<li>group-ID = ID of group of atoms to (optionally) displace</li>
<li>one or more parameter/arg pairs may be appended</li>
</ul>
<pre class="literal-block">
parameter = <em>x</em> or <em>y</em> or <em>z</em> or <em>xy</em> or <em>xz</em> or <em>yz</em> or <em>boundary</em> or <em>ortho</em> or <em>triclinic</em> or <em>set</em> or <em>remap</em>
<span class="n">change_box</span> <span class="n">boundary</span> <span class="n">s</span> <span class="n">s</span> <span class="n">s</span> <span class="c1"># this will work</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Unlike the earlier “displace_box” version of this command, atom
remapping is NOT performed by default. This command allows remapping
to be done in a more general way, exactly when you specify it (zero or
more times) in the sequence of transformations. Thus if you do not
use the <em>remap</em> keyword, atom coordinates will not be changed even if
the box size/shape changes. If a uniformly strained state is desired,
the <em>remap</em> keyword should be specified.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">It is possible to lose atoms with this command. E.g. by
changing the box without remapping the atoms, and having atoms end up
outside of non-periodic boundaries. It is also possible to alter
bonds between atoms straddling a boundary in bad ways. E.g. by
converting a boundary from periodic to non-periodic. It is also
possible when remapping atoms to put them (nearly) on top of each
other. E.g. by converting a boundary from non-periodic to periodic.
All of these will typically lead to bad dynamics and/or generate error
messages.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The simulation box size/shape can be changed by arbitrarily
large amounts by this command. This is not a problem, except that the
mapping of processors to the simulation box is not changed from its
initial 3d configuration; see the <a class="reference internal" href="processors.html"><span class="doc">processors</span></a>
command. Thus, if the box size/shape changes dramatically, the
mapping of processors to the simulation box may not end up as optimal
as the initial mapping attempted to be.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Because the keywords used in this command are applied one at a
time to the simulation box and the atoms in it, care must be taken
with triclinic cells to avoid exceeding the limits on skew after each
transformation in the sequence. If skew is exceeded before the final
transformation this can be avoided by changing the order of the
sequence, or breaking the transformation into two or more smaller
transformations. For more information on the allowed limits for box
skew see the discussion on triclinic boxes on <a class="reference internal" href="Section_howto.html#howto-12"><span class="std std-ref">this page</span></a>.</p>
</div>
<hr class="docutils" />
<p>For the <em>x</em>, <em>y</em>, and <em>z</em> parameters, this is the meaning of their
styles and values.</p>
<p>For style <em>final</em>, the final lo and hi box boundaries of a dimension
are specified. The values can be in lattice or box distance units.
See the discussion of the units keyword below.</p>
<p>For style <em>delta</em>, plus or minus changes in the lo/hi box boundaries
of a dimension are specified. The values can be in lattice or box
distance units. See the discussion of the units keyword below.</p>
<p>For style <em>scale</em>, a multiplicative factor to apply to the box length
of a dimension is specified. For example, if the initial box length
is 10, and the factor is 1.1, then the final box length will be 11. A
factor less than 1.0 means compression.</p>
<p>The <em>volume</em> style changes the specified dimension in such a way that
the overall box volume remains constant with respect to the operation
performed by the preceding keyword. The <em>volume</em> style can only be
used following a keyword that changed the volume, which is any of the
<em>x</em>, <em>y</em>, <em>z</em> keywords. If the preceding keyword “key” had a <em>volume</em>
style, then both it and the current keyword apply to the keyword
preceding “key”. I.e. this sequence of keywords is allowed:</p>
command. This command allows the boundary conditions to be changed
later in your input script. Also note that the
<a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> will change boundary conditions to
match what is stored in the restart file. So if you wish to change
them, you should use the change_box command after the read_restart
command.</p>
<hr class="docutils" />
<p>The <em>ortho</em> and <em>triclinic</em> keywords convert the simulation box to be
orthogonal or triclinic (non-orthongonal). See <a class="reference internal" href="Section_howto.html#howto-13"><span class="std std-ref">this section</span></a> for a discussion of how non-orthongal
boxes are represented in LAMMPS.</p>
<p>The simulation box is defined as either orthogonal or triclinic when
it is created via the <a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a>,
<p>These keywords allow you to toggle the existing simulation box from
orthogonal to triclinic and vice versa. For example, an initial
equilibration simulation can be run in an orthogonal box, the box can
be toggled to triclinic, and then a <a class="reference internal" href="Section_howto.html#howto-13"><span class="std std-ref">non-equilibrium MD (NEMD) simulation</span></a> can be run with deformation
via the <a class="reference internal" href="fix_deform.html"><span class="doc">fix deform</span></a> command.</p>
<p>If the simulation box is currently triclinic and has non-zero tilt in
xy, yz, or xz, then it cannot be converted to an orthogonal box.</p>
<hr class="docutils" />
<p>The <em>set</em> keyword saves the current box size/shape. This can be
useful if you wish to use the <em>remap</em> keyword more than once or if you
wish it to be applied to an intermediate box size/shape in a sequence
of keyword operations. Note that the box size/shape is saved before
any of the keywords are processed, i.e. the box size/shape at the time
the create_box command is encountered in the input script.</p>
<p>The <em>remap</em> keyword remaps atom coordinates from the last saved box
size/shape to the current box state. For example, if you stretch the
box in the x dimension or tilt it in the xy plane via the <em>x</em> and <em>xy</em>
keywords, then the <em>remap</em> commmand will dilate or tilt the atoms to
conform to the new box size/shape, as if the atoms moved with the box
as it deformed.</p>
<p>Note that this operation is performed without regard to periodic
boundaries. Also, any shrink-wrapping of non-periodic boundaries (see
the <a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> command) occurs after all keywords,
including this one, have been processed.</p>
<p>Only atoms in the specified group are remapped.</p>
<hr class="docutils" />
<p>The <em>units</em> keyword determines the meaning of the distance units used
to define various arguments. A <em>box</em> value selects standard distance
units as defined by the <span class="xref doc">units</span> command, e.g. Angstroms for
units = real or metal. A <em>lattice</em> value means the distance units are
in lattice spacings. The <a class="reference internal" href="lattice.html"><span class="doc">lattice</span></a> command must have
been previously used to define the lattice spacing.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>If you use the <em>ortho</em> or <em>triclinic</em> keywords, then at the point in
the input script when this command is issued, no <a class="reference internal" href="dump.html"><span class="doc">dumps</span></a> can
be active, nor can a <a class="reference internal" href="fix_ave_spatial.html"><span class="doc">fix ave/spatial</span></a> or <a class="reference internal" href="fix_deform.html"><span class="doc">fix deform</span></a> be active. This is because these commands
test whether the simulation box is orthogonal when they are first
issued. Note that these commands can be used in your script before a
change_box command is issued, so long as an <a class="reference internal" href="undump.html"><span class="doc">undump</span></a> or
<a class="reference internal" href="unfix.html"><span class="doc">unfix</span></a> command is also used to turn them off.</p>
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