TrappeTorsionType.hpp

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 *
 * [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).
 */
 
/**
 * @file TrappeTorsionType.hpp
 * @author    Dan Gezelter
 * @date  06/11/2008
 * @version 1.0
 */
 
#ifndef TYPES_TRAPPETORSIONTYPE_HPP
#define TYPES_TRAPPETORSIONTYPE_HPP
 
#include "types/PolynomialTorsionType.hpp"
 
namespace OpenMD {
 
  /**
   * @class TrappeTorsionType TrappeTorsionType.hpp
   "types/TrappeTorsionType.hpp"
   * These torsion types are defined identically with functional form given
   * in the following paper:
   *
   * "Transferable Potentials for Phase Equilibria. 1. United-Atom
   * Description of n-Alkanes," by
   * Marcus G. Martin and J. Ilja Siepmann,
   * J. Phys. Chem. B; 1998; 102(14) pp 2569 - 2577;
   *
   * Also listed as type A torsions on this page:
   *
   *    http://siepmann6.chem.umn.edu/trappe/intro.php
   *
   * This torsion potential has the form:
   *
   *  \f[
         V_{tors} = c_0 + c_1*(1+\cos(\phi)) + c_2*(1-\cos(2*\phi)) +
                    c_3*(1+\cos(3*\phi))
       \f]
   *
   * Notes:
   *
   * 1) This is very similar to the OplsTorsionType with coefficients
   *    defined without the factor of 1/2, and an extra \f$c_0\f$ term.
   *
   * 2) Coefficients are assumed to be in kcal / mol, although the papers
   *    usually give the parameters in units of K.
   */
  class TrappeTorsionType : public PolynomialTorsionType {
  public:
    TrappeTorsionType(RealType c0, RealType c1, RealType c2, RealType c3,
                      bool trans180) :
        PolynomialTorsionType(),
        c0_(c0), c1_(c1), c2_(c2), c3_(c3) {
      // convert Trappe Torsion Type to Polynomial Torsion type
 
      RealType b0 = c0 + c1 + 2.0 * c2 + c3;
      RealType b1 = c1 - 3.0 * c3;
      RealType b2 = -2.0 * c2;
      RealType b3 = 4.0 * c3;
 
      if (!trans180) {
        b1 = -b1;
        b3 = -b3;
      }
 
      setCoefficient(0, b0);
      setCoefficient(1, b1);
      setCoefficient(2, b2);
      setCoefficient(3, b3);
    }
 
    friend std::ostream& operator<<(std::ostream& os, TrappeTorsionType& ttt);
 
  private:
    RealType c0_;
    RealType c1_;
    RealType c2_;
    RealType c3_;
  };
 
  std::ostream& operator<<(std::ostream& os, TrappeTorsionType& ttt) {
    os << "This TrappeTorsionType has below form:" << std::endl;
    os << ttt.c0_ << " + " << ttt.c1_ << "*(1+cos(phi))"
       << " + " << ttt.c2_ << "*(1-cos(2*phi))"
       << " + " << ttt.c3_ << "*(1+cos(3*phi))" << std::endl;
    return os;
  }
 
}  // namespace OpenMD
 
#endif  // TYPES_TRAPPETORSIONTYPE_HPP