几种过渡态结构的有效优化方法

Efficient locating transition states for several systems

通过双桥反应机理、电环合反应和催化反应三个不同类型的过渡态优化,说明当标准方法难以给出结果时,对物理问题本身的分析有助于给出过渡态优化的线索.第一个例子根据化学问题给出限制条件,通过平衡几何构型优化方法优化得到过渡态;第二个例子是在使用标准过渡态优化方法失败后,根据物理问题从反应途径上用平衡几何构型优化方法选择过渡态优化的初始结构;第三个例子通过Gaussian98程序中的标准方法QST2直接得到过渡态.

Transition state(TS)optimization is the crucial and most difficult step in the investigation of mechanism via computational methods.They show by three kinds of examples that hints form a chemical problems can be used to conceive successful optimizations for transition states when standard methods prove unsuccessful.The three kinds of exmples were discussed in detail involving transition state optimizations for a double bridge mechanism reaction,an electrocyclic reaction,and a catalysis reaction.In the first case the transition state geometries were obtained by constraints derived from the chemical problem itself,thus enabling equilibrium geometry optimization techniques to be applied successfully and convergence to the desired TS to be achieved.In the second case,after failure to obtain the optimized TS by standard methods,the starting structures for all the TS optimizations were obtained from equilibrium geometry optimization technique along their reaction coordinates.In the third case,an optimization example was given by a standard TS optimization method implemented by Gaussian 98 ST2