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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>
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<H3>compute pair command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID pair pstyle evalue
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
<LI>pair = style name of this compute command
<LI>pstyle = style name of a pair style that calculates additional values
<LI>evalue = <I>epair</I> or <I>evdwl</I> or <I>ecoul</I> or blank (optional setting)
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all pair gauss
compute 1 all pair lj/cut/coul/cut ecoul
compute 1 all pair reax
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that extracts additional values calculated by a
pair style, sums them across processors, and makes them accessible for
output or further processing by other commands. The group specified
for this command is ignored.
</P>
<P>The specified <I>pstyle</I> must be a pair style used in your simulation
either by itself or as a sub-style in a <A HREF = "pair_hybrid.html">pair_style hybrid or
hybrid/overlay</A> command.
</P>
<P>The <I>evalue</I> setting is optional; it may be left off the command. All
pair styles tally a potential energy <I>epair</I> which may be broken into
two parts: <I>evdwl</I> and <I>ecoul</I> such that <I>epair</I> = <I>evdwl</I> + <I>ecoul</I>.
If the pair style calculates Coulombic interactions, their energy will
be tallied in <I>ecoul</I>. Everything else (whether it is a Lennard-Jones
style van der Waals interaction or not) is tallied in <I>evdwl</I>. If
<I>evalue</I> is specified as <I>epair</I> or left out, then <I>epair</I> is stored
as a global scalar by this compute. This is useful when using
<A HREF = "pair_hybrid.html">pair_style hybrid</A> if you want to know the portion
of the total energy contributed by one sub-style. If <I>evalue</I> is
specfied as <I>evdwl</I> or <I>ecoul</I>, then just that portion of the energy
is stored as a global scalar.
</P>
<P>Some pair styles tally additional quantities, e.g. a breakdown of
potential energy into a dozen or so components is tallied by the
<A HREF = "pair_reax.html">pair_style reax</A> commmand. These values (1 or more)
are stored as a global vector by this compute. See the doc page for
<A HREF = "pair_style.html">individual pair styles</A> for info on these values.
</P>
<P><B>Output info:</B>
</P>
<P>This compute calculates a global scalar which is <I>epair</I> or <I>evdwl</I> or
<I>ecoul</I>. If the pair style supports it, it also calculates a global
vector of length >= 1, as determined by the pair style. These values
can be used by any command that uses global scalar or vector values
from a compute as input. See <A HREF = "Section_howto.html#4_15">this section</A>
for an overview of LAMMPS output options.
</P>
<P>The scalar and vector values calculated by this compute are
"extensive".
</P>
<P>The scalar value will be in energy <A HREF = "units.html">units</A>. The vector
values will typically also be in energy <A HREF = "units.html">units</A>, but
see the doc page for the pair style for details.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "compute_pe.html">compute pe</A>
</P>
<P><B>Default:</B>
</P>
<P>The default for <I>evalue</I> is <I>epair</I>.
</P>
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