Hf8C12金属碳多面体电子结构的从头计算研究

用赝势从头计算方法研究Hf₈C₁₂多面体．先对T和Td分子构型作几何优化，发现Td对称构型比T构型稳定．利用非限制的Hartre Fock方法及自然键轨道分析研究Td构型的Hf₈C₁₂基团，结果表明：Hf₈C₁₂存在三种自旋不同的基态，这种基态的多样性与成键机制、电子组态和电子能谱分布密切相关．其中S=0时，Hf₈C₁₂主要是由外四面体Hf原子与类乙烯C₂单元形成极性共价键构成．S=1时，6个类乙炔C₂单元吸附在Hf₈金属框架．S=2时，部分C₂中的ｐπ键断裂与Hf原子形成ｄ←ｐπ键．进一步分析发现，Td对称性的结构模型为(Hf₈)^+4.5(C^-0.75₂)₆，在高自旋态下具有铁磁性，电子能级分布及其能隙随自旋态而变化． 关键词：

AB INITIO STUDIES ON THE ELECTRONIC STRUCTURES OF METALLOCARBOHEDRENE Hf8C12 CLUSTER

Ab initio effective core potential calculations have been carried out on Hf₈C₁₂ metallo-carbohedrene cluster. First, the geometries of the ground states have been optimized for structures of T and Td-symmetry, respectively. It has been shown that the Td-symmetry structure is more stable than T's. Then Hf₈C₁₂ cluster with Td-symmetry is studied by unlimited Hartree-Fock method and Natural Bonding Orbital analyzing. It has been found that there are three stable states of different spins, which are related to the bonding mechanism, electronic configuration and structure of the electron energies. For S=0, the Hf。atoms of the outer tetrahedron link the six ethylene-like C₂units through Hf—C polar covalent bonds within Hf₈C₁₂ cluster. For S=1, six acetylene-like C₂ units are adsorpted on the Hf₈ framework. For S=2, some ｐπ bonds on the C₂ units are found broken and bonded with Hf atoms in d←ｐπ bond-type. Most of Hf—C bonds are of Hf。—C type. Furthermore, it is found that the structure model of Hf₈C₁₂ cluster with Td-symmetry is (Hf₈)^+4.5(C^-0.75₂)₆, which is ferromagnetic at the high spin states. Meanwhile, the distribution of electron energies also changes with spin states.