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Manuscript Title: A self-consistent surface Green-function (SSGF) method for the
calculation of isolated adsorbate atoms on a semi-infinite crystal. | ||

Authors: J. Bormet, B. Wenzien, M. Scheffler | ||

Program title: fhi93ssgf | ||

Catalogue identifier: ACPV_v1_0Distribution format: gz | ||

Journal reference: Comput. Phys. Commun. 79(1994)124 | ||

Programming language: Fortran. | ||

Computer: IBM RISC System/6000. | ||

Operating system: AIX 3.2, UNICOS 7.0, OSF/1. | ||

RAM: 9999K words | ||

Word size: 64 | ||

Keywords: Solid state physics, Crystal field, Green function, Adsorbate, Layer kkr, Dft-lda, Total energy, Hellmann-feynman forces. | ||

Classification: 7.3. | ||

Nature of problem:The computer code allows to calculate the Green function of an adsorption problem with a single, isolated adsorbate atom (so-called "adsorbate system") on a semi-infinite metal surface. The following physical quantities are available as output: change in electron density for the adsorbate system, change in density of states, total energy of the adsorbate system, and the Hellmann-Feynman forces on the adsorbate atom. The program uses density-functional theory within the local- density approximation for the exchange-correlation functional and ab initio, norm-conserving pseudopotentials. | ||

Solution method:The Green function of the clean substrate (so-called "reference system") has to be calculated in advance. This reference Green function is needed as input for this code. It is obtainable with the layer KKR method [1,2,3] and has to be projected onto a localized basis of Gaussian orbitals [4,5]. The code described below then solves the Dyson equation self-consistently for the effective potential of the adsorbate atom with the projected Green function of the reference system. | ||

Restrictions:At this time, only one single adsorbate atom can be handled by the code, although the input is made for a finite number of adsorbate atoms. For the evaluation of the exchange-correlation functional the electron- density change, Delta n**v(r), is evaluated on a mesh in real space. This mesh is restricted to be of cubic shape. The treatment of f- electron systems is not possible with the present code, although there are no limitations in principle. | ||

Running time:One iteration on a CRAY Y-MP (single processor) takes 82 seconds, on an IBM RS/6000-350 it takes 493 seconds. About 40 iterations are necessary to converge a typical problem which has a linear dimension of 108 in the Gaussian basis and about 40**3 points in the real-space mesh for Delta n**v(r). There are three time consuming parts: * Solution of the Dyson equation. * Projection of the effective potential onto Gaussians. * Transformation of the density matrix (in the Guassian basis) to the real space mesh. | ||

References: | ||

[1] | F. Maca and M. Scheffler, Comput. Phys. Commun. 38(1985)403, 47(1987)349. | |

[2] | F. Maca and M. Scheffler, Comput. Phys. Commun. 51(1988)381. | |

[3] | B. Wenzien, J. Bormet, and M. Scheffler, Green function for crystal surfaces I. Submitted to Comput. Phys. Commun. | |

[4] | Ch. Droste, Ph. D. thesis, Fachbereich 4 (Physik) der Technischen Universitat Berlin (1990). | |

[5] | B. Wenzien, J. Bormet, and M. Scheffler, Green function for crystal surfaces II: Projection onto Gaussian orbitals. To be published. |

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