METALLIC AND SEMICONDUCTING PHASES OF METAL-DOPED FULLERIDES

We present first-principles calculations of the electronic structure of crystalline fullerite (C-60) and of several metal-doped A(x)C(60) fullerides (A =K,Ca,Sr,Ba and x = 3, and Ca5C60). Whereas the alkali-metal-doped A(3)C(60) phases are metallic for A =K,Rb,Cs, the alkaline-earth-doped A(3)C(60) fullerides with A =Ca,Sr,Ba are narrow-gap semiconductors. This corresponds to complete electron transfers to the C-60 molecules and the formation of C-60(6-) hexa-anions. The Ca5C60 phase is metallic and shows a strong hybridization of the Ca ions over the tetrahedral and octahedral interstices of the face-centered cubic lattice of the C-60 molecules. Detailed calculations of the photoemission and inverse photoemission spectra are presented.