Electronic band structure of crystalline NaF: ionization threshold and excited states related to lattice defects

We study the electronic band structure of crystalline NaF using the perfect and imperfect lattice cluster models embedded in the ionic cage with restricted Hartree–Fock calculations. The calculated ionization threshold is 7.9 eV, the valence bandwidth is 8.7 eV, the band gap is 12.2 eV, and the exciton band is 11.7 eV. The corresponding experimental values are 7.6, 8.3, 11.5–11.7, and 11.0 eV. All the experimental results are well explained by the present calculation. Consideration of lattice defects is vital in discussing the ionization properties, though the perfect lattice remains useful for treating properties of excited band states. The difference in the band parameter between NaF and LiF is also discussed and is explained by the difference of the Madelung potential working on F.