forked from lijiext/lammps
579 lines
41 KiB
HTML
579 lines
41 KiB
HTML
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<!DOCTYPE html>
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<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
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<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
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<head>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>fix spring command — LAMMPS documentation</title>
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<link rel="stylesheet" href="_static/css/theme.css" type="text/css" />
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<link rel="top" title="LAMMPS documentation" href="index.html"/>
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<link rel="up" title="Fixes" href="fixes.html"/>
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<link rel="next" title="fix spring/chunk command" href="fix_spring_chunk.html"/>
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<link rel="prev" title="fix smd/wall_surface command" href="fix_smd_wall_surface.html"/>
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<script src="_static/js/modernizr.min.js"></script>
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</head>
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<body class="wy-body-for-nav" role="document">
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<div class="wy-grid-for-nav">
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<nav data-toggle="wy-nav-shift" class="wy-nav-side">
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<div class="wy-side-nav-search">
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<a href="Manual.html" class="icon icon-home"> LAMMPS
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<div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
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<p class="caption"><span class="caption-text">User Documentation</span></p>
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<ul>
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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_example.html">7. Example problems</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_tools.html">9. Additional tools</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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</ul>
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<p class="caption"><span class="caption-text">Index</span></p>
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<ul class="current">
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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-l1"><a class="reference internal" href="commands.html">Commands</a></li>
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<li class="toctree-l1 current"><a class="reference internal" href="fixes.html">Fixes</a><ul class="current">
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<li class="toctree-l2"><a class="reference internal" href="fix_adapt.html">fix adapt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_adapt_fep.html">fix adapt/fep command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_addforce.html">fix addforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_addtorque.html">fix addtorque command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_append_atoms.html">fix append/atoms command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_atc.html">fix atc command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_atom_swap.html">fix atom/swap command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_atom.html">fix ave/atom command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_chunk.html">fix ave/chunk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_correlate.html">fix ave/correlate command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_correlate_long.html">fix ave/correlate/long command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_histo.html">fix ave/histo command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_histo.html#fix-ave-histo-weight-command">fix ave/histo/weight command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ave_time.html">fix ave/time command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_aveforce.html">fix aveforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_balance.html">fix balance command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_bond_break.html">fix bond/break command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_bond_create.html">fix bond/create command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_bond_swap.html">fix bond/swap command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_box_relax.html">fix box/relax command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_colvars.html">fix colvars command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_controller.html">fix controller command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_deform.html">fix deform command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_deform.html#fix-deform-kk-command">fix deform/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_deposit.html">fix deposit command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_drag.html">fix drag command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_drude.html">fix drude command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_drude_transform.html">fix drude/transform/direct command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_drude_transform.html#fix-drude-transform-inverse-command">fix drude/transform/inverse command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_dt_reset.html">fix dt/reset command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_efield.html">fix efield command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ehex.html">fix ehex command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_enforce2d.html">fix enforce2d command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_eos_cv.html">fix eos/cv command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_eos_table.html">fix eos/table command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_eos_table_rx.html">fix eos/table/rx command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_evaporate.html">fix evaporate command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_external.html">fix external command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_flow_gauss.html">fix flow/gauss command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_freeze.html">fix freeze command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_gcmc.html">fix gcmc command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_gld.html">fix gld command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_gle.html">fix gle command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_gravity.html">fix gravity command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_gravity.html#fix-gravity-omp-command">fix gravity/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_heat.html">fix heat command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_imd.html">fix imd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_indent.html">fix indent command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ipi.html">fix ipi command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_langevin.html">fix langevin command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_langevin.html#fix-langevin-kk-command">fix langevin/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_langevin_drude.html">fix langevin/drude command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_langevin_eff.html">fix langevin/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_lb_fluid.html">fix lb/fluid command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_lb_momentum.html">fix lb/momentum command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_lb_pc.html">fix lb/pc command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_lb_rigid_pc_sphere.html">fix