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lammps/doc/html/fix_orient.html
2025-01-13 14:55:48 +00:00

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<title>fix orient/fcc command &mdash; LAMMPS documentation</title>
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<div class="lammps_version">Version: <b>19 Nov 2024</b></div>
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<li class="toctree-l1"><a class="reference internal" href="Intro.html">1. Introduction</a></li>
<li class="toctree-l1"><a class="reference internal" href="Install.html">2. Install LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Library.html">1. LAMMPS Library Interfaces</a></li>
<li class="toctree-l1"><a class="reference internal" href="Python_head.html">2. Use Python with LAMMPS</a></li>
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<p class="caption" role="heading"><span class="caption-text">Command Reference</span></p>
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<li class="toctree-l1"><a class="reference internal" href="commands_list.html">Commands</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="fixes.html">Fix Styles</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="fix_accelerate_cos.html">fix accelerate/cos command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_acks2_reaxff.html">fix acks2/reaxff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_adapt.html">fix adapt command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_adapt_fep.html">fix adapt/fep command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_add_heat.html">fix add/heat command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_addforce.html">fix addforce command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_addtorque.html">fix addtorque command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_alchemy.html">fix alchemy command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_amoeba_bitorsion.html">fix amoeba/bitorsion command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_amoeba_pitorsion.html">fix amoeba/pitorsion command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_append_atoms.html">fix append/atoms command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_atc.html">fix atc command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_atom_swap.html">fix atom/swap command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_atom.html">fix ave/atom command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_chunk.html">fix ave/chunk command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_correlate.html">fix ave/correlate command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_correlate_long.html">fix ave/correlate/long command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_grid.html">fix ave/grid command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_histo.html">fix ave/histo command</a></li>
<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>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_spatial.html">fix ave/spatial command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_spatial_sphere.html">fix ave/spatial/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ave_time.html">fix ave/time command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_aveforce.html">fix aveforce command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_balance.html">fix balance command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_bocs.html">fix bocs command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_bond_break.html">fix bond/break command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_bond_create.html">fix bond/create command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_bond_create.html#fix-bond-create-angle-command">fix bond/create/angle command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_bond_react.html">fix bond/react command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_bond_swap.html">fix bond/swap command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_box_relax.html">fix box/relax command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_brownian.html">fix brownian command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_brownian.html#fix-brownian-sphere-command">fix brownian/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_brownian.html#fix-brownian-asphere-command">fix brownian/asphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_charge_regulation.html">fix charge/regulation command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_cmap.html">fix cmap command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_colvars.html">fix colvars command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_controller.html">fix controller command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_damping_cundall.html">fix damping/cundall command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_deform.html">fix deform command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_deform_pressure.html">fix deform/pressure command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_deposit.html">fix deposit command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_dpd_energy.html">fix dpd/energy command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_dpd_source.html">fix edpd/source command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_dpd_source.html#fix-tdpd-source-command">fix tdpd/source command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_drag.html">fix drag command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_drude.html">fix drude command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_drude_transform.html">fix drude/transform/direct command</a></li>
<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>
