Calculation of Scattering by the Distorted Wave Born Approximation

An approximate scattering theory that utilizes the exact solutions for spherical defects is being developed. A defect of arbitrary shape can be represented by a sphere S and a remainder volume δv. By treating δv as a perturbation, one obtains an approximate solution that contains non-trivial frequency dependence and phase information. The approach is expected to be useful for studying defects with small but significant deviations (such as sharp edges) from spherical shape

Elastic Wave Scattering by General Shaped Defects: the Distorted Wave Born Approximation

An approximate theory for scattering of elastic wave by general shaped defects has been developed. A defect of arbitrary shape can be represented by a sphere S and a remainder volume R. Using the exact solution for a sphere and treating R as a perturbation, the solution corresponding to the Distorted Wave Born Approximation is obtained. This solution contains non-trivial frequency dependence and phase information. Preliminary comparisons with experiments will be presented

Wade’s rules and the stability of

The properties of clusters formed from two connected Gem cage-like clusters, such as experimentally synthesized Au3Ge185-, are examined using first-principles DFT methods. We focus particularly on AunGe12q- formed from a Wade-rules stable Ge6 cluster, where n = 0–3 and q = 0,2. The geometries, electronic structure, and thermal excitations of these clusters are examined using the SIESTA code. Cluster stability is tested using short molecular dynamics simulations. We find that intercluster bridges between Gem cages, formed of either Ge-Ge or Au-Ge bonds, can either bind a cluster together or tear it apart depending on the orientation of the bridging atoms with respect to the cages. The properties of neutrally charged AuGe12 and Au2Ge12 are characterized, and we observe that radially directed molecular orbitals stabilize AuGe12 while a geometric asymmetry stabilizes Au2Ge12 and Au3Ge18. A two-dimensional 2∞[ Au2Ge6 ] structure is examined and found to be more stable than other periodic [ AunGe6 ] subunits. While no stable neutral isomers of Au3Ge12 are observed in our calculations, our work suggests additional charge stabilizes isomers of both Au2Ge12 and Au3Ge12