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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>improper_style command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>improper_style style
</PRE>
<UL><LI>style = <I>none</I> or <I>hybrid</I> or <I>class2</I> or <I>cvff</I> or <I>harmonic</I>
</UL>
<P><B>Examples:</B>
</P>
<PRE>improper_style harmonic
improper_style cvff
improper_style hybrid cvff harmonic
</PRE>
<P><B>Description:</B>
</P>
<P>Set the formula(s) LAMMPS uses to compute improper interactions
between quadruplets of atoms, which remain in force for the duration
of the simulation. The list of improper quadruplets is read in by a
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A> command
from a data or restart file.
</P>
<P>Hybrid models where impropers are computed using different improper
potentials can be setup using the <I>hybrid</I> improper style.
</P>
<P>The coefficients associated with a improper style can be specified in a
data or restart file or via the <A HREF = "improper_coeff.html">improper_coeff</A> command.
</P>
<P>Note that when both an improper and pair style is defined, the
<A HREF = "special_bond.html">special_bond</A> command often needs to be used to
turn off (or weight) the pairwise interactions that would otherwise
exist between the 4 bonded atoms.
</P>
<HR>
<P>Here is an alphabetic list of improper styles defined in LAMMPS. Click on
the style to display the formula it computes and coefficients
specified by the associated <A HREF = "improper_coeff.html">improper_coeff</A> command:
</P>
<UL><LI><A HREF = "improper_style_none.html">improper_style none</A> - turn off improper interactions
<LI><A HREF = "improper_style_hybrid.html">improper_style hybrid</A> - define multiple styles of improper interactions
</UL>
<UL><LI><A HREF = "improper_style_class2.html">improper_style class2</A> - COMPASS (class 2) improper
<LI><A HREF = "improper_style_cvff.html">improper_style cvff</A> - CVFF improper
<LI><A HREF = "improper_style_harmonic.html">improper_style harmonic</A> - harmonic improper
</UL>
<HR>
<P><B>Restrictions:</B>
</P>
<P>Improper styles can only be set for atom_style choices that allow
impropers to be defined.
</P>
<P>Improper styles are part of the "molecular" package or other packages
as noted in their documentation. They are 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 = "improper_coeff.html">improper_coeff</A>
</P>
<P><B>Default:</B>
</P>
<PRE>improper_style none
</PRE>
</HTML>
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