Theoretical Investigation On Geometries And Electronic Properties Of The Neutral And Charged Nb₂Si_n(n=1～6) Clusters

The properties of materials can be designed by exploring the enormous variability in the size, shape, and composition of constituent clusters. Atomic cluster as a basic cell constructing nano-material has been a hot research field. Fabrication of cluster- assembled materials depends on finding a suitable building block for a cluster that is chemically stable and interacts weakly with each other. The theoretical research on the transition metal-doped silicon mixed clusters which is the important semiconductor clusters in microelectronic technology and materials science is of great significance and practical application value because transition metal doped in silicon clusters can improve the stability, improve its properties. The geometric structures, stabilities and electronic properties of the neutral and charged Nb₂Si_n(n=1- 6) clusters are investigated computationally by density functional method. The most stable structures are obtained. The results indicate that the most stable structure of Nb₂Si_n(n=1-6) clusters keeps the similar framework as the most stable structure of Si_n+2 clusters. Compared with the neutral Nb₂Si_n(n=1-6) clusters, most of the Nb₂Si_n⁺(n=1-6) and Nb₂Si_n^-(n=1-6) structures basically keep similar frameworks of the neutrals, and the serious deformations in geometries are found for Nb₂Si₆^-clusters. The calculated atomic averaged binding energies and fragmentation energies manifest that the Nb₂Si_n(n=1-6) clusters have remarkably enhanced stabilities. The Nb₂Si_n⁺(n=1-6) and Nb₂Si_n^-(n=1-6) clusters universally increase, which indicates that the stabilities of the Nb₂Si_n⁺(n=1-6) and Nb₂Si_n^-(n=1-6) clusters have been proved simultaneously as compared with the corresponding neutrals. Furthermore, the neutral and charged Nb₂Si₃ clusters are the most stable structure in the corresponding Nb₂Si_n(n=1-6) cluster. Meanwhile, natural populations indicate that charges transferr mainly from Si atoms to Nb atom in the lowest-energy Nb₂Si_n(n=3-6), Nb₂Si_n⁺(n=3-6) and Nb₂Si_n^-(n=1-6) clusters, the neutral and cation Nb₂Si and Nb₂Si₂ clusters in reverse. The gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gaps) of most neutral Nb₂Si_n(n=1-6) clusters universally decrease, which indicates that the stabilities of the Nb₂Si_n(n=1-6) have been weaker than that of the pure silicon Si_n+2 cluster; but stronger than that of the NbSi_n(n=1-6) cluster. The HOMO-LUMO gaps of Nb₂Si_n⁺(n=1-6) clusters universally increase, except for n=2 and 6, which indicates losting a charge can improve the chemically stability the Nb₂Si_n(n=1-6) cluster.