The structures and stabilities of small diarsenic-doped silicon clusters

The structures and stabilities of As2-doped Sin (n = 1–7) clusters have been investigated at the B3LYP level of theory, incorporating the 6-311+G∗ basis set. An isosceles triangle is predicted to be the lowest-energy structure of the As2Si cluster, whereas the global minimum of As2Si2 possesses an As–As-butterfly structure. The ground state structures for As2Si3, As2Si4 and As2Si5 are all bipyramids: trigonal, tetragonal and pentagonal, respectively, which could have important applications as building blocks to synthesize silicon nanowires. The most stable isomer of As2Si6 possesses a tricapped trigonal bipyramid structure. The lowest energy structure of As2Si7 can be viewed as a substitutional structure of the tricapped trigonal prism Si9 isomer. In the majority of the lowest energy isomers, the two As atoms tend to be separated from each other, in order to maximize the number of Si–As bonds, and therefore locate at the axial vertex or face-capping atomic positions, especially for As2Si4–As2Si7. According to results of the incremental binding energies, the HOMO–LUMO gaps and the vertical ionization potentials, the As2Si3 and As2Si6 clusters are relatively stable compared to their neighbors. Natural bond orbital analyses suggest that delocalized electrons and multi-centered bonds play an important role in stabilizing the low-energy As2Sin structures.