Polarization of carbon electron-momentum density in lithium-graphite intercalation compounds

Compton-profile measurements on the second-stage lithium-graphite intercalation compound, LiC₁₂, have been performed with the high-resolution spectrometer of Laboratoire pour l'Utilisation du Rayonnement Electromagn\'etique for two directions, parallel to the c axis and average in the basal plane. Simultaneously, a new ab initio self-consistent-field energy-band structure has been calculated for LiC₁₂ with the actual stacking of graphite layers. The wave functions have been used to obtain Compton profiles. Both theory and experiment confirm the failure of the rigid-band model for Li-graphite intercalation compounds, as well as the importance of the polarization of graphite valence orbitals due to the presence of lithium ions.