Skip to content

0.5 COMPASS torsion

Description

The 0.5compass_torsion type of torsion potential calculates half of the torsion potential of the COMPASS force field:

\[ E = \frac{k_1}{2} \left ( 1 - \cos{\phi}\right ) + \frac{k_2}{2} \left ( 1 - \cos{2\phi}\right ) + \frac{k_3}{2} \left ( 1 - \cos{3\phi}\right ) \]

with \(k_1\), \(k_2\) and \(k_3\) the potential parameters decribed in the following table.

Parameter Units Description
\(k_1\) energy force constant
\(k_2\) energy force constant
\(k_3\) energy force constant

YAML syntax

compute_force_torsion:
  potentials_for_torsions:
    - types: [STRING, STRING, STRING, STRING]
      potential: 0.5compass_torsion
      parameters:
        k1: VALUE UNITS
        k2: VALUE UNITS
        k3: 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: [CA, CA, CA, CA]
      potential: 0.5compass_torsion
      parameters:
        k1: 0.000000e-00 J
        k2: 1.008099e-19 J
        k3: 0.000000e-00 J

Systems with several atom types (species)

compute_force_bond:
  potentials_for_bonds:
    - types: [CA, CA, CA, CA]
      potential: 0.5compass_torsion
      parameters:
        k1: 0.000000e-00 J
        k2: 1.008099e-19 J
        k3: 0.000000e-00 J
    - types: [CA, CA, CT, CT]
      potential: 0.5compass_torsion
      parameters:
        k1: 0.000000e-00 J
        k2: 0.000000e-00 J
        k3: 0.000000e-00 J