Structural and electronic properties of germanium clathrates Ge46 and K8Ge46

The structural and electronic properties of germanium clathrates Ge-46 and K8Ge46 are studied by first-principles calculations within the local-density approximation. The equilibrium structures are obtained by ab initio pseudopotential calculation combined with dynamic minimizations. The clathrate structure is found as a low-energy phase for germanium. The electronic band structures for Ge-46 clathrates are calculated and the band gap is found to be considerably larger than that of the diamond phase. Due to the effect of pentagonal rings, strong similarity in electronic properties between clathrate and Ge-24 fullerene structure an found. The effect of doping clathrate cages with metal atoms are examined. The K8Ge46 clathrate is found to be metallic with the conduction bands only slightly modified by K dopants. [S0163-1829(99)02044-5].