CosineBendType.hpp

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 * [1] Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).
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 * [7] Lamichhane, Newman & Gezelter, J. Chem. Phys. 141, 134110 (2014).
 * [8] Bhattarai, Newman & Gezelter, Phys. Rev. B 99, 094106 (2019).
 */
 
/**
 * @file CosineBendType.hpp
 * @author    gezelter
 * @date  06/18/2010
 * @version 1.1
 */
 
#ifndef TYPES_COSINEBENDTYPE_HPP
#define TYPES_COSINEBENDTYPE_HPP
 
#include "types/BendType.hpp"
 
namespace OpenMD {
  /**
   * @class CosineBendType
   *
   * A simple harmonic bend using the cosine of the angle instead of
   * the angle itself:
   * \f[ V_\mathrm{bend} = (\cos(\theta) - \cos(\theta_0))^2 \f]
   */
  class CosineBendType : public BendType {
  public:
    CosineBendType(RealType theta, RealType k) : BendType(theta), k_(k) {
      c0_ = cos(theta);
    }
 
    void setForceConstant(RealType k) { k_ = k; }
 
    RealType getForceConstant() { return k_; }
 
    void calcForce(RealType theta, RealType& V, RealType& dVdtheta) {
      RealType ct    = cos(theta);
      RealType st    = sin(theta);
      RealType delta = ct - c0_;
 
      V = 0.5 * k_ * delta * delta;
 
      dVdtheta = -k_ * delta * st;
    }
 
  private:
    RealType k_;
    RealType c0_;
  };
}  // namespace OpenMD
 
#endif  // TYPES_COSINEBENDTYPE_HPP