lb/rigid/pc/sphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_lb_viscous.html">fix lb/viscous command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_lineforce.html">fix lineforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_manifoldforce.html">fix manifoldforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_meso.html">fix meso command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_meso_stationary.html">fix meso/stationary command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_momentum.html">fix momentum command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_move.html">fix move command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_msst.html">fix msst command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_neb.html">fix neb command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html">fix nvt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nvt-intel-command">fix nvt/intel command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nvt-kk-command">fix nvt/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nvt-omp-command">fix nvt/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-npt-command">fix npt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-npt-intel-command">fix npt/intel command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-npt-kk-command">fix npt/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-npt-omp-command">fix npt/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nph-command">fix nph command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nph-kk-command">fix nph/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nph-omp-command">fix nph/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh_eff.html">fix nvt/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh_eff.html#fix-npt-eff-command">fix npt/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nh_eff.html#fix-nph-eff-command">fix nph/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nph_asphere.html">fix nph/asphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nph_asphere.html#fix-nph-asphere-omp-command">fix nph/asphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nph_body.html">fix nph/body command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nph_sphere.html">fix nph/sphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nph_sphere.html#fix-nph-sphere-omp-command">fix nph/sphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nphug.html">fix nphug command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nphug.html#fix-nphug-omp-command">fix nphug/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_npt_asphere.html">fix npt/asphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_npt_asphere.html#fix-npt-asphere-omp-command">fix npt/asphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_npt_body.html">fix npt/body command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_npt_sphere.html">fix npt/sphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_npt_sphere.html#fix-npt-sphere-omp-command">fix npt/sphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve.html">fix nve command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve.html#fix-nve-intel-command">fix nve/intel command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve.html#fix-nve-kk-command">fix nve/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve.html#fix-nve-omp-command">fix nve/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_asphere.html">fix nve/asphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_asphere.html#fix-nve-asphere-intel-command">fix nve/asphere/intel command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_asphere_noforce.html">fix nve/asphere/noforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_body.html">fix nve/body command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_eff.html">fix nve/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_limit.html">fix nve/limit command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_line.html">fix nve/line command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_manifold_rattle.html">fix nve/manifold/rattle command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_noforce.html">fix nve/noforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_sphere.html">fix nve/sphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_sphere.html#fix-nve-sphere-omp-command">fix nve/sphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nve_tri.html">fix nve/tri command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_asphere.html">fix nvt/asphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_asphere.html#fix-nvt-asphere-omp-command">fix nvt/asphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_body.html">fix nvt/body command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_manifold_rattle.html">fix nvt/manifold/rattle command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sllod.html">fix nvt/sllod command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sllod.html#fix-nvt-sllod-intel-command">fix nvt/sllod/intel command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sllod.html#fix-nvt-sllod-omp-command">fix nvt/sllod/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sllod_eff.html">fix nvt/sllod/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sphere.html">fix nvt/sphere command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sphere.html#fix-nvt-sphere-omp-command">fix nvt/sphere/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_oneway.html">fix oneway command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_orient.html">fix orient/fcc command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_orient.html#fix-orient-bcc-command">fix orient/bcc command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_phonon.html">fix phonon command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_pimd.html">fix pimd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_planeforce.html">fix planeforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_poems.html">fix poems</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_pour.html">fix pour command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_press_berendsen.html">fix press/berendsen command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_print.html">fix print command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_property_atom.html">fix property/atom command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qbmsst.html">fix qbmsst command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq.html">fix qeq/point command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq.html#fix-qeq-shielded-command">fix qeq/shielded command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq.html#fix-qeq-slater-command">fix qeq/slater command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq.html#fix-qeq-dynamic-command">fix qeq/dynamic command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq.html#fix-qeq-fire-command">fix qeq/fire command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq_comb.html">fix qeq/comb command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq_comb.html#fix-qeq-comb-omp-command">fix qeq/comb/omp command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq_reax.html">fix qeq/reax command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qeq_reax.html#fix-qeq-reax-kk-command">fix qeq/reax/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qmmm.html">fix qmmm command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_qtb.html">fix qtb command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_reax_bonds.html">fix reax/bonds command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_reax_bonds.html#fix-reax-c-bonds-command">fix reax/c/bonds command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_reaxc_species.html">fix reax/c/species command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_recenter.html">fix recenter command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_restrain.html">fix restrain command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html">fix