<li class="toctree-l2"><a class="reference internal" href="fix_dt_reset.html">fix dt/reset command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_efield.html">fix efield command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_efield.html#fix-efield-tip4p-command">fix efield/tip4p command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ehex.html">fix ehex command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_electrode.html">fix electrode/conp command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_electrode.html#fix-electrode-conq-command">fix electrode/conq command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_electrode.html#fix-electrode-thermo-command">fix electrode/thermo command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_electron_stopping.html">fix electron/stopping command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_electron_stopping.html#fix-electron-stopping-fit-command">fix electron/stopping/fit command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_enforce2d.html">fix enforce2d command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_eos_cv.html">fix eos/cv command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_eos_table.html">fix eos/table command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_eos_table_rx.html">fix eos/table/rx command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_evaporate.html">fix evaporate command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_external.html">fix external command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ffl.html">fix ffl command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_filter_corotate.html">fix filter/corotate command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_flow_gauss.html">fix flow/gauss command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_freeze.html">fix freeze command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_gcmc.html">fix gcmc command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_gld.html">fix gld command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_gle.html">fix gle command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_gravity.html">fix gravity command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_grem.html">fix grem command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_halt.html">fix halt command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_heat.html">fix heat command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_heat_flow.html">fix heat/flow command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_hyper_global.html">fix hyper/global command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_hyper_local.html">fix hyper/local command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_imd.html">fix imd command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_indent.html">fix indent command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_ipi.html">fix ipi command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_langevin.html">fix langevin command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_langevin_drude.html">fix langevin/drude command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_langevin_eff.html">fix langevin/eff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_langevin_spin.html">fix langevin/spin command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_lb_fluid.html">fix lb/fluid command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_lb_momentum.html">fix lb/momentum command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_lb_viscous.html">fix lb/viscous command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_lineforce.html">fix lineforce command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_manifoldforce.html">fix manifoldforce command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_mdi_qm.html">fix mdi/qm command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_mdi_qmmm.html">fix mdi/qmmm command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_meso_move.html">fix meso/move command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_mol_swap.html">fix mol/swap command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_momentum.html">fix momentum command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_momentum.html#fix-momentum-chunk-command">fix momentum/chunk command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_move.html">fix move command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_msst.html">fix msst command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_mvv_dpd.html">fix mvv/dpd command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_mvv_dpd.html#fix-mvv-edpd-command">fix mvv/edpd command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_mvv_dpd.html#fix-mvv-tdpd-command">fix mvv/tdpd command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_neb.html">fix neb command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_neb_spin.html">fix neb/spin command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh.html">fix nvt command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-npt-command">fix npt command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh.html#fix-nph-command">fix nph command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh_eff.html">fix nvt/eff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh_eff.html#fix-npt-eff-command">fix npt/eff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh_eff.html#fix-nph-eff-command">fix nph/eff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh_uef.html">fix nvt/uef command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nh_uef.html#fix-npt-uef-command">fix npt/uef command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nonaffine_displacement.html">fix nonaffine/displacement command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nph_asphere.html">fix nph/asphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nph_body.html">fix nph/body command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nph_sphere.html">fix nph/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nphug.html">fix nphug command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_npt_asphere.html">fix npt/asphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_npt_body.html">fix npt/body command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_npt_cauchy.html">fix npt/cauchy command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_npt_sphere.html">fix npt/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_numdiff.html">fix numdiff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_numdiff_virial.html">fix numdiff/virial command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve.html">fix nve command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_asphere.html">fix nve/asphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_asphere_noforce.html">fix