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Hard, highly melting materials
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Band 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).

Inorganic 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.


Recent Publications:

F. 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

F. Zürcher and R. Nesper
"Cationic channels with partial anion occupation in the Zintl phases Ba2Mg12Ge7.33 and Ba6Mg17.4Li2.6Ge12O0.64"
Z. Anorg.Allg.Chem., 2002, 628/7,1581-1589
Keywords: Zintl phases, Zintl anions, Supercations, Germanides, Crystal structures, ELF (electron localization function)
abstract | full text

F. 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), 503-504


Electron Localization Function - ELF
ELF-homepage (Editor: Frank R. Wagner)




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modified: 30 August, 2012 by | © ETH Zürich and the authors

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