OPLS improper¶

Description¶

The opls_improper type of improper torsion potential calculates the improper torsion potential of the OPLS force field:

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

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_improper:
  potentials_for_impropers:
    - types: [STRING, STRING, STRING, STRING]
      potential: opls_improper
      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 several atom types (species)

compute_force_bond:
  potentials_for_bonds:
    - types: [CA, CA, CA, CT]
      potential: opls_improper
      parameters:
        k1: 0.000000e-00 J
        k2: 3.476172e-20 J
        k3: 0.000000e-00 J
    - types: [CA, CA, CA, H]
      potential: opls_improper
      parameters:
        k1: 0.000000e-00 J
        k2: 3.476172e-20 J
        k3: 0.000000e-00 J