nve/asphere/noforce command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_awpmd.html">fix nve/awpmd command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_body.html">fix nve/body command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_bpm_sphere.html">fix nve/bpm/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_dot.html">fix nve/dot command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_dotc_langevin.html">fix nve/dotc/langevin command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_eff.html">fix nve/eff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_limit.html">fix nve/limit command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_line.html">fix nve/line command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_manifold_rattle.html">fix nve/manifold/rattle command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_noforce.html">fix nve/noforce command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_sphere.html">fix nve/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_spin.html">fix nve/spin command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nve_tri.html">fix nve/tri command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvk.html">fix nvk command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvt_asphere.html">fix nvt/asphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvt_body.html">fix nvt/body command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvt_manifold_rattle.html">fix nvt/manifold/rattle command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sllod.html">fix nvt/sllod command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sllod_eff.html">fix nvt/sllod/eff command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_nvt_sphere.html">fix nvt/sphere command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_oneway.html">fix oneway command</a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#">fix orient/fcc command</a></li>
<li class="toctree-l2"><a class="reference internal" href="#fix-orient-bcc-command">fix orient/bcc command</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#syntax">Syntax</a></li>
<li class="toctree-l3"><a class="reference internal" href="#examples">Examples</a></li>
<li class="toctree-l3"><a class="reference internal" href="#description">Description</a></li>
<li class="toctree-l3"><a class="reference internal" href="#restart-fix-modify-output-run-start-stop-minimize-info">Restart, fix_modify, output, run start/stop, minimize info</a></li>
<li class="toctree-l3"><a class="reference internal" href="#restrictions">Restrictions</a></li>
<li class="toctree-l3"><a class="reference internal" href="#related-commands">Related commands</a></li>
<li class="toctree-l3"><a class="reference internal" href="#default">Default</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="fix_orient_eco.html">fix orient/eco command</a></li>
<li class="toctree-l2"><a class="reference internal" href="fix_pafi.html">fix pafi command</a></li>
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<p><span class="math notranslate nohighlight">\(\renewcommand{\AA}{\text{Å}}\)</span></p>
<section id="fix-orient-fcc-command">
<span id="index-1"></span><span id="index-0"></span><h1>fix orient/fcc command<a class="headerlink" href="#fix-orient-fcc-command" title="Link to this heading"></a></h1>
</section>
<section id="fix-orient-bcc-command">
<h1>fix orient/bcc command<a class="headerlink" href="#fix-orient-bcc-command" title="Link to this heading"></a></h1>
<section id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Link to this heading"></a></h2>
<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">fix </span><span class="nv nv-Identifier">ID</span><span class="w"> </span><span class="nv nv-Identifier">group-ID</span><span class="w"> </span><span class="n">orient</span><span class="o">/</span><span class="n">fcc</span><span class="w"> </span><span class="n">nstats</span><span class="w"> </span><span class="n">dir</span><span class="w"> </span><span class="n">alat</span><span class="w"> </span><span class="n">dE</span><span class="w"> </span><span class="n">cutlo</span><span class="w"> </span><span class="n">cuthi</span><span class="w"> </span><span class="n">file0</span><span class="w"> </span><span class="n">file1</span>
<span class="k">fix </span><span class="nv nv-Identifier">ID</span><span class="w"> </span><span class="nv nv-Identifier">group-ID</span><span class="w"> </span><span class="n">orient</span><span class="o">/</span><span class="n">bcc</span><span class="w"> </span><span class="n">nstats</span><span class="w"> </span><span class="n">dir</span><span class="w"> </span><span class="n">alat</span><span class="w"> </span><span class="n">dE</span><span class="w"> </span><span class="n">cutlo</span><span class="w"> </span><span class="n">cuthi</span><span class="w"> </span><span class="n">file0</span><span class="w"> </span><span class="n">file1</span>
</pre></div>
</div>
<ul class="simple">
<li><p>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</p></li>
<li><p>nstats = print stats every this many steps, 0 = never</p></li>
<li><p>dir = 0/1 for which crystal is used as reference</p></li>
<li><p>alat = fcc/bcc cubic lattice constant (distance units)</p></li>
<li><p>dE = energy added to each atom (energy units)</p></li>
<li><p>cutlo,cuthi = values between 0.0 and 1.0, cutlo &lt; cuthi</p></li>
<li><p>file0,file1 = files that specify orientation of each grain</p></li>
</ul>
</section>
<section id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Link to this heading"></a></h2>
<div class="highlight-LAMMPS notranslate"><div class="highlight"><pre><span></span><span class="k">fix </span><span class="nv nv-Identifier">gb</span><span class="w"> </span><span class="nv nv-Identifier">all</span><span class="w"> </span><span class="n">orient</span><span class="o">/</span><span class="n">fcc</span><span class="w"> </span><span class="m">0</span><span class="w"> </span><span class="m">1</span><span class="w"> </span><span class="m">4.032008</span><span class="w"> </span><span class="m">0.001</span><span class="w"> </span><span class="m">0.25</span><span class="w"> </span><span class="m">0.75</span><span class="w"> </span><span class="n">xi.vec</span><span class="w"> </span><span class="n">chi.vec</span>
