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<li class="toctree-l2 current"><a class="current reference internal" href="#">3.6. Pair styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Modify_compute.html">3.8. Compute styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Modify_command.html">3.10. Input script command style</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Modify_gran_sub_mod.html">3.16. Granular Sub-Model styles</a></li>
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<li class="toctree-l2"><a class="reference internal" href="Modify_thermo.html">3.17. Thermodynamic output options</a></li>
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<p><span class="math notranslate nohighlight">\(\renewcommand{\AA}{\text{Å}}\)</span></p>
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<section id="pair-styles">
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<h1><span class="section-number">3.6. </span>Pair styles<a class="headerlink" href="#pair-styles" title="Link to this heading"></a></h1>
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<p>Classes that compute pairwise non-bonded interactions are derived from
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the <code class="docutils literal notranslate"><span class="pre">Pair</span></code> class. In LAMMPS, pairwise force calculations include
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many-body potentials such as EAM, Tersoff, or ReaxFF where particles
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interact without an explicit bond topology but include interactions
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beyond pairwise non-bonded contributions. New styles can be created to
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add support for additional pair potentials to LAMMPS. When the
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modifications are small, sometimes it is more effective to derive from
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an existing pair style class. This latter approach is also used by
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<a class="reference internal" href="Speed_packages.html"><span class="doc">Accelerator packages</span></a> where the accelerated style
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names differ from their base classes by an appended suffix.</p>
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<p>The file <code class="docutils literal notranslate"><span class="pre">src/pair_lj_cut.cpp</span></code> is an example of a Pair class with a
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very simple potential function. It includes several optional methods to
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enable its use with <a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> and <a class="reference internal" href="compute_group_group.html"><span class="doc">compute
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group/group</span></a>. <a class="reference internal" href="Developer_write_pair.html"><span class="doc">Writing new pair styles</span></a> contains
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a detailed discussion of writing new pair styles from scratch, and how
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simple and more complex pair styles can be implemented with examples
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from existing pair styles.</p>
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<p>Here is a brief list of some the class methods in the Pair class that
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<em>must</em> be or <em>may</em> be overridden in a derived class for a new pair style.</p>
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<table class="docutils align-default">
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<thead>
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<tr class="row-odd"><th class="head"><p>Required</p></th>
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<th class="head"><p>“pure” methods that <em>must</em> be overridden in a derived class</p></th>
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</tr>
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</thead>
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<tbody>
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<tr class="row-even"><td><p>compute</p></td>
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<td><p>workhorse routine that computes pairwise interactions</p></td>
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</tr>
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<tr class="row-odd"><td><p>settings</p></td>
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<td><p>processes the arguments to the pair_style command</p></td>
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</tr>
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<tr class="row-even"><td><p>coeff</p></td>
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<td><p>set coefficients for one i,j type pair, called from pair_coeff</p></td>
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</tr>
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</tbody>
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</table>
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<table class="docutils align-default">
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<thead>
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<tr class="row-odd"><th class="head"><p>Optional</p></th>
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<th class="head"><p>methods that have a default or dummy implementation</p></th>
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</tr>
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</thead>
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<tbody>
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<tr class="row-even"><td><p>init_one</p></td>
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<td><p>perform initialization for one i,j type pair</p></td>
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</tr>
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<tr class="row-odd"><td><p>init_style</p></td>
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<td><p>style initialization: request neighbor list(s), error checks</p></td>
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</tr>
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<tr class="row-even"><td><p>init_list</p></td>
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<td><p>Neighbor class callback function to pass neighbor list to pair style</p></td>
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</tr>
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<tr class="row-odd"><td><p>single</p></td>
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<td><p>force/r and energy of a single pairwise interaction between two atoms</p></td>
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</tr>
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<tr class="row-even"><td><p>compute_inner/middle/outer</p></td>
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<td><p>versions of compute used by rRESPA</p></td>
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</tr>
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<tr class="row-odd"><td><p>memory_usage</p></td>
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<td><p>return estimated amount of memory used by the pair style</p></td>
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</tr>
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<tr class="row-even"><td><p>modify_params</p></td>
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<td><p>process arguments to pair_modify command</p></td>
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</tr>
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<tr class="row-odd"><td><p>extract</p></td>
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<td><p>provide access to internal scalar or per-type data like cutoffs</p></td>
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</tr>
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<tr class="row-even"><td><p>extract_peratom</p></td>
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<td><p>provide access to internal per-atom data</p></td>
