forked from lijiext/lammps
656 lines
38 KiB
HTML
656 lines
38 KiB
HTML
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<title>change_box command — LAMMPS documentation</title>
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<p class="caption"><span class="caption-text">User Documentation</span></p>
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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_start.html">2. Getting Started</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_packages.html">4. Packages</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_howto.html">6. How-to discussions</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_perf.html">8. Performance & scalability</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_modify.html">10. Modifying & extending LAMMPS</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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<li class="toctree-l1"><a class="reference internal" href="Section_errors.html">12. Errors</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_history.html">13. Future and history</a></li>
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<p class="caption"><span class="caption-text">Index</span></p>
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<li class="toctree-l1"><a class="reference internal" href="tutorials.html">Tutorials</a></li>
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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="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="box.html">box command</a></li>
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<li class="toctree-l2 current"><a class="current reference internal" href="#">change_box 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="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="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="dump.html">dump command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump.html#dump-custom-vtk-command"><code class="docutils literal"><span class="pre">dump</span> <span class="pre">custom/vtk</span></code> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump.html#dump-h5md-command"><code class="docutils literal"><span class="pre">dump</span> <span class="pre">h5md</span></code> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump.html#dump-image-command"><code class="docutils literal"><span class="pre">dump</span> <span class="pre">image</span></code> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump.html#dump-movie-command"><code class="docutils literal"><span class="pre">dump</span> <span class="pre">movie</span></code> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump.html#dump-molfile-command"><code class="docutils literal"><span class="pre">dump</span> <span class="pre">molfile</span></code> command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump_custom_vtk.html">dump custom/vtk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump_h5md.html">dump h5md command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump_image.html">dump image command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump_image.html#dump-movie-command">dump movie command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump_modify.html">dump_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="dump_molfile.html">dump molfile 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="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="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="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="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="min_modify.html">min_modify command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="min_style.html">min_style 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="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="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_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="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="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"><a class="reference internal" href="units.html">units command</a></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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<li class="toctree-l1"><a class="reference internal" href="fixes.html">Fixes</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">Bonds</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>change_box command</li>
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<div class="section" id="change-box-command">
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<span id="index-0"></span><h1>change_box command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<pre class="literal-block">
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change_box group-ID parameter args ... keyword args ...
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</pre>
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<ul>
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<li><p class="first">group-ID = ID of group of atoms to (optionally) displace</p>
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</li>
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<li><p class="first">one or more parameter/arg pairs may be appended</p>
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<pre class="literal-block">
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parameter = <em>x</em> or <em>y</em> or <em>z</em> or <em>xy</em> or <em>xz</em> or <em>yz</em> or <em>boundary</em> or <em>ortho</em> or <em>triclinic</em> or <em>set</em> or <em>remap</em>
