584 lines
40 KiB
HTML
584 lines
40 KiB
HTML
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<!DOCTYPE html>
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<title>fix ti/spring command — LAMMPS documentation</title>
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<a href="Manual.html" class="icon icon-home"> LAMMPS
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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_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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</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_shardlow.html">fix shardlow 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_integrate_ulsph.html">fix smd/integrate_ulsph 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"><a class="reference internal" href="fix_spring.html">fix spring command</a></li>
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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_rg.html">fix spring/rg 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.html">fix temp/rescale 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_tfmc.html">fix tfmc 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 current"><a class="current reference internal" href="#">fix ti/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="#description">Description</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="#restrictions">Restrictions</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="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>
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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">Bond Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="angles.html">Angle Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="dihedrals.html">Dihedral Styles</a></li>
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<li class="toctree-l1"><a class="reference internal" href="impropers.html">Improper Styles</a></li>
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<li>fix ti/spring command</li>
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<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
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<div class="section" id="fix-ti-spring-command">
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<span id="index-0"></span><h1>fix ti/spring 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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fix ID group-ID ti/spring k t_s t_eq keyword value ...
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</pre>
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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">ti/spring = style name of this fix command</p>
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</li>
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<li><p class="first">k = spring constant (force/distance units)</p>
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</li>
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<li><p class="first">t_eq = number of steps for the equilibration procedure</p>
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</li>
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<li><p class="first">t_s = number of steps for the switching procedure</p>
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</li>
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<li><p class="first">zero or more keyword/value pairs may be appended to args</p>
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</li>
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<li><p class="first">keyword = <em>function</em></p>
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<pre class="literal-block">
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<em>function</em> value = function-ID
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function-ID = ID of the switching function (1 or 2)
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</pre>
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</li>
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</ul>
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<p><strong>Example:</strong></p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">ti</span><span class="o">/</span><span class="n">spring</span> <span class="mf">50.0</span> <span class="mi">2000</span> <span class="mi">1000</span> <span class="n">function</span> <span class="mi">2</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>This fix allows you to compute the free energy of crystalline solids
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by performing a nonequilibrium thermodynamic integration between the
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|
solid of interest and an Einstein crystal. A detailed explanation of
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|
how to use this command and choose its parameters for optimal
|
|
performance and accuracy is given in the paper by
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|
<a class="reference internal" href="#freitas"><span class="std std-ref">Freitas</span></a>. The paper also presents a short summary of the
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|
theory of nonequilibrium thermodynamic integrations.</p>
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|
<p>The thermodynamic integration procedure is performed by rescaling the
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|
force on each atom. Given an atomic configuration the force (F) on
|
|
each atom is given by</p>
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|
<img alt="_images/fix_ti_spring_force.jpg" class="align-center" src="_images/fix_ti_spring_force.jpg" />
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<p>where F_solid is the force that acts on an atom due to an interatomic
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|
potential (<em>e.g.</em> EAM potential), F_harm is the force due to the
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|
Einstein crystal harmonic spring, and lambda is the coupling parameter
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of the thermodynamic integration. An Einstein crystal is a solid where
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each atom is attached to its equilibrium position by a harmonic spring
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with spring constant <em>k</em>. With this fix a spring force is applied
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|
independently to each atom in the group defined by the fix to tether
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it to its initial position. The initial position of each atom is its
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|
position at the time the fix command was issued.</p>
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|
<p>The fix acts as follows: during the first <em>t_eq</em> steps after the fix
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is defined the value of lambda is zero. This is the period to
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equilibrate the system in the lambda = 0 state. After this the value
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of lambda changes dynamically during the simulation from 0 to 1
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|
according to the function defined using the keyword <em>function</em>
|
|
(described below), this switching from lambda from 0 to 1 is done in
|
|
<em>t_s</em> steps. Then comes the second equilibration period of <em>t_eq</em> to
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|
equilibrate the system in the lambda = 1 state. After that, the
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switching back to the lambda = 0 state is made using <em>t_s</em> timesteps
