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<div class="section" id="compute-omega-chunk-command">
<span id="index-0"></span><h1>compute omega/chunk command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">omega</span><span class="o">/</span><span class="n">chunk</span> <span class="n">chunkID</span>
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="compute.html"><span class="doc">compute</span></a> command</li>
<li>omega/chunk = style name of this compute command</li>
<li>chunkID = ID of <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="mi">1</span> <span class="n">fluid</span> <span class="n">omega</span><span class="o">/</span><span class="n">chunk</span> <span class="n">molchunk</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Define a computation that calculates the angular velocity (omega) of
multiple chunks of atoms.</p>
<p>In LAMMPS, chunks are collections of atoms defined by a <a class="reference internal" href="compute_chunk_atom.html"><span class="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 <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> doc page and &#8220;<a class="reference internal" href="Section_howto.html#howto-23"><span class="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 velocity
vector for each chunk, via the formula L = Iw where L is the angular
momentum vector of the chunk, I is its moment of inertia tensor, and w
is omega = angular velocity 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 <a class="reference internal" href="compute_chunk_atom.html"><span class="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
&#8220;all&#8221; group for this command if you simply want to include atoms with
non-zero chunk IDs.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The coordinates of an atom contribute to the chunk&#8217;s angular
velocity in &#8220;unwrapped&#8221; form, by using the image flags associated with
each atom. See the <a class="reference internal" href="dump.html"><span class="doc">dump custom</span></a> command for a discussion
of &#8220;unwrapped&#8221; coordinates. See the Atoms section of the
<a class="reference internal" href="read_data.html"><span class="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 <a class="reference internal" href="set.html"><span class="doc">set image</span></a> command.</p>
</div>
<p>The simplest way to output the results of the compute omega/chunk
calculation to a file is to use the <a class="reference internal" href="fix_ave_time.html"><span class="doc">fix ave/time</span></a>
command, for example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="n">cc1</span> <span class="nb">all</span> <span class="n">chunk</span><span class="o">/</span><span class="n">atom</span> <span class="n">molecule</span>
<span class="n">compute</span> <span class="n">myChunk</span> <span class="nb">all</span> <span class="n">omega</span><span class="o">/</span><span class="n">chunk</span> <span class="n">cc1</span>
<span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">ave</span><span class="o">/</span><span class="n">time</span> <span class="mi">100</span> <span class="mi">1</span> <span class="mi">100</span> <span class="n">c_myChunk</span><span class="p">[</span><span class="o">*</span><span class="p">]</span> <span class="n">file</span> <span class="n">tmp</span><span class="o">.</span><span class="n">out</span> <span class="n">mode</span> <span class="n">vector</span>
</pre></div>
</div>
<p><strong>Output info:</strong></p>
<p>This compute calculates a global array where the number of rows = the
number of chunks <em>Nchunk</em> as calculated by the specified <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command. The number of columns =
3 for the 3 xyz components of the angular velocity for each chunk.
These values can be accessed by any command that uses global array
values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">Section_howto 15</span></a> for an overview of LAMMPS output
options.</p>
<p>The array values are &#8220;intensive&#8221;. The array values will be in
velocity/distance <a class="reference internal" href="units.html"><span class="doc">units</span></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="variable.html"><span class="doc">variable omega() function</span></a></p>
<p><strong>Default:</strong> none</p>
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