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<li>pair_style airebo 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="pair-style-airebo-command">
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<span id="index-0"></span><h1>pair_style airebo command</h1>
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</div>
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<div class="section" id="pair-style-airebo-omp-command">
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<h1>pair_style airebo/omp command</h1>
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</div>
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<div class="section" id="pair-style-airebo-morse-command">
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<h1>pair_style airebo/morse command</h1>
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</div>
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<div class="section" id="pair-style-airebo-morse-omp-command">
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<h1>pair_style airebo/morse/omp command</h1>
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</div>
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<div class="section" id="pair-style-rebo-command">
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<h1>pair_style rebo command</h1>
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</div>
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<div class="section" id="pair-style-rebo-omp-command">
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<h1>pair_style rebo/omp command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">style</span> <span class="n">cutoff</span> <span class="n">LJ_flag</span> <span class="n">TORSION_flag</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li>style = <em>airebo</em> or <em>airebo/morse</em> or <em>rebo</em></li>
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<li>cutoff = LJ or Morse cutoff (sigma scale factor) (AIREBO and AIREBO-M only)</li>
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<li>LJ_flag = 0/1 to turn off/on the LJ or Morse term (AIREBO and AIREBO-M only, optional)</li>
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<li>TORSION_flag = 0/1 to turn off/on the torsion term (AIREBO and AIREBO-M only, optional)</li>
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</ul>
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</div>
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<div class="section" id="examples">
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<h2>Examples</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">airebo</span> <span class="mf">3.0</span>
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<span class="n">pair_style</span> <span class="n">airebo</span> <span class="mf">2.5</span> <span class="mi">1</span> <span class="mi">0</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="o">../</span><span class="n">potentials</span><span class="o">/</span><span class="n">CH</span><span class="o">.</span><span class="n">airebo</span> <span class="n">H</span> <span class="n">C</span>
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</pre></div>
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</div>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">airebo</span><span class="o">/</span><span class="n">morse</span> <span class="mf">3.0</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="o">../</span><span class="n">potentials</span><span class="o">/</span><span class="n">CH</span><span class="o">.</span><span class="n">airebo</span><span class="o">-</span><span class="n">m</span> <span class="n">H</span> <span class="n">C</span>
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</pre></div>
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</div>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">rebo</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="o">../</span><span class="n">potentials</span><span class="o">/</span><span class="n">CH</span><span class="o">.</span><span class="n">airebo</span> <span class="n">H</span> <span class="n">C</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>The <em>airebo</em> pair style computes the Adaptive Intermolecular Reactive
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Empirical Bond Order (AIREBO) Potential of <a class="reference internal" href="#stuart"><span class="std std-ref">(Stuart)</span></a> for a
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system of carbon and/or hydrogen atoms. Note that this is the initial
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formulation of AIREBO from 2000, not the later formulation.</p>
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<p>The <em>airebo/morse</em> pair style computes the AIREBO-M potential, which
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is equivalent to AIREBO, but replaces the LJ term with a Morse potential.
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The Morse potentials are parameterized by high-quality quantum chemistry
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(MP2) calculations and do not diverge as quickly as particle density
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increases. This allows AIREBO-M to retain accuracy to much higher pressures
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than AIREBO (up to 40 GPa for Polyethylene). Details for this potential
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and its parameterization are given in <a class="reference internal" href="#oconnor"><span class="std std-ref">(O’Conner)</span></a>.</p>
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<p>The <em>rebo</em> pair style computes the Reactive Empirical Bond Order (REBO)
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Potential of <a class="reference internal" href="#brenner"><span class="std std-ref">(Brenner)</span></a>. Note that this is the so-called
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2nd generation REBO from 2002, not the original REBO from 1990.
