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Manuscript Title: Fast LEED intensity calculations for surface crystallography using
Tensor LEED. | ||

Authors: V. Blum, K. Heinz | ||

Program title: TensErLEED | ||

Catalogue identifier: ADNI_v1_0Distribution format: tar.gz | ||

Journal reference: Comput. Phys. Commun. 134(2001)392 | ||

Programming language: Fortran. | ||

Computer: Digital/Compaq Alpha
Workstations PWS433au, XP1000, Pentium PC. | ||

Operating system: Compaq Tru64 Unix, Linux. | ||

RAM: 100M words | ||

Word size: 8 | ||

Keywords: Electron-solid diffraction, Low energy electron diffraction (LEED), Structure optimization, Surface crystallography, Surface reconstruction, Surface relaxation, Surface structure, Surface segregation, Tensor LEED (TLEED), Solid state physics. | ||

Classification: 7.2, 8. | ||

Nature of problem:The quantitative analysis of low energy electron diffraction (LEED) intensity vs. energy I(E) spectra is an important tool to obtain surface crystallographic information [1-4]. Direct methods to extract such information from LEED data work in special cases only. One generally resorts to a trial-and-error technique, comparing calculated I(E)-curves for different surface geometries to spectra measured from a real surface in order to retrieve the correct structural parameters by way of a best fit. Since experimental techniques are continuously refined and the complexity of studied systems grows dramatically, a fast means to calculate I(E) spectra for many different surface structures, compare them to experimental data and identify the best fit is a prime necessity of the field. The TensErLEED computer code aims to satisy this need. Examples studied with previous versions of this code include open metal surfaces [5], reconstructed alloy surfaces [6], and complex reconstructions of thin films [7-9] and semiconductor surfaces [10]. | ||

Solution method:Standard full dynamic LEED calculations [11] are used to obtain the electron wave field diffracted from a reference surface. Using the Tensor LEED approximation [12-14], geometrical, vibrational [15] and chemical [16,17] parameters in a large portion of the parameter space around that reference structure are then varied. A search algorithm [18] allows to retrieve the best fit between measured data and calculated spectra reliably for typically 15 or more parameters. | ||

Restrictions:The surface is required to be periodic in two dimensions. Aspherical atomic scattering can only be included within the Tensor LEED approximation, not in the full dynamic reference calculation. | ||

Running time:Running times depend very much on the actual problem. Times of 1-10 hours for systems of intermediate complexity including a structure optimization on a 500 MHz Compaq XP1000 workstation may serve as an estimate. | ||

References: | ||

[1] | M.A. Van Hove, W.H. Weinberg, and C.-M. Chan, Low Energy Electron Diffraction (Springer, Berlin, 1986). | |

[2] | K. Heinz, Rep. Prog. Phys. 58 (1995) 637. | |

[3] | M.A. Van Hove, Surf. Rev. Lett. 4 (1997) 479. | |

[4] | K. Heinz, L. Hammer, Z. Kristallogr. 213 (1998) 615. | |

[5] | M. Arnold, A. Fahmi, W. Frie, L. Hammer, K. Heinz, J. Phys. C 11 (1999) 1873. | |

[6] | M. Kottcke, H. Graupner, D.M. Zehner, L. Hammer, K. Heinz, Phys. Rev. B 54 (1996) R5275. | |

[7] | S. Muller, P. Bayer, C. Reischl, K. Heinz, B. Feldmann, H. Zillgen, M. Wuttig, Phys. Rev. Lett. 74 (1995) 765. | |

[8] | K. Heinz, P. Bayer, S. Muller, Surf. Rev. Lett. 2 (1995) 89. | |

[9] | A. Seubert, J. Schardt, W. Weiss, U. Starke, K. Heinz, Appl. Phys. Lett. 76 (2000) 727. | |

[10] | U. Starke, J. Schardt, J. Bernhardt, M. Franke, K. Reuter, H. Wedler, K. Heinz, J. Furthmuller, P. Kackell, F. Bechstedt, Phys. Rev. Lett. 80 (1998) 758. | |

[11] | M. A. Van Hove, S.Y. Tong, Surface Crystallography by LEED (Springer, Berlin, 1979). | |

[12] | P.J. Rous, J.B. Pendry, D.K. Saldin, K. Heinz, K. Muller, N. Bickel, Phys. Rev. Lett. 57 (1986) 2951. | |

[13] | P.J. Rous, J.B. Pendry, Surf. Sci. 219 (1989) 355. | |

[14] | P.J. Rous, Prog. Surf. Sci. 39 (1992) 3. | |

[15] | U. Loffler, R. Doll, K. Heinz, J.B. Pendry, Surf. Sci. 301 (1994) 346. | |

[16] | R. Doll, M. Kottcke, K. Heinz, Phys. Rev. B 48 (1993) 1973. | |

[17] | K. Heinz, R. Doll, M. Kottcke, Surf. Rev. Lett. 3 (1996) 1651. | |

[18] | M. Kottcke, K. Heinz, Surf. Sci. 376 (1997) 352. |

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