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.

Key words: [Ca(NH2)2]n (n＝1～5) clusters, density functional theory, structure and property, hydrogen storage material