中国物理B ›› 2015, Vol. 24 ›› Issue (9): 93101-093101.doi: 10.1088/1674-1056/24/9/093101
• ATOMIC AND MOLECULAR PHYSICS • 上一篇 下一篇
张辉a, 郑桂丽a b, 吕刚c, 耿轶钊a, 纪青a d e
Zhang Hui (张辉)a, Zheng Gui-Li (郑桂丽)a b, Lv Gang (吕刚)c, Geng Yi-Zhao (耿轶钊)a, Ji Qing (纪青)a d e
摘要: Covalent bonds arise from the overlap of the electronic clouds in the internucleus region, which is a pure quantum effect and cannot be obtained in any classical way. If the intermolecular interaction is of covalent character, the result from direct applications of classical simulation methods to the molecular system would be questionable. Here, we analyze the special intermolecular interaction between two NO molecules based on quantum chemical calculation. This weak intermolecular interaction, which is of covalent character, is responsible for the formation of the NO dimer, (NO)2, in its most stable conformation, a cis conformation. The natural bond orbital (NBO) analysis gives an intuitive illustration of the formation of the dimer bonding and antibonding orbitals concomitant with the breaking of the π bonds with bond order 0.5 of the monomers. The dimer bonding is counteracted by partially filling the antibonding dimer orbital and the repulsion between those fully or nearly fully occupied nonbonding dimer orbitals that make the dimer binding rather weak. The direct molecular mechanics (MM) calculation with the UFF force fields predicts a trans conformation as the most stable state, which contradicts the result of quantum mechanics (QM). The lesson from the investigation of this special system is that for the case where intermolecular interaction is of covalent character, a specific modification of the force fields of the molecular simulation method is necessary.
中图分类号: (Electronic structure and bonding characteristics)