中文摘要：

运用密度泛函理论（DFT）的BP86方法，对[M6Om（C25N4H18）n]^2-（M=W,Mo;n=1,2;m=17,18）进行了几何结构优化，其中Mo系列结构化合物优化的几何结构与实验值吻合较好，在净电场为零的条件下，运用DFT／LB94方法计算了体系的二阶非线性光学系数β值：体系1和2的βvec值分别为154．4×10^-20和124．8×10^-30esu．表明它们具有较大的二阶非线性光学系数，且Mo系列比W系列的β值大，而体系3和4的βvec值分别为218．0×10^-30和191.8×10^30esu．体系3和4的展。值分别比体系1和2的大，表明增加给体的数目有利于提高NLO响应．但都小千它们的2倍．

英文摘要：

The geometries of Lindqvist polyoxometalates bonded with terpyridine ligands （systems 1--4） were optimized by using DFT. The optimized main bond lengths are found to be in good agreement with experimental values. On the basis of the stable structures, the second-order nonlinear optical properties were calculated by using DFT/LB94 under the zero field condition. The βvec values of systems 1 and 2 are 154. 4 ×10^-30 and 124.8×10^-30 esu, respectively. These results indicate that systems 1 and 2 have larger nonlinear optical properties. The βvec value for systems containing Mo atom is larger than that of systems containing W atom. With increasing of the number of the segment, the βvec value increases remarkably. The βvec of the system 1 is larger than that of system 2. The βvec of system 3 is larger than system 4. Moreover, theβ3 and β4 are larger than β1 and β2, respectively. But, there is not the obvious multiple relationships between the βvec value and the number of the segment.