Quantum Monte Carlo calculation of Compton profiles of solid lithium

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 electronelectron 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 to 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. @S0163-1829~99!08011-X#