rigid command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-nve-command">fix rigid/nve command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-nvt-command">fix rigid/nvt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-npt-command">fix rigid/npt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-nph-command">fix rigid/nph command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-small-command">fix rigid/small command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-nve-small-command">fix rigid/nve/small command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-nvt-small-command">fix rigid/nvt/small command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-npt-small-command">fix rigid/npt/small command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rigid.html#fix-rigid-nph-small-command">fix rigid/nph/small command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_rx.html">fix rx command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_saed_vtk.html">fix saed/vtk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_setforce.html">fix setforce command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_setforce.html#fix-setforce-kk-command">fix setforce/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_shake.html">fix shake command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_shake.html#fix-rattle-command">fix rattle command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_smd.html">fix smd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_smd_adjust_dt.html">fix smd/adjust_dt command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_smd_integrate_tlsph.html">fix smd/integrate_tlsph command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_smd_move_triangulated_surface.html">fix smd/move_tri_surf command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_smd_setvel.html">fix smd/setvel command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_smd_wall_surface.html">fix smd/wall_surface command</a></li>
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<li class="toctree-l2 current"><a class="current reference internal" href="#">fix spring 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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</ul>
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<li class="toctree-l2"><a class="reference internal" href="fix_spring_chunk.html">fix spring/chunk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_spring_self.html">fix spring/self command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_srd.html">fix srd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_store_force.html">fix store/force command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_store_state.html">fix store/state command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_temp_berendsen.html">fix temp/berendsen command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_temp_csvr.html">fix temp/csvr command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_temp_csvr.html#fix-temp-csld-command">fix temp/csld command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_temp_rescale_eff.html">fix temp/rescale/eff command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_thermal_conductivity.html">fix thermal/conductivity command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ti_rs.html">fix ti/rs command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ti_spring.html">fix ti/spring command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_tmd.html">fix tmd command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ttm.html">fix ttm command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_ttm.html#fix-ttm-mod-command">fix ttm/mod command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_tune_kspace.html">fix tune/kspace command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_vector.html">fix vector command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_viscosity.html">fix viscosity command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_viscous.html">fix viscous command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall.html">fix wall/lj93 command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall.html#fix-wall-lj126-command">fix wall/lj126 command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall.html#fix-wall-lj1043-command">fix wall/lj1043 command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall.html#fix-wall-colloid-command">fix wall/colloid command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall.html#fix-wall-harmonic-command">fix wall/harmonic command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall_gran.html">fix wall/gran command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall_piston.html">fix wall/piston command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall_reflect.html">fix wall/reflect command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall_reflect.html#fix-wall-reflect-kk-command">fix wall/reflect/kk command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall_region.html">fix wall/region command</a></li>
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<li class="toctree-l2"><a class="reference internal" href="fix_wall_srd.html">fix wall/srd command</a></li>
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</ul>
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<li class="toctree-l1"><a class="reference internal" href="computes.html">Computes</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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<div class="section" id="fix-spring-command">
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<span id="index-0"></span><h1>fix spring command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">spring</span> <span class="n">keyword</span> <span class="n">values</span>
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</pre></div>
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</div>
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<ul>
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<li><p class="first">ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</p>
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</li>
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<li><p class="first">spring = style name of this fix command</p>
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</li>
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<li><p class="first">keyword = <em>tether</em> or <em>couple</em></p>
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<pre class="literal-block">
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<em>tether</em> values = K x y z R0
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K = spring constant (force/distance units)
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x,y,z = point to which spring is tethered
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R0 = equilibrium distance from tether point (distance units)
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<em>couple</em> values = group-ID2 K x y z R0
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group-ID2 = 2nd group to couple to fix group with a spring
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K = spring constant (force/distance units)
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x,y,z = direction of spring
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R0 = equilibrium distance of spring (distance units)
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</pre>
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</li>
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</ul>
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</div>
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<div class="section" id="examples">
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<h2>Examples</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">pull</span> <span class="n">ligand</span> <span class="n">spring</span> <span class="n">tether</span> <span class="mf">50.0</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">0.0</span>
