We use variable-cell first principles molecular dynamics as an optimization tool to investigate the structural and electronic properties of Mg-based anhydrous hydrotalcite-like compounds. The formation energy as a function of the ratio R between di- and trivalent cations shows a minimum at R ~ 3, in good agreement with experimental stability ranges for these materials. At the same value R ~ 3, a maximum is found in the calculated interlayer distance, suggesting a correlation between energetic stability and structure. The energies and character of the electronic states of hydrotalcites containing different interlayer anions and trivalent cations have been compared. The nature of the anions is found to have a major influence on the electronic properties. In particular, OH^- anions, rather than, e.g., Cl^-, lead to a significantly smaller HOMO−LUMO gap, with a LUMO spatially more localized in the interlayer region. These features are related to the observed differences in the catalytic properties of hydrotalcites containing OH^- vs Cl^- anions.

We present a local density functional study of Cd4S and Cd4S4 clusters inside sodalite cages of different compositions (Al:Si ratios). The composition of the framework determines the cluster → cage charge transfer and strongly affects the atomic structure of the inclusion. The energy gap and the character of the highest occupied (HOMO) and lowest unoccupied (LUMO) electronic states depend on the size and stoichiometry of the included clusters, as well as on the overall stoichiometry of the composite. The calculated gap for Cd4S inclusions in aluminosilicate and aluminate sodalite (at half and full packing respectively) is 2.5 eV (i.e., about twice the calculated gap of bulk CdS), while for Cd4S4 in aluminosilicate and pure silica sodalite (at half packing) it is 1.7-1.9 eV (i.e., about 1.5 times the gap of bulk CdS). Our results indicate that simple confinement arguments are usually insufficient to predict the behavior of semiconductor−zeolite composites.