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<title>create_box 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_commands.html">3. Commands</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 class="toctree-l1"><a class="reference internal" href="Section_errors.html">12. Errors</a></li>
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<div class="section" id="create-box-command">
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<span id="index-0"></span><h1>create_box command<a class="headerlink" href="#create-box-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>create_box N region-ID keyword value ...
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</pre></div>
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</div>
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<ul class="simple">
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<li>N = # of atom types to use in this simulation</li>
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<li>region-ID = ID of region to use as simulation domain</li>
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<li>zero or more keyword/value pairs may be appended</li>
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<li>keyword = <em>bond/types</em> or <em>angle/types</em> or <em>dihedral/types</em> or <em>improper/types</em> or <em>extra/bond/per/atom</em> or <em>extra/angle/per/atom</em> or <em>extra/dihedral/per/atom</em> or <em>extra/improper/per/atom</em></li>
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</ul>
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<pre class="literal-block">
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<em>bond/types</em> value = # of bond types
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<em>angle/types</em> value = # of angle types
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<em>dihedral/types</em> value = # of dihedral types
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<em>improper/types</em> value = # of improper types
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<em>extra/bond/per/atom</em> value = # of bonds per atom
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<em>extra/angle/per/atom</em> value = # of angles per atom
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<em>extra/dihedral/per/atom</em> value = # of dihedrals per atom
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<em>extra/improper/per/atom</em> value = # of impropers per atom
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<em>extra/special/per/atom</em> value = # of special neighbors per atom
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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<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>create_box 2 mybox
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create_box 2 mybox bond/types 2 extra/bond/per/atom 1
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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>This command creates a simulation box based on the specified region.
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Thus a <a class="reference internal" href="region.html"><em>region</em></a> command must first be used to define a
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geometric domain. It also partitions the simulation box into a
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regular 3d grid of rectangular bricks, one per processor, based on the
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number of processors being used and the settings of the
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<a class="reference internal" href="processors.html"><em>processors</em></a> command. The partitioning can later be
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changed by the <a class="reference internal" href="balance.html"><em>balance</em></a> or <a class="reference internal" href="fix_balance.html"><em>fix balance</em></a> commands.</p>
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<p>The argument N is the number of atom types that will be used in the
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simulation.</p>
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<p>If the region is not of style <em>prism</em>, then LAMMPS encloses the region
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(block, sphere, etc) with an axis-aligned orthogonal bounding box
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which becomes the simulation domain.</p>
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<p>If the region is of style <em>prism</em>, LAMMPS creates a non-orthogonal
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simulation domain shaped as a parallelepiped with triclinic symmetry.
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As defined by the <a class="reference internal" href="region.html"><em>region prism</em></a> command, the
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parallelepiped has its “origin” at (xlo,ylo,zlo) and is defined by 3
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edge vectors starting from the origin given by A = (xhi-xlo,0,0); B =
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(xy,yhi-ylo,0); C = (xz,yz,zhi-zlo). <em>Xy,xz,yz</em> can be 0.0 or
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positive or negative values and are called “tilt factors” because they
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are the amount of displacement applied to faces of an originally
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orthogonal box to transform it into the parallelipiped.</p>
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<p>By default, a <em>prism</em> region used with the create_box command must
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have tilt factors (xy,xz,yz) that do not skew the box more than half
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the distance of the parallel box length. For example, if xlo = 2 and
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xhi = 12, then the x box length is 10 and the xy tilt factor must be
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between -5 and 5. Similarly, both xz and yz must be between
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-(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not a limitation,
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since if the maximum tilt factor is 5 (as in this example), then
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configurations with tilt = ..., -15, -5, 5, 15, 25, ... are all
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geometrically equivalent. If you wish to define a box with tilt
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factors that exceed these limits, you can use the <a class="reference internal" href="box.html"><em>box tilt</em></a>
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command, with a setting of <em>large</em>; a setting of <em>small</em> is the
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default.</p>
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<p>See <a class="reference internal" href="Section_howto.html#howto-12"><span>Section_howto 12</span></a> of the doc pages
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for a geometric description of triclinic boxes, as defined by LAMMPS,
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and how to transform these parameters to and from other commonly used
