中文摘要：

采用基于赝势平面波基组的密度泛函理论（DFT）方法, 研究了有机晶体材料4-（4-二甲氨基苯乙烯基）甲基吡啶对甲苯磺酸盐（DAST）和4-（4-二甲氨基苯乙烯基）甲基吡啶2, 4, 6-三甲基苯磺酸盐（DSTMS）的电子结构和光学性质. 结果表明, 两种化合物具有相似的能带结构, 其中价带顶和导带底分别含有较多二甲氨基和甲基吡啶中N原子的2p轨道成分. 在线性光学性质方面, 两种化合物具有较高的双折射率（Δn〉0.5）, 在中远红外区均具有较好的透过性能. 在二阶非线性光学性质方面, 该类晶体具有较强的二阶倍频（SHG）效应, 静态倍频系数d11约为150 pm·V^-1. 由能带结构分析结果可知, 体系的SHG效应与推拉电子基团之间的电荷转移密切相关, 同时乙烯桥键在该电子转移过程中也起着重要作用.

英文摘要：

The electronic structures and optical properties of 4-N,N-dimethylamino-4＇ -N＇ -methylstilbazolium tosylate （DAST） and 4-N,N-dimethylamino-4＇-N＇-methylstilbazolium 2,4,6-trimethylbenzenesulfonate （DSTMS） were investigated using density functional theory based on the plane wave basis set. The results indicated that the two compounds showed similar band structures, and the top of the valence band and the bottom of the conductive band mainly originated from the N 2p states of dimethylamino and methylpyridine, respectively. In terms of the linear optical properties, the birefringence indexes, ＆n, of the two compounds were very large （An〉0.5）, and they exhibited good light transmission in the mid- and far-infrared regions. With regard to second-order nonlinear optical characteristics, the DAST and DSTMS crystals showed strong second harmonic generation （SHG） responses, and the corresponding SHG coefficients （d11） were about 150 pm. V-1. Analysis of the band structures showed that the SHG responses of the two compounds were closely related to charge transfers between electron-donating and electron-withdrawing groups. Ethylene bridging also played an important role in the charge transfer process.