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angle_cosine_shift_exp.html
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rLAMMPS lammps
angle_cosine_shift_exp.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 cosine/shift/exp command
</H3>
<H3>
angle_style cosine/shift/exp/omp command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
angle_style cosine/shift/exp
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
angle_style cosine/shift/exp
angle_coeff * 10.0 45.0 2.0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
cosine/shift/exp
</I>
angle style uses the potential
</P>
<CENTER><IMG
SRC =
"Eqs/angle_cosine_shift_exp.jpg"
>
</CENTER>
<P>
where Umin, theta, and a are defined for each angle type.
</P>
<P>
The potential is bounded between [-Umin:0] and the minimum is
located at the angle theta0. The a parameter can be both positive or
negative and is used to control the spring constant at the
equilibrium.
</P>
<P>
The spring constant is given by k = A exp(A) Umin / [2 (Exp(a)-1)].
For a > 3, k/Umin = a/2 to better than 5% relative error. For negative
values of the a parameter, the spring constant is essentially zero,
and anharmonic terms takes over. The potential is furthermore well
behaved in the limit a -> 0, where it has been implemented to linear
order in a for a
< 0
.
001
.
In
this
limit
the
potential
reduces
to
the
cosineshifted
potential
.
</
P
>
<P>
The following coefficients must be defined for each angle type via the
<A
HREF =
"angle_coeff.html"
>
angle_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>
<UL><LI>
umin (energy)
<LI>
theta (angle)
<LI>
A (real number)
</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 angle style can only be used if LAMMPS was built with the
USER-MISC 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>
,
<A
HREF =
"angle_cosineshift.html"
>
angle_cosineshift
</A>
,
<A
HREF =
"dihedral_cosineshift.html"
>
dihedral_cosineshift
</A>
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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