  Recent high resolution Compton scattering experiments in lithium have shown
significant discrepancies with conventional band theoretical results. We
present a pseudopotential quantum Monte Carlo study of electron-electron and
electron-ion correlation effects on the momentum distribution of lithium. We
compute the correlation correction to the valence Compton profiles obtained
within Kohn-Sham density functional theory in the local density approximation
and determine that electronic correlation does not account for the discrepancy
with the experimental results. Our calculations lead do different conclusions
than recent GW studies and indicate that other effects (thermal disorder,
core-valence separation etc.) must be invoked to explain the discrepancy with
experiments.