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<em>x</em>, <em>y</em>, <em>z</em> args = style value(s)
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style = <em>final</em> or <em>delta</em> or <em>scale</em> or <em>volume</em>
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<em>final</em> values = lo hi
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lo hi = box boundaries after displacement (distance units)
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<em>delta</em> values = dlo dhi
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dlo dhi = change in box boundaries after displacement (distance units)
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<em>scale</em> values = factor
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factor = multiplicative factor for change in box length after displacement
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<em>volume</em> value = none = adjust this dim to preserve volume of system
|
|
<em>xy</em>, <em>xz</em>, <em>yz</em> args = style value
|
|
style = <em>final</em> or <em>delta</em>
|
|
<em>final</em> value = tilt
|
|
tilt = tilt factor after displacement (distance units)
|
|
<em>delta</em> value = dtilt
|
|
dtilt = change in tilt factor after displacement (distance units)
|
|
<em>boundary</em> args = x y z
|
|
x,y,z = <em>p</em> or <em>s</em> or <em>f</em> or <em>m</em>, one or two letters
|
|
<em>p</em> is periodic
|
|
<em>f</em> is non-periodic and fixed
|
|
<em>s</em> is non-periodic and shrink-wrapped
|
|
<em>m</em> is non-periodic and shrink-wrapped with a minimum value
|
|
<em>ortho</em> args = none = change box to orthogonal
|
|
<em>triclinic</em> args = none = change box to triclinic
|
|
<em>set</em> args = none = store state of current box
|
|
<em>remap</em> args = none = remap atom coords from last saved state to current box
|
|
</pre>
|
|
</li>
|
|
<li><p class="first">zero or more keyword/value pairs may be appended</p>
|
|
</li>
|
|
<li><p class="first">keyword = <em>units</em></p>
|
|
<pre class="literal-block">
|
|
<em>units</em> value = <em>lattice</em> or <em>box</em>
|
|
lattice = distances are defined in lattice units
|
|
box = distances are defined in simulation box units
|
|
</pre>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="section" id="examples">
|
|
<h2>Examples</h2>
|
|
<pre class="literal-block">
|
|
change_box all xy final -2.0 z final 0.0 5.0 boundary p p f remap units box
|
|
change_box all x scale 1.1 y volume z volume remap
|
|
</pre>
|
|
</div>
|
|
<div class="section" id="description">
|
|
<h2>Description</h2>
|
|
<p>Change the volume and/or shape and/or boundary conditions for the
|
|
simulation box. Orthogonal simulation boxes have 3 adjustable size
|
|
parameters (x,y,z). Triclinic (non-orthogonal) simulation boxes have
|
|
6 adjustable size/shape parameters (x,y,z,xy,xz,yz). Any or all of
|
|
them can be adjusted independently by this command. Thus it can be
|
|
used to expand or contract a box, or to apply a shear strain to a
|
|
non-orthogonal box. It can also be used to change the boundary
|
|
conditions for the simulation box, similar to the
|
|
<a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> command.</p>
|
|
<p>The size and shape of the initial simulation box are specified by the
|
|
<a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a> or <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> or
|
|
<a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> command used to setup the simulation.
|
|
The size and shape may be altered by subsequent runs, e.g. by use of
|
|
the <a class="reference internal" href="fix_nh.html"><span class="doc">fix npt</span></a> or <a class="reference internal" href="fix_deform.html"><span class="doc">fix deform</span></a> commands.
|
|
The <a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a>, <a class="reference internal" href="read_data.html"><span class="doc">read data</span></a>, and
|
|
<a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> commands also determine whether the
|
|
simulation box is orthogonal or triclinic and their doc pages explain
|
|
the meaning of the xy,xz,yz tilt factors.</p>
|
|
<p>See <a class="reference internal" href="Section_howto.html#howto-12"><span class="std std-ref">Section 6.12</span></a> of the doc pages
|
|
for a geometric description of triclinic boxes, as defined by LAMMPS,
|
|
and how to transform these parameters to and from other commonly used
|
|
triclinic representations.</p>
|
|
<p>The keywords used in this command are applied sequentially to the
|
|
simulation box and the atoms in it, in the order specified.</p>
|
|
<p>Before the sequence of keywords are invoked, the current box
|
|
size/shape is stored, in case a <em>remap</em> keyword is used to map the
|
|
atom coordinates from a previously stored box size/shape to the
|
|
current one.</p>
|
|
<p>After all the keywords have been processed, any shrink-wrap boundary
|
|
conditions are invoked (see the <a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> command)
|
|
which may change simulation box boundaries, and atoms are migrated to
|
|
new owning processors.</p>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">This means that you cannot use the change_box command to enlarge
|
|
a shrink-wrapped box, e.g. to make room to insert more atoms via the
|
|
<a class="reference internal" href="create_atoms.html"><span class="doc">create_atoms</span></a> command, because the simulation box
|
|
will be re-shrink-wrapped before the change_box command completes.
