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<title>The Quantum Package &mdash; Quantum Package 2.0 documentation</title>
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<p class="caption"><span class="caption-text">Introduction</span></p>
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<li class="toctree-l1"><a class="reference internal" href="intro/install.html">Installation</a></li>
<li class="toctree-l1"><a class="reference internal" href="intro/selected_ci.html">Selected Configuration Interaction</a></li>
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<li class="toctree-l1"><a class="reference internal" href="users_guide/printing.html">Printing the near-<abbr title="Full Configuration Interaction">FCI</abbr> wave function</a></li>
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<p class="caption"><span class="caption-text">Appendix</span></p>
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<li class="toctree-l1"><a class="reference internal" href="appendix/research.html">Some research made with the <em>Quantum Package</em></a></li>
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<div class="section" id="the-qp">
<h1>The <em>Quantum Package</em><a class="headerlink" href="#the-qp" title="Permalink to this headline"></a></h1>
<a class="reference internal image-reference" href="_images/qp2.png"><img alt="Quantum Package" class="align-center" src="_images/qp2.png" style="width: 200px;" /></a>
<div class="section" id="what-it-is">
<h2>What it is<a class="headerlink" href="#what-it-is" title="Permalink to this headline"></a></h2>
<p>The <em>Quantum Package</em> is an open-source <strong>programming environment</strong> for quantum chemistry.
It has been built from the <strong>developper</strong> point of view in order to help
the design of new quantum chemistry methods,
especially for <a class="reference external" href="https://en.wikipedia.org/wiki/Ab_initio_quantum_chemistry_methods">wave function theory</a> (<abbr title="Wave Function Theory">WFT</abbr>).</p>
<p>From the <strong>user</strong> point of view, the <em>Quantum Package</em> proposes a stand-alone path
to use optimized selected configuration interaction <abbr title="Selected-CI">sCI</abbr> based on the
<abbr title="Configuration Interaction using a Perturbative Selection">CIPSI</abbr> algorithm that can efficiently reach near-full configuration interaction
<abbr title="Full Configuration Interaction">FCI</abbr> quality for relatively large systems (see for instance <a class="reference internal" href="appendix/research.html#caffarel-2016" id="id1">[18]</a><a class="reference internal" href="appendix/research.html#caffarel-2016-2" id="id2">[19]</a><a class="reference internal" href="appendix/research.html#loos-2018" id="id3">[6]</a><a class="reference internal" href="appendix/research.html#scemama-2018" id="id4">[7]</a><a class="reference internal" href="appendix/research.html#dash-2018" id="id5">[9]</a><a class="reference internal" href="appendix/research.html#garniron-2017-2" id="id6">[13]</a><a class="reference internal" href="appendix/research.html#loos-2018" id="id7">[6]</a><a class="reference internal" href="appendix/research.html#garniron-2018" id="id8">[10]</a><a class="reference internal" href="appendix/research.html#giner2018oct" id="id9">[5]</a>).
To have a simple example of how to use the <abbr title="Configuration Interaction using a Perturbative Selection">CIPSI</abbr> program, go to the <cite>users_guide/quickstart</cite>.</p>
<p>The main goal is the development of selected configuration interaction <abbr title="Selected-CI">sCI</abbr>
methods and multi-reference perturbation theory <abbr title="Multi-Reference Perturbation Theory">MRPT</abbr> in the
determinant-driven paradigm. It also contains the very basics of Kohn-Sham <a class="reference external" href="https://en.wikipedia.org/wiki/Density_functional_theory">density functional theory</a> <abbr title="Kohn-Sham Density Functional Theory">KS-DFT</abbr> and <a class="reference external" href="https://aip.scitation.org/doi/10.1063/1.1383587">range-separated hybrids</a> <abbr title="Range Separated Hybrids">RSH</abbr>.</p>
<p>The determinant-driven framework allows the programmer to include any arbitrary set of
determinants in the variational space, and thus gives a complete freedom in the methodological
development. The basic ingredients of <abbr title="Range Separated Hybrids">RSH</abbr> together with those of the <abbr title="Wave Function Theory">WFT</abbr> framework available in the <em>Quantum Package</em> library allows one to easily develop range-separated DFT (<abbr title="Range Separated Density Functional Theory">RSDFT</abbr>) approaches (see for instance the plugins at <a class="reference external" href="https://gitlab.com/eginer/qp_plugins_eginer">https://gitlab.com/eginer/qp_plugins_eginer</a>).</p>
<p>All the programs are developed with the <a class="reference external" href="http://irpf90.ups-tlse.fr">IRPF90</a> code generator, which considerably simplifies
the collaborative development, and the development of new features.</p>
</div>
<div class="section" id="what-it-is-not">
<h2>What it is not<a class="headerlink" href="#what-it-is-not" title="Permalink to this headline"></a></h2>
<p>The <em>Quantum Package</em> is <em>not</em> a general purpose quantum chemistry program.
