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<title>replicate command — LAMMPS 15 May 2015 version documentation</title>
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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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<li class="toctree-l1"><a class="reference internal" href="Section_howto.html">6. How-to discussions</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_python.html">11. Python interface to LAMMPS</a></li>
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<li>replicate command</li>
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<div class="section" id="replicate-command">
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<span id="index-0"></span><h1>replicate command<a class="headerlink" href="#replicate-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>replicate nx ny nz
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</pre></div>
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</div>
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<ul class="simple">
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<li>nx,ny,nz = replication factors in each dimension</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>replicate 2 3 2
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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>Replicate the current simulation one or more times in each dimension.
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For example, replication factors of 2,2,2 will create a simulation
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with 8x as many atoms by doubling the simulation domain in each
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dimension. A replication factor of 1 in a dimension leaves the
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simulation domain unchanged. When the new simulation box is created
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it is also partitioned into a regular 3d grid of rectangular bricks,
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one per processor, based on the number of processors being used and
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the settings of the <a class="reference internal" href="processors.html"><em>processors</em></a> command. The
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partitioning can later be changed by the <a class="reference internal" href="balance.html"><em>balance</em></a> or
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<a class="reference internal" href="fix_balance.html"><em>fix balance</em></a> commands.</p>
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<p>All properties of the atoms are replicated, including their
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velocities, which may or may not be desirable. New atom IDs are
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assigned to new atoms, as are molecule IDs. Bonds and other topology
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interactions are created between pairs of new atoms as well as between
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old and new atoms. This is done by using the image flag for each atom
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to “unwrap” it out of the periodic box before replicating it.</p>
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<p>This means that any molecular bond you specify in the original data
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file that crosses a periodic boundary should be between two atoms with
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image flags that differ by 1. This will allow the bond to be
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unwrapped appropriately.</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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<p>A 2d simulation cannot be replicated in the z dimension.</p>
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<p>If a simulation is non-periodic in a dimension, care should be used
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when replicating it in that dimension, as it may put atoms nearly on
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top of each other.</p>
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<div class="admonition warning">
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<p class="first admonition-title">Warning</p>
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<p class="last">You cannot use the replicate command on a system which
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has a molecule that spans the box and is bonded to itself across a
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periodic boundary, so that the molecule is efffectively a loop. A
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simple example would be a linear polymer chain that spans the
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simulation box and bonds back to itself across the periodic boundary.
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More realistic examples would be a CNT (meant to be an infinitely long
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CNT) or a graphene sheet or a bulk periodic crystal where there are
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explicit bonds specified between near neighbors. (Note that this only
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applies to systems that have permanent bonds as specified in the data
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file. A CNT that is just atoms modeled with the <a class="reference internal" href="pair_airebo.html"><em>AIREBO potential</em></a> has no such permanent bonds, so it can be
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replicated.) The reason replication does not work with those systems
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is that the image flag settings described above cannot be made
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consistent. I.e. it is not possible to define images flags so that
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when every pair of bonded atoms is unwrapped (using the image flags),
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they will be close to each other. The only way the replicate command
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could work in this scenario is for it to break a bond, insert more
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atoms, and re-connect the loop for the larger simulation box. But it
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is not clever enough to do this. So you will have to construct a
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larger version of your molecule as a pre-processing step and input a
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new data file to LAMMPS.</p>
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</div>
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<p>If the current simulation was read in from a restart file (before a
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run is performed), there can have been no fix information stored in
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the file for individual atoms. Similarly, no fixes can be defined at
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the time the replicate command is used that require vectors of atom
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information to be stored. This is because the replicate command does
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not know how to replicate that information for new atoms it creates.</p>
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<p>Replicating a system that has rigid bodies (defined via the <a class="reference internal" href="fix_rigid.html"><em>fix rigid</em></a> command), either currently defined or that
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created the restart file which was read in before replicating, can
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cause problems if there is a bond between a pair of rigid bodies that
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straddle a periodic boundary. This is because the periodic image
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information for particles in the rigid bodies are set differently than
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for a non-rigid system and can result in a new bond being created that
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spans the periodic box. Thus you cannot use the replicate command in
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this scenario.</p>
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<p><strong>Related commands:</strong> none</p>
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<p><strong>Default:</strong> none</p>
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