The Calculation Of Structrue And Optical Properties Of LiNbO₃ With Density Function Theory

In this paper, we calculated the electronic structure and optical properties of ideal LiNbO3, of LiNbO3 with oxygen defect and of doped LiNbO3 with density function theory, and also discussed relation between the structure and properties.We modeled the ideal LiNbO3 and chose a proper set of the parameters, including cutoff, k-point, pseudopotential and functional. The results of electronic structure clearly showed that the conduct band was contributed by Nb4d, while the valent band was contributed by O2p. There were strongly covalent bond between them. The calculated results of optical properties indicated that it showed obvious anisotropy in LiNbO3 along different polarized directions and the ascription of the imaginary part of dielectric function peaks had closely relation with the transition of different atom orbital.Three oxygen defect models of LiNbO3 were optimized. According to the binding energy, we found the oxygen defect in LiNbO3 was unfavorable as far as the energetics was concerned. The calculations of electronic structure and optical properties of LiNbO3 with oxygen defect revealed the band gap and absorption coefficient got smaller, the division of Nb4d turned unobvious. The behavior should be derived from the impact of oxygen defect to the electronic populations.The electronic structure and optical properties of LiNbO3 doped with Mg²⁺, Fe²⁺, Fe³⁺ were also calculated. The calculated results showed the doping of Mg²⁺ had little effect on the energy gap and the optical properties in the low energy range. The optical properties changed in high energy range because new states were introduced by Mg²⁺. There was a narrow energy band at 0eV which was contributed by the Fe3d orbital. From the imaginary part of dielectric function, a small and acute peak appeared at 1.0592eV due to the doping of Fe²⁺. As for the doping of Fe3+, there were some peaks with less intensity in that area. The above results indicated that the energy band gap is reduced greatly, due to the doping of Fe²⁺/Fe3+, consequently, the absorption was enhanced in the low energy range.