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triclinic representations.</p>
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<p>When a prism region is used, the simulation domain should normally be
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periodic in the dimension that the tilt is applied to, which is given
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by the second dimension of the tilt factor (e.g. y for xy tilt). This
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is so that pairs of atoms interacting across that boundary will have
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one of them shifted by the tilt factor. Periodicity is set by the
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<a class="reference internal" href="boundary.html"><em>boundary</em></a> command. For example, if the xy tilt factor
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is non-zero, then the y dimension should be periodic. Similarly, the
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z dimension should be periodic if xz or yz is non-zero. LAMMPS does
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not require this periodicity, but you may lose atoms if this is not
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the case.</p>
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<p>Also note that if your simulation will tilt the box, e.g. via the <a class="reference internal" href="fix_deform.html"><em>fix deform</em></a> command, the simulation box must be setup to
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be triclinic, even if the tilt factors are initially 0.0. You can
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also change an orthogonal box to a triclinic box or vice versa by
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using the <a class="reference internal" href="change_box.html"><em>change box</em></a> command with its <em>ortho</em> and
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<em>triclinic</em> options.</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">If the system is non-periodic (in a dimension), then
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you should not make the lo/hi box dimensions (as defined in your
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<a class="reference internal" href="region.html"><em>region</em></a> command) radically smaller/larger than the extent
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of the atoms you eventually plan to create, e.g. via the
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<a class="reference internal" href="create_atoms.html"><em>create_atoms</em></a> command. For example, if your atoms
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extend from 0 to 50, you should not specify the box bounds as -10000
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and 10000. This is because as described above, LAMMPS uses the
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specified box size to layout the 3d grid of processors. A huge
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(mostly empty) box will be sub-optimal for performance when using
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“fixed” boundary conditions (see the <a class="reference internal" href="boundary.html"><em>boundary</em></a>
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command). When using “shrink-wrap” boundary conditions (see the
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<a class="reference internal" href="boundary.html"><em>boundary</em></a> command), a huge (mostly empty) box may cause
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a parallel simulation to lose atoms the first time that LAMMPS
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shrink-wraps the box around the atoms.</p>
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</div>
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<hr class="docutils" />
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<p>The optional keywords can be used to create a system that allows for
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bond (angle, dihedral, improper) interactions, or for molecules with
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special 1-2,1-3,1-4 neighbors to be added later. These optional
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keywords serve the same purpose as the analogous keywords that can be
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used in a data file which are recognized by the
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<a class="reference internal" href="read_data.html"><em>read_data</em></a> command when it sets up a system.</p>
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<p>Note that if these keywords are not used, then the create_box command
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creates an atomic (non-molecular) simulation that does not allow bonds
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between pairs of atoms to be defined, or a <a class="reference internal" href="bond_style.html"><em>bond potential</em></a> to be specified, or for molecules with
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special neighbors to be added to the system by commands such as
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<a class="reference internal" href="create_atoms.html"><em>create_atoms mol</em></a>, <a class="reference internal" href="fix_deposit.html"><em>fix deposit</em></a>
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or <a class="reference internal" href="fix_pour.html"><em>fix pour</em></a>.</p>
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<p>As an example, see the examples/deposit/in.deposit.molecule script,
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which deposits molecules onto a substrate. Initially there are no
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molecules in the system, but they are added later by the <a class="reference internal" href="fix_deposit.html"><em>fix deposit</em></a> command. The create_box command in the
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script uses the bond/types and extra/bond/per/atom keywords to allow
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this. If the added molecule contained more than 1 special bond
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(allowed by default), an extra/special/per/atom keyword would also
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need to be specified.</p>
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</div>
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<hr class="docutils" />
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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>An <a class="reference internal" href="atom_style.html"><em>atom_style</em></a> and <a class="reference internal" href="region.html"><em>region</em></a> must have
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been previously defined to use this command.</p>
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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="read_data.html"><em>read_data</em></a>, <a class="reference internal" href="create_atoms.html"><em>create_atoms</em></a>,
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<a class="reference internal" href="region.html"><em>region</em></a></p>
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<p><strong>Default:</strong> none</p>
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