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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>pair_style lj/smooth command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style lj/smooth Rin cutoff
</PRE>
<UL><LI>Rin = global inner cutoff beyond which force smoothing will be applied (distance units)
<LI>cutoff = global cutoff for lj/smooth interactions (distance units)
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style lj/smooth 8.0 10.0
pair_coeff * * 10.0 1.5
pair_coeff 1 1 20.0 1.3 7.0 9.0
</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>lj/smooth</I> computes a LJ interaction with a force smoothing
applied between the inner and outer cutoff.
</P>
<CENTER><IMG SRC = "Eqs/pair_lj_smooth.jpg">
</CENTER>
<P>The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to
cause the force to vary smoothly from Rin to Rc. At Rin the force and
its 1st derivative will match the unsmoothed LJ formula. At Rc the
force and its 1st derivative will be 0.0.
</P>
<P>IMPORTANT NOTE: this force smoothing causes the energy to be
discontinuous both in its values and 1st derivative. This can lead to
poor energy conservation and may require the use of a thermostat.
Plot the energy and force resulting from this formula via the
<A HREF = "pair_write.html">pair_write</A> command to see the effect.
</P>
<P>The following coefficients must be defined for each pair of atoms
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the examples
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>epsilon (energy units)
<LI>sigma (distance units)
<LI>Rin (distance units)
<LI>cutoff (distance units)
</UL>
<P>The last 2 coefficients are optional. If not specified, the global
Rin and cutoff are used. Rin cannot be 0.0. If Rin = cutoff, then no
force smoothing is performed for this type pair; the standard LJ
formula is used.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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