Electronic structure of semiconducting<i>β</i>-NaSn

Abstract

In this paper we report calculations on the electronic structure of solid NaSn. The NaSn crystal consists of almost perfect tin tetrahedra separated by sodium atoms. This peculiar crystal structure is reflected in the electronic structure. The density of states is determined predominantly by the tin tetrahedra, which are isoelectronic to the phosphorous molecule ${\mathrm{P}}_{4}$. The Fermi level is positioned in a gap of the predominantly tin p states---the fully occupied p states correspond to bonding states of the tetrahedron and the empty p states just above the Fermi level correspond to antibonding p states. The role of the sodium atoms is to supply electrons for filling the bonding states and to keep the tin tetrahedra separated, thus prohibiting the formation of a metallic tin band.