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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>pair_style lj/expand command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style lj/expand cutoff
</PRE>
<UL><LI>cutoff = global cutoff for lj/expand interactions (distance units)
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style lj/expand 2.5
pair_coeff * * 1.0 1.0 0.5
pair_coeff 1 1 1.0 1.0 -0.2 2.0
</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>lj/expand</I> computes a LJ interaction with a distance shifted by
delta which can be useful when particles are of different sizes, since
it is different that using different sigma values in a standard LJ
formula:
</P>
<CENTER><IMG SRC = "Eqs/pair_lj_expand.jpg">
</CENTER>
<P>Rc is the cutoff which does not include the delta distance. I.e. the
actual force cutoff is the sum of cutoff + delta.
</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>delta (distance units)
<LI>cutoff (distance units)
</UL>
<P>The delta values can be positive or negative. The last coefficient is
optional. If not specified, the global LJ cutoff is used.
</P>
<P>If the pair_coeff command is not used to define coefficients for a
particular I != J type pair, the mixing rule is set by the
<A HREF = "pair_modify.html">pair_modify</A> command. Additionally, the delta
coefficient is always mixed by the rule
</P>
<PRE>delta_ij = (delta_i + delta_j) / 2
</PRE>
<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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