|
|
Instead you could do something like this, assuming the simulation box
|
|
is non-periodic and atoms extend from 0 to 20 in all dimensions:</p>
|
|
</div>
|
|
<pre class="literal-block">
|
|
change_box all x final -10 20
|
|
create_atoms 1 single -5 5 5 # this will fail to insert an atom
|
|
</pre>
|
|
<pre class="literal-block">
|
|
change_box all x final -10 20 boundary f s s
|
|
create_atoms 1 single -5 5 5
|
|
change_box boundary s s s # this will work
|
|
</pre>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">Unlike the earlier “displace_box” version of this command, atom
|
|
remapping is NOT performed by default. This command allows remapping
|
|
to be done in a more general way, exactly when you specify it (zero or
|
|
more times) in the sequence of transformations. Thus if you do not
|
|
use the <em>remap</em> keyword, atom coordinates will not be changed even if
|
|
the box size/shape changes. If a uniformly strained state is desired,
|
|
the <em>remap</em> keyword should be specified.</p>
|
|
</div>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">It is possible to lose atoms with this command. E.g. by
|
|
changing the box without remapping the atoms, and having atoms end up
|
|
outside of non-periodic boundaries. It is also possible to alter
|
|
bonds between atoms straddling a boundary in bad ways. E.g. by
|
|
converting a boundary from periodic to non-periodic. It is also
|
|
possible when remapping atoms to put them (nearly) on top of each
|
|
other. E.g. by converting a boundary from non-periodic to periodic.
|
|
All of these will typically lead to bad dynamics and/or generate error
|
|
messages.</p>
|
|
</div>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">The simulation box size/shape can be changed by arbitrarily
|
|
large amounts by this command. This is not a problem, except that the
|
|
mapping of processors to the simulation box is not changed from its
|
|
initial 3d configuration; see the <a class="reference internal" href="processors.html"><span class="doc">processors</span></a>
|
|
command. Thus, if the box size/shape changes dramatically, the
|
|
mapping of processors to the simulation box may not end up as optimal
|
|
as the initial mapping attempted to be.</p>
|
|
</div>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">Because the keywords used in this command are applied one at a
|
|
time to the simulation box and the atoms in it, care must be taken
|
|
with triclinic cells to avoid exceeding the limits on skew after each
|
|
transformation in the sequence. If skew is exceeded before the final
|
|
transformation this can be avoided by changing the order of the
|
|
sequence, or breaking the transformation into two or more smaller
|
|
transformations. For more information on the allowed limits for box
|
|
skew see the discussion on triclinic boxes on <a class="reference internal" href="Section_howto.html#howto-12"><span class="std std-ref">this page</span></a>.</p>
|
|
</div>
|
|
<hr class="docutils" />
|
|
<p>For the <em>x</em>, <em>y</em>, and <em>z</em> parameters, this is the meaning of their
|
|
styles and values.</p>
|
|
<p>For style <em>final</em>, the final lo and hi box boundaries of a dimension
|
|
are specified. The values can be in lattice or box distance units.
|
|
See the discussion of the units keyword below.</p>
|
|
<p>For style <em>delta</em>, plus or minus changes in the lo/hi box boundaries
|
|
of a dimension are specified. The values can be in lattice or box
|
|
distance units. See the discussion of the units keyword below.</p>
|
|
<p>For style <em>scale</em>, a multiplicative factor to apply to the box length
|
|
of a dimension is specified. For example, if the initial box length
|
|
is 10, and the factor is 1.1, then the final box length will be 11. A
|
|
factor less than 1.0 means compression.</p>
|
|
<p>The <em>volume</em> style changes the specified dimension in such a way that
|
|
the overall box volume remains constant with respect to the operation
|
|
performed by the preceding keyword. The <em>volume</em> style can only be
|
|
used following a keyword that changed the volume, which is any of the
|
|
<em>x</em>, <em>y</em>, <em>z</em> keywords. If the preceding keyword “key” had a <em>volume</em>
|
|
style, then both it and the current keyword apply to the keyword
|
|
preceding “key”. I.e. this sequence of keywords is allowed:</p>
|
|
<pre class="literal-block">
|
|
change_box all x scale 1.1 y volume z volume
|
|
</pre>
|
|
<p>The <em>volume</em> style changes the associated dimension so that the
|
|
overall box volume is unchanged relative to its value before the
|
|
preceding keyword was invoked.</p>
|
|
<p>If the following command is used, then the z box length will shrink by
|
|
the same 1.1 factor the x box length was increased by:</p>
|
|
<pre class="literal-block">
|
|
change_box all x scale 1.1 z volume
