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<div class="section" id="interface-to-dftd3-by-s-grimme">
<span id="sec-dftd3"></span><span id="index-0"></span><h1>Interface to DFTD3 by S. Grimme<a class="headerlink" href="#interface-to-dftd3-by-s-grimme" title="Permalink to this headline">¶</a></h1>
<p><em>Code author: Lori A. Burns</em></p>
<p><em>Section author: Lori A. Burns</em></p>
<p><em>Module:</em> <a class="reference internal" href="autodoc_testsuite_dftd3.html#apdx-testsuitedftd3"><span>Samples</span></a></p>
<p><span class="sc">Psi4</span> contains code to interface to the DFTD3 program of S. Grimme, which is freely
downloadable from <a class="reference external" href="http://www.thch.uni-bonn.de/tc/index.php?section=downloads&subsection=getd3&lang=english">http://www.thch.uni-bonn.de/tc/index.php?section=downloads&subsection=getd3&lang=english</a>).</p>
<div class="section" id="installation">
<h2>Installation<a class="headerlink" href="#installation" title="Permalink to this headline">¶</a></h2>
<p>Follow the instructions provided with the source to build the DFTD3
program (essentially, unpack the source, edit the Makefile to select a
Fortran compiler, and run make). For the moment, you must apply a patch,
<a class="reference external" href="https://github.com/psi4/psi4public/blob/master/lib/scripts/patch_grimme_dftd3.3.0.2">psi4/lib/scripts/patch_grimme_dftd3.3.0.2</a>, to the dftd3 source before building.
To be used by <span class="sc">Psi4</span>, the program binary (<code class="docutils literal"><span class="pre">dftd3</span></code>) must be found in
your <span class="target" id="index-1"></span><a class="reference internal" href="external.html#envvar-PATH"><code class="xref std std-envvar docutils literal"><span class="pre">PATH</span></code></a>. If <span class="sc">Psi4</span> is unable to execute the binary, an
error will be reported.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">cd</span> <span class="n">dftd3</span>
<span class="gp">>>> </span><span class="n">ls</span>
<span class="go">dftd3.tar</span>
<span class="go">patch_grimme_dftd3.3.0.2</span>
<span class="gp">>>> </span><span class="n">tar</span> <span class="o">-</span><span class="n">xvf</span> <span class="n">dftd3</span><span class="o">.</span><span class="n">tar</span>
<span class="go">copyc6.f</span>
<span class="go">dftd3.f</span>
<span class="go">Makefile</span>
<span class="go">man.pdf</span>
<span class="go">pars.f</span>
<span class="go">param</span>
<span class="gp">>>> </span><span class="n">patch</span> <span class="o"><</span> <span class="n">patch_grimme_dftd3</span><span class="o">.</span><span class="mf">3.0</span><span class="o">.</span><span class="mi">2</span>
<span class="go">patching file dftd3.f</span>
<span class="gp">>>> </span><span class="n">make</span>
<span class="go">making dftd3.o from dftd3.f</span>
<span class="go">ifort -O -c dftd3.f -o dftd3.o</span>
<span class="go">making copyc6.o from copyc6.f</span>
<span class="go">ifort -O -c copyc6.f -o copyc6.o</span>
<span class="go">ifort dftd3.o copyc6.o -o ./dftd3</span>
<span class="gp">>>> </span><span class="n">ls</span>
<span class="go">Makefile copyc6.o dftd3.f dftd3.tar param patch_grimme_dftd3.3.0.2</span>
<span class="go">copyc6.f dftd3 dftd3.o man.pdf pars.f</span>
</pre></div>
</div>
</div>
<div class="section" id="theory">
<h2>Theory<a class="headerlink" href="#theory" title="Permalink to this headline">¶</a></h2>
<p>The local or semilocal character of conventional density functionals
necessarily leads to neglect of the long-range correlation interactions
which capture attractive van der Waals forces. Initially proposed by Yang
<a class="reference internal" href="bibliography.html#wu-2002-515" id="id1">[Wu:2002:515]</a> and assiduously developed by Grimme, <a class="reference internal" href="bibliography.html#grimme-2004-1463" id="id2">[Grimme:2004:1463]</a>
