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 Y _N ofn complete shells (units Y: rare gases, molecules, ion pairs). The influence of surface definition on size effects has been discussed.     

Vergleich der Elektronendichteverteilungen des Hydrido-Interstitialkomplexes HNb6I11 und des Interstitalhydrids HNb Ein Beitrag zur Cluster-bulk-Analogie

Comparison of Electron Density Distributions in the Hydrido-interstitial Complex HNb₆I₁₁ and in the Interstital Hydride HNb: A Contribution to Cluster-Bulk-Analogy The SW? Xα? SCF method has been used to compare changes of the electronic distributions in Nb₆I₁₁ and in Nb-metal caused by hydrogen at the octahedrally coordinated interstitial sites. Density maps of clusters Nb₆, Nb₆, Nb₆I₈³⁺, and HNb₆I₈³⁺ show: 1. The influence of the iodine ligands on the electronic distribution at the interstitial site is slight. 2. The spherically symmetric electron density of hydrogen at the interstitial sites is only deformed by the bonds to the neighbouring niobium atoms in both cases. Difference electron density maps illustrate that the interstitial hydrogen is weakly polarized in HNb₆I₁₁ as well as in HNb.     

Analytical calculation of binding energies of highly symmetrical particles

Analytical formulae of binding energies per atom are derived for icosahedral, cuboctahedral and face-centered cubic particles A_N by means of summation of pair potentials. Asymptotical relations for larger particles E/N = V (A – BN^−1/3) as well as the topological model of clusters are discussed.     

Begriffe und Definitionen zur Automation in und mit der analytischen Chemie

Ohne Zusammenfassung     

Mitteilungen aus chemischen Gesellschaften

Ohne Zusammenfassung     

Viable improvement of the full potential linearized augmented plane wave (FLAPW) method

A characteristic feature of the Full Potential Linearized Augmented Plane Wave (FLAPW)-method consists in the spatial subdivision of the charge density analogous to that of the one-particle wavefunctions, i.e. into a portion that is expanded in terms of spherical harmonics Y_lm inside the muffin-tin spheres and into a plane wave expansion of the interstitial charge density. To obtain the Hartree potential inside the spheres one is hence forced to solve a boundary value problem at the sphere surface. In addition, in all non-equivalent spheres each (l,m)-component of the charge density is mapped onto 300-400 radial grid points. To ensure an accelerated convergence of the calculation, the pertinent schemes require this rather large data set to be stored and mixed within 3-6 iteration steps. We show and illustrate for the example of a spin-polarized Ni-film with and without an oxygen overlayer and for bulk Si that this data set can be compressed by at least two orders of magnitude if one partitions the charge density in a different way so that the relevant portion determining the interatomic bonding can be Fourier expanded throughout the lattice cell. One thereby arrives at a modified FLAPW-scheme that combines favorable features of the original method with virtues of the pseudopotential method which consist in the simple construction of the Hartree potential and the efficient way of achieving self-consistency. These advantages can be exploited to the fullest by using Fast Fourier Transform. Moreover, forces that atoms experience in off-equilibrium positions attain a particularly simple form in terms of the charge density expansion coefficients. Received: 31 May 1997 / Revised: 12 December 1997 / Accepted: 18 December 1997