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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 class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<div class="section" id="compute-dipole-chunk-command">
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<span id="index-0"></span><h1>compute dipole/chunk command<a class="headerlink" href="#compute-dipole-chunk-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>compute ID group-ID dipole/chunk chunkID charge-correction
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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"><em>compute</em></a> command</li>
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<li>dipole/chunk = style name of this compute command</li>
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<li>chunkID = ID of <a class="reference internal" href="compute_chunk_atom.html"><em>compute chunk/atom</em></a> command</li>
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<li>charge-correction = <em>mass</em> or <em>geometry</em>, use COM or geometric center for charged chunk correction (optional)</li>
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</ul>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>compute 1 fluid dipole/chunk molchunk
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compute dw water dipole/chunk 1 geometry
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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<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>Define a computation that calculates the dipole vector and total dipole
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for multiple chunks of 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"><em>compute chunk/atom</em></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"><em>compute chunk/atom</em></a> doc page and “<a class="reference internal" href="Section_howto.html#howto-23"><span>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 the x,y,z coordinates of the dipole vector
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and the total dipole moment for each chunk, which includes all effects
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due to atoms passing thru periodic boundaries. For chunks with a net
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charge the resulting dipole is made position independent by subtracting
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the position vector of the center of mass or geometric center times the
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net charge from the computed dipole vector.</p>
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<p>Note that only atoms in the specified group contribute to the
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calculation. The <a class="reference internal" href="compute_chunk_atom.html"><em>compute chunk/atom</em></a> command
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defines its own group; atoms will have a chunk ID = 0 if they are not
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in that group, signifying they are not assigned to a chunk, and will
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thus also not contribute to this calculation. You can specify the
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“all” group for this command if you simply want to include atoms with
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non-zero chunk IDs.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">The coordinates of an atom contribute to the chunk’s
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dipole in “unwrapped” form, by using the image flags
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associated with each atom. See the <a class="reference internal" href="dump.html"><em>dump custom</em></a> command
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for a discussion of “unwrapped” coordinates. See the Atoms section of
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the <a class="reference internal" href="read_data.html"><em>read_data</em></a> command for a discussion of image flags
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and how they are set for each atom. You can reset the image flags
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(e.g. to 0) before invoking this compute by using the <a class="reference internal" href="set.html"><em>set image</em></a> command.</p>
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</div>
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<p>The simplest way to output the results of the compute com/chunk
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calculation to a file is to use the <a class="reference internal" href="fix_ave_time.html"><em>fix ave/time</em></a>
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command, for example:</p>
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<div class="highlight-python"><div class="highlight"><pre>compute cc1 all chunk/atom molecule
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compute myChunk all dipole/chunk cc1
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fix 1 all ave/time 100 1 100 c_myChunk file tmp.out mode vector
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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 array where the number of rows = the
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number of chunks <em>Nchunk</em> as calculated by the specified <a class="reference internal" href="compute_chunk_atom.html"><em>compute chunk/atom</em></a> command. The number of columns =
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4 for the x,y,z dipole vector components and the total dipole of each
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chunk. These values can be accessed by any command that uses global
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array values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span>Section_howto 15</span></a> for an overview of LAMMPS output
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options.</p>
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<p>The array values are “intensive”. The array values will be in
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dipole units, i.e. charge units times distance <a class="reference internal" href="units.html"><em>units</em></a>.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></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<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="compute_com_chunk.html"><em>compute com/chunk</em></a></p>
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<p><strong>Default:</strong> none</p>
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