lammps/doc/dihedral_class2.txt

"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)

:line

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.

Coefficients for the Ed, Embt, Eebt, Eat, Eaat, and Ebb13 formulas
must be defined for each dihedral type via the
"dihedral_coeff"_dihedral_coeff.html command as in the example above,
or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands.

These are the 6 coefficients for the Ed formula:

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

For the Embt formula, each line in a
"dihedral_coeff"_dihedral_coeff.html command in the input script lists
5 coefficients, the first of which is "mbt" to indicate they are
MiddleBondTorsion coefficients.  In a data file, these coefficients
should be listed under a "MiddleBondTorsion Coeffs" heading and you
must leave out the "mbt", i.e. only list 4 coefficients after the
dihedral type.

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

For the Eebt formula, each line in a
"dihedral_coeff"_dihedral_coeff.html command in the input script lists
9 coefficients, the first of which is "ebt" to indicate they are
EndBondTorsion coefficients.  In a data file, these coefficients
should be listed under a "EndBondTorsion Coeffs" heading and you must
leave out the "ebt", i.e. only list 8 coefficients after the dihedral
type.

ebt
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, each line in a
"dihedral_coeff"_dihedral_coeff.html command in the input script lists
9 coefficients, the first of which is "at" to indicate they are
AngleTorsion coefficients.  In a data file, these coefficients should
be listed under a "AngleTorsion Coeffs" heading and you must leave out
the "at", i.e. only list 8 coefficients after the dihedral type.

at
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, each line in a
"dihedral_coeff"_dihedral_coeff.html command in the input script lists
4 coefficients, the first of which is "aat" to indicate they are
AngleAngleTorsion coefficients.  In a data file, these coefficients
should be listed under a "AngleAngleTorsion Coeffs" heading and you
must leave out the "aat", i.e. only list 3 coefficients after the
dihedral type.

aat
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, each line in a
"dihedral_coeff"_dihedral_coeff.html command in the input script lists
4 coefficients, the first of which is "bb13" to indicate they are
BondBond13 coefficients.  In a data file, these coefficients should be
listed under a "BondBond13 Coeffs" heading and you must leave out the
"bb13", i.e. only list 3 coefficients after the dihedral type.

bb13
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

:line

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