Clusters stuffed inside frameworks: Electronic structure theory

Abstract

A zeolite, or other framework material, can be used as a template to form regular 3D arrays of nanosize clusters stuffed inside the framework cages. The aluminosilicate zeolite framework materials have wide electronic bandgaps, so that the stuffed species can produce new active electronic states within that bandgap. We discuss several real and model examples of such systems. We start with a framework of pure silicon, which is the silicon clathrate, and discuss its properties when stuffed with a single alkali atom in each cage. Caged structures of clathrates are similar to those of zeolites and can house alkali metal atoms in a periodic fashion with spacing varying from 5 to 15 A Next we investigate a model system of semiconductor clusters (Si) in the SiO2 framework in the sodalite geometry. Sodalite contains \-cages which are building blocks common to the structure of many important zeolites. We investigate theoretically atomic geometries, energetics and electronic properties of small semiconductor clusters in silica-sodalite. We also consider metal atom Na clusters in naturally occurring sodalite. We find that introducing Si semiconductor clusters within the cages of zeolites gives rise to flat electronic bands in the bandgap of the host, while alkali metal clusters give broad bands. The electronic properties are found in many cases to be dominated by many-body electronic correlation effects.