<a class="reference internal" href="bibliography.html#grimme-2006-1787" id="id3">[Grimme:2006:1787]</a> <a class="reference internal" href="bibliography.html#grimme-2010-154104" id="id4">[Grimme:2010:154104]</a> the DFT+Dispersion method
appends to the base functional a scaled, damped, and fitted leading term
to the well-known dispersion energy series, <img class="math" src="_images/math/648b4f151df758919089b0a51136673238a51898.png" alt="E_{disp} = -C_6/R^6
-C_8/R^8 -C_{10}/R^{10}-\cdots" style="vertical-align: -6px"/>. The DFT-D2 <a class="reference internal" href="bibliography.html#grimme-2006-1787" id="id5">[Grimme:2006:1787]</a> variant
takes the explicit form below. Here, dispersion coefficients,
<img class="math" src="_images/math/84fee3be89b8b36bbe733fe121c197fd9780afc4.png" alt="C_6^{ij}" style="vertical-align: -4px"/>, obtained from the geometric mean of tabulated elemental
values, are summed over interatomic distances, <img class="math" src="_images/math/6f2bdb7b5619c49366f40970a65b39ef03496d58.png" alt="R_{ij}" style="vertical-align: -6px"/>, modulated
by a damping function, <img class="math" src="_images/math/467f2bcac965f762aff59260f57659d8c0ab2d04.png" alt="f_{damp}(R_{ij})" style="vertical-align: -6px"/>, that gradually activates
the dispersion correction (at a rate characterized by <img class="math" src="_images/math/85faa0504f5c77aaea82491a6cabafcc3883475e.png" alt="\alpha_6" style="vertical-align: -3px"/>)
over a distance characterized by the sum of the two atomic vdW radii,
<img class="math" src="_images/math/091f95a8e412cba99f87e736cb3ad36362cc1414.png" alt="R_{vdW}" style="vertical-align: -3px"/>, while an overall scaling term, <img class="math" src="_images/math/86ed8b743f7451965614c642ef3cf069a7a655dd.png" alt="s_6" style="vertical-align: -3px"/>, is optimized
to be unique to each <img class="math" src="_images/math/6decc1e6be9bbafb099c59651c88f689a2767a17.png" alt="E_{xc}" style="vertical-align: -3px"/> functional. (<img class="math" src="_images/math/85faa0504f5c77aaea82491a6cabafcc3883475e.png" alt="\alpha_6" style="vertical-align: -3px"/> is
sometimes allowed to vary as well.)</p>
<div class="math" id="equation-DFTD2">
<p><span class="eqno">(1)</span><img src="_images/math/a935b8519fa4dddba7dc07f6b0e186bc8eab357f.png" alt="E_{disp}^{\text{D2}}=-s_6 \sum_{i,j>i}^{N_{at}} \frac{C_6^{ij}}{(R_{ij})^6} f_{damp}(R_{ij})"/></p>
</div><div class="math">
<p><img src="_images/math/165142dc15635c6a1c31a3cd6fe0cb45f5a0829a.png" alt="f_{damp}(R_{ij}) = \frac{1}{1 + e^{- \alpha_6 (R_{ij}/R_{vdW} - 1)}}"/></p>
</div><p>Grimme recently presented a refined method, DFT-D3, <a class="reference internal" href="bibliography.html#grimme-2010-154104" id="id6">[Grimme:2010:154104]</a>
which incorporates an additional <img class="math" src="_images/math/1c9dbc9aa8ed129e95672515d95576eacbb6df2a.png" alt="R^{-8}" style="vertical-align: 0px"/> term in the dispersion
series and adjusts the <img class="math" src="_images/math/0f0837f894ae62b29ac829c294132d2cf0c3733c.png" alt="C_{6}^{ij}" style="vertical-align: -4px"/> combination formula and damping
function. The individual atomic <img class="math" src="_images/math/84a30e1cfb5ae2ad3b421b0af3b165e5f10b0be8.png" alt="C_6^i" style="vertical-align: -5px"/> are interpolated from
several reference values based upon coordination numbers extracted from
the molecular structure, rather than assigned solely by atomic identity as
in DFT-D2, and thereby incorporate some awareness of the chemical
environment into an otherwise largely heuristic correction. The -D3
dispersion has the following form, where <img class="math" src="_images/math/cf1594d9be246fdc8d9e967427968dd5cd95cd96.png" alt="s_{r,6}" style="vertical-align: -6px"/> and <img class="math" src="_images/math/7924a78edea28f01bf1f4de6b2adb773daade023.png" alt="s_8" style="vertical-align: -3px"/>
