Special stability of cationic MPb_(12)~+ clusters and superalkali character of neutral MPb_(12)clusters (M=B,Al,Ga,In,and Tl)

摘要

The electronic structures and stabilities of cationic MPb_(12)~+ clusters (M=B,Al,Ga,In,and Tl)with 50 valence electrons are investigated within density functional theory.It is shown that,at the B3LYP/cc-pVDZ(-PP)and BPW91/cc-pVDZ(-PP)levels of theory,the structures of MPb_(12)~+ with icosahedra (I_h)symmetry are energetically favorable,and their high stabilities may arise from the closed-shell nature of the pi subsystems which are subject to the 2(N_(pi)+l)~2 rule with N_(pi)=l.In addition,the possessing of large nucleus-independent chemical shifts of the five kinds of clusters reflects the common aromatic character of these clusters.From the comparison of our studies on the binding energies and the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gaps,the cluster AlPb_(12)~+ has higher stability than the others and this is consistent with the recent mass-spectrometric discovery of Al-doped Pb_n~+ clusters,in which AlPb_(12)~+ is highly abundant.The same methods are used to search for the structures of the neutral MPb_(12)clusters.The calculations reveal that the most stable geometries of the BPb_(12)and GaPb_(12)clusters have I_h symmetry,the AlPb_(12)and InPb_(12)clusters have T_h symmetry,and the TlPb_(12)cluster has C_(5v)symmetry.Furthermore,the vertical ionization potentials of the neutral MPb_(12)clusters are smaller than that of some alkali atoms,indicating that the neutral MPb_(12)clusters possess superalkali character.