Transition metal image intermetallics: Structure maps based on quantum mechanical stability

We study a two-dimensional structure map for image binary transition metal compounds with variables appropriate for direct quantum-mechanical energy calculations. The variables are the electron count and image, the difference in image-orbital Coulombic integrals. The experimental structure map differentiates between the six known image transition metal structure types: image and image. The theoretical quantum mechanical map (based on image-Hückel calculations) gives good agreement with the experimental map. The numerical accuracy of the image-Hückel energies is assessed by direct comparison to LDA-DFT calculations carried out on image. For this system, both the image-Hückel and LDA-DFT calculations place the six structure types in the same energetic order. The image-Hückel theory, in addition, allows further analysis on the structural origins of these differences in energy. The chief structural features responsible for differences in energy prove to be the varying number of three- and four-member rings of bonded atoms. These results help delineate the principal factors responsible for transition metal icosahedral, Frank–Kasper vs. closest-packed structures.