<span class="k">fix </span><span class="nv nv-Identifier">gb</span><span class="w"> </span><span class="nv nv-Identifier">all</span><span class="w"> </span><span class="n">orient</span><span class="o">/</span><span class="n">bcc</span><span class="w"> </span><span class="m">0</span><span class="w"> </span><span class="m">1</span><span class="w"> </span><span class="m">2.882</span><span class="w"> </span><span class="m">0.001</span><span class="w"> </span><span class="m">0.25</span><span class="w"> </span><span class="m">0.75</span><span class="w"> </span><span class="n">ngb.left</span><span class="w"> </span><span class="n">ngb.right</span>
</pre></div>
</div>
</section>
<section id="description">
<h2>Description<a class="headerlink" href="#description" title="Link to this heading"></a></h2>
<p>The fix applies an orientation-dependent force to atoms near a planar
grain boundary which can be used to induce grain boundary migration
(in the direction perpendicular to the grain boundary plane). The
motivation and explanation of this force and its application are
described in <a class="reference internal" href="#janssens"><span class="std std-ref">(Janssens)</span></a>. The adaptation to bcc crystals
is described in <a class="reference internal" href="#wicaksono1"><span class="std std-ref">(Wicaksono1)</span></a>. The computed force is only
applied to atoms in the fix group.</p>
<p>The basic idea is that atoms in one grain (on one side of the
boundary) have a potential energy dE added to them. Atoms in the
other grain have 0.0 potential energy added. Atoms near the boundary
(whose neighbor environment is intermediate between the two grain
orientations) have an energy between 0.0 and dE added. This creates
an effective driving force to reduce the potential energy of atoms
near the boundary by pushing them towards one of the grain
orientations. For dir = 1 and dE &gt; 0, the boundary will thus move so
that the grain described by file0 grows and the grain described by
file1 shrinks. Thus this fix is designed for simulations of two-grain
systems, either with one grain boundary and free surfaces parallel to
the boundary, or a system with periodic boundary conditions and two
equal and opposite grain boundaries. In either case, the entire
system can displace during the simulation, and such motion should be
accounted for in measuring the grain boundary velocity.</p>
<p>The potential energy added to atom I is given by these formulas</p>
<div class="math notranslate nohighlight">
\[\begin{split} \xi_{i} = &amp; \sum_{j=1}^{12} \left| \mathbf{r}_{j} - \mathbf{r}_{j}^{\rm I} \right| \qquad\qquad\left(1\right) \\
\\
\xi_{\rm IJ} = &amp; \sum_{j=1}^{12} \left| \mathbf{r}_{j}^{\rm J} - \mathbf{r}_{j}^{\rm I} \right| \qquad\qquad\left(2\right)\\
\\
\xi_{\rm low} = &amp; {\rm cutlo} \, \xi_{\rm IJ} \qquad\qquad\qquad\left(3\right)\\
\xi_{\rm high} = &amp; {\rm cuthi} \, \xi_{\rm IJ} \qquad\qquad\qquad\left(4\right) \\
\\
\omega_{i} = &amp; \frac{\pi}{2} \frac{\xi_{i} - \xi_{\rm low}}{\xi_{\rm high} - \xi_{\rm low}} \qquad\qquad\left(5\right)\\
\\
u_{i} = &amp; 0 \quad\quad\qquad\qquad\qquad \textrm{ for } \qquad \xi_{i} &lt; \xi_{\rm low}\\
= &amp; {\rm dE}\,\frac{1 - \cos(2 \omega_{i})}{2}
\qquad \mathrm{ for }\qquad \xi_{\rm low} &lt; \xi_{i} &lt; \xi_{\rm high} \quad \left(6\right) \\
= &amp; {\rm dE} \quad\qquad\qquad\qquad\textrm{ for } \qquad \xi_{\rm high} &lt; \xi_{i}\end{split}\]</div>
<p>which are fully explained in <a class="reference internal" href="#janssens"><span class="std std-ref">(Janssens)</span></a>. For fcc crystals
this order parameter Xi for atom I in equation (1) is a sum over the
12 nearest neighbors of atom I. For bcc crystals it is the
corresponding sum of the 8 nearest neighbors. Rj is the vector from
atom I to its neighbor J, and RIj is a vector in the reference
(perfect) crystal. That is, if dir = 0/1, then RIj is a vector to an
atom coord from file 0/1. Equation (2) gives the expected value of
the order parameter XiIJ in the other grain. Hi and lo cutoffs are
defined in equations (3) and (4), using the input parameters <em>cutlo</em>
and <em>cuthi</em> as thresholds to avoid adding grain boundary energy when
the deviation in the order parameter from 0 or 1 is small (e.g. due to
thermal fluctuations in a perfect crystal). The added potential
energy Ui for atom I is given in equation (6) where it is interpolated
between 0 and dE using the two threshold Xi values and the Wi value of
equation (5).</p>
<p>The derivative of this energy expression gives the force on each atom
which thus depends on the orientation of its neighbors relative to the
2 grain orientations. Only atoms near the grain boundary feel a net
force which tends to drive them to one of the two grain orientations.</p>
<p>In equation (1), the reference vector used for each neighbor is the
reference vector closest to the actual neighbor position. This means
it is possible two different neighbors will use the same reference
vector. In such cases, the atom in question is far from a perfect
orientation and will likely receive the full dE addition, so the
effect of duplicate reference vector usage is small.</p>
<p>The <em>dir</em> parameter determines which grain wants to grow at the
expense of the other. A value of 0 means the first grain will shrink;
a value of 1 means it will grow. This assumes that <em>dE</em> is positive.
The reverse will be true if <em>dE</em> is negative.</p>
<p>The <em>alat</em> parameter is the cubic lattice constant for the fcc or bcc
material and is only used to compute a cutoff distance of 1.57 * alat
/ sqrt(2) for finding the 12 or 8 nearest neighbors of each atom
(which should be valid for an fcc or bcc crystal). A longer/shorter
cutoff can be imposed by adjusting <em>alat</em>. If a particular atom has
less than 12 or 8 neighbors within the cutoff, the order parameter of
equation (1) is effectively multiplied by 12 or 8 divided by the
actual number of neighbors within the cutoff.</p>
<p>The <em>dE</em> parameter is the maximum amount of additional energy added to
each atom in the grain which wants to shrink.</p>
<p>The <em>cutlo</em> and <em>cuthi</em> parameters are used to reduce the force added
to bulk atoms in each grain far away from the boundary. An atom in
the bulk surrounded by neighbors at the ideal grain orientation would
compute an order parameter of 0 or 1 and have no force added.
