512 lines
35 KiB
HTML
512 lines
35 KiB
HTML
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<title>units command — LAMMPS documentation</title>
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<div class="lammps_version">Version: <b>19 Nov 2024</b></div>
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<p class="caption" role="heading"><span class="caption-text">User Guide</span></p>
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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="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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<ul class="current">
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<li class="toctree-l1 current"><a class="reference internal" href="commands_list.html">Commands</a><ul class="current">
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<li class="toctree-l2"><a class="reference internal" href="angle_coeff.html">angle_coeff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="angle_style.html">angle_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="angle_write.html">angle_write command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="atom_modify.html">atom_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="atom_style.html">atom_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="balance.html">balance command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="bond_coeff.html">bond_coeff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="bond_style.html">bond_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="bond_write.html">bond_write command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="boundary.html">boundary command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="change_box.html">change_box command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="clear.html">clear command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="comm_modify.html">comm_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="comm_style.html">comm_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="compute.html">compute command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="compute_modify.html">compute_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="create_atoms.html">create_atoms command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="create_bonds.html">create_bonds command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="create_box.html">create_box command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="delete_atoms.html">delete_atoms command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="delete_bonds.html">delete_bonds command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dielectric.html">dielectric command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dihedral_coeff.html">dihedral_coeff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dihedral_style.html">dihedral_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dihedral_write.html">dihedral_write command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dimension.html">dimension command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="displace_atoms.html">displace_atoms command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dynamical_matrix.html">dynamical_matrix command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="echo.html">echo command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix.html">fix command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_modify.html">fix_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fitpod_command.html">fitpod command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="geturl.html">geturl command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="group.html">group command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="group2ndx.html">group2ndx command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="group2ndx.html#ndx2group-command">ndx2group command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="hyper.html">hyper command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="if.html">if command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="improper_coeff.html">improper_coeff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="improper_style.html">improper_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="include.html">include command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="info.html">info command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="jump.html">jump command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="kim_commands.html">kim command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="kspace_modify.html">kspace_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="kspace_style.html">kspace_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="label.html">label command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="labelmap.html">labelmap command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="lattice.html">lattice command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="log.html">log command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="mass.html">mass command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="mdi.html">mdi command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_modify.html">min_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_spin.html">min_style spin command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_spin.html#min-style-spin-cg-command">min_style spin/cg command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_spin.html#min-style-spin-lbfgs-command">min_style spin/lbfgs command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html">min_style cg command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-hftn-command">min_style hftn command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-sd-command">min_style sd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-quickmin-command">min_style quickmin command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-fire-command">min_style fire command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-spin-command"><span class="xref std std-doc">min_style spin</span> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-spin-cg-command"><span class="xref std std-doc">min_style spin/cg</span> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html#min-style-spin-lbfgs-command"><span class="xref std std-doc">min_style spin/lbfgs</span> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="minimize.html">minimize command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="molecule.html">molecule command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="neb.html">neb command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="neb_spin.html">neb/spin command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="neigh_modify.html">neigh_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="neighbor.html">neighbor command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="newton.html">newton command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="next.html">next command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="package.html">package command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pair_coeff.html">pair_coeff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pair_modify.html">pair_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pair_style.html">pair_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pair_write.html">pair_write command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="partition.html">partition command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="plugin.html">plugin command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="prd.html">prd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="print.html">print command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="processors.html">processors command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="python.html">python command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="quit.html">quit command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="read_data.html">read_data command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="read_dump.html">read_dump command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="read_restart.html">read_restart command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="region.html">region command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="replicate.html">replicate command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="rerun.html">rerun command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="reset_atoms.html">reset_atoms