LEED Calculation Home Page

Overview

Several of our LEED program packages are available for free downloading from this site. This page describes general features of the packages. Consult the Guide below for help in choosing the right package(s) for you: normally the choice will be one of the LEED packages together with the phase shift program package, also available on this page. 

Purpose

The LEED packages are designed for surface structure determination from experimental LEED IV curves. They are primarily used with ordered, commensurate surface structures. They can also be applied unchanged to adsorbate systems with lattice-gas disorder (and some incommensurate structures), by simulating diffuse LEED. No spin polarization is included. Relativistic effects are only included through (spin-averaged) relativistic phase shifts.

Computer platforms

The programs can run on PCs, workstations and larger computers, with a few exceptions (such as some SGI workstations for LEEDSATL). The LEED programs are supplied as Fortran source. They can be compiled under Fortran 77. The phase shift programs require Fortran 90.

Conditions of use

The programs can be downloaded for free and may be freely used, but not distributed. We ask that new users obtain copies from this web site. No guarantee of correct results can be given: the calculations are performed at the users' own risk.

Acknowledgments

The authors require that an acknowledgment be included in publications, such as: "The LEED calculations were performed using programs from [or derived from] the Barbieri/Van Hove Symmetrized Automated LEED [or SATLEED] package." Also, a reference to the origin of the LEED programs should be included in your publications, as follows:

• for symmetrized and non-symmetrized automated tensor LEED programs (LEEDSATL, LEEDSATC, LEEDATLM):
  A. Barbieri and M.A. Van Hove, private communication (http://www.icts.hkbu.edu.hk/vanhove/)
• for conventional LEED programs (files LEEDCON):
  M.A. Van Hove and S.Y. Tong, "Surface Crystallography by LEED", Springer-Verlag (Heidelberg) 1979
  (http://www.icts.hkbu.edu.hk/vanhove/)
• for the phase shift package:
  A. Barbieri and M.A. Van Hove, private communication (http://www.icts.hkbu.edu.hk/vanhove/)

Guide to the selection of a LEED package

Several LEED packages are available, with different capabilities. Generally speaking, the symmetrized automated tensor LEED program (SATLEED = LEEDSATL) is the most recommended, versatile and up-to-date package. SATLEED, like the other packages, should normally be supplemented by the phase shift package: the phase shifts are needed as input to the LEED calculations. A tabulation of some older phase shifts and related data is also available as a package.

The different packages are briefly outlined and contrasted below. Each package contains its own more detailed documentation, viewable after downloading.

NOTE: The packages contain FORTRAN source code and sample input and output files.

WARNING: DO NOT MIX SUBROUTINES BETWEEN THE DIFFERENT PACKAGES! They are generally incompatible, even when they have the same names.

NOTE: R-factor programs are embedded within all automated tensor LEED packages, and thus need not be obtained or used separately.

