# angle_style cosine/buck6d command

## Syntax

``` LAMMPS
angle_style cosine/buck6d
```

## Examples

``` LAMMPS
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](angle_coeff) command as in the example above, or in the
data file or restart files read by the [read_data](read_data) or
[read_restart](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](pair_buck6d_coul_gauss) between the end atoms of the angle. For
this reason this angle style only works in combination with the
[pair_style buck6d](pair_buck6d_coul_gauss) styles and needs the
[special_bonds](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](pair_buck6d_coul_gauss) style and with a
[special_bonds](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](Build_package) doc page for more info.

## Related commands

[angle_coeff](angle_coeff)

## Default

none