|
|
</pre>
|
|
<p>If the following command is used, then the y,z box lengths will each
|
|
shrink by sqrt(1.1) to keep the volume constant. In this case, the
|
|
y,z box lengths shrink so as to keep their relative aspect ratio
|
|
constant:</p>
|
|
<pre class="literal-block">
|
|
change_box all"x scale 1.1 y volume z volume
|
|
</pre>
|
|
<p>If the following command is used, then the final box will be a factor
|
|
of 10% larger in x and y, and a factor of 21% smaller in z, so as to
|
|
keep the volume constant:</p>
|
|
<pre class="literal-block">
|
|
change_box all x scale 1.1 z volume y scale 1.1 z volume
|
|
</pre>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">For solids or liquids, when one dimension of the box is
|
|
expanded, it may be physically undesirable to hold the other 2 box
|
|
lengths constant since that implies a density change. For solids,
|
|
adjusting the other dimensions via the <em>volume</em> style may make
|
|
physical sense (just as for a liquid), but may not be correct for
|
|
materials and potentials whose Poisson ratio is not 0.5.</p>
|
|
</div>
|
|
<p>For the <em>scale</em> and <em>volume</em> styles, the box length is expanded or
|
|
compressed around its mid point.</p>
|
|
<hr class="docutils" />
|
|
<p>For the <em>xy</em>, <em>xz</em>, and <em>yz</em> parameters, this is the meaning of their
|
|
styles and values. Note that changing the tilt factors of a triclinic
|
|
box does not change its volume.</p>
|
|
<p>For style <em>final</em>, the final tilt factor is specified. The value
|
|
can be in lattice or box distance units. See the discussion of the
|
|
units keyword below.</p>
|
|
<p>For style <em>delta</em>, a plus or minus change in the tilt factor is
|
|
specified. The value can be in lattice or box distance units. See
|
|
the discussion of the units keyword below.</p>
|
|
<p>All of these styles change the xy, xz, yz tilt factors. In LAMMPS,
|
|
tilt factors (xy,xz,yz) for triclinic boxes are required to be no more
|
|
than half the distance of the parallel box length. For example, if
|
|
xlo = 2 and xhi = 12, then the x box length is 10 and the xy tilt
|
|
factor must be between -5 and 5. Similarly, both xz and yz must be
|
|
between -(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is not a
|
|
limitation, since if the maximum tilt factor is 5 (as in this
|
|
example), then configurations with tilt = ..., -15, -5, 5, 15, 25,
|
|
... are all equivalent. Any tilt factor specified by this command
|
|
must be within these limits.</p>
|
|
<hr class="docutils" />
|
|
<p>The <em>boundary</em> keyword takes arguments that have exactly the same
|
|
meaning as they do for the <a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> command. In each
|
|
dimension, a single letter assigns the same style to both the lower
|
|
and upper face of the box. Two letters assigns the first style to the
|
|
lower face and the second style to the upper face.</p>
|
|
<p>The style <em>p</em> means the box is periodic; the other styles mean
|
|
non-periodic. For style <em>f</em>, the position of the face is fixed. For
|
|
style <em>s</em>, the position of the face is set so as to encompass the
|
|
atoms in that dimension (shrink-wrapping), no matter how far they
|
|
move. For style <em>m</em>, shrink-wrapping occurs, but is bounded by the
|
|
current box edge in that dimension, so that the box will become no
|
|
smaller. See the <a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> command for more
|
|
explanation of these style options.</p>
|
|
<p>Note that the “boundary” command itself can only be used before the
|
|
simulation box is defined via 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> or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
|
|
command. This command allows the boundary conditions to be changed
|
|
later in your input script. Also note that the
|
|
<a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> will change boundary conditions to
|
|
match what is stored in the restart file. So if you wish to change
|
|
them, you should use the change_box command after the read_restart
|
|
command.</p>
|
|
<hr class="docutils" />
|
|
<p>The <em>ortho</em> and <em>triclinic</em> keywords convert the simulation box to be
|
|
orthogonal or triclinic (non-orthongonal). See <a class="reference internal" href="Section_howto.html#howto-13"><span class="std std-ref">this section</span></a> for a discussion of how non-orthongal
|
|
boxes are represented in LAMMPS.</p>
|
|
<p>The simulation box is defined as either orthogonal or triclinic when
|
|
it is created via the <a class="reference internal" href="create_box.html"><span class="doc">create_box</span></a>,
|
|
<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a>, or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
|
|
commands.</p>
|
|