• The symmetrized automated tensor LEED programs (download SATLEED = LEEDSATL, 213 kB) form the core of the Barbieri/Van Hove package. They were developed in 1992-1995 by Barbieri from a previous non-symmetrized automated tensor LEED (ATLEED = LEEDATL) package due to Rous and Wander. They apply to ordered structures, but can also be used to approximate I-V curves of diffuse LEED for disordered overlayers. They can automatically fit 30 or more unknown atomic coordinates. They are however restricted to normal incidence, and can NOT handle glide-plane symmetries (they can be used by ignoring any glide-plane symmetry). These programs require relatively little adaptation by the user to specific structures and are therefore very general. This package is of the most general interest. There are currently no plans to further develop this package.
• The symmetrized automated tensor LEED programs for very COMPLEX structures (download SATCLEED = LEEDSATC, 41 kB) were developed in 1994 by Barbieri from the symmetrized automated tensor LEED (SATLEED) package (you must also download SATLEED = LEEDSATL, 213 kB, in which two files are to be replaced by those in SATCLEED). The main difference compared to the SATLEED package is more efficient use of memory and computer resources by avoiding computing and storing redundant quantities: this change is transparent to the user (i.e. its use is identical to that of SATLEED), but this package has not been tested as thoroughly as the SATLEED package. It has been tested with the Si(111)-(7x7) and other complex structures on a workstation. There are currently no plans to further develop this package.
• The multi-termination symmetrized automated tensor LEED programs for multiple coexisting surface structures (download MSATLEED = LEEDMSAT, 226 kB) were developed in 1999 by Ketteler from the symmetrized automated tensor LEED (SATLEED) package. Their principle is that first full dynamical LEED calculations are performed for several different coexisting structures. Then structural optimization with tensor LEED is performed simultaneously for the different structures. This includes the case of "split positions". This package has not been tested extensively. Compared to ATLMLEED described below, MSATLEED is much faster when symmetry is exploited (glide plane symmetry may NOT be used), and MSATLEED requires normal incidence. There are currently no plans to further develop this package.
• The non-symmetrized automated tensor LEED programs for multiple angles of incidence and/or surface structures (download ATLMLEED = LEEDATLM, 192 kB) were developed in 1993-1994 by Barbieri from the older automated tensor LEED (ATLEED) package. They can also be used for the special case of an arbitrary single angle of incidence and a single surface structure. Their principle is that first full dynamical LEED calculations are performed for one structure at several angles of incidence and/or for several different coexisting structures. Then structural optimization with tensor LEED is performed simultaneously for the different angles of incidence and/or the different structures. This package has not been tested extensively. There are currently no plans to further develop this package.
• The non-symmetrized automated tensor LEED programs (download ATLEED = LEEDATL, 140 kB) were developed in 1989-1992 by Rous, Wander and Barbieri from the Van Hove/Tong package to include tensor LEED and automated structural search algorithms. They apply to ordered structures, but can be used to approximate I-V curves of diffuse LEED for disordered overlayers. They include no symmetry and can therefore explore (automatically) asymmetrical distortions of any given structure, by fitting 30 or more unknown atomic coordinates. These programs require relatively little adaptation by the user to specific structures and are therefore very easy to use. This package will not be further developed.
• The conventional LEED programs - the Van Hove/Tong package - (download LEEDCON, 420 kB) have been used by Van Hove et al from 1975 to 1990. They were developed starting from codes of Pendry and of Tong. For structural determination, the tensor LEED packages are preferred. The conventional LEED programs contain plane-wave symmetrization and various selectable approximations that allow somewhat complex structures to be handled without automated structural search (no R-factor routines are included). Some diffuse LEED programs are included, as well as some for incommensurate overlayers. These programs require adaptation to each structure being investigated, i.e. an understanding of the use of many subroutines. Therefore, over 100 different main programs are available in this package (using a common subroutine library), for a variety of surface structures: they cover many simple structures, or can serve as starting points for new types of surface structure. This package can also serve as a source of various subroutines. There are currently no plans to further develop this package.
• The Barbieri/Van Hove phase shift calculation package (download phase shift codes, 71 kB) is needed to produce phase shifts for any of the LEED packages describes above. The phase shift calculation is performed in several steps:
  (1) calculation of the radial charge density for a free atom;
  (2) calculation of the radial muffin-tin potential for atoms embedded in a surface defined by the user (the surface is represented by a slab that is periodically repeated in 3 dimensions, within vacuum between the repeated slabs); various approximations to the exchange potential are available; relativistic effects are taken into account
  (3) calculation of phase shifts from the muffin-tin potential;
  (4) elimination of pi-jumps in the energy dependence of the phase shifts.
• Tabulations of some atomic wave functions, potentials and phase shifts (download phase shift data, 262 kB). These come from a variety of sources, mentioned when known. Caution: mixing phase shifts from different sources can lead to small errors in structural determinations: for accurate work, one should produce phase shifts in a single calculation using the Barbieri/Van Hove phase shift package.

Bibliography

• LEED theory: J.B. Pendry, "Low Energy electron Diffraction", Academic (London) 1974
• LEED theory and applications: M.A. Van Hove, W.H. Weinberg and C.-M. Chan, "Low-Energy Electron Diffraction", Springer-Verlag (Heidelberg) 1986
• LEED theory: L.J. Clarke, "Surface Crystallography, An Introduction to LEED", Wiley (Chichester) 1985
• theory and conventional LEED programs: M.A. Van Hove and S.Y. Tong, "Surface Crystallography by LEED", Springer-Verlag (Heidelberg) 1979
• diffuse LEED: G.S. Blackman, M.-L. Xu, D.F. Ogletree, M.A. Van Hove and G.A. Somorjai, Phys. Rev. Lett. 61, 2352 (1988); M.A. Van Hove, in "Chemistry and Physics of Solid Surfaces VII", Eds. R.F. Howe and R. Vanselow, Springer (Heidelberg) 1988, p. 513; K. Heinz, "Diffuse LEED and Local Surface Structure", Phys. Stat. Sol. A146, 195 (1994).
• incommensurate LEED: Z.P. Hu, D.F. Ogletree, M.A. Van Hove and G.A. Somorjai, Surf. Sci. 180, 433-59 (1987).
• structure determination: M.A. Van Hove, "Solving Complex and Disordered Surface Structures with Electron Diffraction", in "Chemistry and Physics of Solid Surfaces VII", R.F. Howe and R. Vanselow, Eds., Springer Series in Surface Science 10, 513 (1988)
• advanced methods: M.A. Van Hove, "Advanced Multiple Scattering Theories of Low-Energy Electron Diffraction (LEED)", in Applications of Multiple Scattering Theory to Materials Science, Eds. W.H. Butler, P.H. Dederichs, A. Gonis and R.L. Weaver, Mat. Res. Soc. Symp. Proc. 253 (Pittsburgh, PA, p. 471 (1992).
• automated structural optimization: M.A. Van Hove, W. Moritz, H. Over, P.J. Rous, A. Wander, A. Barbieri, N. Materer, U. Starke and G.A. Somorjai, "Automated Determination of Complex Surface Structures by LEED", in Proc. ISISS-10 (Milwaukee, July 1992), Surf. Sci. Rep. 19, 191 (1993).

Contact

• Michel A. Van Hove
  Email vanhove@hkbu.edu.hk