【作者】 孙晓颖；

【导师】 唐敖庆； 李志儒；

【作者基本信息】 吉林大学 ， 物理化学， 2006， 博士

【摘要】 本论文对分子间相互作用体系的键,结构和性质进行了理论研究。主要包括以下几个体系:（1）（He-Ne-He）⁺体系的有趣的不对称线性结构已经被报道。在含稀有气体原子的（ABA）⁺型的三原子阳离子的分子间相互体系Ne3⁺,（Ar-He-Ar）⁺, （Ar-Ne-Ar）⁺, （Ar-O-Ar）⁺和（He-O-He）⁺中,使用CCSD（T）/aug-cc-pVDZ方法,并经Counterpoise校正,我们发现了五个新的不对称线性结构。并且揭示了这些不对称线性结构形成的原因是前两个原子的相互作用占优势。特别是发现了这些相互作用可分为四类:三电子σ型半键,三电子π型半键,弱的σ键和阳离子与原子之间的吸引。（2）含单碱金属的极性分子体系具有电子化物特性并且有大的非线性光学响应。为了了解增加碱金属原子引起相应体系的结构和性质的效应。使用从头算的方法优化Li₂（HF）n （n = 1～4）体系,得到带着实频的八个结构。根据Li₂子体系的成键特征,这个八个结构被分成四类。由于Li₂子体系的弥散电子的存在,我们预测了Li₂（HF）_n （n = 1～4）（除了中心对称的4a结构之外）具有大的一阶超极化率（β₀） （1496–4700 au）。并且发现了提高一阶超极化率的方法。那就是在Li₂（HF）_n （n = 1～4）体系中,在带大正电荷的锂原子附近增加HF分子的数目并且在带着小正电荷或是负电荷的锂原子附近减少HF分子的数目。（3）我们发现了一个新的超原子Li（HF）₃Li,与已知的超原子不同,它是分子间相互作用的体系。这个Li（HF）₃Li有着金属-非金属-金属类似夹心型的结构。这个Li（HF）₃Li有着一个被额外电子云包围着的复杂核,更多还原

【Abstract】 (1) By the counterpoise （CP） geometry optimization at the level ofCCSD（T）/aug-cc-pVDZ, the asymmetrical linear structures with all thereal frequencies were obtained for the triatomic cations of （ABA）⁺ type:Ne₃^<sup>+, （He-Ne-He）⁺, （Ar-Ne-Ar）⁺, （Ar-He-Ar）⁺, （He-O-He）⁺ and（Ar-O-Ar）⁺. The validity of this optimization method is confirmed bythe comparing with the method of the potential energy surface for thecalculations of Ne₃⁺ and （He-Ne-He）⁺. Using the molecular orbitaltheory, it is found that the interaction within the triatomic cations isdominated by the contribution from the first two atoms while thecontribution from the third atom is small. This result is justified as adirect consequence of forming an asymmetrical linear structure.Specifically, four types of interaction within the triatomic cations areidentified: three-electron σ-type hemibond, three-electron π-typehemibond, two-electron σ bond and the attraction between cation andatoms. For Ne3+, （He-Ne-He）+ and （He-O-He）+ clusters, it is shown thatthe electron correlation effect supports the asymmetry.（2） Using ab initio calculation, eight structures with all realfrequencies are obtained for the Li2（HF）n （n = 1 4） clusters.According to the bonding characteristic of the Li2 subunit, thesestructures are classified into four kinds. Firstly, one structure includesthe Li-Li covalent bond with about distance of Li2. Secondly, threestructures include {Li-Li}+ hemibonds with about distance of Li2+.Thirdly, one structure has {Li Li}+ with van der Waals Li-Li distance.Fourthly, three structures have Li+ ···Li with more than van der WaalsLi-Li distance. The Li2（HF）n clusters, except cluster 4a with the centralsymmetry, are predicted to have the large first hyperpolarizabilities （β0）（1496 – 4700 au）) due to the existence of the diffuse electrons of Li2subunit. We find that increasing the number of HF molecule near Liatom with the large positive charge （atom Li2） or decreasing thenumber of HF molecule near Li atom with the small positive ornegative charge （atom Li1）, the β0 value is enhanced. Thus the methodof increasing the β0 value is that decreasing the number of HF moleculenear Li atom with the small positive or negative charge （atom Li1） andincreasing the number of HF molecule near Li atom with the largepositive charge （atom Li2） in Li 2（HF） n （n = 1 4）.（3） The structure and properties of the Li（HF）3Li cluster with C3hsymmetry are investigated using ab initio calculation. The Li（HF）3Li isa metal-nonmetal-metal sandwich-like cluster mainly connected by theintermolecular interactions. In the especial cluster, the （HF）3 containingthe triangular F ring with the negative charges is sandwiched inbetween two Li atom. It is interesting that under the action of thetriangular F ring with the negative charges, the valence electrons of twoLi atoms are pushed out to form the distended excess electron cloudthat surrounds the Li（HF）3Li as a core. So the Li（HF）3Li cluster showsnot only the electride characteristic but also new superatomcharacteristics. Some characteristics of the especial superatom arefound. （1） The superatom contains the double shell nucleus. Theinternal nucleus is the regular triangular ring made of three F atomswith the negative charge and the outer-shell nucleus is made of three Hand two Li atoms with the positive charge. （2） The bonding force of thissuperatom framework is mainly the intermolecular interaction force,the lithium bond, which is different from that （covalent bond or ionicbond） of the general superatoms. （3） The interaction between theouter-shell nucleus and the excess electron cloud is mainly theanti-excess-electron hydrogen bond. （4） The especial superatomexhibits the new aromaticity （NICS = -8.37 ppm at the center of theregular triangular F ring）, which is the aromaticity found in the clusterof the intermolecular interaction. This is the new knowledge on thearomaticity. （5） The large polarizability of the superatom is revealed.Further, the vertical ionization energy （VIE） of the superatom is verylow, 4.51eV （smaller than 5.210eV of the alkaline-earth metal Ba） sothat it may be viewed as a super alkaline-earth metal atom.（4） Using ab initio calculation, three structures with all realfrequencies are obtained for the Li （HF）n （n = 1 4） clusters. Thedipole moments （μ）, polarizabilities（α0） and the firsthyperpolarizabilities （β0） of Li（HF）n （n = 2 4） are investigated atMP2/6-311++G（3df,3pd） method. The large first hyperpolarizabilities（β0） （5572 11751 au） are found. It is revealed that the contributions ofLi polarized to α0 and β0 values are dominant.更多还原