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rLAMMPS lammps
dihedral_class2.html
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<HTML>
<CENTER><A
HREF =
"http://lammps.sandia.gov"
>
LAMMPS WWW Site
</A>
-
<A
HREF =
"Manual.html"
>
LAMMPS Documentation
</A>
-
<A
HREF =
"Section_commands.html#comm"
>
LAMMPS Commands
</A>
</CENTER>
<HR>
<H3>
dihedral_style class2 command
</H3>
<H3>
dihedral_style class2/omp command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
dihedral_style class2
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
dihedral_style class2
dihedral_coeff 1 100 75 100 70 80 60
dihedral_coeff * mbt 3.5945 0.1704 -0.5490 1.5228
dihedral_coeff * ebt 0.3417 0.3264 -0.9036 0.1368 0.0 -0.8080 1.0119 1.1010
dihedral_coeff 2 at 0.0 -0.1850 -0.7963 -2.0220 0.0 -0.3991 110.2453 105.1270
dihedral_coeff * aat -13.5271 110.2453 105.1270
dihedral_coeff * bb13 0.0 1.0119 1.1010
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
class2
</I>
dihedral style uses the potential
</P>
<CENTER><IMG
SRC =
"Eqs/dihedral_class2.jpg"
>
</CENTER>
<P>
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.
</P>
<P>
Theta1 and theta2 are equilibrium angles and r1 r2 r3 are equilibrium
bond lengths.
</P>
<P>
See
<A
HREF =
"#Sun"
>
(Sun)
</A>
for a description of the COMPASS class2 force field.
</P>
<P>
Coefficients for the Ed, Embt, Eebt, Eat, Eaat, and Ebb13 formulas
must be defined for each dihedral type via the
<A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
command as in the example above,
or in the data file or restart files read by the
<A
HREF =
"read_data.html"
>
read_data
</A>
or
<A
HREF =
"read_restart.html"
>
read_restart
</A>
commands.
</P>
<P>
These are the 6 coefficients for the Ed formula:
</P>
<UL><LI>
K1 (energy)
<LI>
phi1 (degrees)
<LI>
K2 (energy)
<LI>
phi2 (degrees)
<LI>
K3 (energy)
<LI>
phi3 (degrees)
</UL>
<P>
For the Embt formula, each line in a
<A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
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.
</P>
<UL><LI>
mbt
<LI>
A1 (energy/distance)
<LI>
A2 (energy/distance)
<LI>
A3 (energy/distance)
<LI>
r2 (distance)
</UL>
<P>
For the Eebt formula, each line in a
<A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
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.
</P>
<UL><LI>
ebt
<LI>
B1 (energy/distance)
<LI>
B2 (energy/distance)
<LI>
B3 (energy/distance)
<LI>
C1 (energy/distance)
<LI>
C2 (energy/distance)
<LI>
C3 (energy/distance)
<LI>
r1 (distance)
<LI>
r3 (distance)
</UL>
<P>
For the Eat formula, each line in a
<A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
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.
</P>
<UL><LI>
at
<LI>
D1 (energy/radian)
<LI>
D2 (energy/radian)
<LI>
D3 (energy/radian)
<LI>
E1 (energy/radian)
<LI>
E2 (energy/radian)
<LI>
E3 (energy/radian)
<LI>
theta1 (degrees)
<LI>
theta2 (degrees)
</UL>
<P>
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.
</P>
<P>
For the Eaat formula, each line in a
<A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
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.
</P>
<UL><LI>
aat
<LI>
M (energy/radian^2)
<LI>
theta1 (degrees)
<LI>
theta2 (degrees)
</UL>
<P>
Theta1 and theta2 are specified in degrees, but LAMMPS converts them
to radians internally; hence the units of M are in energy/radian^2.
</P>
<P>
For the Ebb13 formula, each line in a
<A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
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.
</P>
<UL><LI>
bb13
<LI>
N (energy/distance^2)
<LI>
r1 (distance)
<LI>
r3 (distance)
</UL>
<HR>
<P>
Styles with a
<I>
cuda
</I>
,
<I>
gpu
</I>
,
<I>
intel
</I>
,
<I>
kk
</I>
,
<I>
omp
</I>
, or
<I>
opt
</I>
suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in
<A
HREF =
"Section_accelerate.html"
>
Section_accelerate
</A>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.
</P>
<P>
These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
enabled if LAMMPS was built with those packages. See the
<A
HREF =
"Section_start.html#start_3"
>
Making
LAMMPS
</A>
section for more info.
</P>
<P>
You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the
<A
HREF =
"Section_start.html#start_7"
>
-suffix command-line
switch
</A>
when you invoke LAMMPS, or you can
use the
<A
HREF =
"suffix.html"
>
suffix
</A>
command in your input script.
</P>
<P>
See
<A
HREF =
"Section_accelerate.html"
>
Section_accelerate
</A>
of the manual for
more instructions on how to use the accelerated styles effectively.
</P>
<HR>
<P><B>
Restrictions:
</B>
</P>
<P>
This dihedral style can only be used if LAMMPS was built with the
CLASS2 package. See the
<A
HREF =
"Section_start.html#start_3"
>
Making LAMMPS
</A>
section for more info on packages.
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"dihedral_coeff.html"
>
dihedral_coeff
</A>
</P>
<P><B>
Default:
</B>
none
</P>
<HR>
<A
NAME =
"Sun"
></A>
<P><B>
(Sun)
</B>
Sun, J Phys Chem B 102, 7338-7364 (1998).
</P>
</HTML>
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