command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="reset_timestep.html">reset_timestep command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="restart.html">restart command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="run.html">run command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="run_style.html">run_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="set.html">set command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="shell.html">shell command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="special_bonds.html">special_bonds command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="suffix.html">suffix command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="tad.html">tad command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="temper.html">temper command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="temper_grem.html">temper/grem command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="temper_npt.html">temper/npt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="thermo.html">thermo command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="thermo_modify.html">thermo_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="thermo_style.html">thermo_style command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="third_order.html">third_order command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="timer.html">timer command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="timestep.html">timestep command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="uncompute.html">uncompute command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="undump.html">undump command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="unfix.html">unfix command</a></li>
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<li class="toctree-l2 current"><a class="current reference internal" href="#">units command</a><ul>
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<li class="toctree-l3"><a class="reference internal" href="#syntax">Syntax</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#examples">Examples</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#description">Description</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#restrictions">Restrictions</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#related-commands">Related commands</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#default">Default</a></li>
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</ul>
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</li>
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<li class="toctree-l2"><a class="reference internal" href="variable.html">variable command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="velocity.html">velocity command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="write_coeff.html">write_coeff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="write_data.html">write_data command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="write_dump.html">write_dump command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="write_restart.html">write_restart command</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="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="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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</ul>
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<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
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<div itemprop="articleBody">
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<p><span class="math notranslate nohighlight">\(\renewcommand{\AA}{\text{Å}}\)</span></p>
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<section id="units-command">
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<span id="index-0"></span><h1>units command<a class="headerlink" href="#units-command" title="Link to this heading"></a></h1>
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<section id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Link to this heading"></a></h2>
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<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">units</span><span class="w"> </span><span class="n">style</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li><p>style = <em>lj</em> or <em>real</em> or <em>metal</em> or <em>si</em> or <em>cgs</em> or <em>electron</em> or <em>micro</em> or <em>nano</em></p></li>
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</ul>
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</section>
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<section id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Link to this heading"></a></h2>
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<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">units</span><span class="w"> </span><span class="n">metal</span>
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<span class="k">units</span><span class="w"> </span><span class="n">lj</span>
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</pre></div>
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</div>
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</section>
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<section id="description">
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<h2>Description<a class="headerlink" href="#description" title="Link to this heading"></a></h2>
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<p>This command sets the style of units used for a simulation. It
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determines the units of all quantities specified in the input script
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and data file, as well as quantities output to the screen, log file,
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and dump files. Typically, this command is used at the very beginning
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of an input script.</p>
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<p>For all units except <em>lj</em>, LAMMPS uses physical constants from
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www.physics.nist.gov. For the definition of kcal in real units,
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LAMMPS uses the thermochemical calorie = 4.184 J.</p>
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<p>The choice you make for units simply sets some internal conversion
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factors within LAMMPS. This means that any simulation you perform for
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one choice of units can be duplicated with any other unit setting
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LAMMPS supports. In this context “duplicate” means the particles will
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have identical trajectories and all output generated by the simulation
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will be identical. This will be the case for some number of timesteps
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until round-off effects accumulate, since the conversion factors for
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two different unit systems are not identical to infinite precision.</p>
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<p>To perform the same simulation in a different set of units you must
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change all the unit-based input parameters in your input script and
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other input files (data file, potential files, etc) correctly to the
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new units. And you must correctly convert all output from the new
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units to the old units when comparing to the original results. That
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is often not simple to do.</p>
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<p>Potential or table files may have a <code class="docutils literal notranslate"><span class="pre">UNITS:</span></code> tag included in the
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first line indicating the unit style those files were created for.
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If the tag exists, its value will be compared to the chosen unit style
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and LAMMPS will stop with an error message if there is a mismatch.
