<p>Define a computation that calculates the angular momemtum of multiple
chunks of atoms.</p>
<p>In LAMMPS, chunks are collections of atoms defined by a <aclass="reference internal"href="compute_chunk_atom.html"><spanclass="doc">compute chunk/atom</span></a> command, which assigns each atom
to a single chunk (or no chunk). The ID for this command is specified
as chunkID. For example, a single chunk could be the atoms in a
molecule or atoms in a spatial bin. See the <aclass="reference internal"href="compute_chunk_atom.html"><spanclass="doc">compute chunk/atom</span></a> doc page and “<aclass="reference internal"href="Section_howto.html#howto-23"><spanclass="std std-ref">Section_howto 23</span></a> for details of how chunks can be
defined and examples of how they can be used to measure properties of
a system.</p>
<p>This compute calculates the 3 components of the angular momentum
vector for each chunk, due to the velocity/momentum of the individual
atoms in the chunk around the center-of-mass of the chunk. The
calculation includes all effects due to atoms passing thru periodic
boundaries.</p>
<p>Note that only atoms in the specified group contribute to the
calculation. The <aclass="reference internal"href="compute_chunk_atom.html"><spanclass="doc">compute chunk/atom</span></a> command
defines its own group; atoms will have a chunk ID = 0 if they are not
in that group, signifying they are not assigned to a chunk, and will
thus also not contribute to this calculation. You can specify the
“all” group for this command if you simply want to include atoms with
non-zero chunk IDs.</p>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">The coordinates of an atom contribute to the chunk’s angular
momentum in “unwrapped” form, by using the image flags associated with
each atom. See the <aclass="reference internal"href="dump.html"><spanclass="doc">dump custom</span></a> command for a discussion
of “unwrapped” coordinates. See the Atoms section of the
<aclass="reference internal"href="read_data.html"><spanclass="doc">read_data</span></a> command for a discussion of image flags and
how they are set for each atom. You can reset the image flags
(e.g. to 0) before invoking this compute by using the <aclass="reference internal"href="set.html"><spanclass="doc">set image</span></a> command.</p>
</div>
<p>The simplest way to output the results of the compute angmom/chunk
calculation to a file is to use the <aclass="reference internal"href="fix_ave_time.html"><spanclass="doc">fix ave/time</span></a>
<p>This compute calculates a global array where the number of rows = the
number of chunks <em>Nchunk</em> as calculated by the specified <aclass="reference internal"href="compute_chunk_atom.html"><spanclass="doc">compute chunk/atom</span></a> command. The number of columns =
3 for the 3 xyz components of the angular momentum for each chunk.
These values can be accessed by any command that uses global array
values from a compute as input. See <aclass="reference internal"href="Section_howto.html#howto-15"><spanclass="std std-ref">Section_howto 15</span></a> for an overview of LAMMPS output
options.</p>
<p>The array values are “intensive”. The array values will be in
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