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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li>compute property/chunk command</li>
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<div class="section" id="compute-property-chunk-command">
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<span id="index-0"></span><h1>compute property/chunk command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<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="nb">property</span><span class="o">/</span><span class="n">chunk</span> <span class="n">chunkID</span> <span class="n">input1</span> <span class="n">input2</span> <span class="o">...</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li>ID, group-ID are documented in <a class="reference internal" href="compute.html"><span class="doc">compute</span></a> command</li>
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<li>property/chunk = style name of this compute command</li>
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<li>input = one or more attributes</li>
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</ul>
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<pre class="literal-block">
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attributes = count, id, coord1, coord2, coord3
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count = # of atoms in chunk
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id = original chunk IDs before compression by <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a>
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coord123 = coordinates for spatial bins calculated by <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a>
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</pre>
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</div>
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<div class="section" id="examples">
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<h2>Examples</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="nb">property</span><span class="o">/</span><span class="n">chunk</span> <span class="n">count</span>
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<span class="n">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="nb">property</span><span class="o">/</span><span class="n">chunk</span> <span class="n">ID</span> <span class="n">coord1</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description</h2>
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<p>Define a computation that stores the specified attributes of chunks of
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atoms.</p>
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<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
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to a single chunk (or no chunk). The ID for this command is specified
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as chunkID. For example, a single chunk could be the atoms in a
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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 “<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
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defined and examples of how they can be used to measure properties of
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a system.</p>
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<p>This compute calculates and stores the specified attributes of chunks
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as global data so they can be accessed by other <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a> and used in conjunction with
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other commands that generate per-chunk data, such as <a class="reference internal" href="compute_com_chunk.html"><span class="doc">compute com/chunk</span></a> or <a class="reference internal" href="compute_msd_chunk.html"><span class="doc">compute msd/chunk</span></a>.</p>
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<p>Note that only atoms in the specified group contribute to the
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calculation of the <em>count</em> attribute. The <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command defines its own group;
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atoms will have a chunk ID = 0 if they are not in that group,
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signifying they are not assigned to a chunk, and will thus also not
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contribute to this calculation. You can specify the “all” group for
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this command if you simply want to include atoms with non-zero chunk
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IDs.</p>
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<p>The <em>count</em> attribute is the number of atoms in the chunk.</p>
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<p>The <em>id</em> attribute stores the original chunk ID for each chunk. It
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can only be used if the <em>compress</em> keyword was set to <em>yes</em> for the
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<a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command referenced by
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chunkID. This means that the original chunk IDs (e.g. molecule IDs)
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will have been compressed to remove chunk IDs with no atoms assigned
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to them. Thus a compresed chunk ID of 3 may correspond to an original
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chunk ID (molecule ID in this case) of 415. The <em>id</em> attribute will
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then be 415 for the 3rd chunk.</p>
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<p>The <em>coordN</em> attributes can only be used if a <em>binning</em> style was used
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in the <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command referenced
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by chunkID. For <em>bin/1d</em>, <em>bin/2d</em>, and <em>bin/3d</em> styles the attribute
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is the center point of the bin in the corresponding dimension. Style
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<em>bin/1d</em> only defines a <em>coord1</em> attribute. Style <em>bin/2d</em> adds a
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<em>coord2</em> attribute. Style <em>bin/3d</em> adds a <em>coord3</em> attribute.</p>
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<p>Note that if the value of the <em>units</em> keyword used in the <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom command</span></a> is <em>box</em> or <em>lattice</em>, the
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<em>coordN</em> attributes will be in distance <a class="reference internal" href="units.html"><span class="doc">units</span></a>. If the
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value of the <em>units</em> keyword is <em>reduced</em>, the <em>coordN</em> attributes
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will be in unitless reduced units (0-1).</p>
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<p>The simplest way to output the results of the compute property/chunk
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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>
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command, for example:</p>
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<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>
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<span class="n">compute</span> <span class="n">myChunk1</span> <span class="nb">all</span> <span class="nb">property</span><span class="o">/</span><span class="n">chunk</span> <span class="n">cc1</span>
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<span class="n">compute</span> <span class="n">myChunk2</span> <span class="nb">all</span> <span class="n">com</span><span class="o">/</span><span class="n">chunk</span> <span class="n">cc1</span>
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<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_myChunk1</span> <span class="n">c_myChunk2</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>
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</pre></div>
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</div>
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<p><strong>Output info:</strong></p>
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<p>This compute calculates a global vector or global array depending on
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the number of input values. The length of the vector or number of
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rows in the array is the number of chunks.</p>
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<p>This compute calculates a global vector or global array where the
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number of rows = the number of chunks <em>Nchunk</em> as calculated by the
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specified <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command. If a
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single input is specified, a global vector is produced. If two or
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more inputs are specified, a global array is produced where the number
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of columns = the number of inputs. The vector or array can be
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accessed by any command that uses global values from a compute as
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input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">this section</span></a> for an overview
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of LAMMPS output options.</p>
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<p>The vector or array values are “intensive”. The values will be
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unitless or in the units discussed above.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<blockquote>
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<div>none</div></blockquote>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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<p><a class="reference internal" href="fix_ave_chunk.html"><span class="doc">fix ave/chunk</span></a></p>
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<p><strong>Default:</strong> none</p>
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