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rLAMMPS lammps
angle_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>
angle_style class2 command
</H3>
<H3>
angle_style class2/omp command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
angle_style class2
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
angle_style class2
angle_coeff * 75.0
angle_coeff 1 bb 10.5872 1.0119 1.5228
angle_coeff * ba 3.6551 24.895 1.0119 1.5228
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
class2
</I>
angle style uses the potential
</P>
<CENTER><IMG
SRC =
"Eqs/angle_class2.jpg"
>
</CENTER>
<P>
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.
</P>
<P>
See
<A
HREF =
"#Sun"
>
(Sun)
</A>
for a description of the COMPASS class2 force field.
</P>
<P>
Coefficients for the Ea, Ebb, and Eba formulas must be defined for
each angle type via the
<A
HREF =
"bond_coeff.html"
>
bond_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 4 coefficients for the Ea formula:
</P>
<UL><LI>
theta0 (degrees)
<LI>
K2 (energy/radian^2)
<LI>
K3 (energy/radian^3)
<LI>
K4 (energy/radian^4)
</UL>
<P>
Theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of the various K are in per-radian.
</P>
<P>
For the Ebb formula, each line in a
<A
HREF =
"bond_coeff.html"
>
bond_coeff
</A>
command in the input script lists 4 coefficients, the first of which
is "bb" to indicate they are BondBond coefficients. In a data file,
these coefficients should be listed under a "BondBond Coeffs" heading
and you must leave out the "bb", i.e. only list 3 coefficients after
the angle type.
</P>
<UL><LI>
bb
<LI>
M (energy/distance^2)
<LI>
r1 (distance)
<LI>
r2 (distance)
</UL>
<P>
For the Eba formula, each line in a
<A
HREF =
"bond_coeff.html"
>
bond_coeff
</A>
command in the input script lists 5 coefficients, the first of which
is "ba" to indicate they are BondAngle coefficients. In a data file,
these coefficients should be listed under a "BondAngle Coeffs" heading
and you must leave out the "ba", i.e. only list 4 coefficients after
the angle type.
</P>
<UL><LI>
ba
<LI>
N1 (energy/distance^2)
<LI>
N2 (energy/distance^2)
<LI>
r1 (distance)
<LI>
r2 (distance)
</UL>
<P>
The theta0 value in the Eba formula is not specified, since it is the
same value from the Ea formula.
</P>
<HR>
<P>
Styles with a
<I>
cuda
</I>
,
<I>
gpu
</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-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 angle 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 =
"angle_coeff.html"
>
angle_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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