  Two-dimensional angular correlation of annihilation radiation (2D-ACAR) and
Compton scattering are both powerful techniques to investigate the bulk
electronic structure of crystalline solids through the momentum density of the
electrons. Here we apply both methods to a single crystal of Pd to study the
electron momentum density and the occupancy in the first Brillouin zone, and to
point out the complementary nature of the two techniques. To retrieve the 2D
spectra from 1D Compton profiles, a new direct inversion method (DIM) is
implemented and benchmarked against the well-established Cormack's method. The
comparison of experimental spectra with first principles density functional
theory calculations of the electron momentum density and the two photon
momentum density clearly reveals the importance of positron probing effects on
the determination of the electronic structure. While the calculations are in
good agreement with the experimental data, our results highlight some
significant discrepancies.