|
|
and following the same switching function. After this period the value
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|
of lambda is kept equal to zero and the fix has no other effect on the
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dynamics of the system.</p>
|
|
<p>The processes described above is known as nonequilibrium thermodynamic
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|
integration and is has been shown (<a class="reference internal" href="#freitas"><span class="std std-ref">Freitas</span></a>) to present a
|
|
much superior efficiency when compared to standard equilibrium
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|
methods. The reason why the switching it is made in both directions
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|
(potential to Einstein crystal and back) is to eliminate the
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|
dissipated heat due to the nonequilibrium process. Further details
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|
about nonequilibrium thermodynamic integration and its implementation
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|
in LAMMPS is available in <a class="reference internal" href="#freitas"><span class="std std-ref">Freitas</span></a>.</p>
|
|
<p>The <em>function</em> keyword allows the use of two different lambda
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paths. Option <em>1</em> results in a constant rate of change of lambda with
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|
time:</p>
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|
<img alt="_images/fix_ti_spring_function_1.jpg" class="align-center" src="_images/fix_ti_spring_function_1.jpg" />
|
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<p>where tau is the scaled time variable <em>t/t_s</em>. The option <em>2</em> performs
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the lambda switching at a rate defined by the following switching
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function</p>
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<img alt="_images/fix_ti_spring_function_2.jpg" class="align-center" src="_images/fix_ti_spring_function_2.jpg" />
|
|
<p>This function has zero slope as lambda approaches its extreme values
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|
(0 and 1), according to <a class="reference internal" href="#dekoning96"><span class="std std-ref">de Koning</span></a> this results in
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smaller fluctuations on the integral to be computed on the
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thermodynamic integration. The use of option <em>2</em> is recommended since
|
|
it results in better accuracy and less dissipation without any
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|
increase in computational resources cost.</p>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">As described in <a class="reference internal" href="#freitas"><span class="std std-ref">Freitas</span></a>, it is important to keep the
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|
center-of-mass fixed during the thermodynamic integration. A nonzero
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|
total velocity will result in divergences during the integration due
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|
to the fact that the atoms are ‘attached’ to their equilibrium
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|
positions by the Einstein crystal. Check the option <em>zero</em> of <a class="reference external" href="fix_langevin_html">fix langevin</a> and <a class="reference internal" href="velocity.html"><span class="doc">velocity</span></a>. The use of
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|
the Nose-Hoover thermostat (<span class="xref doc">fix nvt</span>) is <em>NOT</em>
|
|
recommended due to its well documented issues with the canonical
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|
sampling of harmonic degrees of freedom (notice that the <em>chain</em>
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option will <em>NOT</em> solve this problem). The Langevin thermostat (<a class="reference external" href="fix_langevin.html"">fix langevin</a>) correctly thermostats the system and we
|
|
advise its usage with ti/spring command.</p>
|
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</div>
|
|
<p><strong>Restart, fix_modify, output, run start/stop, minimize info:</strong></p>
|
|
<p>This fix writes the original coordinates of tethered atoms to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>, so that the spring effect will be the
|
|
same in a restarted simulation. See the <a class="reference internal" href="read_restart.html"><span class="doc">read restart</span></a> command for info on how to re-specify a fix
|
|
in an input script that reads a restart file, so that the operation of
|
|
the fix continues in an uninterrupted fashion.</p>
|
|
<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
|
|
fix to add the energy stored in the per-atom springs to the system’s
|
|
potential energy as part of <a class="reference internal" href="thermo_style.html"><span class="doc">thermodynamic output</span></a>.</p>
|
|
<p>This fix computes a global scalar and a global vector quantities 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 scalar is an energy which
|
|
is the sum of the spring energy for each atom, where the per-atom
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|
energy is 0.5 * k * r^2. The vector has 2 positions, the first one is
|
|
the coupling parameter lambda and the second one is the time
|
|
derivative of lambda. 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,
|
|
invoked by the <a class="reference internal" href="minimize.html"><span class="doc">minimize</span></a> command.</p>
|
|
<div class="admonition note">
|
|
<p class="first admonition-title">Note</p>
|
|
<p class="last">If you want the per-atom 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>
|
|
</div>
|
|
</div>
|
|
<div class="section" id="related-commands">
|
|
<h2>Related commands</h2>
|
|
<p><a class="reference internal" href="fix_spring.html"><span class="doc">fix spring</span></a>, <a class="reference internal" href="fix_adapt.html"><span class="doc">fix adapt</span></a></p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<blockquote>
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<div>none</div></blockquote>
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</div>
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<div class="section" id="default">
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<h2>Default</h2>
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<p>The keyword default is function = 1.</p>
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<hr class="docutils" />
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<p id="freitas"><strong>(Freitas)</strong> Freitas, Asta, and de Koning, Computational Materials
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Science, 112, 333 (2016).</p>
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<p id="dekoning96"><strong>(de Koning)</strong> de Koning and Antonelli, Phys Rev E, 53, 465 (1996).</p>
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<a href="fix_tmd.html" class="btn btn-neutral float-right" title="fix tmd command" accesskey="n">Next <span class="fa fa-arrow-circle-right"></span></a>
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<a href="fix_thermal_conductivity.html" class="btn btn-neutral" title="fix thermal/conductivity command" accesskey="p"><span class="fa fa-arrow-circle-left"></span> Previous</a>
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