md.improper

Overview

Improper

Improper potential base class.

Harmonic

Harmonic improper potential.

Details

Improper potentials.

Impropers add forces between specified quadruplets of particles and are typically used to model rotation about chemical bonds without having bonds to connect the atoms. Their most common use is to keep structural elements flat, i.e. model the effect of conjugated double bonds, like in benzene rings and its derivatives.

class hoomd.md.improper.Harmonic

Bases: hoomd.md.improper.Improper

Harmonic improper potential.

Harmonic computes the harmonic improper potential energy for every defined dihedral quadruplet of particles in the simulation:

\[V(r) = \frac{1}{2}k \left( \chi - \chi_{0} \right )^2\]

where \(\chi\) is angle between two sides of the improper.

params

The parameter of the harmonic impropers for each improper type. The dictionary has the following keys:

  • k (float, required), potential constant \(k\) \([\mathrm{energy}]\).

  • chi0 (float, required), equilibrium angle \(\chi_0\) \([\mathrm{radian}]\).

Type

TypeParameter [improper type, dict]

Example:

harmonic = hoomd.md.improper.Harmonic()
harmonic.params['A-B-C-D'] = dict(k=1.0, chi0=0)
class hoomd.md.improper.Improper

Bases: hoomd.md.force.Force

Improper potential base class.

Note

Use one of the subclasses. Users should not instantiate this class directly.