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<title>compute pe command — LAMMPS 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_python.html">11. Python interface to LAMMPS</a></li>
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<div class="section" id="compute-pe-command">
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<span id="index-0"></span><h1>compute pe command<a class="headerlink" href="#compute-pe-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="compute-pe-cuda-command">
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<h1>compute pe/cuda command<a class="headerlink" href="#compute-pe-cuda-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>compute ID group-ID pe keyword ...
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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="compute.html"><em>compute</em></a> command</li>
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<li>pe = style name of this compute command</li>
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<li>zero or more keywords may be appended</li>
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<li>keyword = <em>pair</em> or <em>bond</em> or <em>angle</em> or <em>dihedral</em> or <em>improper</em> or <em>kspace</em></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>compute 1 all pe
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compute molPE all pe bond angle dihedral improper
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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>Define a computation that calculates the potential energy of the
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entire system of atoms. The specified group must be “all”. See the
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<a class="reference internal" href="compute_pe_atom.html"><em>compute pe/atom</em></a> command if you want per-atom
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energies. These per-atom values could be summed for a group of atoms
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via the <a class="reference internal" href="compute_reduce.html"><em>compute reduce</em></a> command.</p>
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<p>The energy is calculated by the various pair, bond, etc potentials
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defined for the simulation. If no extra keywords are listed, then the
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potential energy is the sum of pair, bond, angle, dihedral, improper,
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and kspace (long-range) energy. If any extra keywords are listed,
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then only those components are summed to compute the potential energy.</p>
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<p>The Kspace contribution requires 1 extra FFT each timestep the energy
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is calculated, if using the PPPM solver via the <a class="reference internal" href="kspace_style.html"><em>kspace_style pppm</em></a> command. Thus it can increase the cost of the
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PPPM calculation if it is needed on a large fraction of the simulation
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timesteps.</p>
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<p>Various fixes can contribute to the total potential energy of the
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system. See the doc pages for <a class="reference internal" href="fix.html"><em>individual fixes</em></a> for
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details. The <em>thermo</em> option of the
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<a class="reference internal" href="compute_modify.html"><em>compute_modify</em></a> command determines whether these
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contributions are added into the computed potential energy. If no
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keywords are specified the default is <em>yes</em>. If any keywords are
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specified, the default is <em>no</em>.</p>
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<p>A compute of this style with the ID of “thermo_pe” is created when
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LAMMPS starts up, as if this command were in the input script:</p>
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<div class="highlight-python"><div class="highlight"><pre>compute thermo_pe all pe
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</pre></div>
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</div>
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<p>See the “thermo_style” command for more details.</p>
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<hr class="docutils" />
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<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.</p>
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<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. 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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<hr class="docutils" />
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<p><strong>Output info:</strong></p>
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<p>This compute calculates a global scalar (the potential energy). This
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value can be used by any command that uses a global scalar value from
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a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span>Section_howto 15</span></a> for an overview of LAMMPS output
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options.</p>
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<p>The scalar value calculated by this compute is “extensive”. The
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scalar value will be in energy <a class="reference internal" href="units.html"><em>units</em></a>.</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="compute_pe_atom.html"><em>compute pe/atom</em></a></p>
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<p><strong>Default:</strong> none</p>
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