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Electron momentum spectroscopy and linear combination of atomic orbitals calculation of bulk Na2O

This paper presents an experimental measurement of the electronic structure of Na2O in the solid phase using electron momentum spectroscopy and compares the results with ab initio calculations performed within the linear combination of atomic orbitals (LCAO) approximation. While Hartree–Fock (HF) can reproduce elastic properties we find it overestimates splitting of the oxygen valence bands by around 30% and the width of the O 2p band by a factor of 2. Our experimental values are 15.85 ± 0.2 and 0.6 ± 0.2 eV for these two quantities, respectively. Density functional methods are significantly better, with the hybrid functional PBE0 predicting the oxygen bandgap to within the experimental error. PBE0 also gives the best estimate of the Na core level energies. In contrast, HF performs best for the splitting between the oxygen and sodium bands. Our experimental values of 32.85 ± 0.2 and 27.45 ± 0.2 eV for the Na 2p–Na 2s and O 2p–Na 2p splittings agree well with previous measurements. Distribution of electron density both within the bands and between the bands is not reproduced by any of the computational methods employed.