SAPI and DIMS Direct Methods structure solution for normal, superstructures, pseudosymmetry and incommensurate structures
l.m.d.cranswick at dl.ac.uk
Tue Jan 15 10:04:46 EST 2002
The following new single crystal direct methods programs for Windows
by Fan, Hai-fu & colleagues are now available for download via the
SAPI Direct Methods for Small Structures, Superstructures and Pseudo
DIMS A direct-method program written in Fortran for solving incommensurate
modulated structures and composite structures.
First the weblinks:
SAPI direct methods structure solution for Windows by Fan, Hai-fu &
colleagues ("Institute of Physics, Academia Sinica".):
SAPI is based on Multan and differs from it mainly by the ability of
resolving phase ambiguities due to pseudo symmetry.
SAPI can automatically handle diffraction data from structures
having pseudo-translational symmetry and lead directly to the correct
solution in favorable cases. This is particularly useful for solving
superstructures without relying on an assumed structure model.
SAPI can recognize pseudo-centrosymmetric solutions when dealing with
non-centrosymmetric structures. In addition, the program can break the
enantiomorphous ambiguity given the "atomic positions" of both
SAPI possesses the ability of intelligent control on the path of phase
development according to the feature and complexity of the structure.
SAPI enables combination of Patterson and direct methods. Besides,
subroutines are provided for automatic Patterson analysis of heavy-atom
Sophisticated graphic interface is provided for data preparation,
program control and for displaying and manipulating output results.
DIMS for Windows (and source code) Direct Methods for Incommensurate
Modulated/Composite Structures by Fan, Hai-fu & colleagues
DIMS (Direct-methods for Incomensurate Modulated Structures) deals with
one-dimensionally modulated structures and composite structures
consists of two sub-systems.
For incommensurate modulated structures, DIMS calculates
E-values independent of atomic scattering factors, hence it can
accept diffraction data from X-rays, electrons or neutrons and
treat them in the same way. However, for composite structures DIMS
can deal with only X-ray diffraction data.
DIMS is written in Fortran. In theory, it can be run in any
operating system provided appropriate Fortran compiler is
DIMS accepts two-line symbols of superspace groups and derives
accordingly symmetry generators. Alternatively, it allows
also manual input of symmetry generators.
Incommensurate modulated/composite structures are solved by
direct methods in two stages. In the first stage, phases of
main reflections are derived using a conventional direct-method,
while in the second stage, phases of satellite reflections
are derived by a multi-dimensional direct method with starting
phases of main reflections.
In case the basic/average structure is known, phases of main
reflections calculated from which can be input to DIMS and the
first stage should be skipped.
The Windows version of DIMS forms a part of the program VEC.
I/O data of DIMS can be displayed and manipulated by the
sophisticated graphic interface of VEC. 4D-Fourier maps phased
by DIMS can be calculated, displayed and interpreted within VEC.
The subroutine MIMS can help with building a 4D-structure model
from the 4D-Fourier map.
PS: Other relavant CCP14 based pages include:
Software for Incommensurate/Modulated Structures
Available Single Crystal Structure Solution Software relevant to
Available Single Crystal Structure Refinement Software relevant to
Available Single Crystal Suites linking to multiple programs relevant
to Chemical Crystallography
Lachlan M. D. Cranswick
Collaborative Computational Project No 14 (CCP14)
for Single Crystal and Powder Diffraction
Birkbeck University of London and Daresbury Laboratory
Postal Address: CCP14 - School of Crystallography,
Malet Street, Bloomsbury,
WC1E 7HX, London, UK
Tel: (+44) 020 7631 6849 Fax: (+44) 020 7631 6803
E-mail: l.m.d.cranswick at dl.ac.uk
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