Cos_two¶

Description¶

The cos_two type of torsion potential calculates the torsion potential given by

\[ E = \frac{k}{2} \left ( 1 - \cos{2(\phi -\phi_0)} \right ) \]

with \(k\) and \(\phi_0\) the potential parameters decribed in the following table.

Parameter	Units	Description
\(k\)	energy	force constant
\(\phi_0\)	angle	equilibrium torsion angle

YAML syntax¶

compute_force_torsion:
  potentials_for_torsions:
    - types: [STRING, STRING, STRING, STRING]
      potential: cos_two
      parameters:
        phi0: VALUE UNITS
        k: VALUE UNITS

STRING = Name of the atom type (specie) involved in the bending angle.
VALUE = Physical value of the intended parameter.
UNITS = Units of the provided value that will be passed to the conversion helper for internal units conversion.

Usage examples¶

Systems with a single atom type (specie)

compute_force_torsion:
  potentials_for_torsions:
    - types: [C, C, C, C]
      potential: cos_two
      parameters:
        phi0: 180.0e+02 degree
        k: 8.0e-19 J

Systems with several atom types (species)

compute_force_bond:
  potentials_for_bonds:
    - types: [C, C, C, C]
      potential: cos_two
      parameters:
        phi0: 180.0e+02 degree
        k: 8.0e-19 J
    - types: [C, C, C, H]
      potential: cos_two
      parameters:
        phi0: 60.0e+02 degree
        k: 8.0e-19 J