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In some select cases and for specific combinations of unit styles,
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LAMMPS is capable of automatically converting potential parameters
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from a file. In those cases, a warning message signaling that an
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automatic conversion has happened is printed to the screen.</p>
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<hr class="docutils" />
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<p>For style <em>lj</em>, all quantities are unitless. Without loss of
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generality, LAMMPS sets the fundamental quantities mass, <span class="math notranslate nohighlight">\(\sigma\)</span>,
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<span class="math notranslate nohighlight">\(\epsilon\)</span>, and the Boltzmann constant <span class="math notranslate nohighlight">\(k_B = 1\)</span>. The
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masses, distances, energies you specify are multiples of these
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fundamental values. The formulas relating the reduced or unitless
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quantity (with an asterisk) to the same quantity with units is also
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given. Thus you can use the mass, <span class="math notranslate nohighlight">\(\sigma\)</span>, and <span class="math notranslate nohighlight">\(\epsilon\)</span>
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values for a specific material and convert the results from a unitless
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LJ simulation into physical quantities. Please note that using
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|
these three properties as base, your unit of time has to conform
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to the relation <span class="math notranslate nohighlight">\(\epsilon = \frac{m \sigma^2}{\tau^2}\)</span> since
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energy is a derived unit (in SI units you equivalently have the relation
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<span class="math notranslate nohighlight">\(1\mathsf{J} = 1\frac{\mathsf{kg}\cdot\mathsf{m}^2}{\mathsf{s}^2}\)</span>).</p>
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<ul class="simple">
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<li><p>mass = mass or <span class="math notranslate nohighlight">\(m\)</span>, where <span class="math notranslate nohighlight">\(M^* = \frac{M}{m}\)</span></p></li>
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<li><p>distance = <span class="math notranslate nohighlight">\(\sigma\)</span>, where <span class="math notranslate nohighlight">\(x^* = \frac{x}{\sigma}\)</span></p></li>
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<li><p>time = <span class="math notranslate nohighlight">\(\tau\)</span>, where <span class="math notranslate nohighlight">\(\tau^* = \tau \sqrt{\frac{\epsilon}{m \sigma^2}}\)</span></p></li>
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<li><p>energy = <span class="math notranslate nohighlight">\(\epsilon\)</span>, where <span class="math notranslate nohighlight">\(E^* = \frac{E}{\epsilon}\)</span></p></li>
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<li><p>velocity = <span class="math notranslate nohighlight">\(\frac{\sigma}{\tau}\)</span>, where <span class="math notranslate nohighlight">\(v^* = v \frac{\tau}{\sigma}\)</span></p></li>
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<li><p>force = <span class="math notranslate nohighlight">\(\frac{\epsilon}{\sigma}\)</span>, where <span class="math notranslate nohighlight">\(f^* = f \frac{\sigma}{\epsilon}\)</span></p></li>
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<li><p>torque = <span class="math notranslate nohighlight">\(\epsilon\)</span>, where <span class="math notranslate nohighlight">\(t^* = \frac{t}{\epsilon}\)</span></p></li>
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<li><p>temperature = reduced LJ temperature, where <span class="math notranslate nohighlight">\(T^* = \frac{T k_B}{\epsilon}\)</span></p></li>
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<li><p>pressure = reduced LJ pressure, where <span class="math notranslate nohighlight">\(p^* = p \frac{\sigma^3}{\epsilon}\)</span></p></li>
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<li><p>dynamic viscosity = reduced LJ viscosity, where <span class="math notranslate nohighlight">\(\eta^* = \eta \frac{\sigma^3}{\epsilon\tau}\)</span></p></li>
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<li><p>charge = reduced LJ charge, where <span class="math notranslate nohighlight">\(q^* = q \frac{1}{\sqrt{4 \pi \varepsilon_0 \sigma \epsilon}}\)</span></p></li>
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<li><p>dipole = reduced LJ dipole, moment where <span class="math notranslate nohighlight">\(\mu^* = \mu \frac{1}{\sqrt{4 \pi \varepsilon_0 \sigma^3 \epsilon}}\)</span></p></li>
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<li><p>electric field = force/charge, where <span class="math notranslate nohighlight">\(E^* = E \frac{\sqrt{4 \pi \varepsilon_0 \sigma \epsilon} \sigma}{\epsilon}\)</span></p></li>
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<li><p>density = mass/volume, where <span class="math notranslate nohighlight">\(\rho^* = \rho \frac{\sigma^{dim}}{m}\)</span></p></li>
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</ul>
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<p>Note that for LJ units, the default mode of thermodynamic output via
