PROGRAM SUMMARY
Title of program:
TensErLEED
Catalogue identifier:
ADNI
Ref. in CPC:
134(2001)392
Distribution format: tar gzip file
Operating system: Compaq Tru64 Unix, Linux
High speed store required:
100MK words
Number of bits in a word:
8
Number of lines in distributed program, including test data, etc:
22538
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.
Programming language used: Fortran
Computer:
Digital/Compaq Alpha ,
Workstations PWS433au, ,
XP1000 ,
Pentium PC .
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].
Method of solution:
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.
Typical 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.