M_2Ge_(17)(M=Ni、Mn)及其阴离子的稳定性和磁性研究

Investigation of stability and magnetism of M_2Ge_(17) (M=Ni,Mn) and their anions

采用密度泛函理论(density functional theory,DFT)中的广义梯度近似(generalized gradient approximation,GGA)对Ni_2Ge_(17),Mn_2Ge_(17),[Ni_2Ge_(17)]^(4-)和[Mn_2Ge_(17)]^(2-)三种同分异构体的几何结构、电子结构和磁性进行了研究.通过对三种同分异构体的稳定性分析,得出D_(4d)结构的[Ni_2Ge_(17)]^(4-)最为稳定.由磁性的分析得到,Ni_2Ge_(17)和[Ni_2Ge_(17)]^(4-)的D_(2d)、D_(4d)、D_(4h)结构的磁矩均为零,体现为非磁性.对于Mn_2Ge_(17)和[Mn_2Ge_(17)]^(2-)的D_(4d)结构出现了自旋分裂能级,分别带有9_(μB)和8_(μB)的磁矩.其中,Mn原子与Ge原子之间存在弱的铁磁相互作用.对于D_(4h)结构的Mn_2Ge_(17),带有7_(μB)的磁矩,Mn原子和Ge原子之间既存在弱的铁磁相互作用又存在弱的反铁磁相互作用,而Mn_2Ge_(17)和[Mn_2Ge_(17)]^(2-)的D_(2d)结构以及[Mn_2Ge_(17)]^(2-)的D_(4h)结构的磁矩为零.

The geometric structures and magnetism of the three probable isomers for Ni_2 Ge_(17), Mn_2Ge_(17), [Ni_2 Ge_(17)]^(4-) and [Mn^2 Ge_(17)]^(2-) have been studied using the genneraliezd gradient approximation based on density functional theory. Through the analysis of stability, it has found that the D_(4d) structure of [Ni_2 Ge_(17) ]^(4-) is the most stable structure among the three possible isomers. By the analysis of magnetism, it. shows that there are no magnetic moments in the D_(2d) structure, the D_(4d) structure and the D_(4h) structure of Ni_2Ge_(17) and [Ni_2Ge_(17)]^(4-), showing no magnetic moment. The D_(4d) structure of Mn_2Ge_(17) and [Mn_2Ge_(17)]^(2-) have spin--splitting,leading to the magnetic moment 9 μB and 8 μs,respectively,there is weak ferromagnetic interaction between the Mn and Ge atoms in the D_(4d) structure. The D_(4h) structure of Mn_2 Ge_(17) have 7 μB magnetic moment, respectively,it is interesting that there is not only weak ferromagnetic interaction but also weak interaction between the Mn and Ge atoms for the D_(4h) structure of Mn_2Ge_(17). However,there are no magnetic moments in the D_(2d) structure of Mn_2Ge_(17), [Mn_2Ge_(17)]^(2-) and the D_(4h) structure of [Mn_2Ge_(17)]^(2-).