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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>compute displace/atom command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID displace/atom fix-ID
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
<LI>displace/atom = style name of this compute command
<LI>fix-ID = ID of a fix of style <A HREF = "fix_coord_original.html">coord/original</A>
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all displace/atom myCoords
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that calculates the current displacement of each
atom in the group from its original coordinates, including all effects
due to atoms passing thru periodic boundaries. The original
coordinates are stored by a <A HREF = "fix_coord_original.html">fix
coord/original</A> command, whose ID must be
specified with this compute. They are the coordinates at the time the
fix command was issued. The displacement can be output directly via
the <A HREF = "dump.html">dump custom</A> command. It could also be used to
calculate a diffusion coefficient for a group of atoms, as is done by
the <A HREF = "fix_msd.html">fix msd</A> command.
</P>
<P>The value of the displacement will be 0.0 for atoms not in the
specified compute group. Note that the fix defines its own group and
stores (0.0,0.0,0.0) for the original coordinates of any atom not in
the fix group.
</P>
<P><B>Output info:</B>
</P>
<P>This compute calculates a vector of length 4 for each atom, which can
be accessed by indices 1-4 by any command that uses per-atom computes
as input. See <A HREF = "Section_howto.html#4_15">this section</A> for an overview
of LAMMPS output options. The first 3 components of the vector are
the x,y,z displacements. The 4th component is the total displacement,
i.e. sqrt(dx*dx + dy*dy + dz*dz).
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "dump.html">dump custom</A>, <A HREF = "fix_msd.html">fix msd</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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