<span id="index-0"></span><h1>pair_style airebo command<a class="headerlink" href="#pair-style-airebo-command" title="Permalink to this headline">¶</a></h1>
<p>By default, all three terms are included. For the <em>airebo</em> style, if
the two optional flag arguments to the pair_style command are
included, the LJ and torsional terms can be turned off. Note that
both or neither of the flags must be included. If both of the LJ an
torsional terms are turned off, it becomes the 2nd-generation REBO
potential, with a small caveat on the spline fitting procedure
mentioned below. This can be specified directly as pair_style rebo
with no additional arguments.</p>
<p>The detailed formulas for this potential are given in
<a class="reference internal" href="#stuart"><span>(Stuart)</span></a>; here we provide only a brief description.</p>
<p>The E_REBO term has the same functional form as the hydrocarbon REBO
potential developed in <a class="reference internal" href="#brenner"><span>(Brenner)</span></a>. The coefficients for
E_REBO in AIREBO are essentially the same as Brenner’s potential, but
a few fitted spline values are slightly different. For most cases the
E_REBO term in AIREBO will produce the same energies, forces and
statistical averages as the original REBO potential from which it was
derived. The E_REBO term in the AIREBO potential gives the model its
reactive capabilities and only describes short-ranged C-C, C-H and H-H
interactions (r < 2 Angstroms). These interactions have strong
coordination-dependence through a bond order parameter, which adjusts
the attraction between the I,J atoms based on the position of other
nearby atoms and thus has 3- and 4-body dependence.</p>
<p>The E_LJ term adds longer-ranged interactions (2 < r < cutoff) using a
form similar to the standard <a class="reference internal" href="pair_lj.html"><em>Lennard Jones potential</em></a>.
The E_LJ term in AIREBO contains a series of switching functions so
that the short-ranged LJ repulsion (1/r^12) does not interfere with
the energetics captured by the E_REBO term. The extent of the E_LJ
interactions is determined by the <em>cutoff</em> argument to the pair_style
command which is a scale factor. For each type pair (C-C, C-H, H-H)
the cutoff is obtained by multiplying the scale factor by the sigma
value defined in the potential file for that type pair. In the
standard AIREBO potential, sigma_CC = 3.4 Angstroms, so with a scale
factor of 3.0 (the argument in pair_style), the resulting E_LJ cutoff
would be 10.2 Angstroms.</p>
<p>The E_TORSION term is an explicit 4-body potential that describes
various dihedral angle preferences in hydrocarbon configurations.</p>
<hr class="docutils" />
<p>Only a single pair_coeff command is used with the <em>airebo</em> or <em>rebo</em>
style which specifies an AIREBO potential file with parameters for C
and H. Note that the <em>rebo</em> style in LAMMPS uses the same
AIREBO-formatted potential file. These are mapped to LAMMPS atom
types by specifying N additional arguments after the filename in the
pair_coeff command, where N is the number of LAMMPS atom types:</p>
<ul class="simple">
<li>filename</li>
<li>N element names = mapping of AIREBO elements to atom types</li>
</ul>
<p>See the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> doc page for alternate ways
to specify the path for the potential file.</p>
<p>As an example, if your LAMMPS simulation has 4 atom types and you want
the 1st 3 to be C, and the 4th to be H, you would use the following
pair_coeff command:</p>
<div class="highlight-python"><div class="highlight"><pre>pair_coeff * * CH.airebo C C C H
</pre></div>
</div>
<p>The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
The first three C arguments map LAMMPS atom types 1,2,3 to the C
element in the AIREBO file. The final H argument maps LAMMPS atom
type 4 to the H element in the SW file. If a mapping value is
specified as NULL, the mapping is not performed. This can be used
when a <em>airebo</em> potential is used as part of the <em>hybrid</em> pair style.
The NULL values are placeholders for atom types that will be used with
other potentials.</p>
<p>The parameters/coefficients for the AIREBO potentials are listed in
the CH.airebo file to agree with the original <a class="reference internal" href="#stuart"><span>(Stuart)</span></a>
paper. Thus the parameters are specific to this potential and the way
it was fit, so modifying the file should be done cautiously.</p>
<hr class="docutils" />
<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
KOKKOS, USER-OMP and OPT packages, respectively. They are only
enabled if LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
<p>These pair styles do not support the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
mix, shift, table, and tail options.</p>
<p>These pair styles do not write their information to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>, since it is stored in potential files. Thus, you
need to re-specify the pair_style and pair_coeff commands in an input
script that reads a restart file.</p>
<p>These pair styles can only be used via the <em>pair</em> keyword of the
<a class="reference internal" href="run_style.html"><em>run_style respa</em></a> command. They do not support the
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