"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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dihedral_style class2 command :h3

[Syntax:]

dihedral_style class2 :pre

[Examples:]

dihedral_style class2
dihedral_coeff 1 100 75 100 70 80 60 :pre

[Description:]

The {class2} dihedral style uses the potential

:c,image(Eqs/dihedral_class2.jpg)

where Ed is the dihedral term, Embt is a middle-bond-torsion term,
Eebt is an end-bond-torsion term, Eat is an angle-torsion term, Eaat
is an angle-angle-torsion term, and Ebb13 is a bond-bond-13 term.

Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
bond lengths.

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

For this style, coefficients for the Ed formula can be specified in
either the input script or data file.  These are the 6 coefficients:

K1 (energy)
phi1 (degrees)
K2 (energy)
phi2 (degrees)
K3 (energy)
phi3 (degrees) :ul

Coefficients for all the other formulas can only be specified in the
data file.

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

A1 (energy/distance)
A2 (energy/distance)
A3 (energy/distance)
r2 (distance) :ul

For the Eebt formula, the coefficients are listed under a
"EndBondTorsion Coeffs" heading and each line lists 8 coefficients:

B1 (energy/distance)
B2 (energy/distance)
B3 (energy/distance)
C1 (energy/distance)
C2 (energy/distance)
C3 (energy/distance)
r1 (distance)
r3 (distance) :ul

For the Eat formula, the coefficients are listed under a "AngleTorsion
Coeffs" heading and each line lists 8 coefficients:

D1 (energy/radian)
D2 (energy/radian)
D3 (energy/radian)
E1 (energy/radian)
E2 (energy/radian)
E3 (energy/radian)
theta1 (degrees)
theta2 (degrees) :ul

Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of D and E are in
energy/radian.

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

M (energy/radian^2)
theta1 (degrees)
theta2 (degrees) :ul

Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of M are in energy/radian^2.

For the Ebb13 formula, the coefficients are listed under a "BondBond13
Coeffs" heading and each line lists 3 coefficients:

N (energy/distance^2)
r1 (distance)
r3 (distance) :ul

[Restrictions:]

This dihedral 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:]

"dihedral_coeff"_dihedral_coeff.html

[Default:] none

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