Octopus (software)



The octopus project is a software package for density-functional theory (DFT)[1][2], and Quantum Monte Carlo procedures, have also increased in recent years [5][6], DFT/TDDFT is still the method of choice for large systems (e.g., molecular systems of biological interest) undergoing complex processes.

Correspondingly, numerous software packages that solve DFT/TDDFT equations are available. Among them the octopus project[7] is one with special focus on TDDFT.

Released under the GPL, Octopus is free software.

Target problems

  • Linear optical (i.e. electronic) response of molecules or clusters.
  • Non-linear response to classical high-intensity electromagnetic fields, taking into account both the ionic and electronic degrees of freedom.
  • Ground-state and excited state electronic properties of systems with lower dimensionality, such as quantum dots.
  • Photo-induced reactions of molecules (e.g., photo-dissociation, photo-isomerization, etc).
  • In the immediate future, extension of these procedures to systems that are infinite and periodic in one or more dimensions (polymers, slabs, nanotubes, solids), and to electronic transport.

Theoretical base

  • 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.
  • Regarding TDDFT, one can use two different approaches: On the one hand, the standard TDDFT-based linear-response theory, which provides the excitation energies and oscillator strengths for ground-state to excited-state transitions. On the other hand, the explicit time-propagation of the TDDFT equations, which allows for the use of large external potentials, well beyond the range of validity of perturbation theory.

Methodology

  • As numerical representation, the code works without a atomic orbitals) 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.
  • For most calculations, the code relies on the use of pseudopotentials[8] of two types: Troullier-Martins [9], and Hartwigsen-Goedecker-Hutter[10].
  • 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.

Technical aspects

  • The code has been designed with emphasis on parallel scalability. In consequence, it allows for multiple task divisions.
  • The language of most of the code is Fortran 90 (almost 50.000 lines at present). Other languages, such as C or Perl, are also used.
  • The package is licensed under the GNU General Public License (GPL). In consequence, it is available for use, inspection, and modification for anyone, at the octopus web page.
  • Web page: http://www.tddft.org/programs/octopus
  • Wiki: http://www.tddft.org/programs/octopus/wiki
  • Trac: http://www.tddft.org/trac/octopus

References

  1. ^ P. Hohenberg and W. Kohn, Phys. Rev. 136, B864 (1964); W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965).
  2. ^ C. Fiolhais, F. Nogueira and M. Marques (Eds.), "A Primer in Density Functional Theory, Lectures Notes in Physics vol. 620, (Springer, Berlin, 2003; ISBN 3-540-03083-2); R. M. Dreizler and E. K. U. Gross, "Density Functional Theory", (Springer, Berlin, 1990; ISBN 3-540-51993-9/ISBN 0-387-51993-9); R. G. Parr and W. Yang, "Density Functional Theory of Atoms and Molecules", (Oxford University Press, New York, 1989; ISBN 0-19-504279-4).
  3. ^ E. Runge and E. K. U. Gross, Phys. Rev. Lett. 52, 997 (1984).
  4. ^ M. A. L. Marques, F. Nogueira, C. Ullrich, K. Burke, A. Rubio and E. K. U. Gross (Eds.), "TDDFT, Lecture notes" (Springer Verlag, Berlin, to be published in 2006); E. K. U. Gross and W. Kohn, Adv. Quantum Chem. 21, 255 (1990); E. K. U. Gross, J. F. Dobson and M. Petersilka, in "Topics in Current Chemistry", edited by R. F. Nalewajski (Springer, Heidelberg, 1996; ISBN 3-540-61092-8); M. A. L. Marques and E. K. U. Gross, Annu. Rev. Phys. Chem. 55, 427 (2004); R. van Leeuwen, Int. J. Mod. Phys. B 15, 1969 (2001).
  5. ^ J. Leszczynski (Ed.), "Computational Chemistry: Reviews of Current Trends", vol. 9, (World Scientific, 2005); R. J. Bartlett, {\em Recent Advances in Computational Chemistry, vol 3: Recent Advances in Coupled Cluster Methods}, (World Scientific, 1997).
  6. ^ W. M. C. Foulkes, L. Mitas, R. J. Needs and G. Rajagopal, Rev. Mod. Phys. 73, 33 (2001); "Quantum Monte Carlo Methods in Physics and Chemistry", edited by M. P. Nightingale and C. J. Umrigar (Kluwer, 1999).
  7. ^ M. A. L. Marques, A. Castro, G. F. Bertsch and A. Rubio, Comp. Phys. Comm. 151, 60 (2003).
  8. ^ W. E. Pickett, Comput. Phys. Rep. 9, 115 (1989).
  9. ^ N. Troullier and J. L. Martins, Phys. Rev. B 43, 1993 (1991).
  10. ^ C. Hartwigsen, S. Goedecker and J. Hutter, Phys. Rev. B 58, 3641 (1998).
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Octopus_(software)". A list of authors is available in Wikipedia.