Calculation of the electron momentum density in Zr andZrH2

The electron momentum distributions (EMD’s) and two-photon momentum distributions (TPMD’s) in Zr and ${\mathrm{ZrH}}_2$ have been calculated by means of a self-consistent augmented-plane-wave method. The results of the calculation for the total EMD and TPMD in Zr and ${\mathrm{ZrH}}_2$ along the [100], [110], and [111] directions, as well as the changes which appear on the introduction of hydrogen, can be understood on the basis of the respective energy bands and Fermi-surface topology. We also find the well-known feature that high-momentum components of the EMD have larger amplitudes than those of the corresponding TPMD.