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分别用HF/4 31G(Si =6 2 1G)、B3LYP/6 31G(D)、B3LYP/6 31G、HF/6 31G、MP2 /6 31G(D)对TMS进行了结构优化 ,在此基础上 ,用Hartree Fock、B3LYP理论水平下 ,分别用不同的基组 6 31G、6 31+ +G(D ,P)、6 311+G(2D ,P)、6 311+ +G(D ,P)进行NMR的计算 ;在MP2理论水平上 ,用STO 3G、3 2 1G、4 31G、6 31G、6 31G(D)、6 31+ +G(D ,P)等基组进行NMR的计算 .并用GAUSSION98程序所给出的四种计算NMR的方法 :GIAO、IGAIM、CSGT、SINGLEGAUGEORIGIN ,分别在上述基础上进行了TMS的屏蔽值的计算 .研究结果表明 ,就理论水平而言 ,DFT(B3LYP)比HF计算结果要好 ,而且基组越大 ,计算精度越高 ,但有一饱和基组存在 .就计算方法而言 ,用GIAO有利于计算精度的提高 .计算结果与实验值基本上吻合
Based on the structural optimization of TMS with HF / 4 31G (Si = 6 2 1G), B3LYP / 6 31G (D), B3LYP / 6 31G, HF / 6 31G and MP2 / 6 31G (D) , Using Hartree Fock and B3LYP theory, we used different base sets (631G, 631 + + G (D, P), 631 1 + G (2D, P) NMR calculations were carried out. At the MP2 theoretical level, NMR calculations were performed using basis sets of STO 3G, 3 2 1G, 4 31G, 6 31G, 6 31G (D), 6 31+ + G (D, P) GUSO, IGAIM, CSGT and SINGLEGAUGEORIGIN are used to calculate the shielding value of TMS on the basis of the above four methods which are given in GAUSSION 98. The results show that in theoretical terms, the ratio of DFT (B3LYP) HF calculation results are better, and the larger the base set, the higher the calculation accuracy, but there is a saturated basis set exists.For the calculation method, with the GIAO is conducive to the improvement of the calculation accuracy.The calculated results are basically consistent with the experimental values