论文部分内容阅读
通过使用7个从头计算方法、7个密度泛函理论(DFT)方法和20个常用基组对66个苯、萘、蒽、联二亚苯、苊及其衍生物计算振动频率后发现只有10个分子完全不出现虚频,而且共有1365个方法/基组出现虚频;其中7个DFT方法,HF方法和MP2方法所出现的虚频数占各自总的计算方法/基组数的比例分别为7.01%,7.34%和36.38%.除mPW2PLYPD以外的所有方法计算含甲基或铵基的16个分子的结果都非常不可靠,但DFT和HF方法对除此类分子以外的其它芳香分子从计算所出现虚频的比例可以被忽略的角度来看都显得相当可靠.当45个杂环芳香化合物及其衍生物被类似地计算时,DFT方法,HF方法和MP2方法所出现的虚频比例分别为2.11%,2.78%和27.44%.不但用苯的实验结构进行计算不能消除虚频,而且用苯和甲苯的平面或非平面优化结构计算也都不能消除虚频;同时用一百多个方法和一百多个基组计算苯和甲苯时,出现的虚频比例更高达18.18%.这些均说明从头计算方法和DFT方法计算频率有不可靠或不适用的地方,并且那种认为苯和其它芳烃为非平面结构的观点至少不能说是完全正确的.
Calculating the vibrational frequencies of 66 benzene, naphthalene, anthracene, diphenylene, acenaphthene and their derivatives using seven ab initio methods, seven density functional theory (DFT) methods and twenty common basis sets found only 10 A total of 1365 methods / base groups appear virtual frequency; among them, 7 DFT method, HF method and MP2 method take the ratio of imaginary frequency to their total calculation method / base number respectively 7.01%, 7.34%, and 36.38% .All methods except mPW2PLYPD The calculation of the 16 molecules with methyl or ammonium groups results are very unreliable, but the DFT and HF methods calculate the number of aromatic molecules except for these molecules The ratio of imaginary frequencies appearing can be quite reliable from the point of view of omission.When 45 heterocyclic aromatic compounds and their derivatives are similarly calculated, the ratio of imaginary frequencies appearing in DFT method, HF method and MP2 method respectively 2.11%, 2.78% and 27.44%, respectively.Not only the calculation of the experimental structure of benzene can not eliminate the imaginary frequency, but also the imaginary frequency can not be eliminated by using the planar or non-planar optimization structure of benzene and toluene. At the same time, And more than a hundred base groups calculate benzene and a , The imaginary frequency ratio appears to be as high as 18.18%, all of which indicate that the ab initio calculation method and the DFT method are not reliable or not applicable, and at least the view that benzene and other aromatic hydrocarbons are non-planar structures can not be said to be Completely correct