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<div class="section" id="fix-setforce-command">
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<span id="index-0"></span><h1>fix setforce command<a class="headerlink" href="#fix-setforce-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="fix-setforce-cuda-command">
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<h1>fix setforce/cuda command<a class="headerlink" href="#fix-setforce-cuda-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="fix-setforce-kk-command">
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<h1>fix setforce/kk command<a class="headerlink" href="#fix-setforce-kk-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>fix ID group-ID setforce fx fy fz 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>ID, group-ID are documented in <a class="reference internal" href="fix.html"><em>fix</em></a> command</li>
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<li>setforce = style name of this fix command</li>
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<li>fx,fy,fz = force component values</li>
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<li>any of fx,fy,fz can be a variable (see below)</li>
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<li>zero or more keyword/value pairs may be appended to args</li>
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<li>keyword = <em>region</em></li>
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</ul>
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<pre class="literal-block">
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<em>region</em> value = region-ID
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region-ID = ID of region atoms must be in to have added force
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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>fix freeze indenter setforce 0.0 0.0 0.0
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fix 2 edge setforce NULL 0.0 0.0
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fix 2 edge setforce NULL 0.0 v_oscillate
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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>Set each component of force on each atom in the group to the specified
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values fx,fy,fz. This erases all previously computed forces on the
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atom, though additional fixes could add new forces. This command can
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be used to freeze certain atoms in the simulation by zeroing their
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force, either for running dynamics or performing an energy
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minimization. For dynamics, this assumes their initial velocity is
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also zero.</p>
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<p>Any of the fx,fy,fz values can be specified as NULL which means do not
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alter the force component in that dimension.</p>
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<p>Any of the 3 quantities defining the force components can be specified
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as an equal-style or atom-style <a class="reference internal" href="variable.html"><em>variable</em></a>, namely <em>fx</em>,
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<em>fy</em>, <em>fz</em>. If the value is a variable, it should be specified as
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v_name, where name is the variable name. In this case, the variable
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will be evaluated each timestep, and its value used to determine the
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force component.</p>
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<p>Equal-style variables can specify formulas with various mathematical
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functions, and include <a class="reference internal" href="thermo_style.html"><em>thermo_style</em></a> command
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keywords for the simulation box parameters and timestep and elapsed
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time. Thus it is easy to specify a time-dependent force field.</p>
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<p>Atom-style variables can specify the same formulas as equal-style
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variables but can also include per-atom values, such as atom
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coordinates. Thus it is easy to specify a spatially-dependent force
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field with optional time-dependence as well.</p>
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<p>If the <em>region</em> keyword is used, the atom must also be in the
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specified geometric <a class="reference internal" href="region.html"><em>region</em></a> in order to have force added
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to it.</p>
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<hr class="docutils" />
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<p>Styles with a <em>cuda</em> or <em>kk</em> suffix are functionally the same as the
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corresponding style without the suffix. They have been optimized to
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run faster, depending on your available hardware, as discussed in
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<a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual. The
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accelerated styles take the same arguments and should produce the same
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results, except for round-off and precision issues.</p>
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<p>The region keyword is also supported by Kokkos, but a Kokkos-enabled
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region must be used. See the region <a class="reference internal" href="region.html"><em>region</em></a> command for more
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information.</p>
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<p>These accelerated styles are part of the USER-CUDA or Kokkos package. They are
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only enabled if LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
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<p>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
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use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</p>
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</div>
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<hr class="docutils" />
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<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
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<h2>Restart, fix_modify, output, run start/stop, minimize info<a class="headerlink" href="#restart-fix-modify-output-run-start-stop-minimize-info" title="Permalink to this headline">¶</a></h2>
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<p>No information about this fix is written to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>. None of the <a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a> options
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are relevant to this fix.</p>
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<p>This fix computes a global 3-vector of forces, which can be accessed
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by various <a class="reference internal" href="Section_howto.html#howto-15"><span>output commands</span></a>. This is the
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total force on the group of atoms before the forces on individual
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atoms are changed by the fix. The vector values calculated by this
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fix are “extensive”.</p>
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<p>No parameter of this fix can be used with the <em>start/stop</em> keywords of
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the <a class="reference internal" href="run.html"><em>run</em></a> command.</p>
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<p>The forces due to this fix are imposed during an energy minimization,
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invoked by the <a class="reference internal" href="minimize.html"><em>minimize</em></a> command, but you cannot set
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forces to any value besides zero when performing a minimization. Use
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the <a class="reference internal" href="fix_addforce.html"><em>fix addforce</em></a> command if you want to apply a
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non-zero force to atoms during a minimization.</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="fix_addforce.html"><em>fix addforce</em></a>, <a class="reference internal" href="fix_aveforce.html"><em>fix aveforce</em></a></p>
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<p><strong>Default:</strong> none</p>
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