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有机化学
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有机化学 ›› 2014, Vol. 34 ›› Issue (1): 178-189.DOI: 10.6023/cjoc201306040 上一篇    下一篇

研究论文

振动频率与芳香分子稳定性的判定

张贻亮a, 张钢b   

  1. a 吉林大学化学学院 长春 130012;
    b 吉林大学理论化学研究所 长春 130023
  • 收稿日期:2013-06-28 修回日期:2013-08-06 发布日期:2013-09-06
  • 通讯作者: 张贻亮 E-mail:yiliang@jlu.edu.cn

Vibrational Frequencies and Determination of Stability of Aromatic Molecules

Zhang Yilianga, Zhang Gangb   

  1. a College of Chemistry, Jilin University, Changchun 130012;
    b State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023
  • Received:2013-06-28 Revised:2013-08-06 Published:2013-09-06

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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.

关键词: 计算化学, 从头计算, 密度泛函理论（DFT）, 取代芳烃, 杂环芳香化合物, 虚频, 稳定性, 可靠性

After the vibrational frequencies of 66 benzene, naphthalene, anthracene, biphenylene, acenaphthylene molecules and their derivatives are computed by 7 ab initio methods [i.e., HF, MP2, MP2(Full), MP3, CISD, QCISD and CCSD], 7 density functional theory (DFT) methods (i.e., B3LYP, B3P86, LSDA, HCTH, M06, B97D and mPW2PLYPD) and 20 popular basis sets (i.e., 18 k-nlmG type basis sets, cc-pVDZ and aug-cc-pVDZ), it is found that no imaginary frequency appears only for 10 molecules and imaginary frequencies appear for 1365 method/basis sets. The percentages of the numbers of imaginary frequencies relative to their total computed method/basis sets for the 7 DFT methods, HF method and MP2 method are 7.01%, 7.34%, and 36.38%, respectively. The results of the 16 substituted arenes containing methyl or ammonium group computed by all the methods except mPW2PLYPD are very unreliable, but the results of the other molecules computed by the DFT and HF methods are very reliable when determined from the criterion that the percentage of imaginary frequency which will exclude the stability of a computed molecule is negligible. When 45 heterocyclic aromatic compounds and their derivatives are similarly computed, the percentages of imaginary frequencies of the DFT methods, HF method, and MP2 method are 2.11%, 2.78%, and 27.44%, respectively. Imaginary frequencies do not disappear when the experimental structure of benzene is used to compute or when the planar or nonplanar optimized structures of benzene and toluene are used to compute. Moreover, when benzene and toluene are computed by more than one hundred methods and more than one hundred basis sets, their percentage of imaginary frequencies is also as high as 18.18%. Then the ab initio and DFT methods are not always reliable or suitable for computing frequencies, and the viewpoint that benzene and other arenes are nonplanar is at least not completely correct.

Key words: computational chemistry, ab initio computation, density functional theory (DFT), substituted arene, heterocyclic aromatic compound, imaginary frequency, stability, reliability