Calculation of electronic and optical properties of ferroelectric NaNO2

The electronic structure of the ferroelectric crystal NaNO2 is studied by means of first-principles local density calculation. Band structure and density of states show very localized bands, typical of a molecular solid. An indirect band gap of 2.95 eV is obtained. Detailed charge density analysis shows the Na atom to be completely ionized, while the NO2 group form a strongly bonded ionic unit with substantial covalent bonding character between O and N atoms. Calculation of the electronic dielectric function shows strong absorption features at 3.0, 5.8, 11.1, and 12.0 eV. The anisotropic nature of the optical absorption in NaNO2 is revealed by resolving the dielectric function into three principal directions. The calculated static dielectric constant for NaNO2 in the x-, y-, z- directions are 1.60, 1.58, and 2.20 respectively in good agreement with the experiment.