are the customary nonunity parameters fitted for individual functionals.</p>
<div class="math" id="equation-DFTD3ZERO">
<p><span class="eqno">(2)</span><img src="_images/math/5cc537cfa27cefaa4728a78ae854002c2ae337d3.png" alt="E_{disp}^{\text{D3ZERO}}=-\sum_{n=6,8} s_n \sum_{i,j>i}^{N_{at}}
\frac{C_n^{ij}}{(R_{ij})^n} f_{damp}(R_{ij})"/></p>
</div><div class="math">
<p><img src="_images/math/3359aff0d97dd7b8ac108b9a5c48d7843fddf85a.png" alt="f_{damp}(R_{ij}) = \frac{1}{1 + 6 (R_{ij}/(s_{r,n} R_0^{ij}))^{- \alpha_n}}"/></p>
</div><p>A modified damping scheme for DFT-D3 using the rational damping form of
Becke and Johnson was introduced in <a class="reference internal" href="bibliography.html#grimme-2011-1456" id="id7">[Grimme:2011:1456]</a>. The parameters
fit for individual functionals are now <img class="math" src="_images/math/86ed8b743f7451965614c642ef3cf069a7a655dd.png" alt="s_6" style="vertical-align: -3px"/>, <img class="math" src="_images/math/7924a78edea28f01bf1f4de6b2adb773daade023.png" alt="s_8" style="vertical-align: -3px"/>,
<img class="math" src="_images/math/0cea09413197c28625ecd0261f720c9e7f04bec1.png" alt="a_1" style="vertical-align: -4px"/>, and <img class="math" src="_images/math/17af53352142b3c084dfdb514a1fa00657379792.png" alt="a_2" style="vertical-align: -3px"/>.</p>
<div class="math">
<p><img src="_images/math/4de8012748f2eaa93a4070a9db1c215eab9f2eae.png" alt="E_{disp}^{\text{D3BJ}}=-\sum_{n=6,8} s_n \sum_{i,j>i}^{N_{at}}
\frac{C_n^{ij}}{(R_{ij})^n + (f_{damp})^n}"/></p>
</div><div class="math">
<p><img src="_images/math/11837cfbfcbf8cb3f94222e0c5a35abdcc4ea41a.png" alt="f_{damp} = a_1 \sqrt{\frac{C_8^{ij}}{C_6^{ij}}} + a_2"/></p>
</div><p>All parameters characterizing the dispersion correction are taken from
<a class="reference external" href="http://toc.uni-muenster.de/DFTD3/">http://toc.uni-muenster.de/DFTD3/</a>
or else from the literature.</p>
</div>
<div class="section" id="running-dftd3">
<h2>Running DFTD3<a class="headerlink" href="#running-dftd3" title="Permalink to this headline">¶</a></h2>
<p>A number of <em>a posteriori</em> dispersion corrections are available in
<span class="sc">Psi4</span>. While most are computed within <span class="sc">Psi4</span>‘s codebase (-D1, -D2,
-CHG, -DAS2009, -DAS2010), the -D3 correction and its variants are
available only through the <code class="docutils literal"><span class="pre">DFTD3</span></code> program. Once installed, the
<code class="docutils literal"><span class="pre">dftd3</span></code>/<span class="sc">Psi4</span> interface is transparent, and all corrections are
interfaced exactly alike.</p>
<p>Dispersion corrections are built into DFT functionals, so appending an <em>a
posteriori</em> correction to a computation is as simple as
<code class="docutils literal"><span class="pre">energy('b2plyp-d')</span></code> <em>vs.</em> <code class="docutils literal"><span class="pre">energy('b2plyp')</span></code>. For example, the
following input file computes (with much redundant work) for water a
B3LYP, a B3LYP-D2, and a B3LYP-D3 (zero-damping) energy.</p>
<div class="highlight-python"><div class="highlight"><pre>molecule h2o {
O
H 1 1.0
H 1 1.0 2 104.5
}
set {
basis cc-pVDZ
}
energy('b3lyp')
energy('b3lyp-d')
energy('b3lyp-d3')
</pre></div>
</div>
<p>Consult the table <a class="reference internal" href="dft_byfunctional.html#table-dft-disp"><span>-D Functionals</span></a> to see for each
functional what corrections are available and what default parameters
define them. The dispersion correction is available after a calculation in
the PSI variable <a class="reference internal" href="glossary_psivariables.html#psivar-DISPERSIONCORRECTIONENERGY"><code class="xref std std-psivar docutils literal"><span class="pre">DISPERSION</span> <span class="pre">CORRECTION</span> <span class="pre">ENERGY</span></code></a>.
