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<div class="section" id="angle-style-dipole-command">
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<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>
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<div class="section" id="angle-style-dipole-omp-command">
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<h1>angle_style dipole/omp command<a class="headerlink" href="#angle-style-dipole-omp-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>angle_style dipole
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</pre></div>
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</div>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>angle_style dipole
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angle_coeff 6 2.1 180.0
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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<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>The <em>dipole</em> angle style is used to control the orientation of a dipolar
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atom within a molecule <a class="reference internal" href="#orsi"><span>(Orsi)</span></a>. Specifically, the <em>dipole</em> angle
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style restrains the orientation of a point dipole mu_j (embedded in atom
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‘j’) with respect to a reference (bond) vector r_ij = r_i - r_j, where ‘i’
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is another atom of the same molecule (typically, ‘i’ and ‘j’ are also
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covalently bonded).</p>
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<p>It is convenient to define an angle gamma between the ‘free’ vector mu_j
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and the reference (bond) vector r_ij:</p>
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<img alt="_images/angle_dipole_gamma.jpg" class="align-center" src="_images/angle_dipole_gamma.jpg" />
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<p>The <em>dipole</em> angle style uses the potential:</p>
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<img alt="_images/angle_dipole_potential.jpg" class="align-center" src="_images/angle_dipole_potential.jpg" />
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<p>where K is a rigidity constant and gamma0 is an equilibrium (reference)
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angle.</p>
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<p>The torque on the dipole can be obtained by differentiating the
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potential using the ‘chain rule’ as in appendix C.3 of
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<a class="reference internal" href="pair_gayberne.html#allen"><span>(Allen)</span></a>:</p>
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<img alt="_images/angle_dipole_torque.jpg" class="align-center" src="_images/angle_dipole_torque.jpg" />
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<p>Example: if gamma0 is set to 0 degrees, the torque generated by
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the potential will tend to align the dipole along the reference
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direction defined by the (bond) vector r_ij (in other words, mu_j is
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restrained to point towards atom ‘i’).</p>
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<p>The dipolar torque T_j must be counterbalanced in order to conserve
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the local angular momentum. This is achieved via an additional force
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couple generating a torque equivalent to the opposite of T_j:</p>
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<img alt="_images/angle_dipole_couple.jpg" class="align-center" src="_images/angle_dipole_couple.jpg" />
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<p>where F_i and F_j are applied on atoms i and j, respectively.</p>
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<p>The following coefficients must be defined for each angle type via the
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<a class="reference internal" href="angle_coeff.html"><em>angle_coeff</em></a> command as in the example above, or in
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the data file or restart files read by the <a class="reference internal" href="read_data.html"><em>read_data</em></a>
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or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a> commands:</p>
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<ul class="simple">
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<li>K (energy)</li>
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<li>gamma0 (degrees)</li>
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</ul>
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<hr class="docutils" />
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<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
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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"><em>Section_accelerate</em></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 USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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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>
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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-6"><span>-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"><em>suffix</em></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<p>This angle style can only be used if LAMMPS was built with the
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USER-MISC package. See the <span class="xref std std-ref">Making LAMMPS</span>
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section for more info on packages.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">In the “Angles” section of the data file, the atom ID ‘j’
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corresponding to the dipole to restrain must come before the atom ID
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of the reference atom ‘i’. A third atom ID ‘k’ must also be provided,
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although ‘k’ is just a ‘dummy’ atom which can be any atom; it may be
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useful to choose a convention (e.g., ‘k’=’i’) and adhere to it. For
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example, if ID=1 for the dipolar atom to restrain, and ID=2 for the
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reference atom, the corresponding line in the “Angles” section of the
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data file would read: X X 1 2 2</p>
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</div>
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<p>The “newton” command for intramolecular interactions must be “on”
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(which is the default).</p>
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<p>This angle style should not be used with SHAKE.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<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>
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<p><strong>Default:</strong> none</p>
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<hr class="docutils" />
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<p id="orsi"><strong>(Orsi)</strong> Orsi & Essex, The ELBA force field for coarse-grain modeling of
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lipid membranes, PloS ONE 6(12): e28637, 2011.</p>
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<p id="allen"><strong>(Allen)</strong> Allen & Tildesley, Computer Simulation of Liquids,
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Clarendon Press, Oxford, 1987.</p>
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