<span id="index-0"></span><h1>pair_style gayberne command<a class="headerlink" href="#pair-style-gayberne-command" title="Permalink to this headline">¶</a></h1>
<p>More details of the Gay-Berne formulation are given in the references
listed below and in <a class="reference external" href="PDF/pair_gayberne_extra.pdf">this supplementary document</a>.</p>
<p>Use of this pair style requires the NVE, NVT, or NPT fixes with the
<em>asphere</em> extension (e.g. <a class="reference internal" href="fix_nve_asphere.html"><em>fix nve/asphere</em></a>) in
order to integrate particle rotation. Additionally, <a class="reference internal" href="atom_style.html"><em>atom_style ellipsoid</em></a> should be used since it defines the
rotational state and the size and shape of each ellipsoidal particle.</p>
<p>The following coefficients must be defined for each pair of atoms
types via the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command as in the examples
above, or in the data file or restart files read by the
<a class="reference internal" href="read_data.html"><em>read_data</em></a> or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a>
<li>epsilon_i_a = relative well depth of type I for side-to-side interactions</li>
<li>epsilon_i_b = relative well depth of type I for face-to-face interactions</li>
<li>epsilon_i_c = relative well depth of type I for end-to-end interactions</li>
<li>epsilon_j_a = relative well depth of type J for side-to-side interactions</li>
<li>epsilon_j_b = relative well depth of type J for face-to-face interactions</li>
<li>epsilon_j_c = relative well depth of type J for end-to-end interactions</li>
<li>cutoff (distance units)</li>
</ul>
<p>The last coefficient is optional. If not specified, the global
cutoff specified in the pair_style command is used.</p>
<p>It is typical with the Gay-Berne potential to define <em>sigma</em> as the
minimum of the 3 shape diameters of the particles involved in an I,I
interaction, though this is not required. Note that this is a
different meaning for <em>sigma</em> than the <a class="reference internal" href="pair_resquared.html"><em>pair_style resquared</em></a> potential uses.</p>
<p>The epsilon_i and epsilon_j coefficients are actually defined for atom
types, not for pairs of atom types. Thus, in a series of pair_coeff
commands, they only need to be specified once for each atom type.</p>
<p>Specifically, if any of epsilon_i_a, epsilon_i_b, epsilon_i_c are
non-zero, the three values are assigned to atom type I. If all the
epsilon_i values are zero, they are ignored. If any of epsilon_j_a,
epsilon_j_b, epsilon_j_c are non-zero, the three values are assigned
to atom type J. If all three epsilon_j values are zero, they are
ignored. Thus the typical way to define the epsilon_i and epsilon_j
coefficients is to list their values in “pair_coeff I J” commands when
I = J, but set them to 0.0 when I != J. If you do list them when I !=
J, you should insure they are consistent with their values in other
pair_coeff commands, since only the last setting will be in effect.</p>
<p>Note that if this potential is being used as a sub-style of
<a class="reference internal" href="pair_hybrid.html"><em>pair_style hybrid</em></a>, and there is no “pair_coeff I I”
setting made for Gay-Berne for a particular type I (because I-I
interactions are computed by another hybrid pair potential), then you
still need to insure the epsilon a,b,c coefficients are assigned to
that type. e.g. in a “pair_coeff I J” command.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">If the epsilon a = b = c for an atom type, and if the
shape of the particle itself is spherical, meaning its 3 shape
parameters are all the same, then the particle is treated as an LJ
sphere by the Gay-Berne potential. This is significant because if two
LJ spheres interact, then the simple Lennard-Jones formula is used to
compute their interaction energy/force using the specified epsilon and
sigma as the standard LJ parameters. This is much cheaper to compute
than the full Gay-Berne formula. To treat the particle as a LJ sphere
with sigma = D, you should normally set epsilon a = b = c = 1.0, set
the pair_coeff sigma = D, and also set the 3 shape parameters for the
particle to D. The one exception is that if the 3 shape parameters
are set to 0.0, which is a valid way in LAMMPS to specify a point
particle, then the Gay-Berne potential will treat that as shape
parameters of 1.0 (i.e. a LJ particle with sigma = 1), since it
requires finite-size particles. In this case you should still set the
pair_coeff sigma to 1.0 as well.</p>
</div>
<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>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for this pair style can be mixed. The default mix
value is <em>geometric</em>. See the “pair_modify” command for details.</p>
<p>This pair styles supports the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> shift
option for the energy of the Lennard-Jones portion of the pair
interaction, but only for sphere-sphere interactions. There is no
shifting performed for ellipsoidal interactions due to the anisotropic
dependence of the interaction.</p>
<p>The <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> table option is not relevant
for this pair style.</p>
<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
tail option for adding long-range tail corrections to energy and
pressure.</p>
<p>This pair style writes its information to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.</p>
<p>This pair style 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. It does not support the
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<p>The <em>gayberne</em> style is part of the ASPHERE package. It is only
enabled if LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
<p>These pair style require that atoms store torque and a quaternion to
represent their orientation, as defined by the
<a class="reference internal" href="atom_style.html"><em>atom_style</em></a>. It also require they store a per-type
<code class="xref doc docutils literal"><span class="pre">shape</span></code>. The particles cannot store a per-particle
diameter.</p>
<p>This pair style requires that atoms be ellipsoids as defined by the
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