Structure Calculations and ELF (Electron Localization function)
Applications of the extended-Hückel procedure, one of the simplest
semi-empirical quantum chemical methods including COOP
- Crystal Orbital Overlap
Populations, have greatly influenced our way of
chemical reasoning due to transparent information.
The extended-Hückel method for periodic systems is used to
calculate the band structure, density of states and the electronic
properties of compounds, wich we investigate.
Our implementation "mehmacc"
together with the programs "colture" and "CURVIS"
allow to visualize real-space properties such as Becke's electron
localization function (ELF), the electron density, and partial electron
densities (PED), which help to gain a better understanding of 3D
chemical bonding in complicated extended systems.
The TB-LMTO ASA program, a first principle band structure method
based on density functional theory, is widely used aswell for
t he calculation of band structure, density of states (DOS), together
with the topological analysis of real space properties based on
the LMTO wavefunction like as electronic density, partial densities
(PDEN) and electron localization function (ELF).
compounds which, however, comprise several 100 atoms in their unit
cell or even do not exhibit any periodicity are out of reach for
periodic ab initio or semiempirical methods.To this class belong
e.g. the zeolites or oxometallates, such as the transition metal
oxide nanotubes synthesized in our group. An open question is which
factors drive the bending of vanadium oxide layers to tubular structures.
One approach to these materials is to employ ab initio calculations
on cluster models, classical molecular mechanics, or a combination
of both. Density functional calculations are carried out on clusters
cut out of a variety of known vanadium oxides. Based on their structures
and forces (energy gradients), interionic potential functions (shell
model) are derived. This inorganic force field will serve to predict
novel layered and curved structures and to investigate the mechanism
of bending of the vanadium oxide layers to tubes. It will be employed
in combined QM/MM calculations to investigate interaction of template
molecules with the layer surface.
Zürcher, S. Leoni, R. Nesper
Chemical, thermal, and theoretical analysis
of the a-b phase transition of Ba3Tt4 compounds
Z. f. Kristallogr. 2003, 218, 171-177
Zürcher and R. Nesper
"Cationic channels with partial anion
occupation in the Zintl phases Ba2Mg12Ge7.33
Z. Anorg.Allg.Chem., 2002, 628/7,1581-1589
Keywords: Zintl phases, Zintl anions, Supercations, Germanides,
Crystal structures, ELF (electron localization function)
Zürcher, S. Wengert, R. Nesper
Crystal structure of barium dimagnesium dilithium
disilicide, BaMg2Li2Si2, and of
barium dimagnesium dilithium digermanide, BaLi2Mg2Ge2.
Z. Kristallogr. - New Cryst. Struc. 2001, 216(4),
Localization Function - ELF
(Editor: Frank R. Wagner)