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<div class="lammps_version">Version: <b>19 Nov 2024</b></div>
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<li class="toctree-l1"><a class="reference internal" href="Intro.html">1. Introduction</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Install.html">2. Install LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Build.html">3. Build LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Run_head.html">4. Run LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Commands.html">5. Commands</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Packages.html">6. Optional packages</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Speed.html">7. Accelerate performance</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Howto.html">8. Howto discussions</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Examples.html">9. Example scripts</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Errors.html">11. Errors</a></li>
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<p class="caption" role="heading"><span class="caption-text">Programmer Guide</span></p>
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<li class="toctree-l1"><a class="reference internal" href="Library.html">1. LAMMPS Library Interfaces</a></li>
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<li class="toctree-l1 current"><a class="reference internal" href="Python_head.html">2. Use Python with LAMMPS</a><ul class="current">
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<li class="toctree-l2 current"><a class="current reference internal" href="#">2.1. Overview</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_install.html">2.2. Installation</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_run.html">2.3. Run LAMMPS from Python</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_module.html">2.4. The <code class="docutils literal notranslate"><span class="pre">lammps</span></code> Python module</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_ext.html">2.5. Extending the Python interface</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_call.html">2.6. Calling Python from LAMMPS</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_formats.html">2.7. Output Readers</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_examples.html">2.8. Example Python scripts</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_error.html">2.9. Handling LAMMPS errors</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Python_trouble.html">2.10. Troubleshooting</a></li>
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</ul>
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</li>
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<li class="toctree-l1"><a class="reference internal" href="Modify.html">3. Modifying & extending LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Developer.html">4. Information for Developers</a></li>
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<p class="caption" role="heading"><span class="caption-text">Command Reference</span></p>
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<li class="toctree-l1"><a class="reference internal" href="pairs.html">Pair Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="bonds.html">Bond Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="angles.html">Angle Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="dihedrals.html">Dihedral Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="impropers.html">Improper Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="dumps.html">Dump Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="fix_modify_atc_commands.html">fix_modify AtC commands</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Bibliography.html">Bibliography</a></li>
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<li class="breadcrumb-item active"><span class="section-number">2.1. </span>Overview</li>
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<a href="https://www.lammps.org"><img src="_static/lammps-logo.png" width="64" height="16" alt="LAMMPS Homepage"></a> | <a href="Commands_all.html">Commands</a>
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<p><span class="math notranslate nohighlight">\(\renewcommand{\AA}{\text{Å}}\)</span></p>
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<section id="overview">
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<h1><span class="section-number">2.1. </span>Overview<a class="headerlink" href="#overview" title="Link to this heading"></a></h1>
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<p>The LAMMPS distribution includes a <code class="docutils literal notranslate"><span class="pre">python</span></code> directory with the Python
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code needed to run LAMMPS from Python. The <code class="docutils literal notranslate"><span class="pre">python/lammps</span></code> package
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contains <a class="reference internal" href="Python_module.html"><span class="doc">the “lammps” Python module</span></a> that wraps the
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LAMMPS C-library interface. This module makes it is possible to do the
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following either from a Python script, or interactively from a Python
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prompt:</p>
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<ul class="simple">
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<li><p>create one or more instances of LAMMPS</p></li>
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<li><p>invoke LAMMPS commands or read them from an input script</p></li>
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<li><p>run LAMMPS incrementally</p></li>
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<li><p>extract LAMMPS results</p></li>
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<li><p>and modify internal LAMMPS data structures.</p></li>
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</ul>
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<p>From a Python script you can do this in serial or in parallel. Running
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Python interactively in parallel does not generally work, unless you
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have a version of Python that extends Python to enable multiple
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instances of Python to read what you type.</p>
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<p>To do all of this, you must build LAMMPS in <a class="reference internal" href="Build_basics.html#exe"><span class="std std-ref">“shared” mode</span></a>
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and make certain that your Python interpreter can find the <code class="docutils literal notranslate"><span class="pre">lammps</span></code>
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Python package and the LAMMPS shared library file.</p>
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<p>The Python wrapper for LAMMPS uses the <a class="reference external" href="https://docs.python.org/3/library/ctypes.html">ctypes</a> package in
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Python, which auto-generates the interface code needed between Python
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and a set of C-style library functions. Ctypes has been part of the
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standard Python distribution since version 2.5. You can check which
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version of Python you have by simply typing “python” at a shell prompt.
