Structural and electronic properties of germanium clathrates Ge-46 and K8Ge46

The structural and electronic properties of germanium clathrates Ge-46 and K8Ge46 are studied by first-principles calculations within the local-densit y approximation. The equilibrium structures are obtained by ab initio pseud opotential calculation combined with dynamic minimizations. The clathrate s tructure 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 o f pentagonal rings, strong similarity in electronic properties between clat hrate and Ge-24 fullerene structure an found. The effect of doping clathrat e cages with metal atoms are examined. The K8Ge46 clathrate is found to be metallic with the conduction bands only slightly modified by K dopants. [S0 163-1829(99)02044-5].