First of all, it is a <em>library</em> to develop new theories and algorithms in quantum chemistry.
Therefore, beside the use of the programs of the core modules, the users of the <em>Quantum Package</em> should develop their own programs.</p>
<p>The <em>Quantum Package</em> has been designed specifically for <abbr title="Selected-CI">sCI</abbr>, so all the
algorithms which are programmed are not adapted to run SCF or DFT calculations
on thousands of atoms. Currently, the systems targeted have less than 600
molecular orbitals. This limit is due to the memory bottleneck induced by the storring of the two-electron integrals (see <code class="docutils literal notranslate"><span class="pre">mo_two_e_integrals</span></code> and <code class="docutils literal notranslate"><span class="pre">ao_two_e_integrals</span></code>).</p>
<p>The <em>Quantum Package</em> is <em>not</em> a massive production code. For conventional
methods such as Hartree-Fock, CISD or MP2, the users are recommended to use the
existing standard production codes which are designed to make these methods run
fast. Again, the role of the <em>Quantum Package</em> is to make life simple for the
developer. Once a new method is developed and tested, the developer is encouraged
to consider re-expressing it with an integral-driven formulation, and to
implement the new method in open-source production codes, such as <a class="reference external" href="http://www.nwchem-sw.org/">NWChem</a>
or <a class="reference external" href="https://www.msg.chem.iastate.edu/gamess/">GAMESS</a>.</p>
</div>
<div class="section" id="a-few-examples-of-applications">
<h2>A few examples of applications<a class="headerlink" href="#a-few-examples-of-applications" title="Permalink to this headline"></a></h2>
<p>Multiple programs were developed with the <em>Quantum Package</em>, such as:</p>
<ul class="simple">
<li>Selected Full-CI + Epstein-Nesbet PT2 (CIPSI) <a class="reference internal" href="appendix/research.html#caffarel-2016" id="id10">[18]</a><a class="reference internal" href="appendix/research.html#caffarel-2016-2" id="id11">[19]</a><a class="reference internal" href="appendix/research.html#loos-2018" id="id12">[6]</a><a class="reference internal" href="appendix/research.html#scemama-2018" id="id13">[7]</a><a class="reference internal" href="appendix/research.html#dash-2018" id="id14">[9]</a></li>
<li>Hybrid stochastic/deterministic MR-PT2 <a class="reference internal" href="appendix/research.html#garniron-2017-2" id="id15">[13]</a><a class="reference internal" href="appendix/research.html#loos-2018" id="id16">[6]</a></li>
<li>Orbital optimization for open-shell systems <a class="reference internal" href="appendix/research.html#giner2016mar" id="id17">[16]</a><a class="reference internal" href="appendix/research.html#giner-2017-3" id="id18">[15]</a></li>
<li>CIS, CISD, MP2</li>
<li>Selected CISD</li>
<li>Jeziorsky-Monkhorst MR-PT2 <a class="reference internal" href="appendix/research.html#giner-2017" id="id19">[11]</a></li>
<li>Effective Hamiltonian for variational MR wave functions <a class="reference internal" href="appendix/research.html#giner-2017-2" id="id20">[14]</a></li>
<li>Selected CAS+SD</li>
<li>Selected difference-dedicated CI (DD-CI)</li>
<li>Multi-Reference Coupled Cluster (MR-CCSD) <a class="reference internal" href="appendix/research.html#giner-2016" id="id21">[17]</a><a class="reference internal" href="appendix/research.html#garniron-2017" id="id22">[12]</a></li>
<li>Shifted-Bk with CIPSI <a class="reference internal" href="appendix/research.html#garniron-2018" id="id23">[10]</a></li>
<li>CIPSI with range-separated DFT (plugins at <a class="reference external" href="https://gitlab.com/eginer/qp_plugins_eginer">https://gitlab.com/eginer/qp_plugins_eginer</a>)</li>
<li>DFT for basis set corrections <a class="reference internal" href="appendix/research.html#giner-2018" id="id25">[4]</a></li>
</ul>
<p>All these programs can generate ground and excited states, and spin pure wave
functions (eigenstates of <span class="math notranslate nohighlight">\(\widehat{S^2}\)</span>).</p>
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