force2.getNumGlobalParameters());
ASSERT_EQUAL(force.getNumParticleParameterOffsets(), force2.getNumParticleParameterOffsets());
ASSERT_EQUAL(force.getNumExceptionParameterOffsets(), force2.getNumExceptionParameterOffsets());
double alpha2;
int nx2, ny2, nz2;
force2.getPMEParameters(alpha2, nx2, ny2, nz2);
ASSERT_EQUAL(alpha, alpha2);
ASSERT_EQUAL(nx, nx2);
ASSERT_EQUAL(ny, ny2);
ASSERT_EQUAL(nz, nz2);
double dalpha2;
int dnx2, dny2, dnz2;
force2.getLJPMEParameters(dalpha2, dnx2, dny2, dnz2);
ASSERT_EQUAL(dalpha, dalpha2);
ASSERT_EQUAL(dnx, dnx2);
ASSERT_EQUAL(dny, dny2);
ASSERT_EQUAL(dnz, dnz2);
for (int i = 0; i < force.getNumGlobalParameters(); i++) {
ASSERT_EQUAL(force.getGlobalParameterName(i), force2.getGlobalParameterName(i));
ASSERT_EQUAL(force.getGlobalParameterDefaultValue(i), force2.getGlobalParameterDefaultValue(i));
}
for (int i = 0; i < force.getNumParticleParameterOffsets(); i++) {
int index1, index2;
string param1, param2;
double charge1, sigma1, epsilon1;
double charge2, sigma2, epsilon2;
force.getParticleParameterOffset(i, param1, index1, charge1, sigma1, epsilon1);
force2.getParticleParameterOffset(i, param2, index2, charge2, sigma2, epsilon2);
ASSERT_EQUAL(index1, index1);
ASSERT_EQUAL(param1, param2);
ASSERT_EQUAL(charge1, charge2);
ASSERT_EQUAL(sigma1, sigma2);
ASSERT_EQUAL(epsilon1, epsilon2);
}
for (int i = 0; i < force.getNumExceptionParameterOffsets(); i++) {
int index1, index2;
string param1, param2;
double charge1, sigma1, epsilon1;
double charge2, sigma2, epsilon2;
force.getExceptionParameterOffset(i, param1, index1, charge1, sigma1, epsilon1);
force2.getExceptionParameterOffset(i, param2, index2, charge2, sigma2, epsilon2);
ASSERT_EQUAL(index1, index1);
ASSERT_EQUAL(param1, param2);
ASSERT_EQUAL(charge1, charge2);
ASSERT_EQUAL(sigma1, sigma2);
ASSERT_EQUAL(epsilon1, epsilon2);
}
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);
}
}
