MP6方法在分子构型优化中的应用

Molecular geometry optimizations at MP6:examples and discussions

用多体微扰方法MP6对三个非氢原子组成的分子体系 ,分别在cc pVDZ、cc pVTZ、和cc pVQZ基组下 ,进行了构型优化计算 ,并利用Dunning提出的经验公式把结果外推到CBS极限。由于各种误差的相互抵消 ,MP2的构型优化结果较MP6或MP4的好。用耦合簇方法 (CCSD(T) )在同样条件下进行了优化计算 ,结果比微扰方法更具有优势。

MP6 geometry optimizations with cc-pVDZ,cc-pVTZ,and cc-pVQZ basis ests were carried out for the systems with three atoms,e.g.CO_2 and O_3,then CBS limits were obtained by using Dunning,sextrapolation equation.Because of error cancellation,MP2 can provide better quality geometry than MP6 or MP4.For comparison,coupled cluster methods (CCSD(T))were applied to the same geometry optimization cases,and the results show that CC methods have more advantages than MP methods in geometry optimizations.