ObjectRestraint.cpp

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 *
 * SUPPORT OPEN SCIENCE!  If you use OpenMD or its source code in your
 * research, please cite the appropriate papers when you publish your
 * work.  Good starting points are:
 *
 * [1] Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).
 * [2] Fennell & Gezelter, J. Chem. Phys. 124, 234104 (2006).
 * [3] Sun, Lin & Gezelter, J. Chem. Phys. 128, 234107 (2008).
 * [4] Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
 * [5] Kuang & Gezelter, Mol. Phys., 110, 691-701 (2012).
 * [6] Lamichhane, Gezelter & Newman, J. Chem. Phys. 141, 134109 (2014).
 * [7] Lamichhane, Newman & Gezelter, J. Chem. Phys. 141, 134110 (2014).
 * [8] Bhattarai, Newman & Gezelter, Phys. Rev. B 99, 094106 (2019).
 */
 
#include "restraints/ObjectRestraint.hpp"
 
namespace OpenMD {
 
  void ObjectRestraint::calcForce(Vector3d struc) {
    pot_   = 0.0;
    force_ = V3Zero;
 
    if (restType_ & rtDisplacement) {
      Vector3d del = struc - refPos_;
      RealType r   = del.length();
      Vector3d frc = -kDisp_ * del;
      RealType p   = 0.5 * kDisp_ * del.lengthSquare();
 
      pot_ += p;
      force_ += frc * scaleFactor_;
      if (printRest_) restInfo_[rtDisplacement] = std::make_pair(r, p);
    }
 
    if (restType_ & rtAbsoluteZ) {
      RealType r   = struc(2) - posZ0_;
      Vector3d frc = Vector3d(0.0, 0.0, -kAbs_ * r);
      RealType p   = 0.5 * kAbs_ * r * r;
 
      pot_ += p;
      force_ += frc * scaleFactor_;
      if (printRest_) restInfo_[rtAbsoluteZ] = std::make_pair(r, p);
    }
  }
 
  void ObjectRestraint::calcForce(Vector3d struc, RotMat3x3d A) {
    calcForce(struc);
 
    // rtDisplacement is 1, rtAbsolute is 2, so anything higher than 3
    // that requires orientations:
    if (restType_ > 3) {
      Vector3d tBody(0.0);
 
      RotMat3x3d temp = A * refA_.transpose();
      Quat4d quat     = temp.toQuaternion();
 
      RealType twistAngle;
      RealType swingX, swingY;
 
      quat.toTwistSwing(twistAngle, swingX, swingY);
 
      RealType p;
      Vector3d tTwist, tSwing;
 
      if (restType_ & rtTwist) {
        RealType dTwist = twistAngle - twist0_;
        /// RealType dVdtwist = kTwist_ * sin(dTwist);
        /// p = kTwist_ * (1.0 - cos(dTwist) );
        RealType dVdtwist = kTwist_ * dTwist;
        p                 = 0.5 * kTwist_ * dTwist * dTwist;
        pot_ += p;
        tBody -= dVdtwist * V3Z;
 
        if (printRest_) restInfo_[rtTwist] = std::make_pair(twistAngle, p);
      }
 
      if (restType_ & rtSwingX) {
        RealType dSwingX = swingX - swingX0_;
        /// RealType dVdswingX = kSwingX_ * 0.5 * sin(2.0 * dSwingX);
        /// p = 0.25 * kSwingX_ * (1.0 - cos(2.0 * dSwingX));
        RealType dVdswingX = kSwingX_ * dSwingX;
        p                  = 0.5 * kSwingX_ * dSwingX * dSwingX;
        pot_ += p;
        tBody -= dVdswingX * V3X;
        if (printRest_) restInfo_[rtSwingX] = std::make_pair(swingX, p);
      }
 
      if (restType_ & rtSwingY) {
        RealType dSwingY = swingY - swingY0_;
        /// RealType dVdswingY = kSwingY_ * 0.5 * sin(2.0 * dSwingY);
        /// p = 0.25 * kSwingY_ * (1.0 - cos(2.0 * dSwingY));
        RealType dVdswingY = kSwingY_ * dSwingY;
        p                  = 0.5 * kSwingX_ * dSwingY * dSwingY;
        pot_ += p;
        tBody -= dVdswingY * V3Y;
        if (printRest_) restInfo_[rtSwingY] = std::make_pair(swingY, p);
      }
 
      Vector3d tLab = A.transpose() * tBody;
      torque_       = tLab * scaleFactor_;
    }
  }
}  // namespace OpenMD