Metallic and semiconducting phases of metal-doped fullerides

We present first-principles calculations of the electronic structure of crystalline fullerite (${\mathrm{C}}_{60}$) and of several metal-doped ${\mathit{A}}_{\mathit{x}}$${\mathrm{C}}_{60}$ fullerides (A=K,Ca,Sr,Ba and x=3, and ${\mathrm{Ca}}_5$${\mathrm{C}}_{60}$). Whereas the alkali-metal-doped ${\mathit{A}}_3$${\mathrm{C}}_{60}$ phases are metallaic for A=K,Rb,Cs, the alkaline-earth-doped ${\mathit{A}}_3$${\mathrm{C}}_{60}$ fullerides with A=Ca,Sr,Ba are narrow-gap semiconductors. This corresponds to complete electron transfers to the ${\mathrm{C}}_{60}$ molecules and the formation of ${\mathrm{C}}_{60}^{6\mathrm{-}}$ hexa-anions. The ${\mathrm{Ca}}_5$${\mathrm{C}}_{60}$ 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 ${\mathrm{C}}_{60}$ molecules. Detailed calculations of the photoemission and inverse photoemission spectra are presented.