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improper_cvff.html
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Thu, Jul 10, 04:19
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rLAMMPS lammps
improper_cvff.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 cvff command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
improper_style cvff
</PRE>
<P><B>
Examples:
</B>
</P>
<PRE>
improper_style cvff
improper_coeff 1 80.0 -1 4
</PRE>
<P><B>
Description:
</B>
</P>
<P>
The
<I>
cvff
</I>
improper style uses the potential
</P>
<CENTER><IMG
SRC =
"Eqs/improper_cvff.jpg"
>
</CENTER>
<P>
where phi is the Wilson out-of-plane angle.
</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
the Wilson angle is between the plane of I,J,K and the plane of J,K,L.
This is essentially a dihedral angle, which is why the formula for
this improper style is the same as for
<A
HREF =
"dihedral_harmonic.html"
>
dihedral_style
harmonic
</A>
. Alternatively, you can think of
atoms J,K,L as being in a plane, and atom I above the plane, and the
Wilson angle 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)
<LI>
d (+1 or -1)
<LI>
n (0,1,2,3,4,6)
</UL>
<P><B>
Restrictions:
</B>
</P>
<P>
This improper 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 =
"improper_coeff.html"
>
improper_coeff
</A>
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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