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 latticegas disorder
(and some incommensurate structures), by simulating diffuse LEED.
No spin polarization is included. Relativistic effects are only included
through (spinaveraged) 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 nonsymmetrized 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", SpringerVerlag (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 uptodate 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: Rfactor 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 19921995 by Barbieri from a previous nonsymmetrized
automated tensor LEED (ATLEED = LEEDATL)
package due to Rous and Wander. They apply to ordered structures,
but can also be used to approximate IV 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
glideplane symmetries (they can be used by ignoring any
glideplane 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 multitermination 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 nonsymmetrized automated tensor LEED programs for multiple angles of
incidence and/or surface structures (download ATLMLEED = LEEDATLM,
192 kB) were developed in
19931994 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 nonsymmetrized automated tensor LEED programs (download ATLEED = LEEDATL,
140 kB) were developed in
19891992 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 IV 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 planewave symmetrization and various selectable
approximations that allow somewhat complex structures to be handled
without automated structural search (no Rfactor 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 muffintin 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 muffintin potential;
(4) elimination of pijumps 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,
"LowEnergy Electron Diffraction", SpringerVerlag (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",
SpringerVerlag (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, 43359 (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 LowEnergy 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. ISISS10 (Milwaukee, July 1992), Surf. Sci. Rep.
19, 191 (1993).
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