Hans-Gerhard Fritsche

Exact analytical formulae for mean coordination numbers in clusters

Rigorous analytical formulae for mean nearest-neighbour coordination numbers in clusters as a function of cluster size have been derived for a range of geometries: the tetrahedron, octahedron, cuboctahedron, icosahedron and bcc rhombic dodecahedron. Formulae for outer-neighbour coordination numbers are also reported, including a complete analysis of interatomic distances and mean coordination numbers in icosahedra. The formulae will find application in studies of electronic structure and interpretation of EXAFS data.

MODIFICATION OF THE LATTICE CONTRACTION OF SMALL METALLIC PARTICLES BY CHEMICAL AND/OR GEOMETRICAL STABILIZATION

The uniform lattice contraction of naked, shell-like metallic particles of palladium, platinum, and gold will be compared with the lattice contraction of chemically and/or geometrically stabilized particles : particles deposited on films, particles in cages of zeolites, colloidal particles, and cluster compounds with big metallic cores. It will be discussed, how surface stabilization diminishes the contraction of particles.

SW-Xα-Untersuchungen zur Bindung eines interstitiellen Fe-Atoms in einem Zr-Oktaeder

SummaryOn the basis of SW-Xα results we have found that the Fe-Zr bonds in the cluster FeZr6 (Oh) are realized by the bond orbitals t2g, eg, and a1g. 97% of the charge within the Fe sphere is given by the contribution of these orbitals. Their electron densities are concentrated within the atomic spheres as well as in the region between the atoms Fe and Zr. Furthermore, we have discussed the electron distribution of the orbitals t1u, t′2g, and e′g near the HOMO which have no or only a very small influence on the interstitial bond.

Particle size effects of clusters and crystallites

Size effects of pair distance, cohesive energy, surface stress, and compressibility have been calculated for shell-like structurated particles YN ofn complete shells (units Y: rare gases, molecules, ion pairs). The influence of surface definition on size effects has been discussed.

Kohlenstoff an und in Palladium - Clusterorbitaluntersuchungen in Xα-Potential-Näherung

^«-calculations of PdnCand Pd„-clusters (n ¿ 14) of Ohand C4»-symmetry are carried out to investigate the bonding mechanism of carbon being chemisorbed at the (100)-surface, entering the lattice and being adsorbed at octahedrally interstitial sites of palladium. Correlation schemes of orbital energies, charges as well as spatial structure of the main C-Pd interacting orbitals are discussed in order to characterize the carbon-palladium bonds.