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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 epair/atom command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID epair/atom
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
<LI>epair/atom = style name of this compute command
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all epair/atom
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that computes the per-atom pairwise energy for
each atom in a group. This can be output via the <A HREF = "dump.html">dump
custom</A> command.
</P>
<P>The pairwise energy for each atom is computed by looping over its
neighbors and computing the energy associated with the defined
<A HREF = "pair_style.html">pair_style</A> command for each I,J pair (divided by 2).
Thus the sum of per-atom energy for all atoms should give the total
pairwise energy of the system.
</P>
<P>If two atoms interact and only one of them is in the compute group,
the energy of the pairwise interaction is included in the per-atom
energy of the atom in the group.
</P>
<P>For force fields that include a contribution to the pairwise energy
that is computed as part of dihedral terms (i.e. 1-4 interactions),
this contribution is NOT included in the per-atom pairwise energy.
</P>
<P>Computation of per-atom pairwise energy requires a loop thru the
neighbor list and inter-processor communication, so it can be
inefficient to compute/dump this quantity too frequently or to have
multiple compute/dump commands, each of a <I>epair/atom</I> style.
</P>
<P><B>Restrictions:</B>
</P>
<P>Some pair potentials do not allow the calculation of per-atom energy
via this command. An error will be generated if this is the case.
</P>
<P><B>Related commands:</B> none
</P>
<P><B>Default:</B> none
</P>
</HTML>
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