angle_style cross command — LAMMPS documentation

\(\renewcommand{\AA}{\text{Å}}\)

# angle_style cross command

## Syntax

    angle_style cross

## Examples

    angle_style cross
    angle_coeff 1 200.0 100.0 100.0 1.25 1.25 107.0

## Description

The cross angle style uses a potential that couples the bond stretches of a bend with the angle stretch of that bend:

\[E = K_{SS} \left(r_{12}-r_{12,0}\right)\left(r_{32}-r_{32,0}\right) + K_{BS0}\left(r_{12}-r_{12,0}\right)\left(\theta-\theta_0\right) + K_{BS1}\left(r_{32}-r_{32,0}\right)\left(\theta-\theta_0\right)\]

where \(r_{12,0}\) is the rest value of the bond length between atom 1 and 2, \(r_{32,0}\) is the rest value of the bond length between atom 3 and 2, and \(\theta_0\) is the rest value of the angle. \(K_{SS}\) is the force constant of the bond stretch-bond stretch term and \(K_{BS0}\) and \(K_{BS1}\) are the force constants of the bond stretch-angle stretch terms.

The following 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:

- \(K_{SS}\) (energy/distance^2)

- \(K_{BS0}\) (energy/distance)

- \(K_{BS1}\) (energy/distance)

- \(r_{12,0}\) (distance)

- \(r_{32,0}\) (distance)

- \(\theta_0\) (degrees)

\(\theta_0\) is specified in degrees, but LAMMPS converts it to radians internally; hence the \(K_{BS0}\) and \(K_{BS1}\) are effectively energy/distance per radian.

## Restrictions

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

## Related commands

angle_coeff

## Default

none