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### angle_style class2 command

Syntax:

    angle_style class2

Examples:

    angle_style class2
    angle_coeff * 75.0

Description:

The class2 angle style uses the potential

where Ea is the angle term, Ebb is a bond-bond term, and Eba is a bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are the equilibrium bond lengths.

See (Sun) for a description of the COMPASS class2 force field.

For this style, coefficients for the Ea formula can be specified in the input script or data file. These are the 4 coefficients:

- theta0 (degrees)
- K2 (energy/radian^2)
- K3 (energy/radian^3)
- K4 (energy/radian^4)

Theta0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of the various K are in per-radian.

Coefficients for the Ebb and Eba formulas can only be specified in the data file.

For the Ebb formula, the coefficients are listed under a "BondBond Coeffs" heading and each line lists 3 coefficients:

- M (energy/distance^2)
- r1 (distance)
- r2 (distance)

For the Eba formula, the coefficients are listed under a "BondAngle Coeffs" heading and each line lists 4 coefficients:

- N1 (energy/distance^2)
- N2 (energy/distance^2)
- r1 (distance)
- r2 (distance)

The theta0 value in the Eba formula is not specified, since it is the same value from the Ea formula.

Restrictions:

This angle style can only be used if LAMMPS was built with the "class2" package. See the Making LAMMPS section for more info on packages.

Related commands:

angle_coeff

Default: none

(Sun) Sun, J Phys Chem B 102, 7338-7364 (1998).