By default, the output from the <code class="docutils literal"><span class="pre">dftd3</span></code>
program is suppressed; to see it in the output file, set print > 2.</p>
<table border="1" class="docutils" id="id18">
<span id="table-dashd"></span><caption><span class="caption-text">Variants of S. Grimme’s -D correction</span><a class="headerlink" href="#id18" title="Permalink to this table">¶</a></caption>
<colgroup>
<col width="18%" />
<col width="51%" />
<col width="31%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Extension <a class="footnote-reference" href="#f0" id="id8">[1]</a></th>
<th class="head">Variant and Computing Program</th>
<th class="head"><a class="reference internal" href="autodoc_glossary_options_c.html#term-dft-dispersion-parameters-scf"><span class="xref std std-term">DFT_DISPERSION_PARAMETERS</span></a></th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>-D</td>
<td>alias to -D2P4</td>
<td> </td>
</tr>
<tr class="row-odd"><td>-D1</td>
<td>-D1 <a class="footnote-reference" href="#f1" id="id9">[2]</a> within <span class="sc">Psi4</span></td>
<td> </td>
</tr>
<tr class="row-even"><td>-D2</td>
<td>alias to -D2P4</td>
<td> </td>
</tr>
<tr class="row-odd"><td>-D2P4</td>
<td>-D2 <a class="footnote-reference" href="#f2" id="id10">[3]</a> within <span class="sc">Psi4</span></td>
<td>[<img class="math" src="_images/math/86ed8b743f7451965614c642ef3cf069a7a655dd.png" alt="s_6" style="vertical-align: -3px"/>]</td>
</tr>
<tr class="row-even"><td>-D2GR</td>
<td>-D2 <a class="footnote-reference" href="#f2" id="id11">[3]</a> through <code class="docutils literal"><span class="pre">dftd3</span></code></td>
<td>[<img class="math" src="_images/math/86ed8b743f7451965614c642ef3cf069a7a655dd.png" alt="s_6" style="vertical-align: -3px"/>, <img class="math" src="_images/math/85faa0504f5c77aaea82491a6cabafcc3883475e.png" alt="\alpha_6" style="vertical-align: -3px"/>]</td>
</tr>
<tr class="row-odd"><td>-D3</td>
<td>alias to -D3ZERO</td>
<td> </td>
</tr>
<tr class="row-even"><td>-D3ZERO</td>
<td>-D3 <a class="footnote-reference" href="#f3" id="id12">[4]</a> w/ original zero-damping through <code class="docutils literal"><span class="pre">dftd3</span></code></td>
<td>[<img class="math" src="_images/math/86ed8b743f7451965614c642ef3cf069a7a655dd.png" alt="s_6" style="vertical-align: -3px"/>, <img class="math" src="_images/math/7924a78edea28f01bf1f4de6b2adb773daade023.png" alt="s_8" style="vertical-align: -3px"/>, <img class="math" src="_images/math/cf1594d9be246fdc8d9e967427968dd5cd95cd96.png" alt="s_{r,6}" style="vertical-align: -6px"/>, <img class="math" src="_images/math/85faa0504f5c77aaea82491a6cabafcc3883475e.png" alt="\alpha_6" style="vertical-align: -3px"/>]</td>
</tr>
<tr class="row-odd"><td>-D3BJ</td>
<td>-D3 <a class="footnote-reference" href="#f4" id="id13">[5]</a> w/ newer Becke-Johnson rational damping through <code class="docutils literal"><span class="pre">dftd3</span></code></td>
<td>[<img class="math" src="_images/math/86ed8b743f7451965614c642ef3cf069a7a655dd.png" alt="s_6" style="vertical-align: -3px"/>, <img class="math" src="_images/math/7924a78edea28f01bf1f4de6b2adb773daade023.png" alt="s_8" style="vertical-align: -3px"/>, <img class="math" src="_images/math/0cea09413197c28625ecd0261f720c9e7f04bec1.png" alt="a_1" style="vertical-align: -4px"/>, <img class="math" src="_images/math/17af53352142b3c084dfdb514a1fa00657379792.png" alt="a_2" style="vertical-align: -3px"/>]</td>