However, thermal vibrations in the solid will cause the order
parameters to be greater than 0 or less than 1. The cutoff parameters
mask this effect, allowing forces to only be added to atoms with
order-parameters between the cutoff values.</p>
<p><em>File0</em> and <em>file1</em> are filenames for the two grains which each
contain 6 vectors (6 lines with 3 values per line) which specify the
grain orientations. Each vector is a displacement from a central atom
(0,0,0) to a nearest neighbor atom in an fcc lattice at the proper
orientation. The vector lengths should all be identical since an fcc
lattice has a coordination number of 12. Only 6 are listed due to
symmetry, so the list must include one from each pair of
equal-and-opposite neighbors. A pair of orientation files for a
Sigma=5 tilt boundary are shown below. A tutorial that can help for
writing the orientation files is given in <a class="reference internal" href="#wicaksono2"><span class="std std-ref">(Wicaksono2)</span></a></p>
</section>
<section id="restart-fix-modify-output-run-start-stop-minimize-info">
<h2>Restart, fix_modify, output, run start/stop, minimize info<a class="headerlink" href="#restart-fix-modify-output-run-start-stop-minimize-info" title="Link to this heading"></a></h2>
<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>
<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 potential energy of atom interactions with the
grain boundary driving force to the global potential energy of the
system as part of <a class="reference internal" href="thermo_style.html"><span class="doc">thermodynamic output</span></a>. The
default setting for this fix is <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify energy no</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
these fixes. 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 a fix is adding its forces. Default is the
outermost level.</p>
<p>This fix calculates a global scalar which can be accessed by various
<a class="reference internal" href="Howto_output.html"><span class="doc">output commands</span></a>. The scalar is the potential
energy change due to this fix. The scalar value calculated by this
fix is “extensive”.</p>
<p>This fix also calculates a per-atom array which can be accessed by
various <a class="reference internal" href="Howto_output.html"><span class="doc">output commands</span></a>. The array stores the
order parameter Xi and normalized order parameter (0 to 1) for each
atom. The per-atom values can be accessed on any timestep.</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>This fix is not invoked during <a class="reference internal" href="minimize.html"><span class="doc">energy minimization</span></a>.</p>
</section>
<section id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Link to this heading"></a></h2>
<p>These fixes are part of the ORIENT package. They are only enabled if LAMMPS
was built with that package. See the <a class="reference internal" href="Build_package.html"><span class="doc">Build package</span></a> page for more info.</p>
<p>These fixes should only be used with fcc or bcc lattices.</p>
</section>
<section id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Link to this heading"></a></h2>
<p><a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a></p>
</section>
<section id="default">
<h2>Default<a class="headerlink" href="#default" title="Link to this heading"></a></h2>
<p>none</p>
<hr class="docutils" />
<p id="janssens"><strong>(Janssens)</strong> Janssens, Olmsted, Holm, Foiles, Plimpton, Derlet, Nature
Materials, 5, 124-127 (2006).</p>
<p id="wicaksono1"><strong>(Wicaksono1)</strong> Wicaksono, Sinclair, Militzer, Computational Materials
Science, 117, 397-405 (2016).</p>
<p id="wicaksono2"><strong>(Wicaksono2)</strong> Wicaksono, figshare,
<a class="reference external" href="https://doi.org/10.6084/m9.figshare.1488628.v1">https://doi.org/10.6084/m9.figshare.1488628.v1</a> (2015).</p>
<hr class="docutils" />
<p>For illustration purposes, here are example files that specify a
Sigma=5 &lt;100&gt; tilt boundary. This is for a lattice constant of 3.5706
Angs.</p>
<p>file0:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span> 0.798410432046075 1.785300000000000 1.596820864092150
-0.798410432046075 1.785300000000000 -1.596820864092150
2.395231296138225 0.000000000000000 0.798410432046075
0.798410432046075 0.000000000000000 -2.395231296138225
1.596820864092150 1.785300000000000 -0.798410432046075
1.596820864092150 -1.785300000000000 -0.798410432046075
</pre></div>
</div>
<p>file1:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>-0.798410432046075 1.785300000000000 1.596820864092150
0.798410432046075 1.785300000000000 -1.596820864092150
0.798410432046075 0.000000000000000 2.395231296138225
2.395231296138225 0.000000000000000 -0.798410432046075
1.596820864092150 1.785300000000000 0.798410432046075
1.596820864092150 -1.785300000000000 0.798410432046075
</pre></div>
</div>
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