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<div class="section" id="fix-store-force-command">
<span id="index-0"></span><h1>fix store/force command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">store</span><span class="o">/</span><span class="n">force</span>
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</li>
<li>store/force = style name of this fix command</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">store</span><span class="o">/</span><span class="n">force</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Store the forces on atoms in the group at the point during each
timestep when the fix is invoked, as described below. This is useful
for storing forces before constraints or other boundary conditions are
computed which modify the forces, so that unmodified forces can be
<a class="reference internal" href="dump.html"><span class="doc">written to a dump file</span></a> or accessed by other <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a> that use per-atom quantities.</p>
<p>This fix is invoked at the point in the velocity-Verlet timestepping
immediately after <a class="reference internal" href="pair_style.html"><span class="doc">pair</span></a>, <a class="reference internal" href="bond_style.html"><span class="doc">bond</span></a>,
<a class="reference internal" href="angle_style.html"><span class="doc">angle</span></a>, <a class="reference internal" href="dihedral_style.html"><span class="doc">dihedral</span></a>,
<a class="reference internal" href="improper_style.html"><span class="doc">improper</span></a>, and <a class="reference internal" href="kspace_style.html"><span class="doc">long-range</span></a>
forces have been calculated. It is the point in the timestep when
various fixes that compute constraint forces are calculated and
potentially modify the force on each atom. Examples of such fixes are
<a class="reference internal" href="fix_shake.html"><span class="doc">fix shake</span></a>, <a class="reference internal" href="fix_wall.html"><span class="doc">fix wall</span></a>, and <a class="reference internal" href="fix_indent.html"><span class="doc">fix indent</span></a>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The order in which various fixes are applied which operate at
the same point during the timestep, is the same as the order they are
specified in the input script. Thus normally, if you want to store
per-atom forces due to force field interactions, before constraints
are applied, you should list this fix first within that set of fixes,
i.e. before other fixes that apply constraints. However, if you wish
to include certain constraints (e.g. fix shake) in the stored force,
then it could be specified after some fixes and before others.</p>
</div>
</div>
<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
<p>No information about this fix is written to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>. None of the <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> options
are relevant to this fix.</p>
<p>This fix produces a per-atom array which can be accessed by various
<a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. The number of columns
for each atom is 3, and the columns store the x,y,z forces on each
atom. The per-atom values be accessed on any timestep.</p>
<p>No parameter of this fix can be used with the <em>start/stop</em> keywords of
the <a class="reference internal" href="run.html"><span class="doc">run</span></a> command. This fix is not invoked during <a class="reference internal" href="minimize.html"><span class="doc">energy minimization</span></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="fix_store_state.html"><span class="doc">fix store_state</span></a></p>
<p><strong>Default:</strong> none</p>
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