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|
<span class="n">fix</span> <span class="n">pull</span> <span class="n">ligand</span> <span class="n">spring</span> <span class="n">tether</span> <span class="mf">50.0</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">5.0</span>
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|
<span class="n">fix</span> <span class="n">pull</span> <span class="n">ligand</span> <span class="n">spring</span> <span class="n">tether</span> <span class="mf">50.0</span> <span class="n">NULL</span> <span class="n">NULL</span> <span class="mf">2.0</span> <span class="mf">3.0</span>
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<span class="n">fix</span> <span class="mi">5</span> <span class="n">bilayer1</span> <span class="n">spring</span> <span class="n">couple</span> <span class="n">bilayer2</span> <span class="mf">100.0</span> <span class="n">NULL</span> <span class="n">NULL</span> <span class="mf">10.0</span> <span class="mf">0.0</span>
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<span class="n">fix</span> <span class="n">longitudinal</span> <span class="n">pore</span> <span class="n">spring</span> <span class="n">couple</span> <span class="n">ion</span> <span class="mf">100.0</span> <span class="n">NULL</span> <span class="n">NULL</span> <span class="o">-</span><span class="mf">20.0</span> <span class="mf">0.0</span>
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|
<span class="n">fix</span> <span class="n">radial</span> <span class="n">pore</span> <span class="n">spring</span> <span class="n">couple</span> <span class="n">ion</span> <span class="mf">100.0</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="n">NULL</span> <span class="mf">5.0</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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|
<h2>Description</h2>
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|
<p>Apply a spring force to a group of atoms or between two groups of
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|
atoms. This is useful for applying an umbrella force to a small
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|
molecule or lightly tethering a large group of atoms (e.g. all the
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|
solvent or a large molecule) to the center of the simulation box so
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|
that it doesn’t wander away over the course of a long simulation. It
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|
can also be used to hold the centers of mass of two groups of atoms at
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|
a given distance or orientation with respect to each other.</p>
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|
<p>The <em>tether</em> style attaches a spring between a fixed point <em>x,y,z</em> and
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|
the center of mass of the fix group of atoms. The equilibrium
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|
position of the spring is R0. At each timestep the distance R from
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|
the center of mass of the group of atoms to the tethering point is
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computed, taking account of wrap-around in a periodic simulation box.
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A restoring force of magnitude K (R - R0) Mi / M is applied to each
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atom in the group where <em>K</em> is the spring constant, Mi is the mass of
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the atom, and M is the total mass of all atoms in the group. Note
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that <em>K</em> thus represents the spring constant for the total force on
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|
the group of atoms, not for a spring applied to each atom.</p>
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<p>The <em>couple</em> style links two groups of atoms together. The first
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group is the fix group; the second is specified by group-ID2. The
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groups are coupled together by a spring that is at equilibrium when
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the two groups are displaced by a vector <em>x,y,z</em> with respect to each
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other and at a distance R0 from that displacement. Note that <em>x,y,z</em>
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is the equilibrium displacement of group-ID2 relative to the fix
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group. Thus (1,1,0) is a different spring than (-1,-1,0). When the
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relative positions and distance between the two groups are not in
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equilibrium, the same spring force described above is applied to atoms
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in each of the two groups.</p>
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|
<p>For both the <em>tether</em> and <em>couple</em> styles, any of the x,y,z values can
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|
be specified as NULL which means do not include that dimension in the
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|
distance calculation or force application.</p>
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|
<p>The first example above pulls the ligand towards the point (0,0,0).
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|
The second example holds the ligand near the surface of a sphere of
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|
radius 5 around the point (0,0,0). The third example holds the ligand
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|
a distance 3 away from the z=2 plane (on either side).</p>
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|
<p>The fourth example holds 2 bilayers a distance 10 apart in z. For the
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|
last two examples, imagine a pore (a slab of atoms with a cylindrical
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|
hole cut out) oriented with the pore axis along z, and an ion moving
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|
within the pore. The fifth example holds the ion a distance of -20
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|
below the z = 0 center plane of the pore (umbrella sampling). The
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|
last example holds the ion a distance 5 away from the pore axis
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(assuming the center-of-mass of the pore in x,y is the pore axis).</p>
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|
<div class="admonition note">
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|
<p class="first admonition-title">Note</p>
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|
<p class="last">The center of mass of a group of atoms is calculated in
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|
“unwrapped” coordinates using atom image flags, which means that the
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|
group can straddle a periodic boundary. See the <a class="reference internal" href="dump.html"><span class="doc">dump</span></a> doc
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|
page for a discussion of unwrapped coordinates. It also means that a
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|
spring connecting two groups or a group and the tether point can cross
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a periodic boundary and its length be calculated correctly. One
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|
exception is for rigid bodies, which should not be used with the fix
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|
spring command, if the rigid body will cross a periodic boundary.
