Quartic bend¶

Description¶

The quar_bond type of bending potential calculates a quartic bending potential given by:

\[ E = k_2 \left ( \theta -\theta_0 \right )^2 + k_3 \left ( \theta -\theta_0 \right )^3 + k_4 \left ( \theta -\theta_0 \right )^4 \]

with \(k_2\), \(k_3\), \(k_4\) and \(\theta_0\) the potential parameters decribed in the following table.

Parameter	Units	Description
\(k_2\)	energy	force constant
\(k_3\)	energy	force constant
\(k_4\)	energy	force constant
\(\theta_0\)	angle	equilibrium bending angle

YAML syntax¶

compute_force_bend:
  potentials_for_bends:
    - types: [STRING, STRING, STRING]
      potential: quar_bend
      parameters:
        theta0: VALUE UNITS
        k2: VALUE UNITS
        k3: VALUE UNITS
        k4: VALUE UNITS

STRING = Name of the atom type (specie) involved in the bond.
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_bend:
  potentials_for_bends:
    - types: [CA, CA, CA]
      potential: quar_bend
      parameters:
        theta0: 1.200000e+02 degree
        k2: 8.759953e-19 J
        k3: 0.0 J
        k4: 0.0 J

Systems with several atom types (species)

compute_force_bend:
  potentials_for_bends:
    - types: [CA, CA, CA]
      potential: quar_bend
      parameters:
        theta0: 1.200000e+02 degree
        k2: 8.759953e-19 J
        k3: 0.0 J
        k4: 0.0 J
    - types: [CA, CA, CR4]
      potential: quar_bend
      parameters:
        theta0: 1.200000e+02 degree
        k: 9.733281e-19 J
        k3: 0.0 J
        k4: 0.0 J