二面角弯曲异构体：M2Pt20/-团簇的理论研究

本文采用密度泛函理论和波函数理论研究了M₂Pt₂^0/-团簇(M表示碱土金属元素)在气相中的几何结构和电子性质. 研究表明，拥有平面结构的D_2h异构体比拥有较小二面角及较短Pt-Pt键长的C_2v异构体更稳定. M(s,p)与Pt(5d)的相互作用和Pt-Pt共价键之间的相互竞争导致了这两种异构体在稳定性方面有所不同. M(s,p)与Pt(5d)的相互作用支持D_2h异构体的平面结构；Pt-Pt共价键作用导致了C_2v异构体的弯曲结构. Be₂Pt₂的单重态和三重态的势能曲线有两个不同的交点，但是Ra₂Pt₂和Ca₂Pt₂^-的不同多重度的势能曲线间只有一个交点，这可能是由于三重态Ra₂Pt₂和四重态Ca₂Pt₂^-较平坦的势能曲线造成的. 上述结果揭示了一个拥有最小原子数的二面角弯曲异构现象，并且为解释其他潜在的角度弯曲异构体提供了理论帮助.

Theoretical Studies on Dihedral Angle-Bending Isomers of M2Pt20/- Clusters

The structures and electronic properties of the gaseous M₂Pt₂^0/- clusters (M represents the alkaline earth metal) were investigated using the density functional theory (B3LYP and PBE0) and wave function theory (SCS-MP2, CCSD and CCSD (T)). The results indicate that the D_2h isomers with the planar structures are more stable than the C_2v isomers with smaller dihedral angles and shorter Pt-Pt bond lengths. The mutual competition of M(s,p)-Pt(5d) interaction and Pt-Pt covalent bonding contributes to the different stabilizations of the two kinds of isomers. The M(s,p)-Pt(5d) interaction favors the planar isomers with D_2h symmetry, while the Pt-Pt covalent bonding leads to the C_2v isomers with bending structures. Two different crossing points are determined in the potential energy curves of Be₂Pt₂ with the singlet and triplet states. But there is just one crossing point in potential energy curves of Ra₂Pt₂ and Ca₂Pt₂^? because of flatter potential energy curves of Ra₂Pt₂ with the triplet state or Ca₂Pt₂^? with quartet state. The results reveal a unique example of dihedral angle-bending isomers with the smallest number of atoms and may help the understanding of the bonding properties of other potential angle-bending isomers.