23Na and 29Si NMR Knight shifts in the silicon clathrate Na16Cs8Si136

Large Na-23 and Si-29 Knight shifts are observed for the silicon clathrate Na16Cs8Si136 in magic angle spinning NMR experiments. Electrical conductivity measurements on cold-pressed samples of the material also indicate metallic behavior, with a room temperature value of rho approximate to 41 m Omega cm. An ab initio calculation of the s-projected density of states at the Fermi level leads to a simple interpretation of the distinct resonances observed for each of the three framework sites in Si-29 NMR experiments.