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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 current"><a class="reference internal" href="Commands.html">5. Commands</a><ul class="current">
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<li class="toctree-l2 current"><a class="current reference internal" href="#">5.1. LAMMPS input scripts</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_parse.html">5.2. Parsing rules for input scripts</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_structure.html">5.3. Input script structure</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_category.html">5.4. Commands by category</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_all.html">5.5. General commands</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_fix.html">5.6. Fix styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_compute.html">5.7. Compute styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_pair.html">5.8. Pair styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_bond.html">5.9. Bond styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_bond.html#angle-styles">5.10. Angle styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_bond.html#dihedral-styles">5.11. Dihedral styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_bond.html#improper-styles">5.12. Improper styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_kspace.html">5.13. KSpace styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_dump.html">5.14. Dump styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Commands_removed.html">5.15. Removed commands and packages</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="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="Tools.html">10. Auxiliary tools</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"><a class="reference internal" href="Python_head.html">2. Use Python with LAMMPS</a></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="commands_list.html">Commands</a></li>
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<li class="toctree-l1"><a class="reference internal" href="fixes.html">Fix Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="computes.html">Compute Styles</a></li>
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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="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"><a href="Commands.html"><span class="section-number">5. </span>Commands</a></li>
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<li class="breadcrumb-item active"><span class="section-number">5.1. </span>LAMMPS input scripts</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="lammps-input-scripts">
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<h1><span class="section-number">5.1. </span>LAMMPS input scripts<a class="headerlink" href="#lammps-input-scripts" title="Link to this heading"></a></h1>
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<p>LAMMPS executes calculations by reading commands from a input script (text file), one
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line at a time. When the input script ends, LAMMPS exits. This is different
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from programs that read and process the entire input before starting a calculation.</p>
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<p>Each command causes LAMMPS to take some immediate action without regard
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for any commands that may be processed later. Commands may set an
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internal variable, read in a file, or run a simulation. These actions
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can be grouped into three categories:</p>
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<ol class="loweralpha simple">
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<li><p>commands that change a global setting (examples: <a class="reference internal" href="timestep.html"><span class="doc">timestep</span></a>, <a class="reference internal" href="newton.html"><span class="doc">newton</span></a>,
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<a class="reference internal" href="echo.html"><span class="doc">echo</span></a>, <a class="reference internal" href="log.html"><span class="doc">log</span></a>, <a class="reference internal" href="thermo.html"><span class="doc">thermo</span></a>, <a class="reference internal" href="restart.html"><span class="doc">restart</span></a>),</p></li>
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<li><p>commands that add, modify, remove, or replace “styles” that are
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executed during a “run” (examples: <a class="reference internal" href="pair_style.html"><span class="doc">pair_style</span></a>, <a class="reference internal" href="fix.html"><span class="doc">fix</span></a>, <a class="reference internal" href="compute.html"><span class="doc">compute</span></a>, <a class="reference internal" href="dump.html"><span class="doc">dump</span></a>,
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<a class="reference internal" href="thermo_style.html"><span class="doc">thermo_style</span></a>, <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a>), and</p></li>
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<li><p>commands that execute a “run” or perform some other computation or
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operation (examples: <a class="reference internal" href="print.html"><span class="doc">print</span></a>, <a class="reference internal" href="run.html"><span class="doc">run</span></a>, <a class="reference internal" href="minimize.html"><span class="doc">minimize</span></a>, <a class="reference internal" href="temper.html"><span class="doc">temper</span></a>, <a class="reference internal" href="write_dump.html"><span class="doc">write_dump</span></a>, <a class="reference internal" href="rerun.html"><span class="doc">rerun</span></a>,
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<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a>, <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>)</p></li>
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</ol>
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<p>Commands in category a) have default settings, which means you only
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need to use the command if you wish to change the defaults.</p>
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<p>In many cases, the ordering of commands in an input script is not
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important, but can have consequences when the global state is changed
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between commands in the c) category. The following rules apply:</p>
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<ol class="arabic">
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<li><p>LAMMPS does not read your entire input script and then perform a
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simulation with all the settings. Rather, the input script is read
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one line at a time and each command takes effect when it is read.
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Thus this sequence of commands:</p>
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<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">timestep</span><span class="w"> </span><span class="m">0.5</span>
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<span class="k">run</span><span class="w"> </span><span class="m">100</span>
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<span class="k">run</span><span class="w"> </span><span class="m">100</span>
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</pre></div>
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</div>
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<p>does something different than this sequence:</p>
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<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">run</span><span class="w"> </span><span class="m">100</span>
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<span class="k">timestep</span><span class="w"> </span><span class="m">0.5</span>
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<span class="k">run</span><span class="w"> </span><span class="m">100</span>
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</pre></div>
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</div>
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<p>In the first case, the specified timestep (0.5 fs) is used for two
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simulations of 100 timesteps each. In the second case, the default
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timestep (1.0 fs) is used for the first 100 step simulation and a
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0.5 fs timestep is used for the second one.</p>
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</li>
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<li><p>Some commands are only valid when they follow other commands. For
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example you cannot set the temperature of a group of atoms until
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atoms have been defined and a group command is used to define which
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atoms belong to the group.</p></li>
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<li><p>Sometimes command B will use values that can be set by command A.
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This means command A must precede command B in the input script if
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it is to have the desired effect. For example, the <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command initializes the system by setting up the
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simulation box and assigning atoms to processors. If default values
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are not desired, the <a class="reference internal" href="processors.html"><span class="doc">processors</span></a> and
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<a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> commands need to be used before <code class="docutils literal notranslate"><span class="pre">read_data</span></code>
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to tell LAMMPS how to map processors to the simulation box.</p></li>
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</ol>
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<p>Many input script errors are detected by LAMMPS and an ERROR or
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WARNING message is printed. The <a class="reference internal" href="Errors.html"><span class="doc">Errors</span></a> page gives
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more information on what errors mean. The documentation for each
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command lists restrictions on how the command can be used.</p>
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<p>You can use the <a class="reference internal" href="Run_options.html#skiprun"><span class="std std-ref">-skiprun</span></a> command-line flag
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to have LAMMPS skip the execution of any <code class="docutils literal notranslate"><span class="pre">run</span></code>, <code class="docutils literal notranslate"><span class="pre">minimize</span></code>, or similar
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commands to check the entire input for correct syntax to avoid crashes
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on typos or syntax errors in long runs.</p>
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</section>
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