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As discussed below, 2nd generation REBO is closely related to the
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intial AIREBO; it is just a subset of the potential energy terms.</p>
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<p>The AIREBO potential consists of three terms:</p>
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<img alt="_images/pair_airebo.jpg" class="align-center" src="_images/pair_airebo.jpg" />
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<p>By default, all three terms are included. For the <em>airebo</em> style, if
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the two optional flag arguments to the pair_style command are
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included, the LJ and torsional terms can be turned off. Note that
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both or neither of the flags must be included. If both of the LJ an
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torsional terms are turned off, it becomes the 2nd-generation REBO
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potential, with a small caveat on the spline fitting procedure
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mentioned below. This can be specified directly as pair_style <em>rebo</em>
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with no additional arguments.</p>
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<p>The detailed formulas for this potential are given in
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<a class="reference internal" href="#stuart"><span class="std std-ref">(Stuart)</span></a>; here we provide only a brief description.</p>
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<p>The E_REBO term has the same functional form as the hydrocarbon REBO
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potential developed in <a class="reference internal" href="#brenner"><span class="std std-ref">(Brenner)</span></a>. The coefficients for
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E_REBO in AIREBO are essentially the same as Brenner’s potential, but
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a few fitted spline values are slightly different. For most cases the
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E_REBO term in AIREBO will produce the same energies, forces and
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statistical averages as the original REBO potential from which it was
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derived. The E_REBO term in the AIREBO potential gives the model its
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reactive capabilities and only describes short-ranged C-C, C-H and H-H
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interactions (r < 2 Angstroms). These interactions have strong
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coordination-dependence through a bond order parameter, which adjusts
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the attraction between the I,J atoms based on the position of other
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nearby atoms and thus has 3- and 4-body dependence.</p>
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<p>The E_LJ term adds longer-ranged interactions (2 < r < cutoff) using a
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form similar to the standard <a class="reference internal" href="pair_lj.html"><span class="doc">Lennard Jones potential</span></a>.
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The E_LJ term in AIREBO contains a series of switching functions so
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that the short-ranged LJ repulsion (1/r^12) does not interfere with
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the energetics captured by the E_REBO term. The extent of the E_LJ
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interactions is determined by the <em>cutoff</em> argument to the pair_style
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command which is a scale factor. For each type pair (C-C, C-H, H-H)
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the cutoff is obtained by multiplying the scale factor by the sigma
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value defined in the potential file for that type pair. In the
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standard AIREBO potential, sigma_CC = 3.4 Angstroms, so with a scale
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factor of 3.0 (the argument in pair_style), the resulting E_LJ cutoff
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would be 10.2 Angstroms.</p>
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<p>The E_TORSION term is an explicit 4-body potential that describes
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various dihedral angle preferences in hydrocarbon configurations.</p>
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<hr class="docutils" />
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<p>Only a single pair_coeff command is used with the <em>airebo</em>, <em>airebo</em>
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or <em>rebo</em> style which specifies an AIREBO or AIREBO-M potential file
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with parameters for C and H. Note that the <em>rebo</em> style in LAMMPS
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uses the same AIREBO-formatted potential file. These are mapped to
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LAMMPS atom types by specifying N additional arguments after the
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filename in the pair_coeff command, where N is the number of LAMMPS
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atom types:</p>
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<ul class="simple">
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<li>filename</li>
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<li>N element names = mapping of AIREBO elements to atom types</li>
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</ul>
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<p>See the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> doc page for alternate ways
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to specify the path for the potential file.</p>
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<p>As an example, if your LAMMPS simulation has 4 atom types and you want
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the 1st 3 to be C, and the 4th to be H, you would use the following
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pair_coeff command:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="n">CH</span><span class="o">.</span><span class="n">airebo</span> <span class="n">C</span> <span class="n">C</span> <span class="n">C</span> <span class="n">H</span>
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</pre></div>
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</div>
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<p>The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
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The first three C arguments map LAMMPS atom types 1,2,3 to the C
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element in the AIREBO file. The final H argument maps LAMMPS atom
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type 4 to the H element in the SW file. If a mapping value is
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specified as NULL, the mapping is not performed. This can be used
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when a <em>airebo</em> potential is used as part of the <em>hybrid</em> pair style.
