Phonon frequencies and CC bond distances in graphite and graphite intercalation compounds

First-principles, total-energy electronic structure calculations have been carried out for pure graphite, with results in excellent agreement with experiment. The effects of charge transfer on phonon frequencies ω_i and in-plane C-C bond lengths d_cc in graphite intercalation compounds have been studied using similar first-principles methods. We find that charge transfer is the determining factor for d_cc, but for the zone-center ω_i, intercalate coupling effects of a novel form, introduced via a simple model, are needed to explain the experimental data.