Electronic structure, chemical bonding, and optical properties of ferroelectric and antiferroelectric NaNO2

The electronic-energy band structure, site and angular momentum decomposed density of states (DOS), and charge-density contours for ferroelectric sodium nitrite have been calculated using an accurate full-potential linear muffin-tin orbital method. The calculated total DOS is found to be in good agreement with experimental x-ray-photoemission spectra. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Na and NO2 is ionic and that the NO2 entities bond covalently. The polarized reflectivity spectra, calculated in a large energy range up to 30 eV, are directly compared with recent experimental spectra. The optical anisotropy in this material is analyzed through the optical functions such as refractive indices and static dielectric constants along the principal axes. Our calculated band structure and optical spectra are also compared with results obtained from the orthogonalized linear combination of atomic orbital method. The role of antiferroelectric distortion on the optical property and structural stability is discussed. [S0163-1829(99)00503-2].