# 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 USER-MOFFF package. See the Build package doc page for more info.

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