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<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>dihedral_style charmm command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>dihedral_style charmm
</PRE>
<P><B>Examples:</B>
</P>
<PRE>dihedral_style charmm
dihedral_coeff 1 120.0 1 60 0.5
</PRE>
<P><B>Description:</B>
</P>
<P>The <I>charmm</I> dihedral style uses the potential
</P>
<CENTER><IMG SRC = "Eqs/dihedral_charmm.jpg">
</CENTER>
<P>The following coefficients must be defined for each dihedral type via the
<A HREF = "dihedral_coeff.html">dihedral_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>n (integer >= 0)
<LI>d (integer value of degrees)
<LI>weighting factor (0.0 to 1.0)
</UL>
<P>The weighting factor is applied to pairwise interaction between the
1st and 4th atoms in the dihedral. Note that this weighting factor is
unrelated to the weighting factor specified by the <A HREF = "doc/special_bonds.html">special
bonds</A> command which applies to all 1-4
interactions in the system. For CHARMM force fields, the latter
should typically be set to 0.0, else the 1-4 interactions in a
dihedral will be computed twice (once by the pair potential, and once
by the dihedral/charmm potential).
</P>
<P><B>Restrictions:</B>
</P>
<P>Dihedral styles can only be set for atom styles that allow dihedrals to be
defined.
</P>
<P>This dihedral style is part of the "molecular" package. It is only
enabled if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_2">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "dihedral_coeff.html">dihedral_coeff</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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