Artacho, E. and Gale, J. and Garcia, A. and Junquera, J. and Sánchez-Portal, D. and Ordejón, P. and Soler, J. M.
(2005)
*Electronic structure calculations with localized orbitals. The Siesta method.*
In:
Handbook of Materials Modeling.
Springer, Berlin.
ISBN 978-1-4020-3287-5

## Abstract

Practical quantum mechanical simulations of materials, which take into account explicitly the electronic degrees of freedom, are presently limited to about 1000 atoms. In contrast, the largest classical simulations, using empirical interatomic potentials, involve over 109 atoms. Much of this 106-factor difference is due to the existence of well-developed order-N algorithms for the classical problem, in which the computer time and memory scale linearly with the number of atoms N of the simulated system. Furthermore, such algorithms are well suited for execution in parallel computers, using rather small interprocessor communications. In contrast, nearly all quantum mechanical simulations involve a computational effort which scales as O(N 3), that is, as the cube of the number of atoms simulated. Such an intrinsically more expensive dependence is due to the delocalized character of the electron wavefunctions. Since the electrons are fermions, every one of the ~N occupied wavefunctions must be kept orthogonal to every other one, thus requiring ~N 2 constraints, each involving an integral over the whole system, whose size is also proportional to N.

Item Type: | Book Section |
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Uncontrolled Keywords: | 2005 AREP 2005 P IA48 |

Subjects: | 03 - Mineral Sciences |

Divisions: | 03 - Mineral Sciences |

Depositing User: | Sarah Humbert |

Date Deposited: | 19 Nov 2011 12:22 |

Last Modified: | 23 Jul 2013 09:57 |

URI: | http://eprints.esc.cam.ac.uk/id/eprint/1528 |

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