Electronic band structure of calcium oxide

We employed electron momentum spectroscopy (EMS) to measure the bulk electronic structure of calcium oxide. We extracted the electron momentum density (EMD), density of occupied states (DOS), band dispersions, bandwidths and intervalence bandgaps from the data. The results are compared with calculations based on the full potential linear muffin-tin orbital (FP-LMTO) approximation. While the bandwidths of 0.6 ± 0.2 and 1.2 ± 0.1 eV for the s- and p-bands, respectively, and their dispersions agree well with the LMTO calculation, the relative intensity of the two bands is at odds with the theory. The measured intervalence bandgap at the Γ-point of 16.5 ± 0.2 eV is larger by 2.1 eV than that from the LMTO calculation. The experimental bandwidth of the Ca 3p semi-core level of 0.7 ± 0.1 eV agrees with the LMTO prediction. The measured bandgap between this level and the s-band is 3.6 ± 0.2 eV. The Ca 3s–3p level splitting is in excellent agreement with the literature.