含两种次级姜泰勒畸变基元晶体非线性光学性质的微观机制模拟

The discovery of novel inorganic nonlinear optical crystals has been the research hotspots in chemistry and material field. Combining two kinds of second-order Jahn-Teller distortion groups in one compounds could employ the synergy effect and obtain the perfect novel nonlinear optical crystals. Due to containing two kinds of distortion groups, the microscopic structures and the functional mechanism of nonlinear optical effect in these crystals are more complicated than the single-group crystals. Understanding the effects of the interations between different groups and spacial arrangement on the nonlinear optical properties to achieve the controllable preparation of NLO crystals is a challenge in current NLO research. In this project, we employ density functional theory to calculate the geometric structures, electronic structures and nonlinear optical properties of these complex crystals, and study the intrinsic relations of nonlinear optical properties and the group structures, interations between different groups as well as the spacial arrangement. It will be aimed at conclude the influencing laws of the second group distortion and electronic long-range transition caused by interations between different groups and group spacial arrangement on the NLO properties, and reveal the microscopic mechanism of NLO properties in these crystals. The project will promote to understand the intrinsic relations of nonlinear optical properties and the microscopic structures and to offer some reliable theoretical basis and strategic help for designing novel nonlinear optcial crystals.

新型无机非线性光学(NLO)晶体的研制一直是化学和材料学领域的研究热点。将两种次级姜泰勒畸变基元复合到同一化合物中利用其协同效应可获得性能优异的新型NLO晶体。但由于包含两种畸变基元，此类晶体的微观结构和NLO作用机制比单一基元晶体更加复杂。如何把握不同基元间相互作用及空间排列对宏观NLO性能的影响规律以实现晶体的可控制备，是当前此类NLO材料研究面临的挑战。本项目采用密度泛函理论方法结合自编的倍频计算程序计算一系列此类晶体的几何结构、电子结构及NLO性质，深入系统地研究其非线性光学性质与基元结构、基元间相互作用、空间排列之间的内在联系。旨在总结出各基元间相互作用导致的二次结构畸变和电子长程跃迁，以及基元空间排列对宏观倍频效应的影响规律，揭示其NLO性质的微观机理。项目的开展有助于了解此类晶体NLO性质与微观结构的内在联系规律，为实现NLO晶态材料的调控设计提供一定的理论依据和策略支持。

我们采用周期性密度泛函理论和独立粒子近似方法，深入系统地研究了一系列含两种次级姜泰勒畸变基元（d0过渡金属离子和含孤对电子的离子）的无机复合晶体的电子结构、线性及非线性光学性质。通过深入分析此类晶体中各基团之间的电子跃迁和相互作用，以及各基团对晶体倍频效应的贡献，我们发现这两种次级姜泰勒畸变基团都对晶体倍频效应有重要贡献；此类晶体的倍频效应源自阴离子基团中的 O-2p非键态向过渡金属d轨道及含孤对电子离子的p轨道的电子跃迁。当基团中的O-2p非键态被饱和时，化合物的倍频效应将显著降低；而当用电负性更高的F原子部分取代O时，将导致化合物的导带底变平并下移，进而可使其倍频效应增强。此外，我们发现由于d8-Au特别的电子组态，Au的d轨道对带隙两侧都有不小的贡献，使得含Au(III) 化合物的倍频效应不仅来自O-2p非键态的跃迁，而且还来自Au-dxy非键态到导带的电子跃迁。这些结果为进一步建立此类非线性光学晶体的结构—性能关系作了很好的铺垫。. 在本项目资助下，共发表标注文章15篇。