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This is because image flags for rigid bodies are used in a different
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|
way, as explained on the <a class="reference internal" href="fix_rigid.html"><span class="doc">fix rigid</span></a> doc page.</p>
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|
</div>
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|
<p><strong>Restart, fix_modify, output, run start/stop, minimize info:</strong></p>
|
|
<p>No information about this fix is written to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>.</p>
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|
<p>The <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> <em>energy</em> option is supported by this
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|
fix to add the energy stored in the spring to the system’s potential
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|
energy as part of <a class="reference internal" href="thermo_style.html"><span class="doc">thermodynamic output</span></a>.</p>
|
|
<p>The <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> <em>respa</em> option is supported by this
|
|
fix. This allows to set at which level of the <a class="reference internal" href="run_style.html"><span class="doc">r-RESPA</span></a>
|
|
integrator the fix is adding its forces. Default is the outermost level.</p>
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|
<p>This fix computes a global scalar which can be accessed by various
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|
<a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. The scalar is the
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|
spring energy = 0.5 * K * r^2.</p>
|
|
<p>This fix also computes global 4-vector which can be accessed by
|
|
various <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. The first 3
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quantities in the vector are xyz components of the total force added
|
|
to the group of atoms by the spring. In the case of the <em>couple</em>
|
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style, it is the force on the fix group (group-ID) or the negative of
|
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the force on the 2nd group (group-ID2). The 4th quantity in the
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vector is the magnitude of the force added by the spring, as a
|
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positive value if (r-R0) > 0 and a negative value if (r-R0) < 0. This
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sign convention can be useful when using the spring force to compute a
|
|
potential of mean force (PMF).</p>
|
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<p>The scalar and vector values calculated by this fix are “extensive”.</p>
|
|
<p>No parameter of this fix can be used with the <em>start/stop</em> keywords of
|
|
the <a class="reference internal" href="run.html"><span class="doc">run</span></a> command.</p>
|
|
<p>The forces due to this fix are imposed during an energy minimization,
|
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invoked by the <a class="reference internal" href="minimize.html"><span class="doc">minimize</span></a> command.</p>
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<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">If you want the spring energy to be included in the total
|
|
potential energy of the system (the quantity being minimized), you
|
|
MUST enable the <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> <em>energy</em> option for this
|
|
fix.</p>
|
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</div>
|
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</div>
|
|
<div class="section" id="restrictions">
|
|
<h2>Restrictions</h2>
|
|
<blockquote>
|
|
<div>none</div></blockquote>
|
|
</div>
|
|
<div class="section" id="related-commands">
|
|
<h2>Related commands</h2>
|
|
<p><a class="reference internal" href="fix_drag.html"><span class="doc">fix drag</span></a>, <a class="reference internal" href="fix_spring_self.html"><span class="doc">fix spring/self</span></a>,
|
|
<a class="reference internal" href="fix_spring_rg.html"><span class="doc">fix spring/rg</span></a>, <a class="reference internal" href="fix_smd.html"><span class="doc">fix smd</span></a></p>
|
|
<p><strong>Default:</strong> none</p>
|
|
</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="fix_spring_chunk.html" class="btn btn-neutral float-right" title="fix spring/chunk command" accesskey="n">Next <span class="fa fa-arrow-circle-right"></span></a>
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<a href="fix_smd_wall_surface.html" class="btn btn-neutral" title="fix smd/wall_surface command" accesskey="p"><span class="fa fa-arrow-circle-left"></span> Previous</a>
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<p>
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