Zone-center phonon frequencies for graphite and graphite intercalation compounds: Charge-transfer and intercalate-coupling effects

The frequencies of several zone-center vibrational modes in graphite have been calculated from first principles, with results in very good agreement with experiment. By studying the effect of charge transfer and lattice-constant change on E2g-mode frequencies, we find that the systematic stage dependences of both Raman- and infrared-active modes in graphite intercalation compounds can be understood by introducing a coupling to the intercalate of unconventional form.