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rLAMMPS lammps
improper_harmonic.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>
improper_style harmonic command
</H3>
<H3>
improper_style harmonic/kk command
</H3>
<H3>
improper_style harmonic/omp command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
improper_style harmonic
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
improper_style harmonic
improper_coeff 1 100.0 0
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
harmonic
</I>
improper style uses the potential
</P>
<CENTER><IMG
SRC =
"Eqs/improper_harmonic.jpg"
>
</CENTER>
<P>
where X is the improper angle, X0 is its equilibrium value, and K is a
prefactor. Note that the usual 1/2 factor is included in K.
</P>
<P>
If the 4 atoms in an improper quadruplet (listed in the data file read
by the
<A
HREF =
"read_data.html"
>
read_data
</A>
command) are ordered I,J,K,L then X
is the angle between the plane of I,J,K and the plane of J,K,L.
Alternatively, you can think of atoms J,K,L as being in a plane, and
atom I above the plane, and X as a measure of how far out-of-plane I
is with respect to the other 3 atoms.
</P>
<P>
Note that defining 4 atoms to interact in this way, does not mean that
bonds necessarily exist between I-J, J-K, or K-L, as they would in a
linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an
improper to be defined between the 4 atoms.
</P>
<P>
The following coefficients must be defined for each improper type via
the
<A
HREF =
"improper_coeff.html"
>
improper_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>
K (energy/radian^2)
<LI>
X0 (degrees)
</UL>
<P>
X0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.
</P>
<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 improper style can only be used if LAMMPS was built with the
MOLECULE 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 =
"improper_coeff.html"
>
improper_coeff
</A>
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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