</tr>
</tbody>
</table>
<p class="rubric">Footnotes</p>
<table class="docutils footnote" frame="void" id="f0" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id8">[1]</a></td><td>Note that there are functionals with these extensions (<em>e.g.</em>, wB97X-D) that,
not being Grimme corrections, have nothing to do with this table.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="f1" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id9">[2]</a></td><td><a class="reference internal" href="bibliography.html#grimme-2004-1463" id="id14">[Grimme:2004:1463]</a></td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="f2" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label">[3]</td><td><em>(<a class="fn-backref" href="#id10">1</a>, <a class="fn-backref" href="#id11">2</a>)</em> <a class="reference internal" href="bibliography.html#grimme-2006-1787" id="id15">[Grimme:2006:1787]</a></td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="f3" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id12">[4]</a></td><td><a class="reference internal" href="bibliography.html#grimme-2010-154104" id="id16">[Grimme:2010:154104]</a></td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="f4" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id13">[5]</a></td><td><a class="reference internal" href="bibliography.html#grimme-2011-1456" id="id17">[Grimme:2011:1456]</a></td></tr>
</tbody>
</table>
<p>A few practical examples:</p>
<ul>
<li><p class="first">DFT-D2 single point with default parameters (<code class="docutils literal"><span class="pre">dftd3</span></code> not called)</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">energy</span><span class="p">(</span><span class="s">'bp86-d'</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p class="first">DFT-D3BJ optimization with default parameters</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">optimize</span><span class="p">(</span><span class="s">'pbe-d3bj'</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p class="first">DFT-D2 optimization with custom s6 parameter</p>
<div class="highlight-python"><div class="highlight"><pre>set dft_dispersion_parameters [1.20]
optimize('b3lyp-d2')
</pre></div>
</div>
</li>
<li><p class="first">DFT-D3ZERO single point (b3lyp) with custom s8 parameter (reset all four values)</p>
<div class="highlight-python"><div class="highlight"><pre>set dft_dispersion_parameters [1.0, 2.0, 1.261, 14.0]
energy('b3lyp-d3')
</pre></div>
</div>
</li>
</ul>
<p>If only dispersion corrections (rather than total energies) are of
interest, the <code class="docutils literal"><span class="pre">dftd3</span></code> program can be run independently of the scf
through the python function <a class="reference internal" href="#interface_dftd3.run_dftd3" title="interface_dftd3.run_dftd3"><code class="xref py py-func docutils literal"><span class="pre">run_dftd3()</span></code></a>. (This function
is the same <span class="sc">Psi4</span>/<code class="docutils literal"><span class="pre">dftd3</span></code> interface that is called during an scf job.)
