[Ca(NH_2)_2]_n(n=1～5)团簇的密度泛函理论研究

Density Functional Theory Study on [Ca(NH_2)_2]_n(n=1～5) Clusters

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对[Ca(NH2)2]n(n=1～5)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、成键特性、电荷特性等进行了理论研究.结果表明:团簇易形成环状结构,以金属Ca原子团簇作为骨架,NH2基结合在金属团簇骨架上,并主要是Ca—N成键和Ca—Ca成键.团簇中Ca—N键长为0.225～0.257nm,Ca—Ca键长为0.312～0.354nm,N—H键长为0.102～0.103nm,H—N—H键角为102.9°～104.2°;团簇中Ca原子的自然电荷在1.657e～1.720e之间,N原子的自然电荷在-1.543e～-1.592e之间,H原子的自然电荷在0.349e～0.367e之间,Ca原子和NH2基之间相互作用呈现较强的离子性;对比团簇和晶体的结构及IR谱表明,NH2基在团簇和晶体中的结构基本一致。

Possible geometrical structures and relative stabilities of [Ca（NH2）2]n （n= 1-5） clusters are studied by using the hybrid density functional theory （B3LYP） with 6-31G＊ basis sets. For the most stable isomers, electronic structures, vibrational properties, bonds properties, and ionization potentials are analyzed. The calculated results show that N--Ca and Ca--Ca bonds are favorable in the clusters, in which NH2 is bound to the framework of Ca atomic clusters forming ring-like structures. The bond lengths in [Ca（NH2）2]n （n=1-5） clusters are 0.225-0.257 nm for Ca-N, 0.312-0.354 nm for Ca--Ca, and 0.102-0.103 nm for N-H bonds, respectively. The bond angles of H-N-H are 102.9°-104.2°. The population analysis suggests that the bonds between Ca and NH2 are of strong ionicity. The natural charges are -1.543e--1.592e for N atoms, 1.657e- 1.720e for Ca atoms, and 0.349e-0.367e for H atom, respectively. The comparative study of structures and spectrum between clusters and crystal shows that the structure of NH2 in clusters is consistent with that in crystal.