Abstract:
Measured and calculated band structures for the six lightest Group I and II oxides are
reported. Band structures have been measured using electron momentum spectroscopy, a
technique that maps the ground state occupied orbitals resolved both in energy and momentum.
Measurements are compared with first principles calculations carried out within the linear
combination of atomic orbitals (LCAO) approximation using both Hartree-Fock (HF) and
Density Functional methods (DFT). Three DFT functionals are used representative of the local
density approximation (LDA), the generalised gradient approximation (GGA) and a hybrid
method incorporating exact exchange. The calculated O 2p bandwidths and O 2p -2s band gaps
generally scale linearly with the inverse of the oxygen-oxygen separation squared, but
consistently show an anomaly at Li2O. These trends, including the anomaly, are also observed in
the experimental data. HF calculations consistently overestimate the oxygen 2p - 2s band gap by
almost a factor of 2. Measured band gaps lie within the range of the three DFT functionals
Mikajlo et al
2
employed, with evidence that the description of exchange becomes more important as the cation
size increases. Both HF and DFT overestimate the oxygen valence bandwidths, with DFT giving
more accurate predictions. Both observed and calculated bandwidths converge as the cation size
increases, indicating that exchange-correlation effects become less important as the metallic ion
becomes larger.
