In the scope of this work three visualization programs and a data-base
application for transferring multipole parameters were developed.
These programs and methods were used in four charge-density studies.
Moliso enables the transparent visualization of color-mapped
iso-surfaces together with the molecular structure, which could optionally
include thermal ellipsoids. Beside the iso-surface, a cut-plane could
also be displayed. For the correct transparent visualization a new
approach was developed, which makes normally necessary sorting of polygons dispensable.
Molecool is a simple molecule-visualization program, which can
directly read XD-files. It can display local coordinate systems and thermal parameters. The crystal
environment can be calculated and a hydrogen bonding table will be plotted.
Rlat4XDS helps analyzing the reciprocal space if the program XDS has been
used. It can exclude regions of the reciprocal space from the cell
determination and correct the X-Ray data for phosphorus-absorption of the CCD-detector.
InvariomTool transfers theoretically calculated multipole parameters,
called invarioms, from a data base into XD input files. It assigns
invariom names to each atom of the structure. A database of invarioms
can also be built up with this program. Additionally it can be used to
generate XD input files for multipole refinement automatically,
without using Invarioms. With the invariom approach it is possible
to determine the charge density of low resolved X-Ray data
sets. This enables the replacement of the independent atom model in future.
The charge-density study of the halogenated fullerene CF
shows C-C bonds of very different strength which could be found in good
agreement with the theory. The electrostatic potential (ESP) shows a strong
dipolarization of the molecule. Weak inter-molecular interactions could be
analyzed with the use of the electron density mapped on Hirshfeld surfaces.
The validity of the nearest neighbor approach could be shown for all
carbon and oxygen atoms in thymidine by application of two different
invariom models and a classical multipole refinement. A perfect agreement
between the two invariom models could be found. Only small differences between
the invariom models and the classical refinement were found while thees
differences could be assigned to the crystal environment. Relative bond strengths
of thymidine could be found by the topological analysis of the electron density
(ED) and the integration of the ED in the electron localization function (ELF),
which was calculated from an ``experimental'' wavefunction, in agreement with the expection from
resonance structure formulae. The experimental ELF was used here for bond characterization
for the first time. Effects of the crystal environment could be best studied with
the analysis of the ESP and the Hirshfeld surfaces.
Adenosine was described with an invariom model and two classical multipole models
with a different degree of freedom in the refinement. Also a good agreement between
the models could be found here. The relative bond strengths do not vary that much
as in thymidine, but the same trends could be found in the topological analysis of
the ED and the integration of the ED in the ELF basins of adenosine.
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