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rLAMMPS lammps
angle_cosine_periodic.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/periodic command
</H3>
<H3>
angle_style cosine/periodic/omp command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
angle_style cosine/periodic
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
angle_style cosine/periodic
angle_coeff * 75.0 1 6
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
cosine/periodic
</I>
angle style uses the following potential, which
is commonly used in the
<A
HREF =
"Section_howto.html#howto_4"
>
DREIDING
</A>
force
field, particularly for organometallic systems where
<I>
n
</I>
= 4 might be
used for an octahedral complex and
<I>
n
</I>
= 3 might be used for a
trigonal center:
</P>
<CENTER><IMG
SRC =
"Eqs/angle_cosine_periodic.jpg"
>
</CENTER>
<P>
where C, B and n are coefficients defined for each angle type.
</P>
<P>
See
<A
HREF =
"#Mayo"
>
(Mayo)
</A>
for a description of the DREIDING force field
</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>
C (energy)
<LI>
B = 1 or -1
<LI>
n = 1, 2, 3, 4, 5 or 6 for periodicity
</UL>
<P>
Note that the prefactor C is specified and not the overall force
constant K = C / n^2. When B = 1, it leads to a minimum for the
linear geometry. When B = -1, it leads to a maximum for the linear
geometry.
</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
MOLECULAR package (which it is by default). 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 =
"Mayo"
></A>
<P><B>
(Mayo)
</B>
Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
(1990).
</P>
</HTML>
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