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The NULL values are placeholders for atom types that will be used with
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other potentials.</p>
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<p>The parameters/coefficients for the AIREBO potentials are listed in
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the CH.airebo file to agree with the original <a class="reference internal" href="#stuart"><span class="std std-ref">(Stuart)</span></a>
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paper. Thus the parameters are specific to this potential and the way
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it was fit, so modifying the file should be done cautiously.</p>
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<p>Similarly the parameters/coefficients for the AIREBO-M potentials are
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listed in the CH.airebo-m file to agree with the <a class="reference internal" href="#oconnor"><span class="std std-ref">(O’Connor)</span></a>
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paper. Thus the parameters are specific to this potential and the way
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it was fit, so modifying the file should be done cautiously. The
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AIREBO-M Morse potentials were parameterized using a cutoff of
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3.0 (sigma). Modifying this cutoff may impact simulation accuracy.</p>
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<p>This pair style tallies a breakdown of the total AIREBO potential
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energy into sub-categories, which can be accessed via the <a class="reference internal" href="compute_pair.html"><span class="doc">compute pair</span></a> command as a vector of values of length 3.
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The 3 values correspond to the following sub-categories:</p>
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<ol class="arabic simple">
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<li><em>E_REBO</em> = REBO energy</li>
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<li><em>E_LJ</em> = Lennard-Jones energy</li>
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<li><em>E_TORSION</em> = Torsion energy</li>
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</ol>
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<p>To print these quantities to the log file (with descriptive column
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headings) the following commands could be included in an input script:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="mi">0</span> <span class="nb">all</span> <span class="n">pair</span> <span class="n">airebo</span>
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<span class="n">variable</span> <span class="n">REBO</span> <span class="n">equal</span> <span class="n">c_0</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
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<span class="n">variable</span> <span class="n">LJ</span> <span class="n">equal</span> <span class="n">c_0</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span>
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<span class="n">variable</span> <span class="n">TORSION</span> <span class="n">equal</span> <span class="n">c_0</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span>
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<span class="n">thermo_style</span> <span class="n">custom</span> <span class="n">step</span> <span class="n">temp</span> <span class="n">epair</span> <span class="n">v_REBO</span> <span class="n">v_LJ</span> <span class="n">v_TORSION</span>
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</pre></div>
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</div>
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<hr class="docutils" />
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<p>Styles with a <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.</p>
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<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
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<p>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span class="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
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use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</p>
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<hr class="docutils" />
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<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
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<p>These pair styles do not support the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a>
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mix, shift, table, and tail options.</p>
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<p>These pair styles do not write their information to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>, since it is stored in potential files. Thus, you
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need to re-specify the pair_style and pair_coeff commands in an input
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script that reads a restart file.</p>
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<p>These pair styles can only be used via the <em>pair</em> keyword of the
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<a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> command. They do not support the
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<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</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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<p>These pair styles are part of the MANYBODY package. They are only
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enabled if LAMMPS was built with that package (which it is by
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default). See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section
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for more info.</p>
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<p>These pair potentials require the <a class="reference internal" href="newton.html"><span class="doc">newton</span></a> setting to be
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“on” for pair interactions.</p>
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<p>The CH.airebo and CH.airebo-m potential files provided with LAMMPS
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(see the potentials directory) are parameterized for metal <a class="reference internal" href="units.html"><span class="doc">units</span></a>.
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You can use the AIREBO, AIREBO-M or REBO potential with any LAMMPS units,
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but you would need to create your own AIREBO or AIREBO-M potential file
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with coefficients listed in the appropriate units, if your simulation
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doesn’t use “metal” units.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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<p><a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a></p>
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<p><strong>Default:</strong> none</p>
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<p id="stuart"><strong>(Stuart)</strong> Stuart, Tutein, Harrison, J Chem Phys, 112, 6472-6486
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<p id="brenner"><strong>(Brenner)</strong> Brenner, Shenderova, Harrison, Stuart, Ni, Sinnott, J
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Physics: Condensed Matter, 14, 783-802 (2002).</p>
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<p id="oconnor"><strong>(O’Connor)</strong> O’Connor et al., J. Chem. Phys. 142, 024903 (2015).</p>
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