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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>
<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#4_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>
<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#2_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>