Abstract:
The electronic band structures of Be and BeO have been measured by transmission electron
momentum spectroscopy (EMS). The low atomic number of beryllium and the use of ultrathin solid
films in these experiments reduce the probability of electron multiple scattering within the sample,
resulting in very clean “benchmark” measurements for the EMS technique. Experimental data are
compared to tight-binding (LCAO) electronic structure calculations using Hartree-Fock (HF), and local
density (LDA-VWN), gradient corrected (PBE) and hybrid (PBE0) density functional theory. Overall,
DFT calculations reproduce the EMS data for metallic Be reasonably well. PBE predictions for the
valence bandwidth of Be are in excellent agreement with EMS data, provided the calculations employ a
large basis set augmented with diffuse functions. For BeO, PBE calculations using a moderately-sized
basis set are in reasonable agreement with experiment, slightly underestimating the valence bandgap
and overestimating the O(2s) and O(2p) bandwidths. The calculations also underestimate the EMS
intensity of the O(2p) band around the Γ-point. Simulation of the effects of multiple scattering in the
calculated oxide bandstructures do not explain these systematic differences.
