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<div class="section" id="angle-style-dipole-command">
<span id="index-0"></span><h1>angle_style dipole command<a class="headerlink" href="#angle-style-dipole-command" title="Permalink to this headline"></a></h1>
</div>
<div class="section" id="angle-style-dipole-omp-command">
<h1>angle_style dipole/omp command<a class="headerlink" href="#angle-style-dipole-omp-command" title="Permalink to this headline"></a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline"></a></h2>
<div class="highlight-python"><div class="highlight"><pre>angle_style dipole
</pre></div>
</div>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline"></a></h2>
<div class="highlight-python"><div class="highlight"><pre>angle_style dipole
angle_coeff 6 2.1 180.0
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
<p>The <em>dipole</em> angle style is used to control the orientation of a dipolar
atom within a molecule <a class="reference internal" href="#orsi"><span>(Orsi)</span></a>. Specifically, the <em>dipole</em> angle
style restrains the orientation of a point dipole mu_j (embedded in atom
&#8216;j&#8217;) with respect to a reference (bond) vector r_ij = r_i - r_j, where &#8216;i&#8217;
is another atom of the same molecule (typically, &#8216;i&#8217; and &#8216;j&#8217; are also
covalently bonded).</p>
<p>It is convenient to define an angle gamma between the &#8216;free&#8217; vector mu_j
and the reference (bond) vector r_ij:</p>
<img alt="_images/angle_dipole_gamma.jpg" class="align-center" src="_images/angle_dipole_gamma.jpg" />
<p>The <em>dipole</em> angle style uses the potential:</p>
<img alt="_images/angle_dipole_potential.jpg" class="align-center" src="_images/angle_dipole_potential.jpg" />
<p>where K is a rigidity constant and gamma0 is an equilibrium (reference)
angle.</p>
<p>The torque on the dipole can be obtained by differentiating the
potential using the &#8216;chain rule&#8217; as in appendix C.3 of
<a class="reference internal" href="pair_gayberne.html#allen"><span>(Allen)</span></a>:</p>
<img alt="_images/angle_dipole_torque.jpg" class="align-center" src="_images/angle_dipole_torque.jpg" />
<p>Example: if gamma0 is set to 0 degrees, the torque generated by
the potential will tend to align the dipole along the reference
direction defined by the (bond) vector r_ij (in other words, mu_j is
restrained to point towards atom &#8216;i&#8217;).</p>
<p>Note that the angle dipole potential does not give rise to any force,
because it does not depend on the distance between i and j (it only
depends on the angle between mu_j and r_ij).</p>
<p>The following coefficients must be defined for each angle type via the
<a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a> command as in the example 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> commands:</p>
<ul class="simple">
<li>K (energy)</li>
<li>gamma0 (degrees)</li>
</ul>
<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-6"><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>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline"></a></h2>
<p>This angle style can only be used if LAMMPS was built with the
USER-MISC package. See the <span class="xref std std-ref">Making LAMMPS</span>
section for more info on packages.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">In the &#8220;Angles&#8221; section of the data file, the atom ID
&#8216;j&#8217; corresponding to the dipole to restrain must come before the atom
ID of the reference atom &#8216;i&#8217;. A third atom ID &#8216;k&#8217; must also be
provided, although &#8216;k&#8217; is just a &#8216;dummy&#8217; atom which can be any atom;
it may be useful to choose a convention (e.g., &#8216;k&#8217;=&#8217;i&#8217;) and adhere to
it. For example, if ID=1 for the dipolar atom to restrain, and ID=2
for the reference atom, the corresponding line in the &#8220;Angles&#8221; section
of the data file would read: X X 1 2 2</p>
</div>
<p>The &#8220;newton&#8221; command for intramolecular interactions must be &#8220;on&#8221;
(which is the default).</p>
<p>This angle style should not be used with SHAKE.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline"></a></h2>
<p><a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a>, <a class="reference internal" href="angle_hybrid.html"><em>angle_hybrid</em></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="orsi"><strong>(Orsi)</strong> Orsi &amp; Essex, The ELBA force field for coarse-grain modeling of
lipid membranes, PloS ONE 6(12): e28637, 2011.</p>
<p id="allen"><strong>(Allen)</strong> Allen &amp; Tildesley, Computer Simulation of Liquids,
Clarendon Press, Oxford, 1987.</p>
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