std::vector<chemkit::Vector3> OplsAngleBendCalculation::gradient() const
{
const chemkit::ForceFieldAtom *a = atom(0);
const chemkit::ForceFieldAtom *b = atom(1);
const chemkit::ForceFieldAtom *c = atom(2);
chemkit::Float ka = parameter(0);
chemkit::Float theta0 = parameter(1);
chemkit::Float theta = bondAngleRadians(a, b, c);
std::vector<chemkit::Vector3> gradient = bondAngleGradientRadians(a, b, c);
// dE/dtheta
chemkit::Float de_dtheta = (2.0 * ka * (theta - theta0));
gradient[0] *= de_dtheta;
gradient[1] *= de_dtheta;
gradient[2] *= de_dtheta;
return gradient;
}
std::vector<chemkit::Vector3> UffAngleBendCalculation::gradient() const
{
const chemkit::ForceFieldAtom *a = atom(0);
const chemkit::ForceFieldAtom *b = atom(1);
const chemkit::ForceFieldAtom *c = atom(2);
chemkit::Real ka = parameter(0);
chemkit::Real c1 = parameter(2);
chemkit::Real c2 = parameter(3);
chemkit::Real theta = bondAngleRadians(a, b, c);
// dE/dtheta
chemkit::Real de_dtheta = -ka * (c1 * sin(theta) + 2 * c2 * sin(2 * theta));
std::vector<chemkit::Vector3> gradient = bondAngleGradientRadians(a, b, c);
gradient[0] *= de_dtheta;
gradient[1] *= de_dtheta;
gradient[2] *= de_dtheta;
return gradient;
}