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</tr>
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<tr class="row-odd"><td><p>setup</p></td>
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<td><p>initialization at the beginning of a run</p></td>
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</tr>
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<tr class="row-even"><td><p>finish</p></td>
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<td><p>called at the end of a run, e.g. to print</p></td>
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</tr>
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<tr class="row-odd"><td><p>write & read_restart</p></td>
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<td><p>write/read i,j pair coeffs to restart files</p></td>
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</tr>
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<tr class="row-even"><td><p>write & read_restart_settings</p></td>
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<td><p>write/read global settings to restart files</p></td>
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</tr>
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<tr class="row-odd"><td><p>write_data</p></td>
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<td><p>write Pair Coeffs section to data file</p></td>
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</tr>
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<tr class="row-even"><td><p>write_data_all</p></td>
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<td><p>write PairIJ Coeffs section to data file</p></td>
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</tr>
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<tr class="row-odd"><td><p>pack & unpack_forward_comm</p></td>
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<td><p>copy data to and from buffer if style uses forward communication</p></td>
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</tr>
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<tr class="row-even"><td><p>pack & unpack_reverse_comm</p></td>
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<td><p>copy data to and from buffer if style uses reverse communication</p></td>
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</tr>
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<tr class="row-odd"><td><p>reinit</p></td>
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<td><p>reset all type-based parameters, called by fix adapt for example</p></td>
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</tr>
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<tr class="row-even"><td><p>reset_dt</p></td>
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<td><p>called when the time step is changed by timestep or fix reset/dt</p></td>
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</tr>
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</tbody>
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</table>
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<p>Here is a list of flags or settings that should be set in the
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constructor of the derived pair class when they differ from the default
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setting.</p>
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<table class="docutils align-default">
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<thead>
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<tr class="row-odd"><th class="head"><p>Name of flag</p></th>
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<th class="head"><p>Description</p></th>
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<th class="head"><p>default</p></th>
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</tr>
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</thead>
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<tbody>
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<tr class="row-even"><td><p>single_enable</p></td>
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<td><p>1 if single() method is implemented, 0 if missing</p></td>
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<td><p>1</p></td>
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</tr>
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<tr class="row-odd"><td><p>respa_enable</p></td>
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<td><p>1 if pair style has compute_inner/middle/outer()</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>restartinfo</p></td>
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<td><p>1 if pair style writes its settings to a restart</p></td>
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<td><p>1</p></td>
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</tr>
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<tr class="row-odd"><td><p>one_coeff</p></td>
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<td><p>1 if only a pair_coeff * * command is allowed</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>manybody_flag</p></td>
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<td><p>1 if pair style is a manybody potential</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-odd"><td><p>unit_convert_flag</p></td>
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<td><p>value != 0 indicates support for unit conversion</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>no_virial_fdotr_compute</p></td>
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<td><p>1 if pair style does not call virial_fdotr_compute()</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-odd"><td><p>writedata</p></td>
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<td><p>1 if write_data() and write_data_all() are implemented</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>comm_forward</p></td>
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<td><p>size of buffer (in doubles) for forward communication</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-odd"><td><p>comm_reverse</p></td>
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<td><p>size of buffer (in doubles) for reverse communication</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>ghostneigh</p></td>
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<td><p>1 if cutghost is set and style uses neighbors of ghosts</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-odd"><td><p>finitecutflag</p></td>
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<td><p>1 if cutoff depends on diameter of atoms</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>reinitflag</p></td>
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<td><p>1 if style has reinit() and is compatible with fix adapt</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-odd"><td><p>ewaldflag</p></td>
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<td><p>1 if compatible with kspace_style ewald</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-even"><td><p>pppmflag</p></td>
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<td><p>1 if compatible with kspace_style pppm</p></td>
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<td><p>0</p></td>
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</tr>
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<tr class="row-odd"><td><p>msmflag</p></td>
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<td><p>1 if compatible with kspace_style msm</p></td>
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<td><p>0</p></td>
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</tr>
|
|
<tr class="row-even"><td><p>dispersionflag</p></td>
|
|
<td><p>1 if compatible with ewald/disp or pppm/disp</p></td>
|
|
<td><p>0</p></td>
|
|
</tr>
|
|
<tr class="row-odd"><td><p>tip4pflag</p></td>
|
|
<td><p>1 if compatible with kspace_style pppm/tip4p</p></td>
|
|
<td><p>0</p></td>
|
|
</tr>
|
|
<tr class="row-even"><td><p>dipoleflag</p></td>
|
|
<td><p>1 if compatible with dipole kspace_style</p></td>
|
|
<td><p>0</p></td>
|
|
</tr>
|
|
<tr class="row-odd"><td><p>spinflag</p></td>
|
|
<td><p>1 if compatible with spin kspace_style</p></td>
|
|
<td><p>0</p></td>
|
|
</tr>
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