<p>These keywords allow you to toggle the existing simulation box from
|
|
orthogonal to triclinic and vice versa. For example, an initial
|
|
equilibration simulation can be run in an orthogonal box, the box can
|
|
be toggled to triclinic, and then a <a class="reference internal" href="Section_howto.html#howto-13"><span class="std std-ref">non-equilibrium MD (NEMD) simulation</span></a> can be run with deformation
|
|
via the <a class="reference internal" href="fix_deform.html"><span class="doc">fix deform</span></a> command.</p>
|
|
<p>If the simulation box is currently triclinic and has non-zero tilt in
|
|
xy, yz, or xz, then it cannot be converted to an orthogonal box.</p>
|
|
<hr class="docutils" />
|
|
<p>The <em>set</em> keyword saves the current box size/shape. This can be
|
|
useful if you wish to use the <em>remap</em> keyword more than once or if you
|
|
wish it to be applied to an intermediate box size/shape in a sequence
|
|
of keyword operations. Note that the box size/shape is saved before
|
|
any of the keywords are processed, i.e. the box size/shape at the time
|
|
the create_box command is encountered in the input script.</p>
|
|
<p>The <em>remap</em> keyword remaps atom coordinates from the last saved box
|
|
size/shape to the current box state. For example, if you stretch the
|
|
box in the x dimension or tilt it in the xy plane via the <em>x</em> and <em>xy</em>
|
|
keywords, then the <em>remap</em> commmand will dilate or tilt the atoms to
|
|
conform to the new box size/shape, as if the atoms moved with the box
|
|
as it deformed.</p>
|
|
<p>Note that this operation is performed without regard to periodic
|
|
boundaries. Also, any shrink-wrapping of non-periodic boundaries (see
|
|
the <a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a> command) occurs after all keywords,
|
|
including this one, have been processed.</p>
|
|
<p>Only atoms in the specified group are remapped.</p>
|
|
<hr class="docutils" />
|
|
<p>The <em>units</em> keyword determines the meaning of the distance units used
|
|
to define various arguments. A <em>box</em> value selects standard distance
|
|
units as defined by the <a class="reference internal" href="units.html"><span class="doc">units</span></a> command, e.g. Angstroms for
|
|
units = real or metal. A <em>lattice</em> value means the distance units are
|
|
in lattice spacings. The <a class="reference internal" href="lattice.html"><span class="doc">lattice</span></a> command must have
|
|
been previously used to define the lattice spacing.</p>
|
|
</div>
|
|
<hr class="docutils" />
|
|
<div class="section" id="restrictions">
|
|
<h2>Restrictions</h2>
|
|
<p>If you use the <em>ortho</em> or <em>triclinic</em> keywords, then at the point in
|
|
the input script when this command is issued, no <a class="reference internal" href="dump.html"><span class="doc">dumps</span></a> can
|
|
be active, nor can a <a class="reference internal" href="fix_deform.html"><span class="doc">fix deform</span></a> be active. This is
|
|
because these commands test whether the simulation box is orthogonal
|
|
when they are first issued. Note that these commands can be used in
|
|
your script before a change_box command is issued, so long as an
|
|
<a class="reference internal" href="undump.html"><span class="doc">undump</span></a> or <a class="reference internal" href="unfix.html"><span class="doc">unfix</span></a> command is also used to
|
|
turn them off.</p>
|
|
</div>
|
|
<div class="section" id="related-commands">
|
|
<h2>Related commands</h2>
|
|
<p><a class="reference internal" href="fix_deform.html"><span class="doc">fix deform</span></a>, <a class="reference internal" href="boundary.html"><span class="doc">boundary</span></a></p>
|
|
</div>
|
|
<div class="section" id="default">
|
|
<h2>Default</h2>
|
|
<p>The option default is units = lattice.</p>
|
|
</div>
|
|
</div>
|
|
|
|
|
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</div>
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</div>
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<footer>
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<div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
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<a href="clear.html" class="btn btn-neutral float-right" title="clear command" accesskey="n">Next <span class="fa fa-arrow-circle-right"></span></a>
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<a href="box.html" class="btn btn-neutral" title="box command" accesskey="p"><span class="fa fa-arrow-circle-left"></span> Previous</a>
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<hr/>
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<p>
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© Copyright 2013 Sandia Corporation.
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</p>
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