angle_style cosine/buck6d command — LAMMPS documentation

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# angle_style cosine/buck6d command

## Syntax

    angle_style cosine/buck6d

## Examples

    angle_style cosine/buck6d
    angle_coeff 1  cosine/buck6d  1.978350  4  180.000000

## Description

The cosine/buck6d angle style uses the potential

\[E = K \left[ 1 + \cos(n\theta - \theta_0)\right]\]

where \(K\) is the energy constant, \(n\) is the periodic multiplicity and \(\theta_0\) is the equilibrium angle.

The coefficients must be defined for each angle type via the angle_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands in the following order:

- \(K\) (energy)

- \(n\)

- \(\theta_0\) (degrees)

\(\theta_0\) is specified in degrees, but LAMMPS converts it to radians internally.

Additional to the cosine term the cosine/buck6d angle style computes the short range (vdW) interaction belonging to the pair_style buck6d between the end atoms of the angle. For this reason this angle style only works in combination with the pair_style buck6d styles and needs the special_bonds 1-3 interactions to be weighted 0.0 to prevent double counting.

## Restrictions

cosine/buck6d can only be used in combination with the pair_style buck6d style and with a special_bonds 0.0 weighting of 1-3 interactions.

This angle style can only be used if LAMMPS was built with the MOFFF package. See the Build package doc page for more info.

## Related commands

angle_coeff

## Default

none