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the <a class="reference internal" href="thermo_style.html"><span class="doc">thermo_style</span></a> command is to normalize all
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extensive quantities by the number of atoms. E.g. potential energy is
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extensive because it is summed over atoms, so it is output as
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|
energy/atom. Temperature is intensive since it is already normalized
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|
by the number of atoms, so it is output as-is. This behavior can be
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changed via the <a class="reference internal" href="thermo_modify.html"><span class="doc">thermo_modify norm</span></a> command.</p>
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<p>For style <em>real</em>, these are the units:</p>
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<ul class="simple">
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<li><p>mass = grams/mole</p></li>
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<li><p>distance = Angstroms</p></li>
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<li><p>time = femtoseconds</p></li>
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<li><p>energy = kcal/mol</p></li>
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<li><p>velocity = Angstroms/femtosecond</p></li>
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<li><p>force = (kcal/mol)/Angstrom</p></li>
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<li><p>torque = kcal/mol</p></li>
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<li><p>temperature = Kelvin</p></li>
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<li><p>pressure = atmospheres</p></li>
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<li><p>dynamic viscosity = Poise</p></li>
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<li><p>charge = multiple of electron charge (1.0 is a proton)</p></li>
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<li><p>dipole = charge*Angstroms</p></li>
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<li><p>electric field = volts/Angstrom</p></li>
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<li><p>density = g/cm^dim</p></li>
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</ul>
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<p>For style <em>metal</em>, these are the units:</p>
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<ul class="simple">
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<li><p>mass = grams/mole</p></li>
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<li><p>distance = Angstroms</p></li>
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<li><p>time = picoseconds</p></li>
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<li><p>energy = eV</p></li>
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<li><p>velocity = Angstroms/picosecond</p></li>
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<li><p>force = eV/Angstrom</p></li>
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<li><p>torque = eV</p></li>
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<li><p>temperature = Kelvin</p></li>
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<li><p>pressure = bars</p></li>
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<li><p>dynamic viscosity = Poise</p></li>
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<li><p>charge = multiple of electron charge (1.0 is a proton)</p></li>
|
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<li><p>dipole = charge*Angstroms</p></li>
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<li><p>electric field = volts/Angstrom</p></li>
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<li><p>density = gram/cm^dim</p></li>
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</ul>
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<p>For style <em>si</em>, these are the units:</p>
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<ul class="simple">
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<li><p>mass = kilograms</p></li>
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<li><p>distance = meters</p></li>
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<li><p>time = seconds</p></li>
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<li><p>energy = Joules</p></li>
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<li><p>velocity = meters/second</p></li>
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<li><p>force = Newtons</p></li>
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<li><p>torque = Newton-meters</p></li>
|
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<li><p>temperature = Kelvin</p></li>
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<li><p>pressure = Pascals</p></li>
|
|
<li><p>dynamic viscosity = Pascal*second</p></li>
|
|
<li><p>charge = Coulombs (1.6021765e-19 is a proton)</p></li>
|
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<li><p>dipole = Coulombs*meters</p></li>
|
|
<li><p>electric field = volts/meter</p></li>
|
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<li><p>density = kilograms/meter^dim</p></li>
|
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</ul>
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<p>For style <em>cgs</em>, these are the units:</p>
|
|
<ul class="simple">
|
|
<li><p>mass = grams</p></li>
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<li><p>distance = centimeters</p></li>
|
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<li><p>time = seconds</p></li>
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<li><p>energy = ergs</p></li>
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<li><p>velocity = centimeters/second</p></li>
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<li><p>force = dynes</p></li>