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Below is an example output for Python version 3.8.5.</p>
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<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>python
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<span class="go">Python 3.8.5 (default, Aug 12 2020, 00:00:00)</span>
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<span class="go">[GCC 10.2.1 20200723 (Red Hat 10.2.1-1)] on linux</span>
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<span class="go">Type "help", "copyright", "credits" or "license" for more information.</span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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<div class="admonition warning">
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<p class="admonition-title">Warning</p>
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<p>The options described in this section of the manual for using Python
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with LAMMPS currently support either Python 2 or 3. Specifically
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version 2.7 or later and 3.6 or later. Since the Python community no
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longer maintains Python 2 (see <a class="reference external" href="https://www.python.org/doc/sunset-python-2/">this notice</a>), we recommend use of
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Python 3 with LAMMPS. While Python 2 code should continue to work,
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that is not something we can guarantee long-term. If you notice
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Python code in the LAMMPS distribution that is not compatible with
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Python 3, please contact the LAMMPS developers or submit <a class="reference external" href="https://github.com/lammps/lammps/issues">and issue
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on GitHub</a></p>
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</div>
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<hr class="docutils" />
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<p>LAMMPS can work together with Python in three ways. First, Python can
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wrap LAMMPS through the its <a class="reference internal" href="Library.html"><span class="doc">library interface</span></a>, so
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that a Python script can create one or more instances of LAMMPS and
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launch one or more simulations. In Python terms, this is referred to as
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“extending” Python with a LAMMPS module.</p>
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<figure class="align-center align-default" id="id1">
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<img alt="_images/python-invoke-lammps.png" src="_images/python-invoke-lammps.png" />
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<figcaption>
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<p><span class="caption-text">Launching LAMMPS via Python</span><a class="headerlink" href="#id1" title="Link to this image"></a></p>
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</figcaption>
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</figure>
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<p>Second, the lower-level Python interface in the <a class="reference internal" href="Python_module.html#lammps.lammps" title="lammps.lammps"><code class="xref py py-class docutils literal notranslate"><span class="pre">lammps</span> <span class="pre">Python</span>
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<span class="pre">class</span></code></a> can be used indirectly through the provided
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<a class="reference internal" href="Python_module.html#lammps.PyLammps" title="lammps.PyLammps"><code class="xref py py-class docutils literal notranslate"><span class="pre">PyLammps</span></code></a> and <a class="reference internal" href="Python_module.html#lammps.IPyLammps" title="lammps.IPyLammps"><code class="xref py py-class docutils literal notranslate"><span class="pre">IPyLammps</span></code></a> wrapper classes, also written in Python. These
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wrappers try to simplify the usage of LAMMPS in Python by providing a
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more object-based interface to common LAMMPS functionality. They also
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reduce the amount of code necessary to parameterize LAMMPS scripts
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through Python and make variables and computes directly accessible.</p>
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<figure class="align-center align-default" id="id2">
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<img alt="_images/pylammps-invoke-lammps.png" src="_images/pylammps-invoke-lammps.png" />
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<figcaption>
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<p><span class="caption-text">Using the PyLammps / IPyLammps wrappers</span><a class="headerlink" href="#id2" title="Link to this image"></a></p>
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</figcaption>
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</figure>
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<p>Third, LAMMPS can use the Python interpreter, so that a LAMMPS input
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script or styles can invoke Python code directly, and pass information
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back-and-forth between the input script and Python functions you write.
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This Python code can also call back to LAMMPS to query or change its
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attributes through the LAMMPS Python module mentioned above. In Python
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terms, this is called “embedding” Python into LAMMPS. When used in this
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mode, Python can perform script operations that the simple LAMMPS input
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script syntax can not.</p>
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<figure class="align-center align-default" id="id3">
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<img alt="_images/lammps-invoke-python.png" src="_images/lammps-invoke-python.png" />
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<figcaption>
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<p><span class="caption-text">Calling Python code from LAMMPS</span><a class="headerlink" href="#id3" title="Link to this image"></a></p>
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</figcaption>
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</figure>
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</section>
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<p>© Copyright 2003-2025 Sandia Corporation.</p>
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