lammps/doc/angle_class2.txt

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angle_style class2 command :h3

[Syntax:]

angle_style class2 :pre

[Examples:]

angle_style class2
angle_coeff * 75.0 :pre

[Description:]

The {class2} angle style uses the potential

:c,image(Eqs/angle_class2.jpg)

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)"_#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^2)
K4 (energy/radian^2) :ul

Theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.

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) :ul

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) :ul

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_start.html#2_3
section for more info on packages.

[Related commands:]

"angle_coeff"_angle_coeff.html

[Default:] none

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:link(Sun)
[(Sun)] Sun, J Phys Chem B 102, 7338-7364 (1998).