The Study Of The Complex Nonlinear Optical Crystals By The Density Function Theory

Since 1980 years, the novel nonlinear optical crystal thiocyanate coordination complexes have been gradually investigated as a hotspot, which have higher nonlinear optical (NLO) coefficients and excellent nonlinear optical performance compared with inorganic NLO functional materials. But the exploitation and application for the materials have been restricted in a certain extent for the microcosmic theory studies have been lagged. At moment the First-principles theory studies for these crystals have not been reported. So the electronic and band structure together with linear and NLO optical properties of the thiocyanate coordination complexes have calculated based on a plane-wave pseudo-potential method in order to study the primary origin of NLO behavior of these materials and deep the acquaintanceship of their microcosmic structures and give some useful information for molecular project's designing novel materials with excellent NLO performance in this article.Among many methods for First-principles theory, the plane-wave pseudo-potential method based on First principle is a method with higher precision and excellent performance. It is adapted to study crystal materials.Some investigations have been performed by using the plane-wave pseudo-potential method in this article. Based on the first principles plane-wave pseudo-potential method, the electronic structure and band structure, linear and nonlinear optical (NLO) coefficients of urea (CO(NH2)2) crystal have been calculated. It is found that 2p orbitals of C,O and N atoms of urea are hybridized obviously, and that the primary contribution to the NLO behavior comes from the hybridization of the 2p electron states with higher energy. The electronic structure and band structure, linear and non-linear optical (NLO) coefficient of LiNbO3 crystal have been calculated based on first principle plane-wave pseudo-potential method. It is found that the 4d electron state of Nb atom and the 2p electron state of O atom in LiNbO3 crystal are obviously in hybridized state, which contributes primarily to the NLO behavior of the crystal. The electronic structure and band structure, linear and non-linear optical (NLO) coefficient of zinc cadmium tetrathiocyanate (ZnCd(SCN)4) have been calculated. It is found that 2p orbitals of C,S and N atoms of ZnCd(SCN)4 are hybridized obviously, and that the primary contribution to the NLO behaviour comes from the hybridization of the 2p electron states.