Octopus (software)

<h2 id="target-problems">Target problems</h2>
<ul><li>Linear optical (i.e. electronic) response of molecules or clusters, also second-order nonlinear response.</li>
<li>Non-linear response to classical high-intensity electromagnetic fields, taking into account both the ionic and electronic degrees of freedom.</li>
<li>Ground-state and excited state electronic properties of systems with lower dimensionality, such as quantum dots.</li>
<li>Photo-induced reactions of molecules (e.g., photo-dissociation, photo-isomerization, etc.).</li>
<li>In the immediate future, extension of these procedures to systems that are infinite and periodic in one or more dimensions (<a href="/facts/Polymer/eF32E50K">polymers</a>, slabs, <a href="/facts/Carbon_nanotube/atuDPPaG">nanotubes</a>, solids), and to electronic transport.</li></ul>
<h2 id="theoretical-basis">Theoretical basis</h2>
<ul><li>The underlying theories are DFT and TDDFT. Also, the code may perform dynamics by considering the classical (i.e. point-particle) approximation for the nuclei. These dynamics may be non-adiabatic, since the system evolves following the Ehrenfest path. It is, however, a mean-field approach.</li>
<li>Regarding TDDFT, one can use three different approaches:
<ul><li>the standard TDDFT-based linear-response theory of Casida, which provides the excitation energies and oscillator strengths for ground-state to excited-state transitions.</li>
<li>the explicit time-propagation of the TDDFT equations, which allows for the use of large external potentials, well beyond the range of validity of <a href="/facts/Perturbation_theory/JWrNgbVm">perturbation theory</a>.</li>
<li>the Sternheimer equation (density-functional perturbation theory) in the frequency domain, using only occupied states.</li></ul></li></ul>
<h2 id="methodology">Methodology</h2>
<ul><li>As numerical representation, the code works without a <a href="/facts/Basis_set_(chemistry)/rQCPt3yl">basis set</a>, relying on numerical meshes. Nevertheless, auxiliary basis sets (<a href="/facts/Plane_wave/0aDUbNhQ">plane waves</a>, <a href="/facts/Atomic_orbital/tKhgl6mL">atomic orbitals</a>) are used when necessary. Recently, the code offers the possibility of working with non-uniform grids, which adapt to the inhomogeneity of the problem, and of making use of multigrid techniques to accelerate the calculations.</li>
<li>For most calculations, the code relies on the use of <a href="/facts/Pseudopotential/2ckPRjIr">pseudopotentials</a><a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> of two types: Troullier-Martins,<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> and Hartwigsen-Goedecker-Hutter.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li>
<li>In addition to being able to treat systems in the standard 3 dimensions, 2D and 1D modes are also available. These are useful for studying, e.g., the two-dimensional electron gas that characterizes a wide class of quantum dots.</li></ul>
<h2 id="technical-aspects">Technical aspects</h2>
<ul><li>The code has been designed with emphasis on parallel scalability. In consequence, it allows for multiple task divisions, this utilises mesh division software, <a href="/facts/Message_Passing_Interface/BEuBgDpm">MPI</a> and <a href="/facts/OpenMP/69IpI80o">OpenMP</a>.</li>
<li>The language of most of the code is <a href="/facts/Fortran/m1KqjcMU">Fortran</a> 90. Other languages, such as <a href="/facts/C_(programming_language)/Ky2No763">C</a>, are also used.</li>
<li>The package is licensed under the <a href="/facts/GNU_General_Public_License/S75KhLSX">GNU General Public License</a> (GPL). In consequence, it is available for use, inspection, and modification for anyone, at the <a href="https://gitlab.com/octopus-code/octopus">Octopus git repository</a>.</li></ul>
<h2 id="see-also">See also</h2>
<ul>
<li>Chemistry portal</li><li>Free and open-source software portal</li></ul>
<ul><li><a href="/facts/Quantum_chemistry_computer_programs/WpF4uoKD">Quantum chemistry computer programs</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://octopus-code.org/">Official website</a> </li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Castro, Alberto; Heiko Appel; Micael Oliveira; Carlo A. Rozzi; Xavier Andrade; Florian Lorenzen; M. A. L. Marques; E. K. U. Gross; Angel Rubio (2006). "octopus: a tool for the application of time-dependent density functional theory". Physica Status Solidi B. 243 (11): 2465–2488. Bibcode:2006PSSBR.243.2465C. doi:10.1002/pssb.200642067. hdl:10316/8208. S2CID 55356805. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Pickett, Warren E. (1989). "Pseudopotential methods in condensed matter applications". Computer Physics Reports. 9 (3). Elsevier BV: 115–197. Bibcode:1989CoPhR...9..115P. doi:10.1016/0167-7977(89)90002-6. ISSN 0167-7977. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Troullier, N.; Martins, José Luriaas (1991-01-15). "Efficient pseudopotentials for plane-wave calculations". Physical Review B. 43 (3). American Physical Society (APS): 1993–2006. Bibcode:1991PhRvB..43.1993T. doi:10.1103/physrevb.43.1993. ISSN 0163-1829. PMID 9997467. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Hartwigsen, C.; Goedecker, S.; Hutter, J. (1998-08-15). "Relativistic separable dual-space Gaussian pseudopotentials from H to Rn". Physical Review B. 58 (7). American Physical Society (APS): 3641–3662. arXiv:cond-mat/9803286. Bibcode:1998PhRvB..58.3641H. doi:10.1103/physrevb.58.3641. ISSN 0163-1829. S2CID 119450371. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
</ol>

Octopus (software) open-in-new

Octopus (software)