N_2-N_2二聚物分子间相互作用势的从头算

Ab initio calculations for intermolecular interactions in N2-N2 dimer

采用改进的MP2方法和传统的MP2、MP3、MP4方法,结合6-31+G(2df)、6-311+G(2df)、AUG-cc-pVTZ在内的多种基组对N2-N2分子间相互作用势进行了比较研究.结果表明:用MP4方法计算得到的相互作用势介于MP2与MP3的结果之间,与传统意义上的MP2计算结果介于MP3与MP4的结果之间不同.分子间的相对方位对分子键长影响很大.分子间相隔很近时,这种影响越为明显.改进的MP2方法,在平衡位置对传统方式得到的势能曲线有明显的改善.同时发现BSSE误差不容忽视.

Intermolecular potential energy for the N2-N2 dimer has been obtained for three structures using the MPn（n =2,3,4） method and 6-31 ＋ G（2df）,6-311 ＋ G（2df）,cc-pVTZ etc basis set with N≡N bond length fixation or left relaxed to be optimized. The results are as follow. Firstly, the results of the MP4 method are between those of MP2 method and MP3 method, which is not consistent with our previous awareness that the results of MP2 method should be between those of the MP3 method and MP4 method. Secondly, the optimized bond length using MP2 method indicates that the relative orientation of molecules markedly affects bond length of the N2 molecules. Especially when the intermolecular interval is small, the change of the bond length is large and that is required by the high pressure environment. Thirdly, the results of the MP2 method with N≡N bond length left relaxed to be optimized exist a deeper potential well than the ones with N≡N bond length fixation. Finally, the counterpoise correction to eliminate the basis superposition error is essential.