The electronic structure of Be and BeO: benchmark EMS measurements and LCAO calculations

School of Chemistry, Physics and Earth Science, Flinders University of South Australia, GPO Box 2100, Adelaide SA 5001, Australia Defence Science & Technology Organisation, PO Box 44, Pyrmont NSW 2009, Australia Institute of Nanoscale Technology, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia 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.