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<li><p>torque = dyne-centimeters</p></li>
|
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<li><p>temperature = Kelvin</p></li>
|
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<li><p>pressure = dyne/cm^2 or barye = 1.0e-6 bars</p></li>
|
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<li><p>dynamic viscosity = Poise</p></li>
|
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<li><p>charge = statcoulombs or esu (4.8032044e-10 is a proton)</p></li>
|
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<li><p>dipole = statcoul-cm = 10^18 debye</p></li>
|
|
<li><p>electric field = statvolt/cm or dyne/esu</p></li>
|
|
<li><p>density = grams/cm^dim</p></li>
|
|
</ul>
|
|
<p>For style <em>electron</em>, these are the units:</p>
|
|
<ul class="simple">
|
|
<li><p>mass = atomic mass units</p></li>
|
|
<li><p>distance = Bohr</p></li>
|
|
<li><p>time = femtoseconds</p></li>
|
|
<li><p>energy = Hartrees</p></li>
|
|
<li><p>velocity = Bohr/atomic time units [1.03275e-15 seconds]</p></li>
|
|
<li><p>force = Hartrees/Bohr</p></li>
|
|
<li><p>temperature = Kelvin</p></li>
|
|
<li><p>pressure = Pascals</p></li>
|
|
<li><p>charge = multiple of electron charge (1.0 is a proton)</p></li>
|
|
<li><p>dipole moment = Debye</p></li>
|
|
<li><p>electric field = volts/cm</p></li>
|
|
</ul>
|
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<p>For style <em>micro</em>, these are the units:</p>
|
|
<ul class="simple">
|
|
<li><p>mass = picograms</p></li>
|
|
<li><p>distance = micrometers</p></li>
|
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<li><p>time = microseconds</p></li>
|
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<li><p>energy = picogram-micrometer^2/microsecond^2</p></li>
|
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<li><p>velocity = micrometers/microsecond</p></li>
|
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<li><p>force = picogram-micrometer/microsecond^2</p></li>
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<li><p>torque = picogram-micrometer^2/microsecond^2</p></li>
|
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<li><p>temperature = Kelvin</p></li>
|
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<li><p>pressure = picogram/(micrometer-microsecond^2)</p></li>
|
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<li><p>dynamic viscosity = picogram/(micrometer-microsecond)</p></li>
|
|
<li><p>charge = picocoulombs (1.6021765e-7 is a proton)</p></li>
|
|
<li><p>dipole = picocoulomb-micrometer</p></li>
|
|
<li><p>electric field = volt/micrometer</p></li>
|
|
<li><p>density = picograms/micrometer^dim</p></li>
|
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</ul>
|
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<p>For style <em>nano</em>, these are the units:</p>
|
|
<ul class="simple">
|
|
<li><p>mass = attograms</p></li>
|
|
<li><p>distance = nanometers</p></li>
|
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<li><p>time = nanoseconds</p></li>
|
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<li><p>energy = attogram-nanometer^2/nanosecond^2</p></li>
|
|
<li><p>velocity = nanometers/nanosecond</p></li>
|
|
<li><p>force = attogram-nanometer/nanosecond^2</p></li>
|
|
<li><p>torque = attogram-nanometer^2/nanosecond^2</p></li>
|
|
<li><p>temperature = Kelvin</p></li>
|
|
<li><p>pressure = attogram/(nanometer-nanosecond^2)</p></li>
|
|
<li><p>dynamic viscosity = attogram/(nanometer-nanosecond)</p></li>
|
|
<li><p>charge = multiple of electron charge (1.0 is a proton)</p></li>
|
|
<li><p>dipole = charge-nanometer</p></li>
|
|
<li><p>electric field = volt/nanometer</p></li>
|
|
<li><p>density = attograms/nanometer^dim</p></li>
|
|
</ul>
|
|
<p>The units command also sets the timestep size and neighbor skin
|
|
distance to default values for each style:</p>
|
|
<ul class="simple">
|
|
<li><p>For style <em>lj</em> these are dt = 0.005 <span class="math notranslate nohighlight">\(\tau\)</span> and skin = 0.3 <span class="math notranslate nohighlight">\(\sigma\)</span>.</p></li>
|
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<li><p>For style <em>real</em> these are dt = 1.0 femtoseconds and skin = 2.0 Angstroms.</p></li>
|
|
<li><p>For style <em>metal</em> these are dt = 0.001 picoseconds and skin = 2.0 Angstroms.</p></li>
|
|
<li><p>For style <em>si</em> these are dt = 1.0e-8 seconds and skin = 0.001 meters.</p></li>
|
|
<li><p>For style <em>cgs</em> these are dt = 1.0e-8 seconds and skin = 0.1 centimeters.</p></li>
|
|
<li><p>For style <em>electron</em> these are dt = 0.001 femtoseconds and skin = 2.0 Bohr.</p></li>
|
|
<li><p>For style <em>micro</em> these are dt = 2.0 microseconds and skin = 0.1 micrometers.</p></li>
|
|
<li><p>For style <em>nano</em> these are dt = 0.00045 nanoseconds and skin = 0.1 nanometers.</p></li>
|
|
</ul>
|
|
</section>
|
|
<section id="restrictions">
|
|
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Link to this heading"></a></h2>
|
|
<p>This command cannot be used after the simulation box is defined by a
|
|
<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> or <a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a> command.</p>
|
|
</section>
|
|
<section id="related-commands">
|
|
<h2>Related commands<a class="headerlink" href="#related-commands" title="Link to this heading"></a></h2>
|
|
<p>none</p>
|
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</section>
|
|
<section id="default">
|
|
<h2>Default<a class="headerlink" href="#default" title="Link to this heading"></a></h2>
|
|
<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">units</span><span class="w"> </span><span class="n">lj</span>
|
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</pre></div>
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</div>
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</section>
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