Theoretical investigation of alkali-metal doping in Si clathrates

The effects of doping Si clathrate structures with alkali metals have been investigated theoretically. We discuss (a) the electronic structure of Na and other alkali-metal-doped Si clathrates, and (b) the possibility of a Jahn-Teller effect. We also discuss band-gap engineering for Si materials, as well as Mott’s conjecture for the electrical and magnetic properties of ${\mathrm{Na}}_{\mathit{x}}$ ${\mathrm{Si}}_{136}$ clathrate compounds. We use the self-consistent plane-wave technique to study the electronic structure, and an ab initio tight-binding-like molecular dynamics is performed to determine geometries, energetics, and Jahn-Teller effects.