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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/expand command
</H3>
<H3>pair_style lj/expand/cuda command
</H3>
<H3>pair_style lj/expand/gpu command
</H3>
<H3>pair_style lj/expand/omp 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, or by mixing as described below:
</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>
<HR>
<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>omp</I>, or <I>opt</I> suffix are functionally
the same as the corresponding style without the suffix. They have
been optimized to run faster, depending on your available hardware,
as discussed in <A HREF = "Section_accelerate.html">this section</A> of the manual.
The accelerated styles take the same arguments and should produce the
same results, except for round-off and precision issues.
</P>
<P>These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
packages, respectively. They are only enabled if LAMMPS was built with
those packages. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
section for more info.
</P>
<P>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <A HREF = "Section_start.html#start_6">-suffix command-line
switch</A> when you invoke LAMMPS, or you can
use the <A HREF = "suffix.html">suffix</A> command in your input script.
</P>
<P>See <A HREF = "Section_accelerate.html">this section</A> of the manual for more
instructions on how to use the accelerated styles effectively.
</P>
<HR>
<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
</P>
<P>For atom type pairs I,J and I != J, the epsilon, sigma, and shift
coefficients and cutoff distance for this pair style can be mixed.
Shift is always mixed via an <I>arithmetic</I> rule. The other
coefficients are mixed according to the pair_modify mix value. The
default mix value is <I>geometric</I>. See the "pair_modify" command for
details.
</P>
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
option for the energy of the pair interaction.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
for this pair style.
</P>
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> tail
option for adding a long-range tail correction to the energy and
pressure of the pair interaction.
</P>
<P>This pair style writes its information to <A HREF = "restart.html">binary restart
files</A>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.
</P>
<P>This pair style can only be used via the <I>pair</I> keyword of the
<A HREF = "run_style.html">run_style respa</A> command. It does not support the
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
</P>
<HR>
<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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