This route is much faster than running a DFT-D energy.</p>
<ul>
<li><p class="first">Some set-up:</p>
<div class="highlight-python"><div class="highlight"><pre>molecule nene {
Ne
Ne 1 2.0
}
nene.update_geometry()
</pre></div>
</div>
</li>
<li><p class="first">The same four dispersion corrections/gradients as the section above:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">print</span> <span class="n">nene</span><span class="o">.</span><span class="n">run_dftd3</span><span class="p">(</span><span class="s">'bp86'</span><span class="p">,</span> <span class="s">'d'</span><span class="p">,</span> <span class="n">dertype</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="go">-7.735e-05</span>
<span class="gp">>>> </span><span class="n">E</span><span class="p">,</span> <span class="n">G</span> <span class="o">=</span> <span class="n">nene</span><span class="o">.</span><span class="n">run_dftd3</span><span class="p">(</span><span class="s">'pbe'</span><span class="p">,</span> <span class="s">'d3bj'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">G</span>
<span class="go">[[0.0, 0.0, -1.1809087569358e-05], [0.0, 0.0, 1.1809087569358e-05]]</span>
<span class="gp">>>> </span><span class="n">E</span><span class="p">,</span> <span class="n">G</span> <span class="o">=</span> <span class="n">nene</span><span class="o">.</span><span class="n">run_dftd3</span><span class="p">(</span><span class="s">'b3lyp'</span><span class="p">,</span> <span class="s">'d2'</span><span class="p">,</span> <span class="p">{</span><span class="s">'s6'</span><span class="p">:</span> <span class="mf">1.20</span><span class="p">})</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">E</span>
<span class="go">-8.84e-05</span>
<span class="gp">>>> </span><span class="n">E</span><span class="p">,</span> <span class="n">G</span> <span class="o">=</span> <span class="n">nene</span><span class="o">.</span><span class="n">run_dftd3</span><span class="p">(</span><span class="n">dashlvl</span><span class="o">=</span><span class="s">'d3'</span><span class="p">,</span> <span class="n">dashparam</span><span class="o">=</span><span class="p">{</span><span class="s">'s8'</span><span class="p">:</span> <span class="mf">2.0</span><span class="p">,</span> <span class="s">'alpha6'</span><span class="p">:</span> <span class="mf">14.0</span><span class="p">,</span> <span class="s">'sr6'</span><span class="p">:</span> <span class="mf">1.261</span><span class="p">,</span> <span class="s">'s6'</span><span class="p">:</span> <span class="mf">1.0</span><span class="p">})</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">E</span>
<span class="go">-0.00024762</span>
</pre></div>
</div>
</li>
</ul>
<dl class="function">
<dt id="interface_dftd3.run_dftd3">
<code class="descname">run_dftd3</code><span class="sig-paren">(</span><em>self</em>, <em>func=None</em>, <em>dashlvl=None</em>, <em>dashparam=None</em>, <em>dertype=None</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/interface_dftd3.html#run_dftd3"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#interface_dftd3.run_dftd3" title="Permalink to this definition">¶</a></dt>
<dd><p>Function to call Grimme’s dftd3 program (<a class="reference external" href="http://toc.uni-muenster.de/DFTD3/">http://toc.uni-muenster.de/DFTD3/</a>)
to compute the -D correction of level <em>dashlvl</em> using parameters for
the functional <em>func</em>. The dictionary <em>dashparam</em> can be used to supply
a full set of dispersion parameters in the absense of <em>func</em> or to supply
individual overrides in the presence of <em>func</em>. Returns energy if <em>dertype</em> is 0,
gradient if <em>dertype</em> is 1, else tuple of energy and gradient if <em>dertype</em>
unspecified. The dftd3 executable must be independently compiled and found in
<span class="target" id="index-2"></span><a class="reference internal" href="external.html#envvar-PATH"><code class="xref std std-envvar docutils literal"><span class="pre">PATH</span></code></a> or <span class="target" id="index-3"></span><a class="reference internal" href="external.html#envvar-PSIPATH"><code class="xref std std-envvar docutils literal"><span class="pre">PSIPATH</span></code></a>.</p>
</dd></dl>
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<h3><a href="index.html">Table Of Contents</a></h3>
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<li><a class="reference internal" href="#">Interface to DFTD3 by S. Grimme</a><ul>
<li><a class="reference internal" href="#installation">Installation</a></li>
<li><a class="reference internal" href="#theory">Theory</a></li>
<li><a class="reference internal" href="#running-dftd3">Running DFTD3</a></li>
</ul>
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