Electronic Structure of C₇₈and C₇₈-Graphite Cointercalation Compound

Abstract

We study the electronic structure of C₇₈ and that of C₇₈-graphite cointercalation compound. First we show the electronic structure of five isomers of C₇₈. Their geometric structures have been optimized by an empirical model potential and their electronic structure has been calculated using the tight-binding model. The C_2v-symmetry C₇₈, a major isomer experimentally extracted, is found to have a considerably deep lowest unoccupied state. Using this C_2v C₇₈, we design a stage-1 C₇₈-graphite cointercalation compound. Its electronic structure calculated with the tight-binding model shows that the deep lowest unoccupied state of the C_2v C₇₈ causes charge transfer from a graphite sheet to C₇₈. Although the material is formed with only carbon atoms, C₇₈-graphite cointercalation compound is the hole doped graphite intercalation compound.