First principles study of cubane and alkali doped C60 solids

Alkali doped fullerene (C60) solids have been studied widely due to their interesting physical properties. Lately, an experimental group succeeded to dope cubane (C8H8) into the octahedral voids of faced-centered-cubic (FCC) C60 solids, demonstrating that not only atoms (and polyatomic cations), but also small neutral molecules can intercalated into C60 solids. We study the electronic properties of cubane-doped C60 solids using first-principles techniques and show that C60 solids doped with both cubane and alkali metals, in which alkali metals such as K and Rb occupy the tetrahedral voids are energetically favorable. Cubane molecules substantially dilate the C60 lattice, resulting in a very large density of states in a single-particle treatment and pronounced tendency towards electronic instability.